Identifying EZH2-dependent vulnerabilities in RB deficient prostate cancer

项目摘要 转移性前列腺癌（mPCa）是不可治愈的，是大多数PCa相关死亡的原因。 因此，迫切需要确定拦截性治疗策略，以提供持久的反应， 患者雄激素剥夺治疗（ADT）是mPCa的一线治疗。ADT最初扩展 存活但不能治愈，因为患者的肿瘤获得去势抵抗（mCRPC）。大多数mCRPC 仍然依赖于雄激素受体（AR）的功能。然而，越来越多地依赖于更有效的 AR拮抗剂，如恩杂鲁胺，在一部分病例中（约20%）， 不依赖于AR活性的耐药机制（CRPC-AI）。CRPC-AI通过谱系可塑性适应ADT， 采用不再依赖于AR表达和信号传导的表型。这些肿瘤可能表现为 神经内分泌特征，干细胞或基底细胞样表型，改变的激酶信号传导，和特征性 表观遗传改变最近，我们和其他人已经确定并验证了新的治疗靶点和驱动因素 CRPC-AI，包括视网膜母细胞瘤-1（RB）和TP 53的缺失，以及特异性 表观遗传/重编程因子，例如（Zeste增强子同源物2）EZH 2和SOX 2。 此外，我们的工作验证了RB 1缺失作为转录变化的主要驱动因素的重要性。 与谱系可塑性、神经内分泌特征增加和对ADT敏感性降低相关。 此外，我们证明了这种谱系重编程在很大程度上依赖于EZH 2，因为EZH 2的抑制， EZH 2使谱系逆转并使RB缺陷型前列腺癌对ADT重新敏感。重要的是，最近的数据 来自mCRPC患者的研究发现，RB遗传畸变是不良结局的最强预测因子。 这些数据暗示RB是驱动致死性前列腺癌的主要分子机制。目前 没有能够为RB功能丧失患者提供持久缓解的治疗选择 （LOF）。因此，迫切需要描述RB LOF的下游效应物，以便治疗性地调节RB LOF的下游效应物。 可以在临床试验中鉴定和验证靶点。我们假设RB缺失显著改变了EZH 2 结合伙伴，并能够形成新的复合物，导致改变的甲基化模式的EZH 2 靶点，并有助于我们先前观察到的对EZH 2功能的依赖。这些改变的 复合物可以提供针对抑制由RB损失驱动的谱系可塑性的唯一脆弱性。具体 对于这种应用，我们将描述在含EZH 2的复合物中发生的变化， 在不存在RB的情况下靶向甲基转移酶，并验证其在肿瘤发展中的功能相关性， 线性可塑性（Aim 1）。我们将进一步进行功能基因组筛选， 这些靶点将在RB缺陷型CRPC-AI的治疗中与EZH 2抑制合作，并将验证这些靶点。 潜在目标（目标2）。最终，这些信息将使我们能够收集足够的初步证据， 提出一个令人信服的理由，开始制药商发起的多中心临床试验。

PROJECT SUMMARY Metastatic prostate cancer (mPCa) is incurable and responsible for the majority of PCa associated mortality. Therefore, there is a critical need to identify interceptive therapeutic strategies to provide durable responses in patients. Androgen deprivation therapy (ADT) is the primary line of treatment for mPCa. ADT initially extends survival but is not curative as the patient’s tumor acquires castration resistance (mCRPC). A majority of mCRPC remain dependent on the function of the androgen receptor (AR). However, increasing reliance on more potent AR antagonists, such as enzalutamide, has led to the emergence, in a subset of cases (approximately 20%), of resistance mechanisms independent of AR activity (CRPC-AI). CRPC-AI adapt to ADT via lineage plasticity, adopting a phenotype no longer reliant on AR expression and signaling. These tumors may display neuroendocrine features, a stem or basal cell-like phenotype, altered kinase signaling, and characteristic epigenetic alterations. Recently, we and others have identified and validated new therapeutic targets and drivers of CRPC-AI, including loss of Retinoblastoma-1 (RB) and TP53, and induction of specific epigenetic/reprogramming factors such as (Enhancer of Zeste Homolog 2) EZH2 and SOX2. Additionally, our work validated the importance of loss of RB1 as the primary driver of transcriptional changes correlating with lineage plasticity, increased neuroendocrine features, and decreased sensitivity to ADT. Moreover, we demonstrated that this lineage reprogramming was largely dependent upon EZH2, as inhibition of EZH2 enabled lineage reversal and re-sensitized RB-deficient prostate cancer to ADT. Importantly, recent data from patients with mCRPC identified RB genetic aberrations as the strongest predictor of poor outcome. These data implicate RB as a dominant molecular mechanism driving lethal prostate cancer. Currently there is no therapeutic option able to provide durable response in patients with RB loss-of-function (LOF). Therefore, there is a critical need to delineate downstream effectors of RB LOF so that therapeutic targets can be identified and validated in clinical trials. We hypothesize that RB loss significantly alters EZH2 binding partners and enables formation of novel complexes, resulting in altered methylation patterns of EZH2 targets and contributing to the dependence on EZH2 function that we have previously observed. These altered complexes may provide exclusive vulnerabilities towards inhibiting lineage plasticity driven by RB loss. Specific to this application, we will characterize the changes which occur in EZH2-containing complexes and methyltransferase targets in the absence of RB and validate their functional relevance in tumor development and linage plasticity (Aim 1). We will further perform a functional genomic screen which will identify synthetic lethal targets which will cooperate with EZH2 inhibition in treatment of RB-deficient CRPC-AI and will validate these potential targets (Aim 2). Ultimately, this information will enable us to gather sufficient preliminary evidence to make a compelling case to commence investigator-initiated multi-center clinical trials.