Inhibition of Tumor Growth and Metastasis by a Combination of Anti-VEGF-C and Enhanced IL-12 Therapy in an Immunocompetent Mouse Mammary Cancer Model

Breast cancer represents a major health problem in women, with more than 1,000,000 new cases and 370,000 deaths yearly worldwide [1]. Perhaps more worrisome is an apparently increasing incidence of breast cancer among younger women under 40 years of age recently reported in many countries worldwide [2-4]. The lethality of breast cancer is largely due to metastasis, preferentially to the lymph nodes, lungs and bones [5]; in order to delay the progression of breast cancer and prolong patient life, more effective chemopreventive and antimetastatic treatments and less toxic chemotherapeutic agents are desperately required. Vascular endothelial growth factor-C (VEGF-C) is expressed in a variety of malignant tumors including mammary cancer [6] and over-expression of VEGF-C has been reported to be associated with lymph node metastasis and poor prognosis in breast cancer patients [7,8]. A number of animal studies using cell lines [9-11] and transgenic mice[12] have been conducted in an attempt to demonstrate that VEGF-C over-expression is able to promote cancer metastasis. Using a ‘RNA interference’ approach with an immunocompetent mouse mammary cancer model, we previously demonstrated that inhibition of VEGF-C or VEGF-A by gene silencing using vectors expressing short interfering RNA (siRNA) leads to suppression of lymphatic and/or hematogenous metastasis [13]. The cytokine interleukin-12 (IL-12), a heterodimer composed of p35 and p40 subunits, is produced primarily by dendritic cells, macrophages/monocytes, and neutrophils and functions in enhancing the activity of cytotoxic T lymphocytes and NK cells. Both subunits are necessary to exert biological activity [14]. IL-12 plays an important role in the induction of a cell-mediated immune response [15]. This cytokine is also involved in the differentiation of native T cells to the Th1 subset, and induces production of interferon- (IFN) in both T and NK cells. In addition, IL-12 has been shown to exert a potent anti-neoplastic effect in a