Why Search for Alternative GPCR Agonists?

Intuitively, it is easy to understand why we search for G protein-coupled receptor (GPCR) antagonists. It is obviously to block a functionality of a specific receptor potentially linked to some aspects of disease. Whether by focused research or by serendipity, many drugs were discovered in the last century that function as antagonist at a precise receptor. A current idea is that at least half of the drugs on the market are antagonist ligands of GPCRs. Then, why are we searching for alternative receptor agonists while the endogenous activating molecule is known? In the present commentary we try to rationalize these fields of research, since they proved to be very successful over the years, with receptor pharmacology populated with dozens of alternative agonists, particularly to bioaminergic receptors, and to a lesser extent to peptidergic ones. However, the action of such compounds is not well-characterized: are they surrogates to the endogenous agonist, and if yes in which context and for which purpose? The present essay is a reflection on this subject that leads to fundamental interrogations of our understanding of GPCR roles and functions.