Unique Positive Cooperativity Between the β-Arrestin–Biased β-Blocker Carvedilol and a Small Molecule Positive Allosteric Modulator of the β2-Adrenergic Receptor

Abstract

Among β -blockers that are clinically prescribed for heart failure, carvedilol is a first-choice agent with unique pharmacological properties. Carvedilol is distinct from other β -blockers in its ability to elicit β -arrestin–biased agonism, which has been suggested to underlie its cardioprotective effects. Augmenting the pharmacologic properties of carvedilol thus holds the promise of developing more efficacious and/or biased β -blockers. We recently identified compound-6 (cmpd-6), the first small molecule positive allosteric modulator of the β 2-adrenergic receptor ( β 2AR). Cmpd-6 is positively cooperative with orthosteric agonists at the β 2AR and enhances agonist-mediated transducer (G-protein and β -arrestin) signaling in an unbiased manner. Here, we report that cmpd-6, quite unexpectedly, displays strong positive cooperativity only with carvedilol among a panel of structurally diverse β -blockers. Cmpd-6 enhances the binding affinity of carvedilol for the β 2AR and augments its ability to competitively antagonize agonist-induced cAMP generation. Cmpd-6 potentiates β -arrestin1– but not Gs-protein–mediated high-affinity binding of carvedilol at the β 2AR and β -arrestin–mediated cellular functions in response to carvedilol including extracellular signal-regulated kinase phosphorylation, receptor endocytosis, and trafficking into lysosomes. Importantly, an analog of cmpd-6 that selectively retains positive cooperativity with carvedilol acts as a negative modulator of agonist-stimulated β 2AR signaling. These unprecedented cooperative properties of carvedilol and cmpd-6 have implications for fundamental understanding of G-protein–coupled receptor (GPCR) allosteric modulation, as well as for the development of more effective biased beta blockers and other GPCR therapeutics. SIGNIFICANCE STATEMENT This study reports on the small molecule–mediated allosteric modulation of the β -arrestin–biased β -blocker, carvedilol. The small molecule, compound-6 (cmpd-6), displays an exclusive positive cooperativity with carvedilol among other β -blockers and enhances the binding affinity of carvedilol for the β 2-adrenergic receptor. Cooperative effects of cmpd-6 augment the β -blockade property of carvedilol while potentiating its β -arrestin–mediated signaling functions. These findings have potential implications in advancing G-protein–coupled receptor allostery, developing biased therapeutics and remedying cardiovascular ailments.