Blockade of VEGF/VEGFR pathway enhances chemo-sensitivity in hepatocellular carcinoma

Abstract

Background: Systemic and local chemotherapy for hepatocellular carcinoma (HCC) remains a tough task due to chemo-resistance of tumor cells to cytotoxic agents. Interaction between vascular endothelial growth factor (VEGF) and its receptors plays an important role in the proliferation and survival of tumor cells. Since HCC cells express high levels of VEGF and VEGFRs, we postulate that VEGF/VEGFR pathway might be involved in chemo-resistance of tumor cells to cytotoxic agents. Methods: In vitro, HCC cell lines with wild type (wt) p53 (HepG2), mutant/null p53 (PLC/Hep3B) and p53 stable transfectant (Hep3B/p53+) were treated with cisplatin, VEGF, PTK787 (a VEGFR inhibitor), and cisplatin combined with PTK787, respectively. Cell apoptosis was determined by Annexin V/PI staining, and the mechanism of cell death was explored by poly(ADP-ribose) polymerase (PARP) degradation, and alterations in pro-apoptotic and anti-apoptotic molecules. In vivo, the effects of PTK787 combined with cisplatin was evaluated in a HCC xenograft model in nude mice. Results: The three HCC cell lines express different levels of VEGFRs, Flt-1 and Flk-1. PTK787 enhanced cisplatin-induced PARP degradation and apoptosis in all the three cell lines tested, especially in PLC cells. PTK787, or cisplatin alone down-regulated the expression of pro-survival molecules, cyclin D1 and Bcl-2, and a synergistic effect was observed when PTK787 was combined with cisplatin. Administration of VEGF recombinant protein could abrogate the synergistic effects of PTK787 and cisplatin. VEGF treatment stimulated up-regulation of survivin in tumor cells, while knockdown of survivin reversed the protective effects of VEGF on cisplatin-induced cell apoptosis. Prominent retardation of tumor growth was observed in the HCC xenografts treated with PTK787 and cisplatin in vivo. Conclusions: This study demonstrated that VEGF/VEGFR pathway played an important role in protecting tumor cells from cisplatin-induced cell death, and blockade of VEGF/VEGFR pathway could enhance cisplatin-induced chemo-cytotoxicity in HCC.