Mol Pharmacol. 2021 Sep 27:MOLPHARM-AR-2021-000363. doi: 10.1124/molpharm.121.000363. Online ahead of print.
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 (PAM) of the β2AR. Cmpd-6 is positively cooperative with orthosteric agonists at the β2AR 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 amongst a panel of structurally diverse β-blockers. Cmpd-6 enhances the binding affinity of carvedilol for the β2AR 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 β2AR and β-arrestin-mediated cellular functions in response to carvedilol including ERK phosphorylation, receptor endocytosis and trafficking into lysosomes. Importantly, an analog of cmpd-6 which selectively retains positive cooperativity with carvedilol acts as a negative modulator of agonist-stimulated β2AR signaling. These unprecedented cooperative properties of carvedilol and cmpd-6 have implications for fundamental understanding of GPCR allosteric modulation, as well as for the development of more effective biased beta blockers and other GPCR therapeutics. Significance Statement This study reports small molecule-mediated allosteric modulation of the β-arrestin-biased β-blocker, carvedilol. The small molecule, cmpd-6, displays an exclusive positive cooperativity with carvedilol amongst other b-blockers and enhances the binding affinity of carvedilol for the β2AR. Cooperative effects of cmpd-6 augment the β-blockade property of carvedilol while potentiating its β-arrestin-mediated signaling functions. Our findings have potential implications in advancing GPCR allostery, developing biased therapeutics and remedying cardiovascular ailments.