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

混合谱系白血病（MLL）重排导致大约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 重排显示出特别差的预后，具有显著较低的存活率。至今没有 靶向剂已经被批准，临床医生目前依赖于相对非特异性的细胞毒性剂， 基本上是无效的，因此，突出了未满足的医疗需求。EZH 2（zeste同源物2的增强子）和 EZH 1是催化组蛋白H3赖氨酸27（H3 K27 me 3）三甲基化的两种密切相关的酶， 转录抑制性翻译后修饰。已经表明，EZH 2和EZH 1补偿 这两种酶对于维持MLL重排的白血病都是至关重要的。所以我们 假设EZH 2和EZH 1两者的药理学靶向将提供一种新的靶向药物， 用于治疗MLL重排白血病的治疗方法。我们之前发现了UNC 1999， 对EZH 2和EZH 1都具有高效力（IC 50 < 50 nM）小分子抑制剂。我们已经证明 UNC 1999抑制细胞和小鼠癌症中ML重排白血病细胞的增殖 模型然而，UNC 1999的体内功效是适度的，并且其肿瘤杀伤作用是缓慢的。为了解决这个 主要弱点，我们已经应用PROTAC（蛋白水解靶向嵌合体）技术来产生 EZH 2和EZH 1的二价抑制剂，其通过将UNC 1999连接至E3泛素连接酶结合部分。我们有 开发了原型二价抑制剂，其抑制EZH 2/1酶活性，显著降低 EZH 2蛋白水平，而UNC 1999没有，在抑制多个细胞增殖方面更有效。 在非肿瘤细胞中没有表现出毒性，并且是口服生物可利用的。基于 这些有希望的初步结果，我们建议：（1）优化EZH 2和EZH 1的双价抑制剂， 它们具有与候选药物一致的效力、选择性、药代动力学和其它药物样性质， 和（2）在MLL重排的白血病细胞和小鼠模型中评估EZH 2和EZH 1的二价抑制剂。 我们的目标是产生用于治疗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.