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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

Uptake of [18F]FDG-6-P and [18F]FDG byS. aureusand mammalian cells. (a)S. aureus RN6390 and the isogenic UHPT-deficient mutant were incubated with either [18F]FDG or [18F]FDG-6-P. The activity associated with each of the strains after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. Counts were normalised to remove ‘no cell’ control counts and to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. **P = 0.0015; ****P < 0.0001. Data were collected from three independent repeats. (b) The activity associated with mammalian cell lines HL60, Jurkat, AGS, THP1, HIB-1B and 3 T3-L1 after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. The counts were normalised to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. Differences in the means of cells incubated with [18F]FDG-6-P were not significant.
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Fig2: Uptake of [18F]FDG-6-P and [18F]FDG byS. aureusand mammalian cells. (a)S. aureus RN6390 and the isogenic UHPT-deficient mutant were incubated with either [18F]FDG or [18F]FDG-6-P. The activity associated with each of the strains after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. Counts were normalised to remove ‘no cell’ control counts and to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. **P = 0.0015; ****P < 0.0001. Data were collected from three independent repeats. (b) The activity associated with mammalian cell lines HL60, Jurkat, AGS, THP1, HIB-1B and 3 T3-L1 after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. The counts were normalised to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. Differences in the means of cells incubated with [18F]FDG-6-P were not significant.

Mentions: Despite [18F]FDG-6-P being a homologue of glucose-6-phosphate, it was not known whether this radiopharmaceutical would be transported by the staphylococcal UHPT. S. aureus RN6390 and UHPT-deficient S. aureus RN6390 ΔuhpT were incubated with 2 MBq of [18F]FDG or [18F]FDG-6-P. After incubation, the relative activity of each radiopharmaceutical associated with the bacterial cells was calculated (Figure 2a).Figure 2


[(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)

Uptake of [18F]FDG-6-P and [18F]FDG byS. aureusand mammalian cells. (a)S. aureus RN6390 and the isogenic UHPT-deficient mutant were incubated with either [18F]FDG or [18F]FDG-6-P. The activity associated with each of the strains after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. Counts were normalised to remove ‘no cell’ control counts and to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. **P = 0.0015; ****P < 0.0001. Data were collected from three independent repeats. (b) The activity associated with mammalian cell lines HL60, Jurkat, AGS, THP1, HIB-1B and 3 T3-L1 after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. The counts were normalised to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. Differences in the means of cells incubated with [18F]FDG-6-P were not significant.
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Fig2: Uptake of [18F]FDG-6-P and [18F]FDG byS. aureusand mammalian cells. (a)S. aureus RN6390 and the isogenic UHPT-deficient mutant were incubated with either [18F]FDG or [18F]FDG-6-P. The activity associated with each of the strains after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. Counts were normalised to remove ‘no cell’ control counts and to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. **P = 0.0015; ****P < 0.0001. Data were collected from three independent repeats. (b) The activity associated with mammalian cell lines HL60, Jurkat, AGS, THP1, HIB-1B and 3 T3-L1 after incubation with [18F]FDG (black) or [18F]FDG-6-P (white) was measured using a gamma counter. The counts were normalised to compare [18F]FDG-6-P uptake with [18F]FDG uptake. Error bars show SEM. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. Differences in the means of cells incubated with [18F]FDG-6-P were not significant.
Mentions: Despite [18F]FDG-6-P being a homologue of glucose-6-phosphate, it was not known whether this radiopharmaceutical would be transported by the staphylococcal UHPT. S. aureus RN6390 and UHPT-deficient S. aureus RN6390 ΔuhpT were incubated with 2 MBq of [18F]FDG or [18F]FDG-6-P. After incubation, the relative activity of each radiopharmaceutical associated with the bacterial cells was calculated (Figure 2a).Figure 2

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