Structure-Based Discovery and Prioritization of Selective Tryptophan Hydroxylase 1 Inhibitors through Drug Repurposing for Hepatocellular Carcinoma

TPH1 is the rate-limiting enzyme responsible for peripheral serotonin biosynthesis. TPH1 is an established therapeutic target for several serotonin-associated disorders and has emerged as a novel drug target to treat hepatocellular carcinoma. However, its high structural similarity to other aromatic amino acid hydroxylases presents a major challenge in the development of TPH1-specific therapeutics. The current study employed an integrative structure-based drug-repurposing strategy to identify selective TPH1 inhibitors through computational selectivity profiling against closely related paralogous enzymes.

Four experimentally determined structures of human TPH1, representing distinct inhibitor-binding pockets, were used to screen potential inhibitors against FDA-approved and investigational drugs from commercial drug competitive intelligence databases. The docking protocol was validated by successfully docking the co-crystallized ligands before conducting high-throughput virtual screening and Glide Standard Precision docking with the Schrodinger suite. Top-ranked compounds were subsequently subjected to selectivity profiling against paralogous enzymes, followed by Prime MM/GBSA binding free-energy calculations to prioritize selective TPH1 binders. Molecular dynamics simulations of the candidate hits revealed variable ligand-binding stability, emphasizing the importance of receptor flexibility in accurate binding-mode prediction. To account for receptor flexibility and further refine ligand-binding conformations, induced fit docking studies are currently in progress. Collectively, the study identified promising candidate compounds with potential TPH1 selectivity, providing a foundation for further structural optimization and experimental validation toward the development of TPH1-targeted therapeutics for HCC.