Induction of apoptosis by parthenolide in human oral cancer cell lines and tumor xenografts

Objectives: Parthenolide (PTL), a representative sesquiterpene lactone that is responsible for medicinal properties of the feverfew, is known to modulate diverse intracellular signaling pathways, thereby exerting the tumor growth-inhibitory effects. In this study, authors attempted to examine the pro-apoptotic effects and possible biochemical mechanisms of PTL in human oral cancer cell lines and tumor xenografts. Material and methods: The apoptotic effects and related molecular mechanisms of PTL on oral cancer were evaluated using cell viability assay, MTS assay, DAPI staining, western blot analysis, reverse transcriptase-polymerase chain reaction, small interfering RNA transfection and nude mouse xenograft assay. Results: PTL treatment increased the cleavage of caspase-3 and poly (ADP-ribose) polymerase (PARP), and the nuclear fragmentation in a concentration-or time-dependent manner. PTL treatment increased Bim protein expression by enhancing the Bim mRNA expression as well as stabilizing Bim protein level. PTL treatment also induced the translocation of cytosolic Bim into the mitochondria and, more importantly, PTL-induced apoptosis was significantly attenuated, when the Bim expression was knockdown by siRNA transfection. PTL treatment also induced death receptor 5 (DR5) protein expression and this event was closely correlated with an increase in the cleavage of caspase-8 and formation of truncation of Bid (t-Bid). Finally, PTL shrunk tumor size and volume resulting from apoptotic cell death by increasing Bim and DR5 whereas there were no abnormal histopathological findings in normal organs. Conclusion: This study proposes that PTL is a strong apoptotic inducer that deserves the further investigations for potential chemotherapeutic agent of human oral cancers. (C) 2015 Elsevier Ltd. All rights reserved.