Role of Estrogen Receptor alpha-p53 Interaction in Resistance to Tamoxifen Therap

描述(由申请人提供)：抗激素药物他莫昔芬被批准用于治疗患有早期和晚期以及早期雌激素受体(ER)阳性乳腺癌的妇女。已知他莫昔芬通过与雌激素受体结合而对乳腺癌细胞发挥作用，从而阻止雌激素的结合。然而，一个主要的临床问题是，大量ER阳性的乳腺肿瘤患者要么对他莫昔芬治疗没有反应，要么对他莫昔芬产生耐药性。尽管已经提出了这种耐药性的几个看似合理的原因，但对他莫昔芬治疗的耐药性机制仍很不清楚。ER介导雌激素促进乳腺癌细胞增殖的作用。肿瘤抑制蛋白P53通过介导细胞周期停滞和/或细胞凋亡来预防肿瘤的发生。目前尚不清楚这两条拮抗途径之间是否存在直接联系。我们的实验证明ER1与P53结合并抑制其在人乳腺癌细胞中的功能。重要的是，雌激素增强了ER1-P53的相互作用，而抗激素药物他莫昔芬和弗维斯特则破坏了这种相互作用。我们回顾性临床研究的结果与我们的细胞和分子观察相关联，并与报道的野生型P53状态与他莫昔芬治疗反应更好的报道相一致。基于这些发现，推测ER1对野生型P53的抑制可能是他莫昔芬作用的一个重要机制。如果肿瘤有突变的(因此功能失调的)P53，他莫昔芬的作用的益处就变得无关紧要了。为了验证这些假设，对50名新诊断为ER阳性、表达野生型P53的绝经前妇女进行了一项试验性随机临床试验。其具体目的是：(1)与未经治疗的患者相比，在手术前接受20 mg他莫昔芬治疗四周的患者中，调查ER-P53相互作用的状态；(2)通过监测手术前接受或未接受20 mg三苯氧胺治疗四周的患者肿瘤中选定的P53靶基因的表达，确认P53的野生型状态，并分析P53通路的功能状态。这些研究将结合临床、病理学、细胞学和分子生物学的专业知识，在主办机构的新诊断乳腺癌患者中进行前瞻性研究。ER和P53在乳腺肿瘤中的地位、相互作用及其后果将通过免疫组织化学、细胞和分子方法进行分析。这项拟议的工作有可能将范式转变为分析他莫昔芬治疗耐药的潜在机制。公共卫生相关性：这项研究从一个新的角度解决了他莫昔芬治疗的耐药性问题，提出了一项试点临床试验，以分析他莫昔芬是否可以通过破坏ER-P53相互作用来恢复肿瘤抑制基因P53的功能。这项研究的结果将有助于制定策略，以确定哪些乳腺癌患者将从他莫昔芬治疗中受益最大，并避免不必要的接触这种药物及其众多副作用。因此，这项拟议研究的结果可能会影响乳腺癌患者个体化治疗的发展。

DESCRIPTION (provided by applicant): The anti hormonal drug tamoxifen is approved for the treatment of women with early and advanced and early stage estrogen receptor (ER)-positive breast cancer. Tamoxifen is known to exert its effects on breast cancer cells by binding to the estrogen receptor, thereby preventing the binding of estrogen. However, a major clinical problem is that a large number of patients with ER-positive breast tumors either do not respond to tamoxifen therapy or develop resistance to it. Although several plausible reasons for such resistance have been suggested, the mechanisms of resistance to tamoxifen therapy remain largely unclear. ER mediates effects of estrogen in promoting proliferation of breast cancer cells. Tumor suppressor protein p53 guards against tumorigenesis by mediating cell cycle arrest and/or apoptosis in response to various cellular stressors. Whether there is a direct link between these two antagonistic pathways has remained unclear. Our experiments have demonstrated that ER1 binds to p53 and represses its function in human breast cancer cells. Importantly, estrogen enhances ER1-p53 interaction, whereas anti-hormonal drugs tamoxifen and fulvestrant disrupt the interaction. Results from our retrospective clinical studies correlate with our cellular and molecular observations and are consistent with the reported association of wild type p53 status with better response to tamoxifen therapy. Based on these findings, it is hypothesized that relieving suppression of wild type p53 by ER1 could be an important mechanism underlying tamoxifen action. The benefit of tamoxifen's effect becomes irrelevant if the tumor has mutant (and therefore dysfunctional) p53. To test these hypotheses, a pilot randomized clinical trial of 50 pre- menopausal women with newly diagnosed ER-positive breast cancer expressing wild type p53 is proposed. The Specific Aims are: (1) Investigate the status of ER-p53 interaction in patients treated with 20 mg of tamoxifen for four weeks prior to surgery as compared to the interaction in untreated patients, and (2) Confirm the wild type status of p53 and analyze the functional status of p53 pathway by monitoring expression of selected p53-target genes in tumors in patients who have or have not been treated with 20 mg tamoxifen for four weeks prior to surgery. These studies will be conducted prospectively in newly diagnosed breast cancer patients at the host institution using a combination of clinical, pathological, cellular, and molecular biology expertise. The status of ER and p53, their interaction, and its consequences in breast tumors will be analyzed with immunohistochemical, cellular, and molecular approaches. The proposed work has the potential to bring about a paradigm shift to the analysis of mechanisms underlying resistance to tamoxifen therapy. PUBLIC HEALTH RELEVANCE: This research addresses resistance to tamoxifen therapy from a novel angle by proposing a pilot clinical trial to analyze if tamoxifen can restore functional tumor suppressor p53 by disrupting ER-p53 interaction. Results from this study will help develop strategies to identify breast cancer patients who would most benefit from tamoxifen therapy, and avoid unnecessary exposure to this drug and its numerous side effects. Thus, results from the proposed study could impact the development of individualized therapy for breast cancer patients.