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Other names | RO-5203648 |
Drug class | Trace amine-associated receptor 1 (TAAR1) partial agonist |
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Formula | C9H8Cl2N2O |
Molar mass | 231.08 g·mol−1 |
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RO5203648 is a trace amine-associated receptor 1 (TAAR1) partial agonist. [1] [2] [3] It is a potent and highly selective partial agonist of both rodent and primate TAAR1. [2] [3] The drug suppresses the effects of psychostimulants like cocaine and methamphetamine. [1] [2] It also produces a variety of other behavioral effects, such as antidepressant-like, antipsychotic-like, and antiaddictive effects. [1] [2] [4] Research with RO5203648 has led to interest in TAAR1 agonists for potential treatment of drug addiction. [1] RO5203648 itself was not developed for potential medical use due to poor expected human pharmacokinetics. [3]
RO5203648 binds to the mouse, rat, cynomolgus monkey, and human TAAR1 all with high affinity (Ki = 0.5–6.8 nM). [1] [2] It is a potent partial agonist in all species (EC50 = 4.0 to 31 nM), with an efficacy of 48 to 73% relative to the endogenous TAAR1 agonists β-phenethylamine and tyramine and the TAAR1 full agonist RO5166017. [1] [2] [3] RO5203648 is highly selective for the TAAR1, showing ≥130-fold selectivity for the mouse TAAR1 over 149 other targets. [2] [3]
Species | Affinity (Ki, nM) | EC50 (nM) | Emax (%) |
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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 of ventral tegmental area (VTA) dopaminergic neurons and dorsal raphe nucleus (DRN) serotonergic neurons in mouse brain slices ex vivo . [1] [5] [2] This is in contrast to the TAAR1 full agonist RO5166017, which suppresses their firing rates, but is analogous to the TAAR1 antagonist EPPTB, which dramatically increases their firing rates. [1] [5] [2] RO5203648 failed to show these effects in the neurons of TAAR1 knockout mice, indicating that its actions are mediated by interactions with the TAAR1. [2] RO5203648 alone does not affect electrically evoked dopamine release or reuptake (as measured by tau) in rat nucleus accumbens (NAc) slices ex vivo. [5] [6] Conversely, RO5203648 prevented cocaine-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 of dopamine transporter (DAT) interactions. [1] [6] RO5203648 did not affect methamphetamine-induced dopamine efflux or reuptake inhibition in rat striatal synaptosomes in vitro . [7] [8] [4] However, RO5203648 blunted and delayed methamphetamine-induced dopamine elevations in the NAc in rodents in vivo . [5] [4] Hence, as with cocaine, RO5203648's regulation of methamphetamine's actions appears to be independent of DAT interactions. [7] [5] [4]
Some in-vitro studies have suggested that TAAR1 agonism by amphetamines and β-phenethylamine may mediate induction of monoamine release and reuptake 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 synaptosomes in vitro. [7] [8] [5] [4] The dopamine elevations and psychostimulant-like effects of amphetamines are not only preserved but are actually augmented in TAAR1 knockout mice in vivo . [9] [8] [15] [16] Concordant in-vivo findings have been made with amphetamines combined with TAAR1 agonists and antagonists as well as with TAAR1 overexpression. [8] It appears that TAAR1 agonism by amphetamines, such as amphetamine, methamphetamine, and MDMA, auto-inhibits their monoaminergic effects. [17] [18] [19] Conversely, most cathinones lack TAAR1 agonism, and this might enhance their effects compared to amphetamines. [18] [20]
RO5203648 does not significantly affect basal locomotion. [2] Conversely, the drug has been found to dose-dependently suppress cocaine-induced hyperlocomotion in mice and rats, whereas it only suppressed dextroamphetamine-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 like RO5166017 and RO5256390 also suppress psychostimulant-induced hyperlocomotion. [21] RO5203648 suppressed spontaneous hyperactivity in a novel environment in dopamine transporter (DAT) knockout mice, similarly to antipsychotics like haloperidol and olanzapine. [2] [22] RO5203648 has also been found to suppress hyperlocomotion induced by the NMDA receptor antagonist L-687,414 or in genetically modified mice with a hypoactive NMDA 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 shown anti-cataleptic, pro-cognitive, antipsychotic-like, antidepressant-like, anxiolytic-like, anti-addictive, and wakefulness-promoting effects in animals. [2] [3] [1] [6] [23] RO5203648, as well as the TAAR1 full agonist RO5256390, have been found to suppress cocaine and methamphetamine self-administration, and hence presumably their rewarding and reinforcing effects. [1] [5] [23] RO5203648 also blocked methamphetamine-induced locomotor 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 and misuse liability of its own. [21] [4]
RO5203648 showed favorable pharmacokinetics orally and intravenously in mice, rats, and monkeys. [2] However, it was found to be very rapidly metabolized in human hepatocytes in vitro . [3]
In terms of chemical structure, RO5203648 is a 2-aminooxazoline derivative. [3] [24] This group also includes a number of other selective TAAR1 ligands, including the near-full agonist RO5166017, the full agonist RO5256390, and the partial agonist RO5263397. [3] RO5203648 is also very closely structurally related to the monoamine releasing agents and psychostimulants aminorex and clominorex. [24]
RO5203648 was first described by 2012. [2] It was the first selective TAAR1 partial agonist to be developed. [1] [2] [3] The drug followed the first TAAR1 antagonist EPPTB and the first TAAR1 full agonist RO5166017. [2] It was under investigation for potential clinical use in humans, but showed indication of very rapid human metabolism in vitro . [3] As a result, it was deselected from development, and other compounds, such as the TAAR1 partial agonist RO5263397, were pursued instead. [3]
Phenethylamine (PEA) is an organic compound, natural monoamine alkaloid, and trace amine, which acts as a central nervous system stimulant in humans. In the brain, phenethylamine regulates monoamine neurotransmission by binding to trace amine-associated receptor 1 (TAAR1) and inhibiting vesicular monoamine transporter 2 (VMAT2) in monoamine neurons. To a lesser extent, it also acts as a neurotransmitter in the human central nervous system. In mammals, phenethylamine is produced from the amino acid L-phenylalanine by the enzyme aromatic L-amino acid decarboxylase via enzymatic decarboxylation. In addition to its presence in mammals, phenethylamine is found in many other organisms and foods, such as chocolate, especially after microbial fermentation.
3,4-Methylenedioxyamphetamine (MDA), sometimes referred to as sass, is an empathogen-entactogen, stimulant, and psychedelic drug of the amphetamine family that is encountered mainly as a recreational drug. In its pharmacology, MDA is a serotonin–norepinephrine–dopamine releasing agent (SNDRA). In most countries, the drug is a controlled substance and its possession and sale are illegal.
Phentermine, sold under the brand name Adipex-P among others, is a medication used together with diet and exercise to treat obesity. It is available by itself or as the combination phentermine/topiramate. Phentermine is taken by mouth.
The dopamine transporter is a membrane-spanning protein coded for in humans by the SLC6A3 gene, that pumps the neurotransmitter dopamine out of the synaptic cleft back into cytosol. In the cytosol, other transporters sequester the dopamine into vesicles for storage and later release. Dopamine reuptake via DAT provides the primary mechanism through which dopamine is cleared from synapses, although there may be an exception in the prefrontal cortex, where evidence points to a possibly larger role of the norepinephrine transporter.
Aminorex, sold under the brand names Menocil and Apiquel among others, is a weight loss (anorectic) stimulant drug. It was withdrawn from the market after it was found to cause pulmonary hypertension (PPH). In the United States, aminorex is a Schedule I controlled substance.
Trace amines are an endogenous group of trace amine-associated receptor 1 (TAAR1) agonists – and hence, monoaminergic neuromodulators – that are structurally and metabolically related to classical monoamine neurotransmitters. Compared to the classical monoamines, they are present in trace concentrations. They are distributed heterogeneously throughout the mammalian brain and peripheral nervous tissues and exhibit high rates of metabolism. Although they can be synthesized within parent monoamine neurotransmitter systems, there is evidence that suggests that some of them may comprise their own independent neurotransmitter systems.
Etilamfetamine, also known as N-ethylamphetamine and formerly sold under the brand names Apetinil and Adiparthrol, is a stimulant drug of the amphetamine family. It was invented in the early 20th century and was subsequently used as an anorectic or appetite suppressant in the 1950s, but was not as commonly used as other amphetamines such as amphetamine, methamphetamine, and benzphetamine, and was largely discontinued once newer drugs such as phenmetrazine were introduced.
Naphthylaminopropane, also known as naphthylisopropylamine (NIPA), is an experimental drug that was under investigation for the treatment of alcohol and stimulant addiction.
Norfenfluramine, or 3-trifluoromethylamphetamine, is a never-marketed drug of the amphetamine family and a major active metabolite of the appetite suppressants fenfluramine and benfluorex. The compound is a racemic mixture of two enantiomers with differing activities, dexnorfenfluramine and levonorfenfluramine.
Trace amine-associated receptor 1 (TAAR1) is a trace amine-associated receptor (TAAR) protein that in humans is encoded by the TAAR1 gene.
3-Methoxytyramine (3-MT), also known as 3-methoxy-4-hydroxyphenethylamine, is a human trace amine and the major metabolite of the monoamine neurotransmitter dopamine. It is formed by the introduction of a methyl group to dopamine by the enzyme catechol-O-methyltransferase (COMT). 3-MT can be further metabolized by the enzyme monoamine oxidase (MAO) to form homovanillic acid (HVA), which is then typically excreted in the urine.
para-Chloroamphetamine (PCA), also known as 4-chloroamphetamine (4-CA), is a serotonin–norepinephrine–dopamine releasing agent (SNDRA) and serotonergic neurotoxin of the amphetamine family. It is used in scientific research in the study of the serotonin system, as a serotonin releasing agent (SRA) at lower doses to produce serotonergic effects, and as a serotonergic neurotoxin at higher doses to produce long-lasting depletions of serotonin.
A monoamine releasing agent (MRA), or simply monoamine releaser, is a drug that induces the release of one or more monoamine neurotransmitters from the presynaptic neuron into the synapse, leading to an increase in the extracellular concentrations of the neurotransmitters and hence enhanced signaling by those neurotransmitters. The monoamine neurotransmitters include serotonin, norepinephrine, and dopamine; MRAs can induce the release of one or more of these neurotransmitters.
RO5166017, or RO-5166017, is a drug developed by Hoffmann-La Roche which acts as a potent and selective agonist for the trace amine-associated receptor 1 (TAAR1), with no significant activity at other targets. It is a partial agonist or near-full agonist depending on the species.
EPPTB, also known as RO5212773 or RO-5212773, is a drug developed by Hoffmann-La Roche which acts as a potent and selective antagonist or inverse agonist of the trace amine-associated receptor 1 (TAAR1). The drug was the first selective antagonist developed for the TAAR1. It is a potent agonist of the mouse and rat TAAR1, but is dramatically less potent as an agonist of the human TAAR1. EPPTB has been used in scientific research to demonstrate an important role for TAAR1 in regulation of dopaminergic signaling in the limbic system.
o-Phenyl-3-iodotyramine (o-PIT) is a drug which acts as a selective agonist for the trace amine-associated receptor 1 (TAAR1). It has reasonable selectivity for TAAR1 but relatively low potency, and is rapidly metabolised in vivo, making it less useful for research than newer ligands such as RO5166017. Its EC50Tooltip half-maximal effective concentration values have been reported to be 35 nM for the mouse TAAR1, 2.4 nM at the rat TAAR1, and 9.5 nM at the human TAAR1.
Locomotor activity is a measure of animal behavior which is employed in scientific research.
RO5256390 or RO-5256390 is a drug developed by Hoffmann-La Roche which acts as an agonist for the trace amine associated receptor 1 (TAAR1). It is a full agonist of the rat, cynomolgus monkey, and human TAAR1, but a partial agonist of the mouse TAAR1.
RO5263397, or RO-5263397, is a trace amine-associated receptor 1 (TAAR1) partial or full agonist which is used in scientific research. It is the most well-studied of all of the synthetic TAAR1 ligands. In addition to its use in research, RO5263397 is or was under development for potential clinical use as a medication.
RO5073012 is a selective low-efficacy partial agonist of the trace amine-associated receptor 1 (TAAR1) which has been used in scientific research. TAAR1 partial agonists like RO5073012 can have agonist- or antagonist-like effects at the TAAR1 depending on the context and level of TAAR1 signaling.
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).