RNAi-mediated abrogation of cathepsin B and MMP-9 gene expression in a malignant meningioma cell line leads to decreased tumor growth, invasion and angiogenesis

Malignant meningiomas are highly aggressive and frequently recur after surgical resection of the tumor. Earlier studies have reported that the cysteine protease cathepsin B and the matrix metalloproteinase MMP-9 play important roles in tumor progression. In the present study, we made an attempt to evaluate the roles of these proteases in the malignant meningioma tumor microenvironment and determined the effectiveness of using single or bicistronic siRNA constructs for cathepsin B and MMP-9, in both in vitro and in vivo models. Transfection of a plasmid vector expressing double-stranded RNA for cathepsin B and MMP-9 significantly inhibited mRNA and protein levels of cathepsin B and MMP-9. The migration and invasion of meningioma cells were decreased after treatment with single or bicistronic siRNA constructs for cathepsin B and MMP-9 compared to controls and vector controls. Inhibition of angiogenesis was observed when the cells were transfected with single or bicistronic constructs for cathepsin B and MMP-9, when compared to controls or empty vector controls. Our study revealed that abrogation of cathepsin B and MMP-9 expression decreased the activation of major proteins involved in MAP kinase and PI3 kinase pathways indicating that targeting these proteases may hinder intracellular signaling and thus decrease cell survival and proliferation in malignant meningiomas. In addition to the in vitro evidence, we observed a significant regression of pre-established orthotopic tumors after treatment with RNAi plasmid vectors targeting cathepsin B and MMP-9. Furthermore, these observations demonstrate that the simultaneous RNAi-mediated targeting of cathepsin B and MMP-9 has potential application for the treatment of human meningiomas.