425 Background: Pancreatic cancer is one of the malignant tumors which exhibit resistance to chemotherapy. Gemcitabine-based therapy is a standard for advanced pancreatic cancer though it brings severe side-effect and average median survival is only 6 months. Hence increasing interest has focused on new agent with targeted therapies. Here we investigated the growth-inhibitory and apoptotic effect of triptolide, a diterpenoid triepoxide, and the role of 14-3-3γ expression in the apoptotic pathway induced by triptolide in human pancreatic cancer cells (AsPC-1 and PANC-1). Methods: Cell proliferation was measured by SRB, apoptotic cells were assessed by flow cytometry for Annexin V/PI staining and western blot for cleaved caspase-8, 9, 3 and fluorescent substrate assay for activities of caspase-8, 9, 3. To explore further mechanism of triptolide triggering death receptor pathway, specific siRNA targeted for 14-3-3γ was used to knock down 14-3-3γ expression measured by ELISA. In vivo, AsPC-1 xenografts in the absence or presence of stable down-regulation of 14-3-3γ expression by RNAi were treated with triptolide for 4 weeks and the tumor growth was compared, tumor samples were tested by ELISA and western blot for 14-3-3γ level. Results: Triptolide inhibits the proliferation at extremely low concentrations (12.5-50 nM) and induces apoptosis of pancreatic cancer cells through activating the caspase cascade associated with Bid cleavage. Moreover triptolide inhibited 14-3-3γ expression at dose and time-dependent manner and 14-3-3γ down-regulation sensitized cells to triptolide-induced apoptosis. Likewise, in vivo experiment of AsPC-1 xenografts, stable down-regulation of 14-3-3γ expression by RNAi significantly enhances triptolide-induced apoptosis and tumor growth delay. Conclusions: Triptolide exerted significant growth inhibitory effects and induced apoptosis in vitro and in vivo. Triptolide may have a potential to be an effective agent against pancreatic cancer and its mechanism of action is mediated by the inhibition of 14-3-3γ expression. The role of 14-3-3γ expression involved in resistance to apoptosis pathway make it be a potential therapeutic target in pancreatic cancer.
Role of GSK-3β in triptolide induced apoptosis of pancreatic cancer cells
