Inhibition of P-glycoprotein and recovery of drug sensitivity of human acute leukem1c blast cells by multidrug resistance gene (marl) antisense oligonucleotides

Abstract

To overcome the problem of multidrug resistance, we investigated the effectiveness of phosphrothioate antisense oligonucleolides (MDR1-AS) in suppressing multidrug resistance gene (mdrl) expression in drug-resistant acute myelogenous leukemia (AML) blast cells and the K562 adriamycin-resistant cell line K562/ADM. The percentage of cells with the mdrl gene product P-glycoprotein (P-gp) was decreased from 100% to 26% by 20 /J.M MDR1-AS in the K562/ADM cells, and from 48.1% (±15.1%) to 10.2% (±6.8%) by 2.5 MM MDR1-AS in 10 AML blast cells from patients. This effect was specific to MDR1-AS, and not observed with sense or random control oligonucleotides. The expression of mdrl mRNA in K562/ADM and AML blast cells treated with MDR1-AS was decreased compared to the random control. Intracellular rhodamine retention and pHJdaunorubicin also increased after antisense treatment. Chemosensitivity to daunorubicin increased in MDRl-AS-treated blast cells up to 5.9-fold in the K562/ADM cells and 3.0 to 6.4-fold in the AML blast cells by leukemic blast colony assay. The expression of mdrl mRNA derived from colony cells decreased in the MDRl-AS-treated groups. No inhibitory effect of the oligonucleotides on colony formation of normal bone marrow progenitors was observed. These findings suggest that MDR1-AS is useful to overcome multidrug resistance in the treatment of leukemia.