Beta‐agonist Profiling Reveals Novel Biased Signaling Phenotypes for the Beta 2‐adrenergic Receptor with Implications in the Treatment of Asthma

Abstract

Asthma is characterized by chronic airway inflammation and airway smooth muscle (ASM) cell contraction. Current treatments for asthma include beta‐agonists which activate the beta 2‐adrenergic receptor, a G protein‐coupled receptor (GPCR) that promotes Gs‐dependent production of cAMP leading to ASM relaxation. Unfortunately, beta‐agonists can also promote severe side effects including an increased risk of having a severe asthmatic attack that can result in death. Such side effects have been correlated with the action of beta‐arrestins, scaffolding proteins that mediate GPCR desensitization and internalization as well as G protein independent signaling. In this scenario, biased ligands that promote selective receptor interaction with Gs should be beneficial in promoting airway relaxation while attenuating beta‐arrestin‐induced side effects. To test this, we have used high‐throughput screening to identify Gs‐biased beta‐agonists. The initial lead candidates were further analyzed for their ability to modulate receptor induced Gs and Gi interaction, cAMP production, and beta‐arrestin interaction using bioluminescence resonance energy transfer (BRET) analysis. We identified three compounds with Gs‐biased properties which showed minimal beta‐arrestin recruitment. These compounds were also able to decrease beta‐arrestin mediated outputs including receptor internalization and ERK activation. These compounds also showed reduced GRK‐mediated phosphorylation of the receptor as well as decreased agonist‐promoted desensitization in a physiological model of asthma (human ASM cells). In conclusion, these Gs‐biased beta‐agonists may pave the way for the development of more effective drugs for the treatment of asthma and may help to clarify the structural determinants of receptor mediated biased signaling.