Background and Aim: Pancreatic ductal adenocarcinoma (PDAC) is an almost uniformly lethal disease in humans. Previously, we have reported a genetically engineered mouse PDAC progression model which has pancreatic-specific transforming growth factor-beta receptor type II knockout in the context of Kras activation (Ijichi H, et al 2006). This model shows PDAC with 100% penetrance and recapitulates the signature of human PDAC well. Using this model, we explored novel treatment for PDAC.
Materials and Methods: At first, to investigate whether the mice model is suitable for the drug screening, the mice were treated with gemcitabine (12.5 mg/kg) by intraperitoneal (i.p.) injection or S-1 (8.4 mg/kg) per oral, which are the standard drug for human PDAC. To the next, for single agent treatment, mice were treated orally 6 times a week with vehicle (0.5 % carboxymethyl cellulose, CMC), sunitinib (40 mg/kg), and axitinib (30mg/kg), both of which are multikinase inhibitors targeting vascular endothelial growth factor receptor (VEGFR) and platelet derived growth factor receptor (PDGFR) from the 3 weeks of age. For combined agent experiment, mice were treated orally with vehicle (0.5 % CMC) or axitinib from the 3 weeks of age and also treated with saline or gemcitabine, i.p. twice a week from the 4 weeks of age. Treatment continued until 8 weeks of age. Moreover, for the survival analysis, the drug treatment was continued until the mice became distressed according to the same schedule stated above. In vivo anti-tumor effect and survival time were assessed. Immunostaining of tumor tissue for caspase 3, Ki67, CD31, F4/80 and VEGF was performed. Azan staining also performed for the assessment of fibrosis in the tumor.
Results: Gemcitabine and S-1 showed antiproliferative effect and prolonged overall survival of these mice compared to control, as well as human cases. Median survival time of single use of axtinib and sunitinib group was significantly longer (p <0.01) than that of control group. Axitinib and sunitinib group showed significantly stronger anti-tumor effect in vivo (p <0.01). In the combined treatment experiment, gemcitabine plus axitinib-treated group showed statistically significant longer survival and more anti-tumor effect than that of gemcitabine or axtinib alone-treated group (p <0.01). Axitinib and sunitinib group showed significantly higher caspase 3 stainng and lower Ki67 staining than that of control (p <0.01). Microvessel density (CD 31 staining) of axitinib and sunitinib group was significantly lower than that of control (p <0.01). F4/80 staining was significantly lower in axitinib and sunitinib-treated group than that of control (p <0.05). VEGF expression of axitinib and sunitinib group was significantly lower than that of control a (p <0.001). Azan staining showed significantly lower fibrosis in axitinib and sunitinib-treated group compared to control (p <0.01).
Conclusion: Targeting not only cancer cells but also tumor microenvironment, such as angiogenesis, infiltration of immune cells, and fibrosis, with the use of multikinase inhibitors in addition to gemcitabine, may be a promising therapeutics for PDAC.