Decreased DNA topoisomerase II in daunorubicin-resistant Ehrlich ascites tumor cells.
We have previously shown that the multidrug-resistant EHR2/DNR+ cells, which overexpress P-glycoprotein, accumulate only about 20-30% of daunorubicin at steady state compared to the sensitive cells. These cells have been thought to be a "pure" P-glycoprotein cell line. We now report that the EHR2/DNR+ cells exhibit decreased DNA topoisomerase II catalytic activity. We also found that the amount of immunoreactive DNA topoisomerase II from these cells is about one-third that seen in the drug-sensitive cell line. In agreement with the decreased activity and amount of topoisomerase II, the number of DNA-protein complexes stabilized by teniposide (VM-26) was reduced by about 50% in nuclear extracts from EHR2/DNR+ cells. Furthermore, using an intact cell assay for DNA protein complexes, we found that the VM-26-stimulated complexes formed in the drug-resistant cells never reached the level seen in the drug-sensitive cells. Verapamil and Cremophor EL block P-glycoprotein-mediated efflux of "natural product" drugs and increase their accumulation in resistant cells. Coincubation of the EHR2/DNR+ cells with VM-26 and either of these modulators increased the number of complexes formed in the resistant cells. However, neither modulator increased the number of topoisomerase II-DNA complexes in the drug-resistant cells to the level seen in the EHR2 cells. We conclude that the resistance of EHR2/DNR+ cells is due in part to reduced amounts of DNA topoisomerase II. Furthermore, we note that a single cell line can express features of both P-glycoprotein-associated multidrug resistance and altered topoisomerase II-associated multidrug resistance.
Department of Medicine and Hematology, Rigshospitalet-University Hospital, Copenhagen, Denmark.
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E
Friche
M K
MK
Danks
C A
CA
Schmidt
W T
WT
Beck
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000201:enzymology*; D002467:Cell Nucleus / Q000201:enzymology*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D003630:Daunorubicin / Q000494:pharmacology*; D003852:Deoxyribonucleoproteins / Q000378:metabolism; D004351:Drug Resistance / Q000502:physiology; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000235:genetics; D051379:Mice; D013713:Teniposide / Q000494:pharmacology*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003852:Deoxyribonucleoproteins; D008562:Membrane Glycoproteins; D013713:Teniposide; D004250:DNA Topoisomerases, Type II; D003630:Daunorubicin