Probing the binding site of novel selective positive allosteric modulators at the M1 muscarinic acetylcholine receptor

Khajehali, E., Valant, C., Jörg, M., Tobin, A. B. , Conn, P. J., Lindsley, C. W., Sexton, P. M., Scammells, P. J. and Christopoulos, A. (2018) Probing the binding site of novel selective positive allosteric modulators at the M1 muscarinic acetylcholine receptor. Biochemical Pharmacology, 154, pp. 243-254. (doi: 10.1016/j.bcp.2018.05.009) (PMID:29777683) (PMCID:PMC6066355)

Abstract

Subtype-selective allosteric modulation of the M1 muscarinic acetylcholine (ACh) receptor (M1 mAChR) is an attractive approach for the treatment of numerous disorders, including cognitive deficits. The discovery of benzyl quinolone carboxylic acid, BQCA, a selective M1 mAChR positive allosteric modulator (PAM), spurred the subsequent development of newer generation M1 PAMs representing diverse chemical scaffolds, different pharmacodynamic properties and, in some instances, improved pharmacokinetics. Key exemplar molecules from such efforts include PF-06767832 (N-((3R,4S)-3-hydroxytetrahydro-2H-pyran-4-yl)-5-methyl-4-(4-(thiazol-4-yl)benzyl)pyridine-2-carboxamide), VU6004256 (4,6-difluoro-N-(1S,2S)-2-hydroxycyclohexyl-1-((6-(1-methyl-1H-pyrazol-4-yl)pyridine-3-yl)methyl)-1H-indole-3-carboxamide) and MIPS1780 (3-(2-hydroxycyclohexyl)-6-(2-((4-(1-methyl-1H-pyrazol-4-yl)-benzyl)oxy)phenyl)pyrimidin-4(3H)-one). Given these diverse scaffolds and pharmacodynamics, the current study combined pharmacological analysis and site-directed mutagenesis to explore the potential binding site and function of newer M1 mAChR PAMs relative to BQCA. Interestingly, the mechanism of action of the novel PAMs was consistent with a common model of allostery, as previously described for BQCA. Key residues involved in the activity of BQCA, including Y179 in the second extracellular loop (ECL) and W4007.35 in transmembrane domain (TM) 7, were critical for the activity of all PAMs tested. Overall, our data indicate that structurally distinct PAMs share a similar binding site with BQCA, specifically, an extracellular allosteric site defined by residues in TM2, TM7 and ECL2. These findings provide valuable insights into the structural basis underlying modulator binding, cooperativity and signaling at the M1 mAChR, which is essential for the rational design of PAMs with tailored pharmacological properties.

• Item Type: Articles
• Keywords: Allosteric modulation, BQCA, drug discovery, muscarinic acetylcholine receptor, mutagenesis.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Tobin, Andrew
• Authors: Khajehali, E., Valant, C., Jörg, M., Tobin, A. B., Conn, P. J., Lindsley, C. W., Sexton, P. M., Scammells, P. J., and Christopoulos, A.
• College/School: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
• Journal Name: Biochemical Pharmacology
• Publisher: Elsevier
• ISSN: 0006-2952
• ISSN (Online): 1873-2968
• Published Online: 17 May 2018
• Copyright Holders: Copyright © 2018 The Authors
• First Published: First published in Biochemical Pharmacology 154: 243-254
• Publisher Policy: Reproduced under a Creative Commons License

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
75016	1	Collaborative Network to Define the Molecular Determinants of G Protein Coupled Receptor Clinical Efficacy	Andrew Tobin	Wellcome Trust (WELLCOTR)	201529/Z/16/Z	RI MOLECULAR CELL & SYSTEMS BIOLOGY