Modulation of MCF-7 cell proliferative responses by manipulation of assay conditions

The use of MCF-7 cell proliferation assays has been proposed as one of a number of available in vitro assays to determine the oestrogenic potential of chemicals. However, there is concern that differences between strains of MCF-7 cells and protocols used may lead to significant interlaboratory variability, particularly in their response to the natural oestrogen 17beta-oestradiol, and inability to detect weak oestrogens (Villalobos et al., 1995). This investigation adds to the debate by demonstrating that manipulation of assay conditions may modulate the proliferative response of a particular MCF-7 cell strain to 17beta-oestradiol. MCF-7 cells were put in 12-well plates, then exposed for 6 days to 17)3-oestradiol in EMEM without phenol red using serum stripped of endogenous oestrogens (EMEM/H-). A maximum proliferation of 200-250% control (assessed by fluorescein diacetate uptake) was observed, which is lower than some reported values (up to eightfold increase) and would probably reduce the sensitivity of detection of a weak oestrogen. Preincubation of cells in EMEM/H- for 48 hr, prior to the addition of 17beta-estradiol, resulted in an increased maximum proliferation of 400% control or more. Differences were also seen in the shape of the time course of response to 10(-9)m 17beta-oestradiol; preincubated cells exhibited exponential growth after 6 days whereas those exposed directly after plating plateaued after 4 days. The increased response to 17beta-oestradiol may be due to oestrogen receptor induction following transfer of the cells to oestrogen-free medium. This increase in responsiveness of the cells may increase the sensitivity of this strain of MCF-7 cells for the detection of oestrogenic chemicals.