Abstract
Pancreatic cancer is often resistant to chemotherapy. We previously showed the efficacy of combination treatment using gemcitabine and nafamostat mesilate (FUT-175) for patients with unresectable pancreatic cancer. However, the mechanisms that affect the sensitivity of FUT-175 are not fully understood. The purpose of the present study was to clarify the mechanism of the sensitivity to FUT-175, with a focus on the activity of glycogen synthase kinase-3β (GSK-3β). In vitro, we assessed sensitivity to FUT-175 in human pancreatic cancer cell lines (PANC-1 and MIAPaCa-2) and difference of signaling in these cells by cell proliferation assay, Western blot analysis and microarray. Next, we assessed cell viability, apoptotic signal and nuclear factor-kappa B (NF-κB) activity in response to treatment with FUT-175 alone and in combination with GSK-3 inhibitor or protein phosphatase 2A (PP2A) by cell proliferation assay, Western blot analysis and enzyme-linked immunosorbent assay. Phosphorylated GSK-3β level was significantly higher in MIAPaCa-2 (high sensitivity cell) than in PANC-1 (low sensitivity cell). Cell viability and NF-κB activity were significantly decreased by addition of GSK-3 inhibitor to FUT-175, and levels of cleaved caspase-8 were increased by inhibition of GSK-3. PP2A inhibitor increased the levels of phosphorylated GSK-3β and sensitized both cell lines to FUT-175 as measured by cell viability and apoptotic signal. The results indicate that GSK-3β activity plays a key role in the antitumor effect of FUT-175 in pancreatic cancer cells, and regulation of GSK-3β by PP2A inhibition could be a novel therapeutic approach for pancreatic cancer.