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Tumor growth and metastasis are dependent upon blood supply, which hitherto, is believed to be mainly derived by sprouting of new capillaries from pre-existing blood vessels (angiogenesis). More recently, it has been demonstrated that endothelial progenitor cells (EPCs) are capable of contributing to the formation of tumor blood vessels. However, the contribution of circulating EPCs to the vascular supply of prostate cancer and the progression of the disease remain to be established. To obtain an insight into the development and potential role of EPCs in prostate cancer growth, we used immunofluorescence staining and multi-parameter flow cytometry (FACS) analysis to determine the levels of mature endothelial cells and EPCs in the peripheral blood and prostate sections from normal and transgenic mice with adenocarcinoma of the prostate (TRAMP). Following euthanasia of the animals, peripheral blood was collected and processed for plasma and light density mononuclear cells. Quantitative ELISA was utilized to determine the plasma concentration of various growth factors. Colony forming units in culture (CFU-C) assay was used to evaluate the activity of the hematopoietic stem cells (HSCs) and EPCs. Flow cytometry was used to assess the percentage of mature endothelial cells, progenitor endothelial cells and lineage negative cells expressing c-kit and Sca-1 antigens (Lin-c-kit+Sca-1+). Prostate tissues were also obtained from normal and TRAMP mice, and processed for histology and immunofluorescence. In tumor-bearing mice, there was a 9.2-fold increase in circulating endothelial cells (CECs) as compared to controls (212.6 ± 1.8 x 1000, n = 20 versus 23 ± 0.16 x 1000, n = 20; p < 0.001). About 56% of the CECs in tumor-bearing mice were immature endothelial cells as opposed to 13% in the normal mice. Also, a 27- and 14-fold increase in the percentage and proliferative capacity of peripheral blood HSCs, respectively, and a 10-fold increase in the number of CFU-EPCs were detected in the TRAMP mice when compared to the controls. Furthermore, 30 to 40% of cells in and around the vasculature of prostate tumors expressed antigens characteristic of EPCs as opposed to less than 1% in normal prostate. The increase in immature endothelial cell population of tumor-bearing mice was associated with a 24-fold in plasma G-CSF when compared to controls (4.1 ± 0.8 ng/ml, n = 20 versus 0.17 ± 0.2 ng/ml, n = 20; p < 0.001). However, plasma concentrations of TGF-beta, VEGF, basic FGF, acidic FGF, stem cell factor and Flt-3 ligand were similar in both study groups. These results suggest that a high proportion of endothelial cells in the peripheral blood and tumors of TRAMP mice with aberrant G-CSF are derived from progenitor cells, and that tumor-associated G-CSF may play a role in the induction of tumor blood supply and growth through the mobilization of endothelial cell precursors.

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