Metronomic Chemotherapy Enhances the Efficacy of Antivascular Therapy in Ovarian Cancer

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Abstract
Metronomic chemotherapy is the frequent administration of low doses of chemotherapeutic agents targeting tumor-associated endothelial cells. We examined the efficacy of metronomic taxanes alone and in combination with AEE788—a dual epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) inhibitor—in an orthotopic mouse model of ovarian cancer. Growth-modulating effects of metronomic and maximum tolerated dose (MTD) regimens on overall survival were tested in vivo using both chemotherapy-sensitive (HeyA8 and SKOV3ip1) and chemotherapy-resistant (HeyA8-MDR) models. Treated tumors were stained for microvessel density (CD31), proliferation index (proliferating cell nuclear antigen), and apoptosis (terminal deoxyribonucleotide transferase–mediated nick-end labeling). The cytotoxic effects of MTD and metronomic dosing were tested with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Effects of metronomic regimens on circulating endothelial precursors (CEP) and tumor-specific cell-free DNA levels were assessed. In vivo, metronomic docetaxel resulted in significant reduction of tumor growth in the taxane-sensitive cell lines, whereas metronomic docetaxel plus AEE788 had an additive effect resulting in significant prolongation in survival. Combination therapy was effective even in the taxane-resistant model. Metronomic chemotherapy alone and combined with AEE788 resulted in a decrease in the proliferative index and microvessel density of treated tumors, whereas combination therapy increased the apoptotic index (P < 0.001). In vitro, metronomic taxanes caused endothelial cell toxicity at 10- to 100-fold lower concentrations compared with MTD dosing. Metronomic regimens inhibited mobilization of CEPs (P < 0.05) and led to a decrease in cell-free DNA levels (P < 0.05). Our results suggest that metronomic taxane chemotherapy with dual EGFR and VEGFR inhibition is highly efficacious and should be considered for future clinical trials. [Cancer Res 2007;67(1):281–8]

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