Our studies have focused on the angiogenic factor PD-ECGF (platelet-derived endothelial cell growth factor), one of several polypeptide factors that are produced by tumor epithelial and stromal cells and that promote tumor angiogenic activity. Sequencing of the of human PD-ECGF cDNA revealed it to be identical to human thymidine phosphorylase (TP), an enzyme which catalyzes the conversion of thymidine to thymine and 2-deoxyribose-1-phosphate (dR-1-P). Tumor xenografts grew more rapidly and were more highly vascularized when derived from cells that were transfected with TP, and there are extensive clinical data correlating elevated TP expression in human solid tumors with increased microvessel density, increased tumor invasiveness, and poor patient prognosis. Unlike VEGF and other cytokines, TP is not directly angiogenic, rather its effects are due to its catalytic activity. In the previous grant period, we defined the mechanisms regulating TP transcription in tumors and in monocytes, obtained definitive evidence that the angiogenic actions of TP are mediated by 2-deoxyribose (2dR) which is formed intracellularty from dR-1-P and then released from cells expressing TP, showed that 2dR is a chemotactic factor for human endothelial cells (HUVEC), provided the first data illustrating an effect of 2dR on integrin-related signaling pathways in HUVEC, and identified and synthesized an inhibitor of TP activity and of TP-induced HUVEC migration. We propose to extend these studies in the next grant period, specifically to: 1) determine if 2dR's actions are mediated by its activation of the VEGF receptor-2 and/or VEGF receptor-3;2) test the hypothesis that microvascular endothelial cells (EC), and lymphatic EC in particular, will be highly responsive to 2dR;3) determine if 2dR acts on inside/out and/or outside/in integrin signaling pathways;4) determine if 2dR protects EC from apoptosis;5) determine if there is a specific 2dR receptor in EC, and 6) use a human lung cancer heterotransplant mouse model in which tumors contain human EC to evaluate the in vivo anti- angiogenic and anti-tumor activities of agents targeting TP, alone and in combination with a VEGF inhibitor. The long term objectives of this project are to define the molecular mechanisms regulating the anti- angiogenic actions of TP, and to determine whether targeting TP-mediated angiogenic pathways is a viable therapeutic approach to treat cancer. This information could lead to new drug treatments for cancer.
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