title: Effect of cyclosporin A on daunorubicin accumulation in multidrug-resistant P388 leukemia cells measured by real-time flow cytometry.
abstract: We investigated the mode of action of cyclosporin A (Cy-A) as a modifier of multidrug resistance in P388 mouse leukemia cells. A fluorescence-activated flow cytometer (FCM) was modified with a flow-through cuvette to allow continuous on-line monitoring of daunorubicin uptake in vitro. The addition of Cy-A to multidrug-resistant P388/R cells at steady-state daunorubicin uptake, led to a dose-dependent increase in cellular daunorubicin accumulation, as measured by FCM and high-performance liquid chromatography (HPLC). A linear relationship was found between the daunorubicin concentration in the incubation medium and the Cy-A concentration required for optimal stimulation of cellular anthracycline accumulation. The results of a cytotoxicity assay indicated that Cy-A completely restored the chemosensitivity of the P388/R cells. Intracellular Cy-A measurements in P388/S and P388/R cells showed that P388/R cells accumulated significantly less Cy-A than P388/S cells. Relatively high daunorubicin concentrations could not restore that accumulation defect. These results suggest that Cy-A promotes cellular anthracycline accumulation by competing for an outward drug-transport system that operates in multidrug-resistant cells.
authors.affiliation: Radiobiological Institute TNO, Rijswijk, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: Nooter
authors.forename: R
authors.initials: R
authors.lastname: Oostrum
authors.forename: R
authors.initials: R
authors.lastname: Jonker
authors.forename: H
authors.initials: H
authors.lastname: van Dekken
authors.forename: W
authors.initials: W
authors.lastname: Stokdijk
authors.forename: G
authors.initials: G
authors.lastname: van den Engh
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003524:Cyclosporins / Q000032:analysis / Q000493:pharmacokinetics / Q000494:pharmacology*; D003630:Daunorubicin / Q000032:analysis / Q000493:pharmacokinetics* / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004351:Drug Resistance; D005434:Flow Cytometry; D007834:Lasers; D007941:Leukemia P388 / Q000188:drug therapy / Q000378:metabolism*; D007942:Leukemia, Experimental / Q000378:metabolism*; D051379:Mice; D011863:Radioimmunoassay; D014407:Tumor Cells, Cultured
chemical_list: D003524:Cyclosporins; D003630:Daunorubicin