Growth inhibitory effect of xanthorrhizol is associated with the induction of apoptosis and up-regulation of non-steroidal anti-inflammatory drug-activated gene expression in hct116 human colon cancer cells

478 Xanthorrhizol is a sesquiterpenoid isolated from the rhizome of Curcuma xanthorrhiza (Zingiberaceae). In our previous studies, xanthorrhizol has been exhibited with several biological activities including the suppressions of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expression, inhibition of cancer cell growth, and anti-metastatic effect in in vivo animal model. However, the exact mechanisms of the growth inhibitory effects of cancer cells were not fully elucidated yet. In the present study, we investigated the growth inhibitory effect of xanthorrhizol on cancer cells in points of cell cycle regulation and events of apoptosis in HCT116 human colon cancer cells. Primarily, treatment of xanthorrhizol exhibited the antiproliferative effects of HCT116 cells in a concentration-dependent manner. Flow cytometric analysis indicated that xanthorrhizol arrested cell cycle progression at G0/G1 and G2/M phase, and induced the increase of sub-G1 peaks in concentration- and time-dependent manners. Induction of cell cycle arrest was highly correlated with the downregulation of cyclins and cyclin dependent kinases such as cyclin A, cyclin B1, CDK2, CDK4 and also the induction of cyclin kinase inhibitors p21 and p27. The increase of sub-G1 peaks by xanthorrhizol was closely related to the induction of apoptosis, which was evidenced by the induction of DNA fragmentation, truncation of bid, inhibition of bcl-XL expression, increase of the release of cytochrome c from mitochondria, activation of caspase-3, -8 and -9, and cleavage of poly-(ADP-ribose) polymerase. Further study revealed that xanthorrhizol increased the expression and promoter activity of the pro-apoptotic protein non-steroidal anti-inflammatory activated gene (NAG-1), suggesting up-regulation of NAG-1 might in part be involved in the induction of apoptosis by xanthorrhizol. These findings provide one plausible mechanism in the growth inhibitory activity of xanthorrhizol against cancer cells by arresting cell cycle and induction of apoptosis, and thus it might be a potential lead candidate in the preventive and/or therapeutic point of human colon cancers.