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.

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]

Cytosol (200 μL) is incubated for 30 min at 4°C with different concentrations of oestradiol, tamoxifen and (4-Hydroxytamoxifen) or dihydroxytamoxifen administered in 10 μL methanol. Control tubes are incubated with 10 μL methanol alone and non-specific binding is determined in a parallel incubation of cytosol (200 μL) with methanol (10 μL) containing DES (5 × 106 M). [2,4,6,7-3H]Oestradiol solution (50 μL) in TED buffer is added to each tube to give a final concentration of 2 × 10-9 M. Incubation is continued for 4 h (4°C) and then 400 μL of a suspension of dextran-coated charcoal (250 mg % Norit A, 2.5 mg % dextran) in TED buffer is added and allowed to stand for 20 min. Tubes are centrifuged at 800 g for 10 min (4°C) and 400 μL samples of the supernatant are added to 10 mL tritium scintillator (6 g butyl PBD, 135 mL toluene, 720 ml dioxane, 100 g naphthalene, 45 mL absolute methanol). Samples are counted for 10 min in a liquid scintillation spectrometer. Counting efficiency is determined by external standardization (35-36 %). Results are represented as a percentage of the specifically bound radioactivity (c.p.m.) in the control tubes[1].

4-Hydroxytamoxifen is formulated in sesame oil[3].Animals of each sex are divided into two groups: one group receives 4-Hydroxytamoxifen [6 μg/0.1 mL sesame oil/day, subcutaneously (s.c.) starting at 06.00 h] injections for three consecutive days, while the other group receives an equivalent amount of sesame oil injection for 3 days. Four hours following the third injection, each group is then subdivided into two groups: one receives four cumulative doses of methamphetamine hydrochloride (10 mg/kg, s.c.), and the other receives a comparable volume of saline at 2-h intervals. Bilateral gonadectomy is performed under pentobarbital anesthesia (50 mg/kg, intraperitoneally). Five weeks after surgery, gonadectomized mice of each sex are randomly divided into six groups. Five groups of each sex receive three daily injections of various concentrations of 4-Hydroxytamoxifen (0, 1.5, 3.0, 6.0, and 12.0 μg/0.1 mL sesame oil/day). Four hours following the third injection, mice receive four doses of methamphetamine (MA, 10 mg/kg) at 2-h intervals. The remaining group of each sex receives sesame oil pretreatment for three consecutive days, followed by saline injections, and serves as the control group[3].