Targeting Lysine Methyltransferases EZH2 and EZH1 for Treating MLL-rearranged Leukemias

混合血统白血病(MLL)重排导致约70%的婴儿急性白血病 髓系、淋巴系或混合系白血病约占成人病例的7-10%。携带MLL的白血病 重排显示预后特别差，存活率显著降低。到目前为止，没有 靶向药物已经获得批准，临床医生目前依赖于相对非特异性的细胞毒剂 在很大程度上是无效的，因此，突显了未得到满足的医疗需求。EZH2(ZAST同源基因2的增强子)和 EZH1是催化组蛋白H3赖氨酸27(H3K27me3)三甲基化的两种密切相关的酶，a 转录抑制的翻译后修饰。结果表明，EZH2和EZH1具有补偿能力 对于彼此来说，这两种酶对维持MLL重排白血病至关重要。因此，我们 假设EZH2和EZH1的药理学靶向将提供一种新的、靶向的 MLL重排白血病的治疗途径。我们之前发现了UN1999，唯一的 对EZH2和EZH1都有高效的小分子缓蚀剂(IC50和50纳米)。我们已经证明了 UNC1999抑制MLL重排白血病细胞在细胞癌和小鼠肿瘤中的增殖 模特们。然而，UNC1999的体内疗效并不明显，其杀瘤作用也很缓慢。要解决这个问题 主要缺点是，我们应用了PROTAC(蛋白质水解靶向嵌合体)技术来生成 通过将UNC1999连接到E3泛素连接酶结合部分来抑制EZH2和EZH1的二价。我们有 开发的原型二价抑制剂，抑制EZH2/1酶活性，显著降低 EZH2蛋白水平，而UNC1999没有，在抑制多发性骨髓瘤的增殖方面要有效得多 肿瘤细胞系比UNC1999，在非肿瘤细胞中没有表现出毒性，并且是口服生物利用度。基于 这些有希望的初步结果，我们建议：(1)优化EZH2和EZH1的二价抑制剂，使其 它们具有与候选药物一致的效力、选择性、药代动力学和其他类似药物的性质， (2)在MLL重排白血病细胞和小鼠模型中评价EZH2和EZH1的二价抑制剂。 我们的目标是产生一种治疗MLL重排白血病的候选药物。

Mixed Lineage Leukemia (MLL) rearrangements are responsible for approximately 70% of infant acute myeloid, lymphoid or mixed-lineage leukemia and about 7-10% of adult cases. Leukemias bearing MLL rearrangement display a particularly poor prognosis with a significantly lower rate of survival. To date, no targeted agents have been approved and clinicians currently rely on relatively non-specific cytotoxic agents that are largely ineffective, thus, highlighting an unmet medical need. EZH2 (enhancer of zeste homolog 2) and EZH1 are the two closely related enzymes that catalyze tri-methylation of histone H3 lysine 27 (H3K27me3), a transcriptionally repressive post-translational modification. It has been shown that EZH2 and EZH1 compensate for one another and both enzymes are critical for sustaining MLL-rearranged leukemias. Therefore, we hypothesized that pharmacological targeting of both EZH2 and EZH1 would provide a novel, targeted therapeutic approach for treating MLL-rearranged leukemias. We previously discovered UNC1999, the only small-molecule inhibitor with high potency (IC50 < 50 nM) for both EZH2 and EZH1. We have shown that UNC1999 suppressed the proliferation of MLL-rearranged leukemia cells in both cellular and mouse cancer models. However, in vivo efficacy of UNC1999 is modest and its tumor-killing action is slow. To address this major weakness, we have applied the PROTAC (proteolysis targeting chimeras) technology to generating bivalent inhibitors of EZH2 and EZH1 by linking UNC1999 to an E3 ubiquitin ligase-binding moiety. We have developed prototype bivalent inhibitors, which inhibited the EZH2/1 enzymatic activity, significantly reduced EZH2 protein levels while UNC1999 did not, were much more effective at inhibiting the proliferation of multiple tumor cell lines than UNC1999, did not exhibit toxicity in non-tumor cells, and were orally bioavailable. Based on these promising preliminary results, we propose to: (1) optimize bivalent inhibitors of EZH2 and EZH1 so that they have potency, selectivity, pharmacokinetic and other drug-like properties consistent with a drug candidate, and (2) evaluate bivalent inhibitors of EZH2 and EZH1 in MLL-rearranged leukemia cellular and mouse models. Our goal is to generate a drug candidate for the treatment of MLL-rearranged leukemias.