title: A comparative study of N.C.A. fluorine-18 labeling of proteins via acylation and photochemical conjugation.
abstract: 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.
authors.affiliation: Institut für Nuklearchemie, Forschungszentrum Jülich GMBH, Germany.
authors.forename: H J
authors.initials: HJ
authors.lastname: Wester
authors.forename: K
authors.initials: K
authors.lastname: Hamacher
authors.forename: G
authors.initials: G
authors.lastname: Stöcklin
mesh_terms: D000215:Acylation; D000818:Animals; D001360:Avidin; D001386:Azides; D001565:Benzoates; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics; D006801:Humans; D007074:Immunoglobulin G; D007202:Indicators and Reagents; D007553:Isotope Labeling / Q000379:methods; D051379:Mice; D008815:Mice, Inbred Strains; D010777:Photochemistry; D011506:Proteins / Q000493:pharmacokinetics; D012709:Serum Albumin; D013388:Succinimides; D014018:Tissue Distribution; D014168:Transferrin
chemical_list: D001386:Azides; D001565:Benzoates; D005462:Fluorine Radioisotopes; D007074:Immunoglobulin G; D007202:Indicators and Reagents; D011506:Proteins; D012709:Serum Albumin; D013388:Succinimides; D014168:Transferrin; D001360:Avidin; C075713:N-succinimidyl-4-fluorobenzoate; C102277:4-nitrophenyl 2-fluoropropionate; C102276:4-azidophenacyl fluoride