The pharmacologic characterization of allosteric molecules: Gq protein activation

Abstract

Context: Drugs such as positive allosteric modulators (PAMs) produce complex behaviors when acting on tissues in different physiological contexts in vivo.

Objective: This study describes the use of functional assays of varying receptor sensitivity to unveil the various behaviors of PAMs and thus quantify allosteric effect through system independent scales.

Materials and methods: Muscarinic receptor activation with acetylcholine (ACh) was used to the demonstrate activity of the PAM agonist 1–(4-methoxybenzyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid, Benzyl quinolone carboxylic acid (BQCA) in terms of direct agonism, potentiation of ACh affinity, and ACh efficacy. Concentration–response curves were fit to the functional allosteric model to yield indices of agonism (τ_B), effects on affinity (α cooperativity), and efficacy (β cooperativity).

Results: It is shown that a highly sensitive functional assay revealed the direct efficacy of BQCA as an agonist and relatively insensitive cells (produced by chemical alkylation of muscarinic receptor with phenoxybenzamine) revealed a positive allosteric effect of BQCA on ACh efficacy. A wide range of functional assay sensitivities produced a complex pattern of behavior for BQCA all of which was accurately quantified through the system-independent parameters of the functional allosteric model.

Conclusions: The study of complex allosteric molecules in a range of functional assays of varying sensitivity allows the measurement of the complete array of activities of these molecules on receptors and also better predicts which will be seen with these in vivo where a range of tissue sensitivities is encountered.

Keywords:

• Receptor allosterism
• drug discovery and development
• positive allosteric modulation
• Gq-coupled receptors

Acknowledgments

All authors conceived the research; Bdioui and Verdi performed the experiments; all authors participated in discussing and revising the manuscript.

Availability of data and materials

All data generated or analyzed during this study are included in this published article.

Disclosure statement

No potential conflict of interest was reported by the authors.