4’-hydroxy Tamoxifen is one of five main phase I metabolites of tamoxifen , a well-known estrogen receptor antagonist in breast but partial estrogen receptor agonist in endometrium. 4’-hydroxy Tamoxifen is a product of cytochrome P450 (CYP)2D6 and CYP2B6 activity. With the addition of a hydroxyl group, 4’-hydroxy tamoxifen has been shown to have a higher affinity for estrogen receptors compared to tamoxifen. At 10-100 μM, 4’-hydroxy tamoxifen is cytotoxic, in a non-apoptotic manner, to HEC-1B and HEC-1A human endometrial adenocarcinoma cell lines.
