ABCB1 and neoplasm: It has been found that protein phosphatase 2A (PP2A), which is a key tumor suppressor; cyclosporine A, which is a modifier of multidrug resistance; and anti-multidrug resistance protein 1 (anti-MDR1) hammerhead ribozymes, which are modulators of MDR1-mediated drug resistance, potentiate the anticancer activity of doxorubicin in experimental hepatocellular carcinoma models [8–10].