Katzenellenbogen J A, Carlson K E, Katzenellenbogen B S
J Steroid Biochem. 1985 May;22(5):589-96. doi: 10.1016/0022-4731(85)90210-9.
In many estrogen responsive systems the isomers of tamoxifen are known to have different biological character-the trans isomer is generally an antagonist and the cis isomer an agonist. Attempts to similarly characterize the isomers of hydroxytamoxifen (which differ greatly in their affinity for the estrogen receptor) are shown to be complicated by their facile isomerization. This isomerization was studied in cultures of estrogen receptor positive MCF-7 human breast cancer cells and monitored by HPLC under reversed phase conditions. Hydroxytamoxifen isomers that are initially 99% pure, undergo a time and temperature dependent isomerization, so that after 2 days in tissue culture medium at 37 degrees C they have isomerized to the extent of 20%. This isomerization occurs in the cell-free medium alone and cannot be attributed to a metabolic conversion by the cells. The isomerization occurs much more slowly at 4 than at 37 degrees C and can be reduced considerably by various antioxidants (butylated hydroxytoluene, ascorbate, alpha-tocopherol, retinoic acid and retinal); however, at concentrations that block isomerization, these antioxidants are toxic to the cells. Although the medium contains both the cis and trans isomers of hydroxytamoxifen, the MCF-7 cells preferentially accumulate the trans isomer and the material associated with the nuclear estrogen receptor is, in all cases, mainly the higher affinity trans isomer. A similar preference of the estrogen receptor for the trans isomer is seen with diethylstilbestrol, resulting again in almost exclusive accumulation of the trans isomer in the receptor binding site. These experiments indicate the importance of verifying the isomer compositions of easily isomerizable non-steroidal estrogens and antiestrogens, such as diethylstilbestrol and hydroxytamoxifen, both in stock solutions and in experimental samples (especially those derived from receptor-associated material), so as to ascertain that the activity of the individual isomers is being correctly assigned.
在许多雌激素反应系统中，已知他莫昔芬的异构体具有不同的生物学特性——反式异构体通常是拮抗剂，而顺式异构体是激动剂。羟基他莫昔芬的异构体（它们对雌激素受体的亲和力差异很大），试图进行类似的特性描述时，却因它们容易异构化而变得复杂。在雌激素受体阳性的MCF-7人乳腺癌细胞培养物中研究了这种异构化，并在反相条件下通过高效液相色谱法进行监测。最初纯度为99%的羟基他莫昔芬异构体，会发生时间和温度依赖性的异构化，因此在37℃的组织培养基中培养2天后，它们异构化的程度达到20%。这种异构化仅在无细胞培养基中发生，不能归因于细胞的代谢转化。在4℃时异构化比在37℃时慢得多，并且可以被各种抗氧化剂（丁基化羟基甲苯、抗坏血酸盐、α-生育酚、视黄酸和视黄醛）显著降低；然而，在阻止异构化的浓度下，这些抗氧化剂对细胞有毒。尽管培养基中同时含有羟基他莫昔芬的顺式和反式异构体，但MCF-7细胞优先积累反式异构体，并且在所有情况下，与核雌激素受体相关的物质主要是亲和力较高的反式异构体。己烯雌酚也显示出雌激素受体对反式异构体有类似的偏好，这再次导致反式异构体几乎只在受体结合位点积累。这些实验表明，在储备溶液和实验样品（特别是那些来自受体相关物质的样品）中，验证易异构化的非甾体雌激素和抗雌激素（如己烯雌酚和羟基他莫昔芬）的异构体组成非常重要，以便确定各个异构体的活性是否被正确归因。
