Bardoxolone Methyl Induces Partially Caspase-dependent Apoptosis of Oral Squamous Cell Carcinoma Cells

BACKGROUND/AIM: Oral squamous cell carcinoma (OSCC) is an aggressive head and neck malignancy with frequent recurrence and poor outcomes in advanced disease. Bardoxolone methyl (CDDO-Me) is a synthetic triterpenoid with reported anticancer activity in several malignancies; however, its therapeutic effects in OSCC remain insufficiently defined. The present study investigated the effects of CDDO-Me on cell viability, apoptosis and autophagy-related protein expression in OSCC cells. MATERIALS AND METHODS: Human OSCC cell lines, OC2 and OECM-1, were treated with increasing concentrations of CDDO-Me for 24 h. Cell viability was assessed using the MTT assay, apoptosis was examined using Muse® Annexin V & Dead Cell Kit and flow cytometry, and the expression of cleaved caspase-3, cleaved poly(ADP-ribose) polymerase, microtubule-associated protein 1 light chain 3 beta (LC3B), and sequestosome 1 (p62/SQSTM1) was analyzed by western blotting. RESULTS: CDDO-Me reduced cell viability of both OC2 and OECM-1 cells in a concentration-dependent manner, with OC2 cells showing greater sensitivity. Flow-cytometric analysis demonstrated that CDDO-Me increased apoptotic cell populations in both cell lines. Nonlinear regression analysis yielded estimated half-maximal inhibitory concentrations of approximately 490 nM for OC2 cells and 684 nM for OECM-1 cells. Moreover, co-treatment with the pan-caspase inhibitor Z-VAD-FMK partially restored cell viability and reduced CDDO-Me-induced apoptosis, indicating that the cytotoxic effects of CDDO-Me were at least partially caspase dependent. Western blotting further showed increased expression of cleaved caspase-3 in both cell lines and more prominent induction of cleaved poly(ADP-ribose) polymerase in OC2 cells. In addition, CDDO-Me increased the LC3B-II/LC3B-I ratio and p62 accumulation, indicating altered expression of autophagy-related proteins. CONCLUSION: These findings suggest that CDDO-Me exerts antitumor effects in OSCC cells by suppressing cell viability and inducing apoptosis, accompanied by changes in autophagy-related proteins.