Salicylate sensitizes oral squamous cell carcinoma to chemotherapy through targeting mTOR pathway

Oral squamous cell carcinoma (OSCC) is an extremely aggressive neoplasm, which is usually diagnosed in the advanced stage of the disease. Extensive studies have shown a link between chronic inflammation and various types of cancer, including OSCC. Salicylate is a biotransformation product of aspirin, with similar anti-inflammatory ability to aspirin but lacks aspirin's inhibitory effect on the isolated cyclooxygenase activity. Our study indicates that salicylate sensitizes OSCC to anti-cancer drugs, but the mechanisms of its action are unclear. Here, OSCC cells were used to evaluate the cytotoxicity of salicylate alone or in combination with cisplatin (CDDP). RPPA proteomic array and Western blotting were employed to determine the signaling pathways affected by salicylate. Salicylate decreased cell survival rate and induced cell apoptosis in OSCC cells but not human normal oral mucosal epithelial cells (hTERT-OME). The use of sodium salicylate (SS) dramatically sensitized OSCC cells to CDDP. RPPA array showed that SS reduced many oncogenes such as PI3K/mTOR signaling and cancer stem cell (CSC)-related genes versus control. Western and transcriptional analyses substantiated that salicylate down-regulated these CSC-associated genes and the mTOR pathway dose dependently. Salicylate preferentially repressed the ability of sorted ALDH1+ cells to form tumor spheres. Finally, salicylate suppressed tumor growth in vivo, and the combination of salicylate and CDDP further synergistically reduced the growth of tumors. Salicylate hinders OSCC cell growth and sensitizes OSCC cells to CDDP through targeting CSCs and the mTOR signaling pathway. We propose that salicylate is beneficial for OSCC patients, and salicylate may be combined with chemotherapies to effectively treat OSCC patients.