Progress in the discovery of small molecule modulators of the Cys-loop superfamily receptors

The vertebrate Cys-loop family of ligand-gated ion channels (LGICs) are comprised of nicotinic acetylcholine (nAChR), serotonin type 3 (5-HT₃R), γ-aminobutyric acid (GABA_AR), and glycine (GlyR) receptors. Here, we review efforts to discover selective small molecules targeting one or more Cys-loop receptors, with a focus on state-of-the-art modulators that have been reported over the past five years. Several highlighted compounds offer robust oral bioavailability and central exposure and have thus been useful in delineating pharmacokinetic/pharmacodynamic relationships in pre-clinical disease models. Others offer high levels of subtype and/or inter-superfamily selectivity and have facilitated understanding of complex SAR and pharmacodynamics.