Angiotensin II type 2 receptor signaling significantly attenuates growth of murine pancreatic carcinoma grafts in syngeneic mice

Background: Pancreatic cancer is one of the most aggressive human malignancies, with a very poor prognosis. To evaluate the effect of angiotensin II (Ang II) type 2 receptor (AT(2)) expression in the host's body on the growth of pancreatic carcinoma, we have investigated the growth of mouse pancreatic ductal carcinoma grafts in syngeneic wild type and AT(2) receptor-deficient (AT(2)-KO) mice. Methods: The role of AT(2) receptor-signaling in stromal cells on the growth of murine pancreatic carcinoma cells (PAN02) was studied using various in vitro and in vivo assays. In vivo cell proliferation, apoptosis, and vasculature in tumors were monitored by Ki-67 immunostaining, TUNEL assay, and von Willebrand factor immunostaining, respectively. In the co-culture study, cell proliferation was measured by MTT cell viability assay. All the data were analyzed using t-test and data were treated as significant when p < 0.05. Results: Our results show that the growth of subcutaneously transplanted syngeneic xenografts of PAN02 cells, mouse pancreatic ductal carcinoma cells derived from the C57/BL6 strain, was significantly faster in AT(2)-KO mice compared to control wild type mice. Immunohistochemical analysis of tumor tissue revealed significantly more Ki-67 positive cells in xenografts grown in AT(2)-KO mice than in wild type mice. The index of apoptosis is slightly higher in wild type mice than in AT(2)-KO mice as evaluated by TUNEL assay. Tumor vasculature number was significantly higher in AT(2)-KO mice than in wild type mice. In vitro co-culture studies revealed that the growth of PAN02 cells was significantly decreased when grown with AT(2) receptor gene transfected wild type and AT(2)-KO mouse-derived fibroblasts. Faster tumor growth in AT(2)-KO mice may be associated with higher VEGF production in stromal cells. Conclusions: These results suggest that Ang II regulates the growth of pancreatic carcinoma cells through modulating functions of host stromal cells; Moreover, Ang II AT(2) receptor signaling is a negative regulator in the growth of pancreatic carcinoma cells. These findings indicate that the AT(2) receptor in stromal fibroblasts is a potentially important target for chemotherapy for pancreatic cancer.