Defining the metabolic phenotype of low grade gliomas in vivo

描述(由申请人提供)：低级别胶质瘤(LGG)占成人所有胶质瘤的三分之一。它们发生在年轻患者中，中位年龄30岁，在5-10年内有超过80%的风险转化为胶质母细胞瘤(GBM)。目前还没有有效的治疗LGG的方法，也没有化疗可以防止转化为GBM。最近，在70%的LGG中发现了异柠檬酸脱氢酶(胞浆中的IDH1或线粒体中的IDH2)的两种亚型的突变。临床上，IDH突变的存在与IDH-WT肿瘤的总体生存率相关，当分级与分级比较时，也与仅表达野生型酶的肿瘤相比，与LGG中更长的转化时间有关。IDH1和ID2突变是从躯体获得的，是酶结合部位的激活突变，导致β-酮戊二酸产生高水平的2-羟基戊二酸(2HG)。2HG产生的功能致癌和代谢后果尚未阐明，但突变酶的鉴定已引起人们对LGG代谢的浓厚兴趣，以及代谢途径的改变可能是细胞转化、肿瘤生长和/或向高级别胶质瘤转化的基础。我们开发了利用稳定的同位素13C(13C)在原位研究LGG细胞代谢的方法。~(13)C标记的葡萄糖可以安全地注入手术切除的患者体内，然后可以通过~(13)C-核磁共振对标记的肿瘤进行体外分析，以探索细胞中活跃的代谢途径。这种方法可以直接评估IDH突变的影响，因为IDH突变和IDH-WT肿瘤都存在于相同的微环境中，组织学上彼此无法区分，并且在切除前没有通过治疗而改变。这是一种在患者身上独一无二的实验范式，可以用来直接比较突变代谢酶对对肿瘤细胞生存和增殖至关重要的代谢途径的影响。为了补充这些原位研究，我们开发了一种新的方法，在接受脑部磁共振成像的患者中使用非侵入性质子磁共振波谱(1H-MRS)在体内识别IDH突变肿瘤中的2HG，用于临床随访。当与肿瘤的分子分析相结合时，这些互补的方法提供了一个极好的机会，可以极大地提高对LGG细胞中基本代谢过程的了解，并确定它们受基因调控的程度。

DESCRIPTION (provided by applicant): Low grade gliomas (LGG) represent a third of all gliomas in adults. They occur in young patients, with a median age of 30, and have a greater than 80% risk of transformation to glioblastoma (GBM) over a 5-10 year period. There are currently no effective treatments for LGG and no chemotherapy that can prevent the transformation to GBM. Recently mutations have been identified in two isoforms of isocitrate dehydrogenase (IDH1 in the cytosol or IDH2 in the mitochondria) in >70% of LGGs. Clinically, the presence of an IDH mutation has been shown to be associated with a better overall survival than IDH-WT tumors, when compared grade for grade, and also is associated with a longer time to transformation in LGGs when compared with tumors expressing only the wild type enzymes. Acquired somatically, IDH1 and 2 mutations are activating mutations in the enzyme binding site which leads to production of high levels of 2 hydroxyglutarate (2HG) from ?-ketoglutarate. The functional oncogenic and metabolic consequences of 2HG production have not yet been elucidated but identification of the mutant enzymes has focused intense interest on LGG metabolism and the possibility that alterations in metabolic pathways may underlie cellular transformation, tumor growth and/or transformation to high grade glioma. We have developed methods to study LGG cell metabolism in situ, taking advantage of the stable isotope, 13Carbon (13C). 13C-labeled glucose can be safely infused in patients undergoing surgical resection and then labeled tumor can be analyzed ex vivo by 13C-NMR to probe the metabolic pathways that are active in the cell. This method provides a direct assessment of the impact of an IDH mutation since both the IDH- mutant and IDH-WT tumors reside in the same microenvironment, are histological indistinguishable from each other, and have not been altered by treatment prior to resection. This is a unique experimental paradigm in patients that can be exploited to directly compare the effects of the mutant metabolic enzyme on the metabolic pathways that are important for tumor cell survival and proliferation. To compliment these in situ studies, we have developed a novel method to identify 2HG in IDH-mutated tumors in vivo using non-invasive proton magnetic resonance spectroscopy (1H-MRS) in patients undergoing brain MR imaging for clinical follow up. When combined with molecular analysis of the tumors, these complimentary methods provide an excellent opportunity to greatly improve the understanding of the fundamental metabolic processes in the LGG cell and determine to what extent they are modulated by genotype.