Tumor cells depend on angiogenesis to survive, proliferate, and metastasize. Head & neck tumors are highly vascularized, invasive, and frequently develop local metastasis. Therefore, disruption of the tumor vascular network might be beneficial for treatment of patients with oral cancer. It is known that vascular endothelial growth factor (VEGF) is a strong inducer of tumor angiogenesis, and that VEGF enhances endothelial cell survival by upregulating the expression of the anti-apoptotic Bcl-2. Inhibition of VEGF signaling with an antibody (e.g. Avastin), or with an inhibitor of one its receptors (e.g. PTK787) results in selective ablation of tumor blood vessels and inhibition of tumor growth. These results demonstrate that the VEGF/Bcl-2 pathway is critical for the maintenance of tumor vasculature. Structure based 30-database searching led to the development of a novel small molecule inhibitor of Bcl-2 (TW-37). TW-37 induces apoptosis of tumor cells in vitro, and, inhibits growth of prostate tumors (PC-3) in vivo. Recent experiments demonstrated that TW-37 also induces apoptosis of neovascular endothelial cells in vitro, but not human dermal fibroblasts or normal prostate cells. However, it is not known if blockade of Bcl-2's function with TW-37 is sufficient to disrupt tumor blood vessels and to inhibit head & neck tumor growth. The broad long-term goals of this research are to understand the effect of therapeutic inhibition of Bcl-2 on tumor angiogenesis and tumor growth. The objectives of this application are to evaluate the effect of TW-37 on angiogenesis, and to evaluate its effect on the microvessel density and growth of oral tumors. We plan to accomplish these objectives by studying the mechanisms involved in the process of TW-37-induced endothelial cell apoptosis, and its effects on capillary sprouting in vitro. The SCID Mouse Model of Human Angiogenesis will be used to evaluate the effect of TW-37 in human blood vessels developed in immunodeficient mice. In addition, we will implant oral tumor cells transduced with Luciferase in SCID mice to analyze the effect of TW-37 on tumor growth, invasion, and metastasis by in vivo bioluminescence. The impact of endothelial cell apoptosis on TW-37's anti-tumor effect will be evaluated by generating tumors vascularized with endothelial cells stably transduced with dominant negative Caspase-9 (resistant to TW-37-induced apoptosis) in SCID mice, or by implanting murine oral tumor cells in Bax mice. The knowledge generated here will enhance our understanding about the role of Bcl-2 in neovascular endothelial cells of tumors, and may provide support for Bcl-2 as a molecular target for further development of drugs for treatment of highly vascularized tumors. This work may demonstrate that small molecule inhibitors of Bcl-2 represent a novel class of drugs that induce tumor cell apoptosis and are anti-angiogenic, two distinct and perhaps synergistic anti-tumor effects.
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