Down-Regulation of Vascular Endothelial Cell Growth Factor-C Expression Using Small Interfering RNA Vectors in Mammary Tumors Inhibits Tumor Lymphangiogenesis and Spontaneous Metastasis and Enhances Survival

Tumor production of vascular endothelial cell growth factor (VEGF)-C is associated with tumor lymphangiogenesis and lymph node metastasis. In this study, we examined the effects of small interfering RNA (siRNA)-mediated inhibition of VEGF-C on murine mammary tumor growth, metastasis, and survival. The mRNA and protein expression of VEGF-C in murine mammary tumor cells stably transfected with a VEGF-C siRNA vector were significantly lower compared with VEGF-C-control vector-transfected cells. Cl66-siVEGFC tumors had lower levels of lymphangiogenesis and lymph node and spontaneous lung metastasis than Cl66-control tumors. However, we did not observe significant differences in primary tumor growth and experimental lung metastasis between mice injected with Cl66-siVEGFC and Cl66-control cells. In addition, mice bearing Cl66-siVEGFC tumors lived significantly longer than mice bearing Cl66-control tumors. Furthermore, our data suggest that inhibition of VEGF-C modulates immune cell infiltration and their function, which might be critical in tumor immunity. In summary, our data show that inhibition of VEGF-C expression using siRNA-mediated gene silencing vectors reduces lymphangiogenesis and lymph node and spontaneous lung metastasis, and enhances survival.