ABCB1 and cancer: To counteract ABCB1 overexpression mediated drug resistance, proteasome inhibitors were combined with ABCB1 inhibitors (Verapamil, Nelfinavir, and Lopinavir) to block the efflux of proteasome inhibitors to the extracellular space, which will definitely increase the concentration of proteasome inhibitors inside the cells to eliminate the cancer cells 119, 120.