Behavioral pharmacology of tandospirone in baboons: chronic administration and withdrawal, self-injection and drug discrimination

Ulotaront, a novel TAAR1 agonist with 5-HT1A agonist activity, lacks abuse liability and attenuates cocaine cue-induced relapse in rats

BACKGROUND

Ulotaront (SEP-363856) is a trace amine-associated receptor 1 (TAAR1) agonist with 5-hydroxytryptamine type 1A (5-HT1A) agonist activity that is currently in Phase 3 clinical development for the treatment of schizophrenia. Unlike available antipsychotics, the efficacy of ulotaront is not mediated by blockade of dopamine D2 or serotonin 5-HT2A receptors. In a short-term randomized clinical trial, ulotaront has demonstrated significant efficacy in the treatment of adults with an acute exacerbation of schizophrenia. Given ulotaront's novel mechanism of action a series of preclinical studies were performed to evaluate its potential abuse liability.

METHODS

A battery of studies were conducted in male and female rats to evaluate whether ulotaront produces behavioral changes suggestive of human abuse potential. In addition, studies were undertaken to probe the potential for ulotaront to block reinstatement of cocaine-seeking behavior in male rats.

RESULTS

Ulotaront was not self-administered by rats trained to self-administer amphetamine, cocaine, or heroin. The subjective qualities of ulotaront were distinct from those produced by amphetamine in a drug discrimination procedure. Ulotaront, and buspirone, a non-scheduled anxiolytic with 5-HT1A agonism, partially generalized to the interoceptive cue elicited by 3, 4-methylenedioxymethamphetamine (MDMA). In addition, ulotaront demonstrated a trend to reduce cocaine-primed induced reinstatement, and dose-dependently reduced cue-reinstated responding.

CONCLUSION

The current results suggest that the TAAR1/5-HT1A agonist ulotaront is not likely to pose a risk for recreational abuse in humans and may have potential therapeutic utility as a treatment of substance use disorders.

Behavioral evidence for the significance of serotoninergic (5-HT) receptors in cocaine addiction

Cocaine addiction has somatic, psychological, psychiatric, socio-economic and legal implications in the developed world. Presently, there is no medication approved for the treatment of cocaine addiction. In recent years, data from the literature (pre-clinical studies and clinical trials) have provided several lines of evidence that serotonin (5-HT) and 5-HT receptors play a modulatory role in the mechanisms of action of cocaine. Here we review the contribution of 5-HT receptor subtypes to cocaine sensitization, discrimination, conditioned place preference, self-administration, reinstatement of seeking behavior and withdrawal symptoms in laboratory animals. Additionally, the consequences of chronic cocaine exposure on particular 5-HT receptor-assigned functions in pre-clinical studies are presented.

Rebound insomnia induced by abrupt withdrawal of hypnotics in sleep-disturbed rats

The present study was performed to examine whether or not rebound insomnia is caused by an abrupt withdrawal of benzodiazepine hypnotics and tandospirone in rats. Etizolam and triazolam caused a significant shortening of sleep latency, increase in non-REM sleep time, and decrease in wake time in a dose-dependent manner. Etizolam and triazolam caused a significant shortening of sleep latency during drug administration (for 7 days), whereas a significant prolongation of sleep latency was observed by the abrupt withdrawal of these drugs. Tandospirone caused a shortening of sleep latency, whereas no effect was observed on non-REM sleep time and wake time during drug administration (for 7 days). On the other hand, tandospirone showed no significant effect on sleep latency through its abrupt withdrawal, differing from etizolam and triazolam. From these findings, a rebound phenomenon in terms of sleep latency was confirmed with etizolam and triazolam in rats. Furthermore, the 5-HT(1A) agonist, tandospirone, caused no rebound phenomenon regarding sleep latency in rats.

Serotonin and psychostimulant addiction: Focus on 5-HT1A-receptors

Serotonin(1A)-receptors (5-HT(1A)-Rs) are important components of the 5-HT system in the brain. As somatodendritic autoreceptors they control the activity of 5-HT neurons, and, as postsynaptic receptors, the activity in terminal areas. Cocaine (COC), amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine ("Ecstasy", MDMA) are psychostimulant drugs that can lead to addiction-related behavior in humans and in animals. At the neurochemical level, these psychostimulant drugs interact with monoamine transporters and increase extracellular 5-HT, dopamine and noradrenalin activity in the brain. The increase in 5-HT, which, in addition to dopamine, is a core mechanism of action for drug addiction, hyperactivates 5-HT(1A)-Rs. Here, we first review the role of the various 5-HT(1A)-R populations in spontaneous behavior to provide a background to elucidate the contribution of the 5-HT(1A)-Rs to the organization of psychostimulant-induced addiction behavior. The progress achieved in this field shows the fundamental contribution of brain 5-HT(1A)-Rs to virtually all behaviors associated with psychostimulant addiction. Importantly, the contribution of pre- and postsynaptic 5-HT(1A)-Rs can be dissociated and frequently act in opposite directions. We conclude that 5-HT(1A)-autoreceptors mainly facilitate psychostimulant addiction-related behaviors by a limitation of the 5-HT response in terminal areas. Postsynaptic 5-HT(1A)-Rs, in contrast, predominantly inhibit the expression of various addiction-related behaviors directly. In addition, they may also influence the local 5-HT response by feedback mechanisms. The reviewed findings do not only show a crucial role of 5-HT(1A)-Rs in the control of brain 5-HT activity and spontaneous behavior, but also their complex role in the regulation of the psychostimulant-induced 5-HT response and subsequent addiction-related behaviors.

Principles of drug abuse liability assessment in laboratory animals

This paper describes the rationale for use of preclinical assessments of abuse liability in laboratory animals, and then discusses "cross-cutting" methodological issues that apply to behavioral evaluations intended to contribute to an abuse liability evaluation package. Issues include use of: (1) positive and negative control conditions; (2) full dose-effect evaluations, (3) multiple dependent measures, (4) pharmacokinetic evaluations to guide choice of dose ranges, (5) a species for which good methodological and comparative data are available to aid interpretation of results, and (6) appropriate methods for the group or single-subject experimental design selected. The remainder of the paper describes basic methodology by which three core pieces of behavioral data required by the Food and Drug Administration for its use in the overall abuse liability analysis can be obtained preclinically. Reinforcing effects are assessed in study of drug self-administration; drug discrimination assesses degree of overlap of interoceptive stimulus effects with relevant comparison drugs; physical dependence potential is determined by assessing whether a withdrawal syndrome occurs after chronic drug administration. Background and methodological issues specific to each procedure are discussed. A key consideration for cross-cutting and specific methodological issues is that choices made enable confident interpretation of both positive and negative results.

Clinical efficacy of tandospirone augmentation in patients with major depressive disorder: a randomized controlled trial

The purpose of the present paper was to investigate the efficacy of augmentation of clomipramine (CMI) by tandospirone in 36 untreated outpatients with major depressive disorder. Twelve patients were treated with CMI and tandospirone (T group), 12 with CMI and diazepam (D group) and 12 with CMI alone (C group) for 6 weeks. No statistically significant differences in the percentage improvement of the Hamilton Depression Rating Scale (17 items; HDRS-17) and the Hamilton Anxiety Rating Scale (14 items; HARS-14) scores were shown among the three treatment groups. However, at 2 weeks, the percentage improvement of HDRS-17 score in the T group tended to be higher than that in the D and C groups, although there was no statistically significant difference among the three treatment groups. No change in plasma prolactin level or adverse events was induced by the addition of tandospirone. These results suggest that 6 weeks of treatment with tandospirone or diazepam was not effective for augmentation of CMI in major depressive disorder patients. However, augmentation of antidepressants by tandospirone administration for a few weeks might induce early expression of antidepressive effects.

Assessment of the dependence potential of the potent high-efficacy 5-HT1A agonist S-14506 in rats

This study assessed the dependence potential of S-14506 [ 1- [ 2-(4-fluorobenzoylamino)ethyl]-4-(7-methoxy napthyl) piperazine], a novel, potent 5-HT(1A) full agonist with anxiolytic and antidepressant actions in animal models. The dependence potential of S-14506 was compared with that of the benzodiazepine (BZ) chlordiazepoxide (CDP). BZ withdrawal caused weight loss, aphagia and hyperthermia after chronic b.i.d. treatment for 21 days. None of these withdrawal effects were seen after similar b.i.d. S-14506 treatment at high doses. However, the acute pharmacological actions of CDP and S-14506 differed on a number of indices. Specifically, CDP increased food intake and body weight, whilst S-14506 decreased these measures, possibly due to the induction of the serotonin syndrome. Of particular interest was the observation that S-14506 induced marked hypothermia, to which complete tolerance developed very rapidly (after only 1 day). The observation of marked, rapid tolerance to S-14506-induced hypothermia, in conjunction with the absence of withdrawal hyperthermia after prolonged chronic treatment at high doses, suggests that tolerance to this effect of S-14506 can be dissociated from dependence. Collectively, the data reported suggest that the full 5-HT(1A) agonist S-14506 is devoid of dependence potential, other human and animal studies having previously suggested that partial 5-HT(1A) agonists typically induce no, or minimal, dependence.