Description_x000D_ Biochem/physiol Actions_x000D_ 4-Hydroxytamoxifen is an active metabolite of Tamoxifen. 4-Hydroxytamoxifen is formed by cytochrome P450 2D6 in human liver and is a potent and selective estrogen receptor antagonist. 4-Hydroxytamoxifen has been used to stimulate LC3 lipidation and to form autophagic vesicles in a superoxide-dependent manner. Tamoxifen and 4-Hydroxytamoxifen markedly induce cytochrome P450 3A4 (a major drug-metabolizing enzyme) in primary cultures of human hepatocytes. 4-Hydroxytamoxifen undergoes a cis-trans (E-Z) isomerization, a process that occurs in all common laboratory solvents._x000D_ Trans isoform of 4-hydroxytamoxifen possesses antiestrogenic activity, while the cis 4-hydroxytamoxifen serves as a key agonist for estrogen receptor. 4-Hydroxytamoxifen promotes apoptosis via activation of p38 pathway in breast cancer cell cultures._x000D_ Preparation Note_x000D_ 4-Hydroxytamoxifen is provided in a 13 mM solution. The recommended working concentration is 10-100 μM. Therefore, 4-Hydroxytamoxifen Ready Made Solution should be diluted 1:130 - 1:1,300 in cell culture media.