Circulating endothelial cells in preclinical models of cancer

A49

Circulating endothelial cells (CEC) are detected at elevated concentrations in cancer patients. Endothelial cells contribute to tumor angiogenesis by incorporation into newly forming blood vessels to support tumor growth and metastasis. A set of flow cytometry reagents for murine models has been established. The enumerated mouse CEC, demonstrate the following phenotype CD31⁺/CD34⁺/CD45^- and nucleated. A positive relationship between CEC concentration and tumor volume was determined for 11/12 murine models including the PC3 xenograft model of prostate cancer and the HT1080 sarcoma xenograft model. CEC concentrations have been characterized in normal, tumor bearing and tumor-bearing compound-treated mice using HT1080 (human fibrosarcoma), B16 (murine melanoma) and bEND.3 (murine hemangioma) tumor models and indicate that an elevated number of CEC are detected in tumor-bearing mice when compared to normal mice.We are conducting systematic CEC analysis in preclinical models of cancer to study changes in this biomarker in relationship to tumor type, tumor burden, compound dose, dose regimen, and class of compound. Preliminary data from tumor growth inhibition studies using angiogenisis inhibitors, including TSP mimetic peptides and tyrosine kinase inhibitors, demonstrate a decrease in the number of CEC detected at the treatment endpoints in drug-treated animals vs. vehicle-treated controls. Time-course analyses of these changes in CEC concentration have been performed in several models including HT-1080 and B16. Further, having shown that CEC number is elevated in tumor bearing mice and reduced in tumor bearing mice treated with anti-angiogenic agents, experiments to explore the characteristics of the CEC, specifically, the activation status demonstrated by co-expression of CD105 in the CEC and the apoptotic status of the cells by measuring the annexin V positivity has been explored. Using the HT1080 model, correlations between CEC concentration, activation status and apoptotic state with tumor volume has been observed. CEC will be monitored in patients undergoing clinical trials with our angiogenesis inhibitors.