931. Inhibition of VEGF Signaling Pathway and Tumor Metastasis

Abstract

Top of pageAbstract Blocking vascular endothelial growth factor (VEGF) signaling pathway appears to be an effective approach to suppress tumor angiogenesis and metastasis. Because degree of tumor malignancy correlates with the expression of VEGF and the inverse expression of tumor suppressor gene p16, we examined whether restoration of wild-type p16 in cancer cells that lack p16 expression would modulate VEGF expression, and if so, how is the effect of p16 expression on tumor angiogenesis and metastasis. Human breast cancer cell lines MDA-MB-231, MCF-7 and mouse breast cancer cell line JygMC(A) were used as models for this study. To facilitate induction of p16 expression, a replication-defective recombinant adenovirus expressing human wild-type p16 (AdRSVp16) has been generated. Our study showed that adenoviral-mediated p16 expression downregulated VEGF expression at both mRNA and protein levels in breast cancer cells, as well as VEGF receptor activation. By using a chimeric VEGF promoter-reporter gene construct, we demonstrated that p16 downregulated VEGF gene expression at the transcriptional level. A molecular mechanism of how p16 modulates VEGF expression at the transcriptional level is proposed. By comparing with control virus-treated group, AdRSVp16 inhibited breast cancer angiogenesis in dorsal air sac and matrigel plug models, in vitro and in vivo growth of breast cancer cells, and metastasis in a subcutaneous metastasis model. The dual effects of p16's anti-proliferation and anti-angiogenesis were examined by simultaneously analyzing proliferation marker PCNA and neovascularization marker CD31 (immunohistochemistry), and apoptosis (TUNEL) inside the tumors. Our results showed that p16 has combinative effects on breast tumor angiogenesis and proliferation. Taken together, these results demonstrate that p16 downregulates VEGF gene expression at the transcriptional level, inhibits angiogenesis, and suppresses tumor growth and metastasis in breast cancer cells. This study suggests that viral vector-based p16 gene therapy may have a clinical potential to treat breast cancer in conjunction with other therapeutic modalities.