Flow cytometry analysis of the growth inhibitory effect of 4-hydroxy-tamoxifen on a human breast carcinoma cell line.

Growth kinetics of BT-20 cells (an ER- cell line) have been studied with flow cytometry, cell counting and 3H-thymidine incorporation. The cell cycle lasts about 40 hours, with a maximum SG2M about 25h after seeding. 4-Hydroxy-tamoxifen (OH-Tamoxifen) (10(-7) M to 10(-5) M) inhibits BT-20 cell growth with maximum inhibition at 24-28h after plating. The inhibitory effect of OH-Tamoxifen is also demonstrated by a decrease in 3H-thymidine incorporation and by a reduction in cell number. These results suggest that OH-Tamoxifen is able to act upon an ER-cell line through a pathway which is different from that of estrogens.