Targeting histone methyltransferase EZH2 for the treatment of hematological cancer

项目总结与摘要 多梳抑制复合体2(PRC2)的催化亚单位Zust Homolog 2的增强子(EZH2)诱导 组蛋白H3赖氨酸27(H3K27me3)三甲基化抑制靶基因表达。无数的研究 有报道称，EZH2促进了一系列人类癌症的发生。特别是，独立研究 已证实EZH2的表达在急性白血病与混合性白血病的致瘤性中是必不可少的 遗传性白血病基因重排(MLL-r)，约占婴儿和 约10%的成人急性淋巴细胞白血病(ALL)病例，以及~50%的婴儿和~7%的成人急性淋巴细胞白血病 髓系白血病(AML)病例。带有MLL-r的白血病患者在临床上通常表现出非常差的预后， 需要新的治疗策略。然而，包括我们在内的越来越多的证据现在支持EZH2的S 致癌功能超越了PRC2及其对H3K27me3沉积的酶功能，并具有新的， PRC2-维持肿瘤发生的独立活动(非规范)。EZH2的后一种非正则函数 部分解释了为什么目前存在的EZH2酶抑制剂的抗肿瘤作用相当有限。在这 项目，我们的目标是利用蛋白质水解靶向嵌合体(PROTAC)技术来开发新的 用于耗尽癌症EZH2功能的药物降解剂是一种新的更有效的药物 治疗剂。我们已经产生了非常有希望的初步结果，表明与EZH2相比 酶抑制剂，我们基于E3连接酶的先导EZH2靶向PROTAC(又名EZH2降解物)有效地诱导 耗尽EZH2，从而抑制规范(依赖于PRC2)和非规范(PRC2- EZH2在肿瘤中的活性。EZH2降解剂也显示出更强的杀伤力 体外侵袭性MLL-r AML细胞。此外，这种先导化合物的初步表征揭示了 在小鼠身上有很好的类药物潜力。在这个项目中，我将进一步(I)确定我们的 利用基因工程小鼠模型(GEMM)体内抑制肿瘤生长的EZH2降解物 和人类患者来源的异种移植(PDX)MLL-r白血病模型(目标1)和(Ii)定义其分子 在MLL-r白血病细胞中的作用，集中在EZH2的规范和非规范功能上，通过使用 综合基因组图谱技术(目标2)。这个项目的结果将揭示一个很有前途的临床前 显示EZH2依赖的人类癌症的治疗策略。FDA最近批准的化合物 以表观遗传蛋白为目标提出了一个强有力的论点。

PROJECT SUMMARY & ABSTRACT Enhancer of Zeste Homolog 2 (EZH2), the catalytic subunit of Polycomb Repressive Complex 2 (PRC2), induces trimethylation of histone H3 lysine 27 (H3K27me3) for repressing the target gene expression. Numerous studies have reported that EZH2 promotes oncogenesis in a range of human cancers. In particular, independent studies have demonstrated the expression of EZH2 to be essential for tumorigenicity of acute leukemias with the Mixed Lineage Leukemia gene rearrangement (MLL-r), which accounts for approximately 60–80% of infantile and ~10% of adult acute lymphoblastic leukemia (ALL) cases, as well as ~50% of infantile and ~7% of adult acute myeloid leukemia (AML) cases. Leukemia patients with MLL-r generally exhibit very poor prognosis in the clinic, demanding new treatment strategies. However, increasing evidence including ours now support that EZH2’s oncogenic functions go beyond PRC2 and its enzymatic function for H3K27me3 deposition, and has the new, PRC2-independent activity (non-canonical) to sustain oncogenesis. The latter non-canonical function of EZH2 partly explains why the current existing enzymatic inhibitors of EZH2 have rather limited antitumor effect. In this project, we aim to employ the Proteolysis Targeting Chimera (PROTAC) technology to develop novel pharmacological ‘degraders’ for depleting EZH2 functions in cancer as a new and more effective therapeutic agent. We have generated highly promising preliminary results showing that, compared to the EZH2 enzymatic inhibitor, our lead E3 ligase-based EZH2-targeting PROTAC (aka EZH2 degrader) efficiently induced depletion of EZH2, thereby suppressing both canonical (PRC2-dependent) and non-canonical (PRC2- independent) activities of EZH2 in tumor. The EZH2 degrader also displays a much stronger potency in killing the aggressive MLL-r AML cells in vitro. Additionally, preliminary characterization of this lead compound revealed an excellent drug-like potential in mice. In this project, I will further (i) determine the effect and potency of our EZH2 degrader in suppressing tumor growth in vivo by using the genetically engineered mouse model (GEMM) and human patient-derived xenograft (PDX) models of MLL-r leukemias (Aim 1) and (ii) define its molecular effects in the MLL-r leukemia cells, focusing on both canonical and non-canonical functions of EZH2, by using the integrated genomic profiling technologies (Aim 2). Results from this project will reveal a promising preclinical strategy for the treatment of human cancers showing EZH2 dependency. Recent FDA approval of compounds targeting epigenetic proteins makes a strong argument.