 | |
| Clinical data | |
|---|---|
| Other names | RO-5203648 |
| Drug class | Trace amine-associated receptor 1 (TAAR1)partial agonist |
| Identifiers | |
| |
| CAS Number | |
| PubChemCID | |
| ChemSpider | |
| ChEMBL | |
| Chemical and physical data | |
| Formula | C9H8Cl2N2O |
| Molar mass | 231.08 g·mol−1 |
| 3D model (JSmol) | |
| |
| |
RO5203648 is atrace amine-associated receptor 1 (TAAR1)partial agonist.[1][2][3] It is apotent and highlyselective partial agonist of both rodent and primate TAAR1.[2][3] The drug suppresses the effects ofpsychostimulants likecocaine andmethamphetamine.[1][2] It also produces a variety of other behavioral effects, such asantidepressant-like,antipsychotic-like, andantiaddictive effects.[1][2][4] Research with RO5203648 has led to interest in TAAR1 agonists for potential treatment ofdrug addiction.[1] RO5203648 itself was not developed for potential medical use due to poor expected humanpharmacokinetics.[3]
RO5203648 binds to the mouse, rat,cynomolgus monkey, and human TAAR1 all with highaffinity (Ki = 0.5–6.8 nM).[1][2] It is apotentpartial agonist in all species (EC50Tooltip half-maximal effective concentration = 4.0 to 31 nM), with anefficacy of 48 to 73% relative to theendogenous TAAR1 agonistsβ-phenethylamine andtyramine and the TAAR1 full agonistRO5166017.[1][2][3] RO5203648 is highlyselective for the TAAR1, showing ≥130-fold selectivity for the mouse TAAR1 over 149 othertargets.[2][3]
| Species | Affinity (Ki, nM) | EC50Tooltip half-maximal effective concentration (nM) | EmaxTooltip maximal efficacy (%) |
|---|---|---|---|
| Mouse | 0.5 | 2.1–4.0 | 48–71% |
| Rat | 1.0 | 6.8 | 59% |
| Monkey | 2.6 | 31 | 69% |
| Human | 6.8 | 30 | 73% |
RO5203648 has been found to increase the firing rate ofventral tegmental area (VTA)dopaminergicneurons anddorsal raphe nucleus (DRN)serotonergic neurons in mousebrain slicesex vivo.[1][5][2] This is in contrast to the TAAR1full agonistRO5166017, which suppresses their firing rates, but is analogous to the TAAR1antagonistEPPTB, which dramatically increases their firing rates.[1][5][2] RO5203648 failed to show these effects in the neurons of TAAR1knockout mice, indicating that its actions are mediated by interactions with the TAAR1.[2] RO5203648 alone does not affect electrically evoked dopamine release orreuptake (as measured by tau) in ratnucleus accumbens (NAc) slicesex vivo.[5][6] Conversely, RO5203648 preventedcocaine-induced dopamine elevations in this system without affecting the dopamine reuptake inhibition of cocaine.[1][5][6] As such, its inhibition of cocaine's dopaminergic actions is likely to be independent ofdopamine transporter (DAT) interactions.[1][6] RO5203648 did not affectmethamphetamine-induced dopamine efflux or reuptake inhibition in ratstriatalsynaptosomesin vitro.[7][8][4] However, RO5203648 blunted and delayed methamphetamine-induced dopamine elevations in the NAc in rodentsin vivo.[5][4] Hence, as with cocaine, RO5203648's regulation of methamphetamine's actions appears to be independent of DAT interactions.[7][5][4]
Somein-vitro studies have suggested that TAAR1 agonism byamphetamines andβ-phenethylamine may mediateinduction of monoamine release andreuptake inhibition by these agents.[9][10][11][12][13][14][14] However, a subsequent study failed to replicate these findings under similar conditions.[7] In addition, as previously described, RO5203648 did not affect methamphetamine-induced dopamine release and reuptake inhibition in synaptosomesin vitro.[7][8][5][4] The dopamine elevations andpsychostimulant-like effects of amphetamines are not only preserved but are actually augmented in TAAR1 knockout micein vivo.[9][8][15][16] Concordantin-vivo findings have been made with amphetamines combined with TAAR1 agonists andantagonists as well as with TAAR1overexpression.[8] It appears that TAAR1 agonism by amphetamines, such as amphetamine, methamphetamine, andMDMA, auto-inhibits theirmonoaminergic effects.[17][18][19] Conversely, mostcathinones lack TAAR1 agonism, and this might enhance their effects compared to amphetamines.[18][20]
RO5203648 does not significantly affect basallocomotion.[2] Conversely, the drug has been found todose-dependently suppress cocaine-inducedhyperlocomotion in mice and rats, whereas it only suppresseddextroamphetamine-induced hyperactivity at a high dose in rats and did not affect dextroamphetamine-induced hyperlocomotion in mice.[1][21][5][2] RO5203648 reduced early but potentiated late hyperlocomotion induced by methamphetamine.[1][4] With chronic administration of RO5203648 and methamphetamine, RO5203648 dose-dependently and progressively decreased methamphetamine-induced hyperlocomotion.[1][4] TAAR1 full agonists likeRO5166017 andRO5256390 also suppress psychostimulant-induced hyperlocomotion.[21] RO5203648 suppressed spontaneous hyperactivity in a novel environment indopamine transporter (DAT) knockout mice, similarly toantipsychotics likehaloperidol andolanzapine.[2][22] RO5203648 has also been found to suppress hyperlocomotion induced by theNMDA receptor antagonistL-687,414 or in genetically modified mice with a hypoactiveNMDA receptor.[1][2] The effects of RO5203648 on hyperdopaminergic- and hypoglutamatergic-mediated hyperlocomotion are similar to those of the TAAR1 full agonist RO5166017.[21][2]
The drug has shownanti-cataleptic,pro-cognitive,antipsychotic-like,antidepressant-like,anxiolytic-like,anti-addictive, andwakefulness-promoting effects in animals.[2][3][1][6][23] RO5203648, as well as the TAAR1 full agonistRO5256390, have been found to suppress cocaine and methamphetamineself-administration, and hence presumably theirrewarding andreinforcing effects.[1][5][23] RO5203648 also blocked methamphetamine-inducedlocomotor sensitization, but cross-sensitized with methamphetamine at the highest dose.[5][4] RO5203648 by itself is not self-administered in animals, suggesting that it lacks reinforcing effects andmisuse liability of its own.[21][4]
RO5203648 showed favorablepharmacokineticsorally andintravenously in mice, rats, and monkeys.[2] However, it was found to be very rapidlymetabolized in humanhepatocytesin vitro.[3]
In terms ofchemical structure, RO5203648 is a 2-aminooxazolinederivative.[3][24] This group also includes a number of otherselective TAAR1ligands, including the near-full agonistRO5166017, the full agonistRO5256390, and thepartial agonistRO5263397.[3] RO5203648 is also very closelystructurally related to themonoamine releasing agents andpsychostimulantsaminorex andclominorex.[24]
RO5203648 was first described by 2012.[2] It was the firstselective TAAR1partial agonist to be developed.[1][2][3] The drug followed the first TAAR1antagonistEPPTB and the first TAAR1full agonistRO5166017.[2] It was under investigation for potential clinical use in humans, but showed indication of very rapid humanmetabolismin vitro.[3] As a result, it was deselected from development, and other compounds, such as the TAAR1 partial agonistRO5263397, were pursued instead.[3]
Psychostimulants like cocaine and d-amphetamine interact with the DA transporter (DAT) to elevate extracellular DA concentration. In rodents, this translates into excessive [locomotor activity (LMA)] (Figures 2A, B; Figure S3A, B in Supplement 1), the reversal of which can be used to predict the potential antipsychotic activity of drugs (22). RO5203648 given orally reduced hyperlocomotion in both rats and mice treated with cocaine (Figure 2A, B), although not at the highest dose in mice (10 mg/kg). RO5203648 reduced d-amphetamine-induced hyperlocomotion by one half at a high dose (30 mg/kg) in rats, whereas in mice it had no effect at the doses tested (Figure S3A, B in Supplement 1).
In the synaptosomal preparation RO5203648 did not affect METH-induced striatal DA release and DA uptake inhibition, suggesting that RO5203648 regulation of METH's behavioral effects is unlikely to depend on direct, local actions at the DAT. As previously indicated, the in vivo microdialysis data revealed transient but significant reduction in METH-induced DA overflow following RO5203648 treatment.
[...] while the selective TAAR1 full agonists, RO5166017 and RO5256390, decreased the firing frequency of DA neurons in the VTA and of 5-HT neurons in the dorsal raphe nucleus, the partial agonists, RO5203648 and RO5263397, enhanced the firing rate of these same neurons, [...] the partial agonist, RO5203648, prevented cocaine-induced DA-overflow, in vitro, (Pei et al., 2014) and transiently attenuated methamphetamine-induced DA accumulation in the NAc, in vivo (Cotter et al., 2015), although it increased the firing rate of DA neurons in the VTA under basal conditions. [...] Revel and collaborators provided the first evidence that the partial agonist, RO5203648, decreased cocaine-induced locomotor activity and self-administration in rats (Revel et al., 2012b). Subsequent work revealed that the partial and full agonists, RO5203648 and RO5256390, respectively, both produced downward shifts in the dose-response curve for cocaine self-administration and prevented cocaine-induced lowering of ICSS thresholds (Pei et al., 2015), indicating that partial or full TAAR1 activation blocks the reinforcing properties of cocaine. [...] In the case of methamphetamine, the partial agonists, RO5203648, and RO5263397, reduced methamphetamine-induced behavioral sensitization, and self-administration (Jing et al., 2014; Cotter et al., 2015). [...] using a progressive ratio schedule of reinforcement, the partial agonist, RO5203648, decreased the break point for cocaine self-administration but enhanced responding for food (Pei et al., 2014), [...] Although, the mechanisms by which TAAR1 activation decreases motor stimulant effects are not well-understood, using fast-scan cyclic voltammetry we have shown previously that activation of TAAR1 with the partial agonist, RO5203648, prevented the potentiation of DA transmission caused by cocaine in the NAc without affecting DA uptake kinetics. This suggests that the TAAR1 agonist attenuated cocaine-stimulated DA overflow by mechanisms other than direct interference with DA uptake (Pei et al., 2014).
[The] TAAR1 partial agonist [RO5203648 (1 μM)] by itself did not affect significantly [evoked] DA outflow (107±21%, p>0.05, vs predrug values) or tau measure (106±14% vs predrug levels, p>0.05), suggesting that DA release and uptake are not influenced by the TAAR1 partial agonist. However, co-application of RO5203648 with cocaine significantly reduced cocaine-induced DA efflux (95±9%, p<0.05 vs cocaine-induced levels), without altering the effects of cocaine on tau measure of DA uptake (Tau; 150±13%, p<0.05 vs predrug levels, p<0.05 vs cocaine-induced levels) (Figures 3b and c). [...] neurochemical measurements of DA overflow in the nucleus accumbens showed the ability of RO5203648 to reduce cocaine-induced DA accumulation without significantly altering DA uptake rates, [...] We used fast cycling voltammetry in slices through the nucleus accumbens to assess the ability of RO5203648 to modulate cocaine-stimulated DA transmission. As predicted, RO5203648 diminished cocaine-induced DA overflow in the nucleus accumbens. However, RO5203648 did not significantly affect the tau measure of DA uptake in the presence of cocaine, thus suggesting that TAAR1 regulation of cocaine's effects on DA levels is likely to be independent of direct actions on the DAT. [...] As the DA uptake blocking activity of cocaine seems not to be affected by RO5203648 pretreatment, it is likely that TAAR1 activation causes a decrease in DA release kinetics resulting in less accumulation of extracellular DA resulting from blockade of the DAT by cocaine.
We were unable to replicate the results of Xie and Miller (2009) under similar in vitro conditions (Fig. 3). There was no difference in IC50 values for [3H]DA uptake inhibition by MA between synaptosomes from Taar1 WT and KO mice. [...] our results do not support an earlier hypothesis that TAAR1 modulates DAT (Xie and Miller, 2007, 2009; Xie et al., 2008b), as there was no evidence of an interaction under conditions described above. Recent reports support our findings that the DAT is unaffected by TAAR1. Coadministration of MA and the TAAR1 partial agonist RO523648 did not alter [3H]DA uptake and release in striatal synaptosomes in rats (Cotter et al., 2015). [...] Given the lack of interaction, DAT is an improbable mediator of TAAR1 regulation of MA-induced neurotoxicity. [...] activation of TAAR1 did not modulate in vitro MA-impairment of DAT function or DAT expression. As TAAR1 activation did not alter the function or expression of DAT in whole synaptosomes [...], these results indicate TAAR1 does not interact with these transporters on the plasma membrane [...]
Interestingly, the concentrations of amphetamine found to be necessary to activate TAAR1 are in line with what was found in drug abusers [3, 51, 52]. Thus, it is likely that some of the effects produced by amphetamines could be mediated by TAAR1. Indeed, in a study in mice, MDMA effects were found to be mediated in part by TAAR1, in a sense that MDMA auto-inhibits its neurochemical and functional actions [46]. Based on this and other studies (see other section), it has been suggested that TAAR1 could play a role in reward mechanisms and that amphetamine activity on TAAR1 counteracts their known behavioral and neurochemical effects mediated via dopamine neurotransmission.
Another feature that distinguishes [synthetic cathinones (SCs)] from amphetamines is their negligible interaction with the trace amine associated receptor 1 (TAAR1). Activation of this receptor reduces the activity of dopaminergic neurones, thereby reducing psychostimulatory effects and addictive potential (Miller, 2011; Simmler et al., 2016). Amphetamines are potent agonists of this receptor, making them likely to self‐inhibit their stimulating effects. In contrast, SCs show negligible activity towards TAAR1 (Kolaczynska et al., 2021; Rickli et al., 2015; Simmler et al., 2014, 2016).
RO5203648 alone did not maintain self-administration behavior using a substitution procedure in rats self-administering METH, indicating that RO5203648 itself had no reinforcing effect (Cotter et al., 2015). [...] TAAR1 partial agonist RO5203648 dose-dependently reduced cocaine-induced hyperlocomotion and cocaine self-administration (Revel et al., 2012a). [...] Pei et al. also showed that the partial TAAR1 agonist RO5203648 and the full agonist RO5256390 decreased cocaine self-administration and cocaine-seeking behaviors (Pei et al., 2014, 2015). [...] Cotter et al. showed that the selective TAAR1 partial agonist RO5203648 inhibited METH-induced increase in extracellular dopamine level in the NAc in vivo (Cotter et al., 2015). However, RO5203648 did not affect METH-mediated inhibition of DA efflux and reuptake in striatal synaptosomes in vitro. Given that the in vivo data and in vitro results are not expected to be always consistent, these results might to some extent suggest that TAAR1 in the NAc but not dorsal striatum participated in METH-induced neurochemical alterations and behaviors. In another study, it was demonstrated that RO5203648 blocked cocaine-induced DA overflow in the NAc (Pei et al., 2014). Interestingly, RO5203648 did not change the clearance of DA, indicating that TAAR1 regulating cocaine-induced DA overflow by mechanisms other than interaction with DAT (Pei et al., 2014).