4-Hydroxytamoxifen (ICI 79280) is the active metabolite of Tamoxifen, an estrogen receptor modulator (SERM) with selective and oral potency. 4-Hydroxytamoxifen has antitumor activity and may be used in breast cancer research.

MCF-10A cells:10 μM, Vero cells:15.1 μM, Ishikawa cells:3.57 μg/mL, DU-145 cells:10 μM (EC50), MDA-MB-231 cells:18.43 μM, DU-145 cells:15.3 μM, HEK293 cells:0.07 μM, Ishikawa cells:11.5 μM (EC50), MCF-7 cells:0.0034 μM, ERR:3.3 nM, T47D cells:0.01 μM

METHODS: The human endometrial adenocarcinoma cell line HEC-1B was treated with 4-Hydroxytamoxifen (0.01-100 µM) for 3 days, and cell viability was measured using the CellTiter 96 AQueous One Solution Cell Proliferation Assay.
RESULTS: HEC-1B cells exposed to higher concentrations (1-100 µM) of 4-Hydroxytamoxifen showed significant differences in cell viability between concentrations. [1]
METHODS: ER-positive breast cancer cell lines MCF-7, T47D and BT-474 were treated with 4-Hydroxytamoxifen (0.5-1 µM) and sulforaphane (5 µM) for 48 h. The expression levels of target proteins were detected using Western Blot.
RESULTS: Sulforaphane induced PARP cleavage, the intensity of which was dependent on the cell line, and the combination of sulforaphane and 4-Hydroxytamoxifen further enhanced PARP cleavage. [2]

METHODS: To detect the antitumor activity in vivo, 4-Hydroxytamoxifen (1 mg/kg) was injected intraperitoneally into Nu/Nu mice carrying human breast cancer tumor MCF-7 once a day for twenty-three days.
RESULTS: 4-Hydroxytamoxifen effectively inhibited tumor growth in mice. [3]
METHODS: To induce Cre recombinase activity, 4-Hydroxytamoxifen (30-60 mg/kg) was injected intraperitoneally into Rosa26BEST1-CreERT2 mice once daily for four days.
RESULTS: TdTomato was strongly expressed in the RPE of mice of both sexes. [4]