Different responses of circulating endothelial progenitor cells and VEGF-plasma concentrations to low-dose metronomic and conventional chemotherapy

Abstract

14053 Background: Endothelial progenitor cells (EPCs) may participate in tumor angiogenesis by providing cellular supply. This is a study that compares the effects of two conventional combination chemotherapy schedules to low-dose metronomic trofosfamide (an oral derivate of cyclophosphamide), using the number of circulating EPCs and vascular endothelial growth factor (VEGF) plasma levels in cancer patients. Methods: We measured circulating EPC and VEGF levels in 24 patients that received conventional chemotherapy for either breast cancer in an adjuvant setting or malignant lymphoma, and in 18 patients receiving metronomic chemotherapy with or without celecoxib for advanced cancer. Blood samples were obtained three times: before starting chemotherapy, 10 and 21 days after starting chemotherapy. Peripheral blood EPC levels were determined by fluorescence flow cytometry and defined by CD34- and VEGF-R2-positivity. VEGF plasma concentration was determined by ELISA. Results: The number of circulating EPCs showed a two-fold increase 21 days after conventional chemotherapy but a significant decrease under metronomic chemotherapy. VEGF-plasma-concentrations remained stable in patients under metronomic chemotherapy but significantly increased under conventional chemotherapy.This increase in VEGF plasma levels occurred even in patients that received chemotherapy in an adjuvant setting in supposed absence of tumor. Conclusions: Low-dose metronomic trofosfamide significantly decreased circulating EPCs while conventional chemotherapy increased both the number of circulating EPC and VEGF-concentrations. The increase of VEGF even in an adjuvant setting of chemotherapy without the presence of a tumor may be caused by chemotherapy-induced endothelial cell destruction. Metronomic scheduling of certain cytotoxic drugs may thus prevent tumor progression by inhibiting both tumor cell proliferation and angiogenesis. No significant financial relationships to disclose.