Sharma Naina, Carlson Kathryn E, Nwachukwu Jerome C, Srinivasan Sathish, Sharma Abhishek, Nettles Kendall W, Katzenellenbogen John A
Department of Chemistry, University of Illinois at Urbana-Champaign , 600 South Mathews Avenue, Urbana, Illinois 61801, United States.
Department of Cancer Biology, The Scripps Research Institute ,130 Scripps Way, Jupiter, Florida 33458, United States.
ACS Chem Biol. 2017 Feb 17;12(2):494-503. doi: 10.1021/acschembio.6b00918. Epub 2016 Dec 29.
The estrogen receptors (ERs) bind with high affinity to many structurally diverse ligands by significantly distorting the contours of their ligand-binding pockets. This raises a question: To what degree is ER able to distinguish between structurally related regioisomers and enantiomers? We have explored the structural compliance and specificity of ERα with a set of ligands having a 7-oxa-bicyclo[2.2.1]hept-5-ene sulfonate core and basic side chains typical of selective ER modulators (SERMs). These ligands have two regioisomers, each of which is a racemate of enantiomers. Using orthogonal protecting groups and chiral HPLC, we isolated all 4 isomers and assigned their absolute stereochemistry by X-ray analysis. The 1S,2R,4S isomer has a 80-170-fold higher affinity for ERα than the others, and it profiles as a partial agonist/antagonist in cellular reporter gene assays and in suppressing proliferation of MCF-7 breast cancer cells with subnanomolar potency, far exceeding that of the other isomers. It is the only isomer found bound to ERα by X-ray analysis after crystallization with four-isomer mixtures of closely related analogs. Thus, despite the general compliance of this receptor for binding a large variety of ligand structures, ER demonstrates marked structural specificity and stereospecificity by selecting a single component from a mixture of structurally related isomers to drive ER-regulated cellular activity. Our findings lay the necessary groundwork for seeking unique ER-mediated pharmacological profiles by rational structural perturbations of two different types of side chains in this unprecedented class of ER ligands, which may prove useful in developing more effective endocrine therapies for breast cancer.
雌激素受体（ERs）通过显著扭曲其配体结合口袋的轮廓，以高亲和力与许多结构多样的配体结合。这就引出了一个问题：ER在多大程度上能够区分结构相关的区域异构体和对映异构体？我们用一组具有7-氧杂-双环[2.2.1]庚-5-烯磺酸盐核心和选择性雌激素调节剂（SERMs）典型碱性侧链的配体，研究了ERα的结构适应性和特异性。这些配体有两种区域异构体，每种都是对映体的外消旋体。我们使用正交保护基团和手性高效液相色谱法分离出了所有4种异构体，并通过X射线分析确定了它们的绝对立体化学结构。1S,2R,4S异构体对ERα的亲和力比其他异构体高80-170倍，在细胞报告基因检测中，它表现为部分激动剂/拮抗剂，在抑制MCF-7乳腺癌细胞增殖方面具有亚纳摩尔级别的效力，远远超过其他异构体。在用密切相关类似物的四种异构体混合物结晶后，通过X射线分析发现它是唯一与ERα结合的异构体。因此，尽管该受体对结合多种配体结构具有普遍适应性，但ER通过从结构相关异构体混合物中选择单一成分来驱动ER调节的细胞活性，表现出显著的结构特异性和立体特异性。我们的研究结果为通过对这类前所未有的ER配体中两种不同类型侧链进行合理的结构扰动来寻找独特的ER介导的药理学特征奠定了必要基础，这可能有助于开发更有效的乳腺癌内分泌治疗方法。
