Hybridization of β-Adrenergic Agonists and Antagonists Confers G Protein Bias

Starting from the β-adrenoceptor agonist isoprenaline and beta-blocker carvedilol, we designed and synthesized three different chemotypes of agonist/antagonist hybrids. Investigations of ligand-mediated receptor activation using bioluminescence resonance energy transfer biosensors revealed a predominant effect of the aromatic head group on the intrinsic activity of our ligands, as ligands with a carvedilol head group were devoid of agonistic activity. Ligands composed of a catechol head group and an antagonist-like oxypropylene spacer possess significant intrinsic activity for the activation of Gα_s, while they only show weak or even no β-arrestin-2 recruitment at both β₁- and β₂-AR. Molecular dynamics simulations suggest that the difference in G protein efficacy and β-arrestin recruitment of the hybrid ( S)-22, the full agonist epinephrine, and the β₂-selective, G protein-biased partial agonist salmeterol depends on specific hydrogen bonding between Ser^5.46 and Asn^6.55, and the aromatic head group of the ligands.