A new method for evaluating the inhibitory potency of antiestrogens on breast cancer cell lines.

Breast cancer cell lines in monolayer culture are helpful in evaluating the potential antitumor activity of antiestrogens. A new method has been developed to rapidly measure the inhibitory potency of a given compound without any cell harvest and counting. Cells are incubated in 96-multiwell culture dishes in the absence or presence of an antiestrogen at 3 concentrations. At the end of incubation, cells are fixed with ethanol and colored with hematoxylin. The intensity of the coloration, which is measured with a multiscan spectrophotometer, gives an accurate evaluation of the cell number and, thereby, an estimate of the inhibitory potency of the antiestrogen. Addition of estradiol to the culture allows to evaluate the antagonistic effect of this hormone towards the inhibition of the antiestrogen. Because of its rapidity and low cost, our method should offer a new dimension in the in vitro screening of antiestrogens and probably most other antineoplastic drugs.