ALTERED INTRACELLULAR-DISTRIBUTION OF DAUNORUBICIN IN IMMATURE ACUTE MYELOID-LEUKEMIA CELLS

We have used laser-assisted confocal microscopy to evaluate the intrac ellular distribution of daunorubicin (DNR) in acute myeloid leukemia ( AML) cell lines and fresh AML cells according to their differentiation phenotype, In KG1a, KG1, TF-I and HEL cells, which express the early differentiation marker CD34, DNR was distributed in perinuclear vesicl es which could be associated with the Golgi apparatus, as suggested by the distribution of fluorescent probes specific for intracellular org anelles. In contrast, U937 and HL-60 cells, which display a more matur e phenotype, exhibited nuclear and disuse cytoplasmic DNR fluorescence , DNR sequestration was not correlated with P-glycoprotein (P-gp) or m ultidrug resistance protein expression, Furthermore, PSC833, a potent P-gp blocker, had little effect on drug sequestration in CD34(+) AML c ells, We also tested the effect of metabolic inhibitors, cytoskeleton inhibitors and carboxy-ionophores on DNR distribution in both CD34(-) and CD34(+) AML cells, However, only non-specific metabolic inhibitors restored nucleic/cytoplasmic distribution in CD34(+) cells, In these cells, the intracellular distribution of doxorubicin and idarubicin wa s very similar to that of DNR, while the distribution of methoxymorpho linyl-doxorubicin was nuclear and diffusely cytoplasmic, In fresh AML cells, DNR was also concentrated in the perinuclear region in CD34(+) but not in CD34(-) cells, However, DNR sequestration was not observed in normal CD34(+) cells, Finally, our results show that DNR is sequest ered in organelles in CD34(+) AML cells via an active mechanism which appears to be different from P-gp-mediated transport, Abnormal DNR dis tribution may account for the natural resistance of immature AML cells to anthracyclines. (C) 1997 Wiley-Liss. Inc.