Metabolic control of normal and malignant hematopoiesis

项目摘要/摘要 异柠檬酸脱氢酶(IDH)酶的体细胞突变在急性 髓系白血病(AML)和其他恶性肿瘤通过产生‘肿瘤代谢物’D-2-羟基戊二酸 (d-2HG)。D-2HG通过抑制α-酮戊二酸(-KG)依赖性阻断肿瘤细胞分化 调节染色质结构和基因表达的酶。突变型IDH的小分子抑制剂 酶是治疗急性髓细胞白血病很有前途的新疗法，但其疗效仍然局限于患有急性髓细胞白血病的患者亚群 IDH突变。这就提出了一个问题，即类似的代谢异常是否可能导致 IDH-野生型AML的白血病发生。有趣的是，2HG是一种手性分子，可以存在于D-或L-中- 对映体。尽管与癌症相关的IDH突变体只产生D-2HG，但生化研究 表明L-2HG对许多KG依赖的酶具有~10倍的抑制作用， 包括染色质修饰物和缺氧诱导因子(HIF)稳定性的调节剂。然而，生物的 L-2HG的来源和活动一直知之甚少。我们发现了一种新陈代谢途径 正常和非IDH突变的肿瘤细胞选择性地产生L-2HG以响应氧限制 (也就是低氧)通过乳酸脱氢酶(LDHA)催化的一种不寻常的反应。我们证明了 低氧诱导的L-2HG增强缺氧诱导因子的稳定性，增加抑制性染色质修饰，并阻断 干细胞/祖细胞的分化。这些发现表明L-2HG可能至少在一定程度上解释了 低氧生态位、低氧诱导因子和低密度脂蛋白在平衡干细胞自我更新和分化中的重要性 包括造血干/祖细胞(HSPC)和白血病干细胞。因此，我们 假设L-2HG作为代谢信号将低氧生态位耦合到 维持正常的血液干细胞和白血病干细胞。这一假设将被严格地 具体目标有三个。目标1将确定L-2HG调节的分子机制 血细胞的体外分化。在这一目标中，我们将确定L-2HG对基因表达和 染色质结构，并决定这些输入如何平衡HSPC的干性和谱系分化。目标 2将确定L-2HG在体内控制正常和恶性造血的作用。这一目标将使用 允许组织特异性、诱导性操作L-2HG的新型基因工程小鼠模型 以探讨L-2HG在正常造血和白血病中的作用。目标3将阐明 L-2HG对人白血病的致癌机制及治疗潜力。在这个目标中，我们将使用主要 急性髓系白血病生物标本和患者来源的异种移植，以确定导致解除管制的机制L- 2HG在AML的一个子集中，并评估耗尽L-2HG是否为治疗人类AML提供了一种有前途的策略。 拟议的研究将为正常和恶性干细胞的代谢控制提供基本的见解。 细胞生物学，并扩大代谢靶向治疗白血病和其他癌症的适用性。

PROJECT SUMMARY/ABSTRACT Somatic mutations in the isocitrate dehydrogenase (IDH) enzymes contribute to the pathogenesis of acute myeloid leukemia (AML) and other malignancies via production of the ‘oncometabolite’ D-2-hydroxyglutarate (D-2HG). D-2HG blocks differentiation of malignant cells by inhibiting alpha-ketoglutarate (KG)-dependent enzymes that regulate chromatin structure and gene expression. Small molecule inhibitors of mutant IDH enzymes are promising new therapies for AML, but their efficacy remains limited to the subset of patients with IDH mutations. This raises the question as to whether analogous metabolic aberrations might contribute to leukemogenesis in IDH-wildtype AML. Intriguingly, 2HG is a chiral molecule that can exist in either the D- or L- enantiomer. Although cancer-associated IDH mutants exclusively produce D-2HG, biochemical studies indicate that L-2HG can function as a ~10-fold more potent inhibitor of many KG-dependent enzymes, including chromatin modifiers and regulators of hypoxia-inducible factor (HIF) stability. However, biological sources and activities of L-2HG have been poorly understood. We identified a metabolic pathway wherein normal and malignant cells without IDH mutations selectively produce L-2HG in response to oxygen limitation (a.k.a. hypoxia) through an unusual reaction catalyzed by lactate dehydrogenase (LDHA). We show that hypoxia-induced L-2HG enhances stability of HIF, increases repressive chromatin modifications, and blocks differentiation of stem/progenitor cells. These findings suggest that L-2HG might account, at least in part, for the importance of hypoxic niches, HIF, and LDHA in balancing self-renewal and differentiation of stem cell populations, including hematopoietic stem/progenitor cells (HSPC) and leukemia stem cells. Thus, we hypothesize that L-2HG functions as a metabolic signal that couples hypoxic niches to the maintenance of normal blood stem cells and leukemia stem cells. This hypothesis will be rigorously addressed in three Specific Aims. Aim 1 will define the molecular mechanisms by which L-2HG regulates blood cell differentiation in vitro. In this Aim, we will define the effects of L-2HG on gene expression and chromatin structure and determine how these inputs balance HSPC stemness and lineage differentiation. Aim 2 will determine how L-2HG functions to control normal and malignant hematopoiesis in vivo. This Aim will use novel genetically engineered mouse models that allow for tissue-specific, inducible manipulation of L-2HG levels in order to dissect the role of L-2HG in normal hematopoiesis and leukemia. Aim 3 will elucidate the oncogenic mechanisms and therapeutic potential of L-2HG in human leukemia. In this Aim, we will use primary AML biospecimens and patient-derived xenografts to determine the mechanisms that lead to deregulated L- 2HG in a subset of AML and assess whether depleting L-2HG offers a promising strategy to treat human AML. The proposed studies will offer fundamental insights into the metabolic control of normal and malignant stem cell biology and expand the applicability of metabolic targeted therapies for leukemia and other cancers.