Energy is necessary for tumor cell viability and growth. Aerobic glucose-driven lactic
acid fermentation is a common metabolic phenotype seen in most cancers including malignant
gliomas. This metabolic phenotype is linked to abnormalities in mitochondrial structure
and function. A luciferin-luciferase bioluminescence ATP assay was used to measure
the influence of amino acids, glucose, and oxygen on ATP content and viability in
mouse (VM-M3 and CT-2A) and human (U-87MG) glioma cells that differed in cell biology,
genetic background, and species origin. Oxygen consumption was measured using the
Resipher system. Extracellular lactate and succinate were measured as end products
of the glycolysis and glutaminolysis pathways, respectively. The results showed that:
(1) glutamine was a source of ATP content irrespective of oxygen. No other amino acid
could replace glutamine in sustaining ATP content and viability; (2) ATP content persisted
in the absence of glucose and under hypoxia, ruling out substantial contribution through
either glycolysis or oxidative phosphorylation (OxPhos) under these conditions; (3)
Mitochondrial complex IV inhibition showed that oxygen consumption was not an accurate
measure for ATP production through OxPhos. The glutaminase inhibitor, 6-diazo-5-oxo-L-norleucine
(DON), reduced ATP content and succinate export in cells grown in glutamine. The data
suggests that mitochondrial substrate level phosphorylation in the glutamine-driven
glutaminolysis pathway contributes to ATP content in these glioma cells. A new model
is presented highlighting the synergistic interaction between the high-throughput
glycolysis and glutaminolysis pathways that drive malignant glioma growth and maintain
ATP content through the aerobic fermentation of both glucose and glutamine.