TC299423, a Novel Agonist for Nicotinic Acetylcholine Receptors.

(E)-5-(Pyrimidin-5-yl)-1,2,3,4,7,8-hexahydroazocine (TC299423) is a novel agonist for nicotinic acetylcholine receptors (nAChRs). We examined its efficacy, affinity, and potency for alpha 6 beta 2* (alpha 6 beta 2-containing), alpha 4 beta 2*, and alpha 3 beta 4* nAChRs, using [I-125]-epibatidine binding, whole-cell patch-clamp recordings, synaptosomal Rb-86(+) efflux, [H-3]-dopamine release, and [H-3]-acetylcholine release. TC299423 displayed an EC50 of 30-60 nM for alpha 6 beta 2* nAChRs in patch-clamp recordings and [H-3]-dopamine release assays. Its potency for alpha 6 beta 2* in these assays was 2.5-fold greater than that for alpha 4 beta 2*, and much greater than that for alpha 3 beta 4*-mediated [H-3]-acetylcholine release. We observed no major off-target binding on 70 diverse molecular targets. TC299423 was bioavailable after intraperitoneal or oral administration. Locomotor assays, measured with gainof- function, mutant alpha 6 (alpha 6L9'S) nAChR mice, show that TC299423 elicits alpha 6 beta 2* nAChR-mediated responses at low doses. Conditioned place preference assays show that low-dose TC299423 also produces significant reward in alpha 6L9'S mice, and modest reward in WT mice, through a mechanism that probably involves alpha 6(non-alpha 4)beta 2* nAChRs. However, TC299423 did not suppress nicotine self-administration in rats, indicating that it did not block nicotine reinforcement in the dosage range that was tested. In a hot-plate test, TC299423 evoked antinociceptive responses in mice similar to those of nicotine. TC299423 and nicotine similarly inhibited mouse marble burying as a measure of anxiolytic effects. Taken together, our data suggest that TC299423 will be a useful small-molecule agonist for future in vitro and in vivo studies of nAChR function and physiology.