Zaveri_2015_Nicotine.Tob.Res_17_361

INTRODUCTION: Genome-wide association studies linking the alpha3, beta4, and alpha5 nicotinic acetylcholine receptor (nAChR) subunits to nicotine dependence suggest that alpha3beta4* nAChR may be targets for smoking cessation pharmacotherapies. We previously reported that AT-1001, a selective alpha3beta4* nAChR ligand binds with high affinity to rat alpha3beta4 and human alpha3beta4alpha5 nAChR, antagonizes epibatidine-induced activation of rat alpha3beta4 nAChR in HEK cells and potently inhibits nicotine self-administration in rats.
METHODS: Two-electrode voltage clamp was used for functional characterization of AT-1001 at recombinant human alpha3beta4 and alpha4beta2 nAChR expressed in Xenopus oocytes.
RESULTS: Concentration-response curves show that AT-1001 is a partial agonist at human alpha3beta4 nAChR, evoking up to 35% of the maximal acetylcholine (ACh) response (50% effective concentration [EC50] = 0.37 muM). AT-1001 showed very little agonist activity at the alpha4beta2 nAChR, evoking only 6% of the ACh response (EC50 = 1.5 muM). Pre- and co-application of various concentrations of AT-1001 with 50 muM ACh revealed a complex pattern of activation-inhibition by AT-1001 at alpha3beta4 nAChR, which was best fitted by a 2-site equation. At alpha4beta2 nAChR, co-exposure of AT-1001 with ACh only showed inhibition of ACh current with a shallower curve.
CONCLUSIONS: AT-1001 is a partial agonist at the human alpha3beta4 nAChR and causes desensitization at concentrations at which it evokes an inward current, resulting in an overall functional antagonism of alpha3beta4 nAChR. AT-1001 does not significantly activate or desensitize alpha4beta2 nAChR at the same concentrations as at the alpha3beta4 nAChR, but does inhibit ACh responses at alpha4beta2 nAChR at higher concentrations. A combination of these mechanisms may underlie the inhibition of nicotine self-administration by AT-1001, suggesting that AT-1001 and compounds from this class may have clinical potential for smoking cessation pharmacotherapy.