CARCINOGENICITY OF B RING UNSATURATED ESTROGENS

关于雌激素替代疗法（ERT）的主要问题是长期使用会导致乳腺癌风险的显著增加。 ERT最常用的制剂是倍美力，这是一种主要由B环不饱和雌激素组成的制剂，包括马烯雌酚（Eq）和马烯雌酚（Eqn）的共轭形式。 我们的初步研究表明，在表达细胞色素P4501 B1（CYP 1B 1）的几种人乳腺衍生细胞系中，Ah受体调节Eqn代谢为4-羟基化代谢物。 从这些4-羟基代谢物衍生的半醌和醌类，它们是加合的并导致自由基的产生，可能参与致癌作用。 我们假设雌激素参与了致癌的启动和促进阶段，甾体雌激素B环的芳香性增加了致癌效力。我们广泛的，长期的目标是确定是否甾体雌激素，包括B环不饱和雌激素，Eq和Eqn，通过代谢活化通过儿茶酚雌激素致癌。 我们的具体目标是：1）表征一系列永生化肿瘤和非肿瘤来源的人乳腺细胞系中的Eq和Eqn代谢。 将研究Eq和Eqn生物活化的途径，包括偶联物的水解、还原为17 β-二氢形式和羟基化为儿茶酚雌激素。 2)以Eq、Eqn及其17 α-和17 β-二氢形式作为底物，测定CYP 1、CYP 2和CYP 3家族的人细胞色素P450的儿茶酚合成活性。 3)建立在乳腺上皮中表达人CYP 1B 1的转基因小鼠系，4）确定用Eq和Eqn处理对人CYP 1B 1转基因小鼠中DNA损伤和乳腺肿瘤发生率的影响。 本文所述的研究将提供关于乳腺上皮细胞中人酶代谢B环不饱和雌激素的新结果，并可能提供支持Eq、Eqn和内源性代谢活化在人乳腺癌发生中的作用的机制数据。

The major concern regarding estrogen replacement therapy (ERT) is the significant increase in the risk of breast cancer that accompanies long-term use. The most commonly used formulation for ERT is Premarin, a preparation consisting largely of B-ring unsaturated estrogens including conjugated forms of equilin (Eq) and equilenin (Eqn). Our preliminary studies show Ah-receptor-regulated metabolism of Eqn to 4-hydroxylated metabolites in several human breast-derived cell lines expressing cytochrome P4501B1 (CYP1Bl). Semiquinones and quinones derived from these 4-hydroxy metabolites, which are adductive and lead to free radical production, may be involved in carcinogenesis. We hypothesize that estrogens are involved in both the initiation and promotion phases of carcinogenesis, and that aromaticity of the B-ring of steroidal estrogens increases carcinogenic potency. Our broad, long-term goal is to determine whether steroidal estrogens, including the B-ring unsaturated estrogens, Eq and Eqn, are carcinogenic through metabolic activation via catechol estrogens. 0ur Specific Aims are to: 1) Characterize Eq and Eqn metabolism in a series of immortalized tumor- and non-tumor-derived human breast-cell lines. Pathways of Eq and Eqn bioactivation involving hydrolysis of conjugates, reduction to 17beta-dihydro forms and hydroxyation to catechol estrogens will be investigated. 2) Determine the catechol synthetic activities of human cytochromes P450 of the CYP1, CYP2, and CYP3 families with Eq, Eqn, and their 17alpha- and 17beta-dihydro forms as substrates. 3) Establish transgenic mouse lines expressing human CYP1B1 in the mammary epithelium, 4) Determine the effects of treatment with Eq and Eqn on DNA damage and the incidence of mammary-gland tumors in human CYP1B1-transgenic mice. The studies described here will provide novel results regarding the metabolism of the B-ring unsaturated estrogens by human enzymes in breast epithelial cells, and may provide mechanistic data supporting a role of metabolic activation of Eq, Eqn, and endogenous in the initiation of carcinogenesis in the human breast.