A Novel Structural Landscape for Ligand Binding to the α7 Nicotinic Acetylcholine Receptor

Abstract

In our previous study we identified a series of 4,6‐disubstituted 2‐aminopyrimidines interacting with Acetylcholine Binding Proteins (AChBP) in a cooperative fashion [Kaczanowska et al., Proc. Natl. Acad. Sci. USA 111, 10749 (2014)]. Based on X‐ray crystal structures of AChBP in complex with the cooperative ligands, we designed a new subset of these molecules that target the α7‐nicotinic acetylcholine receptor (nAChR). Seventeen compounds corresponding to this design were synthesized and characterized in cell based functional assays and radioligand binding assay using HEK cell lines overexpressing transfected cDNAs of human α7‐nAChRs, α4β2‐nAChRs and mouse 5HT3A receptors and Lymnaea (Ls) AChBP, respectively. We found a subset of structures that show Kd values in radioligand binding for AChBP between 51–68 nM and elicited responses for α7‐nAChRs in cell based assays (EC50's) as low as 60–70 nM, reflecting high affinity for α7‐nAChRs. Differential selectivity was characterized using α4β2‐nAChRs and 5HT3A receptors as references. Selected Ls‐AChBP and α7‐nAChRs ligands (AC‐171A, AC‐171A2, AC‐171C, AC‐171D) were then crystallized with the Ls‐AChBP revealing a unique binding pose at the five subunit interfaces. These 4,6‐disubsituted 2‐aminopyrimidines may hold potential in treatment of various CNS developmental disorders. For example, in schizophrenia nicotine addiction and resistance to abstinence prevails and may be modulated by these α7‐nAChRs ligands.Support or Funding InformationSupported by NIH grant GM18360 and the Tobacco‐related Disease Research Program (TRDRP).