Synergistic Antitumor Effects of Endostar in Combination with Oxaliplatin via Inhibition of HIF and CXCR4 in the Colorectal Cell Line SW1116

Combination treatment with endostar, a novel modified endostatin, and cytotoxic chemotherapies showed a survival benefit in Chinese clinical trials. However, the exact mechanism for this synergism remains unclear. In this study, we report for the first time that the chemokine receptor CXCR4 and the hypoxia-inducible transcription factors (HIF)-1α and HIF-2α are involved in these synergistic antitumor effects in human colorectal cancer SW1116 cells in vitro when endostar treatment is combined with the cytotoxic drug oxaliplatin. Under normoxia, we demonstrate that endostar and oxaliplatin treatments synergize to inhibit SW1116 cell proliferation, Matrigel adhesion and invasion by reduction of CXCR4 expression. Consistently, these antitumor abilities of endostar and oxaliplatin were markedly reduced by silencing of CXCR4 in SW1116 cells. Under low oxygen conditions (hypoxia, 1% oxygen), enhanced proliferation of SW1116 cells exposed to oxaliplatin was observed due to the emergence of drug resistance. Strikingly, endostar overcame oxaliplatin-resistance, most likely as a consequence of reduced HIF-2α and CXCR4 levels. CXCR4, is only dependent on HIF-2α, which promotes more aggressive phenotype and more significant for oxaliplatin resistance in SW1116 cells. Our data not only provide clues to aid understanding of the mechanism of the synergism of endostar and chemotherapy under either normoxia or hypoxia, but also suggests a new strategy of combination endostar and chemotherapy treatments which might potentiate therapeutic efficacies and/or counteract chemotherapy resistance.