Multidrug resistance in leukemia.

Resistance of tumors to chemotherapeutic agents is an important factor that limits the successful treatment of a wide range of malignancies. The multidrug resistant (MDR) phenotype is well recognized in clinical samples, and it has been extensively studied, particularly in acute myeloid leukemia. One of the principle mechanisms underlying this MDR phenotype is the active cellular extrusion of chemotherapeutic agents by the multidrug resistance protein MDR1 (p-glycoprotein). More recently, other drug resistance proteins, notably the multidrug resistance-associated protein, MRP, and the lung resistance protein, LRP, have also been implicated in multidrug resistance. This review summarizes recent contributions in this field. In particular, it focuses on recent efforts to better measure MDR in clinical samples, a critical step in correctly determining the MDR phenotype of a patient's tumor.