Discovery, Synthesis, and Structure Activity of a Highly Selective α7 Nicotinic Acetylcholine Receptor Antagonist

Abstract

Nicotinic acetylcholine receptors (nAChRs) that contain an α7 subunit are widely distributed in neuronal and nonneuronal tissue. These receptors are implicated in the release of neurotransmitters such as glutamate and in functions ranging from thought processing to inflammation. Currently available ligands for α7 nAChRs have substantial affinity for one or more other nAChR subtypes, including those with an α1, α3, α6, and/or α9 subunit. An α-conotoxin gene was cloned from Conus arenatus. Predicted peptides were synthesized and found to potently block α3-, α6-, and α7-containing nAChRs. Structure−activity information regarding conotoxins from distantly related Conus species was employed to modify the C. arenatus derived toxin into a novel, highly selective α7 nAChR antagonist. This ligand, α-CtxArIB[V11L,V16D], has low nanomolar affinity for rat α7 homomers expressed in Xenopus laevis oocytes, and antagonism is slowly reversible. Kinetic analysis provided insight into the mechanism of antagonism. α-CtxArIB interacts with five ligand binding sites per α7 receptor, and occupation of a single site is sufficient to block function. The peptide was also shown to be highly selective in competition binding assays in rat brain membranes. α-CtxArIB[V11L,V16D] is the most selective ligand yet reported for α7 nAChRs.