Figure 1.

Mechanisms of MDR in cancer cells: (1) active drug efflux by drug transporters, such as Pgp, MRP, and BCRP; (2) loss of cell surface receptors and/or drug transporters or alterations in membrane lipid composition; (3) compartmentalization of the drug in cellular vesicles; (4) altered/increased drug targets; (5) alterations in cell cycle; (6) increased drug metabolism/enzymatic inactivation; (7) active damage repair; and (8) inhibition of apoptosis.