Targeting Mechanisms of Endocrine Resistance in Breast Cancer

项目总结/摘要 抑制雌激素受体（ER）信号传导的内分泌疗法是全身治疗雌激素缺乏症的主要方法。 ER+乳腺癌。这些疗法包括降低雌激素水平的方法， 绝经前妇女中的促肾上腺素释放激素（LHRH）激动剂和绝经后妇女中的芳香化酶抑制剂（AI） 绝经后妇女和直接ER拮抗剂如他莫昔芬和氟维司群。在晚期疾病中， 然而，在这种情况下，内分泌治疗抗性癌症几乎总是出现，并且是癌症的主要原因。 乳腺癌死亡人数已经提出了多种遗传和表观遗传机制来解释 出现内分泌治疗抵抗。包括我们自己在内的几个研究小组已经描述了 ER基因（ESR 1）本身在大约20-30%的病例中作为耐药机制。我们已经开发 内分泌治疗耐药性ER+乳腺癌的细胞系和患者源性异种移植（PDX）模型， 这些ESR 1突变，并发现这些突变表现出配体独立的功能， 雌二醇结合的野生型ER以及赋予ER新信号传导的等位基因特异性新变体性质 促进促转移性EMT样表型的功能。此外，使用全基因组CRISPR筛选， 我们已经鉴定出ER+乳腺癌生长所必需的基因。重要的是，我们还确定了 在野生型ER的情况下其缺失赋予内分泌治疗抗性的基因，包括NF 1，TSC 1/2， PTEN和CSK。在这些研究中，我们发现CSK的缺失导致SRC家族激酶的激活 (SFK)从而促进雌激素非依赖性生长和促转移癌细胞表型。值得注意的是， CSK的表达受雌激素调节，通过ER直接结合到细胞中的转录增强子。 CSK基因这揭示了雌激素诱导的负反馈回路的存在， 因此限制了靶向ER的当前疗法的功效。这种反馈的存在 循环提出了一个挑衅性的假设，即目前的内分泌疗法本身可能促进促 转移表型与该计划的总体主题一致，以定义新的治疗方法 脆弱性，我们将研究遗传和表观遗传异质性如何影响耐药性的发展， 内分泌治疗该项目的成功将使开发综合模型的 内分泌治疗抵抗的机制，包括肿瘤异质性的影响， 用于预测有效的新治疗靶点，并将允许研究 内分泌治疗耐药、内分泌治疗和转移。

Project Summary/Abstract Endocrine therapies that inhibit estrogen receptor (ER) signaling are the mainstay of the systemic treatment of ER+ breast cancers. These therapies consist of approaches to reduce estrogen levels including luteinizing hormone-releasing hormone (LHRH) agonists in premenopausal women and aromatase inhibitors (AI) in postmenopausal women, and direct ER antagonists such as tamoxifen and fulvestrant. In the advanced disease setting, however, endocrine therapy-resistant cancers almost invariably emerge and are the major cause of breast cancer deaths. Multiple genetic and epigenetic mechanisms have been proposed to explain the emergence of endocrine therapy resistance. Several groups including our own have characterized mutations in the ER gene (ESR1) itself as a mechanism of resistance in approximately 20-30% of cases. We have developed cell line and patient-derived xenograft (PDX) models of endocrine therapy-resistant ER+ breast cancer driven by these ESR1 mutations and have found that these mutations exhibit both ligand-independent functions that mimic estradiol-bound wild-type ER as well as allele-specific neomorphic properties that confer on ER novel signaling functions that promote a pro-metastatic EMT-like phenotype. In addition, using genome-wide CRISPR screens, we have identified genes essential for the growth of ER+ breast cancers. Importantly, we have also identified genes whose loss confers endocrine therapy resistance in the setting of the wild-type ER, including NF1, TSC1/2, PTEN and CSK. In these studies, we have found that loss of CSK leads to activation of SRC-family kinases (SFK), thereby promoting estrogen-independent growth and a pro-metastatic cancer cell phenotype. Notably, expression of CSK is regulated by estrogen through binding of ER directly to a transcriptional enhancer in the CSK gene. This reveals the existence of an estrogen-induced negative feedback loop that constrains the growth of ER+ tumors thereby limiting the efficacy of current therapies that target ER. The existence of this feedback loop suggests the provocative hypothesis that current endocrine therapies may themselves promote a pro- metastatic phenotype. Consistent with the overarching theme of this program to define new therapeutic vulnerabilities, we will study how genetic and epigenetic heterogeneity impact the development of resistance to endocrine therapy. Success of this project will allow the development integrative models of the mechanisms of endocrine therapy resistance that include the effect of tumor heterogeneity that can be used to predict effective new therapeutic targets and will allow the investigation of the link between endocrine therapy resistance, endocrine therapy and metastasis.