Biased allosteric modulators as a novel approach to induce biased signalling in G‐protein coupled receptors: The case of beta 2 adrenergic receptor in cardiovascular diseases
Authors: Alcaraz Arfaxad Reyes , Bond Richard A. , McConnell Bradley K. 
Published: April 2020

G protein‐coupled receptors (GPCRs) are the therapeutic target of nearly half of the current drugs in the market. It has been now well established that GPCRs can signal through multiple transducers, including G proteins and beta‐arrestins. These signalling pathways can be activated or blocked by “balanced” agonists or antagonists, but also, they can also be selectively activated in a “biased” response. Until now, biased signalling has been induced by biased ligands and biased receptors, any of which can result in preferential signalling through G proteins or beta‐arrestins. However, the discovery and development of GPCR biased agonists has been quite challenging, since in most GPCRs there is no structure activity relationship studies available, moreover, different active conformations for each pathway are likely very similar. Traditionally, biased agonists have been developed to target only the orthosteric site which is the binding site of the endogenous ligands. Development of biased agonists targeting the orthosteric site might be extremely difficult, especially in the absence of structure‐activity relationship information. Biased agonism holds great promise as a mechanism to significantly reduce the side effects that current drugs in used in the clinic, as well as develop drugs for use on their own. Also, ligands that produce biased signalling will serve as valuable tools for elucidation of the molecular mechanisms underlying GPCR‐signalling. Allosteric modulators are ligands which bind to a receptor at a site distinct from that of the endogenous agonist and they do not activate the receptor rather than stabilize or induce intermediate active or inactive structural conformations modulating signalling of the orthosteric ligands. We tested the hypothesis that biased signalling of the receptor could be achieved by targeting allosteric domains which show high diversity in structure and amino acid sequence among the GPCRs. The rationale is that the development of a novel series of allosteric modulators will regulate GPCR signalling in such way that the endogenous ligand would produce biased signalling only when the target receptor is bound to an allosteric modulator. In this study, we targeted the intracellular domains of the beta 2 adrenergic receptor (b2‐AR) to produce beta‐arrestin biased signalling when activated by traditional orthosteric ligands. A highly selective b2‐AR biased allosteric modulator would be highly desirable to treat a number of cardiovascular diseases. Thus, we used a combination of state of art drug discovery platforms, in silico calculations and peptidomimetics to develop a beta‐arrestin biased allosteric modulator AR1981. This allosteric modulator increased the beta‐arrestin recruitment efficacy of isoproterenol by two‐fold. Also, AR1981 was able to increase the potency of isoproterenol in beta‐arrestin recruitment by more than ten‐fold. Thus, AR1981 is a promising tool to access a novel pharmacological profile stimulating cardioprotective signalling through the b2‐AR and can serve as a model for the next generation of cardiovascular drug development. The outcome of the proposed work will facilitate the development of a new generation of allosteric modulators for GPCRs.