Antiangiogenic potency of various chemotherapeutic drugs for metronomic chemotherapy

From previous preclinical findings continuous low dose (metronomic) chemotherapy is thought to inhibit tumor angiogenesis. This suggests that activated endothelial cells may be more sensitive to chemotherapeutic drugs than tumor cells. Therefore, we assessed the IC50 for several relevant chemotherapeutic drugs in different endothelial and tumor cell lines to identify optimal compounds to be used for metronomic therapy in a murine renal cell carcinoma model. Adriamycin, idarubicin, 5-fluorouracil, paclitaxel and etoposide were chosen for our studies because of their oral availability in patients or previous reports on metronomic potential. IC50s were determined by BrdU cell growth assay after short time as well as long term exposure of the following cell lines: human endothelial cells (HdmVEC/HUVEC), human breast cancer (Mcf-7), melanoma (Skmel), liver cancer (Huh7/Alexander), lung cancer (A549/LXFL), colon cancer (Dld) and murine renal cell carcinoma (RENCA). In addition, FACS analysis was performed to determine the effect on cell cycle. In vivo, doses of 2x12 mg/kg, 2x1.2 mg/kg and 10x0.24 mg/kg adriamycin were applied to 12 RENCA mice each and antitumor as well as antiangiogenic effects were assessed 21 days after tumor cell application. Independent of the exposure time, all chemotherapeutic drugs were more active against the endothelial cell lines. IC50s were significantly lower in endothelial cells (4.02E-06 to 6.16E-14 M) as compared to tumor cells (7.44E-02 to 1.9E-11 M). Cell cycle analysis of all chemotherapeutic drugs revealed a G1-arrest in endothelial cells. Adriamycin applied in metronomic doses of 10x0.24 mg/kg showed significant antiangiogenic activity whereas, in contrast, the application of 2x12 mg/kg significantly increased the vessel density in primary tumors. In summary, all chemotherapeutic agents were more active against endothelial cells in comparison to tumor cells. The hypothesis of an antiangiogenic active metronomic therapy could be confirmed in vivo by the use of adriamycin in RENCA.