ABCB1 and glioblastoma: In vitro, siRNA reduce ABCB1/ABCG2 mRNA and ABCB1/ABCG2 protein expression in drug-resistant cancer cells such as U87 glioblastoma cells or hepatocellular carcinoma cells (Fisher et al., 2007; Zhao et al., 2008; Li et al., 2012).