ABSTRACT
BACKGROUND: Although molecular-targeted agents are still the first choice for advanced hepatocellular carcinoma (HCC) treatment, the therapeutic efficacy of these agents is not satisfactory. Recently, the mammalian target of rapamycin (mTOR) is considered to be a promising molecular target that can enhance the sensitivity of HCC cells to antitumor therapy. However, the reported mTOR inhibitors have some shortcomings, and novel mTOR inhibitors need to be developed to enhance the antitumor effect of molecularly targeted agents on advanced HCC. METHODS: In this study, five small-molecular compounds that could serve as potential mTOR-specific inhibitors were identified by virtual screening. The activity of tert-butyl (4-(9-(2-(1,3-dioxolan-2-yl)ethyl)-6-morpholino-9H-purin-2-yl)phenyl)carbamate (compound 4) was measured by enzyme test and Western blot, and its antitumor effect on HCC was examined in nude mice subcutaneous tumor model. RESULTS: The results showed that 4 is the most effective one in inhibiting the activation of mTOR kinase (mTOR IC50 = 17.52±3.67 nmol/L) among the five lead compounds. Further research in this study indicated that treatment with 4 enhanced the sensitivity of HCC cells to the molecular-targeted agents, such as sorafenib, regorafenib, lenvatinib, anlotinib, and apatinib. In addition, this research indicated that mTOR was correlated with the poor prognosis in patients with advanced HCC who received sorafenib. CONCLUSION: Our study identified a new type of small-molecular inhibitors of mTOR and confirmed their ability to enhance the antitumor effect of molecular-targeted agents on advanced HCC.
ABSTRACT
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 IC50=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.
