EXPRESSION OF THE MULTIDRUG-RESISTANCE ASSOCIATED PROTEIN AND P-GLYCOPROTEIN IN DOXORUBICIN-SELECTED HUMAN MYELOID-LEUKEMIA CELLS

Drug-resistant sublines of the human U-937 myeloid leukemia cell line were selected in doxorubicin concentrations of 10, 40, and 200 ng/mL ( designated U-A10, U-A40, and U-A200, respectively). Northern blot anal ysis showed overexpression of the multidrug resistance-associated prot ein (MRP) gene, but not MDR1, in U-A10 cells as compared with parental U-937 eels. Prolonged passage of U-A10 cells in 10 ng/mL of doxorubic in had little effect on MRP RNA levels, but increased MDR1 expression. The U-A40 and U-A200 cells, derived by selection of U-A10 cells, show ed high levels of both MRP and MDR1 expression. None of the drug-resis tant cell lines showed MRP or MDR1 gene amplification as judged by Sou thern blot analysis. U-A10 cells exhibited minimal decreased net accum ulation of anthracycline, whereas U-A40 and U-A200 cells showed more s ignificantly decreased drug accumulation as compared with U-937 cells. Subcellular anthracycline accumulation in U-937 cells as determined b y fluorescence microscopy showed daunorubicin fluorescence predominate ly in the nucleus, However, the drug-resistant cell lines showed minim al nuclear drug accumulation with marked redistribution of drug into a vesicular compartment. Treatment with sodium azide/2-deoxyglucose. 2, 4-dinitrophenol, or monensin, but not verapamil, abolished the vesicul ar accumulation. These studies in doxorubicin-selected U-937 cells ind icate that induction of MRP overexpression occurs before that for the MDR1 gene. In addition, the drug-resistant cells possess an energy-dep endent redistribution of anthracyclines into a nonnuclear vesicular co mpartment. (C) 1994 by The American Society of Hematology.