Identification of a β-arrestin-biased negative allosteric modulator for the β 2 -adrenergic receptor.

Catecholamine-stimulated β 2 -adrenergic receptor (β 2 AR) signaling via the canonical G s -adenylyl cyclase-cAMP-PKA pathway regulates numerous physiological functions, including the therapeutic effects of exogenous β-agonists in the treatment of airway disease. β 2 AR signaling is tightly regulated by GRKs and β-arrestins, which together promote β 2 AR desensitization and internalization as well as downstream signaling, often antithetical to the canonical pathway. Thus, the ability to bias β 2 AR signaling toward the G s pathway while avoiding β-arrestin-mediated effects may provide a strategy to improve the functional consequences of β 2 AR activation. Since attempts to develop G s -biased agonists and allosteric modulators for the β 2 AR have been largely unsuccessful, here we screened small molecule libraries for allosteric modulators that selectively inhibit β-arrestin recruitment to the receptor. This screen identified several compounds that met this profile, and, of these, a difluorophenyl quinazoline (DFPQ) derivative was found to be a selective negative allosteric modulator of β-arrestin recruitment to the β 2 AR while having no effect on β 2 AR coupling to G s . DFPQ effectively inhibits agonist-promoted phosphorylation and internalization of the β 2 AR and protects against the functional desensitization of β-agonist mediated regulation in cell and tissue models. The effects of DFPQ were also specific to the β 2 AR with minimal effects on the β 1 AR. Modeling, mutagenesis, and medicinal chemistry studies support DFPQ derivatives binding to an intracellular membrane-facing region of the β 2 AR, including residues within transmembrane domains 3 and 4 and intracellular loop 2. DFPQ thus represents a class of biased allosteric modulators that targets an allosteric site of the β 2 AR.