Kupfer D, Mani C, Lee C A, Rifkind A B
Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545.
Cancer Res. 1994 Jun 15;54(12):3140-4.
Tamoxifen has been found to be metabolized by liver primarily into three metabolites, tamoxifen-N-oxide, formed by the flavin-containing monooxygenase, and N-desmethyl- and 4-hydroxytamoxifen, formed by cytochrome P450. The N-demethylation was demonstrated to be catalyzed by P4503A in rat and human liver; however, the P450s catalyzing the 4-hydroxylation have not been identified. Although 4-hydroxytamoxifen exhibits more potent estrogen agonist/antagonist activity than tamoxifen, the relative contributions of the parent drug and its 4-hydroxy metabolite(s) to the activity of tamoxifen in vivo have not been established. We report here that the rate of tamoxifen 4-hydroxylation is higher in livers of adult chicken and chick embryos than in livers of mammalian species. Tamoxifen 4-hydroxylation was increased by treatment of chick embryos with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), beta-naphthoflavone (beta NF), and to a lesser extent by phenobarbital (PB). The major effect of PB treatment was an increase in tamoxifen N-demethylation. Tamoxifen 4-hydroxylase activity of reconstituted purified chicken P450s was highest for TCDDAA, a P450 active in arachidonate epoxygenation and estradiol 2-hydroxylation, and one of the two major P450s induced by TCDD and beta NF in chick embryo liver. The second P450, TCDDAHH, which is active in aryl hydrocarbon hydroxylase and 7-ethoxyresorufin deethylase was inactive in tamoxifen 4-hydroxylation. Anti-TCDDAA IgG immunoinhibited tamoxifen 4-hydroxylation in microsomes from beta NF-treated embryos by over 80%, but was ineffective against this reaction in the controls. The immunochemical findings together with the reconstitution data identify TCDDAA as the P450 responsible for TCDD/beta NF-induced tamoxifen 4-hydroxylation in chick liver. In PB-treated livers, a P450 fraction containing CYP2H1/H2, the major PB-induced P450s, had the highest tamoxifen 4-hydroxylase and N-demethylase activities, a finding compatible with one or both of those P450s being responsible for the PB-induced tamoxifen 4-hydroxylation and N-demethylation. The findings reported here raise the possibility that exposure of women undergoing tamoxifen therapy to agents that induce human CYP1A2 or CYPB1/2 analogues may produce increased levels of 4-hydroxytamoxifen and that this may affect the therapeutic potency of tamoxifen.
已发现他莫昔芬主要在肝脏中代谢为三种代谢产物，即由含黄素单加氧酶形成的他莫昔芬 - N - 氧化物，以及由细胞色素P450形成的N - 去甲基他莫昔芬和4 - 羟基他莫昔芬。已证明大鼠和人肝脏中的N - 去甲基化由P4503A催化；然而，催化4 - 羟基化反应的细胞色素P450尚未确定。尽管4 - 羟基他莫昔芬比他莫昔芬表现出更强的雌激素激动剂/拮抗剂活性，但母体药物及其4 - 羟基代谢产物对他莫昔芬体内活性的相对贡献尚未明确。我们在此报告，成年鸡和鸡胚肝脏中他莫昔芬4 - 羟基化的速率高于哺乳动物肝脏。用2,3,7,8 - 四氯二苯并 - p - 二恶英（TCDD）、β - 萘黄酮（βNF）处理鸡胚可增加他莫昔芬4 - 羟基化，苯巴比妥（PB）的作用较小。PB处理的主要作用是增加他莫昔芬的N - 去甲基化。重组纯化的鸡细胞色素P450中，TCDDAA的他莫昔芬4 - 羟化酶活性最高，TCDDAA是一种在花生四烯酸环氧化和雌二醇2 - 羟基化中起作用的细胞色素P450，也是鸡胚肝脏中由TCDD和βNF诱导的两种主要细胞色素P450之一。第二种细胞色素P450，TCDDAHH，在芳烃羟化酶和7 - 乙氧基异吩恶唑酮脱乙基酶中起作用，但在他莫昔芬4 - 羟基化中无活性。抗TCDDAA IgG对βNF处理胚胎微粒体中的他莫昔芬4 - 羟基化的免疫抑制率超过80%，但对对照组的该反应无效。免疫化学结果与重组数据共同确定TCDDAA是鸡肝脏中TCDD/βNF诱导的他莫昔芬4 - 羟基化反应的细胞色素P450。在PB处理的肝脏中，含有CYP2H1/H2（主要的PB诱导细胞色素P450）的细胞色素P450部分具有最高的他莫昔芬4 - 羟化酶和N - 去甲基酶活性，这一发现表明这些细胞色素P450中的一种或两种可能是PB诱导的他莫昔芬4 - 羟基化和N - 去甲基化的原因。此处报告的结果增加了一种可能性，即接受他莫昔芬治疗的女性接触诱导人CYP1A2或CYPB1/2类似物的药物可能会使4 - 羟基他莫昔芬水平升高，这可能会影响他莫昔芬的治疗效果。
