Abstract 222: Inhibition of cellular FLICE-inhibitory protein and induction of death receptor 5 expression is a major component of δ-tocotrienol-induced apoptosis in pancreatic cancer cells

Abstract

Abstract Background: Previous pre-clinical studies have demonstrated that δ-tocotrienol, is the most bioactive natural vitamin E compound against pancreatic cancer. δ-Tocotrienol induces growth arrest and apoptosis in several human pancreatic cancer cell lines; however, the underlying mechanism remains unknown. In this study, we evaluated the role of the extrinsic and intrinsic apoptotic signaling pathways in δ-tocotrienol induced apoptosis and investigated the modulation of cellular FLICE-inhibitory protein (c-FLIP) and death receptor 5 (DR5) by δ-tocotrienol and the involvement of c-FLIP down-regulation and DR5 up-regulation in δ-tocotrienol-induced apoptosis. Methods: We examined δ-tocotrienol induced apoptosis in human pancreatic cancer cell lines in vitro and in vivo. We used western blot and immunohistochemistry to determine the expression of DR4, DR5, Caspase 8, Caspase 9, Caspase 3, C-FLIPs and PARP. The effect of combination treatment with TRAIL and δ-tocotrienol was also determined. We examined the cellular effects of DR5 knockdown using small interfering RNA oligonucleotides, and c-FLIP overexpression using cDNA, on δ-tocotrienol-induced apoptosis using various assays. Results: Delta-tocotrienol activated caspase-8 and its downstream caspases but not caspase-9, whereas caspase-8 specific inhibitor abrogated δ-tocotrienol-induced apoptosis indicating that δ-tocotrienol induces caspase-8-dependent apoptosis. c-FLIP was rapidly down-regulated by δ-tocotrienol in all of the tested cell lines. δ-Tocotrienol up-regulated DR4 and DR5 significantly and enhanced tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis. Enforced expression of ectopic c-FLIP, and DR5 knockdown partially abolished δ-tocotrienol-induced apoptosis. δ-Tocotrienol inhibition of pancreatic tumor growth in SCID mice was associated with significant induction of apoptosis, activation of caspase 8, and down-regulation of c-FLIP expression. Conclusion: We conclude that DR5 up-regulation and c-FLIP down-regulation contributes to δ-tocotrienol-induced apoptosis in pancreatic cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 222.