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Background:
Early reports showed that 3-fluoro-3-deoxy-glucose and 3-fluoro-3-deoxy-galactose undergo cellular reduction to 3-fluoro-3-deoxy-polyols or oxidation to 3-fluoro-3-deoxy-acids.1,2 The distinct 19F-NMR resonances of these metabolites are applicable for multicolor 19F-MRI with Fluorine Metabolic Imaging (FMI). FMI was found useful for differentiating tumors based on their 19F-MR fingerprints, noninvasively reporting on two redox biomarkers: AKR1B1 and ALDH1A1.3
Hypothesis/Objective:
We aimed to synthesize 3-fluoro-3-deoxy-D-xylose (3FDXyl) and investigate its potential as a 3-fluoro-pentose probe for FMI studies.
Methods:
3FDXyl was synthesized (Fig. 1-1a) by selective fluorination of allofuranose to 3-fluoro-D-glucofuranose, followed by isomerization to the xylofuranose configuration and deprotection. The redox metabolites of 3FDXyl were generated (Fig 1-1b) by its reduction with NaBH4 to produce 3-fluoro-3-deoxy xylitol (FDXtol) and oxidation with NaHCO3/Br2 to yield 3-fluoro-3-deoxy xylonic acid (3FDXylA). 19F-NMR spectra of 3FDXyl, FDXtol, 3FDXylA, or their mixture in aqueous solution were recorded at 9.4 T (Bruker NMR spectrometer). MRI was performed on a Bruker AVIII-400WB 9.4T scanner after intravenous 3FDXyl injection (15 mg/70 μl PBS;~0.6 g/kg) in a C57BL/6 mouse. 3D-FMI was acquired with the mCSSI RARE sequence4, using chemical shift offsets to map the spatial distribution of 3FDXyl, 3FDXtol, and 3FDXylA. 1H-MRI and non-localizing 19F-NMR were collected before and after FMI steps.
Results:
Establishing the synthesis and purification of 3FDXyl, FDXtol, and 3FDXylA (Fig. 1-1a,1b), the 19F-NMR spectra of the three compounds were recorded, revealing spectrally resolved peaks at 9.4 T. Similarly to 3FDG and 3FDGal, 19F-NMR analysis of 3FDXyl revealed two distinct 19F-NMR peaks (-196 and -201 ppm), corresponding to its β- and α-anomeric forms in solution (Fig. 1-1b, bottom). Well separated from these peaks, the 19F-NMR peaks of the synthetic 3FDxylA and 3FDXtol were found to resonate at -207 and -212 ppm (Fig. 1b). 3FDXyl was then injected into a healthy mouse (Fig. 1-2a), revealing the formation of two new 19F-NMR signals at chemical shifts that indicate the in vivo formation of the probe’s redox metabolites (Fig. 1-2b). The obtained multiplexed 19F-MRI metabolic maps (3D-FMI maps, Fig. 1-2c) demonstrate substantial accumulation of 3FDXtol in skeletal muscles, a pattern observed on 2-[18F]FDG PET in non-fasted subjects, potentially indicating that 3FDXyl is transported into cells via insulin-dependent glucose transporters.
Conclusion:
We demonstrated the synthesis and characterization of 3FDXyl and its expected redox metabolites, 3FDXylA and 3FDXtol. The latter two were in vivo generated after systemic administration of 3FDXyl. The results suggest that the trapping mechanism of 3-fluoro-pentoses mimics that of 3-fluoro-hexoses, potentially expanding the library of probes that trace redox biomarkers, broadening the scope of FMI toward alternative sugar backbones. Extending FMI to fluoropentoses broadens its chemical space and biological reach, potentially illuminating new facets of sugar transport and redox biochemistry.
Image/Figure:
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Image/Figure Caption:
Fig.1: (1a-b) Synthesis and characterization of 3FDxyl and its redox metabolites: (1a) The reaction scheme used for the synthesis of 3FDXyl. (1b) The reaction scheme used for the oxidation of 3FDXyl to 3FDXylA (left) and reduction of 3FDXyl to 3FDXtol (right). The 19F-NMR spectrum demonstrates the characteristic chemical shifts of the three synthetic molecules 3FDXyl (cyan), 3FDXylA (gold), and 3FDXtol (magenta). (2a-c) In vivo FMI with 3-fluoro-3-deoxy-xylose in a healthy mouse: (2a) Schematic of the in vivo FMI setup for a healthy mouse after IV 3FDXyl administration. (2b) Time-course 19F-NMR spectra at 0.5, 2, and 3.5 h showing decreasing probe (cyan) over time and increasing redox metabolites 3FDXylA (gold) and 3FDXtol (magenta). (2c) FMI maps acquired ~1.5 h post-injection, overlaid on anatomical 1H-MRI, displaying biodistribution and tissue-specific accumulation of metabolites.
Author
Dan Cohen
Weizmann Institute of Science