Benzyl isothiocyanate (BITC) triggers mitochondria-mediated apoptotic machinery in human cisplatin-resistant oral cancer CAR cells

Benzyl isothiocyanate (BITC), a component of dietary food, possesses a powerful anticancer activity. Previous studies have shown that BITC produces a large number of intracellular reactive oxygen species (ROS) and increases intracellular Ca(2+) release from endoplasmic reticulum (ER), leading to the activation of the apoptotic mechanism in tumor cells. However, there is not much known regarding the inhibitory effect of BITC on cisplatin-resistant oral cancer cells. The purpose of this study was to examine the anticancer effect and molecular mechanism of BITC on human cisplatin-resistant oral cancer CAR cells. Our results demonstrated that BITC significantly reduced cell viability of CAR cells in a concentration- and time-dependent manner. BITC was found to cause apoptotic cell shrinkage and DNA fragmentation by morphologic observation and TUNEL/DAPI staining. Pretreatment of cells with a specific inhibitor of pan-caspase significantly reduced cell death caused by BITC. Colorimetric assay analyses also showed that the activities of caspase-3 and caspase-9 were elevated in BITC-treated CAR cells. An increase in ROS production and loss of mitochondria membrane potential (ΔΨm) occurred due to BITC exposure and was observed via flow cytometric analysis. Western blotting analyses demonstrated that the protein levels of Bax, Bad, cytochrome c, and cleaved caspase-3 were up-regulated, while those of Bcl-2, Bcl-xL and pro-caspase-9 were down-regulated in CAR cells after BITC challenge. In sum, the mitochondria-dependent pathway might contribute to BITC-induced apoptosis in human cisplatin-resistant oral cancer CAR cells.