Discovery of VU6025733 (AG06827): A Highly Selective, Orally Bioavailable, and Structurally Distinct M ₄ Muscarinic Acetylcholine Receptor Positive Allosteric Modulator (PAM) with Robust In Vivo Efficacy

This work describes progress toward an M4 PAM preclinical candidate. The SAR to address potency, clearance, subtype selectivity, CNS exposure, and P-gp efflux are detailed within. A novel 1-(7,8-dimethyl-[1,2,4]triazolo[4,3-b]pyridazin-6-yl)piperidin-4-ol scaffold was identified, and optimization provided a highly potent analog VU6025733 (hM4 EC50 = 23 nM; rM4 EC50 = 55 nM). Further characterization revealed a highly selective compound across muscarinic acetylcholine receptor subtypes with exceptional DMPK properties (in vivo rat CLp = 5.9 mL/min/kg; t1/2 = 4.8 h; CYP1A2 & CYP2C9 IC50s > 30 μM, CYP2D6 IC50 > 9 μM; CYP3A4 IC50 > 25 μM). Moreover, VU6025733 demonstrated robust in vivo efficacy in a rat amphetamine-induced hyperlocomotion model in a dose-dependent manner. However, hepatotoxicity risk precluded further development.