Identifying EZH2-dependent vulnerabilities in RB deficient prostate cancer

项目总结 转移性前列腺癌(MPCA)是不治之症，是前列腺癌相关死亡的主要原因。 因此，迫切需要确定拦截治疗策略，以提供持久的反应。 病人。雄激素剥夺疗法(ADT)是MPCA的主要治疗方法。ADT最初扩展 存活，但无法治愈，因为患者的肿瘤获得了去势抵抗(MCRPC)。MCRPC的大多数人 仍然依赖雄激素受体(AR)的功能。然而，对更强大的 AR拮抗剂，如苯扎鲁胺，在部分病例(约20%)中导致出现 不依赖AR活性的抗性机制(CRPC-AI)。CRPC-AI通过谱系可塑性适应ADT， 采用一种不再依赖AR表达和信号的表型。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，改变的激酶信号和特征 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目标和驱动因素 CRPC-AI，包括视网膜母细胞瘤-1(Rb)和TP53的缺失，以及诱导特异性 表观遗传/重新编程因子，如(Zust Homolog 2的增强子)EZH2和SOX2。 此外，我们的工作证实了RB1缺失作为转录变化的主要驱动因素的重要性 与谱系可塑性相关，神经内分泌特征增加，对ADT的敏感性降低。 此外，我们证明了这种谱系重新编程在很大程度上依赖于EZH2，因为抑制 EZH2使谱系逆转，并使Rb缺陷前列腺癌对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基因异常是预后不良的最强预测因子。 这些数据暗示Rb是导致致命性前列腺癌的主要分子机制。目前 在RB功能丧失的患者中，没有能够提供持久反应的治疗选择 (10f)。因此，迫切需要描绘RB LOF的下游效应器，以便治疗 靶点可以在临床试验中识别和验证。我们假设RB损失显著改变了EZH2 结合配对并能够形成新的复合体，导致EZH2甲基化模式的改变 我们之前观察到的对EZH2功能的依赖是有作用的。这些都被更改了 复合体可能提供独有的脆弱性，以抑制由Rb丢失驱动的谱系可塑性。特定的 对于这一应用，我们将表征含EZH2的络合物中发生的变化和 在缺乏Rb的情况下的甲基转移酶靶标并验证它们在肿瘤发生和发展中的功能相关性 线条塑性(目标1)。我们将进一步进行功能性基因组筛查，以确定合成致命性 将配合EZH2抑制治疗Rb缺乏的CRPC-AI的靶点，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来 提出令人信服的理由，开始由研究人员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.