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[(18)F]FDG-6-P as a novel in vivo tool for imaging staphylococcal infections.

Mills B, Awais RO, Luckett J, Turton D, Williams P, Perkins AC, Hill PJ - EJNMMI Res (2015)

Bottom Line: Yield, purity and stability were confirmed by RP-HPLC and iTLC.Despite conclusive in vitro validation, [(18)F]FDG-6-P did not behave as predicted in vivo.The bacterial UHPT can transport hexose phosphates other than glucose, and therefore alternative sugars may show differential biodistribution and provide a means for specific bacterial detection.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, Centre for Biomolecular Sciences, University of Nottingham, University Boulevard, Nottingham, NG7 2RD UK.

ABSTRACT

Background: Management of infection is a major clinical problem. Staphylococcus aureus is a Gram-positive bacterium which colonises approximately one third of the adult human population. Staphylococcal infections can be life-threatening and are frequently complicated by multi-antibiotic resistant strains including methicillin-resistant S. aureus (MRSA). Fluorodeoxyglucose ([(18)F]FDG) imaging has been used to identify infection sites; however, it is unable to distinguish between sterile inflammation and bacterial load. We have modified [(18)F]FDG by phosphorylation, producing [(18)F]FDG-6-P to facilitate specific uptake and accumulation by S. aureus through hexose phosphate transporters, which are not present in mammalian cell membranes. This approach leads to the specific uptake of the radiopharmaceutical into the bacteria and not the sites of sterile inflammation.

Methods: [(18)F]FDG-6-P was synthesised from [(18)F]FDG. Yield, purity and stability were confirmed by RP-HPLC and iTLC. The specificity of [(18)F]FDG-6-P for the bacterial universal hexose phosphate transporter (UHPT) was confirmed with S. aureus and mammalian cell assays in vitro. Whole body biodistribution and accumulation of [(18)F]FDG-6-P at the sites of bioluminescent staphylococcal infection were established in a murine foreign body infection model.

Results: In vitro validation assays demonstrated that [(18)F]FDG-6-P was stable and specifically transported into S. aureus but not mammalian cells. [(18)F]FDG-6-P was elevated at the sites of S. aureus infection in vivo compared to uninfected controls; however, the increase in signal was not significant and unexpectedly, the whole-body biodistribution of [(18)F]FDG-6-P was similar to that of [(18)F]FDG.

Conclusions: Despite conclusive in vitro validation, [(18)F]FDG-6-P did not behave as predicted in vivo. However at the site of known infection, [(18)F]FDG-6-P levels were elevated compared with uninfected controls, providing a higher signal-to-noise ratio. The bacterial UHPT can transport hexose phosphates other than glucose, and therefore alternative sugars may show differential biodistribution and provide a means for specific bacterial detection.

No MeSH data available.


Related in: MedlinePlus

Accumulation of [18F]FDG and [18F]FDG-6-P at the catheter infection site. Mice with S. aureus infections (or uninfected control mice) were injected with approximately 10 MBq [18F]FDG (n = 3 infected, n = 3 uninfected) or approximately 10 MBq [18F]FDG-6-P (n = 3 infected, n = 2 uninfected) 1 h prior to nanoScan PET-CT imaging. (a) Representative 3D colour map of catheter regions cropped from whole-body nanoScan PET-CT images. Images are shown with and without CT. (b) SUV values were calculated for S. aureus-infected (black circle) and uninfected mice (black square). Mann-Whitney U tests confirmed that there were no significant differences in SUVs between infected and uninfected mice injected with either [18F]FDG (P = 0.7619) or [18F]FDG-6-P (P = 0.0556). Bars on the graph show median SUVs for each group (n = 3 for [18F]FDG infected and n = 3 for uninfected mice; n = 3 for [18F]FDG-6-P infected mice and n = 2 uninfected mice). (c) The infected (I) to uninfected (UI) ratio (I/UI) for the catheter sites of mice injected with [18F]FDG and [18F]FDG-6-P was calculated by dividing the mean infected catheter SUV by the mean uninfected catheter SUV for each cohort of mice.
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Fig5: Accumulation of [18F]FDG and [18F]FDG-6-P at the catheter infection site. Mice with S. aureus infections (or uninfected control mice) were injected with approximately 10 MBq [18F]FDG (n = 3 infected, n = 3 uninfected) or approximately 10 MBq [18F]FDG-6-P (n = 3 infected, n = 2 uninfected) 1 h prior to nanoScan PET-CT imaging. (a) Representative 3D colour map of catheter regions cropped from whole-body nanoScan PET-CT images. Images are shown with and without CT. (b) SUV values were calculated for S. aureus-infected (black circle) and uninfected mice (black square). Mann-Whitney U tests confirmed that there were no significant differences in SUVs between infected and uninfected mice injected with either [18F]FDG (P = 0.7619) or [18F]FDG-6-P (P = 0.0556). Bars on the graph show median SUVs for each group (n = 3 for [18F]FDG infected and n = 3 for uninfected mice; n = 3 for [18F]FDG-6-P infected mice and n = 2 uninfected mice). (c) The infected (I) to uninfected (UI) ratio (I/UI) for the catheter sites of mice injected with [18F]FDG and [18F]FDG-6-P was calculated by dividing the mean infected catheter SUV by the mean uninfected catheter SUV for each cohort of mice.

Mentions: Despite the unexpected whole-body biodistribution of [18F]FDG-6-P in vivo, the accumulation of [18F]FDG-6-P and [18F]FDG at the site of bacterial catheter foreign body infections was characterised. After image reconstruction of data captured from the nanoScan PET-CT scans (Figure 3b), the catheter regions were cropped from the whole body image and scales normalised based on injected activity in order to visualise activity associated with the catheter (Figure 5a). Visually, [18F]FDG was present at the site of both infected and uninfected catheters and as expected, [18F]FDG accumulated to a higher concentration when bacteria were present. The activity present at either end of the uninfected catheter could indicate inflammation at these positions where the rough, cut surface of the catheter was in contact with the tissue. For the infected mice, it was apparent that the majority of the activity was associated on the outside of the catheter and the surrounding tissue, rather than inside the lumen of the catheter where a large bacterial population was expected. These data suggest that the radiopharmaceutical may not be reaching the majority of bacterial cells.Figure 5


[(18)F]FDG-6-P as a novel in vivo tool for imaging staphylococcal infections.

Mills B, Awais RO, Luckett J, Turton D, Williams P, Perkins AC, Hill PJ - EJNMMI Res (2015)

Accumulation of [18F]FDG and [18F]FDG-6-P at the catheter infection site. Mice with S. aureus infections (or uninfected control mice) were injected with approximately 10 MBq [18F]FDG (n = 3 infected, n = 3 uninfected) or approximately 10 MBq [18F]FDG-6-P (n = 3 infected, n = 2 uninfected) 1 h prior to nanoScan PET-CT imaging. (a) Representative 3D colour map of catheter regions cropped from whole-body nanoScan PET-CT images. Images are shown with and without CT. (b) SUV values were calculated for S. aureus-infected (black circle) and uninfected mice (black square). Mann-Whitney U tests confirmed that there were no significant differences in SUVs between infected and uninfected mice injected with either [18F]FDG (P = 0.7619) or [18F]FDG-6-P (P = 0.0556). Bars on the graph show median SUVs for each group (n = 3 for [18F]FDG infected and n = 3 for uninfected mice; n = 3 for [18F]FDG-6-P infected mice and n = 2 uninfected mice). (c) The infected (I) to uninfected (UI) ratio (I/UI) for the catheter sites of mice injected with [18F]FDG and [18F]FDG-6-P was calculated by dividing the mean infected catheter SUV by the mean uninfected catheter SUV for each cohort of mice.
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Fig5: Accumulation of [18F]FDG and [18F]FDG-6-P at the catheter infection site. Mice with S. aureus infections (or uninfected control mice) were injected with approximately 10 MBq [18F]FDG (n = 3 infected, n = 3 uninfected) or approximately 10 MBq [18F]FDG-6-P (n = 3 infected, n = 2 uninfected) 1 h prior to nanoScan PET-CT imaging. (a) Representative 3D colour map of catheter regions cropped from whole-body nanoScan PET-CT images. Images are shown with and without CT. (b) SUV values were calculated for S. aureus-infected (black circle) and uninfected mice (black square). Mann-Whitney U tests confirmed that there were no significant differences in SUVs between infected and uninfected mice injected with either [18F]FDG (P = 0.7619) or [18F]FDG-6-P (P = 0.0556). Bars on the graph show median SUVs for each group (n = 3 for [18F]FDG infected and n = 3 for uninfected mice; n = 3 for [18F]FDG-6-P infected mice and n = 2 uninfected mice). (c) The infected (I) to uninfected (UI) ratio (I/UI) for the catheter sites of mice injected with [18F]FDG and [18F]FDG-6-P was calculated by dividing the mean infected catheter SUV by the mean uninfected catheter SUV for each cohort of mice.
Mentions: Despite the unexpected whole-body biodistribution of [18F]FDG-6-P in vivo, the accumulation of [18F]FDG-6-P and [18F]FDG at the site of bacterial catheter foreign body infections was characterised. After image reconstruction of data captured from the nanoScan PET-CT scans (Figure 3b), the catheter regions were cropped from the whole body image and scales normalised based on injected activity in order to visualise activity associated with the catheter (Figure 5a). Visually, [18F]FDG was present at the site of both infected and uninfected catheters and as expected, [18F]FDG accumulated to a higher concentration when bacteria were present. The activity present at either end of the uninfected catheter could indicate inflammation at these positions where the rough, cut surface of the catheter was in contact with the tissue. For the infected mice, it was apparent that the majority of the activity was associated on the outside of the catheter and the surrounding tissue, rather than inside the lumen of the catheter where a large bacterial population was expected. These data suggest that the radiopharmaceutical may not be reaching the majority of bacterial cells.Figure 5

Bottom Line: Yield, purity and stability were confirmed by RP-HPLC and iTLC.Despite conclusive in vitro validation, [(18)F]FDG-6-P did not behave as predicted in vivo.The bacterial UHPT can transport hexose phosphates other than glucose, and therefore alternative sugars may show differential biodistribution and provide a means for specific bacterial detection.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, Centre for Biomolecular Sciences, University of Nottingham, University Boulevard, Nottingham, NG7 2RD UK.

ABSTRACT

Background: Management of infection is a major clinical problem. Staphylococcus aureus is a Gram-positive bacterium which colonises approximately one third of the adult human population. Staphylococcal infections can be life-threatening and are frequently complicated by multi-antibiotic resistant strains including methicillin-resistant S. aureus (MRSA). Fluorodeoxyglucose ([(18)F]FDG) imaging has been used to identify infection sites; however, it is unable to distinguish between sterile inflammation and bacterial load. We have modified [(18)F]FDG by phosphorylation, producing [(18)F]FDG-6-P to facilitate specific uptake and accumulation by S. aureus through hexose phosphate transporters, which are not present in mammalian cell membranes. This approach leads to the specific uptake of the radiopharmaceutical into the bacteria and not the sites of sterile inflammation.

Methods: [(18)F]FDG-6-P was synthesised from [(18)F]FDG. Yield, purity and stability were confirmed by RP-HPLC and iTLC. The specificity of [(18)F]FDG-6-P for the bacterial universal hexose phosphate transporter (UHPT) was confirmed with S. aureus and mammalian cell assays in vitro. Whole body biodistribution and accumulation of [(18)F]FDG-6-P at the sites of bioluminescent staphylococcal infection were established in a murine foreign body infection model.

Results: In vitro validation assays demonstrated that [(18)F]FDG-6-P was stable and specifically transported into S. aureus but not mammalian cells. [(18)F]FDG-6-P was elevated at the sites of S. aureus infection in vivo compared to uninfected controls; however, the increase in signal was not significant and unexpectedly, the whole-body biodistribution of [(18)F]FDG-6-P was similar to that of [(18)F]FDG.

Conclusions: Despite conclusive in vitro validation, [(18)F]FDG-6-P did not behave as predicted in vivo. However at the site of known infection, [(18)F]FDG-6-P levels were elevated compared with uninfected controls, providing a higher signal-to-noise ratio. The bacterial UHPT can transport hexose phosphates other than glucose, and therefore alternative sugars may show differential biodistribution and provide a means for specific bacterial detection.

No MeSH data available.


Related in: MedlinePlus