Long-term stimulation of areca nut components results in increased chemoresistance through elevated autophagic activity.

BACKGROUND: We previously demonstrated the autophagy-inducing activity in the crude extract of areca nut (ANE) and its 30-100 kDa fraction (ANE 30-100 K). This study aimed to analyze whether chronic ANE and ANE 30-100 K stimulations lead to higher stress resistance and autophagic activity in oral cells, and whether the resulting autophagic status in stimulated cells correlates with stress resistance.

MATERIALS AND METHODS: Malignant cells from the mouth oral epidermoid carcinoma Meng-1 (OECM-1) and blood (Jurkat T) origins were stimulated with non-cytotoxic ANE and ANE 30-100 K for 3 months. Sensitivity to anticancer drugs of and autophagy status in stimulated cells, analyzed respectively by XTT assay and calculating microtubule-associated protein 1 light chain 3-II LC3-II/β-actin ratios from Western blot, were compared to non-treated cells. Autophagy inhibitors, 3-methyladenine (3-MA) and chloroquine (CQ), were used to assess whether autophagy inhibition interferes the altered chemoresistance.

RESULTS: Areca nut extract-stimulated (ANE-s) and ANE 30-100 K-stimulated (30-100 K-s) OECM-1 and Jurkat T cells generally exhibited higher cisplatin and 5-fluorouracil (5-FU) resistances, compared to non-stimulated cells. Most stimulated cells expressed significantly higher levels of LC3-II and Atg4B proteins. Interestingly, these cells also showed stronger tolerances against hypoxia environment and expressed higher LC3-II levels under glucose-deprived and hypoxia conditions. Finally, both 3-MA and CQ alleviated, albeit to different degrees, the increased chemoresistance in ANE-s and/or 30-100 K-s cells.

CONCLUSIONS: Chronic stimulations of ANE or ANE 30-100 K may increase tolerance of oral cancer and leukemia T cells to anticancer drugs, as well as to glucose deprivation and hypoxia conditions, and cause an elevation of autophagy activity responsible for increased drug resistance.