Related Experiment Video

Updated: Jul 1, 2026

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
07:41

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators

Published on: February 20, 2018

Low Agonism and Balanced Pathway Modulation Distinguish an M1 Muscarinic Receptor Positive Allosteric Modulator

Huong T M Nguyen1,2, Elham Khajehali1, Vi Pham1

  • 1Drug Discovery Biology, Monash University, Parkville, Melbourne, Victoria 3052, Australia.

ACS Chemical Neuroscience
|June 30, 2026
PubMed

Insights

Positive allosteric modulators (PAMs) for M1 muscarinic acetylcholine receptors (mAChRs) show promise for cognitive disorders but cause side effects. This study reveals that low allosteric agonism and balanced efficacy modulation are key for safer M1 PAMs.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Molecular Biology

Background:

  • Positive allosteric modulators (PAMs) of the M1 muscarinic acetylcholine receptor (mAChR) are investigated for cognitive disorders like Alzheimer's disease.
  • Clinical translation is hindered by on-target cholinergic adverse effects, potentially linked to excessive allosteric agonism.

Purpose of the Study:

  • To comparatively analyze the pharmacology of five distinct M1 PAMs.
  • To elucidate the roles of allosteric cooperativity, efficacy modulation, and receptor regulation in M1 PAM-associated adverse effects.

Main Methods:

  • Utilized HEK293A cells expressing wild-type (hM1-WT) or phosphorylation-deficient (hM1-PD) human M1 mAChR.
  • Employed radioligand binding and functional assays to quantify binding affinity, cooperativity, allosteric agonism, and efficacy modulation.
  • Assessed G protein-dependent and β-arrestin-associated signaling pathways.

Main Results:

  • VU0486846, a PAM with low reported adverse effects, exhibited low allosteric agonism and weaker cooperativity but comparable efficacy modulation.
  • PAMs linked to adverse effects showed higher allosteric agonism, stronger cooperativity, and preferential β-arrestin signaling enhancement.
  • Phosphorylation site deficiency on M1 mAChR uncoupled allosteric agonism from efficacy modulation, highlighting phosphorylation's regulatory role.

Conclusions:

  • Low allosteric agonism and balanced efficacy modulation are crucial for improved M1 PAM tolerability.
  • Phosphorylation of M1 mAChR is a key regulator of allosteric signaling.
  • This research provides a framework for designing safer M1-targeted therapeutics by differentiating M1 PAM pharmacology beyond intrinsic agonism.
Keywords:
Alzheimer’s diseaseM1 muscarinic acetylcholine receptorsallosteric modulationbiased allosterismcognitionschizophreniasignaling pathways

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