Review of a Withdrawn Drug Candidate: Adipiplon

Adipiplon is a benzodiazepine-site ligand developed for insomnia that was discontinued after phase II trials due to safety concerns. To extract structural insights relevant to drug design, we performed an in silico docking comparison of adipiplon and representative dual orexin receptor antagonists (DORAs) at two sleep-related targets: the GABA_A receptor benzodiazepine binding site and the orexin type 2 receptor (OX2R). Docking calculations using AutoDock Vina showed that adipiplon can form binding poses at both receptors, with intermediate predicted binding scores relative to reference ligands. At the GABA_A benzodiazepine site, adipiplon frequently formed polar anchor-like interactions, whereas at OX2R its anchoring patterns were less consistent. In contrast, DORAs showed more reproducible anchor interactions and more favorable score distributions at OX2R. These results suggest that adipiplon has structural flexibility across multiple receptor pockets but may lack a dominant anchoring mode associated with target selectivity. This docking-based analysis provides a structural hypothesis and illustrates the value of reassessing withdrawn drug candidates for structure-based drug design.