US20220079936A1 - Multi-arm polymer prodrugs - Google Patents

Abstract

Provided herein are water-soluble prodrugs, compositions comprising such prodrugs, and related methods of making and administering the same. The prodrugs of the invention comprise a water-soluble polymer having three or more arms, at least three of which are typically covalently attached to an active agent, e.g., a small molecule. The conjugates of the invention provide an optimal balance of polymer size and structure for achieving improved drug loading, since the conjugates of the invention possess three or more active agents releasably attached to a multi-armed water-soluble polymer. The prodrugs of the invention are therapeutically effective, and exhibit improved properties in-vivo when compared to unmodified parent drug.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application (i) is a continuation of U.S. patent application Ser. No. 16/582,991, filed Sep. 25, 2019, now pending, which is a continuation of U.S. patent application Ser. No. 15/723,943, filed Oct. 3, 2017, now U.S. Pat. No. 10,463,659, which is a continuation of U.S. patent application Ser. No. 15/144,440, filed May 2, 2016, now U.S. Pat. No. 9,808,533, which is a continuation of U.S. patent application Ser. No. 14/323,993, filed Jul. 3, 2014, now U.S. Pat. No. 9,333,200, which is a continuation of U.S. patent application Ser. No. 13/765,433, filed Feb. 12, 2013, now U.S. Pat. No. 8,771,662, which is a continuation of U.S. patent application Ser. No. 11/948,767, filed Nov. 30, 2007, now U.S. Pat. No. 8,394,365, which is a continuation-in-part of U.S. patent application Ser. No. 10/943,799, filed Sep. 17, 2004, now U.S. Pat. No. 7,744,861, which claims the benefit of priority to U.S. Provisional Application No. 60/503,673, filed Sep. 17, 2003, and to U.S. Provisional Application No. 60/584,308, filed Jun. 30, 2004, and (ii) also claims the benefit of priority to U.S. Provisional Application No. 60/861,995, filed Nov. 30, 2006, and to U.S. Provisional Application No. 61/003,163, filed Nov. 14, 2007, the contents of which are incorporated herein by reference in their entireties.
FIELD OF THE INVENTION
• This invention relates generally to multi-arm, water-soluble polymer drug conjugates. In particular, the invention is directed to, among other things, polymer-based prodrugs, pharmaceutical compositions thereof, and methods for preparing, formulating and administering such compositions.
BACKGROUND OF THE INVENTION
• Over the years, numerous methods have been proposed for improving the delivery of biologically active agents. Challenges associated with the formulation and delivery of pharmaceutical agents can include poor aqueous solubility of the pharmaceutical agent, toxicity, low bioavailability, instability, and rapid in-vivo degradation, to name just a few. Although many approaches have been devised for improving the delivery of pharmaceutical agents, no single approach is without its drawbacks. For instance, commonly employed drug delivery approaches aimed at solving or at least ameliorating one or more of these problems include drug encapsulation, such as in a liposome, polymer matrix, or unimolecular micelle, covalent attachment to a water-soluble polymer such as polyethylene glycol, use of gene targeting agents, and the like.
• In looking more closely at some of these approaches, liposome encapsulation is often plagued by low efficiencies of drug loading, resulting in an oftentimes inefficient and cost ineffective process. Moreover, the release rate of the active agent in a liposomal formulation depends upon dissolution or disintegration of the liposome, or diffusion of the active agent through the liposomal layers, thereby limiting the practical availability of the active agent to the biological system. In addition, liposomal formulations are generally restricted to lipid soluble drugs. Polymer matrix-based formulations can suffer from similar shortcomings, such as the inability to well-characterize such drug delivery systems, particular those that are cross-linked, and the variable release rates associated with active agents that must diffuse out of a hydrolytically degradable polymer matrix. In comparison, conjugation of an active agent to a polymer such as polyethylene glycol offers a more well-defined alternative, since the conjugate itself is often although not necessarily well-characterized, particularly in the case of site-specific attachment of the polymer to the active agent. However, protein-based compositions containing mixtures of positional isomers varying in both the site(s) and number of polymer chains attached to a particular protein are not uncommon. This can lead to problems with reproducibly preparing such compositions.
• While modification of therapeutic proteins for the purpose of improving their pharmaceutical utility is perhaps one of the most common applications of PEGylation, PEGylation has also been used, albeit to a limited degree, to improve the bioavailability and ease of formulation of small molecule therapeutics having poor aqueous solubilities. For instance, water-soluble polymers such as PEG have been covalently attached to artilinic acid to improve its aqueous solubility (Bentley, et al., U.S. Pat. No. 6,461,603). Similarly, PEG has been covalently attached to triazine-based compounds such as trimelamol to improve their solubility in water and enhance their chemical stability (Bentley, et al., WO 02/043772). Covalent attachment of PEG to bisindolyl maleimides has been employed to improve poor bioavailability of such compounds due to low aqueous solubility (Bentley, et al., WO 03/037384). Prodrugs of camptothecin having one or two molecules of camptothecin covalently attached to a linear polyethylene glycol have similarly been prepared (Greenwald, et al, U.S. Pat. No. 5,880,131).
• Camptothecin (often abbreviated as “CPT”) is a phytotoxic alkaloid first isolated from the wood and bark ofCamptotheca acuminata(Nyssaceae), and has been shown to exhibit antitumor activity. The compound has a pentacyclic ring system with an asymmetric center in lactone ring E with a 20 S configuration. The pentacyclic ring system includes a pyrrolo[3, 4-b]quinoline (rings A, B and C), a conjugated pyridone (ring D), and a six-membered lactone (ring E) with a 20-hydroxyl group. Due to its insolubility in water, camptothecin was initially evaluated clinically in the form of a water-soluble carboxylate salt having the lactone ring open to form the sodium salt. The sodium salt, although exhibiting much improved water solubility in comparison to camptothecin itself, produced severe toxicity and demonstrated very little in vivo anticancer activity, thus demonstrating the undesirability of this approach.
• It was later discovered that camptothecin and many of its derivatives inhibit topoisomerase, an enzyme that is required for swiveling and relaxation of DNA during molecular events such as replication and transcription. Camptothecin stabilizes and forms a reversible enzyme-camptothecin-DNA ternary complex. The formation of the cleavable complex specifically prevents the reunion step of the breakage/union cycle of the topoisomerase reaction. Topoisomerase I inhibitors are also known to be useful in the treatment of HIV.
• In an effort to address the poor aqueous solubility associated with camptothecin and many of its derivatives, a number of synthetic efforts have been directed to derivatizing the A-ring and/or B-ring or esterifying the 20-hydroxyl to improve water-solubility while maintaining cytotoxic activity. For example, topotecan (9-dimethylaminomethyl-10-hydroxy CPT) and irinotecan (7-ethyl-10[4-(1-piperidino)-1-piperidino] carbonyloxy CPT), otherwise known as CPT-11, are two water-soluble CPT derivatives that have shown clinically useful activity. Conjugation of certain camptothecin derivatives, such as 10-hydroxycamptothecin and 11-hydroxycamptothecin, to a linear poly(ethylene glycol) molecule via an ester linkage has been described as a means to form water soluble prodrugs (Greenwald, et al., U.S. Pat. No. 6,011,042). The approach used relies on reaction of an aromatic, hydroxyl-containing compound with an activated polymer.
• The clinical effectiveness of many small molecule therapeutics, and oncolytics in particular, is limited by several factors. For instance, irinotecan and other camptothecin derivatives undergo an undesirable hydrolysis of the E-ring lactone under alkaline conditions. Additionally, administration of irinotecan causes a number of troubling side effects, including leucopenia, neutropenia, and diarrhea. Due to its severe diarrheal side-effect, the dose of irinotecan that can be administered in its conventional, unmodified form is extremely limited, thus hampering the efficacy of this drug and others of this type.
• These associated side effects, when severe, can be sufficient to arrest further development of such drugs as promising therapeutics. Additional challenges facing small molecules include high clearance rates, and in the instance of anticancer agents, minimal tumor permeation and residence time. Approaches involving the use of polymer attachment must balance the size of the polymer against the molecular weight of the active agent in order to allow therapeutically effective doses to be delivered. Finally, the synthesis of a modified or drug-delivery enhanced active agent must result in reasonable yields, to make any such approach economically attractive. Thus, there exists a need for new methods for effectively delivering drugs, and in particular small molecule drugs, and even more particularly oncolytics, which can reduce their adverse and often toxic side-effects, whilst simultaneously improving their efficacy and ease of formulation. Specifically, there is a need for improved methods for delivering drugs that possess an optimal balance of bioavailability due to reduced clearance times, bioactivity, and efficacy, coupled with reduced side-effects. The present invention meets those needs.
SUMMARY OF THE INVENTION
• In one aspect, the present invention provides a water-soluble prodrug. The prodrug of the invention comprises a water-soluble polymer having three or more arms, typically at least three of which are covalently attached to an active agent, e.g., a small molecule. The conjugates of the invention provide an optimal balance of polymer size and structure for achieving improved drug loading, since the conjugates of the invention generally possess three or more active agents attached, preferably releasably, to a water-soluble polymer. In one embodiment, each arm of the water-soluble polymer possesses an active agent covalently attached thereto, preferably by a hydrolyzable linkage.
• In a particular embodiment, the prodrug conjugate comprises a multi-arm polymer, i.e., having three or more arms, where the conjugate comprises the following generalized structure:
• 
  R(-Q-POLY₁-X-D)_q
• In structure I, R is an organic radical possessing from about 3 to about 150 carbon atoms, preferably from about 3 to about 50 carbon atoms, and even more preferably from about 3 to about 10 carbon atoms, optionally containing one or more heteroatoms (e.g., O, S, or N). In one embodiment, R possesses a number of carbon atoms selected from the group consisting of 3, 4, 5, 6, 7, 8, 9, and 10. R may be linear or cyclic, and typically, emanating therefrom are at least 3 independent polymer arms each typically having at least one active agent moiety covalently attached thereto. Looking at the above structure, “q” corresponds to the number of polymer arms emanating from “R”.
• In structure I, Q is a linker, preferably one that is hydrolytically stable. Typically, Q contains at least one heteratom such as 0, or S, or NH, where the atom proximal to R in Q, when taken together with R, typically represents a residue of the core organic radical R. Illustrative examples are provided herein. Generally, Q contains from 1 to about 10 atoms, or from 1 to about 5 atoms. More particularly, Q typically contains one of the following numbers of atoms: 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. In a particular embodiment, Q is O, S, or —NH—C(O)—.
• In structure I, POLY₁represents a water-soluble and non-peptidic polymer. Representative polymers include poly(alkylene glycol), poly(olefinic alcohol), poly(vinylpyrrolidone), poly(hydroxyalkylmethacrylamide), poly(hydroxyalkylmethacrylate), poly(saccharide), poly(α-hydroxy acid), poly(acrylic acid), poly(vinyl alcohol), polyphosphazene, polyoxazoline, poly(N-acryloylmorpholine), or copolymers or terpolymers thereof.
• In a particular embodiment of structure I, POLY₁is a polyethylene glycol, preferably a linear polyethylene glycol (i.e., in each arm of the overall multi-arm structure). In yet another embodiment, POLY₁corresponds to the structure, —(CH₂CH₂O)_n—, where n ranges from about 10 to about 400, preferably from about 50 to about 350.
• In structure I, X is a spacer that comprises a hydrolyzable linkage, where the hydrolyzable linkage is attached directly to the active agent, D. Typically, at least one atom of the hydrolyzable linkage is contained in the active agent, D, in its unmodified form, such that upon hydrolysis of the hydrolyzable linkage comprised within X, the active agent, D, is released. Generally speaking, the spacer, X, has an atom length of from about 4 atoms to about 50 atoms, or more preferably from about 5 atoms to about 25 atoms, or even more preferably from about 5 atoms to about 20 atoms. Representative spacers have a length of from about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or about 20 atoms.
• In yet another particular embodiment, X possesses the structure: Y—Z, where Y is a spacer fragment covalently attached to Z, a hydrolytically degradable linkage. In certain embodiments, Z itself may not constitute a hydrolytically degradable linkage, however, when taken together with Y, or at least a portion of Y, forms a linkage that is hydrolytically degradable.
• In yet a more particular embodiment of the spacer, X, Y has the structure: —(CR_xR_y)_a—K—(CR_xR_y)_b—(CH₂CH₂O)_c—, wherein each R_xand R_y, in each occurrence, is independently H or an organic radical selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, and substituted aryl, a ranges from 0 to 12 (i.e., can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12), b ranges from 0 to 12 (i.e., can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12), K is selected from —C(O)—, —C(O)NH—, —NH—C(O)—, —O—, —S—, O—C(O)—, C(O)—O—, O—C(O)—O—, O—O(O)—NH—, NH—C(O)—O—, c ranges from 0 to 25, and Z is selected from C(O)—O—, O—C(O)—O—, —O—C(O)—NH—, and NH—C(O)—O—. The particular structure of K and of Z will depend upon the values of each of a, b, and c, such that none of the following linkages result in the overall structure of spacer X, —O—O—, NH—O—, NH—NH—.
• Preferably, Y comprises (CH₂)_a—C(O)NH—(CH₂)_0,1—(CH₂CH₂O)_0-10.
• In yet another embodiment of the spacer, X, Y has the structure: —(CR_xR_y)_a—K—(CR_xR_y)_b—(CH₂CH₂NH)_c—, where the variables have the values previously described. In certain instances, the presence of the short ethylene oxide or ethyl amino fragments in spacer, X, can be useful in achieving good yields during preparation of the prodrug conjugate, since the presence of the linker can help to circumvent problems associated with steric hindrance, due to the multi-armed reactive polymer, the structure of the active agent, or a combination of both. Preferably, c is selected from the group consisting of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.
• Preferably, R_xand R_yin each occurrence are independently H or lower alkyl. In one embodiment, R_xand R_yare in each occurrence H. In yet another embodiment, a ranges from 0 to 5. In yet another embodiment, b ranges from 0 to 5. In yet another embodiment, c ranges from 0 to 10. In yet another embodiment, K is —C(O)—NH. Any of the embodiments described herein is meant to apply not only to generalized structure I, but also to extend to particular combinations of embodiments.
• In yet another embodiment, R_xand R_yin each occurrence are H, a is 1, K is —C(O)—NH, and b is 0 or 1.
• Representative examples of X include —CH₂—C(O)—NH—CH₂—C(O)O— (here, Y corresponds to —CH₂—C(O)—NH—CH₂— and Z corresponds to —C(O)—O—), and —CH₂—O(O)—NH—(CH₂CH₂O)₂—C(O)—O— (here, Y corresponds to —CH₂—C(O)—NH—(CH₂CH₂O)₂— and Z corresponds to —C(O)—O—).
• Returning now to structure I, D is an active agent moiety, and q (the number of independent polymer arms) ranges from about 3 to about 50. Preferably, q ranges from about 3 to about 25. More preferably, q is from 3 to about 10, and possesses a value of 3, 4, 5, 6, 7, 8, 9, or 10.
• In accordance with one embodiment of the invention, the conjugate comprises a polymer having from about 3 to about 25 active agent molecules covalently attached thereto. More particularly, the conjugate comprises a water-soluble polymer having 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 active agent molecules covalently attached thereto. In a further embodiment, the conjugate of the invention has from about 3 to about 8 active agent molecules covalently attached to the multi-armed water-soluble polymer. Typically, although not necessarily, the number of polymer arms will correspond to the number of active agents covalently attached to the water-soluble polymer.
• The active agent moiety, D, is an active agent comprising a functional group suitable for covalent attachment to the multi-armed polymer described herein to form a hydrolyzable linkage, such that upon hydrolysis, the active agent is released in its unmodified form.
• Preferred active agent moieties include anticancer agents.
• In one embodiment, the active agent is a small molecule. In a particular embodiment, the active agent moiety is a small molecule possessing a molecular weight of less than about 1000. In yet additional embodiments, the small molecule drug possesses a molecular weight of less than about 800, or even less than about 750. In yet another embodiment, the small molecule drug possesses a molecular weight of less than about 500 or, in some instances, even less than about 300.
• In yet another embodiment, the small molecule is an oncolytic drug having at least one hydroxyl group.
• In yet a further embodiment, D represents a camptothecin compound having the structure:
• 
• wherein R₁-R₅are each independently selected from the group consisting of hydrogen; halo; acyl; alkyl (e.g., C1-C6 alkyl); substituted alkyl; alkoxy (e.g., C1-C6 alkoxy); substituted alkoxy; alkenyl; alkynyl; cycloalkyl; hydroxyl; cyano; nitro; azido; amido; hydrazine; amino; substituted amino (e.g., monoalkylamino and dialkylamino); hydroxcarbonyl; alkoxycarbonyl; alkylcarbonyloxy; alkylcarbonylamino; carbamoyloxy; arylsulfonyloxy; alkylsulfonyloxy; —C(R₇)═N—(O)_i—R₈wherein R₇is H, alkyl, alkenyl, cycloalkyl, or aryl, i is 0 or 1, and R₈is H, alkyl, alkenyl, cycloalkyl, or heterocycle; and R₉C(O)O— wherein R₉is halogen, amino, substituted amino, heterocycle, substituted heterocycle, or R₁₀—O—(CH₂)_m— where m is an integer of 1-10 and R₁₀is alkyl, phenyl, substituted phenyl, cycloalkyl, substituted cycloalkyl, heterocycle, or substituted heterocycle; or
• R₂together with R₃or R₃together with R₄form substituted or unsubstituted methylenedioxy, ethylenedioxy, or ethyleneoxy;
• R₆is H or OR′, wherein R′ is alkyl, alkenyl, cycloalkyl, haloalkyl, or hydroxyalkyl; and
• L is the site of attachment to X.
• In yet another particular embodiment, D is irinotecan (structure shown below).
• 
• In yet another particular embodiment, D is docetaxel.
• Alternatively, D is a small molecule selected from the group consisting of platins, oxymorphone analogues, steroids, quinolones, and nucleosides.
• In one embodiment, D is a platin such as cis-platin, hydroxyplatin, carboplatin, or oxaliplatin.
• In yet a further embodiment, D is an oxymorphone analogue such as naloxone, methylnaltrexone, oxymorphone, codeine, oxycodone, or morphone.
• In yet an additional embodiment, D is a steroid such as budesonide, triamcinolone, or fluticasone.
• In yet another embodiment, D is a quinolone, isoquinolone or fluoroquinolone such as ciprofloxacin, moxifloxacin, or palonosetron.
• In yet an additional embodiment, D is a nucleoside or nucleotide such as gemcitabine, cladribine, or fludarabine.
• In yet another aspect, the invention encompasses a pharmaceutical composition comprising a multi-armed polymer prodrug as described above. In one embodiment, the composition further comprises a multi-arm polymer prodrug, where one or more of ‘q’ polymer arms is absent D.
• More particularly, the invention includes a composition comprising a multi-arm polymer prodrug having the structure R(-Q-POLY₁-X′-D_0,1)_q. In the foregoing structure, R, Q, POLY₁, and q are as previously described; X′ is either (i) a spacer, X, comprising a hydrolyzable linkage, such that upon hydrolysis of said hydrolyzable linkage, D, is released, or is (ii) X″, a terminal moiety; and D is a small molecule, where D₁indicates the presence of D and Do indicates its absence, where the following conditions also apply: if X′ is X, then D is D₁, and if X′ is X″, then D is D₀. Typically, the composition comprises at least one multi-arm polymer prodrug species wherein X′ is X. The terminal moiety, X″, typically corresponds to an unreacted functional group present on one or more arms of the multi-armed polymer, or, is an inert derivative thereof, e.g., resulting from work-up, such as a hydrolysis product.
• More particularly, a composition of the invention may comprise one or more prodrug species having the structure:
• 
  R-(Q-POLY₁-X-D₁)_m(Q-POLY₁-X″)_s.
• where the variables are as previously described. The preceding structure may also be represented as follows:
• 
• In the above structures (which are identical), m and s are each integers, where the sum of m and s is q, and where m and s each independently have values ranging from 0 to q. As described above, q (the number of polymer arms emanating from R) typically ranges from about 3 to about 50. Preferably, q ranges from about 3 to about 25. More preferably, q is from 3 to about 10, and possesses a value of 3, 4, 5, 6, 7, 8, 9, or 10.
• In one embodiment, the composition possesses an average number of D per multi-arm polymer ranging from 2.1-3.75.
• In yet another embodiment, the composition possesses an average number of D per multi-arm polymer ranging from 2.3-3.5.
• In another embodiment, the composition comprises a mixture of “q” prodrug species.
• In yet a more particular embodiment of a composition in accordance with the invention, X″ is —CH₂COOH.
• Also forming part of the invention is a composition comprising a mixture of one or more prodrug species having the structure:
• 
• wherein O-Irinotecan is a residue of irinotecan as shown below:
• 
• m+s=4, and n ranges from 40 to 500.
• In yet another embodiment, the invention encompasses a composition comprising a mixture of one or more prodrug species having the structure:
• 
• where m+s=4, and n ranges from 40 to 500.
• The multi-armed polymer prodrugs of the invention possess many unique features, particularly in the instance where the small molecule is an anticancer compound. For example, in one embodiment, provided is a multi-arm polymer prodrug, which when evaluated in a suitable animal model for solid tumor-type cancers and administered in a therapeutically effective amount, is effective to suppress tumor growth to an extent that is at least 1.5 times that, or even twice that observed for the unmodified anticancer agent, when evaluated over a time course of 30 days. In yet another embodiment, the prodrug is effective to suppress tumor growth to the above extent or even greater when evaluated over a time course of 60 days. The small molecule employed is one known to possess anticancer properties, however, by virtue of its conjugation to a multi-armed polymer as described herein, possesses significantly improved efficacy and/or pharmacokinetics in comparison to the small molecule, e.g., anticancer compound, itself. Suitable solid tumor types include but are not limited to malignant sarcomas, carcinomas and lymphomas of the breast, ovaries, colon, kidney, bile duct, lung and brain.
• In another aspect, the invention encompasses reactive multi-arm polymers suitable for preparing any of the above-described prodrug conjugates.
• In another aspect, the invention encompasses a pharmaceutical composition comprising a multi-arm polymer prodrug conjugate as described above in combination with a pharmaceutically acceptable carrier.
• Another aspect of the invention provides a method for treating various medical conditions in a mammalian subject. More specifically, the invention encompasses a method of administering to a mammalian subject in need thereof a therapeutically effective amount of a multi-arm prodrug conjugate of the invention. In one embodiment, the drug moiety, D, is an anticancer agent such as a camptothecin (e.g., irinotecan) or docetaxel, and is effective to suppress tumor growth. In a particularly preferred embodiment, a multi-armed prodrug conjugate of the invention, particularly one where D is an anticancer agent, exhibits one or more of the following characteristics: (i) suppresses tumor growth to an extent greater than that of unmodified D, (ii) demonstrates a tumor retention time that is increased over that of unmodified D, (iii) exhibits a rate of clearance that is reduced in comparison to that of unmodified D, and/or (iv) produces reduced adverse side effects in comparison to unmodified D.
• Also provided herein is a method of treating cancer or a viral infection (where D is an anticancer or an antiviral agent, respectively) by administering a multi-arm polymer conjugate as described herein.
• In yet another aspect, the invention provides a method of treating a topoisomerase I inhibitor-related disease in a mammalian subject by administering a therapeutically effective amount of a multi-arm polymer prodrug to a mammalian subject in need thereof, where the small molecule is a camptothecin type molecule.
• Also forming part of the invention is a method of targeting a solid tumor in a mammalian subject. The method includes the step of administering a therapeutically effective amount of a multi-arm polymer prodrug of an anticancer agent known to be effective in the treatment of solid tumors to a subject diagnosed as having one or more cancerous solid tumors. As a result of said administering, the prodrug is effective to produce an inhibition of solid tumor growth in the subject that is increased over the inhibition of solid tumor growth resulting from administration of the anticancer agent alone.
• In a further aspect, a method for preparing a multi-arm polymer prodrug conjugate of the invention is provided. In the method, a small molecule, D, is provided, where the small molecule comprises a functional group, F, suitable for forming a hydrolyzable linkage, Z. The small molecule is reacted with a bifunctional spacer, Y′, comprising each a first and a second functional group, F1 and F2. The functional group F2 is suitable for reaction with F, and F1 may optionally be in protected form (F1-Y′-F2). The reaction is carried out under conditions effective to form a partially modified active agent comprising a hydrolyzable linkage, Z, resulting from reaction of F and F2, which corresponds to the structure D-Z—Y′—F1. If necessary, the method includes the optional step of deprotecting F1 contained in the partially modified active agent. The method then includes the step of reacting the partially modified active agent, D-Z—Y′—F1, with a multi-armed water-soluble polymer comprising the structure, R(-Q-POLY₁-F3)_q, where R, Q, POLY₁, and Q are as previously defined, and F3 is a functional group that is reactive with F1. The reaction is carried out under conditions effective to promote reaction between F3 and F1 to convert Y′ to Y, to thereby form a polymer prodrug having the structure, R(-Q-POLY₁-Y—Z-D)_q, where Y is a spacer fragment, and Z is a hydrolyzable linkage, which, upon hydrolysis, releases D.
• In one embodiment of the method, a stoichiometric excess in an amount greater than “q” moles of the partially modified active agent, D-Z—Y′—F1, is reacted with the multi-armed water-soluble, R(-Q-POLY₁-F3)_qto drive the reaction to completion, i.e., to covalently attach active agent to each of the reactive polymer arms.
• In yet another embodiment, where the small molecule D possesses additional functional groups reactive with F2, the method further comprises the step of protecting the additional functional groups with suitable protecting groups prior to reaction with the bifunctional spacer. These protecting groups are then removed from the small molecules of the prodrug product, R(-Q-POLY₁-Y—Z-D)_q.
• In yet another embodiment of the above method, the reacting step results in formation of additional prodrug species having the structure:
• 
  R(-Q-POLY₁-Y—Z-D)_m(-Q-POLY₁-X″)_s
• which can also be represented as
• 
• where m and s are integers, each independently ranging in value from 0 to q, and the sum of m and s is q, and X″ is a terminal moiety that is either the same as F3 or is a hydrolysis product or chemical equivalent thereof.
• In yet another embodiment, the method additionally comprises the step of isolating said one or more polymer prodrugs.
• According to yet another aspect of the invention, provided is yet another method for preparing a multi-arm polymer prodrug of the invention. The method includes the step of providing a reactive multi-arm polymer having the structure, R(-Q-POLY₁-F3)_q, where R, Q, POLY₁, and q are as previously described, and F3 is a reactive functional group. The multi-arm polymer is then reacted with a bifunctional spacer, Y′, comprising each a first and a second functional group, F1 and F2, wherein F1 is suitable for reaction with F3, and F1 is optionally in protected form (F1-Y′-F2). The reaction is carried out under conditions effective to form an intermediate multi-arm polymer resulting from reaction of F3 and F1, and having the structure, R(-Q-POLY₁-Y—F2)_q. The method further includes the optional step of deprotecting F2 in the intermediate multi-arm polymer, R(-Q-POLY₁-Y—F2)_qif such is in protected form. The intermediate multi-arm polymer, R(-Q-POLY₁-Y—F2)_q, is then reacted with a small molecule, D, comprising a functional group, F, suitable for forming a hydrolyzable linkage, Z, upon reaction of F with F2, under conditions effective to thereby form a prodrug having the structure, R(-Q-POLY₁-Y—Z-D)q, where Z is a hydrolyzable linkage, which, upon hydrolysis, releases D.
• Reactive functional groups such as those described above as F1, F2 and F3, are numerous and may be selected from, for example, hydroxyl, active ester (e.g., N-hydroxysuccinimidyl ester and 1-benzotriazolyl ester), active carbonate (e.g., N-hydroxysuccinimidyl carbonate, 1-benzotriazolyl carbonate, p-nitrophenyl carbonate), acid halide, acetal, aldehyde having a carbon length of 1 to 25 carbons (e.g., acetaldehyde, propionaldehyde, and butyraldehyde), aldehyde hydrate, alkenyl, acrylate, methacrylate, acrylamide, active sulfone, amine, hydrazide, thiol, alkanoic acids having a carbon length (including the carbonyl carbon) of 1 to about 25 carbon atoms (e.g., carboxylic acid, carboxymethyl, propanoic acid, and butanoic acid), isocyanate, isothiocyanate, maleimide, vinylsulfone, dithiopyridine, vinylpyridine, iodoacetamide, epoxide, glyoxal, and dione.
• In one embodiment, the bifunctional spacer, Y′ is an amino acid or derived from an amino acid. Representative amino acids have the structure HO—C(O)—CH(R″)—NH-Gp wherein R″ is H, C1-C6 alkyl, or substituted C1-C6 alkyl and Gp is an amino-protecting group. In an alternative embodiment, the bifunctional spacer, Y′ possesses the structure: —C(O)—(OCH₂CH₂)_1-10—NH-Gp.
• In yet another embodiment of the foregoing method, the reacting step results in formation of additional prodrug species having the structure, R(-Q-POLY₁-Y—Z-D)_m(-Q-POLY₁-X″)_s, where m and s are integers each independently having a value ranging from 0 to q, wherein the sum of m and s is q, and X″ is a terminal moiety that is either the same as F2 or is a hydrolysis product or chemical equivalent thereof.
• The above methods for preparing a prodrug of the invention may include the additional steps of purifying the intermediates and/or the final prodrug products, for example by size exclusion chromatography or ion exchange chromatography in instances in which the compounds to be purified contain one or more ionizable groups, such as carboxyl or amino.
• Each of the herein-described features of the invention is meant to apply equally to each and every embodiment as described herein, unless otherwise indicated.
• These and other objects and features of the invention will become more fully apparent when read in conjunction with the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a graph illustrating the effect of an exemplary multi-arm PEG-irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, on the growth of HT29 human colon tumors implanted in athymic nude mice in comparison to an untreated control group and a group treated with irinotecan as described in detail in Example 2.
• FIG. 2 is a graph illustrating the effects of a variety of doses (90 mg/kg; 60 mg/kg; and 40 mg/kg) of an exemplary multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k on the growth of NCI-H460 human lung tumors implanted in athymic nude mice in comparison to a control group and a group treated with irinotecan as described in Example 6.
• FIG. 3 is a graph illustrating the effects of a variety of doses (90 mg/kg; 60 mg/kg; and 40 mg/kg) of an exemplary 40 kilodalton (40K) multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, on the growth of NCI-H460 human lung tumors implanted in athymic nude mice in comparison to a control group and a group treated with irinotecan as described in Example 6.
• FIG. 4 is a graph illustrating the effects of a variety of doses (90 mg/kg; 60 mg/kg; and 40 mg/kg) of an exemplary 20 kilodalton (20K) multi-arm PEG-irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, on the growth of HT29 human colon tumors implanted in athymic nude mice in comparison to an untreated control group and a group treated with irinotecan as described in detail in Example 6.
• FIG. 5 is a graph illustrating the effects of a variety of doses (90 mg/kg; 60 mg/kg; and 40 mg/kg) of an exemplary 40 kilodalton (40K) multi-arm PEG-irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, on the growth of HT29 human colon tumors implanted in athymic nude mice in comparison to an untreated control group and a group treated with irinotecan as described in detail in Example 6.
• FIG. 6 is a graph illustrating the concentration in venous plasma over time of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, and (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, following IV administration as a single dose in athymic nude mice implanted with either HT29 human colon tumors or NCI-H460 human lung tumors as described in Example 7.
• FIG. 7 is a graph illustrating the concentration in tumor tissue over time of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, and (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, following IV administration as a single dose in athymic nude mice implanted with HT29 human colon tumors as described in Example 7.
• FIG. 8 is a graph illustrating the concentration of 4-arm-PEG-GLY-SN-38-20 k or 4-arm-PEG-GLY-SN-38-40 k in plasma over time following IV administration of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, or (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, respectively, as a single dose in athymic nude mice implanted with HT29 human colon tumors as described in Example 7.
• FIG. 9 is a graph illustrating the concentration of 4-arm-PEG-GLY-SN-38-20 k or 4-arm-PEG-GLY-SN-38-40 k in tumor tissue over time following IV administration of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, or (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, respectively, as a single dose in athymic nude mice implanted with HT29 human colon tumors as described in Example 7.
• FIG. 10 is a graph illustrating the concentration of irinotecan in venous plasma over time following IV administration of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, or (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, or (iii) irinotecan itself as a single dose in athymic nude mice implanted with HT29 human colon tumors as described in Example 7.
• FIG. 11 is a graph illustrating the concentration of irinotecan in tumor tissue over time following IV administration of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, or (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, or (iii) irinotecan itself, as a single dose in athymic nude mice implanted with HT29 human colon tumors as described in Example 7.
• FIG. 12 is a graph illustrating the concentration of SN-38 in plasma over time following IV administration of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, or (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, or (iii) irinotecan itself, as a single dose in athymic nude mice implanted with HT29 human colon tumors as described in Example 7.
• FIG. 13 is a graph illustrating the concentration of SN-38 in tumor tissue over time following IV administration of (i) an exemplary 20 kilodalton (20K) multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-20 k, or (ii) a 40 kilodalton multi-arm PEG irinotecan conjugate, 4-arm-PEG-GLY-IRINO-40 k, or (iii) irinotecan itself, as a single dose in athymic nude mice implanted with HT29 human colon tumors as described in Example 7.
• FIG. 14 is a graph illustrating the in vitro release of irinotecan from 4-arm-PEG-GLY-IRINO-20K in phosphate buffer (pH 7.4, 37° C.) over time as described in detail in Example 10.
• FIGS. 15A and 15B are plots demonstrating the mean tumor volume (i.e., tumor growth) over time in athymic mice implanted with MCF-7 human breast tumors following administration of 4-arm-PEG-GLY-IRINO-20K (FIG. 15A) or irinotecan (FIG. 15B) as described in Example 11.
• FIG. 15C contains plots comparing mean tumor weight (mg) over time (days) in athymic mice implanted with MCF-7 human breast tumors following administration of 4-arm-PEG-GLY-IRINO-20K, irinotecan, or a control. Subjects were administered 20 mg/kg irinotecan equivalent per dose; dosing occurred every four days for a total of three doses administered.
• FIGS. 16A, 16B and 16C are plots illustrating the results of a dose ranging study to evaluate the effect of a single dose of docetaxel versus 4-arm-PEG-GLY-DOC-20K on H-460 non-small cell lung cancer tumor suppression in female xenograft athymic nude mice over time. Dosage amounts were as follows: 10 mg/kg (based upon docetaxel dosage) (FIG. 16A), 20 mg/kg (FIG. 16B), and 40 mg/kg (FIG. 16C). Details of the study are provided in Example 16.
• FIG. 17 is a plot demonstrating the effects of two doses of each of three different dosage amounts of docetaxel (10 mg/kg, 20 mg/kg, and 30 mg/kg) and 4-arm-PEG-GLY-DOC-20K (20 mg/kg, 40 mg/kg, and 60 mg/kg) in female xenograft athymic nude mice implanted with H460 non-small cell lung cancer tumors over time as described in Example 16.
• FIG. 18 is a plot demonstrating the effects of two doses of each of three different dosage amounts of docetaxel (10 mg/kg, 20 mg/kg, and 30 mg/kg) and 4-arm-PEG-GLY-DOC-20K (20 mg/kg, 40 mg/kg, and 60 mg/kg) in female xenograft athymic nude mice implanted with DU-145 prostate tumors over time as described in Example 17.
• FIG. 19 is a plot demonstrating the anti-tumor effect of docetaxel and 4-arm-PEG-GLY-DOC-20K, respectively, over time in mice implanted with MCF-7 breast tumors as described in Example 18.
• FIG. 20 illustrates exposure to SN-38 in HT-29 colorectal tumors in mice resulting from administration of 4-arm-PEG-gly-irino-20K.
• FIG. 21 is a plot demonstrating reduced neutropenia in dogs administered 4-arm-PEG-GLY-IRINO-20K when compared to dogs administered irinotecan at an equivalent dose.
• FIG. 22 is a bar graph illustrating the maximum tolerated dose (MTR) of 4-arm-PEG-GLY-IRINO-20K when compared to irinotecan in both rat and dog.
• FIG. 23 is a bar graph illustrating an additional advantage of administering 4-arm-PEG-GLY-IRINO-20K when compared to irinotecan: fewer diarrhea episodes in dogs.
• FIG. 24 is a plot illustrating plasma levels of SN-38 in dogs administered 4-arm-PEG-GLY-IRINO-20K or irinotecan. SN-38 levels in dogs administered 4-arm-PEG-GLY-IRINO-20K are elevated and sustained over a longer period of time when compared to SN-38 levels in dogs administered unmodified irinotecan.
• FIG. 25 provides a pharmacokinetic profile resulting from administration of a single dose of 4-arm-PEG-GLY-IRINO-20K to a breast cancer patient in comparison to the profile resulting from administration of irinotecan.
• FIG. 26 is a plot demonstrating the neutrophil effects of 4-arm-PEG-GLY-DOC-20K versus docetaxel when administered to dogs, where 4-arm-PEG-GLY-DOC-20K resulted in less neutropenia than docetaxel when administered at a higher single dose.
DETAILED DESCRIPTION OF THE INVENTION
• The present invention now will be described more fully hereinafter. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
Definitions
• It must be noted that, as used in this specification, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “polymer” includes a single polymer as well as two or more of the same or different polymers, reference to a “conjugate” refers to a single conjugate as well as two or more of the same or different conjugates, reference to an “excipient” includes a single excipient as well as two or more of the same or different excipients, and the like.
• In describing and claiming the present invention, the following terminology will be used in accordance with the definitions described below.
• A “functional group” is a group that may be used, under normal conditions of organic synthesis, to form a covalent linkage between the structure to which it is attached and another structure, which typically bears a further functional group. The functional group generally includes multiple bond(s) and/or heteroatom(s). Preferred functional groups for use in the polymers of the invention are described below.
• The term “reactive” refers to a functional group that reacts readily or at a practical rate under conventional conditions of organic synthesis. This is in contrast to those groups that either do not react or require strong catalysts or impractical reaction conditions in order to react (i.e., a “nonreactive” or “inert” group).
• “Not readily reactive”, with reference to a functional group present on a molecule in a reaction mixture, indicates that the group remains largely intact under conditions effective to produce a desired reaction in the reaction mixture.
• An “activated derivative” of a carboxylic acid refers to a carboxylic acid derivative which reacts readily with nucleophiles, generally much more readily than the underivatized carboxylic acid. Activated carboxylic acids include, for example, acid halides (such as acid chlorides), anhydrides, carbonates, and esters. Such esters include, for example, imidazolyl esters, and benzotriazole esters, and imide esters, such as N-hydroxysuccinimidyl (NHS) esters. An activated derivative may be formed in situ by reaction of a carboxylic acid with one of various reagents, e.g. benzotriazol-1-yloxy tripyrrolidinophosphonium hexafluorophosphate (PyBOP), preferably used in combination with 1-hydroxy benzotriazole (HOBT) or 1-hydroxy-7-azabenzotriazole (HOAT); O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU); or bis(2-oxo-3-oxazolidinyl)phosphinic chloride (BOP-Cl).
• A “chemical equivalent” of a functional group is one that possesses essentially the same type of reactivity as the functional group. For instance, one functional group that undergoes an SN2 reaction is considered to be a functional equivalent of another such functional group.
• A “protecting group” is a moiety that prevents or blocks reaction of a particular chemically reactive functional group in a molecule under certain reaction conditions. The protecting group will vary depending upon the type of chemically reactive group being protected as well as the reaction conditions to be employed and the presence of additional reactive or protecting groups in the molecule. Functional groups that may be protected include, by way of example, carboxylic acid groups, amino groups, hydroxyl groups, thiol groups, carbonyl groups and the like. Representative protecting groups for carboxylic acids include esters (such as a p-methoxybenzyl ester), amides and hydrazides; for amino groups, carbamates (such as tert-butoxycarbonyl) and amides; for hydroxyl groups, ethers and esters; for thiol groups, thioethers and thioesters; for carbonyl groups, acetals and ketals; and the like. Such protecting groups are well-known to those skilled in the art and are described, for example, in T. W. Greene and G. M. Wuts,Protecting Groups in Organic Synthesis, Third Edition, Wiley, New York, 1999, and references cited therein.
• A functional group in “protected form” refers to a functional group bearing a protecting group. As used herein, the term “functional group” or any synonym thereof is meant to encompass protected forms thereof.
• “PEG” or “poly(ethylene glycol)” as used herein, is meant to encompass any water-soluble poly(ethylene oxide). Typically, PEGs for use in the present invention will comprise one of the two following structures: “—(CH₂CH₂O)_n—” or “—(CH₂CH₂O)_n-1CH₂CH₂—,” depending upon whether or not the terminal oxygen(s) has been displaced, e.g., during a synthetic transformation. The variable (n) is 3 to 3000, and the terminal groups and architecture of the overall PEG may vary. When PEG further comprises a spacer as in structure I above (to be described in greater detail below), the atoms comprising the spacer (X), when covalently attached to a PEG segment, do not result in formation of (i) an oxygen-oxygen bond (—O—O—, a peroxide linkage), or (ii) a nitrogen-oxygen bond (N—O, O—N). “PEG” means a polymer that contains a majority, that is to say, greater than 50%, of subunits that are —CH₂CH₂O—. PEGs for use in the invention include PEGs having a variety of molecular weights, structures or geometries to be described in greater detail below.
• “Water-soluble”, in the context of a polymer of the invention or a “water-soluble polymer segment” is any segment or polymer that is soluble in water at room temperature. Typically, a water-soluble polymer or segment will transmit at least about 75%, more preferably at least about 95% of light, transmitted by the same solution after filtering. On a weight basis, a water-soluble polymer or segment thereof will preferably be at least about 35% (by weight) soluble in water, more preferably at least about 50% (by weight) soluble in water, still more preferably about 70% (by weight) soluble in water, and still more preferably about 85% (by weight) soluble in water. It is most preferred, however, that the water-soluble polymer or segment is about 95% (by weight) soluble in water or completely soluble in water.
• An “end-capping” or “end-capped” group is an inert group present on a terminus of a polymer such as PEG. An end-capping group is one that does not readily undergo chemical transformation under typical synthetic reaction conditions. An end capping group is generally an alkoxy group, —OR, where R is an organic radical comprised of 1-20 carbons and is preferably lower alkyl (e.g., methyl, ethyl) or benzyl. “R” may be saturated or unsaturated, and includes aryl, heteroaryl, cyclo, heterocyclo, and substituted forms of any of the foregoing. For instance, an end capped PEG will typically comprise the structure “RO—(CH₂CH₂O)_n—”, where R is as defined above. Alternatively, the end-capping group can also advantageously comprise a detectable label. When the polymer has an end-capping group comprising a detectable label, the amount or location of the polymer and/or the moiety (e.g., active agent) to which the polymer is coupled, can be determined by using a suitable detector. Such labels include, without limitation, fluorescers, chemiluminescers, moieties used in enzyme labeling, colorimetric (e.g., dyes), metal ions, radioactive moieties, and the like.
• “Non-naturally occurring” with respect to a polymer of the invention means a polymer that in its entirety is not found in nature. A non-naturally occurring polymer of the invention may however contain one or more subunits or segments of subunits that are naturally occurring, so long as the overall polymer structure is not found in nature.
• “Molecular mass” in the context of a water-soluble polymer of the invention such as PEG, refers to the nominal average molecular mass of a polymer, typically determined by size exclusion chromatography, light scattering techniques, or intrinsic velocity determination in 1,2,4-trichlorobenzene. Molecular weight in the context of a water-soluble polymer, such as PEG, can be expressed as either a number-average molecular weight or a weight-average molecular weight. Unless otherwise indicated, all references to molecular weight herein refer to the weight-average molecular weight. Both molecular weight determinations, number-average and weight-average, can be measured using gel permeation chromatographic or other liquid chromatographic techniques. Other methods for measuring molecular weight values can also be used, such as the use of end-group analysis or the measurement of colligative properties (e.g., freezing-point depression, boiling-point elevation, or osmotic pressure) to determine number-average molecular weight or the use of light scattering techniques, ultracentrifugation or viscometry to determine weight-average molecular weight. The polymers of the invention are typically polydisperse (i.e., number-average molecular weight and weight-average molecular weight of the polymers are not equal), possessing low polydispersity values such as less than about 1.2, less than about 1.15, less than about 1.10, less than about 1.05, and less than about 1.03. As used herein, references will at times be made to a single water-soluble polymer having either a weight-average molecular weight or number-average molecular weight; such references will be understood to mean that the single-water soluble polymer was obtained from a composition of water-soluble polymers having the stated molecular weight.
• The term “linker” is used herein to refer to an atom or a collection of atoms used to link interconnecting moieties, such as an organic radical core and a polymer segment, POLY₁. A linker moiety may be hydrolytically stable or may include a physiologically hydrolyzable or enzymatically degradable linkage. A linker designated herein as Q is hydrolytically stable.
• The term “spacer” is used herein to refer to a collection of atoms used to link interconnecting moieties, such as POLY₁and the active agent, D. A spacer moiety may be hydrolytically stable or may include a physiologically hydrolyzable or enzymatically degradable linkage. A spacer designated herein as X comprises a hydrolyzable linkage, where the hydrolyzable linkage is attached directly to the active agent, D, such that upon hydrolysis, the active agent is released in its parent form.
• A “hydrolyzable” bond is a relatively weak bond that reacts with water (i.e., is hydrolyzed) under physiological conditions. The tendency of a bond to hydrolyze in water will depend not only on the general type of linkage connecting two central atoms but also on the substituents attached to these central atoms. Illustrative hydrolytically unstable linkages include carboxylate ester, phosphate ester, anhydrides, acetals, ketals, acyloxyalkyl ether, imines, orthoesters, peptides and oligonucleotides.
• An “enzymatically degradable linkage” means a linkage that is subject to degradation by one or more enzymes. Such a linkage requires the action of one or more enzymes to effect degradation.
• A “hydrolytically stable” linkage or bond refers to a chemical bond, typically a covalent bond, that is substantially stable in water, that is to say, does not undergo hydrolysis under physiological conditions to any appreciable extent over an extended period of time. Examples of hydrolytically stable linkages include but are not limited to the following: carbon-carbon bonds (e.g., in aliphatic chains), ethers, amides, urethanes, and the like. Generally, a hydrolytically stable linkage is one that exhibits a rate of hydrolysis of less than about 1-2% per day under physiological conditions. Hydrolysis rates of representative chemical bonds can be found in most standard chemistry textbooks.
• “Multi-armed” in reference to the geometry or overall structure of a polymer refers to polymer having 3 or more polymer-containing “arms”. Thus, a multi-armed polymer may possess 3 polymer arms, 4 polymer arms, 5 polymer arms, 6 polymer arms, 7 polymer arms, 8 polymer arms or more, depending upon its configuration and core structure. One particular type of highly branched polymer is a dendritic polymer or dendrimer, that, for the purposes of the invention, is considered to possess a structure distinct from that of a multi-armed polymer.
• “Branch point” refers to a bifurcation point comprising one or more atoms at which a polymer splits or branches from a linear structure into one or more additional polymer arms. A multi-arm polymer may have one branch point or multiple branch points.
• A “dendrimer” is a globular, size monodisperse polymer in which all bonds emerge radially from a central focal point or core with a regular branching pattern and with repeat units that each contribute a branch point. Dendrimers exhibit certain dendritic state properties such as core encapsulation, making them unique from other types of polymers.
• “Substantially” or “essentially” means nearly totally or completely, for instance, 95% or greater of some given quantity.
• “Alkyl” refers to a hydrocarbon chain, typically ranging from about 1 to 20 atoms in length. Such hydrocarbon chains are preferably but not necessarily saturated and may be branched or straight chain, although typically straight chain is preferred. Exemplary alkyl groups include methyl, ethyl, propyl, butyl, pentyl, 1-methylbutyl, 1-ethylpropyl, 3-methylpentyl, and the like. As used herein, “alkyl” includes cycloalkyl when three or more carbon atoms are referenced.
• “Lower alkyl” refers to an alkyl group containing from 1 to 6 carbon atoms, and may be straight chain or branched, as exemplified by methyl, ethyl, n-butyl, i-butyl, t-butyl.
• “Cycloalkyl” refers to a saturated or unsaturated cyclic hydrocarbon chain, including bridged, fused, or spiro cyclic compounds, preferably made up of 3 to about 12 carbon atoms, more preferably 3 to about 8.
• “Non-interfering substituents” are those groups that, when present in a molecule, are typically non-reactive with other functional groups contained within the molecule.
• The term “substituted” as in, for example, “substituted alkyl,” refers to a moiety (e.g., an alkyl group) substituted with one or more non-interfering substituents, such as, but not limited to: C₃-C₈cycloalkyl, e.g., cyclopropyl, cyclobutyl, and the like; halo, e.g., fluoro, chloro, bromo, and iodo; cyano; alkoxy, lower phenyl; substituted phenyl; and the like. For substitutions on a phenyl ring, the substituents may be in any orientation (i.e., ortho, meta, or para).
• “Alkoxy” refers to an —O—R group, wherein R is alkyl or substituted alkyl, preferably C₁-C₂₀alkyl (e.g., methoxy, ethoxy, propyloxy, etc.), preferably C₁-C₇.
• As used herein, “alkenyl” refers to a branched or unbranched hydrocarbon group of 1 to 15 atoms in length, containing at least one double bond, such as ethenyl, n-propenyl, isopropenyl, n-butenyl, isobutenyl, octenyl, decenyl, tetradecenyl, and the like.
• The term “alkynyl” as used herein refers to a branched or unbranched hydrocarbon group of 2 to 15 atoms in length, containing at least one triple bond, ethynyl, n-propynyl, isopropynyl, n-butynyl, isobutynyl, octynyl, decynyl, and so forth.
• “Aryl” means one or more aromatic rings, each of 5 or 6 core carbon atoms. Aryl includes multiple aryl rings that may be fused, as in naphthyl or unfused, as in biphenyl. Aryl rings may also be fused or unfused with one or more cyclic hydrocarbon, heteroaryl, or heterocyclic rings. As used herein, “aryl” includes heteroaryl.
• “Heteroaryl” is an aryl group containing from one to four heteroatoms, preferably N, O, or S, or a combination thereof. Heteroaryl rings may also be fused with one or more cyclic hydrocarbon, heterocyclic, aryl, or heteroaryl rings.
• “Heterocycle” or “heterocyclic” means one or more rings of 5-12 atoms, preferably 5-7 atoms, with or without unsaturation or aromatic character and having at least one ring atom which is not a carbon. Preferred heteroatoms include sulfur, oxygen, and nitrogen.
• “Substituted heteroaryl” is heteroaryl having one or more non-interfering groups as substituents.
• “Substituted heterocycle” is a heterocycle having one or more side chains formed from non-interfering substituents.
• “Electrophile” refers to an ion, atom, or collection of atoms that may be ionic, having an electrophilic center, i.e., a center that is electron seeking, capable of reacting with a nucleophile.
• “Nucleophile” refers to an ion or atom or collection of atoms that may be ionic, having a nucleophilic center, i.e., a center that is seeking an electrophilic center, and capable of reacting with an electrophile.
• “Active agent” as used herein includes any agent, drug, compound, and the like which provides some pharmacologic, often beneficial, effect that can be demonstrated in-vivo or in vitro. As used herein, these terms further include any physiologically or pharmacologically active substance that produces a localized or systemic effect in a patient.
• “Pharmaceutically acceptable excipient” or “pharmaceutically acceptable carrier” refers to an excipient that can be included in the compositions of the invention and that causes no significant adverse toxicological effects to the patient.
• “Pharmacologically effective amount,” “physiologically effective amount,” and “therapeutically effective amount” are used interchangeably herein to mean the amount of a PEG-active agent conjugate present in a pharmaceutical preparation that is needed to provide a desired level of active agent and/or conjugate in the bloodstream or in a target tissue. The precise amount will depend upon numerous factors, e.g., the particular active agent, the components and physical characteristics of pharmaceutical preparation, intended patient population, patient considerations, and the like, and can readily be determined by one skilled in the art, based upon the information provided herein and available in the relevant literature.
• “Multi-functional” in the context of a polymer of the invention means a polymer having 3 or more functional groups, where the functional groups may be the same or different, and are typically present on the polymer termini. Multi-functional polymers of the invention will typically contain from about 3-100 functional groups, or from 3-50 functional groups, or from 3-25 functional groups, or from 3-15 functional groups, or from 3 to 10 functional groups, i.e., contains 3, 4, 5, 6, 7, 8, 9 or 10 functional groups. Typically, in reference to a polymer precursor used to prepare a polymer prodrug of the invention, the polymer possesses 3 or more polymer arms having at the terminus of each arm a functional group suitable for coupling to an active agent moiety via a hydrolyzable linkage.
• “Difunctional” or “bifunctional” as used interchangeable herein means an entity such as a polymer having two functional groups contained therein, typically at the polymer termini. When the functional groups are the same, the entity is said to be homodifunctional or homobifunctional. When the functional groups are different, the polymer is said to be heterodifunctional or heterobifunctional.
• A basic or acidic reactant described herein includes neutral, charged, and any corresponding salt forms thereof.
• “Polyolefinic alcohol” refers to a polymer comprising an olefin polymer backbone, such as polyethylene, having multiple pendant hydroxyl groups attached to the polymer backbone. An exemplary polyolefinic alcohol is polyvinyl alcohol.
• As used herein, “non-peptidic” refers to a polymer backbone substantially free of peptide linkages. However, the polymer may include a minor number of peptide linkages spaced along the repeat monomer subunits, such as, for example, no more than about 1 peptide linkage per about 50 monomer units.
• The terms “subject”, “individual” or “patient” are used interchangeably herein and refer to a vertebrate, preferably a mammal. Mammals include, but are not limited to, murines, rodents, simians, humans, farm animals, sport animals and pets. Such subjects are typically suffering from or prone to a condition that can be prevented or treated by administration of a polymer of the invention, typically but not necessarily in the form of a polymer-active agent conjugate as described herein.
• The term “about”, particularly in reference to a given quantity, is meant to encompass deviations of plus or minus five percent.
• “Treatment” or “treating” of a particular condition includes: (1) preventing such a condition, i.e. causing the condition not to develop, or to occur with less intensity or to a lesser degree in a subject that may be exposed to or predisposed to the condition but does not yet experience or display the condition, (2) inhibiting the condition, i.e., arresting the development or reversing the condition.
• “Optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not.
• A “small molecule” may be defined broadly as an organic, inorganic, or organometallic compound typically having a molecular weight of less than about 1000. Small molecules of the invention encompass oligopeptides and other biomolecules having a molecular weight of less than about 1000.
• An “active agent moiety” in reference to a prodrug conjugate of the invention, refers to the portion or residue of the unmodified parent active agent up to the covalent linkage resulting from covalent attachment of the drug (or an activated or chemically modified form thereof) to a polymer of the invention. Upon hydrolysis of the hydrolyzable linkage between the active agent moiety and the multi-armed polymer, the active agent per se is released.
Multi-Arm Polymer Prodrug Conjugates—Overview
• As described generally above, the polymer conjugates of the invention comprise a multi-arm water-soluble and non-peptidic polymer covalently attached to at least three active agent compounds. The conjugates of the invention are typically prodrugs, meaning that the active agent, attached to the polymer via a hydrolytically degradable linkage, is released over time following administration of the conjugate to a subject. Moreover, the conjugates of the invention are well-characterized, isolable, and purifiable compositions, in comparison to, for example, a degradable polymer-matrix having molecules of drug encapsulated therein. The conjugates of the invention exhibit higher drug loading characteristics when compared to their linear polymer-based counterparts, thus lowering the total dosage weight needed to treat a particular disease state. That is to say, the polymer scaffold of the invention is effective to covalently attach multiple active agent molecules thereto, thereby allowing a greater amount of therapeutic agent (i.e., active agent) to be administered per given weight of polymer when compared to a linear monofunctional or bifunctional polymer of about the same size but having only one or two active agent molecules attached thereto. The polymers employed in the invention are hydrophilic in nature, thereby imparting hydrophilicity to the resulting conjugates, which, particularly in the case of water-insoluble active agents, facilitates their formulation into useful pharmaceutical compositions.
• Typically, the total number average molecular weight of the overall multi-arm polymer portion of a polymer conjugate of the invention is about 800 daltons (Da) to about 100,000 Da, more preferably about 10,000 Da to about 60,000 Da, most preferably about 15,000 to about 60,000 Da. Multi-armed polymers having a number average molecular weight of about 5,000 Da, about 8,000 Da, about 10,000 Da, about 12,000 Da, about 15,000 Da, about 20,000 Da, about 25,000 Da, about 30,000 Da, about 35,000 Da, about 40,000 Da, about 45,000 Da, about 50,000 Da, and about 60,000 Da, among others, are particularly preferred. Multi-armed polymers having a molecular weight of 20,000 Da or greater, i.e., of about 20,000 Da, or 25,000 Da, or 30,000 Da, or 40,000 Da or 50,000 Da, or 60,000 Da, are particularly preferred for tumor-targeting applications. The actual molecular weight of the multi-armed polymer will depend, of course, on the number of polymer arms and the molecular weight of each polymer arm in the overall multi-armed polymer, as well as the degree of polydispersity of the polymer.
• The linkage between the multi-armed polymer portion and the active agent is preferably hydrolytically degradable for in vivo release of the parent drug molecule over time. Representative hydrolytically degradable linkages corresponding to X in structure I include carboxylate ester, carbonate ester, phosphate ester, anhydride, acetal, ketal, acyloxyalkyl ether, imine, orthoester, and oligonucleotides. Esters such as carboxylate and carbonate esters are particularly preferred linkages. The particular linkage and linkage chemistry employed will depend upon the particular active agent, the presence of additional functional groups within the active agent, and the like, and can be readily determined by one skilled in the art based upon the guidance presented herein.
• With respect to the multi-arm prodrug conjugates of the invention, it is not necessary for the polymer conjugate itself to exhibit biological activity, since the parent drug is released upon hydrolysis. However, in certain embodiments, the polymer conjugate maintains at least a measurable degree of activity. That is to say, in some instances, a multi-armed polymer conjugate possesses anywhere from about 1% to about 100% or more of the specific activity of the unmodified parent compound. That is to say, a multi-armed polymer prodrug of the invention will possess from about 1% to about 100% bioactivity relative to the unmodified parent active agent, prior to conjugation. Such activity may be determined using a suitable in-vivo or in-vitro model, depending upon the known activity of the particular parent compound. For anticancer drugs, in vivo anticancer activity is typically evaluated by comparison of growth rates of tumor implants in drug treated and control groups of athymic mice using well-established animal models (See for example, Examples 2, 6, 7, 11, 12, 13, 16, 17, and 18). Anticancer activity is indicated by slower tumor growth rates in the treated group relative to the control group (J. W. Singer, et al., Ann. N.Y. Acad. Sci., 922: 136-150, 2000). In general, certain polymer conjugates of the invention will possess a specific activity of at least about 2%, 5%, 10%, 15%, 25%, 30%, 40%, 50%, 60%, 80%, 90% or more relative to that of the unmodified parent drug when measured in a suitable model.
• As demonstrated in Examples 2, 6, 7, 11, 12, 13, 16, 17 and 18, preferred polymer prodrug conjugates of the invention exhibit enhanced properties in comparison to their unmodified parent drug counterparts. The polymer conjugates of the invention exhibit enhanced permeation and retention (EPR) in target tissues by passively accumulating in such tissues, to provide targeted delivery of the drug to desired sites in the body (See Matsumara Y, Maeda H. “ANEW CONCEPT FOR MACROMOLECULAR THERAPEUTICS IN CANCER THERAPY; MECHANISM OF TUMORITROPIC ACCUMULATION OF PROTEINS AND THE ANTITUMOUR AGENTSMANCS”,Cancer Res1986; 46:6387-92). Moreover, the growth rate of several different types of cancerous tumors when examined in various in-vivo models was significantly decreased following administration of illustrative conjugates of the invention when compared to unmodified drug.
• Additionally, the severity of the side effects associated with administration of the polymer conjugates of the invention is preferably comparable to, or even more preferably, is less than, the side effects associated with administration of the parent compound. In particular, preferred conjugates and conjugate compositions, particularly those comprising about 3 or more molecules of an anticancer agent such as irinotecan per polymer core, when administered to a patient, result in reduced or ameliorated side effects, which may be one or more of leucopenia, neutropenia, and diarrhea, when compared to the unmodified parent drug molecule. The severity of side effects of anticancer agents such as camptothecin and camptothecin-like compounds can be readily assessed (See, for example, Kado, et al., Cancer Chemotherapy and Pharmacology, Aug. 6, 2003). The polymer conjugates of the invention are believed to exhibit reduced side effects as compared to the unconjugated parent drug, in part, due to the accumulation of the conjugate molecules in the target tissue and away from other sites of likely toxicity. Each of these features of the prodrugs of the invention will now be discussed in greater detail below.
Structural Features of the Polymer Prodrug
• As described above, a prodrug of the invention comprises a multi-arm polymer, i.e., having three or more arms, where the conjugate comprises the following generalized structure:
• 
  R(-Q-POLY₁-X-D)_q
• Each arm of the multi-armed prodrug is independent from the other. That is to say, each of the “q” arms of the prodrug may be composed of a different Q, POLY₁, X, D and so forth. Typical of such embodiments, a generalized structure corresponds to: R[(-Q₁-POLY_1A-X₁-D₁)(Q₂-POLY_1B-X₂-D₂)(Q₃-POLY_1c-X₃-D₃)] and so forth for each of the arms emanating from the central organic core. Generally, however, each arm of the multi-armed prodrug is the same.
• Each of the variable components of structure I will now be described in detail.
• Organic Core, “R”
• In structure I, R is an organic core radical possessing from about 3 to about 150 carbon atoms. Preferably, R contains from about 3 to about 50 carbon atoms, and even more preferably, R contains from about 3 to about 10 carbon atoms. That is to say, R may possess a number of carbon atoms selected from the group consisting of 3, 4, 5, 6, 7, 8, 9, and 10. The organic core may optionally contain one or more heteroatoms (e.g., O, S, or N), depending of course on the particular core molecule employed. R may be linear or cyclic, and typically, emanating therefrom are at least 3 independent polymer arms, three or more of which have at least one active agent moiety covalently attached thereto. Looking at Structure I, “q” corresponds to the number of polymer arms emanating from “R”. In some instances one or more of the polymer arms may not have an active agent covalently attached thereto, but rather may have a relatively unreactive or unreacted functional group at its terminus, typically resulting from a synthesis that has failed to go to completion. In this instance, D is absent and the individual structure of at least one of the polymer arms is in its precursor form (or is a derivative thereof), i.e., having at its terminus not an active agent, D, but rather, a functional group.
• The central core organic radical, R, is derived from a molecule that provides a number of polymer attachment sites approximately equal to the desired number of water-soluble and non-peptidic polymer arms. Preferably, the central core molecule of the multi-arm polymer structure is the residue of a polyol, polythiol, or a polyamine bearing at least three hydroxyl, thiol, or amino groups available for polymer attachment. A “polyol” is a molecule comprising a plurality (greater than 2) of available hydroxyl groups. A “polythiol” is a molecule that possesses a plurality (greater than 2) thiol groups. A “polyamine” is a molecule comprising a plurality (greater than 2) of available amino groups. Depending on the desired number of polymer arms, the precursor polyol, polyamine or polythiol, (prior to covalent attachment of POLY₁) will typically contain 3 to about 25 hydroxyl, or amino groups or orthiol groups, respectively, preferably from 3 to about 10 hydroxyl, amino groups or thiol groups, (i.e., 3, 4, 5, 6, 7, 8, 9, 10), most preferably, will contain from 3 to about 8 (e.g., 3, 4, 5, 6, 7, or 8) hydroxyl, amino groups or thiol groups suitable for covalent attachment of POLY₁. The polyol, polyamine or polythiol may also include other protected or unprotected functional groups. Focusing on organic cores derived from polyols or polyamines, although the number of intervening atoms between each hydroxyl or amino group will vary, preferred cores are those having a length of from about 1 to about 20 intervening core atoms, such as carbon atoms, between each hydroxyl or amino group, preferably from about 1 to about 5. In referring to intervening core atoms and lengths, —CH₂—, for example, is considered as having a length of one intervening atom, although the methylene group itself contains three atoms total, since the Hs are substituents on the carbon, and —CH₂CH₂—, for instance, is considered as having a length of two carbon atoms, etc. The particular polyol or polyamine precursor depends on the desired number of polymer arms in the final conjugate. For example, a polyol or polyamine core molecule having 4 functional groups, Q, is suitable for preparing a prodrug in accordance with structure I having four polymer arms extending therefrom and covalently attached to active agent.
• The precursor polyol or polyamine core will typically possess a structure R—(OH)_por R—(NH₂)_pprior to functionalization with a polymer. The value of p corresponds to the value of q in structure I, since each functional group, typically —OH or —NH₂, in the parent core organic molecule, if sterically accessible and reactive, is covalently attached to a polymer arm, POLY₁. Note that in structure I, the variable “Q”, when taken together with R, typically represents a residue of the core organic radical as described herein. That is to say, when describing preferred organic core molecules, particularly by name, the core molecules are described in their precursor form, rather than in their radical form after removal of, for example, a proton. So, if for example, the organic core radical is derived from pentaerythritol, the precursor polyol possesses the structure C(CH₂OH)₄, and the organic core radical, together with Q, corresponds to C(CH₂O—)₄, where Q is O.
• Illustrative polyols that are preferred for use as the polymer core include aliphatic polyols having from 1 to 10 carbon atoms and from 1 to 10 hydroxyl groups, including for example, ethylene glycol, alkane diols, alkyl glycols, alkylidene alkyl diols, alkyl cycloalkane diols, 1,5-decalindiol, 4,8-bis(hydroxymethyl)tricyclodecane, cycloalkylidene diols, dihydroxyalkanes, trihydroxyalkanes, and the like. Cycloaliphatic polyols include straight chained or closed-ring sugars and sugar alcohols, such as mannitol, sorbitol, inositol, xylitol, quebrachitol, threitol, arabitol, erythritol, adonitol, dulcitol, facose, ribose, arabinose, xylose, lyxose, rhamnose, galactose, glucose, fructose, sorbose, mannose, pyranose, altrose, talose, tagitose, pyranosides, sucrose, lactose, maltose, and the like. Additional examples of aliphatic polyols include derivatives of glyceraldehyde, glucose, ribose, mannose, galactose, and related stereoisomers. Aromatic polyols may also be used, such as 1,1,1-tris(4′-hydroxyphenyl) alkanes, such as 1,1,1-tris(4-hydroxyphenyl)ethane, (1,3-adamantanediyl)diphenol, 2,6-bis(hydroxyalkyl)cresols, 2,2′alkylene-bis(6-t-butyl-4-alkylphenols), 2,2′-alkylene-bis(t-butylphenols), catechol, alkylcatechols, pyrogallol, fluoroglycinol, 1,2,4-benzenetriol, resorcinol, alkylresorcinols, dialkylresorcinols, orcinol monohydrate, olivetol, hydroquinone, alkylhydroquinones, 1,1-bi-2-naphthol, phenyl hydroquinones, dihydroxynaphthalenes, 4,4′-(9-fluorenylidene)-diphenol, anthrarobin, dithranol, bis (hydroxyphenyl) methane biphenols, dialkylstilbesterols, bis(hydroxyphenyl)alkanes, bisphenol-A and derivatives thereof, meso-hexesterol, nordihydroguaiaretic acid, calixarenes and derivatives thereof, tannic acid, and the like. Other core polyols that may be used include crown ethers, cyclodextrins, dextrins and other carbohydrates (e.g., monosaccharides, oligosaccharides, and polysaccharides, starches and amylase).
• Preferred polyols include glycerol, trimethylolpropane, reducing sugars such as sorbitol or pentaerythritol, and glycerol oligomers, such as hexaglycerol. A 21-arm polymer can be synthesized using hydroxypropyl-β-cyclodextrin, which has 21 available hydroxyl groups.
• Exemplary polyamines include aliphatic polyamines such as diethylene triamine, N,N′,N″-trimethyldiethylene triamine, pentamethyl diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, dipropylene triamine, tripropylene tetramine, bis-(3-aminopropyl)-amine, bis-(3-aminopropyl)-methylamine, and N,N-dimethyl-dipropylene-triamine. Naturally occurring polyamines that can be used in the present invention include putrescine, spermidine, and spermine. Numerous suitable pentamines, tetramines, oligoamines, and pentamidine analogs suitable for use in the present invention are described in Bacchi et al.,Antimicrobial Agents and Chemotherapy, January 2002, p. 55-61, Vol. 46, No. 1, which is incorporated by reference herein.
• Provided below are illustrative structures corresponding to the organic radical portion of the conjugate, R, and the corresponding idealized conjugate, assuming that each of the hydroxyls in the parent polyol has been transformed to a polymer arm and that each polymer arm has drug covalently attached thereto. Note that the organic radicals shown below, derived from polyols, include the oxygens, which, in the context of structure I, for the arms that are polymer arms, are considered as part of Q. It is not necessary that all hydroxyls in, for example, a polyol-derived organic radical, form part of a polymer arm. In the illustrative examples below, Q is shown as O, but can equally be considered as corresponding to S, —NH—, or —NH—C(O)—.

• ORGANIC RADICAL*	ILLUSTRATIVE CONJUGATE
  II	II-A
  III	III-A
  IV	IV-A
  	see conjugate below
  V
  	V-A
  m = 0-40, preferably 0-10, or 0-5.
  VI	VI-A
  *includes Q
  LINKAGES, Q AND X.

• The linkages between the organic radical, R, and the polymer segment, POLY₁, or between POLY₁and the active agent, D, result from the reaction of various reactive groups contained within R, POLY₁, and D. The particular coupling chemistry employed will depend upon the structure of the active agent, the potential presence of multiple functional groups within the active molecule, the need for protection/deprotection steps, the chemical stability of the active agent, and the like, and will be readily determined by one skilled in the art based upon the guidance herein. Illustrative linking chemistry useful for preparing the polymer conjugates of the invention can be found, for example, in Wong, S. H., (1991), “Chemistry of Protein Conjugation and Crosslinking”, CRC Press, Boca Raton, Fla. and in Brinkley, M. (1992) “A Brief Survey of Methods for Preparing Protein Conjugates with Dyes, Haptens, and Crosslinking Reagents”, inBioconjug. Chem.,3, 2013. As noted above, the overall linkage between the multi-armed polymer core and each drug molecule preferably comprises a hydrolytically degradable portion, such as an ester linkage, so that the active agent is released over time from the multi-armed polymer core.
• The multi-arm polymeric conjugates provided herein (as well as the corresponding reactive polymer precursor molecules, and so forth) comprise a linker segment, Q, and a spacer segment, X. Exemplary spacers or linkers can include segments such as those independently selected from the group consisting of —O—, —S—, —NH, —C(O)—, —O—C(O)—, —C(O)—O—, —C(O)—NH—, —NH—C(O)—NH—, —O—C(O)—NH—, —C(S)—, —CH₂—, —CH₂—CH₂—, —CH₂—CH₂—CH₂—, —CH₂—CH₂—CH₂—CH₂—, —O—CH₂—, —CH₂—O—, —O—CH₂—CH₂—, —CH₂—O—CH₂—, —CH₂—CH₂—O—, —O—CH₂—CH₂—CH₂—, —CH₂—O—CH₂—CH₂—, —CH₂—CH₂—O—CH₂—, —CH₂—CH₂—CH₂—O—, —O—CH₂—CH₂—CH₂—CH₂—, —CH₂—O—CH₂—CH₂—CH₂—, —CH₂—CH₂—O—CH₂—CH₂—, —CH₂—CH₂—CH₂—O—CH₂—, —CH₂—CH₂—CH₂—CH₂—O—, —C(O)—NH—CH₂—, —C(O)—NH—CH₂—CH₂—, —CH₂—C(O)—NH—CH₂—, —CH₂—CH₂—C(O)—NH—, —C(O)—NH—CH₂—CH₂—CH₂—, —CH₂—C(O)—NH—CH₂—CH₂—, —CH₂—CH₂—C(O)—NH—CH₂—, —CH₂—CH₂—CH₂—C(O)—NH—, —C(O)—NH—CH₂—CH₂—CH₂—CH₂—, —CH₂—C(O)—NH—CH₂—CH₂—CH₂—, —CH₂—CH₂—C(O)—NH—CH₂—CH₂—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—, —CH₂—CH₂—CH₂—CH₂—C(O)—NH—, —C(O)—O—CH₂—, —CH₂—C(O)—O—CH₂—, —CH₂—CH₂—C(O)—O—CH₂—, —C(O)—O—CH₂—CH₂—, —NH—C(O)—CH₂—, —CH₂—NH—C(O)—CH₂—, —CH₂—CH₂—NH—C(O)—CH₂—, —NH—C(O)—CH₂—CH₂—, —CH₂—NH—C(O)—CH₂—CH₂—, —CH₂—CH₂—NH—C(O)—CH₂—CH₂—, —C(O)—NH—CH₂—, —C(O)—NH—CH₂—CH₂—, —O—C(O)—NH—CH₂—, —O—C(O)—NH—CH₂—CH₂—, —O—C(O)—NH—CH₂—CH₂—CH₂—, —NH—CH₂—, —NH—CH₂—CH₂—, —CH₂—NH—CH₂—, —CH₂—CH₂—NH—CH₂—, —C(O)—CH₂—, —C(O)—CH₂—CH₂—, —CH₂—C(O)—CH₂—, —CH₂—CH₂—C(O)—CH₂—, —CH₂—CH₂—C(O)—CH₂—CH₂—, —CH₂—CH₂—C(O)—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—C(O)—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—C(O)—CH₂—, —CH₂—CH₂—CH₂—C(O)—NH—CH₂—CH₂—NH—C(O)—CH₂—CH₂—, —O—C(O)—NH—[CH₂]_0-6—(OCH₂CH₂)_0-2—, —C(O)—NH—(CH₂)_1-6—NH—C(O)—, and —NH—C(O)—NH—(CH₂)_1-6—NH—C(O)—.
• In any of the above examples, a simple cycloalkylene group, e.g. 1,3- or 1,4-cyclohexylene, may replace any two, three or four carbon alkylene group. For purposes of the present disclosure, however, a series of atoms is not a spacer moiety when the series of atoms is immediately adjacent to a water-soluble polymer segment and the series of atoms is but another monomer, such that the proposed spacer moiety would represent a mere extension of the polymer chain. A spacer or linker as described herein may also comprise a combination of any two or more of the above groups, in any orientation.
• Referring to structure I, Q is a linker, preferably one that is hydrolytically stable. Typically, Q contains at least one heteratom such as 0, or S, or NH, where the atom proximal to R in Q, when taken together with R, typically represents a residue of the core organic radical R. Generally, Q contains from 1 to about 10 atoms, or from 1 to about 5 atoms. Q typically contains one of the following numbers of atoms: 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. Illustrative Qs include O, S, or —NH—C(O)—.
• Again in reference to structure I, X is a spacer that comprises a hydrolyzable linkage, where the hydrolyzable linkage is attached directly to the active agent, D. Typically, at least one atom of the hydrolyzable linkage is contained in the active agent in its unmodified form, such that upon hydrolysis of the hydrolyzable linkage comprised within X, the active agent, D, is released. Generally speaking, the spacer has an atom length of from about 4 atoms to about 50 atoms, or more preferably from about 5 atoms to about 25 atoms, or even more preferably from about 5 atoms to about 20 atoms. Typically, the spacer is of an atom length selected from the group consisting of 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. When considering atom chain length, only atoms contributing to the overall distance are considered. For example, a spacer having the structure, —CH₂—C(O)—NH—CH₂CH₂O—CH₂CH₂O—C(O)—O— has a chain length of 11 atoms, since substituents are not considered to contribute significantly to the length of the spacer.
• In yet another particular embodiment, X possesses the structure: Y—Z, where Y is a spacer fragment covalently attached to Z, a hydrolytically degradable linkage. In certain embodiments, Z itself may not constitute a hydrolytically degradable linkage, however, when taken together with Y, or at least a portion of Y, forms a linkage that is hydrolytically degradable.
• In yet a more particular embodiment of the spacer, X, Y has the structure: —(CR_xR_y)_a—K—(CR_xR_y)_b—(CH₂CH₂O)_c—, wherein each R₁and R₂, in each occurrence, is independently H or an organic radical selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, and substituted aryl, a ranges from 0 to 12 (i.e., can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12), b ranges from 0 to 12 (i.e., can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12), K is selected from —C(O)—, —C(O)NH—, —NH—C(O)—, —O—, —S—, O—C(O)—, C(O)—O—, O—C(O)—O—, O—O(O)—NH—, NH—C(O)—O—, c ranges from 0 to 25, and Z is selected from C(O)—O—, O—C(O)—O—, —O—C(O)—NH—, and NH—C(O)—O—. The particular structure of K and of Z will depend upon the values of each of a, b, and c, such that none of the following linkages result in the overall structure of spacer X: —O—O—, NH—O—, NH—NH—.
• Preferably, Y comprises (—CH₂)_a—C(O)NH—(CH₂)_0,1—(CH₂CH₂O)_0-10.
• In yet another embodiment of the spacer, X, Y has the structure: —(CR_xR_y)_a—K—(CR_xR_y)_b—(CH₂CH₂NH)_c—, where the variables have the values previously described. In certain instances, the presence of the short ethylene oxide or ethyl amino fragments in spacer, X, can be useful in achieving good yields during preparation of the prodrug conjugate, since the presence of the linker can help to circumvent problems associated with steric hindrance, due to the multi-armed reactive polymer, the structure of the active agent, or a combination of both. Preferably, c is selected from the group consisting of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.
• Preferably, R_xand R_yin each occurrence are independently H or lower alkyl. In one embodiment, R_xand R_yare in each occurrence H. In yet another embodiment, “a” ranges from 0 to 5, i.e., is selected from 0, 1, 2, 3, 4, or 5. In yet another embodiment, b ranges from 0 to 5, i.e., is selected from 0, 1, 2, 3, 4, or 5. In yet another embodiment, c ranges from 0 to 10. In yet another embodiment, K is —C(O)—NH. Any of the embodiments described herein is meant to apply not only to generalized structure I, but also extend to particular combinations of embodiments.
• In yet another embodiment, R_xand R_yin each occurrence are H, a is 1, K is —C(O)—NH, and b is 0 or 1.
• Particular examples of X include —CH₂—C(O)—NH—CH₂—C(O)O— (here, Y corresponds to —CH₂—C(O)—NH—CH₂— and Z corresponds to —C(O)—O—), and —CH₂—O(O)—NH—(CH₂CH₂O)₂—C(O)—O— (here, Y corresponds to —CH₂—C(O)—NH—(CH₂CH₂O)₂— and Z corresponds to —C(O)—O—).
• The Polymer, POLY₁
• In structure I, POLY₁represents a water-soluble and non-peptidic polymer. POLY₁in each polymer arm of structure I is independently selected, although preferably, each polymer arm will comprise the same polymer. Preferably, each of the arms (i.e., each “(-Q-POLY₁-X-D) of structure I is identical. Any of a variety of polymers that are non-peptidic and water-soluble can be used to form a conjugate in accordance with the present invention. Examples of suitable polymers include, but are not limited to, poly(alkylene glycols), copolymers of ethylene glycol and propylene glycol, poly(olefinic alcohol), poly(vinylpyrrolidone), poly(hydroxyalkylmethacrylamide), poly(hydroxyalkylmethacrylate), poly(saccharides), poly(α-hydroxy acid), poly(acrylic acid), poly(vinyl alcohol), polyphosphazene, polyoxazoline, poly(N-acryloylmorpholine), such as described in U.S. Pat. No. 5,629,384, which is incorporated by reference herein in its entirety, and copolymers, terpolymers, and mixtures of any one or more of the above.
• Preferably, POLY₁is a polyethylene glycol or PEG. POLY₁can be in any of a number of geometries or forms, including linear chains, branched, forked, etc., although preferably POLY₁is linear (i.e., in each arm of the overall multi-arm structure) or forked. A preferred structure for a multi-armed polymer prodrug having a “forked” polymer configuration is as follows:
• 
• F represents a forking group, and the remaining variables are as previously described. Preferably, the fork point in the forking group, F, comprises or is (—CH), though it may also be a nitrogen atom (N). In this way, each polymer arm is forked to possess two active agent moieties releasably covalently attached thereto, rather than one.
• Illustrative forked polymers useful for preparing a multi-armed polymer of the type shown in Fig. XII are described in U.S. Pat. No. 6,362,254.
• When POLY₁is PEG, its structure typically comprises —(CH₂CH₂O)_n—, where n ranges from about 5 to about 400, preferably from about 10 to about 350, or from about 20 to about 300.
• In the multi-arm embodiments described here, each polymer arm, POLY₁, typically has a molecular weight corresponding to one of the following: 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 7500, 8000, 9000, 10000, 12,000, 15000, 17,500, 18,000, 19,000, 20,000 daltons or greater. Overall molecular weights for the multi-armed polymer configurations described herein (that is to say, the molecular weight of the multi-armed polymer as a whole) generally correspond to one of the following: 800, 1000, 1200, 1600, 2000, 2400, 2800, 3200, 3600, 4000, 5000, 6000, 8000, 10,000, 12,000, 15,000, 16,000, 20,000, 24,000, 25,000, 28,000, 30,000, 32,000, 36,000, 40,000, 45,000, 48,000, 50,000, 60,000, 80,000 or greater.
• Typically, the overall molecular weight for a multi-armed polymer of the invention ranges from about 800 to about 60,000 daltons. Other preferred molecular weight ranges for a multi-armed polymer of the invention are from about 1,000 to about 40,000 daltons, or from about 5,000 to about 30,000 daltons, or even from about 20,000 to about 80,000 daltons.
• Active Agent, D.
• Returning now to structure I, D is an active agent moiety, and q (the number of independent polymer arms) ranges from about 3 to about 50. Preferably, q ranges from about 3 to about 25. More preferably, q is from 3 to about 10, and possesses a value of 3, 4, 5, 6, 7, 8, 9, or 10. The active agent moiety, D contains at least one functional group suitable for covalent attachment to the multi-armed polymer described herein to form a hydrolyzable linkage, such that upon hydrolysis, the active agent is released in its unmodified form.
• In accordance with one embodiment of the invention, a prodrug conjugate is characterized as a polymer having from about 3 to about 25 active agent molecules covalently attached thereto. More particularly, the conjugate is characterized as a water-soluble polymer having 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 active agent molecules covalently attached thereto. In a further embodiment, the conjugate of the invention has from about 3 to about 8 active agent molecules covalently attached to the water-soluble polymer. Typically, although not necessarily, the number of polymer arms will correspond to the number of active agents covalently attached to the water-soluble polymer. That is to say, in the case of a polymer having a certain number of polymer arms (e.g., X), each having a reactive functional group at its terminus, the number of active agents covalently attached thereto in the resulting conjugate is preferably X.
• In yet another embodiment, rather than having multiple polymer arms emanating from a central organic radical core, a conjugate of the invention is characterized as a water-soluble polymer having pendant active agent moieties covalently attached thereto, each preferably covalently attached by a degradable linkage. In such an embodiment, the structure of the polymer prodrug conjugate is described generally as POLY₁(X-D)_q, where and POLY₁, X, D, and q are as set forth above, and the polymer, typically a linear polymer, possesses “q” active agent moieties attached thereto, typically at discrete lengths along the polymer chain, via the spacer X which contains a hydrolyzable linkage.
• In a specific embodiment, the active agent moiety is a small molecule possessing a molecular weight of less than about 1000. In yet additional embodiments, the small molecule drug possesses a molecular weight of less than about 800, or even less than about 750. In yet another embodiment, the small molecule drug possesses a molecular weight of less than about 500 or, in some instances, even less than about 300.
• Preferred active agent moieties include anticancer agents. Particularly preferred are oncolytics having at least one hydroxyl group.
• One preferred class of active agents is the camptothecins. In one embodiment, a camptothecin for use in the invention corresponds to the structure:
• 
• wherein R₁-R₅are each independently selected from the group consisting of hydrogen; halo; acyl; alkyl (e.g., C1-C6 alkyl); substituted alkyl; alkoxy (e.g., C1-C6 alkoxy); substituted alkoxy; alkenyl; alkynyl; cycloalkyl; hydroxyl; cyano; nitro; azido; amido; hydrazine; amino; substituted amino (e.g., monoalkylamino and dialkylamino); hydroxcarbonyl; alkoxycarbonyl; alkylcarbonyloxy; alkylcarbonylamino; carbamoyloxy; arylsulfonyloxy; alkylsulfonyloxy; —C(R₇)═N—(O)_i—R₈wherein R₇is H, alkyl, alkenyl, cycloalkyl, or aryl, i is 0 or 1, and R₈is H, alkyl, alkenyl, cycloalkyl, or heterocycle; and R₉C(O)O— wherein R₉is halogen, amino, substituted amino, heterocycle, substituted heterocycle, or R₁₀—O—(CH₂)_m— where m is an integer of 1-10 and R₁₀is alkyl, phenyl, substituted phenyl, cycloalkyl, substituted cycloalkyl, heterocycle, or substituted heterocycle; or
• R₂together with R₃or R₃together with R₄form substituted or unsubstituted methylenedioxy, ethylenedioxy, or ethyleneoxy;
• R₆is H or OR′, wherein R′ is alkyl, alkenyl, cycloalkyl, haloalkyl, or hydroxyalkyl; and
• L is the site of attachment to X.
• The term “camptothecin compound” as used herein includes the plant alkaloid 20(S)-camptothecin, as well as pharmaceutically active derivatives, analogues and metabolites thereof. Examples of camptothecin derivatives include, but are not limited to, 9-nitro-20(S)-camptothecin, 9-amino-20(S)-camptothecin, 9-methyl-camptothecin, 9-chloro-camptothecin, 9-flouro-camptothecin, 7-ethyl camptothecin, 10-methyl-camptothecin, 10-chloro-camptothecin, 10-bromo-camptothecin, 10-fluoro-camptothecin, 9-methoxy-camptothecin, 11-fluoro-camptothecin, 7-ethyl-10-hydroxy camptothecin (SN38), 10,11-methylenedioxy camptothecin, and 10,11-ethylenedioxy camptothecin, and 7-(4-methylpiperazinomethylene)-10,11-methylenedioxy camptothecin, 7-ethyl-10-(4-(1-piperdino)-1-piperdino)-carbonyloxy-camptothecin, 9-hydroxy-camptothecin, and 11-hydroxy-camptothecin. Particularly preferred camptothecin compounds include camptothecin, irinotecan, and topotecan.
• Native and unsubstituted, the plant alkaloid camptothecin can be obtained by purification of the natural extract, or may be obtained from the Stehlin Foundation for Cancer Research (Houston, Tex.). Substituted camptothecins can be obtained using methods known in the literature or can be obtained from commercial suppliers. For example, 9-nitro-camptothecin may be obtained from SuperGen, Inc. (San Ramon, Calif.), and 9-amino-camptothecin may be obtained from Idec Pharmaceuticals (San Diego, Calif.). Camptothecin and various analogues and derivatives may also be obtained from standard fine chemical supply houses, such as Sigma Chemicals.
• Certain preferred camptothecin compounds correspond to the generalized structure below.
• 
• wherein R₁-R₅are each independently selected from the group consisting of hydrogen; halo; acyl; alkyl (e.g., C1-C6 alkyl); substituted alkyl; alkoxy (e.g., C1-C6 alkoxy); substituted alkoxy; alkenyl; alkynyl; cycloalkyl; hydroxyl; cyano; nitro; azido; amido; hydrazine; amino; substituted amino (e.g., monoalkylamino and dialkylamino); hydroxcarbonyl; alkoxycarbonyl; alkylcarbonyloxy; alkylcarbonylamino; carbamoyloxy; arylsulfonyloxy; alkylsulfonyloxy; —C(R₇)═N—(O)_i—R₈wherein R₇is H, alkyl, alkenyl, cycloalkyl, or aryl, i is 0 or 1, and R₈is H, alkyl, alkenyl, cycloalkyl, or heterocycle; and R₉C(O)O— wherein R₉is halogen, amino, substituted amino, heterocycle, substituted heterocycle, or R₁₀—O—(CH₂)_m— where m is an integer of 1-10 and R₁₀is alkyl, phenyl, substituted phenyl, cycloalkyl, substituted cycloalkyl, heterocycle, or substituted heterocycle; or
• R₂together with R₃or R₃together with R₄form substituted or unsubstituted methylenedioxy, ethylenedioxy, or ethyleneoxy; and
• R₆is H or OR′, wherein R′ is alkyl, alkenyl, cycloalkyl, haloalkyl, or hydroxyalkyl.
• Exemplary substituting groups include hydroxyl, amino, substituted amino, halo, alkoxy, alkyl, cyano, nitro, hydroxycarbonyl, alkoxycarbonyl, alkylcarbonyloxy, alkylcarbonylamino, aryl (e.g., phenyl), heterocycle, and glycosyl groups.
• In one particularly preferred embodiment, D is irinotecan, where the H on the 20-position hydroxyl is absent in the final multi-armed prodrug conjugate.
• 
• In yet another embodiment, D is paclitaxel or docetaxel. One particularly preferred D is docetaxel, where the H at the 2′ position is absent in the final multi-armed polymer conjugate:
• 
• Active agents for use in the invention also include hypnotics and sedatives, psychic energizers, tranquilizers, respiratory drugs, anticonvulsants, muscle relaxants, antiparkinson agents (dopamine antagnonists), analgesics, anti-inflammatories, antianxiety drugs (anxiolytics), appetite suppressants, antimigraine agents, muscle contractants, anti-infectives (antibiotics, antivirals, antifungals, vaccines) antiarthritics, antimalarials, antiemetics, anepileptics, bronchodilators, cytokines, growth factors, anti-cancer agents, antithrombotic agents, antihypertensives, cardiovascular drugs, antiarrhythmics, antioxicants, anti-asthma agents, hormonal agents including contraceptives, sympathomimetics, diuretics, lipid regulating agents, antiandrogenic agents, antiparasitics, anticoagulants, neoplastics, antineoplastics, hypoglycemics, nutritional agents and supplements, growth supplements, antienteritis agents, vaccines, antibodies, diagnostic agents, and contrasting agents.
• More particularly, the active agent may fall into one of a number of structural classes, including but not limited to small molecules, oligopeptides, polypeptides or protein mimetics, fragments, or analogues, steroids, nucleotides, oligonucleotides, electrolytes, and the like. Preferably, an active agent for use in the invention possesses a free hydroxyl, carboxyl, thio, amino group, or the like (i.e., “handle”) suitable for covalent attachment to the polymer. Preferably, an active agent possesses at least one functional group suitable for forming a hydrolyzable linkage when reacted with a multi-armed polymer precursor suitable for forming a prodrug conjugate of the invention.
• Alternatively, the drug is modified by introduction of a suitable “handle”, preferably by conversion of one of its existing functional groups to a functional group suitable for formation of a hydrolyzable covalent linkage between the multi-armed polymer and the drug. Ideally, such a modification should not adversely impact the therapeutic effect or activity of the active agent to a significant degree. That is to say, any modification of an active agent to facilitate its attachment to a multi-armed polymer of the invention should result in no greater than about a 30% reduction of its bioactivity relative to the known parent active agent prior to modification. More preferably, any modification of an active agent to facilitate its attachment to a multi-armed polymer of the invention preferably results in a reduction of its activity relative to the known parent active agent prior to modification of no greater than about 25%, 20%, 15%, 10% or 5%.
• Specific examples of active agents include proteins, small molecule mimetics thereof, and active fragments (including variants) of the following: aspariginase, amdoxovir (DAPD), antide, becaplermin, calcitonins, cyanovirin, denileukin diftitox, erythropoietin (EPO), EPO agonists (e.g., peptides from about 10-40 amino acids in length and comprising a particular core sequence as described in WO 96/40749), dornase alpha, erythropoiesis stimulating protein (NESP), coagulation factors such as Factor V, Factor VII, Factor Vila, Factor VIII, Factor IX, Factor X, Factor XII, Factor XIII, von Willebrand factor; ceredase, cerezyme, alpha-glucosidase, collagen, cyclosporin, alpha defensins, beta defensins, exedin-4, granulocyte colony stimulating factor (GCSF), thrombopoietin (TPO), alpha-1 proteinase inhibitor, elcatonin, granulocyte macrophage colony stimulating factor (GMCSF), fibrinogen, filgrastim, growth hormones human growth hormone (hGH), growth hormone releasing hormone (GHRH), GRO-beta, GRO-beta antibody, bone morphogenic proteins such as bone morphogenic protein-2, bone morphogenic protein-6, OP-1, acidic fibroblast growth factor, basic fibroblast growth factor, CD-40 ligand, heparin, human serum albumin, low molecular weight heparin (LMWH), interferons such as interferon alpha, interferon beta, interferon gamma, interferon omega, interferon tau, consensus interferon; interleukins and interleukin receptors such as interleukin-1 receptor, interleukin-2, interluekin-2 fusion proteins, interleukin-1 receptor antagonist, interleukin-3, interleukin-4, interleukin-4 receptor, interleukin-6, interleukin-8, interleukin-12, interleukin-13 receptor, interleukin-17 receptor; lactoferrin and lactoferrin fragments, luteinizing hormone releasing hormone (LHRH), insulin, pro-insulin, insulin analogues (e.g., mono-acylated insulin as described in U.S. Pat. No. 5,922,675), amylin, C-peptide, somatostatin, somatostatin analogs including octreotide, vasopressin, follicle stimulating hormone (FSH), influenza vaccine, insulin-like growth factor (IGF), insulintropin, macrophage colony stimulating factor (M-CSF), plasminogen activators such as alteplase, urokinase, reteplase, streptokinase, pamiteplase, lanoteplase, and teneteplase; nerve growth factor (NGF), osteoprotegerin, platelet-derived growth factor, tissue growth factors, transforming growth factor-1, vascular endothelial growth factor, leukemia inhibiting factor, keratinocyte growth factor (KGF), glial growth factor (GGF), T Cell receptors, CD molecules/antigens, tumor necrosis factor (TNF), monocyte chemoattractant protein-1, endothelial growth factors, parathyroid hormone (PTH), glucagon-like peptide, somatotropin,thymosin alpha 1,thymosin alpha 1 IIb/IIIa inhibitor,thymosin beta 10, thymosin beta 9,thymosin beta 4, alpha-1 antitrypsin, phosphodiesterase (PDE) compounds, VLA-4 (very late antigen-4), VLA-4 inhibitors, bisphosponates, respiratory syncytial virus antibody, cystic fibrosis transmembrane regulator (CFTR) gene, deoxyreibonuclease (Dnase), bactericidal/permeability increasing protein (BPI), and anti-CMV antibody. Exemplary monoclonal antibodies include etanercept (a dimeric fusion protein consisting of the extracellular ligand-binding portion of the human 75 kD TNF receptor linked to the Fc portion of IgG1), abciximab, afeliomomab, basiliximab, daclizumab, infliximab, ibritumomab tiuexetan, mitumomab, muromonab-CD3, iodine 131 tositumomab conjugate, olizumab, rituximab, and trastuzumab (herceptin).
• Additional agents suitable include but are not limited to amifostine, amiodarone, aminocaproic acid, aminohippurate sodium, aminoglutethimide, aminolevulinic acid, aminosalicylic acid, amsacrine, anagrelide, anastrozole, asparaginase, anthracyclines, bexarotene, bicalutamide, bleomycin, buserelin, busulfan, cabergoline, capecitabine, carboplatin, carmustine, chlorambucin, cilastatin sodium, cisplatin, cladribine, clodronate, cyclophosphamide, cyproterone, cytarabine, camptothecins, 13-cis retinoic acid, all trans retinoic acid; dacarbazine, dactinomycin, daunorubicin, deferoxamine, dexamethasone, diclofenac, diethylstilbestrol, docetaxel, doxorubicin, epirubicin, estramustine, etoposide, exemestane, fexofenadine, fludarabine, fludrocortisone, fluorouracil, fluoxymesterone, flutamide, gemcitabine, epinephrine, L-Dopa, hydroxyurea, idarubicin, ifosfamide, imatinib, irinotecan, itraconazole, goserelin, letrozole, leucovorin, levamisole, lisinopril, lovothyroxine sodium, lomustine, mechlorethamine, medroxyprogesterone, megestrol, melphalan, mercaptopurine, metaraminol bitartrate, methotrexate, metoclopramide, mexiletine, mitomycin, mitotane, mitoxantrone, naloxone, nicotine, nilutamide, octreotide, oxaliplatin, pamidronate, pentostatin, pilcamycin, porfimer, prednisone, procarbazine, prochlorperazine, ondansetron, raltitrexed, sirolimus, streptozocin, tacrolimus, tamoxifen, temozolomide, teniposide, testosterone, tetrahydrocannabinol, thalidomide, thioguanine, thiotepa, topotecan, tretinoin, valrubicin, vinblastine, vincristine, vindesine, vinorelbine, dolasetron, granisetron; formoterol, fluticasone, leuprolide, midazolam, alprazolam, amphotericin B, podophylotoxins, nucleoside antivirals, aroyl hydrazones, sumatriptan; macrolides such as erythromycin, oleandomycin, troleandomycin, roxithromycin, clarithromycin, davercin, azithromycin, flurithromycin, dirithromycin, josamycin, spiromycin, midecamycin, leucomycin, miocamycin, rokitamycin, andazithromycin, and swinolide A; fluoroquinolones such as ciprofloxacin, ofloxacin, levofloxacin, trovafloxacin, alatrofloxacin, moxifloxicin, norfloxacin, enoxacin, grepafloxacin, gatifloxacin, lomefloxacin, sparfloxacin, temafloxacin, pefloxacin, amifloxacin, fleroxacin, tosufloxacin, prulifloxacin, irloxacin, pazufloxacin, clinafloxacin, and sitafloxacin, aminoglycosides such as gentamicin, netilmicin, paramecin, tobramycin, amikacin, kanamycin, neomycin, and streptomycin, vancomycin, teicoplanin, rampolanin, mideplanin, colistin, daptomycin, gramicidin, colistimethate; polymixins such as polymixin B, capreomycin, bacitracin, penems; penicillins including penicllinase-sensitive agents like penicillin G, penicillin V; penicllinase-resistant agents like methicillin, oxacillin, cloxacillin, dicloxacillin, floxacillin, nafcillin; gram negative microorganism active agents like ampicillin, amoxicillin, and hetacillin, cillin, and galampicillin; antipseudomonal penicillins like carbenicillin, ticarcillin, azlocillin, mezlocillin, and piperacillin; cephalosporins like cefpodoxime, cefprozil, ceftbuten, ceftizoxime, ceftriaxone, cephalothin, cephapirin, cephalexin, cephradrine, cefoxitin, cefamandole, cefazolin, cephaloridine, cefaclor, cefadroxil, cephaloglycin, cefuroxime, ceforanide, cefotaxime, cefatrizine, cephacetrile, cefepime, cefixime, cefonicid, cefoperazone, cefotetan, cefmetazole, ceftazidime, loracarbef, and moxalactam, monobactams like aztreonam; and carbapenems such as imipenem, meropenem, pentamidine isethiouate, albuterol sulfate, lidocaine, metaproterenol sulfate, beclomethasone diprepionate, triamcinolone acetamide, budesonide acetonide, fluticasone, ipratropium bromide, flunisolide, cromolyn sodium, and ergotamine tartrate; taxanes such as paclitaxel; SN-38, and tyrphostines.
• The above exemplary drugs are meant to encompass, where applicable, analogues, agonists, antagonists, inhibitors, isomers, polymorphs, and pharmaceutically acceptable salt forms thereof.
• In yet another embodiment of the invention, the small molecule is not taxol, or is not taxane-based.
• Other preferred active agents for preparing a multi-armed polymer prodrug conjugate as described herein include platins, oxymorphone analogues, steroids, quinolones, isoquinolones, and fluoroquinolones, and nucleosides and nucleotides. Structures of illustrative compounds belonging to each of the above structural classes are provided below.
• 

  

  
• Compositions/Populations of Prodrug Conjugates
• As stated above, in certain instances, a composition comprising a multi-arm polymer prodrug as described herein may comprise the prodrug having one of more of its polymer arms absent drug, D. Such an occurrence may arise, for example, due to incomplete reaction of the multi-armed reactive polymer with drug, D. Often, even in the instance of favorable stoichiometry, i.e., using an excess of drug relative to the number of reactive polymer arms, it can be difficult to drive the reaction to completion such that the product may comprise a mixture polymer species.
• In such instances, a composition of the invention may be described as comprising a multi-arm polymer prodrug having the structure R(-Q-POLY₁-X′-D_0,1)_q. In the foregoing structure, R, Q, POLY₁, and q are as previously described. The variable, X′, is either (i) a spacer, X, comprising a hydrolyzable linkage, such that upon hydrolysis of the hydrolyzable linkage, D, is released, or is (ii) X″, a terminal moiety. The variable D is a small molecule, where D₁indicates the presence of D and Do indicates its absence. In reference to the foregoing structure, R(-Q-POLY₁-X′-D_0,1)_q, the following conditions also apply: if X′ is X, then D is D₁, and if X′ is X″, then D is D₀. Typically, the composition comprises at least one multi-arm polymer prodrug species wherein X′ is X. The terminal moiety, X″, typically corresponds to an unreacted functional group present on one or more arms of the multi-armed polymer, or, is an inert derivative thereof, e.g., resulting from work-up, such as a hydrolysis product.
• More particularly, a composition of the invention may comprise one or more prodrug species having the structure:
• 
  R-(Q-POLY₁-X-D₁)_m(Q-POLY₁-X″)_s.
• In the above structure, m and s are each integers, where the sum of m and s equals q (the total number of polymer arms emanating from the organic radical core), and where m and s each independently have values ranging from 0 to q. Preferably, the value of s is not equal to q, but rather is less than q. Ideally, in the instance of quantitative substitution of active agent, s equals zero and m equals q.
• As an illustration, for a multi-armed polymer having 4 polymer arms, the conjugate composition may comprise one or more of the following polymer prodrug species, where the last component represents unreacted starting material or its equivalent resulting from work up of the reaction mixture: R-(Q-POLY₁-X-D₁)₄, R-(Q-POLY₁-X-D₁)₃(Q-POLY₁-X″), R-(Q-POLY₁-X-D₁)₂(Q-POLY₁-X″)₂, R-(Q-POLY₁-X-D₁)(Q-POLY₁-X″)₃, and R-(Q-POLY₁-X″)₄. Preferably, the latter species, R-(Q-POLY₁-X″)₄, is absent from the conjugate composition, or, if present, is present in minimal amounts, e.g., less than about 5% by weight, preferably less than about 2% by weight.
• Thus, for instance, a prodrug composition based upon a multi-armed polymer in accordance with the invention having four polymer arms may comprise a mixture of up to five different polymer species, and more preferably of up to four different polymer species in the instance where the product composition is essentially absent unreacted polymer starting material. That is to say, in one particular embodiment of the invention, the composition comprises a number of polymer prodrug species corresponding to the number of polymer arms, q.
• In one embodiment, a composition of the invention is characterized by having an average number of drug molecules per multi-armed polymer that ranges from about 52% to about 94% or greater of the idealized value. In an alternative embodiment, a composition comprising a population of multi-armed polymer conjugate species is characterized by having an average number of drug molecules per multi-armed polymer that ranges from about 57% to about 87% or greater of the idealized value. As an illustration, in an instance in which the multi-armed polymer contains four polymer arms, the idealized value of number of covalently attached drug molecules per multi-armed polymer is four, and an average number of drug molecules per multi-armed polymer ranging from about 52% to about 94% or greater of the idealized value corresponds to an average number of D per multi-arm polymer ranging from about 2.1 to 3.75. Alternatively, when the multi-armed polymer contains four polymer arms, and the average number of drug molecules per multi-armed polymer ranges from about 57% to about 87% or greater of the idealized value, then the resulting composition possesses an average number of D per multi-arm polymer ranging from about 2.1 to 3.75.
• An exemplary composition forming part of the invention comprises a mixture of one or more prodrug species having the structure:
• 
• where O-Irinotecan corresponds to:
• 
• m+s=4, and n ranges from about 40 to 500.
• Even more particularly, a preferred multi-armed polymer prodrug composition in accordance with the invention includes one or more of the following conjugate species:
• 
• In yet another embodiment, the composition comprises each of the above conjugate prodrug species. Preferably, in particular for prodrug conjugates having a number of polymer arms ranging from about 3 to about 8, the majority species present in the composition are those having either an idealized number of drug molecules attached to the polymer core (“q”) or those having a combination of (“q”) and (“q-1”) drug molecules attached to the polymer core.
• Yet another exemplary composition forming part of the invention comprises a mixture of one or more prodrug species having the structure:
• 
• where m+s=4, and n ranges from 40 to 500.
• Even more particularly, a preferred multi-armed polymer prodrug composition in accordance with the invention includes one or more of the following conjugate species:
• 
• where O-Docetaxel corresponds to:
• 
• Alternatively, and most preferably, a multi-arm polymer prodrug as provided herein possesses active agent covalently attached to each polymer arm, such that essentially quantitative substitution of active agent in each of the polymer arms has taken place. For example, for a multi-arm polymer having 3 reactive polymer arms, in the resulting multi-arm polymer prodrug, each of the 3 polymer arms possesses active agent covalently attached thereto. In such embodiment, a composition of the invention is characterized by having an average number of drug molecules per multi-armed polymer that corresponds essentially to its idealized value (i.e., is essentially 100% of its idealized value).
• The invention is meant to encompass each prodrug described herein, whether described singly or as forming part of a prodrug composition.
• Method of Forming a Multi-Armed Polymer Prodrug Conjugate
• Multi-armed reactive polymers, such as those for preparing a prodrug of the invention can be readily prepared from commercially available starting materials in view of the guidance presented herein, coupled with what is known in the art of chemical synthesis.
• Hydroxyl-terminated multi-armed PEGs having either a pentaerythritol core or a glycerol core are available from Nektar, Huntsville Ala. Such multi-armed PEGs can be used directly for coupling to active agents having, e.g., a carboxyl group in a position suitable for coupling, e.g., to provide a polymer prodrug having a hydrolyzable carboxyl ester bond. Alternatively, terminal hydroxyls present on a multi-armed polymer precursor can be oxidized to terminal carboxyl groups, e.g., for coupling to hydroxyls present on an active agent.
• Alternatively, a multi-armed reactive polymer for preparing a prodrug of the invention may be synthetically prepared. For instance, any of a number of suitable polyol core materials can be purchased from a chemical supplier such as Aldrich (St. Louis, Mo.). The terminal hydroxyls of the polyol are first converted to their anionic form, using, for example, a strong base, to provide a site suitable for initiating polymerization, followed by direct polymerization of monomer subunits, e.g., ethylene oxide, onto the core. Chain building is allowed to continue until a desired length of polymer chain is reached in each of the arms, followed by terminating the reaction, e.g., by quenching.
• In an alternative approach, an activated multi-armed polymer precursor to the prodrugs of the invention can be synthetically prepared by first providing a desired polyol core material, and reacting the polyol under suitable conditions with a heterobifunctional PEG mesylate of a desired length, where the non-mesylate PEG terminus is optionally protected to prevent reaction with the polyol core. The resulting multi-armed polymer precursor is then suitable for additional transformations or direct coupling to an active agent, following deprotection if necessary.
• Multi-armed polymer precursors based on polyamino cores can be prepared, for example, by direct coupling to a polymer reagent activated with an acylating agent such as an NHS ester, a succinimidyl carbonate, a BTC ester or the like, to provide multi-armed polymer precursors having an amide linker, Q. Alternatively, a core molecule having multiple amino groups can be coupled with an aldehyde terminated polymer, such as a PEG, by reductive amination (using, for example, a reducing agent such as sodium cyanoborohydride) to provide a multi-armed polymer precursor having an internal amine linker, Q.
• Although the polymer PEG is described as a representative polymer in the synthetic descriptions above, such approaches apply equally as well to other water-soluble polymers described herein.
• The prodrugs of the invention can be formed using known chemical coupling techniques for covalent attachment of activated polymers, such as an activated PEG, to a biologically active agent (See, for example, POLY(ETHYLENE GLYCOL) CHEMISTRY ANDBIOLOGICALAPPLICATIONS, American Chemical Society, Washington, D.C. (1997)). Selection of suitable functional groups, linkers, protecting groups, and the like to achieve a multi-arm polymer prodrug in accordance with the invention, will depend, in part, on the functional groups on the active agent and on the multi-armed polymer starting material and will be apparent to one skilled in the art, based upon the contents of the present disclosure.
• A multi-armed polymer of the invention suitable for coupling to an active agent or derivatized active agent will typically have a terminal functional group such as the following: N-succinimidyl carbonate (see e.g., U.S. Pat. Nos. 5,281,698, 5,468,478), amine (see, e.g., Buckmann et al. Makromol. Chem. 182:1379 (1981), Zalipsky et al. Eur. Polym. J. 19:1177 (1983)), hydrazide (See, e.g., Andresz et al. Makromol. Chem. 179:301 (1978)), succinimidyl propionate and succinimidyl butanoate (see, e.g., Olson et al. in Poly(ethylene glycol) Chemistry & Biological Applications, pp 170-181, Harris & Zalipsky Eds., ACS, Washington, D.C., 1997; see also U.S. Pat. No. 5,672,662), succinimidyl succinate (See, e.g., Abuchowski et al. Cancer Biochem. Biophys. 7:175 (1984) and Joppich et al., Makromol. Chem. 180:1381 (1979), succinimidyl ester (see, e.g., U.S. Pat. No. 4,670,417), benzotriazole carbonate (see, e.g., U.S. Pat. No. 5,650,234), glycidyl ether (see, e.g., Pitha et al. Eur. J. Biochem. 94:11 (1979), Elling et al., Biotech. Appl. Biochem. 13:354 (1991), oxycarbonylimidazole (see, e.g., Beauchamp, et al., Anal. Biochem. 131:25 (1983), Tondelli et al. J. Controlled Release 1:251 (1985)), p-nitrophenyl carbonate (see, e.g., Veronese, et al., Appl. Biochem. Biotech., 11:141 (1985); and Sartore et al., Appl. Biochem. Biotech., 27:45 (1991)), aldehyde (see, e.g., Harris et al. J. Polym. Sci. Chem. Ed. 22:341 (1984), U.S. Pat. Nos. 5,824,784, 5,252,714), maleimide (see, e.g., Goodson et al. Bio/Technology 8:343 (1990), Romani et al. in Chemistry of Peptides and Proteins 2:29 (1984)), and Kogan, Synthetic Comm. 22:2417 (1992)), orthopyridyl-disulfide (see, e.g., Woghiren, et al. Bioconj. Chem. 4:314 (1993)), acrylol (see, e.g., Sawhney et al., Macromolecules, 26:581 (1993)), vinylsulfone (see, e.g., U.S. Pat. No. 5,900,461).
• In turning now to one of the preferred classes of active agents, the camptothecins, since the 20-hydroxyl group of the camptothecin compound is sterically hindered, a single step conjugation reaction is difficult to accomplish in significant yields. As a result, a preferred method is to react the 20-hydroxyl group with a short linker or spacer moiety carrying a functional group suitable for reaction with a multi-arm polymer. Such an approach is applicable to many small molecules, particularly those having a site of covalent attachment that is inaccessible to an incoming reactive polymer. Preferred linkers include t-BOC-glycine or other amino acids having a protected amino group and an available carboxylic acid group (See Zalipsky et al., “Attachment of Drugs to Polyethylene Glycols”,Eur. Polym. J., Vol. 19, No. 12, pp. 1177-1183 (1983)). The carboxylic acid group reacts readily with the 20-hydroxyl group in the presence of a coupling agent (e.g., dicyclohexylcarbodiimide (DCC)) and a base catalyst (e.g., dimethylaminopyridine (DMAP)). Thereafter, the amino protecting group, such as t-BOC (N-tert-butoxycarbonyl), is removed by treatment with the appropriate deprotecting agent (e.g., trifluoroacetic acid (TFA) in the case of t-BOC). The free amino group is then reacted with a multi-arm or forked polymer bearing carboxylic acid groups in the presence of a coupling agent (e.g., hydroxybenzyltriazole (HOBT)) and a base (e.g., DMAP).
• In a preferred embodiment, the spacer moiety is derived from and comprises an amino acid and has the structure HO—C(O)—CH(R″)—NH-Gp wherein R″ is H, C1-C6 alkyl, or substituted C1-C6alkyl and Gp is a protecting group protecting the alpha-amino group of the amino acid. Typical labile protecting groups include t-BOC and FMOC (9-flourenylmethloxycarbonyl). t-BOC is stable at room temperature and easily removed with dilute solutions of TFA and dichloromethane. FMOC is a base labile protecting group that is easily removed by concentrated solutions of amines (usually 20-55% piperidine in N-methylpyrrolidone). Preferred amino acids include alanine, glycine, isoleucine, leucine, phenylalanine, and valine.
• Other spacer moieties having an available carboxylic acid group or other functional group reactive with a hydroxyl group and a protected amino group can also be used in lieu of the amino acids described above. For example, a spacer moiety having the structure HOOC-alkylene-NH-Gp may be employed, where Gp is as described above and the alkylene chain is, for example, about 1 to about 20 carbon atoms in length. Spacers comprising short —(CH₂CH₂O)_c— groups or (CH₂CH₂NH)_cgroups are also preferred, where c varies from about 0 to about 25. More particularly, c possesses a value selected from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12.
• In a particular embodiment exemplified in Example 1, conjugation is accomplished by first reacting the camptothecin compound with t-BOC-glycine, followed by deprotection of the glycine amino group and coupling of the glycine-modified camptothecin to a 4-arm PEG molecule comprising a pentaerythritol core.
• In an alternative approach exemplified in Example 8, a bifunctional spacer comprising a number of —(CH₂CH₂O)— subunits is provided. One terminal functional group of the spacer is an acid chloride (—O—C(O)—Cl) suitable for reaction with an active agent hydroxyl group to form a carbonate ester (i.e., a hydrolyzable linkage), while the other terminal functional group is a protected amine. The bifunctional spacer is coupled to irinotecan, in particular to the 20-position hydroxyl thereof, in the presence of a coupling agent such as DMAP to provide a partially modified active agent. In the partially modified active agent, a hydrolyzable bond, Z, has been introduced, coupled to a spacer, Y′ having a protected terminus, which upon deprotection, is suitable for reaction with an activated multi-armed polymer. The partially modified active agent is then reacted with a multi-armed polymer precursor having a reactive terminus suitable for coupling to an amine, to provide a stable amide linkage as part of the overall linkage, X.
• In yet another aspect, the invention encompasses a method that is particularly suited to conjugation of a polymer moiety to an active agent having multiple reactive groups. The method is particularly useful in instances in which single site modification of a drug or active agent is desired.
• Conventional synthetic techniques for preparing a single site polymer-modified active agent from an agent having multiple reactive groups typically involve multi-step reactions requiring multiple selective protection/deprotection steps. Such reactions are often hampered by low yields and difficulty in separation of the desired product(s). In an attempt to avoid use of a protected active agent precursor, the inventors attempted direct coupling of the exemplary small molecule, docetaxel, to a multi-armed polymer. Not unexpectedly, the reaction (i) generated a significant amount of side products when conventional coupling reagents such as dicyclohexylcarbodiimide and dimethylaminopyridine (DCC/DMAP) were utilized, and (ii) was also difficult to analyze and purify. See Example 14.
• To overcome this problem, the inventors developed a coupling reaction that suppressed undesired side-reactions and promoted formation of the desired product in good yields and purity.
• In particular, provided herein is a method for covalently attaching a polyethylene glycol polymer to an active agent. The method includes the steps of (i) providing an active agent comprising a first functional group selected from amino, hydroxyl, and carboxyl (and activated equivalents thereof), and (ii) reacting the active agent with a polyethylene glycol comprising a second functional group that is reactive with the first functional group. The reaction is carried out in the presence of a coupling reagent and 4-(dimethylamino)-pyridinium-p-toluenesulfonate (DPTS) under conditions effective to promote reaction between the first and second functional groups, to thereby form a polyethylene glycol-active agent conjugate.
• Preferred coupling agents are carbodiimides. Representative coupling agents include those selected from the group consisting of dicyclohexylcarbodiimide (DCC), N,N′-diisopropylcarbodiimide (DIC), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDAC), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC), N-tert-butyl-N′-methylcarbodiimide (TBMC), and N-tert-butyl-N′-ethylcarbodiimide (TBEC).
• One particularly preferred coupling reagent is N,N′-diisopropylcarbodiimide.
• The reaction is typically carried out in an organic solvent. Suitable solvents include dichloromethane, chloroform, acetonitrile, and tetrahydrofuran.
• Typically, the coupling reaction is carried out at a temperature ranging from about 0° C. to about 100° C. Preferably, the reaction is carried out at room temperature (i.e., absent heating or cooling).
• Generally, the amount of DPTS ranges from about 0.05 to about 0.75 equivalents relative to the first functional group, more preferably, from about 0.10 to 0.60 equivalents relative to the first functional group. The amount of the coupling reagent generally ranges from about 1.25 to 5 equivalents relative to the first functional group.
• Preferred second functional groups include amino, hydroxyl, and carboxyl, and activated equivalents thereof, where of course, the first and second functional groups are selected to react with each other.
• Active agents suitable for use in the method include proteins, oligopeptides, polypeptides, small molecules, antibodies, nucleotides, oligonucleotides, and lipids. Preferably, the active agent is a small molecule comprising a first functional group that is either hydroxyl or carboxyl. The active agent may, in certain instances, possess more than one first functional group.
• Particularly preferred small molecules include taxanes (e.g., docetaxel or paclitaxel) and camptothecins such as those described herein.
• Preferably, the reaction between the first and second functional groups results in formation of an ester bond (for example, resulting from reaction of a carboxylic acid or activated carboxylic acid with the hydroxyl group of an alcohol).
• In the method, the polyethylene glycol may possess any of a number of geometries, e.g., linear, branched, forked, and multi-armed polyethylene glycol. Preferably, the polyethylene glycol is a multi-armed polymer having from about 3 to about 25 arms. Preferred multi-armed polymers include those previously described.
• In one embodiment of the method, the polyethylene glycol comprises from about 1 to about 10 of the second functional groups. In an even more specific embodiment, the polyethylene glycol comprises a number of second functional groups selected from 1, 2, 3, 4, 5, and 6.
• In yet another embodiment of the method, the active agent comprises more than one first functional group, and the method does not comprise a protection step, such that the resulting conjugate product is modified at only a single “first functional group” site.
• In yet another embodiment, the method is effective to result in formation of less than about 15% of an N-acyl urea side product, and preferably, less than about 10% of an N-acyl urea side product, and even more preferably, less than about 5% of an N-acyl urea side product. See Example 15 in which the synthetic method results in formation of a docetaxel-polyethylene conjugate having polyethylene glycol covalently attached, via an ester linkage, to a single hydroxyl site (e.g., the 2′ hydroxyl site) on docetaxel.
• The prodrug product may be further purified. Methods of purification and isolation include precipitation followed by filtration and drying, as well as chromatography. Suitable chromatographic methods include gel filtration chromatography and ion exchange chromatography.
Pharmaceutical Compositions
• The invention provides pharmaceutical formulations or compositions, both for veterinary and for human medical use, which comprise one or more polymer prodrugs of the invention or a pharmaceutically acceptable salt thereof, with one or more pharmaceutically acceptable carriers, and optionally any other therapeutic ingredients, stabilizers, or the like. The carrier(s) must be pharmaceutically acceptable in the sense of being compatible with the other ingredients of the formulation and not unduly deleterious to the recipient thereof. The compositions of the invention may also include polymeric excipients/additives or carriers, e.g., polyvinylpyrrolidones, derivatized celluloses such as hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose, Ficolls (a polymeric sugar), hydroxyethylstarch (HES), dextrates (e.g., cyclodextrins, such as 2-hydroxypropyl-β-cyclodextrin and sulfobutylether-β-cyclodextrin), polyethylene glycols, and pectin. The compositions may further include diluents, buffers, binders, disintegrants, thickeners, lubricants, preservatives (including antioxidants), flavoring agents, taste-masking agents, inorganic salts (e.g., sodium chloride), antimicrobial agents (e.g., benzalkonium chloride), sweeteners, antistatic agents, surfactants (e.g., polysorbates such as “TWEEN 20” and “TWEEN 80”, and pluronics such as F68 and F88, available from BASF), sorbitan esters, lipids (e.g., phospholipids such as lecithin and other phosphatidylcholines, phosphatidylethanolamines, fatty acids and fatty esters, steroids (e.g., cholesterol)), and chelating agents (e.g., EDTA, zinc and other such suitable cations). Other pharmaceutical excipients and/or additives suitable for use in the compositions according to the invention are listed in “Remington: The Science & Practice of Pharmacy”, 19th ed., Williams & Williams, (1995), and in the “Physician's Desk Reference”, 52^nded., Medical Economics, Montvale, N.J. (1998), and in “Handbook of Pharmaceutical Excipients”, Third Ed., Ed. A. H. Kibbe, Pharmaceutical Press, 2000.
• The prodrugs of the invention may be formulated in compositions including those suitable for oral, rectal, topical, nasal, ophthalmic, or parenteral (including intraperitoneal, intravenous, subcutaneous, or intramuscular injection) administration. The compositions may conveniently be presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. All methods include the step of bringing the active agent or compound (i.e., the prodrug) into association with a carrier that constitutes one or more accessory ingredients. In general, the compositions are prepared by bringing the active compound into association with a liquid carrier to form a solution or a suspension, or alternatively, bring the active compound into association with formulation components suitable for forming a solid, optionally a particulate product, and then, if warranted, shaping the product into a desired delivery form. Solid formulations of the invention, when particulate, will typically comprise particles with sizes ranging from about 1 nanometer to about 500 microns. In general, for solid formulations intended for intravenous administration, particles will typically range from about 1 nm to about 10 microns in diameter. Particularly preferred are sterile, lyophilized compositions that are reconstituted in an aqueous vehicle prior to injection.
• A preferred formulation is a solid formulation comprising the multi-arm polymer prodrug where the active agent, D, is irinotecan. The solid formulation comprises sorbitol and lactic acid, and is typically diluted with 5% dextrose injection or 0.9% sodium chloride injection prior to intravenous infusion.
• The amount of polymer conjugate in the formulation will vary depending upon the specific opioid antagonist employed, its activity in conjugated form, the molecular weight of the conjugate, and other factors such as dosage form, target patient population, and other considerations, and will generally be readily determined by one skilled in the art. The amount of conjugate in the formulation will be that amount necessary to deliver a therapeutically effective amount of camptothecin compound to a patient in need thereof to achieve at least one of the therapeutic effects associated with the camptothecin compound, e.g., treatment of cancer. In practice, this will vary widely depending upon the particular conjugate, its activity, the severity of the condition to be treated, the patient population, the stability of the formulation, and the like. Compositions will generally contain anywhere from about 1% by weight to about 99% by weight prodrug, typically from about 2% to about 95% by weight prodrug, and more typically from about 5% to 85% by weight prodrug, and will also depend upon the relative amounts of excipients/additives contained in the composition. More specifically, the composition will typically contain at least about one of the following percentages of prodrug: 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, or more by weight.
• Compositions of the present invention suitable for oral administration may be presented as discrete units such as capsules, cachets, tablets, lozenges, and the like, each containing a predetermined amount of the active agent as a powder or granules; or a suspension in an aqueous liquor or non-aqueous liquid such as a syrup, an elixir, an emulsion, a draught, and the like.
• A tablet may be made by compression or molding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine, with the active compound being in a free-flowing form such as a powder or granules which is optionally mixed with a binder, disintegrant, lubricant, inert diluent, surface active agent or dispersing agent. Molded tablets comprised with a suitable carrier may be made by molding in a suitable machine.
• A syrup may be made by adding the active compound to a concentrated aqueous solution of a sugar, for example sucrose, to which may also be added any accessory ingredient(s). Such accessory ingredients may include flavorings, suitable preservatives, an agent to retard crystallization of the sugar, and an agent to increase the solubility of any other ingredient, such as polyhydric alcohol, for example, glycerol or sorbitol.
• Formulations suitable for parenteral administration conveniently comprise a sterile aqueous preparation of the prodrug conjugate, which can be formulated to be isotonic with the blood of the recipient.
• Nasal spray formulations comprise purified aqueous solutions of the active agent with preservative agents and isotonic agents. Such formulations are preferably adjusted to a pH and isotonic state compatible with the nasal mucous membranes.
• Formulations for rectal administration may be presented as a suppository with a suitable carrier such as cocoa butter, or hydrogenated fats or hydrogenated fatty carboxylic acids.
• Ophthalmic formulations are prepared by a similar method to the nasal spray, except that the pH and isotonic factors are preferably adjusted to match that of the eye.
• Topical formulations comprise the active compound dissolved or suspended in one or more media such as mineral oil, petroleum, polyhydroxy alcohols or other bases used for topical formulations. The addition of other accessory ingredients as noted above may be desirable.
• Pharmaceutical formulations are also provided which are suitable for administration as an aerosol, by inhalation. These formulations comprise a solution or suspension of the desired polymer conjugate or a salt thereof. The desired formulation may be placed in a small chamber and nebulized. Nebulization may be accomplished by compressed air or by ultrasonic energy to form a plurality of liquid droplets or solid particles comprising the conjugates or salts thereof.
Methods of Use
• The multi-armed polymer prodrugs of the invention can be used to treat or prevent any condition responsive to the unmodified active agent in any animal, particularly in mammals, including humans.
• The prodrugs of the invention are particularly useful as anticancer agents, i.e., have been shown to be effective in significantly reducing the growth of certain solid tumors as evidenced by representative lung and colon cancers in in-vivo studies, among others. In particular, the prodrugs of the invention have been shown to be nearly five times more effective at preventing the growth of human lung cancer tumors and human colon cancer tumors than the corresponding anticancer agent per se, when administered at comparable doses over illustrative time periods ranging from 30 to 80 days.
• Examples 6 and 16 illustrate the effectiveness of illustrative polymer prodrugs of the invention in the treatment of lung cancer, based upon in-vivo lung cancer model results. Example 6 provides a comparison of certain 4-arm polyethylene glycol irinotecan prodrugs with unmodified irinotecan in mouse xenograft studies. Mice having sizable lung tumors were treated with different doses of prodrug, and lung tumor size was then plotted at various times after commencement of treatment. (SeeFIGS. 2 and 3). The rate of tumor growth was slowed significantly in mice treated with 4-arm PEG irinotecan when compared to mice treated with irinotecan per se, thereby illustrating the superiority of the prodrug approach of the present invention when compared to treatment with unmodified drug. Similar results are observed with 4-arm PEG docetaxel as described in detail in Example 16.FIGS. 16A-C andFIG. 17 illustrate the improved anti-tumor effect of a representative prodrug of the invention in comparison to unmodified antitumor agent. Moreover, in addition to providing superior efficacy when compared to their unmodified counterparts, the prodrugs provided herein are also less toxic when evaluated in animal models. For instance, the maximum tolerated dose (MTD) for 4-arm-PEG-gly-irino-20K was significantly higher than for irinotecan (FIG. 22). Additionally, the occurrence and/or extent and/or severity of side-effects such as neutropenia and diarrhea was reduced for 4-arm-PEG-gly-irino-20K when compared to irinotecan administered at equivalent doses (FIG. 23).
• Similar results are provided in Examples 11 and 18 (in vivo breast cancer model), Examples 2 and 12 (in vivo colon cancer model), and in Example 17 (in vivo prostate cancer model). In some cases, administration of a prodrug of the invention not only resulted in an enhanced anti-tumor effect when compared to unmodified drug, but resulted in complete suppression of tumor growth in the animal model employed—thus indicating the superiority of the prodrugs and methods provided herein over unmodified oncolytic in treating various types of cancer.
• The multi-armed polymer prodrugs of the invention, in particular, those where the small molecule drug is an anticancer agent such as a camptothecin compound as described herein or other oncolytic such as docetaxel, are useful in treating breast cancer, ovarian cancer, colon cancer, colorectal cancer, prostate cancer, gastric cancer, malignant melanoma, small cell lung cancer, non-small cell lung cancer, thyroid cancers, kidney cancer, cancer of the bile duct, brain cancer, cancer of the head and neck, lymphomas, leukemias, rhabdomyosarcoma, neuroblastoma, and the like. The prodrugs of the invention are particularly effective in targeting and accumulating in solid tumors. The prodrugs are also useful in the treatment of HIV and other viruses.
• Methods of treatment comprise administering to a mammal in need thereof a therapeutically effective amount of a composition or formulation containing a polymer prodrug of the invention.
• A therapeutically effective dosage amount of any specific prodrug will vary from conjugate to conjugate, patient to patient, and will depend upon factors such as the condition of the patient, the activity of the particular active agent employed, and the route of delivery.
• For camptothecin-type active agents, dosages from about 0.5 to about 100 mg camptothecin/kg body weight, preferably from about 10.0 to about 60 mg/kg, are preferred. For taxane-type active agents, dosages of prodrug are administered in amounts ranging from about 5 to about 500 mg/m²per day, based upon the amount of the taxane moiety. When administered conjointly with other pharmaceutically active agents, even less of the prodrug may be therapeutically effective. The range set above is illustrative and those skilled in the art will determine optimal dosing of the prodrug based on clinical experience and the particular treatment indication.
• Methods of treatment also include administering a therapeutically effective amount of a composition or formulation containing a multi-arm polymer prodrug of an anticancer agent, e.g., a camptothecin or taxane compound as described herein, in conjunction with a second anticancer agent. For example, in the treatment of colorectal cancer, a multi-arm polymer prodrug of a camptothecin or docetaxel type compound may be administered in conjunction with chemotherapeutics such as 5-fluorouracil or leucovorin xeloda, or with agents such as avastin, Erbitux® (cetuximab), or Vectibix™ (panitumumab). In the treatment of breast cancer, therapy may include administration of a multi-arm polymer prodrug as described herein, optionally in combination with xeloda, paclitaxel, docetaxel, or abraxane. In treating lung cancer, therapy may include, along with administration of a prodrug of the invention, administration of cis-platin, carboplatin, gemcitabine, alimpta, and docetaxel (the latter in the instance in which the prodrug itself does not comprise docetaxel).
• In an exemplary course of treatment, a multi-arm polymer prodrug, e.g., 4-arm-PEG-GLY-IRINO-20K, is administered to patients having colorectal cancer. One such patient population comprises patients having advanced colorectal cancer. A therapeutically effective amount of a multi-arm polymer prodrug such as 4-arm-PEG-GLY-IRINO-20K is administered in combination with cetuximab an at initial loading dose, followed by weekly doses at a lower dosage of cetuximab. The efficacy and safety of such treatment is evaluated against unmodified irinotecan similarly administered in conjunction with cetuximab. Typically, up to about four different dosage levels of prodrug are evaluated. A preferred endpoint of the treatment regimen is progression free survival for a period of about several months or longer.
• Preferably, camptothecin type prodrugs are administered in combination with 5-fluorouracil and folinic acid, as described in U.S. Pat. No. 6,403,569.
• The prodrug of the invention may be administered once or several times a day, preferably once a day or less. Illustrative dosing schedules include once per week, once every two weeks, or once every three weeks. In the instance of a maintenance dose, dosing may take place even less frequently than once every three weeks, such as once monthly. The duration of the treatment may be once per day for a period of from two to three weeks and may continue for a period of months or even years. The daily dose can be administered either by a single dose in the form of an individual dosage unit or several smaller dosage units or by multiple administration of subdivided dosages at certain intervals.
• It is to be understood that while the invention has been described in conjunction with the preferred specific embodiments thereof, that the foregoing description as well as the examples that follow are intended to illustrate and not limit the scope of the invention. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.
• All articles, books, patents and other publications referenced herein are hereby incorporated by reference in their entireties.
EXAMPLES
• The practice of the invention will employ, unless otherwise indicated, conventional techniques of organic synthesis and the like, which are within the skill of the art. Such techniques are fully explained in the literature. Reagents and materials are commercially available unless specifically stated to the contrary. See, for example, J. March, Advanced Organic Chemistry: Reactions Mechanisms and Structure, 4th Ed. (New York: Wiley-Interscience, 1992), supra, and Comprehensive Organic Functional Group Transformations II, Volumes 1-7, Second Ed.: A Comprehensive Review of the Synthetic Literature 1995-2003 (Organic Chemistry Series), Eds. Katritsky, A. R., et al., Elsevier Science.
• In the following examples, efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperatures, etc.) but some experimental error and deviation should be accounted for. Unless indicated otherwise, temperature is in degrees C. and pressure is at or near atmospheric pressure at sea level.
• Although other abbreviations known by one having ordinary skill in the art will be referenced, other reagents and materials will be used, and other methods known by one having ordinary skill in the art will be used, the following list and methods description is provided for the sake of convenience.
• Abbreviations.
• • CM carboxymethyl or carboxymethylene (—CH₂COOH)
  • DCC 1,3-dicyclohexylcarbodiimide
  • DCM methylene chloride
  • DIC N,N′-diisopropylcarbodiimide
  • DPTS 4-(dimethylamino)-pyridinium-p-toluenesulfonate
  • DMF dimethylformamide
  • DMAP 4-(N,N-dimethylamino)pyridine
  • DMSO dimethyl sulfoxide
  • DI deionized
  • HCl hydrochloric acid
  • HOBT hydroxybenzyltriazole
  • HPLC high performance liquid chromatography
  • IPA isopropyl alcohol
  • K or kDa kilodaltons
  • MALDI-TOF Matrix Assisted Laser Desorption Ionization Time-of-Flight
  • MeOH methanol
  • MW molecular weight
  • NMR nuclear magnetic resonance
  • RT room temperature
  • SCM succinimidylcarboxymethyl (—CH₂—COO—N-succinimidyl)
  • SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis
  • SEC size exclusion chromatography
  • TFA trifluoroacetic acid
  • THF tetrahydrofuran
  • TLC thin layer chromatography
Materials and Methods
• Irinotecan was purchased from JiangSu HengRui Medicine Co. Ltd. (China).
• Docetaxel (Taxotere®) was purchased from Hangzhou HETD Pharm & Chem Co., Ltd, CHINA.
• 4-Arm-PEG_20K-CM and 4-arm-PEG_20K-SCM were prepared from 4-arm-PEG_20K-OH (Nektar, Huntsville, Ala.).
• Sources of the following reagents were as follows: Glycine tert-butyl ester (98%, Aldrich); 4-dimethylaminopyridine (DMAP, 99%, Aldrich); N, N′-diisopropylcarbodiimide (DIC, 99%, Acros), N, N′-dicyclohexylcarbodiimide (DCC, 99%, Acros), N, N-diisopropylethylamine (DIPEA, 99%, Aldrich), and p-toluenesulfonic acid (PTSA, 98.5%, Aldrich), and all reagents were used as received. Solvents were dried before use.
• All¹HNMR data was generated by a 300 or 400 MHz NMR spectrometer manufactured by Bruker.
Example 1Synthesis of Pentaerythritolyl-4-Arm-(PEG-1-Methylene-2 Oxo-Vinylamino Acetate linked-Irinotecan)-20K
• The product was synthesized via a three-step process using as starting materials irinotecan hydrochloride and 4-arm polyethylene glycol succinimidyl acetate. The yields at each step were typically greater than about 90%.
• A. Synthesis of t-Boc-Glycine-Irinotecan
Reaction Scheme:
• 
• In a flask, 0.1 g Irinotecan (0.1704 mmoles), 0.059 g t-Boc-Glycine (0.3408 mmoles), and 0.021 g DMAP (0.1704 mmoles) were dissolved in 13 mL of anhydrous dichloromethane (DCM). To the solution was added 0.070 g DCC (0.3408 mmoles) dissolved in 2 mL of anhydrous DCM. The solution was stirred overnight at room temperature. The solid was removed through a coarse frit, and the solution was washed with 10 mL of 0.1N HCL in a separatory funnel. The organic phase was further washed with 10 mL of deionized H₂O in a separatory funnel and then dried with Na₂SO₄. The solvent was removed using rotary evaporation and the product was further dried under vacuum.¹H NMR (DMSO): δ 0.919 (t, CH₂CH₃), 1.34 (s, C(CH₃)₃), 3.83 (m, CH₂), 7.66 (d, aromatic H).
• B. Deprotection of t-Boc-Glycine-Irinotecan
• 
• 0.1 g t-Boc-Glycine-Irinotecan (0.137 mmoles) was dissolved in 7 mL of anhydrous DCM. To the solution was added 0.53 mL trifluoroacetic acid (TFA, 6.85 mmoles). The solution was stirred at room temperature under argon for 1 hour. The solvent was removed using rotary evaporation. The crude product was dissolved in 0.1 mL MeOH and then precipitated in 25 mL of ether. The suspension was stirred in an ice bath for 30 minutes. The product, a pale to dark yellow solid, was collected by filtration and dried under vacuum.¹H NMR (DMSO): δ 0.92 (t, CH₂CH₃), 1.29 (t, CH₂CH₃), 5.55 (s, 2H), 7.25 (s, aromatic H).
C. Covalent Attachment of a Multi-Armed Activated Polymer to Glycine Irinotecan.
• 
• A. 0.516 g Glycine-Irinotecan (0.976 mmoles), 3.904 g 4arm-PEG(20K)-CM (0.1952 mmoles), 0.0596 g 4-(dimethylamino)pyridine (DMAP, 0.488 mmoles), and 0.0658 g 2-hydroxybenzyltriazole (HOBT, 0.488 mmoles) were dissolved in 60 mL anhydrous methylene chloride. To the resulting solution was added 0.282g 1,3-dicyclohexylcarbodiimide (DCC, 1.3664 mmoles). The reaction mixture was stirred under argon overnight at room temperature. The mixture was filtered through a coarse frit and the solvent was removed using rotary evaporation. The syrup was precipitated in 200 mL of cold isopropanol over an ice bath. The solid was filtered and then dried under vacuum. Yield: 4.08 g.¹H NMR (DMSO): δ 0.909 (t, CH₂CH₃), 1.28 (m, CH₂CH₃), 3.5 (br m, PEG), 3.92 (s, CH₂), 5.50 (s, 2H).
• The structure of the product was further confirmed by¹³C-NMR, FTIR, and MALDI. The molecular weight of the conjugate was confirmed by MALDI to be approximately 22,000 g/mol.
• Synonyms for the product include: (a) 20-pentaerythritol poly(oxy-1,2,-ethanediyl)-carboxymethyl-glycinate-7-ethyl-10-hydroxycamptothecine 10-[1,4′-bipiperidine]-1′-carboxylate (b) 4-arm branched poly (ethylene glycol) conjugate of (S)-4,11-diethyl-3,4,12,14-tetrahydro-4-hydroxy-3,14-dioxo 1H-pyrano[3′,4′:6,7]-indolizino[1,2-b]quinolin-9-yl-[1,4′-bipiperidine]-1′-carboxylate, (c) irinotecan 20-O-ester of PEG20KDA-glycine, (d) PEG20K-gly-irinotecan, (e) PEG20K-irinotecan, (f) 4-arm PEG20K-gly-irinotecan, (g) PEG-Irinotecan, (h) 20-pentaerythritol poly(oxy-1,2-ethanediyl)-carboxymethyl-glycinate-irinotecan, (i) irinotecan tetra 20-O-ester of PEG20KDA-glycine, (j) 4-arm-PEG-gly-irino-20K.
• Although reaction scheme IX depicts PEG-irinotecan as having a discrete molecular weight and complete polymer loading, i.e., an irinotecan drug molecule attached to each arm of the 4-arm polymer core, more plausibly, upon reaction, the polymer (having a molecular weight distribution) produces a prodrug having an average of 2.3 to 3.0 molecules of irinotecan per 4-armed polymer core. That is to say, based upon irinotecan drug loading calculations, the product is a mixture of 4-armed polymer where the polymer core has one irinotecan molecule attached, two irinotecan molecules attached, three irinotecan molecules attached, and four irinotecan molecules attached, and perhaps even no drug attached, to provide a composition which consistently averages 2.3 to 3 molecules of irinotecan per polymer.
• Purity of the product, based upon analyses of different product lots, was 97.9±0.9%. Free irinotecan in the final product was typically 0.5% or lower.
• B. The reaction described above was carried out essentially as described above with the exception that the multi-arm PEG reagent, 4-arm-PEG-SCM, was added as a solid to a methylene chloride solution of glycine-irinotecan. Characterization of the product revealed essentially complete conversion (essentially 100% conversion) of all ˜PEG-SCM groups in the multi-arm polymer reagent to ˜PEG-glycine-irinotecan to provide the desired product, 4-arm-PEG-GLY-IRINO-20 k.
Example 2Anti-Tumor Activity of Pentaerythritolyl-4-Arm-(PEG-1-Methylene-2 Oxo-Vinylamino Acetate linked-Irinotecan)-20K, “4-ARM-PEG-Gly-Irino-20K” in a Colon Cancer Mouse Xenograft Model
• Human HT29 colon tumor xenografts were subcutaneously implanted in athymic nude mice. After about two weeks of adequate tumor growth (100 to 250 mg), these animals were divided into different groups of ten mice each. One group was dosed with normal saline (control), a second group was dosed with 60 mg/kg of irinotecan, and the third group was dosed with 60 mg/kg of the 4-arm PEG-GLY-Irino-20K (dose calculated per irinotecan content). Doses were administered intravenously, with one dose administered every 4 days for a total of 3 administered doses. The mice were observed daily and the tumors were measured with calipers twice a week.FIG. 1 shows the effect of irinotecan and PEG-irinotecan treatment on HT29 colon tumors in athymic nude mice.
• As can be seen from the results depicted inFIG. 1, mice treated with both irinotecan and 4-arm-PEG-GLY-Irino-20K exhibited a delay in tumor growth (anti-tumor activity) that was significantly improved when compared to the control. Moreover, the delay in tumor growth was significantly better for the 4-arm-PEG-GLY-Irino-20K group of mice when compared to the group of animals administered unconjugated irinotecan.
Example 3Synthesis of Pentaerythritolyl-4-ARM-(PEG-1-Methylene-2 Oxo-Vinylamino Acetate linked-Irinotecan)-40K, “4-ARM-PEG-Gly-Irino-40 k”
• 4-arm-PEG-GLY-IRINO-40K was prepared in an identical fashion to that described for the 20K compound in Example 1, with the exception that in step C, the multi-armed activated PEG reagent employed was 4 arm-PEG(40K)-CM rather than the 20K material.
• In a 2 L round bottom reactor, 4-arm-PEG_{40 k}-SCM (240 g) was dissolved in 1.0 L anhydrous methylene chloride. To a separate 500 mL round bottom reactor, glycine-irinotecan TFA salt (1.0 equiv, 20 g) was dissolved in 53 mL DMF and treated with 8.8 mL TEA, stirred at room temperature for 5 minutes. Then the solution was added to the solution of 4-arm-PEG_{40 k}-SCM in methylene chloride. The reaction was stirred at RT for 15 hrs and then precipitated in 6 L Et₂O and filtered to isolate solid product, which was dissolved in 2.0 L IPA and 200 ml methanol at 60° C. in a 5 L round bottom reactor. While stirred by a mechanical stirrer, the solution was cooled to RT for the product to precipitate out, followed by filtering to give 4-arm-PEG_{40 k}-glycine-irinotecan (241 g, drug content 4.3% based on HPLC analysis, yield based on drug, 67%).
Example 4Synthesis of Pentaerythritolyl-4-ARM-(PEG-1-Methylene-2 Oxo-Vinylamino Acetate linked-SN-38)-20K, “4-Arm-Peg-Gly-SN-38-20 k”
• 4-arm PEG-GLY-SN-38-20K was prepared in a similar fashion to its irinotecan counterpart as described in Example 1, with the exception that the active agent employed was SN-38, an active metabolite of camptothecin, rather than irinotecan, where the phenolic-OH of SN-38 was protected with MEMCl (2-methoxyethoxymethyl chloride) during the chemical transformations, followed by deprotection with TEA to provide the desired multi-armed conjugate.
• 4-arm-PEG_{20 k}-SCM (12.2 g) was dissolved in 100 mL CH₂Cl₂. (20)-glycine-SN38 TFA salt (1.4 g, 2.44 mmol) was dissolved in 20 mL DMF and treated with 0.38 mL TEA, then added to the solution of 4-arm-PEG_{20 k}-SCM. The reaction was stirred at RT for 18 hrs and then precipitated in Et₂O to get solid product, which was dissolved in 100 mL IPA at 50° C., then cooled to RT to gave 4-arm-PEG_{20 k}-glycine-(20)-SN38 (12 g,drug content 6% based on HPLC).
Example 5Synthesis of Pentaerythritolyl-4-Arm-(PEG-1-Methylene-2 Oxo-Vinylamino Acetate linked-SN-38)-40K, “4-Arm-Peg-Gly-SN-38-40 k”
• 4-arm PEG-GLY-SN-38-40K was prepared in a similar fashion to the 20K version described above, with the exception that the multi-armed activated PEG reagent employed was 4 arm-PEG(40K)-CM rather than the 20K material.
• 4-arm-PEG_{40 k}-SCM (34.9 g) was dissolved in 200 mL CH₂Cl₂. (20)-Glycine-SN38 TFA salt (2.0 g, 3.49 mmol) was dissolved in 20 mL DMF and treated with 0.6 mL TEA, then added to the solution of 4-arm-PEG_{20 k}-SCM. The reaction was stirred at RT for 18 hrs and then precipitated in Et₂O to get solid product, which was dissolved in 100 mL IPA at 50° C., then cooled to RT to gave 4-arm-PEG_{20 k}-glycine-(20)-SN38 (34 g, drug content 2.3% based on HPLC analysis).
Example 6Additional Xenograft Studies—Lung and Colon Cancer Models
• Additional mouse xenograft studies were conducted to further examine the efficacy of exemplary multi-armed polymer conjugates of the invention.
• Athymic nude mice were implanted subcutaneously with human cancer cell lines (lung cancer cell line NCI-H460, and colon cancer cell line HT-29) and the tumors allowed to grow to approximately 150 mg in size. The animals were divided into groups of ten mice each.
• Various compounds and doses were evaluated as follows: irinotecan (40, 60 and 90 mg/kg); 4-arm-PEG-GLY-IRINO-20K (40, 60, and 90 mg/kg); 4-arm-PEG-GLY-IRINO-40K ((40, 60, and 90 mg/kg); 4-arm-PEG-GLY-SN-38-20K (7.5, 15, 30 mg/kg), and PEG-GLY-SN-38-40K (7.5, 15, 30 mg/kg). Doses were administered intravenously, with one dose administered every 4 days for a total of 3 administered doses.
• Tumor volume measurements were taken over a period of 60-80 days; tumor volumes were converted to tumor weight. Body weights were also measured over the same period to provide an indication of weight loss. The results are presented graphically inFIGS. 2-5.
Example 7Pharmacokinetic Studies
• A. Single Dose Colon Tumor Xenograft Study in Mice
• A comparative single dose pharmacokinetic (PK) study of a multi-armed PEG-irinotecan versus unmodified irinotecan in nude mice was conducted to assess tumor distribution of parent and metabolite drug.
• The study employed 108 nude mice, 36 mice per group, 4 animals per sample point. Drug was administered intravenously as a single dose. Drug form and doses were as follows: irinotecan (40 mg/kg); 4-arm-PEG-GLY-IRINO-20K (40 mg/kg equivalents); 4-arm-PEG-GLY-IRINO-40K ((40 mg/kg equivalents). Venous plasma and tumor tissue samples were taken at the following time points: 20 minutes, 40 minutes, and 1, 2, 4, 12, 24, 48, and 72 hours, and evaluated for concentrations of the following species: 4-arm-PEG-GLY-IRINO-20K, 4-arm-PEG-GLY-IRINO-40K, irinotecan and SN-38. The results are plotted inFIGS. 6 to 13.
• As can be seen inFIGS. 6-13, based upon the rate of decline of the multi-armed PEGylated species in tumor tissue in comparison to plasma, the PEGylated species demonstrate a notable increase in tumor retention time when compared to unmodified parent drug.
• In looking at the metabolite results, the concentrations of SN-38 derived from the PEGylated compounds appear to be increasing at the end of the 72 hour period, while in contrast, SN-38 derived from irinotecan is essentially cleared in 12 hours. In sum, the tumor exposure to SN38 following administration of either of the PEGylated compounds is approximately five times greater than for irinotecan over the same 72 hour sampling period. In sum, both multi-arm PEGylated compounds provide an increased inhibition of tumor growth (colon and lung) for both in-vivo tumor models investigated in comparison to unmodified drug. More specifically, both multi-arm PEGylated compounds demonstrated a marked suppression of tumor growth when compared to unmodified drug in mouse xenograft models, indicating the effectiveness of such compounds as anti-cancer agents. Lastly, administration of the multi-arm PEGylated irinotecan compounds described herein appears to cause less diarrhea in rats than irinotecan itself.
• B. Additional Single Dose Pharmacokinetic Studies
• Single dose pharmacokinetic studies were additionally carried out in rats and dog (data not shown). In all species examined, dosing of 4-arm-PEG-GLY-IRINO-20K resulted in sustained and greater exposure to irinotecan and SN38 than dosing with irinotecan per se.
• Following dosing with 4-arm-PEG-GLY-IRINO-20K, SN38 t½ values were approximately one order of magnitude greater than those following irinotecan dosing in both rodent and dogs. Differences in SN38 AUC values were in the range of 400- to 500-fold for rodents and 2- to 6-fold in dogs. The PK of 4-arm-PEG-GLY-IRINO-20K was dominated by the disposition properties of the PEG moiety. In the rodent and dog, PEG-Irinotecan had a plasma half-life of 2.7 to 5.9 hours and 23 to 92 hours, respectively, low plasma clearance (CL) relative to hepatic blood flow, and a small volume of distribution (Vd) relative to total body water volume. In contrast, irinotecan CL and Vd values were greater than those of PEG-Irinotecan. At pharmacologically relevant doses, t½ values for irinotecan derived from 4-arm-PEG-GLY-IRINO-20K were about 61 to 68 hours in the dog at 6 mg/kg (120 mg/m²), 123 hours in the rat at 20 mg/kg (120 mg/m²), and 6 to 10 hours in the mouse at 40 mg/kg (120 mg/m²). At pharmacologically relevant doses, t½ values for SN38 derived from PEG-Irinotecan were 75 to 130 hours in the dog at 6 mg/kg (120 mg/m²), 40 hours in the rat at 20 mg/kg (120 mg/m²), and 12 to 16 hours in the mouse at 40 mg/kg (120 mg/m²). At pharmacologically relevant doses of irinotecan, SN38 t½ values were about 3 to 7 hours and in rats at 60 mg/kg and 3 to 10 hours in dogs at 6 mg/kg.
• Interspecies differences in the metabolism of PEG-Irinotecan were observed (Table 1). SN38 reached high levels and had very high AUCs in rodents, presumably because of more rapid and extensive cleavage of irinotecan due to higher level of esterases in rodent plasma than that of dogs or humans. The systemic clearance of PEG-Irinotecan in rats decreased with increasing doses (4 to 20 mg/kg) suggesting dose-dependent kinetics for the drug in the rat. The systemic clearance of PEG-Irinotecan in dogs was dose independent for the dose range of 6 to 60 mg/kg.

• TABLE 1
  Species Comparisons of Single-dose PK Parameters
  Following PEG-Irinotecan Administration

  	AUC	Cmax	t½

  PEG-	mouse < rat < dog	mouse < rat < dog	Dog > rat =
  Irinotecan			mouse
  SN38	mouse >> rat >> dog	Mouse >> rat >> dog	Dog > rat >
  			mouse

• In humans, a clearance rate of 1.82 mL/hr/kg and a half-life of 83 hours are predicted for 4-arm-PEG-GLY-IRINO-20K.
Example 8Synthesis of Pentaerythritolyl-4-Arm-(PEG-2-{2-[2-1-hydroxy-2-oxo-vinyloxy)-ethoxy]-ethylamino}-propen-1-one linked-irinotecan)-20K and -40KIllustrative Reaction Scheme.
• 

  
A. 2-(2-t-Boc-aminoethoxy)ethanol (1)
• 2-(2-Aminoethoxy)ethanol (10.5 g, 0.1 mol) and NaHCO₃(12.6 g, 0.15 mol) were added to 100 mL CH₂Cl₂and 100 mL H₂O. The solution was stirred at RT for 10 minutes, then di-tert-butyl dicarbonate (21.8 g, 0.1 mol) was added. The resulting solution was stirred at RT overnight, then extracted with CH₂Cl₂(3×100 mL). The organic phases were combined and dried over anhydrous sodium sulfate and evaporated under vacuum. The residue was subjected to silica gel column chromatography (CH₂Cl₂:CH₃OH=50:1˜10:1) to afford 2-(2-t-Boc-aminoethoxy)ethanol (1) (16.0 g, 78 mmol, yield 78%).
B. 2-(2-t-Boc-aminoethoxy)ethoxycarbonyl-Irinotecan (2)
• 2-(2-t-Boc-aminoethoxy)ethanol (1) (12.3 g, 60 mmol) and 4-dimethylaminopyridine (DMAP) (14.6 g, 120 mmol) were dissolved in 200 ml anhydrous CH₂Cl₂. Triphosgene (5.91 g, 20 mmol) was added to the solution while stirring at room temperature. After 20 minutes, the solution was added to a solution of irinotecan (6.0 g, 10.2 mmol) and DMAP (12.2 g, 100 mmol) in anhydrous CH₂Cl₂(200 mL). The reaction was stirred at RT for 2 hrs, then washed with HCl solution (pH=3, 2 L) to remove DMAP. The organic phases were combined and dried over anhydrous sodium sulfate. The dried solution was evaporated under vacuum and subjected to silica gel column chromatography (CH₂Cl₂:CH₃OH=40:1˜10:1) to afford 2-(2-t-Boc-aminoethoxy)ethoxycarbonyl-irinotecan (2) (4.9 g, 6.0 mmol, yield 59%).
C. 2-(2-aminoethoxy)ethoxycarbonyl-irinotecan TFA salt (3)
• 2-(2-t-Boc-aminoethoxy)ethoxycarbonyl-irinotecan (2) (4.7 g, 5.75 mmol) was dissolved in 60 mL CH₂Cl₂, and trifluoroacetic acid (TFA) (20 mL) was added at RT. The reaction solution was stirred for 2 hours. The solvents were removed under vacuum and the residue was added to ethyl ether and filtered to give a yellow solid as product 3 (4.3 g, yield 90%).
D. 4-arm-PEG_{20 k}-carbonate-irinotecan (4)
• 4-arm-PEG_{20 k}-SCM (16.0 g) was dissolved in 200 mL CH₂Cl₂. 2-(2-aminoethoxy)ethoxycarbonyl-irinotecan TFA salt (3) (2.85 g, 3.44 mmol) was dissolved in 12 mL DMF and treated with 0.6 mL TEA, then added to a solution of 4-arm-PEG_{20 k}-SCM. The reaction was stirred at RT for 12 hrs then precipitated in Et₂O to yield a solid product, which was dissolved in 500 mL IPA at 50° C. The solution was cooled to RT and the resulting precipitate collected by filtration to give 4-arm-PEG_{20 k}-glycine-irinotecan (4) (16.2 g, drug content 7.5% based on HPLC analysis). Yield: 60%.
E. 4-arm-PEG_{40 k}-carbonate-irinotecan (5)
• 4-arm-PEG_{40 k}N-SCM (32.0 g) was dissolved in 400 mL CH₂Cl₂. 2-(2-aminoethoxy)ethoxycarbonyl-irinotecan TFA salt (3) (2.85 g, 3.44 mmol) was dissolved in 12 mL DMF and treated with 0.6 mL TEA, then added to the solution of 4-arm-PEG_{40 k}-SCM. The reaction was stirred at RT for 12 hrs and then precipitated in Et₂O to get solid product, which was dissolved in 1000 mL isopropyl alcohol (IPA) at 50° C. The solution was cooled to RT and the precipitate collected by filtration to give 4-arm-PEG_{40 k}-glycine-irinotecan (4) (drug content 3.7% based on HPLC analysis). Yield: 59%.
Example 9Formulation of 4-Arm-Peg-Gly-Irino-20K for IV Administration
• 4-arm-PEG-gly-irino-20K (as described in Example 1) was formulated as a sterile lyophilized powder in lactate buffer in a pH range from 3 to 5. The product was packaged in sealed amber glass vials.
• Prior to intravenous administration, the product is diluted with a commercially available dextrose solution, 5% w/w. The reconstituted drug solution is diluted to a final concentration range of approximately 0.12 to 2.8 mg/mL.
Example 10In-Vitro Release of Irinotecan from 4-Arm-Peg-Gly-Irino-20K
• The rate of release of irinotecan from 4-arm-PEG-gly-irino-20K was examined in vitro. Since the prodrug releases free irinotecan upon hydrolysis, its release rate is relevant to the pharmacokinetic properties of the molecule. Thus, a series of experiments was conducted to determine the impact, if any, of drug loading upon release kinetics.
• Using a Type II dissolution tester coupled with HPLC analysis, the hydrolysis rate of irinotecan from 4-arm-PEG-gly-irino-20K in PBS at pH 7.4 was assessed at 37° C.
• The results are depicted inFIG. 14. Hydrolysis rate studies for two typical product batches were run in triplicate over a period of 120 hours. The resultant release profile was consistent and reproducible, and demonstrates a controlled release of irinotecan over the period of study. The results further demonstrate that the hydrolysis rate is independent of the average number of irinotecan molecules per molecule of polymer, as well as the distribution of the irinotecan molecules on the 4-arm PEG.
• This finding was further supported by an additional study using a 4-arm-PEG-gly-irino-20K composition that was synthesized to possess, on average, less than one molecule of irinotecan per 4-armed PEG (“low load product”). The hydrolysis rate was then examined as described above, and the results compared to a batch having the typical load of 2.3 to 3 molecules of irinotecan per 4-armed polymer. The hydrolysis rate of the “low load product” was essentially the same as that shown inFIG. 14 for typical product batches.
Example 11Tumor Growth in Mice Implanted with MCF-7 Breast Tumor Cell Line and Treated with 4-Arm-Peg-Gly-irino-20K
• Female athymic (Nu:Nu) mice were injected subcutaneously with MCF-7 breast tumor cells and the tumors were allowed to reach a median volume of 75 mm³. Each group of mice (n=10) was dosed every fourth day with a total of 3 doses of 4-arm-PEG-gly-irino-20K at 20, 40, 60, or 90 mg/kg or irinotecan at 20 and 40 mg/kg. The control group received normal saline. The animals were weighed and tumors were measured twice weekly after administration of the first drug injection.
• All doses of 4-arm-PEG-gly-irino-20K (referred to simply as “PEG-irinotecan” in Table 2) and irinotecan were well tolerated with a maximum 10% loss in body weight. The effects of the test compounds on tumor regression are shown in Table 2 below.

• TABLE 2
  Summary of Tumor Growth Parameters for MCF-7 Tumor-Bearing Mice

  		Tumor	Median	Days to
  Test	Dosea	Regressionb	Durationc	4 Times	T-Ce

  Compound	(mg/kg)	Partial	Complete	(days)	Tumor Sized	(days)

  Control	0	0	0	NA	20.5	NA
  PEG-Irinotecan	90	1	0	49.0	>72	>52
  PEG-Irinotecan	60	0	0	NA	>72	>52
  PEG-Irinotecan	40	1	0	22.0	>72	>52
  PEG-Irinotecan	20	0	0	NA	>72	>52
  Irinotecan	40	1	0	42.0	42.8	22.3
  Irinotecan	20	0	0	NA	40.2	19.7
  a: Refers to amount active compound administered in each dose.
  b: Tumor regression: smallest tumor size after the beginning of treatment relative to that observed on first day of treatment. Partial: <50% of size observed onDay 1; Complete: unpalpable.
  c: Interval during which partially or completely regressed tumor was below 50% pretreatment size.
  d: Median number of days for tumor to quadruple in size from original volume.
  e: Difference in the median of times for tumors to gain 4 times original size for the drug group minus that for the control group.
  NA: Not applicable

• No tumor regrowth occurred in PEG-irinotecan-treated animals at any dose level (FIG. 15A). The T-C value was significantly higher in the PEG-irinotecan treatment group than with the irinotecan treatment groups at all 4 dose levels tested (p<0.001) showing significant growth delay in the PEG-irinotecan treatment groups compared to the irinotecan treatment groups.
• For ease of comparison,FIG. 15C contains plots comparing mean tumor weight (mg) over time (days) in athymic mice implanted with MCF-7 human breast tumors following administration of 4-arm-PEG-gly-irino-20K, irinotecan, or a control. Subjects were administered 20 mg/kg irinotecan equivalent per dose; dosing occurred every four days for a total of three doses administered.
Example 12Exposure (Auc) of 4-Arm-Peg-Gly-Irino-20K and its Metabolites in a Colon Tumor Model
• A PK/Pharmacodynamic (PD) study was conducted to evaluate whether a greater tumor suppression of 4-arm-PEG-gly-irino-20K over irinotecan observed in a previous study could be explained by a greater accumulation of SN38 in colon tumor tissue.
• Fragments of human HT29 colon tumor were implanted subcutaneously in female athymic mice. Tumors were allowed to reach approximately 170 mg in weight before the commencement of treatment. 4-arm-PEG-gly-irino-20K or irinotecan were administered intravenously every four days for three doses at a dose of 40 mg/kg. Pharmcokinetic sampling for plasma and tumor was at pre-selected time-points up to 60 days for both groups. At each time-point, four mice were sacrificed and blood and tumor samples were collected.
• Pharmacokinetic parameters were estimated by compartmental PK analyses using WiNonlin™ (professional version 2.1; Pharsight Corp., Mountain View, Calif.), commercial software designed for the analysis of PK data. Computation of the AUC and the t½ in blood plasma and tumor tissue was based on estimation of primary kinetic parameters by least-squares nonlinear regression routines for blood plasma and tumor tissue concentration-time data.

• TABLE 3
  Exposure (AUC) of PEG-Irinotecan and
  its Metabolites in a Colon Tumor Model

  Exposure (AUC)

  	PEG-Irinotecan	Irinotecan (I)	Ratio of
  	(PEG-I) Treatment	Treatment	PEG-I / I

  Analytes	Plasma	Tumor	Plasma	Tumor	Plasma	Tumor

  SN38	5.8	11.7	0.01	0.03	531	366
  Irinotecan	1.5	5.8	0.3	1.2	5	4.8
  PEG-Irinotecan	2143	4598	NA	NA	NA	NA
  PEG-SN38	784	2078	NA	NA	NA	NA
  Day
  1 AUC of tumor tissue: days × μg/g
  Day
  1 AUC of venous plasma: days × μg/mL
  Data obtained from nonlinear regression
  NA: Not applicable

• AUC ratios of SN38 in plasma and tumor resulting from 4-arm-PEG-gly-irino-20K administration were found to be of several orders of magnitudes higher when compared to SN38 resulting from irinotecan administration (Table 3). The tumor exposure to SN38 following PEG-Irinotecan dosing was approximately 360-fold greater than that for following irinotecan dosing.
• SN38 concentrations resulting from PEG-Irinotecan administration declined at a much slower rate than with irinotecan administration (Table 4), yielding greater exposure following PEG-Irinotecan administration. The t½ of SN38 measured following PEG-Irinotecan administration in blood plasma and colon tumor tissue were 17 days and 15 days, respectively. In contrast, SN38 resulting from irinotecan administration resulted in more rapid blood plasma and intra-tumoral PK. This observed difference in SN38 PK appears to be the basis for greater inhibition of tumor growth following PEG-Irinotecan administration compared to irinotecan in the in vivo colon tumor model investigated.

• TABLE 4
  Terminal Half-Life of PEG-Irinotecan and its
  Metabolites compared to Irinotecan and SN38
  in the Colon Tumor Xenograft Model

  Terminal Half-life

  		PEG-Irinotecan	Irinotecan
  		Treatment	Treatment

  	Analytes	Plasma	Tumor	Plasma	Tumor

  	SN38	17	d	15 d	2 h	4 h
  	Irinotecan	6	h	10 d	1 h	2 h
  	PEG-Irinotecan	4	h	15 d	NA	NA
  	PEG-SN38	15	d	10 d	NA	NA
  	NLR: Nonlinear regression
  	NA: Not applicable

Example 13Pharmacokinetic Analysis of 4-Arm-Peg-Gly-irino-20K and its Metabolites Compared to Irinotecan in a Lung Tumor Model
• A PK/PD study similar to that in Example 12 was conducted in a different tumor model to evaluate whether the superior tumor suppression of 4-arm-PEG-gly-irino-20K over irinotecan observed in a previous study could be partially explained by an accumulation of SN38 in tumor tissue. Similar procedures and analyses were performed on mice implanted with NCI-H460 human lung tumor tissue as those described in Example 12.

• TABLE 5
  Exposure (AUC) of 4-arm-PEG-gly-irino-20K and its Metabolites in a Lung Tumor Model

  Exposure (AUC)

  	PEG-Irinotecan	Irinotecan (I)	Ratio of
  	(PEG-I) Treatment	Treatment	PEG-I / I

  Analytes	Plasma	Tumor	Plasma	Tumor	Plasma	Tumor

  SN38	2.6	10.5	0.2	0.18	11	59
  Irinotecan	2.0	4.3	0.5	1.2	3.9	3.6
  PEG-Irinotecan	1213	3555	NA	NA	NA	NA
  PEG-SN38	229	1409	NA	NA	NA	NA
  Day
  1 AUC of tumor tissue: days × μg/g
  Day
  1 AUC of venous plasma: days × μg/mL
  NA: Not applicable

• The tumor exposure to SN38 following PEG-Irinotecan dosing was approximately 60-fold greater than that following irinotecan dosing (Table 5). The t % of SN38 in blood plasma and lung tumor tissue following PEG-Irinotecan administration were 1 day and 6 days, respectively. In contrast, SN38 resulting from irinotecan administration resulted in more rapid blood plasma and intra-tumoral PK (Table 6). This observed difference in kinetics of SN38 appears to be the basis for greater inhibition of tumor growth after PEG-Irinotecan administration compared to irinotecan in the in vivo lung tumor model.

• TABLE 6
  Terminal Half-Life of PEG-Irinotecan and its
  Metabolites Compared to Irinotecan and SN38
  in the Lung Tumor Xenograft Model

  Terminal Half-Life

  		PEG-Irinotecan	Irinotecan
  		Treatment	Treatment

  	Analytes	Plasma	Tumor	Plasma	Tumor

  	SN38	1	d	6	d	2 h	15	h
  	Irinotecan	10	h	9	d	1 h	1	h

  	PEG-Irinotecan	4	h	8	d	NA	NA
  	PEG-SN38	2	d	14	d	NA	NA
  	Data obtained from nonlinear regression
  	NA: reliable t½ could not be calculated
  	t½ is represented in hours and in those cases where the t½ was greater than 24 hours, t½ is represented in days

• The observed and predicted concentration time profiles of SN-38 in blood plasma and in lung tumors, respectively, was plotted following repeat dosing with either PEG-irinotecan or irinotecan. SN38 resulting from PEG-irinotecan administration demonstrated a monophasic decline in blood plasma and in lung tumor tissue, as well as significant accumulation in both. In contrast, minor accumulation of SN38 in tumor tissue was observed after dosing of irinotecan.
• In summary, there was marked retention of SN38 in lung tumor in the mouse xenograft model following PEG-Irinotecan dosing compared to irinotecan dosing. The changes were not as pronounced as those observed in the colon model. However, the favorable changes in SN38 kinetics following PEG-Irinotecan dosing correlate well with superior suppression of lung tumor growth demonstrated in this model.
Example 14Synthesis of 4-Arm-Peg_{20 k}-Glycine-Docetaxel: DMAP-DCC Coupling
• 4-Arm-PEG_20K-glycine (500 mg, 0.025 mmol) was dissolved in 10 mL methylene chloride (DCM). 4-Dimethylaminopyridine (19 mg, 0.15 mmol) and DCC (32 mg, 0.15 mmol) were added to the PEG solution with stirring. After 5 minutes, docetaxel (121 mg, 0.15 mmol) was added and the reaction mixture continued to stir for an additional 24 h at room temperature. Upon completion, the reaction mixture was precipitated in a mixed solvent system of ether/IPA (1:1). The resulting white solid was collected by suction filtration, redissolved in DCM (2 mL) and reprecipitated using a single solvent system of diethyl ether (100 mL) to give the desired product after suction filtration.
• ¹H NMR analysis showed the existence of a significant amount of N-acylurea (δ 1-2.5 ppm) byproduct. Subsequent drug release studies by HPLC revealed that about 40% of the PEG (one or more carboxylic groups of each polymer molecule) was partially converted to the N-acylurea (a common side product in a DMAP-DCC coupling reaction). Since the N-acylurea byproduct cannot be hydrolyzed back to the original PEG starting material, the product purity profile becomes extremely complicated. Therefore, it is difficult to acquire accurate analysis, i.e. structural, drug loading, release rates, of the mixed product obtained using this method.
Example 15Synthesis of 4-arm-PEG20K-Glycine-Docetaxel
• 
• The overall synthesis of 4-arm PEG_20K-glycine docetaxel is shown in the scheme above. The “4*” represents the theoretical number of docetaxel molecules per 4-armed polymer assuming complete drug loading.
• A. Preparation of 4-arm-PEG_20K-glycine t-butyl ester
• 4-Arm-PEG_20K-CM (12.5 g, 0.625 mmol) was dissolved in 100 mL DCM. 4-Dimethylaminopyridine (610 mg, 5.00 mmol) and DCC (625 mg, 3.00 mmol) were then added to the solution with stirring. After stirring for 5 minutes, glycine t-butyl ester.HCl (503 mg, 3.00 mmol) was added and the mixture continued to stir overnight at room temperature. Upon completion, the reaction mixture was precipitated using a mixed solvent system of ether/IPA (1:1) to give the desired 4-arm-PEG_20K-glycine t-butyl ester product (10.5 g, 0.525 mmol, yield 84%) after suction filtration.
• ¹H NMR (CDCl₃) δ4.11 (d, 8H), 4.05 (s, 8H), 3.90-3.37 (m, ˜1900H), 1.48 (s, 36H).
• B. Deprotection of 4-arm-PEG_20K-glycine t-butyl Ester to Form 4-arm-PEG_20K-glycine
• 4-arm-PEG_20K-glycine t-butyl ester was deprotected using trifluoroacetic acid/methylene chloride (TFA/DCM, 3:1) and stirring at room temperature for 3 h. The product was precipitated by addition of ether (600 mL) to the reaction mixture giving the desired 4-arm-PEG_20K-glycine (9.2 g) after suction filtration.
• ¹H NMR (CDCl₃) δ 4.11 (d, 8H), 4.05 (s, 8H), 3.90-3.37 (m, ˜1900H).
• C. Preparation of 4-arm-PEG_20K-glycine-docetaxel
• DPTS was prepared as follows: p-Toluenesulfonic acid was dried by azeotropic distillation of a benzene solution, and then an equimolar solution of DMAP in benzene was added. The resulting suspension was cooled to room temperature and the solid collected by suction filtration.
• Docetaxel (776 mg, 0.96 mmol) and 4-arm-PEG_20K-glycine (4.0 g, 0.2 mmol) were dissolved in 50 mL DCM, and then freshly prepared DPTS (155 mg, 0.53 mmol), (Jeffrey S. Moore and Samuel I. Stupp, Macromolecules, 1990, 23, 65-70) and DIC (404 mg, 3.2 mmol) were added with stirring. The reaction mixture continued to stir for 24 h at room temperature. The reaction mixture was precipitated using a mixed solvent system of ether/IPA (1:1). The resulting white solid was collected by suction filtration, redissolved in 5 ml of DCM, and reprecipitated using a single solvent system of ether (300 mL) to give the desired 4-arm-PEG_20K-glycine-docetaxel after suction filtration. Yield: 90%.
• ¹H NMR (CDCl₃) δ 8.12 (d, 8H), 7.73 (m, 4H), 7.61 (m, 4H), 7.52 (m, 8H), 7.41 (m, 8H), 7.33 (m, 8H), 6.20 (t, 4H), 5.69 (m, 8H), 5.60 (m, 4H), 5.36 (s, 4H), 5.22 (m, 4H), 4.97 (d, 4H), 4.33 (m, 8H), 4.30 (m, 12H), 4.06 (d, 8H), 3.98 (s, 8H), 3.90-3.24 (m, ˜1900H), 2.60 (m, 4H), 2.36 (m, 20H), 1.96 (s, 12H), 1.86 (m, 8H), 1.75 (s, 12H), 1.68 (m, 8H), 1.35 (s, 36H), 1.25 (s, 12H), 1.13 (s, 12H). All chemical shift values in ppm (δ).
• D. Drug Loading and Hydrolysis of 4-arm-PEG_20K-glycine-docetaxel
• Drug loading was determined¹H NMR (8%) and RP-HPLC (6.2%) analytical methods while hydrolysis rates (in phosphate buffer) were determined exclusively by RP-HPLC.
• Calculation of the Drug Loading by¹H NMR:
• Samples of different PEG-docetaxel concentrations were prepared, and the number of scans was then varied depending on the concentration of the sample. Based on the averaged proton peak integration of all spectra obtained, the drug loading was determined.
• Calculation of the Drug Loading and Hydrolysis Rate by HPLC
• Instrument: HP 1100
• Column: C18 column
• Mobile Phase: A: 0.1% TFA in H₂O; B: Acetonitrile
• Flow Rate: 0.5 mL/min
• Gradient Table:

• Time	A	B
  (min)	%	%

  0	60%	40%
  15	0	90%

• Drug Loading Determination: Drug loading and hydrolysis rates were determined experimentally as follows: Using the abovementioned HPLC method, 10.8 mg docetaxel was dissolved in a mixed solvent system of acetonitrile/PBS (1:1, 10 mL, pH 7.4). This stock solution was further diluted serially to give the following concentrations of docetaxel solutions: 540 μg/mL, 405 μg/mL, 300 μg/mL, 216 μg/mL, 108 μg/mL and 54 μg/mL. The peak areas were obtained for each concentration and a standard curve was generated. Then 30.4 mg of 4-arm-PEG_20K-docetaxel was dissolved in 10 mL PBS, pH 7.4. The solution was filtered, and then aliquots of 0.3 mL were placed into 10 individual HPLC vials. These vials were stored at 37° C. and prior to use, 0.3 mL of acetonitrile was added to ensure all PEG-docetaxel and free docetaxel present in the sample were dissolved. One vial was used for each injection, and injections were made at various timepoints over a course of 200 h (8.3 d). The appearance of free drug released from the PEG-conjugate was monitored and upon completion the final concentration was determined against the standard curve.
• The drug loading value refers to the average number of docetaxel molecules covalently attached to the polymer in the 4-arm-PEG_20K-glycine-docetaxel product. The calculated molecular weight of the 4-arm PEG_20K-glycine-docetaxel product, assuming 4 docetaxel molecules per 4-arm polymer, is approximately 23,232. The molecular weight of docetaxel is 808. Assuming complete drug loading (4 docetaxels per polymer), the theoretical percent weight of drug contained in the product is (3232/23232)100 or 13.9%. The actual observed weight of drug, as determined by HPLC, was 6.2%, which corresponds to an average number of docetaxels per polymer of 1.78. The drug loading value determined by¹H NMR was 8%, which corresponds to an average number of docetaxel molecules per polymer of about 2.3. Thus, for this preparation, based upon the average of both methods, the average number of docetaxel molecules per polymer is slightly higher than 2.00.
• Half-life Determination. The determination of hydrolysis rate, reported as a half-life, utilized the same analytical method outlined above for the drug loading. Once the drug release was complete, the half-life was calculated by either determining the time at which the concentration (area %) of the free drug equaled 50% or, if perfectly linear, by determining the slope of the plot (In 1-S % vs. hour) and using the following equation:
• $\mathrm{Half}-\mathrm{life}=\ln \left(2\right)/\mathrm{slope}$
• The half-life for 4-arm-PEG_20K-Docetaxel was determined to be 15.3 h.
Example 16
• Anti-Tumor Activity of 4-Arm-PEG_{20 k}-Glycine-Docetaxel in Mice Implanted with NCI-H460 Lung Tumors
• Human NCI-H460 lung tumors (30 to 40 fragments of each) were implanted subcutaneously in the mice (Charles Rivers Labs: NCr nu/nu) near the right axillary area. The day of implantation was designatedDay 0 and the tumors were allowed to reach a weight of 100-245 mg in weight prior to treatment.
• The animals were randomized into groups in a manner such that the median tumor weights on the first day of treatment were as close to each other as possible.
• Treatment: The mice received 1 or 2 intravenous doses of test compound or vehicle (saline).
• Tumor measurement: The animals were weighed and the tumors measured twice weekly after administration of the first injection. The tumor volume was measured by caliper measurements (mm) and using the formula of an ellipsoid sphere: L×W²/2=mm³, where L and W refer to the larger and smaller perpendicular dimensions collected at each measurement. This formula was also used to calculate tumor weight assuming unit density (1 mm³=1 mg).
• Study Duration: Any animal found moribund or any animal whose tumor reached 4000 mg, ulcerated or was sloughed off was euthanized prior to study termination.
• Results: Two different efficacy studies were conducted. The 1^ststudy evaluated the efficacy of 4-arm-PEG_20K-Docetaxel and docetaxel against H460 NSCLC tumors.FIGS. 16A-C illustrate the effect of a single dose of each compound on the tumor growth. It was observed that doses of 20 and 40 mg/kg of the PEGylated docetaxel provided an improved anti-tumor effect over the un-PEGylated free compound. The 10 mg/kg dose showed a significant difference between the two compounds.
• In the 2^ndstudy, the anti-tumor efficacy (H460 NSCLC tumors) was measured up to the maximum tolerated dose for athymic nude mice. The animals tolerated docetaxel up to 30 mg/kg and PEG-docetaxel up to 60 mg/kg.FIG. 17 illustrates the effect of two doses (q7 d×2) of each compound on the tumor growth. It is again evident from the results, that the PEGylated compound provided an improved anti-tumor effect over the Docetaxel compound. A dose response is clearly evident among the three PEGylated drug doses when compared to the three un-PEGylated drug doses.
Example 17Anti-Tumor Activity of 4-Arm-PEG_{20 k}-glycine-docetaxel in Mice Implanted with DU-145 Prostate Tumors
• The study was carried out as described in Example 16 above, with the exception that the tumors used were DU-145 prostate tumors.
• The anti-tumor efficacy was evaluated against prostate tumors (DU-145) up to the maximum tolerated dose of each compound. The animals tolerated docetaxel up to 30 mg/kg and PEG-docetaxel up to 60 mg/kg.
• FIG. 18 illustrates the anti-tumor effect of two doses (q7 d×2) of each compound. It is again evident from the results that the PEGylated compounds completely suppressed the tumor growth at all 3 doses tested and for the 78 day observation period. The docetaxel compound showed good activity, but the tumors did recover and grow after 30-50 days.
Example 18
• Anti-Tumor Activity of 4-Arm-PEG_{20 k}-glycine-docetaxel in Mice Implanted with MCF-7 Breast Tumors
• Up to 100 mice (Charles Rivers Labs: CD-1 Fox nl nu) were surgically implanted in the lateral side of the neck with a subcutaneous 17β-estradiol (estrogen) pellet (1.00 mg/pellet; Innovative Research of America, Sarasota, Fla., USA) at least 2 days prior to cell inoculation. These pellets release estrogen at a rate of 0.011 mg/day for 90 days after implant. Following surgery, approximately 1×10⁶MCF-7 cells in a volume of 0.1 mL phosphate buffered saline (PBS)/Matrigel™ (1:1 v/v) were injected subcutaneously in the right flank. The tumors were allowed to reach a range of 50-150 mm³.Day 0 for this study corresponded to the first day of dosing.
• The animals were randomized into groups in a manner such that the median tumor weights on the first day of treatment were as close to each other as possible.
• Treatment: The mice received 1 or 2 intravenous doses of test compound or vehicle (saline).
• Tumor measurement: The animals were weighed and the tumors measured twice weekly after administration of the first injection. The tumor volume was measured by caliper measurements (mm) and using the formula of an ellipsoid sphere: L×W²/2=mm³, where L and W refer to the larger and smaller perpendicular dimensions collected at each measurement. This formula was also used to calculate tumor weight assuming unit density (1 mm³=1 mg).
• Study Duration: Any animal found moribund or any animal whose tumor reached 1500 cc, ulcerated or was sloughed off was euthanized prior to study termination.
• Results: The anti-tumor efficacy was evaluated against breast tumors (MCF-7) at doses of 10, 20 and 30 mg/kg. The results showed complete suppression of tumor growth at the two high doses and for both compounds tested.FIG. 19 illustrates the anti-tumor effect of the 10 mg/kg dose (q7 d×2).
Example 19
• Treatment of Advanced Colorectal Cancer in Irinotecan-Naïve Subjects with 4-Arm-Peg-Gly-Irino-20 k and Combination with Cetuximab
• The study population consists of patients having advanced colorectal cancer, and who have failed one prior therapy. The subjects are also irinotecan-naïve. The study is an open-label, randomized, double arm study designed to evaluate 4-arm-PEG-gly-irino-20K as a second line treatment for colorectal cancer in irinotecan naïve subjects.
• Subjects are administered either 4-arm-PEG-gly-irino-20K at a starting dose of 100 mg/m²up to 175 mg/m²(irinotecan equivalents) or irinotecan weekly, in combination with cetuximab. Cetuximab, also administered once weekly, is administered at an initial loading dose of 400 mg/m²onDay 1 as a two hour intravenous infusion, and then continued weekly at a dose of 250 mg/m²administered as a one hour intravenous infusion. The primary endpoint of the study is progression-free survival.
Example 20Additional Cytotoxicity Studies with 4-Arm-Peg-Gly-irino-20K and 4-Arm-PEG20K-glycine-docetaxel
• Additional illustrative in-vivo studies were carried out as described previously herein or in accordance with methods well-known to one having ordinary skill in the art. The results of such studies are provided graphically herein asFIGS. 20-26.
• These results provide additional evidence for the superior efficacy of the prodrugs provided herein in preclinical mouse xenograft models of multiple tumor types. These studies indicate superior tumor regression accompanied by reduced toxicities in rats and dogs for the prodrugs provided herein when compared to unmodified drug alone. Moreover, based upon the results illustrated, for example, inFIG. 20, administration of 4-arm-PEG-gly-irino-20K results in a two to three times logarithmic increase in exposure to SN-38 in colorectal tumors in mice in comparison to irinotecan.
• Many modifications and other embodiments of the invention will come to mind to one skilled in the art.
Example 21Antitumor Activity of 4-Arm-Peg-Gly-Irino-20K when Administered as a Single Agent and in Combination with an Anti-Angiogenic Agent in a Human Colorectal Tumor Xenograft Model
• HT29 tumor fragments were implanted into female, athymic nude mice in the monotherapy study. Following establishment of measurable tumors in groups of 10 mice, a total of three irinotecan equivalent doses administered every fourth day (q4 d×3) of 4-arm-PEG-gly-irino-20K or irinotecan (40, 60, or 90 mg/kg). Animals were weighed and tumor volumes measured twice weekly after the first drug injection in both studies.
• For the combination study, athymic nude female mice were inoculated subcutaneously with HT29 tumor cells. Once measurable tumors were established, the mice were dosed onDay 1 with either 20 or 40 mg/kg 4-arm-PEG-gly-irino-20K (irinotecan equivalents), and/or 50 μg/dose Avastin. 4-arm-PEG-gly-irino-20K was administered IV every seven days for a total of three irinotecan equivalent doses (q7 d×3) and Avastin was administered IP onDays 1 and 14. Efficacy was evaluated by determining the in-study tumor growth inhibition (TGI).
• Significant antitumor activity was observed in all mice receiving 4-arm-PEG-gly-irino-20K as a montherapy compared to irinotecan. Tumor growth delay was significantly longer with 4-arm-PEG-gly-irino-20K at all three doses tested (20.9-60.2 days) compared with irinotecan (0.3-1.6 days). 1/10 animals achieved partial tumor regression, and 3/10 animals achieved complete tumor regression at the 90 mg/kg dose. All doses of 4-arm-PEG-gly-irino-20K and irinotecan were well tolerated.
• 20 mg/kg 4-arm-PEG-gly-irino-20K+Avastin resulted in 31% and 30% increases in TGI compared to 4-arm-PEG-gly-irino-20K and Avastin alone, respectively. There were 2/10 partial tumor regressions in this combination group. 40 mg/kg 4-arm-PEG-gly-irino-20K+Avastin resulted in 5% and 46% increases in TGI compared to 4-arm-PEG-gly-irino-20K and Avastin alone, respectively. There were 8/10 partial regressions and one complete regression within this combination group. The combination regimens were well-tolerated with no signs of overt toxicity.
• 4-arm-PEG-gly-irino-20K inhibited tumor growth more effectively than irinotecan in the HT29 human colorectal tumor xenograft model. 4-arm-PEG-gly-irino-20K in combination with Avastin demonstrated greater anti-tumor activity than when administered as a monotherapy in this model.
• Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (15)

What is claimed is:

1. A method of treating cancer in a human subject, the method comprising:

administering a therapeutically effective amount of a composition comprising a prodrug having a structure:

or a pharmaceutically acceptable salt thereof, where n ranges from 40 to 500, to a subject having one or more cancerous solid tumors.

2. The method ofclaim 1, wherein the cancerous solid tumor type is selected from the group consisting of colorectal, ovarian, breast, non-small cell lung and prostate.

3. The method ofclaim 1, wherein the overall nominal average molecular weight of the prodrug ranges from about 20,000 to about 80,000 daltons.

4. The method ofclaim 1, wherein the overall nominal average molecular weight of the prodrug is about 20,000 daltons.

5. The method ofclaim 1, wherein the composition comprises prodrug molecules having an average of from 2.3 to 3.0 molecules of irinotecan per multi-armed polyethylene glycol.

6. The method ofclaim 1, wherein the composition further comprises a pharmaceutically acceptable carrier.

7. The method ofclaim 6, wherein the composition comprises sorbitol and lactic acid.

8. The method ofclaim 1, wherein the composition is administered parenterally.

9. The method ofclaim 8, wherein the composition is administered by intravenous infusion.

10. The method ofclaim 1, wherein the composition is in the form of a sterile aqueous preparation.

11. The method ofclaim 1, wherein the dosage of prodrug administered comprises from about 10.0 to about 60 mg irinotecan/kg body weight of the subject.

12. The method ofclaim 1, wherein the composition is administered once very one, two, or three weeks.

13. The method ofclaim 1, wherein prior to administering, the composition is in the form of a sterile lyophilized solid, and the sterile lyophilized solid composition is reconstituted in an aqueous vehicle.

14. The method ofclaim 13, wherein the aqueous vehicle is 5% dextrose injection or 0.9% sodium chloride injection solution.

15. The method ofclaim 1, wherein the composition is administered in combination with a second anticancer agent.

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