A novel series of [3.2.1] azabicyclic biaryl ethers as alpha3beta4 and alpha6/4beta4 nicotinic receptor agonists.

We report the synthesis of a series of [3.2.1]azabicyclic biaryl ethers as selective agonists of alpha3- and alpha6-containing nicotinic receptors. In particular, compound 17a from this series is a potent alpha3beta4 and alpha6/4beta4 receptor agonist in terms of both binding and functional activity. Compound 17a also shows potent in vivo activity in CNS-mediated animal models that are sensitive to antipsychotic drugs. Compound 17a may thus be a useful tool for studying the role of alpha3beta4 and alpha6/4beta4 nicotinic receptors in CNS pharmacology.

The beta3 nicotinic receptor subunit: a component of alpha-conotoxin MII-binding nicotinic acetylcholine receptors that modulate dopamine release and related behaviors.

Nigrostriatal dopaminergic neurons express many nicotinic acetylcholine receptor (nAChR) subunits capable of forming multiple nAChR subtypes. These subtypes are expressed differentially along the neuron and presumably mediate diverse responses. beta3 subunit mRNA has restricted expression but is abundant in the substantia nigra and ventral tegmental areas. To investigate the potential role(s) of nicotinic receptors containing the beta3 subunit in dopaminergic tracts, we generated mice with a null mutation in the beta3 gene. We were thereby able to identify a population of beta3-dependent alpha-conotoxin MII-binding nAChRs that modulate striatal dopamine release. Changes were also observed in locomotor activity and prepulse inhibition of acoustic startle, behaviors that are controlled, in part, by nigrostriatal and mesolimbic dopaminergic activity, respectively, suggesting that beta3-containing nAChRs modulate these behaviors.

Variability in response to nicotine in the LSxSS RI strains: potential role of polymorphisms in alpha4 and alpha6 nicotinic receptor genes.

Several studies have shown that genetic factors influence the effects of nicotine on respiration, acoustic startle, Y-maze crosses and rears, heart rate and body temperature in the mouse. Recently, we identified restriction fragment length polymorphisms (RFLPs) associated with the alpha4 (Chrna4) and alpha6 (Chrna6) nicotinic cholinergic receptor genes in the recombinant inbred (RI) strains derived from the Long-Sleep (LS) and Short-Sleep (SS) mouse lines. The alpha4 polymorphism has been identified as a point-mutation at position 529 (threonine to alanine) and the alpha6 polymorphism has not yet been identified. The studies described here evaluated the potential role of these polymorphisms in regulating sensitivity to nicotine by constructing dose-response curves for the effects of nicotine on six responses in the LSxSS RI strains. The results obtained suggest that both of the polymorphisms may play a role in regulating variability in sensitivity to nicotine. Those RI strains carrying the LS-like alpha4 RFLP were significantly more sensitive to the effects of nicotine on Y-maze crosses and rears, temperature and respiration and were less sensitive to the effects of nicotine on acoustic startle than those strains carrying the SS-like alpha4 RFLP. Those RI strains carrying the LS-like alpha6 RFLP were more sensitive to the effects of nicotine on respiration and acoustic startle, and less sensitive to the effects of nicotine on Y-maze crosses than those strains carrying the SS-like alpha6 RFLP. These results suggest that genetically determined differences in sensitivity to nicotine may be explained, in part, by variability associated with at least two of the neuronal nicotinic receptor genes, alpha4 and alpha6.

Constrained analogs of CB-1 antagonists: 1,5,6,7-Tetrahydro-4H-pyrrolo[3,2-c]pyridine-4-one derivatives.

A series of pyrrolopyridinones was designed and synthesized as constrained analogs of the pyrazole CB-1 antagonist rimonabant. Certain examples exhibited very potent hCB-1 receptor binding affinity and functional antagonism with Ki and Kb values below 10 nM, and with high selectivity for CB-1 over CB-2 (>100-fold). A representative analog was established to cause significant appetite suppression and reduction in body weight gain in industry-standard rat models used to develop new therapeutics for obesity.

Optimization of imidazole amide derivatives as cannabinoid-1 receptor antagonists for the treatment of obesity.

Several imidazole-based cyclohexyl amides were identified as potent CB-1 antagonists, but they exhibited poor oral exposure in rodents. Incorporation of a hydroxyl moiety on the cyclohexyl ring provided a dramatic improvement in oral exposure, together with a ca. 10-fold decrease in potency. Further optimization provided the imidazole 2-hydroxy-cyclohexyl amide 45, which exhibited hCB-1 K(i)=3.7nM, and caused significant appetite suppression and robust, dose-dependent reduction of body weight gain in industry-standard rat models.

Null mutant analysis of responses to nicotine: deletion of beta2 nicotinic acetylcholine receptor subunit but not alpha7 subunit reduces sensitivity to nicotine-induced locomotor depression and hypothermia.

The nicotinic acetylcholine receptor (nAChR) subtypes alpha4beta2 and alpha7 comprise the majority of brain nicotine-binding sites. Classical genetic strategies using inbred mice and their hybrids suggest that nicotine's effects on locomotor activity and body temperature are influenced by alpha4beta2 but not alpha7 receptors. To evaluate directly the role of these nicotinic subtypes on responses to nicotine, beta2 and alpha7 null mutant (-/-) mice, as well as wild-type (+/+) and heterozygous (+/-) mice, were tested for baseline body temperature and locomotion and nicotine (0-1.5 mg/kg)-induced changes in these responses. Basal responses for these measures were similar for all beta2 genotypes, but baseline Y-maze activity was higher in alpha7-/- mice compared with alpha7+/+ mice. Following nicotine injection, dose-dependent decreases in body temperature and locomotor activity were observed for all three genotypes of both beta2 and alpha7 mice. Although responses in alpha7 mice did not differ among genotypes, beta2 gene deletion was found to have a gene-dependent effect on nicotine's effects. beta2-/- mice were less sensitive to nicotine-induced locomotor depression and hypothermia at low nicotine doses (.25-.5 mg/kg) but were no different from beta2+/+ mice at the highest doses tested (1.0-1.5 mg/kg). Residual responses at high nicotine doses in beta2-/- mice as well as responses in all alpha7 and beta2 mouse genotypes were mediated by nicotinic receptors, since mecamylamine (1.0 mg/kg) blocked all responses following 1.0 mg/kg nicotine. This finding suggests receptors that include the beta2 nAChR subunit partially mediate nicotine's effects on locomotor activity and body temperature.