Proto-oncogene tyrosine-protein kinase ROS is anenzyme that in humans is encoded by theROS1gene.[5][6]
Thisproto-oncogene, highly expressed in a variety of tumor cell lines, belongs to thesevenless subfamily of tyrosine kinase insulin receptor genes. The protein encoded by this gene is a type Iintegral membrane protein withtyrosine kinase activity. The protein may function as a growth or differentiation factor receptor.[6]
Proto-oncogene tyrosine-protein kinase ROS (ROS1) is a type Iintegral membrane protein and a member of thereceptor tyrosine kinase (RTK) family. Structurally, it is a large protein composed of 2,347 amino acid residues and features a singletransmembrane domain that anchors it to theplasma membrane. The extracellular region is responsible for ligand binding, whereas the intracellular region contains the tyrosine kinase domain, which catalyzes the phosphorylation of specific tyrosine residues in substrates. ROS1 shows a typical RTK organization: an extracellular ligand-binding domain, a single α-helical transmembrane segment, and a cytoplasmic domain containing the highly conserved ATP-binding and active sites required for kinase activity. The cytoplasmic segment also includes regions crucial for downstream signaling interactions.[7]
Proto-oncogene tyrosine-protein kinase ROS (ROS1) is a receptor tyrosine kinase (RTK) that is evolutionarily conserved and involved inepithelial cell differentiation duringorgan development. Its precise physiological role in humans is not yet fully defined, but evidence suggests it functions in normalcellular signaling and developmental processes.[7]
Upon ligand binding (e.g., byNELL2), ROS1 activates several downstream cellular signaling pathways, contributing to epithelial cell differentiation, cell growth, and survival.[8]
ROS1 is areceptor tyrosine kinase (encoded by the geneROS1) with structural similarity to theanaplastic lymphoma kinase (ALK) protein; it is encoded by thec-ros oncogene and was first identified in 1986.[9][10][11][12] The exact role of theROS1 protein in normal development, as well as its normal physiologic ligand, have not been defined.[10] Nonetheless, as gene rearrangement events involvingROS1 have been described in lung and other cancers, and since such tumors have been found to be remarkably responsive to small molecule tyrosine kinase inhibitors, interest in identifyingROS1 rearrangements as a therapeutic target in cancer has been increasing.[9][13] In 2016, the small molecule tyrosine kinase inhibitor, crizotinib, was approved for the treatment of patients with metastatic NSCLC whose tumors are ROS1-positive.[9]
Gene rearrangements involving theROS1 gene were first detected inglioblastoma tumors and cell lines.[14][15] In 2007 aROS1 rearrangement was identified in a cell line derived from alung adenocarcinoma patient.[16] Since that discovery, multiple studies have demonstrated an incidence of approximately 1% in lung cancers, demonstrated oncogenicity, and showed that inhibition of tumor cells bearingROS1 gene fusions bycrizotinib or otherROS1tyrosine kinase inhibitors was effective in vitro.[17][18][10] Clinical data supports the use of crizotinib in lung cancer patients withROS1 gene fusions.[19][20] Preclinical and clinical work suggests multiple potential mechanisms of drug resistance inROS1 + lung cancer, including kinase domain mutations inROS1 and bypass signaling viaRAS andEGFR.[21][22][23] Although the most preclinical and clinical studies ofROS1 gene fusions have been performed in lung cancer,ROS1 fusions have been detected in multiple other tumor histologies, includingovarian carcinoma,sarcoma,cholangiocarcinomas and others.[24] Crizotinib or otherROS1 inhibitors may be effective in other tumor histologies beyond lung cancer as demonstrated by a patient with aninflammatory myofibroblastic tumor harboring aROS1 fusion with a dramatic response to crizotinib.[25]
In patients with NSCLC, approximately 2% are positive for aROS1 gene rearrangement, and these rearrangements are mutually exclusive ofALK rearrangement.[18]ROS1 fusion-positive patients tend to be younger, with a median age of 49.8 years, and never-smokers, with a diagnosis of adenocarcinoma. There is a higher representation of Asian ethnicity and patients with Stage IV disease.[18]ROS1 rearrangements are estimated to be roughly half as common asALK-rearranged NSCLCs. Similar toALK-rearranged,ROS1-rearranged NSCLC have younger age of onset and a non-smoking history.[18] A benefit of a small-molecule ALK,ROS1, and cMET inhibitor,crizotinib, was also shown in this patient group.
ROS1 expression was found in approximately 2% of NSCLC patients, and its expression was limited to those patients withROS1 gene fusions.[13] Similar findings were reported in a separate analysis of 447 NSCLC samples, of which 1.2% were found to be positive forROS1 rearrangement; this study also confirmed the activity of the ALK/ROS1 /cMET inhibitor crizotinib inROS1 -positive tumors.[10]ROS1 fusions were also identified in approximately 2% of adenocarcinomas and 1% of glioblastoma samples in an assessment of kinase fusions across different cancers.[26]
Table 1: Sampling ofROS1 Rearrangements Observed in NSCLC and Other Cancers. All of the kinase fusions retain the tyrosine kinase domain ofROS1 . List is not exhaustive. (Adapted from Stumpfova 2012).
Several drugs target ROS1 fusions in cancer, with varying levels of success; most of the drugs to date have been tested only for ROS1-positivenon-small cell lung carcinoma (NSCLC).[27] However, some clinical trials (like those forentrectinib, DS-6051b, and TPX-0005) accept patients with ROS1 cancer in any type of solid tumor.
Crizotinib is approved for treating metastatic ROS1-positive NSCLC in many countries. In clinical trials, crizotinib was shown to be effective for 70-80% of ROS1+ NSCLC patients, but it does not effectively treat the brain. Some patients have a response that lasts for years.[28] Crizotinib is available to patients with solid tumors other than NSCLC through clinical trials.[29][30]
Entrectinib (RXDX-101) is a selective tyrosine kinase inhibitor developed by Ignyta, Inc., with specificity, at low nanomolar concentrations, for all of threeTrk proteins (encoded by the threeNTRK genes, respectively) as well as the ROS1, andALK receptortyrosine kinases. An open label, multicenter, global phase 2 clinical trial called STARTRK-2 started in 2015 to test the drug in patients with ROS1/NTRK/ALK gene rearrangements.[31]
Lorlatinib (also known as PF-06463922) was shown in an ongoing Phase 2 clinical trial to be effective in some ROS1+ NSCLC patients, and treats the cancer in the brain as well as the body. Lorlatinib has the potential to overcome certain resistance mutations that develop during treatment with crizotinib.[32]
Ceritinib demonstrates clinical activity (including treating the brain) in ROS1+ NSCLC patients who had previously received platinum-based chemotherapy. In preclinical studies, ceritinib is unable to overcome most ROS1 resistance mutations, including ROS1 G2032R. It has more severe side effects than crizotinib for some patients. Ceritinib is US FDA approved for first line treatment of ALK+ metastatic non-small cell lung cancer.[33][34]
TPX-0005 preclinical data suggests it is a potent inhibitor of ROS1+ cancer.[35] A Phase I clinical trial opened in March 2017 for patients with advanced solid tumors harboring ALK, ROS1, or NTRK1-3 rearrangements.[36]
DS-6051b preclinical data show it is active against ROS1-positive cancers.[32] It is an ongoing clinical trial.[37]
Cabozantinib preclinical data has shown the drug might overcome crizotinib resistance in ROS1+ cancer in early studies.[38] However, the required dosage makes the drug difficult to tolerate for many patients. Cabozantinib is US FDA approved for metastatic medullary thyroid cancer (as Cometriq) and renal cell carcinoma (as Cabometyx).
From a large-scale survey of tyrosine kinase activity in non-small cell lung cancer (NSCLC), and identified more than 50 distinct tyrosine kinases and over 2500 downstream substrates, with the goal of identifying candidate oncogenes.[16] In a sampling of 96 tissue samples from NSCLC patients, approximately 30% displayed high levels ofphosphotyrosine expression; further analysis was conducted to identify highly phosphorylated tyrosine kinases in NSCLC from a panel of 41 NSCLC cell lines, and 150 patient samples.[16] Among the top 20 receptor tyrosine kinases identified in this analysis, 15 were identified in both cell lines and tumors, and among these were both ALK and ROS1.[16] These initial findings paved the way for more expansive analyses ofROS1 kinase fusions in NSCLC and other cancers.
The ROS1ders[39] is a worldwide collaboration of ROS1+ cancer patients and caregivers with a goal of improving patient outcomes and accelerating research for any type of ROS1+ cancer. It is the first such collaboration focused on cancers driven by a single oncogene. Their website tracks targeted therapies, clinical trials, world experts and new developments for ROS1+ cancers.[40] Partners include patient-focused nonprofits, clinicians who treat ROS1+ patients, ROS1 researchers, pharmaceutical firms and biotech companies.
^"Human PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
^Galland F, Stefanova M, Lafage M, Birnbaum D (July 1992). "Localization of the 5' end of the MCF2 oncogene to human chromosome 15q15----q23".Cytogenetics and Cell Genetics.60 (2):114–116.doi:10.1159/000133316.PMID1611909.
^abAcquaviva J, Wong R, Charest A (January 2009). "The multifaceted roles of the receptor tyrosine kinase ROS in development and cancer".Biochimica et Biophysica Acta (BBA) - Reviews on Cancer.1795 (1):37–52.doi:10.1016/j.bbcan.2008.07.006.PMID18778756.
^Rabin M, Birnbaum D, Young D, Birchmeier C, Wigler M, Ruddle FH (July 1987). "Human ros1 and mas1 oncogenes located in regions of chromosome 6 associated with tumor-specific rearrangements".Oncogene Research.1 (2):169–178.PMID3329713.
^Takeuchi K, Soda M, Togashi Y, Suzuki R, Sakata S, Hatano S, et al. (March 2012). "RET, ROS1 and ALK fusions in lung cancer".Nature Medicine.18 (3):378–381.doi:10.1038/nm.2658.PMID22327623.S2CID26561572.
^Clinical trial numberNCT02465060 for "NCI-MATCH: Targeted Therapy Directed by Genetic Testing in Treating Patients With Advanced Refractory Solid Tumors, Lymphomas, or Multiple Myeloma" atClinicalTrials.gov
^Clinical trial numberNCT02693535 for "TAPUR: Testing the Use of Food and Drug Administration (FDA) Approved Drugs That Target a Specific Abnormality in a Tumor Gene in People With Advanced Stage Cancer (TAPUR)" atClinicalTrials.gov
^Clinical trial numberNCT02568267 for "Basket Study of Entrectinib (RXDX-101) for the Treatment of Patients With Solid Tumors Harboring NTRK 1/2/3 (Trk A/B/C), ROS1, or ALK Gene Rearrangements (Fusions) (STARTRK-2)" atClinicalTrials.gov
^Califano R, Greystoke A, Lal R, Thompson J, Popat S (Sep 2017). "Management of ceritinib therapy and adverse events in patients with ALK-rearranged non-small cell lung cancer".Lung Cancer.111. Amsterdam, Netherlands:51–58.doi:10.1016/j.lungcan.2017.06.004.hdl:10044/1/54441.PMID28838397.
^Clinical trial numberNCT03093116 for "A Study of TPX-0005 in Patients With Advanced Solid Tumors Harboring ALK, ROS1, or NTRK1-3 Rearrangements (TRIDENT-1)" atClinicalTrials.gov
^Clinical trial numberNCT02279433 for "A First-in-human Study to Evaluate the Safety, Tolerability and Pharmacokinetics of DS-6051b" atClinicalTrials.gov
Satoh H, Yoshida MC, Matsushime H, Shibuya M, Sasaki M (August 1987). "Regional localization of the human c-ros-1 on 6q22 and flt on 13q12".Japanese Journal of Cancer Research: Gann.78 (8):772–775.PMID3115921.
Charest A, Lane K, McMahon K, Park J, Preisinger E, Conroy H, et al. (May 2003). "Fusion of FIG to the receptor tyrosine kinase ROS in a glioblastoma with an interstitial del(6)(q21q21)".Genes, Chromosomes & Cancer.37 (1):58–71.doi:10.1002/gcc.10207.PMID12661006.S2CID39776967.
Girish V, Sachdeva N, Minz RW, Radotra B, Mathuria SN, Arora SK (July 2005). "Bcl2 and ROS1 expression in human meningiomas: an analysis with respect to histological subtype".Indian Journal of Pathology & Microbiology.48 (3):325–330.PMID16761743.
