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Angiogenesis is critical for cancer development and progression. Recent approval of anti-angiogenesis agents for the treatment of colon, breast, lung, and kidney cancer demonstrates the clinical value of this therapeutic modality. We recently evaluated the clinical activity of AG013736, a tyrosine kinase inhibitor directed against the VEGF receptor family, in melanoma. While some patients continue to show response for more than one year, significant interpatient variability in activity was noted. Our lab is focusing on identifying tumor specific factors that contribute to response or resistance to agents that target angiogenesis. We developed an in vitro drug response assay to assess how the tumor stromal background influences the response of tumor derived vascular endothelial cells (TDVECs) to currently approved anti-angiogenesis and cytotoxic agents. Our assay system employs three-dimensional spheroids generated from cancer cell lines as well as TDVECs. TDVECs were fluorescently labeled with DiI to monitor their migration into tumor spheroids, as well as their response to drug treatment. We also incorporated fibroblasts into the co-culture system to account for potential stromal effects on VEC’s that might condition their drug response. Whereas numerous models for angiogenesis exist, few allow for the direct analysis of TDVEC-cancer cell/stromal cell interactions. Thrombospondin-1 (TSP-1) is a natural inhibitor of neovascularization and tumorigenesis in healthy tissue via activation of the CD36 receptor on endothelial cells, which can in turn induce apoptosis. We previously reported that spheroids derived from tumor cell lines expressing low levels of TSP-1 have greater endothelial cell invasion than those with high TSP-1, and that similarly, in clinical melanoma specimens, higher mean levels of TSP-1 correlates with lower microvessel counts per 200x field (Cancer Detect Prev 22:185 1998). The activity of cytotoxic and anti-angiogenic chemotherapeutic agents on vascularized melanoma spheroids were evaluated to determine if TDVEC and melanoma response to agent was influenced by stromal TSP-1 levels. Here we report that spheroids containing increased levels of TSP-1 demonstrated greater VEC response to anti-angiogenic therapy.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA