Dissecting the Mechanisms of Tamoxifen Action

剖析他莫昔芬的作用机制

基本信息

批准号：
8250280
负责人：
Manohar Ratnam
金额：
$ 5万
依托单位：
UNIVERSITY OF TOLEDO HEALTH SCI CAMPUS
依托单位国家：
美国
项目类别：
财政年份：
2009
资助国家：
美国
起止时间：
2009-07-01 至 2012-09-21
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/8250280
关键词：
Academia Address Adjuvant Therapy Affect Agonist Animal Model Biology Breast Cancer Cell Cancer cell line Case-Control Studies Cell Proliferation Cell Survival Cells Chemicals Chromatin Classification Clinical Collaborations Collection Complex Coupled Distal Effectiveness Endometrial Carcinoma Endometrial Neoplasms Estradiol Estrogen Receptors Estrogen receptor negative Estrogen receptor positive Estrogens Evaluation Exhibits Frequencies Future Gene Activation Gene Expression Gene Expression Profiling Gene Expression Regulation Gene Targeting Genes Genomics Growth Health High Risk Woman Human In Vitro Incidence Industry Laboratories Lead Libraries Ligands Light MCF7 cell Mammary Neoplasms Modeling Molecular Molecular Profiling Mus Nature Nuclear Receptors Outcome Pattern Pharmaceutical Preparations Physiological Physiological Effects of Drugs Positioning Attribute Postmenopause Premenopause Prevention Process Property Raloxifene Reagent Recurrence Repression Resistance Risk Signal Transduction Site TAF10 gene Tamoxifen Testing Therapeutic Therapeutic Effect Time Tumor Suppression Uterus Withholding Treatment Woman Xenograft Model base cancer cell cell growth comparative experience gene repression improved in vivo malignant breast neoplasm neoplastic cell novel prevent promoter receptor binding success tool treatment duration tumor tumor growth tumor xenograft xenoestrogen

项目摘要

DESCRIPTION (provided by applicant): Tamoxifen is a mainstay in the treatment of estrogen receptor (ER)-positive breast cancer. However, long-term treatment of women at high risk for breast cancer reduces the incidence of both invasive and non-invasive ER+ breast cancer by only about 50 percent and also modestly increases the risk of endometrial cancer. Breast tumors could also become dependent on the drug for growth. Therefore, there is considerable room for improvement over tamoxifen. The clinical limitation of tamoxifen is reflected in breast and endometrial tumor xenograft models. Understanding different molecular mechanistic aspects of tamoxifen is necessary for improving upon this drug in decreasing the incidence and recurrence of breast tumors. A remarkably under-investigated aspect of estrogen (E2) action is gene repression which is frequently prevented by tamoxifen (de-repression). We have established a novel non-classical mechanism for direct gene repression by E2 in which ER forms a TAFII30-associated co-repressor complex; tamoxifen prevents this repression by simply dissociating the complex. We have identified synthetic ER ligands that mimic tamoxifen in a variety of model promoters and genes; however, these compounds differ from tamoxifen in that they behave like E2 with respect to the above mechanism of direct gene repression. Remarkably, the new compounds not only blocked E2-stimulated MCF-7 breast tumor cell proliferation but were also antiproliferative in tamoxifen-resistant MCF-7 cells developed in vivo; they also blocked E2-stimulated growth of Ishikawa uterine endometrial cancer cells in contrast to tamoxifen. The compounds did not affect the growth of ER-negative cells. The findings beg the question of what the physiological correlates of different mechanisms of gene de- repression by tamoxifen might be, particularly in relation to the effects of tamoxifen on the incidence and growth of breast and endometrial tumors. We hypothesize that gene de-repression by tamoxifen offers distinctive mechanisms that can provide the basis for identification of mechanistic classes of ER antagonists with superior therapeutic effects in breast cancer. In other words, tamoxifen's property of de-repressing certain genes may, in itself or by association with other effects, help in creating a condition that would be permissive to the onset or success of different survival/proliferation mechanisms, thereby constraining the drug's beneficial effects in certain cell contexts; the abrogation of such a mechanism(s) in certain ER antagonists may have a net effect of indirectly suppressing cell survival/proliferation, thereby increasing the duration of tumor suppression. The ER antagonists that we have identified (as well as those we expect to identify in the future) are excellent tools to address the hypothesis since they share a common mechanistic difference related to gene repression/de- repression. Since the expected differences in gene de-repression profiles of the compounds vs. tamoxifen are relatively small, it may even be feasible to use bio-statistical analysis coupled with multiple gene knockdown approaches to ultimately relate a group of E2 targets de-repressed by tamoxifen to specific physiological effects of the drug. Regardless of the outcome, it is necessary and feasible at this time to initiate systematic studies to shed light on the nature and extent of the possible impacts of novel and uninvestigated aspects of the genomic action of tamoxifen. The mechanism-based chemical biology approach proposed here is timely because of the availability of a large collection of partially characterized ER ligands, whose classification has been limited and largely empiric. Aim 1: Further investigate molecular mechanisms of gene de-repression by tamoxifen and identify additional model genes to represent each mechanism. Aim 2: Continue to identify new mechanistic classes of ER antagonists; compare tamoxifen and the new compounds with respect to cellular effects in ER+ breast and endometrial cancer cell lines in vitro; determine differential gene repression patterns and attempt to identify critical gene targets. Aim 3: Undertake a comparative evaluation of the effects of tamoxifen and selected new reagents in relation to inhibition and latency of breast and endometrial tumors using ER+ human tumor cells in xenograft models that have previously provided the most predictive clinical information for tamoxifen and also examine uterotropic effects. PUBLIC HEALTH RELEVANCE: The drug, tamoxifen is a mainstay in suppressing the growth and decreasing the incidence/recurrence of breast cancer. To improve upon this drug, it is necessary to understand all aspects of its mechanism of action. We have discovered a new aspect of tamoxifen's molecular actions which, under the appropriate conditions, could limit the drug's effectiveness by counteracting its own ability to inhibit tumor growth. We propose to further investigate this and other mechanisms of tamoxifen action and in the process, to identify lead compounds whose properties are superior to that of tamoxifen.

描述（由申请人提供）：他莫昔芬是治疗雌激素受体（ER）阳性乳腺癌的主要药物。然而，对乳腺癌高危女性进行长期治疗只能将侵袭性和非侵袭性 ER+ 乳腺癌的发病率降低约 50%，并且还会适度增加子宫内膜癌的风险。乳腺肿瘤的生长也可能依赖于药物。因此，与他莫昔芬相比，还有相当大的改进空间。他莫昔芬的临床局限性反映在乳腺癌和子宫内膜肿瘤异种移植模型中。了解他莫昔芬的不同分子机制对于改进该药物降低乳腺肿瘤的发生率和复发是必要的。雌激素 (E2) 作用的一个明显未被充分研究的方面是基因抑制，而基因抑制经常被他莫昔芬（去抑制）所阻止。我们建立了一种通过 E2 直接抑制基因的新型非经典机制，其中 ER 形成 TAFII30 相关的共抑制复合物；他莫昔芬通过简单地解离复合物来防止这种抑制。我们已经在多种模型启动子和基因中鉴定出模拟他莫昔芬的合成 ER 配体；然而，这些化合物与他莫昔芬的不同之处在于，就上述直接基因抑制机制而言，它们的行为类似于 E2。值得注意的是，这些新化合物不仅能阻断 E2 刺激的 MCF-7 乳腺肿瘤细胞增殖，而且还能抑制体内开发的他莫昔芬耐药 MCF-7 细胞的增殖；与他莫昔芬相比，它们还阻断了 E2 刺激的 Ishikawa 子宫内膜癌细胞生长。这些化合物不影响 ER 阴性细胞的生长。这些发现引出了一个问题：他莫昔芬不同基因去抑制机制的生理相关性可能是什么，特别是与他莫昔芬对乳腺和子宫内膜肿瘤的发生和生长的影响有关。我们假设他莫昔芬的基因去抑制提供了独特的机制，可以为鉴定对乳腺癌具有优异治疗效果的 ER 拮抗剂的机制类别提供基础。换句话说，他莫昔芬去抑制某些基因的特性本身或与其他效应相关，可能有助于创造一种允许不同生存/增殖机制发生或成功的条件，从而限制药物的有益作用在某些细胞环境中；消除某些 ER 拮抗剂中的这种机制可能会产生间接抑制细胞存活/增殖的净效应，从而增加肿瘤抑制的持续时间。我们已经鉴定的 ER 拮抗剂（以及我们期望将来鉴定的那些）是解决该假设的极好工具，因为它们具有与基因抑制/去抑制相关的共同机制差异。由于化合物与他莫昔芬的基因去抑制谱的预期差异相对较小，因此甚至可以使用生物统计分析结合多基因敲低方法来最终关联一组由他莫昔芬去抑制的 E2 靶点药物的特定生理作用。无论结果如何，此时启动系统研究是必要且可行的，以阐明他莫昔芬基因组作用的新颖且未经研究的方面可能影响的性质和程度。这里提出的基于机制的化学生物学方法是及时的，因为可以获得大量部分表征的 ER 配体，其分类受到限制并且很大程度上是经验性的。目标 1：进一步研究他莫昔芬去抑制基因的分子机制，并确定代表每种机制的其他模型基因。目标 2：继续鉴定 ER 拮抗剂的新机制类别；比较他莫昔芬和新化合物对 ER+ 乳腺癌和子宫内膜癌细胞系的体外细胞效应；确定差异基因抑制模式并尝试识别关键基因靶标。目标 3：在异种移植模型中使用 ER+ 人类肿瘤细胞，对他莫昔芬和选定的新试剂对乳腺和子宫内膜肿瘤的抑制和潜伏期的影响进行比较评估，该模型先前为他莫昔芬提供了最具预测性的临床信息，并检查了子宫亲和性影响。公共卫生相关性：他莫昔芬是抑制乳腺癌生长和降低乳腺癌发病率/复发率的主要药物。为了改进这种药物，有必要了解其作用机制的各个方面。我们发现了他莫昔芬分子作用的一个新方面，在适当的条件下，它可以通过抵消其自身抑制肿瘤生长的能力来限制药物的有效性。我们建议进一步研究他莫昔芬的这一作用机制和其他机制，并在此过程中鉴定其性质优于他莫昔芬的先导化合物。