ABCB1 and leukemia: Previous studies reported that ABCB1 is expressed in K562/ADR cells (Kato, Ideguchi, Muta, Nishimura, & Nawata, 1990), and the up‐regulation of MCL‐1 protein induces multi–drug resistance to doxorubicin and other standard therapies in leukemia (Hermanson, Das, Li, & Xing, 2013; Ji et al., 2009).