Discovery and structure-activity relationships study of positive allosteric modulators of the M3 muscarinic acetylcholine receptor

The M₃ muscarinic acetylcholine receptor (mAChR) is a member of the family of mAChRs, which are associated with a variety of physiological functions including the contraction of various smooth muscle tissues, stimulation of glandular secretion, and regulation of a range of cholinergic processes in the central nerve system. We report here the discovery and a comprehensive structure­-activity relationships (SARs) study of novel positive allosteric modulators (PAMs) of the M₃ mAChR through a high throughput screening (HTS) campaign. Compound 9 exhibited potent in vitro PAM activity towards the M₃ mAChR and significant enhancement of muscle contraction in a concentration-dependent manner when applied to isolated smooth muscle strips of rat bladder. Compound 9 also showed excellent subtype selectivity over other subtypes of mAChRs including M₁, M₂, and M₄ mAChRs, and moderate selectivity over the M₅ mAChR, indicating that compound 9 is an M₃-preferring M₃/M₅ dual PAM. Moreover, compound 9 displayed acceptable pharmacokinetics profiles after oral dosing to rats. These results suggest that compound 9 may be a promising chemical probe for the M₃ mAChR for further investigation of its pharmacological function both in vitro and in vivo.