No abstract

Background and purpose: In our search for an indirect dopamine agonist as therapy for cocaine addiction, several selective inhibitors of the dopamine transporter (DAT), which are 3-phenyltropane analogues, were assayed for their effect on locomotor activity in mice. Interestingly, several of the compounds showed a poor correlation between stimulation of locomotion and DAT inhibition. One of the compounds, 3b-(4-methylphenyl)-2b-[3-(4-chlorophenyl)isoxazol-5-yl]tropane (RTI-371), was shown to cross the blood-brain barrier, by binding studies in vivo, and block cocaine-induced locomotor stimulation. As poor pharmacokinetics could not explain the behavioural effects of RTI-371, this compound was screened through our functional assays for activity at other CNS receptors. Initial screening identified RTI-371 as a positive allosteric modulator of the human CB1 (hCB1) receptor. Experimental approach: The effect of RTI-371 and other DAT-selective inhibitors on CP55940-stimulated calcium mobilization was characterized in a calcium mobilization-based functional assay for the hCB1 receptor. Selected compounds were also characterized in a similar assay for human m opioid receptor activation to assess the specificity of their effects. Key results: RTI-371 and several other DAT-selective inhibitors with atypical actions on locomotor behaviour increased the efficacy of CP55940 in a concentration-dependent manner. Conclusions and implications:These results suggest that the lack of correlation between the DAT-binding affinity and locomotor stimulation of RTI-371 could be due at least in part to its activity as a positive modulator of the hCB1 receptor. ( British Journal of Pharmacology

Several 3beta-(substituted phenyl)-2beta-(3-substituted isoxazol-5-yl)tropanes (3a-t) were evaluated for their ability to inhibit radioligand binding at the DAT, 5-HTT, and NET as well as in gross observation and locomotor activity in mice and in rats trained to discriminate cocaine. All compounds showed high affinity for the DAT. The IC(50) values ranged from 0.5 to 26 nM. With the exception of 3e and 3f, which have no substituent on the 2beta-(1,2-isoxazole) ring, all compounds were selective for the DAT relative to the 5-HTT and NET. No compound showed death when dosed at 100 mg/kg; however, most compounds did show signs typical of dopamine activity. The ED(50) values for 2beta-(1,2-isoxazoles) that caused locomotor stimulation ranged from 0.2 to 12.8 mg/kg. Most compounds showed slower on-set and longer duration of action relative to cocaine. Surprisingly, 3beta-(4-methylphenyl)-2beta-[3-(4'-chlorophenyl)isoxazol-5-yl]tropane (3p) and 3beta-(4-methylphenyl)-2beta-[3-(4'-methylphenyl)isoxazol-5-yl]tropane (3r) did not produce significant increases in locomotor activity. In the cocaine discrimination test, all analogues showed full or at least 50% generalization with the exception of 3p, which did not show generalization. Importantly, both the locomotor activity and the cocaine discrimination ED(50)values were correlated with the DAT binding but not 5-HTT and NET binding. This provides further support for the dopamine hypothesis of cocaine abuse. High DAT affinity and selectivity, increased locomotor activity with slow onset and long duration of action, and generalization to cocaine shown by the 3beta-(substituted phenyl)-2beta-(3-substituted isoxazol-5-yl)tropanes are properties thought necessary for a pharmacotherapy for treating cocaine abuse.

Synthetic cannabinoids are manufactured clandestinely with little quality control and are distributed as herbal "spice" for smoking or as bulk compound for mixing with a solvent and inhalation via electronic vaporizers. Intoxication with synthetic cannabinoids has been associated with seizure, excited delirium, coma, kidney damage, and other disorders. The chemical alterations produced by heating these structurally novel compounds for consumption are largely unknown. Here, we show that heating synthetic cannabinoids containing tetramethylcyclopropylring substituents produced thermal degradants with pharmacological activity that varied considerably from their parent compounds. Moreover, these degradants were formed under conditions simulating smoking. Some products of combustion retained high affinity at the cannabinoid 1 (CB 1) and CB 2 receptors, were more efficacious than (2)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol (CP55,940) in stimulating CB 1 receptor-mediated guanosine 59-O-(3-thiotriphosphate) (GTPgS) binding, and were potent in producing D 9-tetrahydrocannabinol-like effects in laboratory animals, whereas other compounds had low affinity and efficacy and were devoid of cannabimimetic activity. Degradants that retained affinity and efficacy also substituted in drug discrimination tests for the prototypical synthetic cannabinoid 1-pentyl-3-(1-naphthoyl)indole (JWH-018), and are likely to produce psychotropic effects in humans. Hence, it is important to take into consideration the actual chemical exposures that occur during use of synthetic cannabinoid formulations to better comprehend the relationships between dose and effect.

Rationale-The kappa opioid receptor (KOR) antagonist, JDTic, was reported to prevent stressinduced reinstatement of cocaine-maintained responding and to have antidepressant-like effects.Objectives-Our objectives were to determine whether analogs of JDTic retained KOR antagonist activity and whether an orally effective analog prevented footshock-induced cocaine reinstatement.Methods-RTI-194 (i.g. 1-30 mg/kg, s.c. 0.3-10 mg/kg, and i.p. 30 mg/kg), RTI-212 (s.c. 0.3-10 mg/kg and i.p. 30 mg/kg), and RTI-230 (i.g. 3-30 mg/kg and i.p. 1-30 mg/kg) were evaluated for their ability to block diuresis induced by 10-mg/kg U50,488 in rats. RTI-194 was additionally evaluated i.g. (3-100 mg/kg) for its ability to prevent footshock-induced reinstatement of responding previously reinforced with 0.5-mg/kg/inf cocaine.Results-RTI-194 significantly (p<0.05) attenuated U50,488-induced diuresis when given i.g., s.c., and i.p. RTI-194s effectiveness increased 1 week following administration. RTI-212 was ineffective. RTI-230 was ineffective when given i.g., but blocked diuresis at 24 h and 8 days (1, 10, and 30 mg/ kg), 15 days (10 and 30 mg/kg), 22 and 29 days (30 mg/kg) following i.p. administration. Footshock reinstated responding in vehicle-but not RTI-194 (30 and 100 mg/kg)-treated rats. is now included with JDTic as the only reported compounds capable of antagonizing the KOR following oral administration. The failure of stress to reinstate cocaine seeking in rats treated with RTI-194 is consistent with results reported with JDTic, although it had less efficacy in lowering response levels than JDTic, suggesting a diminished overall effectiveness relative to it. Conclusions-RTI