Background: 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.
Methods: Using the fluorescent properties of the drug, the cellular uptake was investigated by high performance liquid chromatography (HPLC), and by flow cytometry.
Results: 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.
Conclusion: 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.