Figure 3.

Binding affinity of EPTA-Eu to ER in human breast cancer cells. ER-positive and ER-negative MDA-MB-231 human breast cancer cells, grown on microspheres, were incubated in the presence of the indicated concentrations of EPTA-Eu for 1 h at 37°C and subjected to DELFIA assay. (A) Total binding (red) was determined in ER-positive cells and non-specific binding (black) was determined in ER-negative cells. Specific binding (blue) was calculated by subtracting non-specific from total binding. (B) Saturation-binding curve. Data points of specific binding were fitted to one-site binding equation yielding Kd = 0.56 μM, BMAX = 60.9 pmole, and R2 = 0.97. Data of OD scale were converted to molar units by comparing to OD values of known EPTA-Eu concentrations.