ABCB1 and acute lymphoblastic leukemia: We initially hypothesized that the above-mentioned effects of verapamil in T-ALL cells were due to its well-known activity against MDR transporters of the ABC superfamily, including the MDR1/P-glycoprotein (ABCB1), ABCG2, MRP1 (ABCC1), and ABCA2 [20,21,22], which extrude chemotherapeutic drugs, including vinblastine, doxorubicin, daunorubicin, and paclitaxel, out of the cell [10].