Enhancement of Cytotoxicity of Three Apoptosis-inducing Agents Against Human Oral Squamous Cell Carcinoma Cell Line by Benzoxazinotropone.

Tumor-specificity (TS) and anti-inflammatory activity of benzo[b]cyclohept[e][1,4]oxazin-6(11H)-one, generally known as benzoxazinotropone (BOT), have been reported. In order to find a new biological activity, the combination effect of BOT and three apoptosis-inducing agents was investigated. Cytotoxicity against four human oral squamous cell carcinoma (OSCC) cell lines and five human oral normal cells (gingival fibroblasts, periodontal ligament fibroblasts, pulp cells, oral keratinocytes and primary gingival epithelial cells) was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. TS was evaluated by the ratio of the mean 50% cytotoxic concentration (CC50) against normal oral cells to the one against OSCC cell lines. Synergy was evaluated by CompuSyn software program. Expression of cleaved forms of poly ADP-ribose polymerase and caspsase-3 was evaluated by western blot analysis. BOT induced activation of caspase 3, suggesting the apoptosis induction in HSC-2 OSCC cells. BOT enhanced the cytotoxicity of doxorubicin (DXR) additively and that of curcumin and resveratrol synergistically. On the other hand, BOT did not enhance, but rather inhibit the cytotoxicity of DXR against normal keratinocytes. The present study suggests that BOT may enhance the anti-tumor activity of apoptosis-inducing agents, while reducing its cytotoxicity against normal cells.