Mapping of exogenous choline uptake and metabolism in rat glioblastoma using deuterium metabolic imaging (DMI)

Abstract

IntroductionThere is a lack of robust metabolic imaging techniques that can be routinely applied to characterize lesions in patients with brain tumors. Here we explore in an animal model of glioblastoma the feasibility to detect uptake and metabolism of deuterated choline and describe the tumor-to-brain image contrast.MethodsRG2 cells were incubated with choline and the level of intracellular choline and its metabolites measured in cell extracts using high resolution 1H NMR. In rats with orthotopically implanted RG2 tumors deuterium metabolic imaging (DMI) was applied in vivo during, as well as 1 day after, intravenous infusion of 2H9-choline. In parallel experiments, RG2-bearing rats were infused with [1,1′,2,2′-2H4]-choline and tissue metabolite extracts analyzed with high resolution 2H NMR to identify molecule-specific 2H-labeling in choline and its metabolites.ResultsIn vitro experiments indicated high uptake and fast phosphorylation of exogenous choline in RG2 cells. In vivo DMI studies revealed a high signal from the 2H-labeled pool of choline + metabolites (total choline, 2H-tCho) in the tumor lesion but not in normal brain. Quantitative DMI-based metabolic maps of 2H-tCho showed high tumor-to-brain image contrast in maps acquired both during, and 24 h after deuterated choline infusion. High resolution 2H NMR revealed that DMI data acquired during 2H-choline infusion consists of free choline and phosphocholine, while the data acquired 24 h later represent phosphocholine and glycerophosphocholine.DiscussionUptake and metabolism of exogenous choline was high in RG2 tumors compared to normal brain, resulting in high tumor-to-brain image contrast on DMI-based metabolic maps. By varying the timing of DMI data acquisition relative to the start of the deuterated choline infusion, the metabolic maps can be weighted toward detection of choline uptake or choline metabolism. These proof-of-principle experiments highlight the potential of using deuterated choline combined with DMI to metabolically characterize brain tumors.

Advances and prospects in deuterium metabolic imaging (DMI): a systematic review of in vivo studies

“…Most tracers were produced from the deuteration of protonated metabolites that are associated with energy metabolism or cellular proliferation, including glucose, pyruvate, acetate, fumarate, and choline [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , 29 , 31 , 32 , 37 , 41 , 43 , 44 , 46 – 48 , 50 , 52 , 56 , 60 – 62 , 65 , 66 , 69 , 72 – 74 , 81 , 83 ]. For instance, [6,6′- 2 H2]glucose, as a mostly used metabolic tracer, can be used to detect downstream deuterated products, including glutamate, glutamine, lactate, and semiheavy water (Fig.…”

“…For instance, [6,6′- 2 H2]glucose, as a mostly used metabolic tracer, can be used to detect downstream deuterated products, including glutamate, glutamine, lactate, and semiheavy water (Fig. 5 ) [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , 29 , 31 , 32 , 37 , 41 , 43 , 44 , 46 – 48 , 50 , 52 , 56 , 60 – 62 , 65 , 66 , 69 , 72 – 74 , 81 , 83 ]. Among these downstream metabolites, glutamate and glutamine (Glx) can be regarded as products from TCA cycle and lactate from glycolysis [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , 29 , 31 , 32 , 37 , 41 , 43 , 44 , 46 – 48 , 50 , 52 , 56 , 60 – 62 , 65 , 66 , 69 , 72 – 74 , 81 , 83 ].…”

“…5 ) [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , 29 , 31 , 32 , 37 , 41 , 43 , 44 , 46 – 48 , 50 , 52 , 56 , 60 – 62 , 65 , 66 , 69 , 72 – 74 , 81 , 83 ]. Among these downstream metabolites, glutamate and glutamine (Glx) can be regarded as products from TCA cycle and lactate from glycolysis [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , 29 , 31 , 32 , 37 , 41 , 43 , 44 , 46 – 48 , 50 , 52 , 56 , 60 – 62 , 65 , 66 , 69 , 72 – 74 , 81 , 83 ]. By measuring the incorporation of deuterium into these products, the rates of glycolysis and TCA cycle can be estimated [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , …”

“…Among these downstream metabolites, glutamate and glutamine (Glx) can be regarded as products from TCA cycle and lactate from glycolysis [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , 29 , 31 , 32 , 37 , 41 , 43 , 44 , 46 – 48 , 50 , 52 , 56 , 60 – 62 , 65 , 66 , 69 , 72 – 74 , 81 , 83 ]. By measuring the incorporation of deuterium into these products, the rates of glycolysis and TCA cycle can be estimated [ 2 , 3 , 10 , 15 , 17 , 18 , 24 , 28 , 29 , 31 , 32 , 37 , 41 , 43 , 44 , 46 – 48 , 50 , 52 , 56 , 60 – 62 , 65 , 66 , 69 , 72 – 74 , 81 , 83 ]. However, the low deuterium enrichment of [6,6′- 2 H2]glucose restricts its signal intensity [ 15 ].…”

“…As a novel and still evolving technique, most in vivo DMI studies have been performed in animal brains and gliomas because of relatively static organs, and the results from these studies have shown great potential for a range of clinical applications (Table 2 ) [ 2 , 15 , 27 , 31 , 37 , 41 , 47 , 56 , 60 , 66 , 69 , 72 , 81 , 83 ]. The most common application of DMI is to diagnose malignant tumors by detecting abnormal metabolic changes in the material requirement, glycolysis, and TCA cycle [ 2 , 15 , 27 , 37 , 41 , 47 , 56 , 60 , 66 , 69 , 72 , 81 , 83 ].…”