AT-1001: A High Affinity and Selective α3β4 Nicotinic Acetylcholine Receptor Antagonist Blocks Nicotine Self-Administration in Rats

Genomic and pharmacologic data have suggested the involvement of the alpha 3 beta 4 subtype of nicotinic acetylcholine receptors (nAChRs) in drug seeking to nicotine and other drugs of abuse. In order to better examine this receptor subtype, we have identified and characterized the first high affinity and selective alpha 3 beta 4 nAChR antagonist, AT-1001, both in vitro and in vivo. This is the first reported compound with a Ki below 10 nM at alpha 3 beta 4 nAChR and >90-fold selectivity over the other major subtypes, the alpha 3 beta 4 and alpha 7 nAChR. AT-1001 competes with epibatidine, allowing for [H-3]epibatidine binding to be used for structure-activity studies, however, both receptor binding and ligand-induced Ca2+ flux are not strictly competitive because increasing ligand concentration produces an apparent decrease in receptor number and maximal Ca2+ fluorescence. AT-1001 also potently and reversibly blocks epibatidine-induced inward currents in HEK cells transfected with alpha 3 beta 4 nAChR. Importantly, AT-1001 potently and dose-dependently blocks nicotine self-administration in rats, without affecting food responding. When tested in a nucleus accumbens (NAcs) synaptosomal preparation, AT-1001 inhibits nicotine-induced [H-3]dopamine release poorly and at significantly higher concentrations compared with mecamylamine and conotoxin MII. These results suggest that its inhibition of nicotine self-administration in rats is not directly due to a decrease in dopamine release from the NAc, and most likely involves an indirect pathway requiring alpha 3 beta 4 nAChR. In conclusion, our studies provide further evidence for the involvement of alpha 3 beta 4 nAChR in nicotine self-administration. These findings suggest the utility of this receptor as a target for smoking cessation medications, and highlight the potential of AT-1001 and congeners as clinically useful compounds. Neuropsychopharmacology (2012) 37, 1367-1376; doi: 10.1038/npp.2011.322; published online 25 January 2012