High-dose vitamin C preferentially exerts a sustained growth-inhibitory effect in human tongue carcinoma cells over dysplastic oral keratinocytes.

The effects of ascorbic acid (AsA) on human tongue cancer cells have been reported; however, anticancer mechanisms and preferential effects in carcinoma cells compared with those in dysplastic keratinocytes remain unclear. Here, we investigated how high-dose AsA treatment can suppress oral cancer. AsA and its oxidized form, dehydroascorbic acid (DehAsA), exhibited dose-dependent cytotoxicity against three oral cancer cell types. The cytotoxic effect on HSC-4 cells, which was the highest, was markedly more significant than that on non-tumorigenic dysplastic DOK cells, thus indicating a certain preference. Compared with its derivatives, AsA exhibited the most potent and preferential cytotoxic effects. After AsA treatment, extracellular H₂O₂ levels increased in HSC-4 and DOK cells; however, compared with DOK cells, HSC-4 cells exhibited increased intracellular H₂O₂, Fe2+ levels, intracellular F-actin abnormalities, ATP depletion, and DNA damage. Intracellular oxidative stress variations between the two cell types were attributed to reduced gene expression of antioxidative-related enzymes (glutathione reductases and catalase), and increased expression of aquaporin 3, which is involved in intracellular H₂O₂ transport. High-dose AsA exerted preferential cytotoxicity and sustained inhibitory effects on HSC-4 cell proliferation compared with those on DOK cells. Following a 1-h AsA treatment, HSC-4 cell proliferation was inhibited for up to 72 h, accompanied by cellular senescence phenotypes, such as increased cell size, number of senescence-associated β-galactosidase-positive cells, and senescence-associated secretory phenotype-related gene expression. Overall, high-dose AsA exhibited preferential cytotoxicity toward cancer cells and sustained growth-inhibitory effects through cellular senescence.