title: Decreased accumulation of [14C]carboplatin in human cisplatin-resistant cells results from reduced energy-dependent uptake.
abstract: We have isolated cisplatin-resistant human liver carcinoma (7404-CP20) cells with reduced accumulation of cisplatin and other drugs (methotrexate, arsenate, and arsenite) to which these cells are cross-resistant. To determine whether the reduction of drug accumulation in cisplatin-resistant cells results from impaired uptake or from active efflux, [(14)C]carboplatin was used for kinetic analysis of drug uptake and efflux. We demonstrate here that the uptake of [(14)C]carboplatin in 7404 parental cells is time, temperature, and energy dependent, and that the rate of uptake is reduced in 7404-CP20 cells. Efflux of [(14)C]carboplatin in cisplatin-resistant cells was comparable to efflux in the parental cisplatin-sensitive cells. There was little effect of temperature (between 37 degrees C and 4 degrees C) on efflux in cisplatin-resistant cells. Immunoblotting with specific antibodies directed to MRP1 and MRP2 (cMOAT) also showed that expression of these two ABC transporter genes was considerably reduced in 7404-CP20 cells and another cisplatin-resistant cell line KB-CP20, in contradistinction to previous studies suggesting that MRP might be responsible for cisplatin efflux. To rule out a generalized defect in uptake of small molecules, fluorescence-activated cell sorter (FACS) analysis of rhodamine 123 uptake showed that there was no difference between cisplatin-sensitive and -resistant cells. The presence of a pleiotropic defect in uptake of [(14)C]carboplatin, [(3)H]methotrexate, [(73)As]arsenate, and [(73)As]arsenite in cisplatin-resistant cells, in association with reduced expression of related cell surface proteins as demonstrated in our previous work, suggests a novel mechanism for acquisition of resistance to cisplatin associated with reduced activity of many different specific uptake systems.
authors.affiliation: Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
authors.forename: D W
authors.initials: DW
authors.lastname: Shen
authors.forename: S
authors.initials: S
authors.lastname: Goldenberg
authors.forename: I
authors.initials: I
authors.lastname: Pastan
authors.forename: M M
authors.initials: MM
authors.lastname: Gottesman
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000970:Antineoplastic Agents / Q000493:pharmacokinetics* / Q000633:toxicity; D001692:Biological Transport; D002250:Carbon Radioisotopes; D016190:Carboplatin / Q000493:pharmacokinetics* / Q000633:toxicity; D002462:Cell Membrane / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects*; D002945:Cisplatin / Q000633:toxicity*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007624:KB Cells; D007700:Kinetics; D008113:Liver Neoplasms; D008928:Mitochondria / Q000378:metabolism; D020112:Rhodamine 123 / Q000493:pharmacokinetics; D013696:Temperature; D014407:Tumor Cells, Cultured; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D002250:Carbon Radioisotopes; D014475:Uncoupling Agents; D020112:Rhodamine 123; D000255:Adenosine Triphosphate; D016190:Carboplatin; D002945:Cisplatin