The role of HDAC2 in hormone therapy resistance

描述（由申请人提供）：雌激素受体（ER）的调节一直是女性乳腺癌最成功的治疗策略之一。抑制内质网的两种最常用的方法要么是内质网与抗雌激素（如他莫昔芬）的竞争性结合，要么是使用芳香酶抑制剂减少靶组织中雌激素的局部产生。然而，超过50%的肿瘤最初表达ER的患者出现了对激素治疗的耐药性，并且高比例的肿瘤是先天耐药的。引入新型抗雌激素的广泛努力，如选择性雌激素受体下调剂（SERD）氟维司汀，或选择性雌激素调节剂（SERM）雷洛昔芬，与他莫昔芬相比，取得的成功有限。一种新兴的提高激素治疗效果的策略涉及内质网信号的表观遗传调节。我们和其他实验室的临床前研究表明，在他莫昔芬治疗中加入HDAC抑制剂可以逆转他莫昔芬耐药性，并协同诱导细胞死亡。此外，在我们小组最近完成的一项临床试验中，一部分激素治疗耐药肿瘤患者在接受这种联合治疗后出现了持久的肿瘤消退，这为HDAC抑制作为逆转激素治疗耐药的方法提供了临床证据。伴随该试验的外周血单个核细胞的相关研究表明，有反应的患者的组蛋白乙酰化和HDAC2表达高于无治疗获益的患者。为了确定HDAC与他莫昔芬协同作用的相关靶点，我们证明了HDAC2的siRNA缺失足以增强他莫昔芬的细胞毒性作用，并调节ER阳性乳腺癌细胞中的雌激素信号。HDAC2抑制内质网调控的促凋亡基因，因此它的抑制使SERMs即使在内源性雌激素水平高和内源性内质网过敏的情况下也能发挥其抗激动作用。因此，我们假设HDAC2在激素治疗耐药中起重要作用，其选择性消耗可能为逆转抗雌激素治疗耐药提供了一种新的策略。在这项应用中，我们试图确定HDAC2作为激素敏感和激素耐药乳腺癌治疗的治疗靶点和预测标志物的相关性。在SPECIFIC AIM 1中，我们将在体外模型中确定HDAC2抑制-抗雌激素联合治疗乳腺癌的最佳治疗环境。在SPECIFIC AIM 2中，我们将评估患者样本中的HDAC表达，并确定其作为对这种联合治疗反应的预测标志物的潜力。在SPECIFIC AIM 3中，我们将使用体内乳腺癌异种移植模型，评估单独或联合抗雌激素治疗HDAC2去除诱导原发肿瘤消退和减少转移的能力。

DESCRIPTION (provided by applicant): Modulation of the estrogen receptor (ER) has been one of the most successful treatment strategies in women with breast cancer. The two most commonly used methods of ER inhibition are either competitive binding of the ER with anti-estrogens (e.g. tamoxifen) or to decrease the local production of estrogen in target tissues using an aromatase inhibitor. However, resistance to hormonal therapy emerges in more than 50% of patients whose tumors initially express ER, and a high percentage of tumors are a priori resistant. An extensive effort to introduce novel anti-estrogens, such as the selective estrogen receptor down-regulator (SERD) fulvestrant, or the selective estrogen modulator (SERM) raloxifene, has had limited success beyond that achieved with tamoxifen. An emerging strategy to enhance the efficacy of hormone therapy involves epigenetic modulation of ER signaling. Preclinical studies from our and other laboratories have shown that the addition of an HDAC inhibitor to tamoxifen treatment reverses tamoxifen resistance and synergistically induces cell death. Furthermore, in a recently completed clinical trial by our group, a subset of patients with hormone therapy resistant tumors had durable tumor regression when treated with this combination, providing clinical evidence for HDAC inhibition as an approach for reversing hormone therapy resistance. Correlative studies accompanying this trial in peripheral blood mononuclear cells suggest that histone acetylation and HDAC2 expression was higher in patients with a response than those without treatment benefit. In an effort to determine the relevant HDAC targets for synergy with tamoxifen, we demonstrated that siRNA depletion of HDAC2 was sufficient to potentiate the cytotoxic effects of tamoxifen and modulate estrogen signaling in ER- positive breast cancer cells. HDAC2 represses ER regulated pro-apoptotic genes and thus its inhibition allows SERMs to exert their anti-agonistic effects even in settings of ER hypersensitivity and high endogenous estrogen levels. Therefore, we hypothesize that HDAC2 plays an important role in hormone therapy resistance and its selective depletion may offer a novel strategy to reverse resistance to anti-estrogen therapy. In this application, we seek to determine the relevance of HDAC2 as a therapeutic target and predictive marker of response for the treatment of hormone sensitive and hormone resistant breast cancer. In SPECIFIC AIM 1 we will define the optimal therapeutic setting for combined HDAC2 inhibition-anti-estrogen therapy for the treatment of breast cancer in in vitro models. In SPECIFIC AIM 2, we will evaluate HDAC expression in patient samples and determine their potential as a predictive marker for response to this combined therapy. In SPECIFIC AIM 3 we will evaluate the ability of HDAC2 depletion either alone or in combination with anti- estrogen therapy to induce the regression of primary tumors and to reduce metastases using in vivo breast cancer xenograft models. PUBLIC HEALTH RELEVANCE: Patients with metastatic breast cancer have a median survival of approximately 24 months and account for over 40,000 deaths per year in the United States. Hormonal therapy is one of the most successful and least toxic modalities for patients with breast cancer. However more than 50% of the patients are a priori resistant to hormone therapy, or become therapy resistant over time. Our preclinical and clinical data suggest that epigenetic modulation of the estrogen receptor by HDAC inhibitors may introduce a novel strategy to reverse hormone therapy resistance. This application will determine the optimal clinical setting to integrate HDAC inhibitors into hormonal therapy.