Exploring the kinetic selectivity of drugs targeting the beta1-adrenoceptor

In this study, we report the beta1-adrenoceptor binding kinetics of several clinically relevant beta1/2-adrenoceptor (beta1/2AR) agonists and antagonists. We demonstrate that the physicochemical properties of a molecule directly affect its kinetic association rate (kon) and affinity for the target. In contrast to our findings at the beta2-adrenoceptor, a drug’s immobilized artificial membrane partition coefficient (KIAM), reflecting both hydrophobic and electrostatic interactions of the drug with the charged surface of biological membranes, was no better predictor than simple hydrophobicity measurements such as log P or logD7.4, characterized by a distribution between water and a non-aqueous organic phase (e.g. n-octanol) at predicting association rate. Overall, this suggests that hydrophobic interactions rather than a combination of polar and hydrophobic interactions play a more prominent role in dictating the binding of these ligands to the beta1-adrenoceptor. Using a combination of kinetic data, detailed structural and physicochemical information we rationalize the above findings and speculate that the association of positively charged ligands at the beta1AR is curtailed somewhat by its predominantly neutral/positive charged extracellular surface. Consequently, hydrophobic interactions in the ligand binding pocket dominate the kinetics of ligand binding. In comparison at the beta2AR, a combination of hydrophobicity and negative charge attracts basic, positively charged ligands to the receptor’s surface promoting the kinetics of ligand binding. Additionally, we reveal the potential role kinetics plays in the on-target and off-target pharmacology of clinically used beta-blockers