EZH2 in cancer biology and novel inhibitors

Zeste 2增强子（EZH 2），Polycomb抑制复合物2的组蛋白甲基转移酶亚基 （PRC 2）催化组蛋白3上赖氨酸残基27（H3 K27）的甲基化。H3 K27的甲基化抑制了 通过阻断基因激活所必需的蛋白质的募集来抑制附近基因的转录。的 PRC 2复合物及其调节的组蛋白修饰在正常细胞中受到严格控制，但可以 在癌症中变得失调以异常地激活或抑制基因表达。在过去的十年里，许多 独立的研究已经确定EZH 2在许多癌症中高度表达， 在其他几个地方发生了变异EZH 2的过表达与侵袭性进展和不良预后相关。 预后我们最近证实EZH 2的过度表达是肺腺癌的原因， 小鼠同样，已经在B细胞淋巴瘤和恶性淋巴瘤中鉴定了EZH 2的激活体细胞突变。 黑素瘤我们开发了在B细胞中表达EZH 2功能获得性突变体的小鼠模型， 黑素细胞，分别引起高转移率淋巴瘤或黑色素瘤。我们对小鼠的研究 表达EZH 2功能获得性突变体的模型表明EZH 2 Y 641 F诱导淋巴瘤， 黑色素瘤通过大量的染色质结构重组诱导抑制和激活， PRC 2调节基因座。将EZH 2活性与癌症联系起来的广泛证据引起了人们对EZH 2的兴趣。 潜在的生物学机制，包括与肿瘤免疫环境的联系。 因此，我们开发了一种新的EZH 2小分子抑制剂JQEZ 5，它可以有效地阻断酶促反应， 在一些实施方案中，H3 K27抑制野生型和突变型EZH 2的功能并降低H3 K27的甲基化。的抑制活性 JQEZ 5阻碍培养物中以及肺癌、淋巴瘤和肺癌小鼠模型中癌细胞的生长。 黑素瘤从机制上讲，JQEZ 5是一种非共价抑制剂，可与天然辅因子S-腺苷竞争 甲硫氨酸（SAM）与EZH 2结合。目前所有EZH 2抑制剂的SAM竞争性质主要是 限制了它们的体内效力，这可能潜在地限制它们在癌症治疗中的使用。 为了提高EZH 2抑制剂的体内功效并降低脱靶毒性，我们提出开发和 表征一类新的共价EZH 2抑制剂，其可不可逆地结合独特的半胱氨酸残基（C663） 存在于人类和小鼠EZH 2中。我们假设这种新型抑制剂的不可逆结合可以 克服了现有非共价抑制剂的关键限制，并提高了体内效力和选择性。我们 将使用新的共价EZH 2抑制剂进一步研究EZH 2抑制在肺中的癌症生物学。 癌症，包括EZH 2抑制的免疫调节作用。我们将利用我们的细胞培养和小鼠 EZH 2驱动的癌症模型，以探索EZH 2的不可逆抑制对基因表达的影响， 肿瘤免疫微环境，同时驱动共价EZH 2抑制剂的命中优化， 提示临床研究，以充分探索EZH 2抑制剂的翻译潜力。

Enhancer of zeste 2 (EZH2), a histone methyl transferase subunit of the Polycomb Repressive Complex 2 (PRC2), catalyzes the methylation of lysine residue 27 on histone 3 (H3K27). Methylation of H3K27 inhibits the transcription of nearby genes by blocking the recruitment of the proteins necessary for gene activation. The PRC2 complex and the histone modifications that it regulates are tightly controlled in normal cells but can become dysregulated in cancer to aberrantly activate or repress gene expression. Over the last decade, many independent studies have established that EZH2 is highly expressed in numerous cancers and recurrently mutated in several others. Overexpression of EZH2 is associated with aggressive progression and poor prognosis. We recently demonstrated that overexpression of EZH2 is causative of lung adenocarcinoma in mice. Likewise, activating somatic mutations of EZH2 have been identified in B cell lymphoma and malignant melanoma. We developed mouse models to express the gain-of-function mutant of EZH2 in B cells or melanocytes, which caused high-penetrance lymphoma or melanoma, respectively. Our studies with mouse models that express the gain-of-function mutant of EZH2 suggest that EZH2Y641F induces lymphoma and melanoma through a vast reorganization of chromatin structure inducing both repression and activation of PRC2-regulated loci. The extensive evidence linking EZH2 activity to cancer has prompted interest in the underlying biological mechanisms, including the link to the tumor immune environment. As such, we developed a novel EZH2 small molecule inhibitor, JQEZ5, that can efficiently block the enzymatic function of both wild-type and mutant EZH2 and reduce the methylation of H3K27. The inhibitory activity of JQEZ5 impedes the growth of cancer cells in culture and in mouse models of lung cancer, lymphoma and melanoma. Mechanistically, JQEZ5 is a non-covalent inhibitor that competes off natural co-factor S-adenosine methionine (SAM) from binding with EZH2. The SAM-competitive nature of all current EZH2 inhibitors largely limited their in vivo potency, which could potentially limit their usage in cancer therapy. To improve the in vivo efficacy of EZH2 inhibitors and reduce off-target toxicity, we propose to develop and characterize a new class of covalent EZH2 inhibitors that can irreversibly bind to unique cysteine residue (C663) present in human and mouse EZH2. We hypothesize that the irreversible biding of this new class inhibitors can overcome key limitations of the existing non-covalent inhibitors, and improve in vivo potency and selectivity. We will employ the new covalent EZH2 inhibitors to further investigate cancer biology of EZH2 inhibition in lung cancer, including the immunomodulatory effects of EZH2 inhibition. We will utilize our cell culture and mouse models of EZH2-driven cancer to explore the impact of irreversible inhibition of EZH2 on gene expression and the tumor immune microenvironment while driving hit-to-lead optimization of covalent EZH2 inhibitors that can prompt clinical investigation to fully explore the translational potential of EZH2 inhibitors.