Different combination schedules of gemcitabine with endostar affect antitumor efficacy

Antiangiogenic drugs inhibit tumor growth by decreasing blood supply and causing transient normalization of the tumor vasculature, thereby improving the delivery of systemic chemotherapy. A higher dose of antiangiogenic drugs may lead to a more marked decrease in intratumoral blood flow but may concomitantly cause a decrease in delivery of chemotherapeutic agents. The purpose of this study was to define an optimal schedule for the combination of gemcitabine with a recombinant endostatin, endostar. We evaluated the antitumor effects with different schedules of gemcitabine combined with or without endostar. The changes of vascular endothelial growth factor (VEGF) levels in tumor extracts and sera after gemcitabine treatment were examined. Endostar was also assessed for its abilities to inhibit the increase in VEGF levels. Apoptotic cells and microvessel density within tumor tissue were also examined. Endostar administered simultaneously with or following gemcitabine improved the inhibition of tumor growth, compared with gemcitabine alone. VEGF levels decreased immediately after gemcitabine treatment, but increased in the following several days. Endostar administered simultaneously with or following gemcitabine could inhibit the increase in VEGF levels, thereby cause a decreased vessel density and an increased apoptosis in tumor tissue. Our finding suggested that endostar given simultaneously with or following gemcitabine might be optimal to enhance the antitumor effect.