Targeting Metabolic Liabilities of Leukemia-Initiating Cells

项目总结 表观遗传学和新陈代谢在癌症进展中的作用关系尚未被仔细研究。 检查过了。许多催化DNA或组蛋白修饰的表观遗传酶对 代谢的共底物，但关于改变的表观遗传学是否以及如何影响细胞知之甚少 癌症进展中的新陈代谢。组蛋白H3赖氨酸27甲基转移酶EZH2的突变是 常见于髓系恶性肿瘤，预后不良。我们最近开发了一种新的 EZH2失活和致癌NRAS(G12D)激活建立小鼠髓系肿瘤模型。而当 G12D单独导致惰性骨髓增殖，EZH2失活明显加速疾病进展 导致骨髓纤维化、白血病转化和死亡。在这个模型中忠实地概括了 白血病进展，我们意外地发现支链氨基酸(BCAA)的代谢是最多的 显著上调EZH2缺陷白血病启动细胞(LICs)的代谢途径。BCAT1，第一个 催化支链氨基酸转氨酶，在造血过程中被EZH2抑制，并在 小鼠和人类中EZH2缺陷的髓系肿瘤。BCAT1的增加促进了BCAA的生产 LIC，导致激活的mTOR信号。BCAT1的选择性遗传和药理抑制作用 损害EZH2缺陷的LICs，并构成代谢脆弱性。这些发现首次将 在癌症进展中，EZH2的调节失调和代谢途径的改变。这个项目的目标是 关注支链氨基酸的作用阐明LICs代谢负债的因果控制机制 EZH2缺陷性髓系肿瘤的代谢。中心假说是EZH2缺乏导致 通过激活BCAT1和BCAA代谢来重新连接代谢，以创建LICs的代谢依赖关系，以及 抑制BCAT1将通过禁用EZH2缺陷的代谢易感性选择性地消除LICs LIC。这一假说是在我们使用活体模型进行的初步研究的基础上提出的 白血病进展和新发现的表观遗传学改变和新陈代谢之间的分子联系。 在这些初步数据的指导下，这一假设将通过三个具体的目标进行检验：1)定义函数 BCAT1基因敲除和诱导在EZH2缺乏性髓系肿瘤中的作用 表情鼠标模型。2)确定EZH2缺陷的LIC表现代谢的机制 对支链氨基酸代谢的依赖。3)确定靶向支链氨基酸代谢在人急性髓系白血病中的作用 使用遗传、药物和饮食操作的干细胞。这些研究加在一起不仅将 验证EZH2突变髓系肿瘤的选择性代谢易感性，但也发现新的途径 这可以被利用来有选择地根除LIC。这样的结果有望推动我们的机械化 理解表观遗传学和新陈代谢在癌症进展中的功能关系，并 指导设计更有效的治疗方法，以靶向致癌细胞的新陈代谢能力。

PROJECT SUMMARY The functional relationship between epigenetics and metabolism in cancer progression has not been carefully examined. Many epigenetic enzymes catalyzing DNA or histone modifications are susceptible to changes in co-substrates of metabolism, but little is known about whether and how altered epigenetics influences cellular metabolism during cancer progression. Mutations of EZH2, the histone H3 lysine 27 methyltransferase, are frequently found in myeloid malignancies and correlate with poor prognosis. We recently developed a new mouse model of myeloid neoplasms by inactivation of EZH2 and activation of oncogenic NRas (G12D). While G12D alone led to an indolent myeloproliferation, EZH2 inactivation markedly accelerated disease progression resulting in myelofibrosis, leukemic transformation and mortality. With this model that faithfully recapitulates leukemia progression, we unexpectedly identified branched-chain amino acid (BCAA) metabolism as the most significantly upregulated metabolic pathway in EZH2-deficient leukemia-initiating cells (LICs). BCAT1, the first enzyme catalyzing BCAA transamination, is repressed by EZH2 in hematopoiesis and aberrantly activated in EZH2-deficient myeloid neoplasms in mice and humans. Increased BCAT1 promotes BCAA production in LICs, resulting in activated mTOR signaling. Genetic and pharmacological inhibition of BCAT1 selectively impairs EZH2-deficient LICs and constitutes a metabolic vulnerability. These findings for the first time connect dysregulation of EZH2 with altered metabolic pathways in cancer progression. The objective of this project is to elucidate the causal mechanisms controlling metabolic liabilities of LICs by focusing on the role of BCAA metabolism in EZH2-deficient myeloid neoplasms. The central hypothesis is that EZH2 deficiency induces metabolic rewiring by activating BCAT1 and BCAA metabolism to create a metabolic dependency for LICs, and that inhibition of BCAT1 will selectively eradicate LICs by disabling the metabolic liability of EZH2-deficient LICs. This hypothesis has been formulated on the basis of our preliminary studies using an in vivo model of leukemia progression and a newly discovered molecular link between altered epigenetics and metabolism. Guided by these preliminary data, this hypothesis will be tested by three specific aims: 1) Define the functional role of BCAT1 in EZH2-deficiency-induced myeloid neoplasms in vivo using BCAT1 knockout and inducible expression mouse models. 2) Determine the mechanisms by which EZH2-deficient LICs exhibit a metabolic dependency on BCAA metabolism. 3) Determine the effects of targeting BCAA metabolism in human AML stem cells using genetic, pharmacological and dietary manipulations. Together these studies will not only validate a selective metabolic liability for EZH2-mutant myeloid neoplasms, but also uncover new pathways that can be exploited to selectively eradicate LICs. Such results are expected to advance our mechanistic understanding of the functional relationship between epigenetics and metabolism in cancer progression, and to guide the design of more effective therapies to target the metabolic liabilities of cancer-initiating cells.