Reversion of human glioblastoma malignancy by U1 small nuclear RNA/ribozyme targeting of scatter factor/hepatocyte growth factor and c-met expression

Background: Expression of scatter factor (SF), also known as hepatocyte gro wth factor (HGF), and its receptor, c-met, is often associated with maligna nt progression of human tumors, including gliomas, Overexpression of SF/HGF in experimental gliomas enhances tumorigenicity and tumor-associated angio genesis (i.e., growth of new blood vessels). However, the role of endogenou s SF/HGF or c-met expression in the malignant progression of gliomas has no t been examined directly, In this study, we tested the hypothesis that huma n glioblastomas can be SF/HGF-c-met dependent and that a reduction in endog enous SF/HGF or c-met expression can lead to inhibition of tumor growth and tumorigenicity, Methods: Expression of the SF/HGF and c-met genes was inhi bited by transfecting glioblastoma cells with chimeric transgenes consistin g of U1 small nuclear RNA, a hammerhead ribozyme, and antisense sequences; The effects of reduced SF/HGF and c-met expression on 1) SF/HGF-dependent i nduction of immediate early genes (c-fos and c-jun), indicative of signal t ransduction; 2) anchorage-independent colony formation (clonogenicity), an in vitro correlate of solid tumor malignancy; and 3) intracranial tumor for mation in immunodeficient mice were quantified. Statistical tests were two- sided. Results: Introduction of the transgenes into glioblastoma cells redu ced expression of the SF/HGF and c-met genes to as little as 2% of control cell levels. Reduction in c-met expression specifically inhibited SF/HGF-de pendent signal transduction (P<.01). Inhibition of SF/HGF or c-met expressi on in glioblastoma cells possessing an SF/HGF-c-met autocrine loop reduced tumor cell clonogenicity (P =.005 for SF/HGF and P =.009 for c-met) and sub stantially inhibited tumorigenicity (P<.0001) and tumor growth in vivo (P<. 0001). Conclusions: To our knowledge, this is the first successful inhibiti on of SF/HGF and c-met expression in a tumor model directly demonstrating a role for endogenous SF/HGF and c-met in human glioblastoma. Our results su ggest that targeting the SF/HGF-c-met signaling pathway may be an important approach in controlling tumor progression.