METABOLISM IN HUMAN GLIOMAS

点击翻译按钮获取中文摘要

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Glioblastoma, the most common primary brain tumor in adults, is considered to be among the deadliest of human cancers. With a median survival time of 14.6 months and approximately 25% of patients alive at 2 years after the most aggressive treatment regimens, there is clearly a desperate need to improve the understanding of basic biological processes in this disease. Glioblastomas demonstrate the classic cancer phenotype of unregulated proliferation, resistance to apoptosis, and induction of neovascularization. Clinically, glioblastomas are 'hot' on FDG-PET, demonstrating marked abnormal uptake of glucose, thought to reflect the 'Warburg phenomenon', defined as excess flux of glucose through anaerobic glycolysis with production of lactate despite an intact tricarboxylic acid (TCA) cycle. In contrast, low grade gliomas, which are slow growing tumors, show no increase in glucose uptake by FDG-PET until they progress to glioblastoma, a transition that occurs within 5-10 years of initial diagnosis. It is unknown whether the change in metabolism simply reflects an increased rate of glucose utilization as a result of the marked increase in cellular proliferation or is a direct consequence of a molecular switch that governs the transition from low grade glioma to glioblastoma. The molecular aberrations underlying glioblastoma have been well characterized at the level of the genome, including copy number changes, mutations, and methylation, and correlated with changes in the transcriptome. From these data an important framework of critical cancer pathways involved in glioblastoma growth and survival has emerged, centered predominantly on activation of the RAS-MAPK pathway, most commonly driven by EGFR amplification, and dysregulation of the PI3Kinase pathway, due frequently to deletion of PTEN. Methylation of the DNA repair gene, MGMT, may predict for response to alkylator therapy and the recently identified mutation in isocitrate dehydrogenase 1 (IDH1) may modulate a metabolic pathway but, overall, there remains a limited view of how the molecular changes and altered biochemical pathways influence the biology of glioblastoma. In glioblastoma, as in most solid tumors, there is significant interest in understanding mechanisms of altered metabolism since it represents a 'functional readout' of the constellation of genetic mutations that interact to influence cell growth and survival. In order to develop new diagnostic methods and therapeutic targets based on altered metabolism, it is imperative that basic questions related to the genotype-metabolic phenotype connection be addressed. Further, we believe it is critical to understand the effects of disrupted biochemical pathways on both the static concentration of metabolites such as lactate produced in anaerobic glycolysis, as well as fluxes through relevant pathways such as glycolysis, the pentose phosphate pathway, and the citric acid cycle. The characteristic and well established metabolic features of glioblastoma  intense glucose uptake on FDG scans, abundant lactate production, and a defect in NADP+ - dependent isocitrate dehydrogenase  may be interconnected events due to a specific genetic mutation. Alternatively, these features may be a common endpoint reflecting redundancy in the cancer cell's genetic program. Statement of Hypothesis: Activation of the RAS-MAPK pathway and/or dysregulation of the PI3Kinase pathway stimulate increased glucose uptake and a cascade of metabolic changes in glioblastoma cells that sustain high proliferative rates and support extensive cellular infiltration/migration in a heterogeneous tumor microenvironment. Aim 1: To define the metabolic phenotype of glioblastoma in a novel human orthotopic mouse model by 13C NMR spectral analysis of tumors following infusion of [U-13C]glucose or [1,2-13C]glucose to assess, respectively, the pathways intersecting in the citric acid cycle and relative flux through the pentose phosphate pathway. Aim 2: To determine the impact of Ras-MAPK pathway activation by EGFR overexpression and PI3K pathway dysregulation by deletion of PTEN, on the metabolic phenotype in genetically engineered glioblastoma mouse models. Aim 3: To determine whether modulation of IDH1 in the murine models of glioblastoma alters the flux through the citric acid cycle or pentose phosphate pathway. Aim 4: To correlate findings in Aims 1-3 with metabolic studies in patients with glioblastoma.