Diverse Effects on M Signaling and Adverse Effect Liability within a Series of M Ago-PAMs.

Rook JM, Abe M, Cho HP, Nance KD, Luscombe VB, Adams JJ, Dickerson JW, Remke DH, Garcia-Barrantes PM, Engers DW, Engers JL, Chang S, Foster JJ, Blobaum AL, Niswender CM, Jones CK, Conn PJ, Lindsley CW
ACS Chem Neurosci. 2017 8 (4): 866-883

PMID: 28001356 · PMCID: PMC5460155 · DOI:10.1021/acschemneuro.6b00429

Both historical clinical and recent preclinical data suggest that the M muscarinic acetylcholine receptor is an exciting target for the treatment of Alzheimer's disease and the cognitive and negative symptom clusters in schizophrenia; however, early drug discovery efforts targeting the orthosteric binding site have failed to afford selective M activation. Efforts then shifted to focus on selective activation of M via either allosteric agonists or positive allosteric modulators (PAMs). While M PAMs have robust efficacy in rodent models, some chemotypes can induce cholinergic adverse effects (AEs) that could limit their clinical utility. Here, we report studies aimed at understanding the subtle structural and pharmacological nuances that differentiate efficacy from adverse effect liability within an indole-based series of M ago-PAMs. Our data demonstrate that closely related M PAMs can display striking differences in their in vivo activities, especially their propensities to induce adverse effects. We report the discovery of a novel PAM in this series that is devoid of observable adverse effect liability. Interestingly, the molecular pharmacology profile of this novel PAM is similar to that of a representative M PAM that induces severe AEs. For instance, both compounds are potent ago-PAMs that demonstrate significant interaction with the orthosteric site (either bitopic or negative cooperativity). However, there are subtle differences in efficacies of the compounds at potentiating M responses, agonist potencies, and abilities to induce receptor internalization. While these differences may contribute to the differential in vivo profiles of these compounds, the in vitro differences are relatively subtle and highlight the complexities of allosteric modulators and the need to focus on in vivo phenotypic screening to identify safe and effective M PAMs.

MeSH Terms (9)

Allosteric Regulation Animals Drug Discovery Humans Mice Muscarinic Agonists Rats Receptor, Muscarinic M1 Structure-Activity Relationship

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