ATR Dependency as a Novel Therapeutic Target in Lethal RB Deficient ProstateCancer

项目摘要 转移性前列腺癌（mPCa）是不可治愈的，是大多数PC相关死亡的原因。 因此，迫切需要识别mPCa的驱动因素，以实现早期识别和拦截。 为患者提供持久反应的治疗策略。雄激素剥夺疗法（ADT）是 mPCa的一线治疗。ADT最初延长了生存期，但由于患者的肿瘤 获得去势抵抗（mCRPC）。大多数mCRPC仍然依赖于雄激素的功能， 受体（AR），但由于纳入了更强效的AR拮抗剂（例如：Enzalutamide）， 在一个病例子集（约20%）中，出现了独立于AR活性的耐药机制 （CRPC-AI）。CRPC-AI通过谱系可塑性而不是耐药突变的结果来适应ADT， 表型不再依赖于AR表达和信号传导。这些肿瘤可能具有神经内分泌特征， 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， 我们和其他人已经描述了CRPC-AI的分子景观，并确定和验证了新的 治疗靶点和驱动因素，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缺失下游EZH 2重编程的重要性， 谱系可塑性和对ADT的抗性。此外，抑制EZH 2能够逆转谱系并重新致敏。 RB将前列腺癌丢失至ADT。重要的是，mCRPC患者的最新数据发现了RB遗传性 畸变是不良结局的最强预测因子。这些数据表明RB是一种优势分子， 导致致命前列腺癌的机制目前没有治疗选择提供持久的 RB功能丧失（LOF）患者的反应。因此，迫切需要界定 RB LOF的下游效应物，以便可以在临床中鉴定和验证治疗靶点。 审判具体到这一应用，我们的功能基因组筛选已确定依赖于DNA损伤 修复激酶，特别是ATR。这项拟议的工作是创新的，因为它将提供更深层次的机制 RB缺乏前列腺癌的驱动因素和治疗选择的知识， 表型通过这项工作，我们将验证DDR激酶靶向加剧DDR缺陷的能力。 并在RB缺陷的前列腺模型中产生超敏反应（目的1），确定RB 临床前模型中的功能、HR熟练度和对M6620+卡铂和多西他赛+卡铂的应答 和临床样品（目的2），并评估ATR激酶抑制、EZH 2抑制和免疫抑制的协同作用。 在临床前RB缺陷型前列腺小鼠模型中的检查点阻断疗法（目的3）。最终这 信息将使我们能够收集足够的初步证据，使一个令人信服的情况下开始 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 PC associated mortality. Therefore, there is a critical need to identify drivers of mPCa to enable early identification and 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), though due to the inclusion of more potent AR antagonist (eg: 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 rather than a result of resistant mutations, 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 characterized the molecular landscape of CRPC-AI and have identified and validated new therapeutic targets and drivers, 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 EZH2 reprogramming downstream of RB1 loss, driving lineage plasticity and resistance to ADT. Moreover, inhibition of EZH2 enabled lineage reversal and re-sensitized RB loss 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 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. Specific to this application, our functional genomic screen has identified dependence on DNA damage repair kinases – specifically – ATR. This proposed work is innovative because it will provide deeper mechanistic knowledge of drivers of RB deficient prostate cancer and therapeutic options towards a currently untreatable phenotype. Through this work we will validate the ability of DDR kinase targeting to exacerbate DDR deficiency and to generate hypersensitivity in RB-deficient prostate models (Aim 1), determine the correlation between RB function, HR proficiency and response to M6620+carboplatin and docetaxel+carboplatin in preclinical models and clinical samples (Aim 2), and evaluate synergy of ATR kinase inhibition, EZH2 inhibition, and immune checkpoint blockade therapy in pre-clinical RB-deficient prostate mouse models (Aim 3). Ultimately, this information will enable us to gather sufficient preliminary evidence to make a compelling case to commence investigator-initiated multi-center clinical trials.