Examining the effect of a substituted carbamate positive allosteric modulator on the (α4)3(β2)2 and (α4)2(β2)3 nicotinic acetylcholine receptors.

Abstract

The α4β2 nicotinic acetylcholine receptors (nAChR) are the most abundant nAChR subtypes in the brain and exist in two distinct isoforms: (α4)2(β2)3 nAChR, the high sensitivity (HS) isoform, and (α4)3(β2)2 nAChR, the low sensitivity (LS) isoform. Given the pathophysiological and pharmacological importance of these brain receptors, there are ongoing efforts to develop pharmacophores that selectively potentiate α4β2 nAChRs (positive allosteric modulators, PAMs). PAMs selective to the α4β2 nAChRs would be beneficial for neuropsychiatric conditions such as nicotine addiction and Alzheimer's disease. A chemical synthesis and high throughput screens at Amgen laboratories have identified series of compounds that preferentially potentiate the α4β2 nAChRs (Albrecht, Berry et al. 2008, Springer, Woodin et al. 2008). Notable PAMs identified in these screens include CMPI, which selectively potentiates the (α4)3(β2)2 nAChR isoform (Wang, Deba et al. 2017). In this study, we started to pharmacologically characterize additional derivatives (C9M) from these screens, focusing on its effects on the LS and HS nAChR isoforms. Unlike CMPI, C9M potentiated current response of Xenopus oocytes expressing LS and HS nAChR isoforms elicited by submaximal and saturating concentrations of ACh. This potentiation indicates that C9M enhances the agonist's efficacy at both α4β2 nAChR isoforms. Furthermore, mutations known to alter CMPI potentiation of LS nAChR (e.g. α4G41M) did not abolish the potentiating effects of C9M. Additionally, C9M enhancement of agonist's efficacy at HS (α4)2(β2)3 nAChR was notably greater than that for a panel of known nAChR PAMs including dFBr and LY2087101 (all co-applied at 1 µM with 10 µM ACh). Experiments to determine the concentration dependent effect of C9M at both LS and HS nAChR isoforms and to determine the extent of C9M effect on the agonist's potency are ongoing.