Abstract 476: The effect of combination of oncolytic herpes virus HF10 with bevacizumab in the treatment of human breast carcinoma xenograft

Background: Breast cancer is the most common cancer in females, and the second leading cause of cancer death in women. A more specific and effective multimodal therapy is thus urgently needed. Oncolytic HSVs are good candidates because of broad host range and tumor selectivity. HF10 is a spontaneous mutant strain of HSV-1 and its replication ability would be better than other oncolytic viruses which were genetically modified. Studies using oncolytic HSV have shown enhanced angiogenesis and increased micro-vascular density after the HSV-1 treatment. Anti-angiogenic adjuvant treatment is therefore expected to improve oncolytic HSV-1 treatment results. Bevacizumab, a monoclonal antibody against VEGFA, is generally accepted as a good treatment option because it inhibits angiogenesis and slows tumor growth. In our study, combination of HF10 and Bevacizumab is evaluated in the treatment of human breast carcinoma xenograft model. Here we present our preliminary data. Method: The VEGFA gene transcription and protein expression was measured in human breast cancer cell line (MCF-7, T47D and MDA-MB-231) by RT-PCR, Western blot and ELISA. The MTT analysis was performed to evaluate the efficiency of combination therapy in vitro. The effect of various doses of Bevacizumab on viral replication was evaluated by PCR and tittering of the virus replicating. The in vivo study is designed to consist of 192 female BALB/c nude mice that will be inoculated with 10ˆ7 cells into the mammary fat pad. Control group (N=32) will receive no treatment. HF10 group will receive 10ˆ8 pfu of HF10 intratumorally. Bevacizumab group (N=32) will receive 5mg/kg Bevacizumab intra-peritoneally twice a week. Combination group (N=96) will receive both HF10 (10ˆ8 pfu) and Bevacizumab (5mg/kg). Tumor volume will be measured twice a week. Two days after the last dose of the treatment, tumors will be collected and analyzed histopathologically, including CD31 staining for microvascular density, TUNEL assay for apoptosis, and immunostaining for HSV antigen. Results: Among the three candidate cell line, MDA-MB-231 has the highest level of VEGFA expression, while T47D has the lowest VEGFA expression. The in vitro cytotoxic effect of HF10 is both time and dose dependent. Combination therapy did not affect the viral replication in vitro. Our in vivo study is ongoing, and we expect the combination strategy would increase viral distribution, decrease angiogenesis, and enhance the antitumor effects. Conclusion: I