Uptake and distribution of doxorubicin in hormone-manipulated human breast cancer cells in vitro.

Abstract

Kinetic resistance to cytotoxic drugs may account for the moderate responsiveness of breast cancer to chemotherapy. In the present study the in vitro effects of estradiol-mediated DNA stimulation on the cellular uptake of the DNA intercalating drug doxorubicin (DOX) were examined in MCF-7 human breast cancer cells. Using the fluorescent properties of the drug, the cellular uptake was investigated by high performance liquid chromatography (HPLC), and by flow cytometry. The uptake of DOX (0.01-2 microg/ml) by MCF-7 cells in suspension, incubated for 1 and 6 h, showed a strong correlation between the incubation concentration of DOX and the cellular uptake of the drug as measured by HPLC and flow cytometry. Simultaneous exposure of MCF-7 cells, in monolayer culture, to DOX (0.04-0.2 microg/ml) and estradiol (1 nM) for 1-24 h showed no significant difference in uptake of the drug compared to control cultures exposed to DOX in the absence of estradiol. Neither was there a significant difference in uptake of DOX when MCF-7 cells were pretreated with estradiol (1 nM) for 16-24 h followed by a 0.5, 1, 6, and 21/23 h incubation with DOX (0.01-2 microg/ml). Pretreatment with estradiol did not affect the retention of DOX as measured 24 h after a 0.5 h incubation with DOX (2 microg/ml). Furthermore, fluorescence microscopy revealed no difference in the cellular DOX distribution pattern of estradiol-stimulated MCF-7 cultures compared to unstimulated cultures. From this study we can conclude that, for the human MCF-7 breast cancer cells in vitro, the uptake, retention, and cellular distribution of DOX are not influenced by estrogenic manipulation.