Agonists of the beta-2-adrenoceptor (b2AR), commonly referred to as b-agonists, have been a cornerstone of asthma treatment for nearly half a century. Despite their utility, b-agonists used in asthma management have problems, including functional tachyphylaxis, deterioration of asthma control, and mortality concerns. Moreover, lingering safety concerns regarding long-acting b-agonists necessitate the concomitant use of corticosteroids. The inability to understand why such problems exist and the failure to significantly improve b2AR pharmacology is reflected by over 2 decades of NIH Program announcements declaring the need for safer, more efficacious alternatives to asthma treatment. Over the last 2 decades our team has employed a robust combination of genetic and molecular approaches to convincingly demonstrate that both endogenous and exogenous b-agonist promote the asthma phenotype, and that the b2AR regulatory protein, b-arrestin-2 is critical to the limited efficacy, and safety issues, associated with b-agonist use in asthma. Despite our work to date which constitutes compelling proof of principle, a corrective pharmacological approach sufficiently feasible to advance has been unavailable until now. In collaboration with colleagues at Thomas Jefferson University we have characterized a novel b2AR agonist as well as b2AR allosteric modulator (AM) that provide the therapeutic signaling of b-agonists yet allow the b2AR to avoid (pathology-inducing) engagement of b-arrestins. These compounds are the first b2AR ligands/AMs capable of ?biasing? b2AR to increase Gs protein signaling. We propose to use our preclinical in vivo and cell-based models to: 1) establish that these novel compounds are superior to current b-agonists with respect to mitigating the central features of asthma (airway inflammation and hyperresponsiveness (AHR)) while maintaining bronchodilation function, 2) determine the specific cell type(s) through which these drugs work and 3) address a fundamental conundrum in the field of GPCR biology - do b-arrestins impact function and disease by generating their own signal, or are their effects due to their inhibition of canonical b2AR signaling? In Aim 1 we will establish the ability of novel b2AR-biasing compounds to mitigate the asthma phenotype in in vivo and cell-based models.
In Aim 2 we will use using genetic and pharmacological approaches to establish epithelial cell b2AR-arrestin biasing as critical to the permissive effect of b-agonist in promoting the asthma phenotype. Finally, in Aim 3 we will establish the mechanisms by which novel b2AR biasing compounds regulate airway cell functions that contribute to the asthma phenotype.
This project is relevant to public health because it has a high likelihood of finding new, or improving current, asthma medications. Furthermore, the results could alter our understanding of beta-2-adrenergic receptor function in asthma at a paradigm-shifting level. Finally, the signaling pathways and ligands we reveal in this project could be highly applicable to drug discovery for many other diseases.
