Purpose: Metronomic chemotherapy regimens have shown anti-tumor activity by anti-angiogenic mechanisms, however, the efficacy of metronomic topotecan in ovarian cancer is not known and the focus of the current study.
Experimental Design: In vivo dose-finding and therapy experiments with oral metronomic topotecan were performed in an orthotopic model of advanced ovarian cancer. Tumor vascularity (MVD: CD31), proliferation (PCNA), and apoptosis (TUNEL) were examined among treatment arms. In vitro experiments including MTT and western blot analysis were performed to identify specific anti-angiogenic mechanisms of topotecan.
Results: Compared to controls, metronomic (0.5, 1.0 and 1.5 mg/kg; daily) and maximum tolerated therapy (MTD; 7.5 and 15 mg/kg; weekly) dosing regimens reduced tumor growth in dose-finding experiments, but significant morbidity and mortality was observed with higher doses. Metronomic and MTD topotecan therapy significantly reduced tumor growth in both HeyA8 and SKOV3ip1 models: 41-74% (metronomic), and 64-86% (MTD dosing) (p<0.05 for both regiments compared to controls). Compared to controls, the greatest reduction in tumor MVD was noted with metronomic dosing (32-33%; p<0.01). Tumor cell proliferation was reduced (p<0.001 vs. controls) and apoptosis increased in all treatment arms (p<0.01 vs. controls) for both dosing regimens. Endothelial cells demonstrated a significantly higher sensitivity to topotecan using metronomic dosing versus MTD in vitro. Pro-angiogenic regulators Hif-1α and VEGF levels were reduced in vitro (HeyA8 and SKOV3ip1) with topotecan independent of proteasome degradation and topoisomerase I.
Conclusion: Metronomic topotecan may be a novel therapeutic strategy for ovarian carcinoma with significant anti-tumor activity and target modulation of key pro-angiogenic mediators.
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