De Novo Glutamine Synthesis: Importance for the Proliferation of Glioma Cells and Potentials for Its Detection With 13N-Ammonia

Purpose: The aim of this study was to investigate the role of de novo glutamine (Gln) synthesis in the proliferation of C6 glioma cells and its detection with N-13-ammonia. Methods: Chronic Gln-deprived C6 glioma (0.06C6) cells were established. The proliferation rates of C6 and 0.06C6 cells were measured under the conditions of Gln deprivation along with or without the addition of ammonia or glutamine synthetase (GS) inhibitor. N-13-ammonia uptake was assessed in C6 cells by gamma counting and in rats with C6 and 0.06C6 xenografts by micropositron emission tomography (PET) scanning. The expression of GS in C6 cells and xenografts was assessed by Western blotting and immunohistochemistry, respectively. Results: The Gln-deprived C6 cells showed decreased proliferation ability but had a significant increase in GS expression. Furthermore, we found that low concentration of ammonia was sufficient to maintain the proliferation of Gln-deprived C6 cells, and N-13-ammonia uptake in C6 cells showed Gln-dependent decrease, whereas inhibition of GS markedly reduced the proliferation of C6 cells as well as the uptake of N-13-ammoina. Additionally, microPET/computed tomography exhibited that subcutaneous 0.06C6 xenografts had higher N-13-ammonia uptake and GS expression in contrast to C6 xenografts. Conclusion: De novo Gln synthesis through ammonia-glutamate reaction plays an important role in the proliferation of C6 cells. N-13-ammonia can be a potential metabolic PET tracer for Gln-dependent tumors.