MMP2 and neoplasm: Differences in tumor microenvironment, like lower pH, increased matrix metalloproteinase 2 expression and increased glutathione in the cytosol, have been employed to deliver siRNA using activatable CPPs to silence Rac1 in order to reduce hepatic metastases in colon cancer [104] and suppress c-MYC gene expression in breast cancer cell lines in vivo [105].