Defining the role of mutant IDH in glioma initiation and maintenance

描述（由申请人提供）：神经胶质瘤是最常见的原发性中枢神经系统肿瘤，但这些肿瘤发生和进展的分子机制远未完全了解。最近，IV级多形性胶质母细胞瘤（GBM）肿瘤的高通量测序在12%的分析样本中发现了异柠檬酸脱氢酶1（IDH 1）的新突变。进一步的研究发现这种突变存在于约80%的II-III级胶质瘤和继发性GBM中。这种突变以前从未与癌症有关，其功能仍不清楚。该残基位于酶的活性位点，对异柠檬酸结合至关重要。IDH蛋白通过催化异柠檬酸氧化脱羧为1-酮戊二酸（1-KG），从NADP+生成还原型NADPH。由于其受损的酶活性，突变蛋白已被认为具有肿瘤抑制剂的功能。脯氨酰羟化酶，羟化和诱导缺氧诱导因子11（HIF-11）的降解，需要1-KG;因此，IDH活性降低可能稳定HIF-11。该途径的激活导致HIF-1靶基因的诱导，所述靶基因影响血管生成、代谢、生长和分化、凋亡和自噬以及细胞运动。然而，IDH突变是杂合的，这表明这些突变可能是具有致癌潜力的功能获得，而不是功能丧失。体外研究表明，突变的IDH 1蛋白具有新的功能：将1-KG转化为R（-）-2-羟基戊二酸（2-HG）并消耗NADPH。这得到了以下发现的支持，即在含有IDH 1突变的胶质瘤中2-HG水平升高。此外，大脑中2-HG的积累与发展脑肿瘤的风险增加有关。这两个过程的净结果是减少1-KG和NADPH，这是一个重要的辅因子，必须保持正常水平的还原型谷胱甘肽，以打击活性氧（ROS）。在这些条件下，细胞可能会不断积累ROS诱导的氧化DNA损伤和增加的突变数量，这可能会导致恶性转化。有趣的是，IDH突变的存在是阳性预后的独立标志物。本研究的目的是明确IDH突变在胶质瘤形成、维持和治疗反应中的作用。我们假设IDH突变有助于胶质瘤形成，是肿瘤维持所需的，并使肿瘤细胞对常规治疗敏感。为了验证这一假设，我们将使用一个完善的神经胶质瘤模型系统，以确定突变IDH的表达是否赋予体外星形胶质细胞的生长优势，在体内神经胶质瘤的发展和维持中发挥作用，并影响对治疗的反应。更好地了解突变IDH在这些胶质瘤生物学中的作用将指导新疗法的开发，以提高这些患者的生存率并降低发病率。

DESCRIPTION (provided by applicant): Gliomas are the most common primary central nervous system tumor but the molecular mechanisms responsible for the development and progression of these tumors are far from being completely understood. Recently, high-throughput sequencing of grade IV glioblastoma multiforme (GBM) tumors identified a novel mutation in isocitrate dehydrogenase 1 (IDH1) in 12% of the samples analyzed. Further studies have found this mutation to be present in ~80% of grade II-III gliomas and secondary GBM. This mutation has never before been linked to cancer and the function remains unclear. This residue is located in the active site of the enzyme and is critical for isocitrate binding. IDH proteins generate reduced NADPH from NADP+ by catalyzing the oxidative decarboxylation of isocitrate to 1-ketoglutarate (1-KG). The mutant protein has been suggested to function as a tumor suppressor due to its impaired enzymatic activity. Prolylhydroxylases, which hydroxylate and induce the degradation of hypoxia-inducible factor 11 (HIF-11), require 1-KG; therefore, decreased IDH activity may stabilize HIF-11. Activation of this pathway leads to the induction of HIF-1 target genes that affect angiogenesis, metabolism, growth and differentiation, apoptosis and autophagy, as well as cell motility. However, IDH mutations are heterozygous suggesting that these mutations may be gain of function with oncogenic potential rather than loss-of-function. In vitro studies have shown that the mutated IDH1 protein takes on a new function: converting 1-KG to R(-)-2-hydroxyglutarate (2-HG) and consuming NADPH. This is supported by findings that 2-HG levels are elevated in gliomas containing an IDH1 mutation. Furthermore, accumulation of 2-HG in the brain is associated with an increased risk of developing brain tumors. The net result of either process is reduced 1-KG and NADPH, which is an important cofactor necessary to maintain normal levels of reduced glutathione to combat reactive oxygen species (ROS). Under these conditions, cells may continually accumulate ROS-induced oxidative DNA damage and increasing numbers of mutations, which can drive malignant transformation. Interestingly, the presence of an IDH mutation is an independent marker for positive prognosis. The objective of this study is to define the role of IDH mutations in glioma formation, maintenance, and response to therapy. We hypothesize that mutations in IDH contribute to glioma formation, are required for tumor maintenance, and sensitize the tumor cells to conventional therapies. To test this hypothesis we will use a well established glioma model system to determine if expression of mutant IDH confers a growth advantage to astrocytes in vitro, plays a role in the development and maintenance of gliomas in vivo, and influences response to therapy. A better understanding of the role(s) of mutant IDH in the biology of these gliomas will guide the development of new therapies to improve survival and reduce morbidity in these patients.