Introduction

Enhanced glucose uptake is a hallmark of malignant tumors. For diagnostic purposes this is traditionally imaged by 18FDG-PET [1], but recently it also has become possible by MR deuterium metabolic imaging (DMI) using non-radioactive [6,6 2H2]glucose [2]. DMI has several advantages, e.g. by tracking 2H it provides a quantitative biomarker for the Warburg effect [2,3]. Enhanced choline uptake is another hallmark of cancer and the presence of choline compounds in tumors has been assessed by 18F or 11C choline PET and by MR spectroscopy methods [4,5,6]. 11C choline-PET often identifies tumors better than FDG-PET [7]. The aims of this study were to demonstrate 1. that DMI can monitor [2H9]choline uptake in renal tumor models 2. that simultaneous recording of the uptake and conversion of glucose and choline in these tumors by DMI is possible.

Methods

Renal tumors were grown subcutaneously in mice up to ~155 mm3 in size. Mice were aneasthesized with isoflurane. They were IV injected with 12 μg atropine to prevent a cholinergic reaction. Then we infused 0.05gr/kg [2H9]choline in a 0.16 ml saline solution IV in ~15 sec, or a 0.05gr/kg [2H9]choline with 1.3gr/kg [6,6 2H2]glucose combination in a 0.3 ml saline solution IV in ~20 sec. MR was performed on a Bruker Biospec at 11.7T with a home-built 1H/2H coil. After 1H reference imaging and shimming, DMRS was performed with an excitation pulse angle of 900 and a TR = 500 ms. 3D DMI was performed with a nominal spatial resolution of 2x2x2 mm, TR = 400 ms, TE = 0.4 ms and total acquisition time of 36 minutes. Data was processed in DMIWizard. Absolute tissue concentrations were determined using the HOD signal as reference assuming an initial HOD concentration of 13.7mM.

Results and Discussion

After a 15s infusion of 2H9 choline a 2H signal appeared at ~3.2 ppm, well separated from that of HOD, which we assign to choline compounds. It increased to a maximum level of ~1 mM [2H9]choline at ~5 min post-infusion and then slowly decreased to ~0.6 mM at 100 min post-infusion (Fig. 1). The HOD signal remained almost constant, which is expected for choline breakdown with little water formation (Fig. 1). No other clear signals were observed except for possibly a small signal adjacent to the choline signal, which may be betaine the primary breakdown product of choline [5]. A DMI obtained at 60 min showed a clear spot for choline in the tumor (Fig. 1). DMI results of a [2H9]choline and [6,6 2H2]glucose phantom demonstrate that their signals can be separately observed (Fig. 2a). After a 20 sec infusion of a solution with [2H9]choline and [6,6 2H2]glucose in a mouse the 2H MR spectra of the tumor clearly show separated signals for these compounds and also for deuterated lactate (Fig. 2b). In 2H NMR spectra of blood taken at 15 min or longer after infusion no choline signal could be detected in agreement with the rapid half-life of administered choline [8] and validating that in vivo the 3.2 ppm signal arises from the tumor and not blood (Fig 3).

Conclusions

We developed a successful protocol to follow the uptake and to image the presence of [2H9]choline in tumors after a bolus administration of this compound. In addition we were able to perform DMI simultaneously of [2H9]choline and of [6,6 2H2]glucose. As DMI of glucose uptake and its metabolic conversions has been shown to be feasible in patients [2], the simultaneous performance of choline DMI next to that of glucose is an important complementary extension with clinical potential.

Acknowledgements

No acknowledgement found.

References

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