VESICULAR ANTHRACYCLINE ACCUMULATION IN DOXORUBICIN-SELECTED U-937 CELLS - PARTICIPATION OF LYSOSOMES

The U-A10 cell line, a doxorubicin-selected variant of human U-937 mye loid leukemia cells, exhibits a redistribution of anthracyclines into a expanded vesicular compartment. The acidic nature of this compartmen t was confirmed by vital staining with a pH sensitive dye, LysoSensor yellow/blue DND-160. Identification of the vesicular compartment was p erformed by immunofluorescence analysis. Staining for the LAMP-1 and L AMP-2 antigens showed that the vesicles are enlarged lysosomes that ar e eccentrically placed near the nucleus of U-A10 cells. By contrast, t he expression of the multidrug resistance-associated protein and the P -glycoprotein wits observed predominately on the plasma membrane of th e drug-resistant cells. The accumulation of daunorubicin into cellular compartments was quantified using radiolabeled drug. Exposing cells t o (3)[H]-daunorubicin and then isolating intact nuclei showed that nuc lei from U-A10 cells accumulated twofold to threefold less anthracycli ne than nuclei from U-937 cells, However, when nuclei were isolated fi rst and then exposed to (3)[H]-daunorubicin, little difference in net nuclear drug accumulation was detected. Cytoplasts prepared from U-A10 and U-937 cells were exposed to (3)[H]daunorubicin to measure cytopla smic drug accumulation.