Distinctions Between the Metabolic Changes in Glioblastoma Cells and Glioma Stem-like Cells Following Irradiation

Abstract

Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor in adults and, even with aggressive treatment that includes surgical resection, radiation, and chemotherapy administration, prognosis is poor due to tumor recurrence. There is evidence that within GBMs a small number of glioma stem cells exist, which are thought to be radiation resistant and may be capable of repopulating a tumor after treatment. It has been shown that GBM tumors largely employ the Warburg effect, but few studies have examined the metabolism of tumor stem cells, and little data exists linking metabolism to radiation resistance. This study aims to characterize the metabolic differences between glioma stem-like cells (GSCs) and traditional GBM tumor cells with and without irradiation (IR). qPCR, Western blotting, and capillary electrophoresis mass spectrometry were used to evaluate and compare the levels of metabolic enzymes and metabolites of a human derived GSC line (NSC11) with two commonly used GBM cell lines (U87, U251) before and after IR. A Seahorse Bioanalyzer was used to determine the oxygen consumption rate, extracellular acidification rate, and glucose and glutamine dependency of each cell line. At baseline, we find that GSCs are more quiescent than GBM cells, which have higher levels of both glycolysis and oxidative phosphorylation. GBM lines show higher levels of both basal and maximal respiration, as well as basal glycolysis and glycolytic capacity than GSCs. They also express higher levels of energy, glycolysis, and TCA cycle metabolites than GSCs. Inversely, GSCs demonstrate metabolic signs of quiescence such as decreased NEAA synthesis. After IR, the radiation- sensitive GBM tumor cell line (U251) exhibits increases in all metabolic pathways, whereas the levels of glycolytic and oxidative metabolites in the GSCs remain unchanged. All cell lines show an increase of ATP and NAD production following IR. These findings indicate that the metabolism of GSCs undergoes different alterations than that of GBM tumor cells after IR, making them an attractive target for novel therapeutic approaches in conjunction with radiation therapy. Additionally, differences in metabolic signatures between GSC lines could be useful for non-invasive diagnostic modalities such as 13C MR spectroscopy.