Discovery and Characterization of Novel Subtype-Selective Allosteric Agonists for the Investigation of M1 Receptor Function in the Central Nervous System

Cholinergic transmission in the forebrain is mediated primarily by five subtypes of muscarinic acetylcholine receptors (mAChRs), termed M-1-M-5. Of the mAChR subtypes, M-1 is among the most heavily expressed in regions that are critical for learning and memory and has been viewed as the most critical mAChR subtype for memory and attention mechanisms. Unfortunately, it has been difficult to develop selective activators of M-1 and other individual mAChR subtypes, which has prevented detailed studies of the functional roles of selective activation of M-1. Using a functional high-throughput screening and subsequent diversity-oriented synthesis approach, we have discovered a novel series of highly selective M-1 allosteric agonists. These compounds activate M-1 with EC50 values in the 150-500 nM range and have unprecedented, clean ancillary pharmacology (no substantial activity at 10 mu M across a large panel of targets). Targeted mutagenesis revealed a potentially novel allosteric binding site in the third extracellular loop of the M-1 receptor for these allosteric agonists. Optimized compounds, such as VU0357017, provide excellent brain exposure after systemic dosing and have robust in vivo efficacy in reversing scopolamine-induced deficits in a rodent model of contextual fear conditioning. This series of selective M-1 allosteric agonists provides critical research tools to allow dissection of M-1-mediated effects in the CNS and potential leads for novel treatments for Alzheimer's disease and schizophrenia.