Decoding Prolonged Residence Time of 5-HT_2A Receptor Antagonists: Insights from Ritanserin Derivatives

The lifetime of a ligand-receptor complex has been suggested to play an important role in compound activity and sustained pharmacological action. However, due to the multitude of other factors considered during optimization, this aspect is often neglected in the early stages of drug design and development. Consequently, data on ligand residence time (RT) remain limited, and the molecular determinants underlying prolonged binding are not fully understood. In this study, we focused on ritanserin, a known 5-HT_2A receptor (5-HT_2AR) antagonist with an RT of 68 min. By modifying its structure, we synthesized a series of derivatives with varying RT, which was determined in vitro. Comprehensive molecular modeling analyses, including docking and molecular dynamics simulations, enabled us to propose a set of key receptor-ligand contacts contributing to prolonged binding. Both conventional molecular dynamics and enhanced sampling approaches (metadynamics and random-accelerated molecular dynamics) were applied to the native and mutant receptors, providing in-depth insights into the determinants of long ligand occupancy at the 5-HT_2AR. The study indicated that prolonged RT is associated with, for example, stable and geometrically optimized π-π interactions with a hydrophobic aromatic cluster (Trp336^6.48 and Phe340^6.52, in particular). To our knowledge, this represents the first such a comprehensive study of its kind, offering novel hypotheses that may guide the design of new 5-HT_2AR ligands with prolonged duration of action.