β2-Adrenoceptor agonist profiling reveals biased signalling phenotypes for the β2-adrenoceptor with possible implications for the treatment of asthma

Background and Purpose: beta-Adrenoceptor agonists relieve airflow obstruction by activating beta(2)-adrenoceptors, which are G protein-coupled receptors (GPCRs) expressed on human airway smooth muscle (HASM) cells. The currently available beta-adrenoceptor agonists are balanced agonists, however, and signal through both the stimulatory G protein (G(s))- and beta-arrestin-mediated pathways. While G(s) signalling is beneficial and promotes HASM relaxation, beta-arrestin activation is associated with reduced G(s) efficacy. In this context, biased ligands that selectively promote beta(2)-adrenoceptor coupling to G(s) signalling represent a promising strategy to treat asthma. Here, we examined several beta-adrenoceptor agonists to identify G(s)-biased ligands devoid of beta-arrestin-mediated effects. Experimental Approach: G(s)-biased ligands for the beta(2)-adrenoceptor were identified by high-throughput screening and then evaluated for G(s) interaction, G(i) interaction, cAMP production, beta-arrestin interaction, GPCR kinase (GRK) phosphorylation of the receptor, receptor trafficking, ERK activation, and functional desensitization of the beta(2)-adrenoceptor. Key Results: We identified ractopamine, dobutamine, and higenamine as G(s)-biased agonists that activate the G(s)/cAMP pathway upon beta(2)-adrenoceptor stimulation while showing minimal G(i) or beta-arrestin interaction. Furthermore, these compounds did not induce any receptor trafficking and had reduced GRK5-mediated phosphorylation of the beta(2)-adrenoceptor. Finally, we observed minimal physiological desensitization of the beta(2)-adrenoceptor in primary HASM cells upon treatment with biased agonists. Conclusion and Implications: Our work demonstrates that G(s)-biased signalling through the beta(2)-adrenoceptor may prove to be an effective strategy to promote HASM relaxation in the treatment of asthma. Such biased compounds may also be useful in identifying the molecular mechanisms that determine biased signalling and in design of safer drugs.

Automated summary

This study identified several G(s)-biased agonists that relieve airflow obstruction by activating G(s) signaling pathway through β(2)-adrenoceptor. These biased compounds showed minimal β-arrestin-mediated effects and induced minimal desensitization of the receptor in primary HASM cells. These findings may have implications for the treatment of asthma and the development of safer drugs.