TC299423, a Novel Agonist for Nicotinic Acetylcholine Receptors

Teagan R. Wall, Brandon J. Henderson, George Voren, Charles R. Wageman, Purnima Deshpande, Bruce N. Cohen, Sharon R. Grady, Michael J. Marks, Daniel Yohannes, Paul J. Kenny, Merouane Bencherif, Henry A. Lester

(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 α6β2(∗) (α6β2-containing), α4β2(∗), and α3β4(∗) nAChRs, using [(125)I]-epibatidine binding, whole-cell patch-clamp recordings, synaptosomal (86)Rb(+) efflux, [(3)H]-dopamine release, and [(3)H]-acetylcholine release. TC299423 displayed an EC50 of 30-60 nM for α6β2(∗) nAChRs in patch-clamp recordings and [(3)H]-dopamine release assays. Its potency for α6β2(∗) in these assays was 2.5-fold greater than that for α4β2(∗), and much greater than that for α3β4(∗)-mediated [(3)H]-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 gain-of-function, mutant α6 (α6L9'S) nAChR mice, show that TC299423 elicits α6β2(∗) nAChR-mediated responses at low doses. Conditioned place preference assays show that low-dose TC299423 also produces significant reward in α6L9'S mice, and modest reward in WT mice, through a mechanism that probably involves α6(non-α4)β2(∗) 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.