A comparative study of N.C.A. fluorine-18 labeling of proteins via acylation and photochemical conjugation

Nucl Med Biol. 1996 Apr;23(3):365-72. doi: 10.1016/0969-8051(96)00017-0.


Three methods for 18F-labeling of proteins were evaluated with respect to conjugation yields, suitability for remote-controlled routine synthesis, and in vivo stability of the conjugates-i.e., photochemical conjugation (PCC) using 4-azidophenacyl-[18F]fluoride ([18F]APF) as well as classical conjugation using 4-nitrophenyl 2-[18F]fluoropropionate ([18F]NPFP) and N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB). For this purpose, [18F]APF was synthesized in one step with a radiochemical yield (RCY) of up to 70% within about 15 min. The 18F-labeling was performed by photogeneration of the corresponding [18F]arylnitrene by irradiating [18F]APF with UV light in presence of the protein in aqueous buffered solution. Using this procedure, human serum albumin (HSA), transferrin, IgG, and avidin were labeled. The [18F]NPFP was synthesized according to a recently published method. Preparation of [18F]SFB was achieved within 35 min with radiochemical yields of 55 +/- 10% by an improved method using O-(N-succinimidyl)-N-N,N',N'-tetramethyluronium tetrafluoroborate (TSTU) as activating reagent. Compared to [18F]APF, protein labeling with [18F]NPFP and [18F]SFB gave rise to considerably higher RCY, of up to 90%. Labeling studies showed that conjugation yields using [18F]NPFP depend on the lysine, tyrosine, and histidine content of the proteins used, whereas conjugation with [18F]APF and [18F]SFB predominantly depends on the Lys content. Owing to competing O-acylation of Tyr residues, [18F]fluoropropionylated HSA was partially unstable under slightly basic conditions. Biodistribution studies with 18F-labeled HSA in NMRI mice revealed the highest in vivo stability for the [18F]SFB conjugate. Based on these results, [18F]SFB seems to be the most suitable 18F-labeling agent for proteins, particularly for the labeling of antibodies.

Publication types

  • Comparative Study

MeSH terms

  • Acylation
  • Animals
  • Avidin
  • Azides*
  • Benzoates*
  • Fluorine Radioisotopes* / pharmacokinetics
  • Humans
  • Immunoglobulin G
  • Indicators and Reagents
  • Isotope Labeling / methods
  • Mice
  • Mice, Inbred Strains
  • Photochemistry
  • Proteins* / pharmacokinetics
  • Serum Albumin
  • Succinimides*
  • Tissue Distribution
  • Transferrin


  • Azides
  • Benzoates
  • Fluorine Radioisotopes
  • Immunoglobulin G
  • Indicators and Reagents
  • Proteins
  • Serum Albumin
  • Succinimides
  • Transferrin
  • Avidin
  • N-succinimidyl-4-fluorobenzoate
  • 4-nitrophenyl 2-fluoropropionate
  • 4-azidophenacyl fluoride