Tamoxifen (ICI47699) is a selective and orally effective estrogen receptor modulator (SERM). Tamoxifen has both inhibitory (e.g., mammary cells) and activating (e.g., bone, liver, and uterine cells) activity against estrogens.

METHODS: Human breast cancer cells MCF-7 were treated with Tamoxifen (0.25-4 μM) for 24 h. Cell viability was measured using the CCK-8.
RESULTS: Tamoxifen significantly inhibited the proliferation of MCF-7 cells in a dose-dependent manner. [1]
METHODS: ER-negative breast cancer cells SK-BR3, MDA-MB-453, MDA-MB-468, MDA-MB-231, and HCC-1937 were treated with Tamoxifen (1-10 μM) for 24-36 h, and apoptosis was detected using Flow Cytometry.
RESULTS: Tamoxifen induced apoptosis in MDA-MB-231, MDA-MB-468, MDA-MB-453 and SK-BR3 cells in a dose- and time-dependent manner, while no significant apoptotic effect was observed in HCC-1937 cells. [2]

METHODS: To test the antitumor activity in vivo, Tamoxifen (100 mg/kg) was administered orally to NCr athymic nude mice bearing ER-negative breast cancer tumors MDA-MB-468 or HCC-1937 three times per week for four to five weeks.
RESULTS: Tamoxifen significantly inhibited the growth of MDA-MB-468 tumors, whereas the growth of HCC-1937 tumors was not affected. [2]
METHODS: To test the effect on mouse behavior, Tamoxifen (75 mg/kg in 10% ethanol+90% sunflower seed oil) was administered intraperitoneally to C57BL/6 mice once a day for seven days.
RESULTS: Tamoxifen affects motor activity, socialization, and anxiety in mice. [3]