Division of Clinical Pharmacology, Department of Pharmacology and Toxicology, Indiana University Simon Cancer Center, Indiana University School of Medicine, 1001 West 10th Street, Room 7123, Myers Building, Indianapolis, IN 46202, USA.
Breast Cancer Res Treat. 2012 May;133(1):99-109. doi: 10.1007/s10549-011-1699-4. Epub 2011 Aug 4.
To improve the treatment of breast cancer, there has been a need for alternative aromatase inhibitors (AIs) that bring about adequate aromatase inhibition, while limiting side effects. Since two tamoxifen metabolites have been documented as AIs, we tested a wide range of tamoxifen metabolites on aromatase in order to better understand structural interactions with aromatase and constructed structure-function relationships as a first step toward the development of novel inhibitors. The ability of ten tamoxifen metabolites to inhibit recombinant aromatase (CYP19) was tested using microsomal incubations. The selectivity of the most potent aromatase inhibitor identified, norendoxifen, was characterized by studying its ability to inhibit CYP450 enzymes important in clinical drug-drug interactions, including CYP2B6, 2C9, 2C19, 2D6, and 3A. Computerized molecular docking with the X-ray crystallographic structure of aromatase was used to describe the detailed biochemical interactions involved. The inhibitory potency order of the tested compounds was as follows: norendoxifen ≫ 4,4'-dihydroxy-tamoxifen > endoxifen > N-desmethyl-tamoxifen, N-desmethyl-4'-hydroxy-tamoxifen, tamoxifen-N-oxide, 4'-hydroxy-tamoxifen, N-desmethyl-droloxifene > 4-hydroxy-tamoxifen, tamoxifen. Norendoxifen inhibited recombinant aromatase via a competitive mechanism with a K ( i ) of 35 nM. Norendoxifen inhibited placental aromatase with an IC(50) of 90 nM, while it inhibited human liver CYP2C9 and CYP3A with IC(50) values of 990 and 908 nM, respectively. Inhibition of human liver CYP2C19 by norendoxifen appeared even weaker. No substantial inhibition of CYP2B6 and CYP2D6 by norendoxifen was observed. These data suggest that multiple metabolites of tamoxifen may contribute to its action in the treatment of breast cancer via aromatase inhibition. Most of all, norendoxifen may be able to serve as a potent and selective lead compound in the development of improved therapeutic agents. The range of structures tested in this study and their pharmacologic potencies provide a reasonable pharmacophore upon which to build novel AIs.
为了改善乳腺癌的治疗效果，人们需要寻找替代的芳香酶抑制剂（AIs），这些抑制剂既要能充分抑制芳香酶，又要限制副作用。由于已有文献报道两种他莫昔芬代谢物具有 AI 活性，因此我们测试了广泛范围的他莫昔芬代谢物对芳香酶的抑制活性，以更好地了解与芳香酶的结构相互作用，并构建结构-功能关系，作为开发新型抑制剂的第一步。我们使用微粒体孵育实验来测试十种他莫昔芬代谢物抑制重组芳香酶（CYP19）的能力。通过研究其对 CYP450 酶的抑制作用，包括 CYP2B6、2C9、2C19、2D6 和 3A，来确定最有效的芳香酶抑制剂的选择性。计算机分子对接与芳香酶的 X 射线晶体结构一起使用，用于描述涉及的详细生化相互作用。测试化合物的抑制效力顺序如下：诺雷德昔芬>4,4'-二羟基他莫昔芬>依西美坦>N-去甲他莫昔芬、N-去甲-4'-羟基他莫昔芬、他莫昔芬-N-氧化物、4'-羟基他莫昔芬、N-去甲二甲氧基苯并噻吩>4-羟基他莫昔芬、他莫昔芬。诺雷德昔芬通过竞争性抑制机制抑制重组芳香酶，K i 为 35 nM。诺雷德昔芬对胎盘芳香酶的 IC 50 为 90 nM，而对人肝 CYP2C9 和 CYP3A 的 IC 50 值分别为 990 和 908 nM。诺雷德昔芬对人肝 CYP2C19 的抑制作用甚至更弱。诺雷德昔芬对 CYP2B6 和 CYP2D6 没有明显的抑制作用。这些数据表明，他莫昔芬的多种代谢物可能通过抑制芳香酶参与乳腺癌的治疗。最重要的是，诺雷德昔芬可能成为开发改良治疗药物的有效且选择性的先导化合物。本研究中测试的一系列结构及其药理活性提供了一个合理的药效基团，可在此基础上构建新型 AIs。
