Growth inhibition and apoptosis-inducing effects of cudraflavone B in human oral cancer cells via MAPK, NF-κB, and SIRT1 signaling pathway

The goal of this study was to investigate the effect and molecular mechanism of cudraflavone B, a prenylated flavonoid isolated from the root bark of Cudrania tricuspidata, against oral squamous cell carcinoma cells. We observed that cudraflavone B inhibited proliferation of these cells in a time- and dose-dependent manner. At 15 µM, cudraflavone B induced cell death via Apoptosis (characterized by the appearance of nuclear morphology) and increased the accumulation of the sub-G1 peak (portion of apoptotic annexin V positive cells). Treatment with cudraflavone B triggered the mitochondrial apoptotic pathway (indicated by induction of the proapoptotic protein p53 and the p21 and p27 effector proteins), downregulation of cell cycle regulatory proteins (e.g., p-Rb, changing Bax/Bcl-2 ratios, cytochrome-c release), and Caspase-3 activation. Cudraflavone B time-dependently activated NF-κB, the MAP kinases p38, and ERK, and induced the expression of SIRT1. SIRT1 Activator, resveratrol, dose-dependently attenuated the growth-inhibitory and apoptosis-inducing effect of cudraflavone B and blocked cudraflavone B-induced regulatory protein expressions in the mitochondrial pathway such as p53, p21, p27, Bax, Caspase-3, and cytochrome-c. Conversely, treatment with SIRT1 Inhibitor sirtinol caused opposite effects. These results demonstrate for the first time that the molecular mechanism underlying the antitumor effect in oral squamous cell carcinoma cells is related to the activation of MAPK/and NF-κB as well as of the SIRT1 pathway. Therefore, cudraflavone B may be a lead for the development of a potential candidate for human oral squamous cell carcinoma cells.