title: Multidrug resistance-associated protein-mediated multidrug resistance modulated by cyclosporin A in a human bladder cancer cell line.
abstract: A doxorubicin-resistant subline (5637/DR5.5) from human bladder cancer cells (5637) was induced by stepwise increase in the doxorubicin concentration. 5637/DR5.5 cells were cross-resistant to vinblastine and etoposide but not to mitomycin C and cisplatin. We analyzed the mdr1, MRP (multidrug resistance-associated protein), and DNA topoisomerase II gene expression using the reverse transcription polymerase chain reaction assay (RT-PCR) and investigated possible differences in the accumulation and efflux of radiolabeled daunorubicin. 5637/DR5.5 cells do not express the mdr1 gene, but the expression levels of MRP are markedly higher than in drug-sensitive 5637 cells. The intracellular accumulation of radiolabeled daunorubicin was markedly decreased in the 5637/DR5.5 cells in comparison with the parent cells. This reduced drug accumulation was associated with an enhanced drug efflux, but was reversed when cells were incubated with cyclosporin A. Cyclosporin A at the concentration of 5 microM caused 3.4-fold enhancement of daunorubicin-sensitivity in the 5637/DR5.5 cells. On the other hand, there was no difference in DNA-topoisomerase II activity between the parent and resistant cells. The resistance of the 5637/DR5.5 cells is therefore associated with an enhanced drug efflux mediated by the MRP gene overexpression, as distinct from P-glycoprotein, and is modulated by cyclosporin A.
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D001483:Base Sequence; D001692:Biological Transport / Q000187:drug effects; D002467:Cell Nucleus / Q000201:enzymology; D016572:Cyclosporine / Q000494:pharmacology*; D017931:DNA Primers / Q000737:chemistry; D004264:DNA Topoisomerases, Type I / Q000235:genetics; D003630:Daunorubicin / Q000378:metabolism; D018432:Drug Resistance, Multiple; D015870:Gene Expression; D006801:Humans; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000235:genetics*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D017931:DNA Primers; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D016572:Cyclosporine; D004264:DNA Topoisomerases, Type I; D003630:Daunorubicin