Abstract
Allosteric modulation of metabotropic glutamate receptor subtype 1 (mGlu1) represents a viable therapeutic target for treating numerous central nervous system disorders. Although multiple chemically distinct mGlu1 positive (PAMs) and negative (NAMs) allosteric modulators have been identified, drug discovery paradigms have not included rigorous pharmacological analysis. In the present study, we hypothesized that existing mGlu1 allosteric modulators possess unappreciated probe-dependent or biased pharmacology. Using human embryonic kidney 293 (HEK293A) cells stably expressing human mGlu1, we screened mGlu1 PAMs and NAMs from divergent chemical scaffolds for modulation of different mGlu1 orthosteric agonists in intracellular calcium (iCa2+) mobilization and inositol monophosphate (IP1) accumulation assays. Operational models of agonism and allosterism were used to derive estimates for important pharmacological parameters such as affinity, efficacy, and cooperativity. Modulation of glutamate and quisqualate-mediated iCa2+ mobilization revealed probe dependence at the level of affinity and cooperativity for both mGlu1 PAMs and NAMs. We also identified the previously described mGlu5 selective NAM PF-06462894 as an mGlu1 NAM with a different pharmacological profile from other NAMs. Differential profiles were also observed when comparing ligand pharmacology between iCa2+ mobilization and IP1 accumulation. The PAMs Ro67-4853 and CPPHA displayed apparent negative cooperativity for modulation of quisqualate affinity, and the NAMs CPCCOEt and PF-06462894 had a marked reduction in cooperativity with quisqualate in IP1 accumulation and upon extended incubation in iCa2+ mobilization assays. These data highlight the importance of rigorous assessment of mGlu1 modulator pharmacology to inform future drug discovery programs for mGlu1 allosteric modulators.
SIGNIFICANCE STATEMENT Metabotropic glutamate receptor subtype 1 (mGlu1) positive and negative allosteric modulators have therapeutic potential in multiple central nervous system disorders. We show that chemically distinct modulators display differential pharmacology with different orthosteric ligands and across divergent signaling pathways at human mGlu1. Such complexities in allosteric ligand pharmacology should be considered in future mGlu1 allosteric drug discovery programs.
Footnotes
- Received December 15, 2022.
- Accepted February 21, 2023.
This work was supported by a National Ataxia Foundation Early Career Investigator Award to S.D.H. Research on metabotropic glutamate receptor allosteric modulators within the Endocrine and Neuropharmacology laboratory was supported by an Australian Research Council Future Fellowship [FT170100392] and a National Health and Medical Research Council Australia Ideas grant [Grant 2002947] awarded to K.J.G.
No author has an actual or perceived conflict of interest with the contents of this article.
Select data from this work has previously been presented as:
Hellyer SD, Wang Y, Muraleetharan A, Rowe M, Gould A, and Gregory KJ (2022) Rigorous pharmacological characterization of metabotropic glutamate receptor 1. APSA/ASCEPT 2022 Joint Conference; 2022 Nov 29–Dec 2; Perth, WA, Australia; Australasian Pharmaceutical Science Association; and Hellyer SD, Wang Y, Muraleetharan A, and Gregory KJ (2022) Pharmacological characterization of mGlu1 in health and disease. Joint Florey and Monash Institute of Pharmaceutical Sciences Neurotherapeutics Symposium 2022; 2022 Oct 26; Melbourne, VIC, Australia.
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- Copyright © 2023 by The American Society for Pharmacology and Experimental Therapeutics
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