(18)F-Fluoroglucosylation of peptides, exemplified on cyclo(RGDfK).
OBJECTIVE
Oxime formation between an aminooxy-functionalized peptide and an (18)F-labelled aldehyde has recently been introduced as a powerful method for the rapid one-step chemoselective synthesis of radiofluorinated peptides.


METHODS
Here, the potential of using routinely produced and thus readily available [(18)F]fluorodeoxyglucose ([(18)F]FDG) as the aldehydic prosthetic group was investigated using an aminooxyacetyl-conjugated cyclic RGD peptide (cyclo(RGDfK(Aoa-(Boc)) as a model peptide.


RESULTS
The use of [(18)F]FDG from routine production ([(18)F]FDGTUM) containing an excess of D: -glucose did not allow the radiosynthesis of [(18)F]FDG-RGD in activities >37 MBq in reasonable yield, rendering the direct use of clinical grade [(18)F]FDG for the routine clinical synthesis of (18)F-labelled peptides impossible. Using no-carrier-added (n.c.a.) [(18)F]FDG obtained via HPLC separation of [(18)F]FDGTUM from excess glucose, however, afforded [(18)F]FDG-RGD in yields of 56-93% (decay corrected) and activities up to 37 MBq. Suitable reaction conditions were 20 min at 120 degrees C and pH 2.5, and a peptide concentration of 5 mM. In a preliminary in vivo biodistribution study in M21 melanoma-bearing nude mice, [(18)F]FDG-RGD showed increased tumour accumulation compared to the "gold standard" [(18)F]galacto-RGD (2.18 vs 1.49 %iD/g, respectively, at 120 min after injection), but also slightly increased uptake in non-target organs, leading to comparable tumour/organ ratios for both compounds.


CONCLUSIONS
These data demonstrate that chemoselective (18)F-labelling of aminooxy-functionalized peptides using n.c.a. [(18)F]FDG represents a radiofluorination/glycosylation strategy that allows preparation of (18)F-labelled peptides in high yield with suitable pharmacokinetics. As soon as the necessary n.c.a. preparation of [(18)F]FDG prior to reaction with the Aoa-peptide can be implemented in a fully automated [(18)F]FDG-synthesis, [(18)F]fluoroglucosylation of peptides may represent a promising alternative to currently used chemoselective one-step (18)F-labelling protocols.
Hultsch
Christina
C
Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, 81675, München, Germany.
Schottelius
Margret
M
Auernheimer
Jörg
J
Alke
Andrea
A
Wester
Hans-Jürgen
HJ
D000818:Animals; D019788:Fluorodeoxyglucose F18 / Q000737:chemistry* / Q000493:pharmacokinetics / Q000494:pharmacology; D006031:Glycosylation; D008546:Melanoma, Experimental / Q000000981:diagnostic imaging; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000493:pharmacokinetics / Q000494:pharmacology; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals / Q000737:chemistry* / Q000493:pharmacokinetics / Q000494:pharmacology; D014018:Tissue Distribution
D010456:Peptides, Cyclic; D019275:Radiopharmaceuticals; C099250:cyclic (arginyl-glycyl-aspartyl-phenylalanyl-lysyl); D019788:Fluorodeoxyglucose F18