Cancer cells in general, relative to normal cells, demonstrate increased glucose metabolism but the mechanism for this is unknown. The clinical utility of these observations has been limited to the use of 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG) and Positron Emission Tomography (PET) to identify cancerous tissues. Head and neck cancers show robust signals using FDG-PET imaging that vary between patients, but the significance of the variability is unknown. Glucose metabolism leads to pyruvate and NADPH formation, which function in hydroperoxide detoxification. This has led to the proposal that cancer cells may increase glucose utilization as a compensatory mechanism protecting from intracellular hydroperoxides formed as byproducts of defects in oxidative metabolism. If tumor glucose metabolism is increased in response to excess production of hydroperoxides, inhibition of glucose and hydroperoxide metabolism should lead to oxidative stress and radiosensitization in cancer cells that is proportional to the rate of glucose utilization. The current proposal tests the hypothesis that: the extent to which human head and neck cancer cells increase their uptake and metabolism of glucose is predictive of cancer cell susceptibility to 2DG-induced radio-/chemo-sensitization and hydroperoxide-mediated oxidative stress.
Aims 1 and 2 will determine if 2DG-induced radiosensitization can be enhanced by inhibitors of hydroperoxide detoxification [i.e., buthionine sulfoximine or manipulations of glucose-6-phosphate dehydrogenase] and/or chemotherapeutic agents believed to increase oxidative stress [i.e., cisplatin and azidothymidine] in human head and neck cancer cells in vitro and in vivo.
Aim 3 will determine if enhancement of 2DG-induced radiosensitization by inhibitors of hydroperoxide detoxification and/or agents that increase oxidative stress is proportional to glucose uptake as determined by FDG-PET imaging in vitro and in vivo. The goal of this work is to provide a novel mechanism based biochemical rationale for the use of glucose metabolic differences and functional imaging to develop biologically guided combined modality therapies to treat head and neck cancer based on tumor specific sensitivity to metabolic oxidative stress.
Increased sensitivity to glucose deprivation-induced oxidative stress in tumor vs. normal cells, has led to the hypothesis that inhibitors of glucose and hydroperoxide metabolism [i.e., 2-deoxyglucose (2DG) and buthionine sulfoximine] could be combined with therapeutic agents that increase oxidative stress (radiation, Cisplatin, and azidothymidine) to improve responses during cancer therapy. Furthermore since FDG-PET imaging can be used as a non-invasive marker of glucose metabolism, tumors with greater FDG uptake should respond better to 2-deoxyglucose-based combined modality therapies via enhancement of oxidative stress. If these hypotheses could be confirmed by the experiments in this proposal, they could provide the first mechanism based biochemical rationale for the use of glucose metabolic differences to develop biologically guided combined modality therapies to treat head and neck cancer.
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