A-85380 [3-(2(S)-azetidinylmethoxy)pyridine]: In vitro pharmacological properties of a novel, high affinity alpha 4 beta 2 nicotinic acetylcholine receptor ligand

The in vitro pharmacological properties of a novel cholinergic channel ligand, A-85380 [3-(2(S)-azetidinylmethoxy)pyridine], were examined using tissue preparations that express different putative nAChR subtypes. In radioligand binding studies, A-85380 is shown to be a potent and selective ligand for the human alpha 4 beta 2 nAChR subtype (K-i = 0.05 +/- 0.01 nM) relative to the human alpha 7 (K-i = 148 +/- 13 nM) and the muscle alpha 1 beta 1dg subtype expressed in Torpedo electroplax (K-i = 314 +/- 12 nM). The R-enantiomer of A-85380, A-159470, displays little enantioselectivity towards the alpha 4 beta 2 and alpha 1 beta 1 delta gamma subtypes but does display 12-fold enantioselectivity towards the alpha 7 subtype (K-i = 1275 +/- 199 nM). (+)- and (-)-Epibatidine display similar potencies at the human human alpha 4 beta 2 (K-i = 0.04 +/- 0.02 nM and 0.07 +/- 0.02 nM, respectively), human alpha 7 (K-i = 16 +/- 2 nM and 22 +/- 3 nM, respectively) and muscle alpha 1 beta 1 delta g (K-i = 2.5 +/- 0.9 nM and 5.7 +/- 1.0 nM, respectively) nAChRs. Functionally, A-85380 is a potent activator of cation efflux through the human alpha 4 beta 2 (EC(50) = 0.7 +/- 0.1 mu M) and ganglionic (EC(50) = 0.8 +/- 0.04 mu M) subtypes,effects that are attenuated by pretreatment with mecamylamine (10 mu M). Further, A-85380 can activate (EC(50) = 8.9 +/- 1.9 mu M) currents through channels formed by injection of the human alpha 7 subunit into Xenopus oocytes, effects that are attenuated by pretreatment with the alpha 7 nAChR antagonist, methyllycaconitine (10 nM). In all cases, A-85380 is more potent than (-)-nicotine but less potent than (+/-)-epibatidine. In neurotransmitter release studies, A-85380 stimulates the release of dopamine with an EC(50) value of 0.003 +/- 0.001 mu M which is equipotent to (+/-)-epibatidine, and 20-fold more potent that (-)-nicotine (EC(50) = 0.04 +/- 0.009 mu M). Thus, A-85380 displays a profile of robust activation of a number of nAChR subtypes with substantially less affinity for [I-125]alpha-BgT sites than [H-3](-)-cytisine sites, suggesting that it may serve as a more selective pharmacologic probe for the alpha 4 beta 2 subtype relative to the alpha 7 and alpha 1 beta 1 delta g nAChRs than (+/-)-epibatidine. Copyright (C) 1996 Elsevier Science Ltd.