Reduction of stromal fibroblast-induced mammary tumor growth, by retroviral ribozyme transgenes to hepatocyte growth factor/scatter factor and its receptor, c-MET

Purpose: Hepatocyte growth factor/scatter factor (HGF/SF) is known to increase the invasiveness and migration of cancer cells in vitro and induce angiogenesis. This study examined if inhibition of HGF/SF receptor expression by cancer cells and HGF/SF expression by stromal fibroblasts affects the growth of mammary cancer. Experimental Design: Transgenes encoding ribozymes to specifically target human HGF/SF receptor (pLXSN-MET) or HGF/SF (pLXSN-HGF) were constructed using a pLXSN retroviral vector. Human mammary cancer cells MDA MB 231 was transduced with pLXSN-MET (MDA^+/+). A human fibroblast cell line MRC5, which produces bioactive HGF/SF, was transduced with pLXSN-HGF (MRC5^+/+). These cells were used in a nude mice breast tumor model. Results: HGF receptor in MDA^+/+ cells and HGF in MRC5^+/+ cells were successfully removed with respective ribozymes as shown by reverse transcription-PCR and Western blotting, respectively. MDA ^+/+ was found to have reduced invasiveness when stimulated with HGF/SF. MRC5^+/+ exhibited a significant reduction in HGF/SF production. When injected into athymic nude mice, MDA^+/+ exhibited a slower rate of growth, compared with the wild type (MDA^-/-), and the cells transduced with control viral vector (MDA^+/-). The growth of MDA^-/- tumor was significantly enhanced when coimplanted with wild-type MRC5 (MRC5^-/-), and the stimulatory effect was reduced when MRC5^+/+ cells were coimplanted instead of MRC5^-/-. The reduction of tumor growth was accompanied by reduction of angiogenesis, as demonstrated by the staining of VE-cadherin in primary tumor tissues. Conclusions: Retroviral ribozyme transgenes targeting HGF/SF in fibroblasts or its receptor cMET in mammary cancer cells can reduce the growth of mammary cancer and associated angiogenesis by inhibiting paracrine stromal-tumor cell interactions.