Abstract 18: Galactose impacts cell growth and redox status of glioblastoma multiforme U87 cell lines
Authors: Lumibao Jan C. , Kolossov Vladimir , Leslie Matthew T. , Gaskins H R. 
Published: July 2016

Abstract
Glioblastoma multiforme (GBM) is the most common and malignant form of brain cancer in adults, with a median survival time of 12-15 months. Characterizing the metabolic alterations of GBM is a crucial step towards identifying potential targets for treatment, with mitochondria, the electron transport chain, and associated reactive oxygen species presenting lucrative targets for therapy. However, the Warburg effect, in which cells generate ATP mainly via glycolysis despite adequate oxygen and functional mitochondria, can render cancer cells resistant to antagonists of the electron transport chain. This prompts investigations into other nodes of oncogenic metabolism such as the epidermal growth factor receptor (EGFR)/phosphoinositide 3-kinase pathway which can regulate glucose metabolism. The present work defined the sensitivity of GBM U87MG, U87OE (over-expressed EGFR), and U87vIII (hyper-activated vIII mutated EGFR) cell lines to media supplemented with galactose versus conventional glucose concentrations. Cells were transfected with a mitochondrial-targeted Glrx-roGFP2 redox biosensor, a mutated GFP protein whose fluorescence reflects the local redox potential, and incubated in Dulbecco's Modified Eagle's Medium (DMEM) supplemented with either 25 mM glucose (DMEM-Glu) or 10 mM galactose with and without 1 mM pyruvate (DMEM-Gal±Pyr). Glucose deprivation combined with galactose supplementation allows metabolic isolation of mitochondrial contributions to ATP generation because the glycolytic metabolism of galactose yields no net ATP, forcing cells to rely on increased mitochondrial respiration. Cells were exposed to differential media conditions and assessed via flow cytometry to monitor mitochondrial redox homeostasis after 24 h of media exposure. Wild type U87 cells exhibited a slight reduction upon glycolytic blockade, while mitochondria in the mutant EGFR U87OE and U87vIII cells exhibited extreme oxidation. The sulforhodamine B assay, which determines cell density based on a colorimetric measurement of cellular protein content, was performed to assess cell concentration in different media after 72 h of media exposure. Mutant EGFR U87OE and U87vIII cells experienced much greater growth inhibition and cell death compared to wild type U87MG cells. Thus, EGFR-activating mutations increase cellular dependence on glycolytic ATP generation for cell growth and redox homeostasis. Future work will build on these findings to characterize how the metabolic phenotypes and preferences of these cells are linked to their migratory behavior in an engineered 3D hydrogel environment.
Citation Format: Jan C. Lumibao, Vladimir Kolossov, Matthew T. Leslie, H R. Gaskins. Galactose impacts cell growth and redox status of glioblastoma multiforme U87 cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 18.