Virtual Screening and Optimization of Novel mTOR Inhibitors for Radiosensitization of Hepatocellular Carcinoma

BACKGROUND: Radiotherapy has an ameliorative effect on a wide variety of tumors, but hepatocellular carcinoma (HCC) is insensitive to this treatment. Overactivated mammalian target of rapamycin (mTOR) plays an important part in the resistance of HCC to radiotherapy; thus, mTOR inhibitors have potential as novel radiosensitizers to enhance the efficacy of radiotherapy for HCC. METHODS: A lead compound was found based on pharmacophore modeling and molecular docking, and optimized according to the differences between the ATP-binding pockets of mTOR and PI3K. The radiosensitizing effect of the optimized compound (2a) was confirmed by colony formation assays and DNA double-strand break assays in vitro. The discovery and preclinical characteristics of this compound are described. RESULTS: The key amino acid residues in mTOR were identified, and a precise virtual screening model was constructed. Compound 2a, with a 4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine scaffold, exhibited promising potency against mTOR (mTOR IC(50)=7.1 nmol/L (nM)) with 126-fold selectivity over PI3Kα. Moreover, 2a significantly enhanced the sensitivity of HCC to radiotherapy in vitro in a dose-dependent manner. CONCLUSION: A new class of selective mTOR inhibitors was developed and their radiosensitization effects were confirmed. This study also provides a basis for developing mTOR-specific inhibitors for use as radiosensitizers for HCC radiotherapy.