Among the causes of death due to cancer, brain tumors are ranked second in the pediatric age group and fourth in middle-aged men. Despite the use of multimodality therapy, malignant gliomas are uniformly fatal. The unfavorable results obtained to date in the treatment of gliomas underscores the need for investigating novel therapeutic approaches to manage this neoplasm that has responded poorly to surgery, radiation, chemotherapy and immunotherapy. The objective of this proposal is to explore the antitumor effect of hydrogen peroxide (H2O2) using preformed H2O2 and enzymatic hydrogen peroxide-generating systems. We will use as our model system the SF763 human glioma in monolayer and as intracerebral xenografts in athymic nude rats. The biochemical and morphological response of the SF763 glioma to therapy will be monitored using in vivo 1H and 31P magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI), respectively. Furthermore, we will use specific enzyme inhibitors to systematically investigate the role of enzymatic antioxidant systems used in the cellular detoxification of H2O2 in vitro. Inhibitors specific for enzymes catalase, GSH peroxidase, GSH reductase, GSH synthesis and glucose-6-phosphate dehydrogenase will be used to determine the role and importance of each enzyme system for protecting glioma cells from injury by preformed H2O2 or enzymatically generated H2O2 using colony forming assays. The inhibitors to be studied are either directly inhibiting a pentose phosphate pathway (PPP) enzyme or an enzyme associated with a biochemical pathway having a metabolite or cofactor in common with the PPP. Therefore, the extent of enzymatic inhibition will be determined by monitoring the relative changes in activity of the PPP following the addition of a specific oxidative probe which stimulated the turnover of the metabolite or cofactor related to the inhibition process. PPP activity will be quantitated using GC/MS analysis of lactic acid produced from the enzymatic degradation of a novel stable isotope of glucose which we have developed for this purpose. The isotope, D-[1,6-13C2,6- 2H2]glucose, will be added to cultured cells or used in conjunction with intracerebral microdialysis techniques for intracranial glioma studies. It is our intent that the information gained from this project will provide the biochemical foundation for new advances towards the effective clinical management and treatment of patients with malignant gliomas.
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