Functional efficacy of adenosine A 2A receptor agonists is positively correlated to their receptor residence time

Abstract

BACKGROUND AND PURPOSE: The adenosine A 2A receptor belongs to the superfamily of GPCRs and is a promising therapeutic target. Traditionally, the discovery of novel agents for the A 2A receptor has been guided by their affinity for the receptor. This parameter is determined under equilibrium conditions, largely ignoring the kinetic aspects of the ligand-receptor interaction. The aim of this study was to assess the binding kinetics of A 2A receptor agonists and explore a possible relationship with their functional efficacy. EXPERIMENTAL APPROACH: We set up, validated and optimized a kinetic radioligand binding assay (a so-called competition association assay) at the A 2A receptor from which the binding kinetics of unlabelled ligands were determined. Subsequently, functional efficacies of A 2A receptor agonists were determined in two different assays: a novel label-free impedance-based assay and a more traditional cAMP determination. KEY RESULTS: A simplified competition association assay yielded an accurate determination of the association and dissociation rates of unlabelled A 2A receptor ligands at their receptor. A correlation was observed between the receptor residence time of A 2A receptor agonists and their intrinsic efficacies in both functional assays. The affinity of A 2A receptor agonists was not correlated to their functional efficacy. CONCLUSIONS AND IMPLICATIONS: This study indicates that the molecular basis of different agonist efficacies at the A 2A receptor lies within their different residence times at this receptor. © 2012 The Authors British Journal of Pharmacology © 2012 The British Pharmacological Society.