S-951

S-951 is a small molecule muscarinic M3 receptor antagonist that was developed by Shionogi for the treatment of overactive bladder (OAB) and chronic obstructive pulmonary disease (COPD). As a selective M3 antagonist, S-951 was designed to inhibit the acetylcholine-mediated contraction of smooth muscles in the bladder (detrusor muscle) and the airways, thereby reducing symptoms of urinary urgency and promoting bronchodilation. By targeting the M3 subtype specifically, the compound aimed to minimize systemic side effects typically associated with non-selective antimuscarinics, such as dry mouth and tachycardia, which are often mediated by M1 and M2 receptors. Although the drug candidate progressed into Phase 2 clinical development for overactive bladder, its development was ultimately discontinued by Shionogi.