Gene therapy for pancreatic cancer using an adenovirus vector encoding soluble flt-1 vascular endothelial growth factor receptor

Introduction: Vascular endothelial growth factor (VEGF) plays an important role in tumor angiogenesis. The soluble form of flt-1 VEGF receptor inhibits VEGF activity in a dominant-negative manner. Aim: This study demonstrated the regional tumor suppression effect of adenovirus-mediated soluble flt-1 in human pancreatic cancer cells. Methodology: The VEGF expression level was examined in nine cell lines. Panc-1 and PK-8 were used as lower- and higher-VEGF-producing cell lines, respectively. The in vitro proliferation of cancer cells infected with adenovirus vectors encoding soluble flt-1 (Adsflt) and control vectors (AdLacZ) was not different. To assess the in vivo tumor growth suppression, cancer cells were inoculated subcutaneously in SCID mice. Adsflt, AdLacZ, or vehicle was injected directly into the tumors. The early process of tumor angiogenesis in a dorsal skinfold chamber was monitored by intravital microscopy. Results: In both Panc-1 cells and PK-8 cells, the tumor growth of the Adsflt-treated group was significantly suppressed. The microvessel density, revealed by CD31 immunostaining, was also significantly lower in the Adsflt-treated group. Apoptosis index was higher in the Adsflt group. Immunofluorescence staining revealed the expression of VEGF not only in cancer cells but also in tumor stromal cells. Wild-type cells and AdLacZ-infected cells prompted strong tumor angiogenesis, whereas Adsflt-infected cells failed to exert such an effect. Conclusion: These results indicate that antiangiogenic gene therapy using soluble flt-1 might be an effective approach for pancreatic cancer treatment.