ABCB1 and neoplasm: Furthermore, P-gp1, the protein product of the ABCB1 (multidrug resistance protein 1), is also responsible for pumping doxorubicin out of cells to reduce the accumulation of doxorubicin in cells [57] and protecting resistant tumor cells from caspase-dependent apoptosis in the mitochondria [58], thus accounting for drug resistance.