NPC-16377

Certain sigma receptor ligands have been shown to block locomotor stimulation produced by cocaine at doses that do not have significant behavioral activity when given alone. Using a potent and selective ligand of sigma binding sites, 6-[6-(4-hydroxypiperidinyl)hexyloxy]-3-methylflavone (NPC 16377), we further investigated the influence of sigma ligands on additional behavioral and toxic effects of cocaine in mice. A behaviorally inactive dose of NPC 16377 shifted the dose-effect function for the locomotor stimulant effects of cocaine to the right by a factor of 2.5. A higher dose of NPC 16377 produced an insurmountable blockade of this stimulant effect of cocaine. Prior exposure to cocaine enhances the locomotor stimulant effects of cocaine (sensitization). NPC 16377 prevented the development of cocaine sensitization without producing behavioral effects of its own. However, NPC 16377 was unable to block the expression of sensitization in mice previously exposed to cocaine. NPC 16377 also did not consistently alter the discriminative stimulus effects of cocaine or methamphetamine in rats discriminating either 3 or 10 mg/kg of cocaine, or 1 mg/kg of methamphetamine from saline. The potential phencyclidine-like behavioral effects of NPC 16377 were also evaluated. Unlike the NMDA channel ligand, dizocilpine, NPC 16377 did not increase responding under a fixed-interval schedule of food presentation in rats nor did it substitute for the discriminative stimulus effects of either 1.5 mg/kg of phencyclidine or 0.2 mg/kg of dizocilpine in rats discriminating these drugs from saline. NPC 16377 displayed limited but significant anticonvulsant activity against diazepam-sensitive cocaine convulsions. The lethal effects of higher doses of cocaine were neither significantly blocked nor enhanced in rats or mice with NPC 16377. These findings extend earlier observations on the cocaine-blocking effects of sigma ligands to a novel structure with exceptional selectivity for sigma sites. These data indicate that some sigma ligands may be capable of altering certain behavioral and toxic actions of cocaine without notable behavioral side effects as evidenced in preclinical tests. As such, these compounds may ultimately be useful in the treatment of cocaine abuse.

6-[6-(4-Hydroxypiperidinyl)hexyloxy]-3-methylflavone HCI, (NPC 16377), a potent and highly selective sigma-site ligand, was evaluated in tests predictive of antipsychotic and neuroprotective potential and for toxicity. Like haloperidol, clozapine and remoxipride, and the sigma-ligands BMY 14802, ifenprodil and rimcazole, NPC 16377 reversed amphetamine-induced hyperactivity and apomorphine-induced climbing in mice. Additional evidence for antipsychotic activity was obtained in rats with NPC 16377, clozapine, BMY 14802, ifenprodil, haloperidol and rimcazole, all of which reduced conditioned avoidance responses at doses that did not reduce escape behavior. NPC 16377 did not induce catalepsy in mice, suggesting a decreased liability for producing extrapyramidal side effects. NPC 16377 extended survival time for mice exposed to a hypoxic environment. In a model of global ischemia using conscious gerbils, NPC 16377 prevented damage to hippocampal CA1 neurons after either intraperitoneal or oral administration. NPC 16377 did not disrupt prepulse inhibition or block the disruption of prepulse inhibition induced by the phencyclidine site-selective ligand (+)MK-801. In rats trained to discriminate phencyclidine from saline, NPC 16377 did not substitute for the psychotomimetic. These data are consistent with the notion that selective sigma-agents may possess antipsychotic and neuroprotective activities. Moreover, the results from prepulse inhibition and drug discrimination experiments suggest that NPC 16377 is devoid of phencyclidine-like effects.