Mouse pancreatic cancer cells from Kras^G12D/p53-/- transgenic mice overexpress Heat shock protein 70 (HSP70), and its inhibition by triptolide decreases cell viability.

LB-190

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in the United States; its 5-year survival rate is less than 5%. To study pancreatic cancer biology and efficacy of drugs against it, mouse spontaneous tumor models are necessary.
 Genetic analysis of PDAC patients showed that specific disease-associated mutations correlate with cancer progression. Kras gene activation as well as the loss of tumor suppressor gene p53 are reportedly associated with pancreatic intraepithelial neoplasias (PanIN). We have previously developed Kras^G12D/p53-/- transgenic mice (Cancer Research 67 (17) 2007). We have also shown that HSP70 inhibitors triptolide (a diterpenoidtriepoxide) and quercetin (a flavonoid compound) decrease the viability of human pancreatic cancer cells in vitro and inhibit tumor growth in vivo (Cancer Research 67(2) and 67 (19) 2007).
 AIM: In this study, we isolated tumor cells (PR53.63) from transgenic mice, and evaluated the efficacy of triptolide on mouse pancreatic cancer cells.
 METHODS: Expression levels of heat shock protein 70 (HSP70) in PR53.63 in vitro and in vivo were examined by western blot, real-time PCR, and histochemical analysis using a confocal microscopy. 2) The efficacies of HSP70 inhibitors, such as triptolide and quercetin, on PR53.63 cell viability in vitro were examined and compared to human pancreatic cell lines. 3) PR53.63 cells were treated with triptolide or quercetin, and their effect on HSP70 levels was examined.
 RESULTS: PR53.63 cells expressed HSP70 significantly more than normal pancreatic duct cells. PR53.63 cells administered subcutaneously in the flank and orthotopically in the pancreas in vivo expressed HSP70 at levels which were significantly higher than other normal organs such as lung, kidney, and liver. Inhibiting HSP70 expression by triptolide and quercetin decreased the viability of PR53.63. The cytotoxicity of triptolide and quercetin to PR53.63 cells is similar to that observed in human pancreatic cancer cell, Panc-1. Treatment with triptolide in vitro significantly decreased HSP70 levels in a dose-dependent manner.
 CONCLUSION: This study suggested that the HSP70 inhibitor, triptolide, decreases viability and HSP70 expression not only in human cancer cell lines but also in mouse pancreatic cancer cells isolated from the Kras^G12D/p53-/- transgenic mice. This spontaneous mouse pancreatic cancer model is very useful for studying cancer biology and developing new pancreatic cancer therapies.