Antagonists binding at 5-HT3RAA, 5-HT3RAB and 5-HT3RAC can potentially counteract nicotine binding

5-hydroxytryptamine (serotonin) subtype 3 receptor (5-HT3R) is a promising target for drug addiction treatment due to its functional role and brain distribution. However, 5-HT3R may be composed of different subunits which potentially lead to different ligand binding properties. This study aimed to construct an in silico model of human 5-HT3R with distinct subunit compositions and to investigate its binding with ligands such as nicotine, compared to 5-HT3R antagonists from both synthetic and natural sources. Homology models of 5-HT3RAA, 5-HT3RAB, and 5-HT3RAC were developed using the murine 5-HT3R crystal structure (4PIR) as a template. Docking studies with AutoDock assessed the binding properties of nicotine and several antagonists (ondansetron, palonosetron, 6-gingerol, and 6-shogaol) across different 5-HT3R compositions. A radioligand binding assay on human 5-HT3RAA characterized the binding affinities of each compound. In silico findings revealed that both homomeric and heteromeric receptors exhibited similar interactions with nicotine and the antagonists. Notably, nicotine, 6-gingerol, and 6-shogaol demonstrated less favorable binding energies compared to ondansetron and palonosetron, with nicotine showing the weakest affinity among all tested ligands in vitro. The study outcomes allow a prediction of nicotine action on 5-HT3R as an antagonist, which can possibly be competed with other 5-HT3R antagonists from different classes.This positions the 5-HT3R as a viable target for pharmacotherapy in smoking cessation.