Metronomic chemotherapy suppresses growth of primary tumors and established metastases. However, its effect on metastatic progression is essentially unknown. We report the treatment of a metastatically competent model of pancreatic cancer with metronomic gemcitabine and sunitinib. Mice with orthotopic, red fluorescent protein-expressing, pancreatic cancer tumorgrafts were treated with gemcitabine on a metronomic (1 mg/kg daily, METG) or maximum tolerated dose (150 mg/kg twice weekly, MTDG) schedule with or without sunitinib (SU). Rates of primary tumor growth, metastasis, ascites, and survival were calculated. Gemcitabine at a daily dose of 2 mg or greater led to toxicity within 1 month in mice without tumors but METG at 1 mg/kg/d was well tolerated. Mice with pancreatic cancer tumorgrafts died with metastatic disease at a median of 25 days. METG/SU significantly prolonged median overall survival (44 days) compared with control or either regimen alone (P < 0.05). Primary tumor growth was inhibited by METG/SU (P = 0.03) but neither METG nor sunitinib alone. In contrast, treatment with METG suppressed metastasis at multiple sites, an effect enhanced by sunitinib. MTDG with or without sunitinib had the most favorable effect on primary tumor growth and survival, but its antimetastatic efficacy was similar to that of METG/SU. von Willebrand factor expression was inhibited by METG. Antimetastatic activity approaching that of MTDG is achieved with a total dose reduced 42 times using METG and is further enhanced by sunitinib. Our results suggest the potential of this therapeutic paradigm against pancreatic cancer in the adjuvant and maintenance settings.
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