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Earlier we have shown that human endostatin having a point mutation at position 125 (P125A-endostatin) improves endothelial cell binding and antiangiogenic activity. These studies also showed that the efficacy of antiangiogenic therapy was dependent on continuous delivery of P125A-endostatin over long periods of time. Therefore, we investigated the sustained expression of P125A-endostatin using adeno-associated viral (AAV) vectors in athymic mouse model systems bearing human ovarian cancer xenografts. AAV vector was efficient in the expression of the transgene when delivered either by intramuscular or intraperitoneal route. Dose dependent expression of P125A-endostatin was observed for more than two months. In the initial experiments subcutaneous growth of ovarian cancer was evaluated. Growth of established tumors was inhibited by 70 % by a single injection of rAAV-P125Aendo. Residual tumors from mice showed decreased vascularity and distinct changes in the architecture of blood vessels. Subsequently, we investigated the effect of AAV mediated gene delivery of P125A-endostatin (rAAV-P125Aendo) in an orthotopic model of ovarian cancer. Human ovarian cancer cells were genetically modified by ‘Sleeping-beauty’ mediated delivery of DsRed fluorescent protein. Transplantation of the tumors expressing DsRed protein enabled in vivo imaging of tumor growth and metastasis inside the peritoneum. Intraperitoneal injection of human ovarian cancer cells expressing DsRed into athymic mice resulted in colonization of ovaries and peritoneal metastasis. Intramuscular injection of 1 x 109 virus particles showed significant reduction in the intraperitoneal growth of ovarian cancer. When compared to the rAAV-LacZ treated control groups, rAAV-P125Aendo injected mice showed a 50 % reduction in total tumor burden, which was statistically significant. About 40 % of the treated animals remained tumor-free over a period of 114 days. Noninvasive methods of imaging during the course of the experiment and internal imaging at the time of necropsy were used to determine the efficacy of rAAV-P125Aendo gene therapy to inhibit orthotopic growth of ovarian cancer. These studies suggest that AAV-mediated gene therapy of P125A-endostatin is useful in inhibiting intraperitoneal growth of ovarian cancer. Future studies using chemotherapy and antiangiogenic gene therapy will determine the potential clinical utility of this approach.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]