Deuterium MRI of serine metabolism in mouse models of glioblastoma

Purpose: Serine is a major source of one-carbon units needed for the synthesis of nucleotides and the production of intramitochondrial nicotinamide adenine dinucleotide phosphate (NADPH), and it plays an important role in cancer cell proliferation. The aim of this study was to develop a deuterium (²H) MRS imaging method for imaging tumor serine metabolism.

Methods: Sequential (²H) spectra and spectroscopic images were used to monitor the metabolism of [2,3,3-²H₃]serine in patient-derived glioblastoma cells in vitro and in tumors obtained by their orthotopic implantation in mouse brain.

Results: [14,14-²H₂] 5,10-methylene-tetrahydrofolate, [²H]glycine, [²H]formate, and labeled water were detected in cell suspensions and water labeling in spectroscopic images of tumors. Studies in cells and tumors with variable mitochondrial content and inhibitor studies in cells demonstrated that most of the labeled serine was metabolized in the mitochondria. Water labeling in the cell suspensions was correlated with formate labeling; therefore, water labeling observed in tumors could be used to provide a surrogate measure of flux in the pathway of one-carbon metabolism in vivo.

Conclusion: The method has the potential to be used clinically to select patients for treatment with inhibitors of one-carbon metabolism and subsequently to detect their early responses to such treatment.