Tamoxifen and hydroxytamoxifen isomers versus estradiol effects on normal human breast cells in culture.

Estradiol and triphenylethylene antiestrogen actions have been studied extensively in breast cancer cell lines. However, their effects are still poorly understood on normal human breast cells. We have developed a culture system of normal human breast epithelial (HBE) cells. It has been shown previously that cultured HBE cells were hormone dependent and well adapted for the study of hormone/antihormone actions. However, until now, no data were available on estradiol receptor (ER) in HBE cells. In this study, the presence of ER was demonstrated by (a) whole-cell biochemical assay on breast cells after enzymatic tissue dissociation and (b) an immunocytochemical method using an anti-ER monoclonal antibody both on enzymatically dissociated cells and on 8-day cultured cells. Immunostaining was nuclear and cell positivity was heterogeneous. However, the percentage of positive cells and staining intensity were far greater in the presence of estradiol in the culture, indicating estradiol stimulation of ER. Moreover, HBE cells were used to study the action on cell growth of estradiol versus trans-tamoxifen (TAM), trans-4-hydroxytamoxifen (trans-4OHTAM), and cis-4-hydroxytamoxifen (cis-4OHTAM) alone or added to estradiol. Cell growth was estimated daily by a histometric method and by DNA assay at the end of the 7-day study. When the medium was minimally supplemented with human serum (1%), estradiol stimulated cell growth in a dose-dependent manner at concentrations varying from 10(-9) to 10(-7) M. TAM and trans-4OHTAM clearly inhibited mammary cell division when estradiol was added to the medium and, to a lesser extent, in the absence of estradiol. This inhibitory effect was dose dependent. trans-4OHTAM was 100 times more active than trans-TAM. cis-4OHTAM also clearly inhibited breast cell division at 10(-7) and 10(-6) M concentrations but was 3-fold less efficient than trans-4OHTAM. In conclusion, (a) the presence and estradiol dependence of ER have been demonstrated in HBE cells, which constitute a fruitful model for the study of hormone/antihormone actions, and (b) in these normal cells, estradiol stimulates growth, whereas TAM and the 4OHTAM isomers are potent inhibitors of cell multiplication, as they are in breast cancer cell lines in culture.