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，中位年龄为30岁，并且在5-10年内有超过80%的风险转化为胶质母细胞瘤（GBM）。目前尚无有效的治疗LGG的方法，也没有能够阻止其向GBM转变的化疗方法。最近，在80% ~ 70%的LGGs中发现了异柠檬酸脱氢酶的两种亚型（细胞质中的IDH1或线粒体中的IDH2）的突变。在临床上，当对分级进行比较时，IDH突变的存在已被证明与IDH- wt肿瘤更好的总生存率相关，并且与仅表达野生型酶的肿瘤相比，IDH突变的存在与LGGs中更长的转化时间相关。体内获得的IDH1和2突变是酶结合位点的激活突变，导致从-酮戊二酸产生高水平的2羟基戊二酸（2HG）。2HG产生的功能性致癌和代谢后果尚未阐明，但突变酶的鉴定引起了人们对LGG代谢的强烈兴趣，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。我们已经开发了利用稳定同位素13Carbon （13C）原位研究LGG细胞代谢的方法。13c标记的葡萄糖可以安全地输注在手术切除的患者体内，然后通过13C-NMR对标记的肿瘤进行离体分析，以探测细胞中活跃的代谢途径。这种方法提供了对IDH突变影响的直接评估，因为IDH突变和IDH- wt肿瘤存在于相同的微环境中，彼此在组织学上难以区分，并且在切除前的治疗中没有改变。这是一个独特的实验范例，可以用来直接比较突变代谢酶对肿瘤细胞存活和增殖的重要代谢途径的影响。为了补充这些原位研究，我们开发了一种新的方法，利用非侵入性质子磁共振波谱（1H-MRS）在接受脑磁共振成像进行临床随访的患者体内识别idh突变肿瘤中的2HG。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，可以大大提高对LGG细胞基本代谢过程的理解，并确定它们受基因型调节的程度。

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.