The relationship between modulation of MDR and glutathione in MRP-overexpressing human leukemia cells.
Multidrug resistance-associated protein (MRP) causes multidrug resistance (MDR) involving the anthracyclines and epipodophyllotoxins. Many studies show modulation of anthracycline levels and cytotoxicity in MRP-overexpressing cells, but there is limited data on the modulation of etoposide levels and cytotoxicity in MRP-overexpressing or in P-glycoprotein-expressing cells. Etoposide accumulation was 50% reduced in both the CEM/E1000 MRP-overexpressing subline and the CEM/VLB100 P-glycoprotein-expressing subline compared to the parental CEM cells, correlating with similar resistance to etoposide (200-fold) of the two sublines. For the CEM/VLB100 subline, the P-glycoprotein inhibitor SDZ PSC 833, but not verapamil, was able to increase etoposide accumulation and cytotoxicity. For the CEM/E1000 subline, neither SDZ PSC 833 nor verapamil had any effect on etoposide accumulation. However, verapamil caused a 4-fold sensitization to etoposide in this subline, along with an 80% decrease in cellular glutathione (P < 0.05). Buthionine sulfoximine (BSO), which depletes glutathione, also caused a 2.5-fold sensitization to etoposide with no effect on accumulation in the CEM/E1000 subline. In contrast, SDZ PSC 833 was able to increase daunorubicin accumulation in the CEM/E1000 subline (P < 0.05), but had no effect on daunorubicin cytotoxicity, or cellular glutathione. These results show that modulation of etoposide cytotoxicity in MRP-overexpressing cells may be through changes in glutathione metabolism rather than changes in accumulation and confirm that changes in drug accumulation are not related to drug resistance in MRP-overexpressing cells.
Department of Cell and Molecular Biology, University of Technology, Sydney, Gore Hill NSW, Australia.
K V
KV
Grech
R A
RA
Davey
M W
MW
Davey
D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D003630:Daunorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple / Q000235:genetics / Q000502:physiology; D019008:Drug Resistance, Neoplasm / Q000235:genetics / Q000502:physiology; D005047:Etoposide / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D019450:Genes, MDR; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D007938:Leukemia; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D014407:Tumor Cells, Cultured
D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D019328:Buthionine Sulfoximine; D003630:Daunorubicin; D005047:Etoposide; D005978:Glutathione; D027425:ATP-Binding Cassette, Sub-Family C Proteins