The effects of MRB on cell viability were evaluated in colon cancer cells (HCT116, SW480 and LoVo), human breast cancer cells (MCF-7 and MDA-MB-231) and hepatocellular carcinoma cells (HepG-2) by MTT assay. As shown in Fig. 1 A, cell proliferation of human colon cancer cells was significantly reduced by the treat- ment of 10 and 20 μg/ml of MRB for 24 h. In addition, MRB sup- pressed the proliferation of MDA-MB-231 and MCF-7 cells ( Fig. 1 B). However, the proliferation of HepG-2 cells did not be affected by MRB treatment ( Fig. 1 C). In addition, MRB induced minimal inhi- bition of cell growth in CCD-18co (colon normal cells) ( Fig. 1 D). These data indicate that MRB’s anti-cancer activity may be cancer- specific.