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Multidrug-resistant human sarcoma cells with a mutant P-glycoprotein, altered phenotype, and resistance to cyclosporins.

Chen G., Duran G.E., Steger K.A., Lacayo N.J., Jaffrezou J.P., Dumontet C., Sikic B.I.

A variant of the multidrug-resistant human sarcoma cell line Dx5 was derived by co-selection with doxorubicin and the cyclosporin D analogue PSC 833, a potent inhibitor of the multidrug transporter P-glycoprotein. The variant DxP cells manifest an altered phenotype compared with Dx5, with decreased cross-resistance to Vinca alkaloids and no resistance to dactinomycin. Resistance to doxorubicin and paclitaxel is retained. The multidrug resistance phenotype of DxP cells is not modulated by 2 microM PSC 833 or cyclosporine. DxP cells manifest a decreased ability to transport [3H]cyclosporine. DNA heteroduplex analysis and sequencing reveal a mutant mdr1 gene (deletion of a phenylalanine at amino acid residue 335) in the DxP cell line. The mutant P-glycoprotein has a decreased affinity for PSC 833 and vinblastine and a decreased ability to transport rhodamine 123. Transfection of the mutant mdr1 gene into drug-sensitive MES-SA sarcoma cells confers resistance to both doxorubicin and PSC 833. Our study demonstrates that survival of cells exposed to doxorubicin and PSC 833 in a multistep selection occurred as a result of a P-glycoprotein mutation in transmembrane region 6. These data suggest that Phe335 is an important binding site on P-glycoprotein for substrates such as dactinomycin and vinblastine and for inhibitors such as cyclosporine and PSC 833.

J. Biol. Chem. 272:5974-5982(1997) [PubMed] [Europe PMC]

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