Dissecting and targeting canonical and non-canonical oncogenic functions of EZH2 in cancer

项目概要/摘要 携带MLL1重排的白血病患者通常显示非常差的预后，需要新的治疗方案。 治疗策略。多项独立研究已经鉴定了EZH2，一种组蛋白甲基转移酶， 多梳抑制复合物2（PRC2）的催化亚基，作为MLL1重排中有吸引力的药物靶点， 白血病然而，目前EZH2的催化抑制剂具有有限的抗肿瘤作用。我们的初步 研究表明EZH2也结合c-MYC，并在癌基因（如 作为细胞周期蛋白E1）在MLL1重排的白血病，这不同于众所周知的PRC2：EZH2驱动的典型 与基因阻遏有关的功能。为了靶向典型和非典型致癌作用， EZH2，我们使用蛋白水解靶向嵌合体（PROTAC）技术来产生新的EZH2小- 分子降解剂，包括MS177。我们广泛的初步研究表明，MS177 有效地降解PRC2：EZH2和EZH2的非PRC2配偶体（例如，c-MYC，其结合EZH2， 激活致癌基因），从而抑制EZH2的典型和非典型致癌活性。 肿瘤重要的是，我们的初步结果还表明，MS 177优于所有的酶抑制剂， EZH2治疗MLL1重排白血病因此，我们假设：（1）EZH2具有较少研究的，非- 典型的致癌功能，与PRC2：EZH2依赖性功能平行发挥作用，产生更多的 MLL1重排白血病中观察到的侵袭性肿瘤表型;和（2）靶向典型和非典型白血病 PROTAC对EZH2的典型活性代表了一种新的和上级的治疗策略， EZH2单独的酶活性。EZH2介导的肿瘤发生机制的剖析， 作为候选药物的最佳EZH2 PROTAC的开发将对改善 MLL1重排白血病患者的治疗。为了实现这一目标，我们将进一步描述这样一个新的 EZH2在MLL1重排白血病（Aim 1a）中的非典型致癌作用，并确定EZH2的作用 PROTAC抑制EZH2的典型和非典型致癌活性（目的1b）。我们将 还通过采用多个独立的方法测定EZH2 PROTAC的体外和体内治疗效果， MLL1重排白血病模型，包括人/鼠癌细胞和患者来源的异种移植物（PDX） (Aim 2）。最后，我们将优化我们的EZH2 PROTAC导致成为候选药物（目标3）。完成 拟议的研究不仅将提供MLL1重排白血病如何在白血病细胞中表达的新的机制理解， 开发，但也将验证创新的治疗策略，并提供有前途的治疗候选人 用于治疗癌症患者。

PROJECT SUMMARY/ABSTRACT Leukemia patients bearing MLL1 rearrangement generally display very poor prognosis, demanding new treatment strategies. Multiple independent studies have identified EZH2, a histone methyltransferase and catalytic subunit of Polycomb Repressive Complex 2 (PRC2), as an attractive drug target in MLL1-rearranged leukemias. However, the current catalytic inhibitors of EZH2 have limited anti-tumor effect. Our preliminary studies show that EZH2 also binds c-MYC and has a non-canonical function in activation of oncogenes (such as Cyclin E1) in MLL1-rearranged leukemias, which differs from the well-known PRC2:EZH2-driven canonical function related to gene repression. In order to target both canonical and non-canonical oncogenic actions by EZH2, we used the Proteolysis Targeting Chimera (PROTAC) technology to generate novel EZH2 small- molecule degraders including MS177. Our extensive preliminary studies have demonstrated that MS177 effectively degrades both PRC2:EZH2 and non-PRC2 partners of EZH2 (e.g., c-MYC, which binds EZH2 to activate oncogenes), thus suppressing both canonical and non-canonical oncogenic activities of EZH2 in tumor. Importantly, our preliminary results also show that MS177 is superior to all of enzymatic inhibitors of EZH2 in treating MLL1-rearranged leukemias. Thus, we hypothesize that: (1) EZH2 has a less-studied, non- canonical oncogenic function, which acts in parallel with the PRC2:EZH2-dependent one to produce more aggressive tumor phenotypes seen in MLL1-rearranged leukemias; and (2) targeting both canonical and non- canonical activities of EZH2 by PROTACs represents a novel and superior therapeutic strategy to inhibition of EZH2’s enzymatic activity alone. Dissection of the mechanisms underlying EZH2-mediated oncogenesis and development of an optimal EZH2 PROTAC as a drug candidate will have significant impact on improving treatments for MLL1-rearranged leukemia patients. Towards this goal, we will further characterize such a new non-canonical oncogenic role of EZH2 in MLL1-rearranged leukemias (Aim 1a) and define effects of EZH2 PROTACs on suppressing both canonical and non-canonical oncogenic activities of EZH2 (Aim 1b). We will also determine in vitro and vivo therapeutic effects of EZH2 PROTACs by employing multiple independent MLL1-rearranged leukemia models including human/murine cancer cells and patient-derived xenografts (PDX) (Aim 2). Lastly, we will optimize our EZH2 PROTAC leads into a drug candidate (Aim 3). Completion of the proposed research will not only provide novel mechanistic understanding of how MLL1-rearranged leukemias develop, but will also validate an innovative therapeutic strategy and deliver a promising therapeutic candidate for the treatment of affected cancer patients.