Vol. 286, Issue 1, 525-530, July 1998

Handling of Doxorubicin by the LLC-PK₁ Kidney Epithelial Cell Line¹

Giuliana Decorti, Ilaria Peloso, Daniela Favarin, Fiora Bartoli Klugmann, Luigi Candussio, Enrico Crivellato, Franco Mallardi and Luciano Baldini

Department of Biomedical Sciences, University of Trieste, Trieste (G.D., I.P., D.F., F.B.K., L.C., L.B.) and Department of Medical and Morphological Research (E.C., F.M.), University of Udine, Udine, Italy

The characteristics of doxorubicin handling have been studied in the cultured kidney epithelial cell line LLC-PK₁, which has structure and function similar to those of renal tubular cells and expresses P-glycoprotein. The uptake of doxorubicin by LLC-PK₁ cells was time dependent, reaching a steady state at about 4 hr, and reduced at low temperature; the initial uptake was saturable. The efflux of doxorubicin from LLC-PK₁ cells was also temperature dependent but, even at 37°C, a significant percentage of the drug remained associated with the cells after 180 min, which suggests a strong cellular binding, and the fluorescence microscopy revealed that the drug was concentrated in intracellular organelles. Substances that are substrates for P-glycoprotein, such as verapamil, vinblastine, vincristine and quinidine, significantly increased doxorubicin concentrations in LLC-PK₁ cells. Similar results were obtained with the metabolic inhibitors sodium metavanadate and 2,4-dinitrophenol. On the other hand, the uptake was not affected by the classic organic cation transport drugs cimetidine, decynium 22 or decynium 24, nor by the organic anion drug probenecid. These results indicate that, in LLC-PK₁ cells, doxorubicin enters by passive diffusion, is trapped in intracellular organelles and then is extruded from cells by a mechanism that probably involves P-glycoprotein. On the contrary, substances that interfere with the renal organic cation or anion secretory system have no effect on doxorubicin net accumulation in these cells.