Cells in Serum-free Culture Effects of Estradiol and Tamoxifen on Human Breast Cancer

ZR-75-1 human mammary cancer cells can be grown in serumfree medium in an estradiciand tamoxifen-sensitive manner. Growth occurs both in monolayer and suspension culture, al though serum is necessary during the initial plating of the cells in monolayer culture. Optimal stimulation of proliferation by estradiol occurs at 10~8 and 10~9 M. Tamoxifen alone weakly stimulated growth in a dose-dependent manner up to 10~7 M, but inhibition was observed at 10~6 M. This inhibition was not seen if the cells were cultured in 10% dextran:charcoal-treated fetal calf serum. This difference is ascribed to tamoxifen binding components in the serum. In the absence of serum, tamoxifen (10~6 M) abolished the proliferative effect of estradiol at all concentrations of estradici below 10~7 M. Higher concentrations of estradiol partially over came the tamoxifen effect. Consistent antiestrogenic effects of tamoxifen required an estradiol:tamoxifen ratio of 1:1000.