Effectsof Estrone, Estradiol,and Estriolon Hormone responsiveHuman Breast Cancer in Long-TermTissue Cultureâ€

SUMMARY The effects of estrone, estnadiol, and estniobon MCF-7 human breast cancer are compared. In this estrogen-me sponsive cell line, all three estrogens are capable of induc ing equivalent stimulation of amino acid and nucleoside incorporation. Estriol is capable of partially overcoming antiestrogen inhibition with Tamoxifen (ICI 46474), even when antiestrogen is present in 1000-fold excess. Antiestro gen effects are completely overcome by 100-fold less es tniol. Studies of metabolism of estrogens by MCF-7 cells revealedno conversionof estniob to eitherestroneonestna diol.Allthreesteroids bindtoa high-affinity estrogenne ceptomfound in these cells. The apparent dissociation con stant is lower for estradiol than for estrone and estriol, but all three bind to an equal number of sites when saturating concentrations are used. Tnitiated estrogens used in bind ing studies were shown to be nadiochemically pure. We conclude that estniol can bind to estrogen receptor and stimulate human breast cancer in tissue culture. Our data do not support an antiestnogenic role for estniol in human breastcancer.