Regulation of a Tumor Target Through Steroid Receptors

描述(申请人提供)：在数量有限的表达叶酸受体(FR)型α的正常组织中，受体被限制在顶端(腔)表面，在那里它无法通过循环到达。因此，FR-α被认为是一个很有前途的肿瘤靶点，特别是在妇科癌症的主要亚型中，它可以选择性地通过血流输送广泛的诊断和治疗药物。尽管来自临床前和临床研究的大量不断增长的证据支持开发这种诊断/治疗的可行性，但将在动物模型中获得的成功转化为人类癌症是混乱的，因为肿瘤中FR-α表达水平的变异性和异质性。我们之前已经证明，在雌激素受体(ER)阳性的肿瘤中，抗雌激素将上调FR-α基因。我们现在发现，FR-α基因可以被孕激素受体(PR)、糖皮质激素受体(GR)和雄激素受体(AR)转录调控，极大地扩大了FR-α肿瘤的组织学范围，在这些肿瘤中，受体的表达可能被优化以实现有效的靶向。PR、GR和AR的激动剂通过明显不同的机制和在缺乏经典激素反应元件的情况下促进FR-α的转录，此外，组蛋白去乙酰化酶(HDAC)抑制剂曲古抑素A似乎增强了这些作用，克服了细胞上下文依赖的共同调节因子的限制。PR、GR和AR对FR-α基因的作用将在体外和动物肿瘤移植模型的生理环境中进行足够详细的机制研究，以建立通过这些核受体调控FR-α表达的生物学背景和临床条件。其具体目的是：(1)FR-α核受体调控的机制研究：阐明核受体的个体作用模式(直接和间接)，建立协同调节要求/限制，绘制FR-α启动子中PRA、PRB、GR和AR的作用部位图，识别和关联相关转录因子的动态，检查耐受性良好的HDAC抑制剂的效果，并测试各种合成激动剂；(Ii)发展和研究稳定的重组细胞系，该重组细胞系将单独和联合表达类固醇受体和FR-α，以反映它们在肿瘤中的联合表达模式，并研究单独和联合核受体在体外对这些细胞中FR-α的调控及其潜在的串扰机制；(Iii)利用AIM II和FR靶向显像剂开发的具有代表性的模型细胞系，测试适当的类固醇受体激动剂和拮抗剂以及HDAC抑制剂在动物肿瘤异种移植模型中的作用。预计拟议的研究将为这一概念的临床试验奠定系统的基础，即操纵肿瘤组织以提高全身成像的敏感性和FR靶向药物的治疗效果。

DESCRIPTION (provided by applicant): In the limited number of normal tissues in which the folate receptor (FR) type alpha is expressed, the receptor is restricted to apical (luminal) surfaces, where it is inaccessible via the circulation. As a consequence, FR-alpha is regarded as a promising tumor target, particularly in major subtypes of gynecological cancers, for the selective delivery of a broad range of diagnostic and therapeutic agents through the blood stream. Even though a large and growing body of evidence from pre-clinical and clinical studies supports the feasibility of developing such diagnostics/therapies, translating the success obtained in animal models to human cancer is confounded by variability and heterogeneity in the expression levels of FR-alpha in the tumors. We have previously shown that antiestrogens will up-regulate the FR-alpha gene in estrogen receptor (ER)-positive tumors. We now show that the FR-alpha gene can be transcriptionally modulated by the progesterone receptor (PR), the glucocorticoid receptor (GR) and the androgen receptor (AR), greatly expanding the histologic range of FR-alpha+ tumors in which the receptor expression may be optimized for effective targeting. Agonists of PR, GR and AR enhance FR-alpha transcription by apparently distinct mechanisms and in the absence of classical hormone response elements and further, trichostatin A, a histone deacetylase (HDAC) inhibitor, appears to potentiate these effects, overcoming cell context-dependent co-regulator limitations. The actions of PR, GR and AR on the FR-alpha gene will be studied in sufficient mechanistic detail in vitro and in the physiologic milieu of animal tumor xenograft models to establish the biological contexts and clinical conditions in which FR-alpha expression may be controlled through these nuclear receptors. The specific aims are: (i) Mechanistic studies of nuclear receptor modulation of FR-alpha: Elucidate the individual modes of action (direct vs. indirect) of the nuclear receptors, establish co-regulator requirements/limitations, map the sites of action of PRa, PRb, GR and AR in the FR-alpha promoter, identify and relate the dynamics of the relevant transcription factors, examine the effects of well tolerated HDAC inhibitors and test various synthetic agonists; (ii) Develop and study stable recombinant cell lines that will express the steroid receptors individually and in combination, together with FR-alpha to reflect their in vivo (co)expression patterns in tumors and characterize individual and combined nuclear receptor mediated modulation of FR-alpha in these cells in vitro and mechanisms of potential cross-talk; (iii) Test the effects of the appropriate steroid receptor agonists and antagonists and HDAC inhibitors in animal tumor xenograft models using representative model cell lines developed in Aim ii and FR-targeted imaging agents. It is anticipated that the proposed studies will systematically establish a foundation for clinical trials of this concept of manipulating tumor tissues to enhance the sensitivity of whole body imaging and the therapeutic efficacy of FR-targeted agents.