title: Lack of competition of substrates for P-glycoprotein in MCF-7 breast cancer cells overexpressing MDR1.
abstract: The MCF-7/Adr cells overexpress MDR-1 which contributes to the drug-resistant phenotype. Our studies show: 1. The retention of daunomycin in the MCF-7/Adr cells relates to a temperature-dependent and energy-dependent process. 2. The MCF-7/Adr cells retain less rhodamine-123 than the parental MCF-7 cells. 3. The MCF-7/Adr cells retain less daunomycin than the parental MCF-7 cells as measured by mean fluorescence or radioactive daunomycin. 4. Cyclosporin A and verapamil effectively block the effluxes of rhodamine-123 and daunomycin from the MCF-7/Adr cells. 5. On short-term incubation, 2-deoxyglucose lowers the NTP levels to a greater extent than sodium azide, showing the importance of glycolysis in the MCF-7 cell lines. 6. Although the MCF-7/Adr cells show cross-resistance to VP-16, actinomycin D and vinblastine, these drugs do not compete with daunomycin for the efflux pump. 7. These data suggest that either there must be multiple MDR-1 pumps that differ in substrate specificity or that there are distinct substrate sites on MDR-1.
authors.affiliation: Department of Biochemistry, East Carolina University School of Medicine, Greenville, NC 27858, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Hall
authors.forename: A H
authors.initials: AH
authors.lastname: Cory
authors.forename: J G
authors.initials: JG
authors.lastname: Cory
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics* / Q000378:metabolism*; D000903:Antibiotics, Antineoplastic / Q000493:pharmacokinetics / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism*; D003630:Daunorubicin / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple / Q000235:genetics; D004734:Energy Metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D009711:Nucleotides / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D009711:Nucleotides; D004317:Doxorubicin; D003630:Daunorubicin