title: Synthesis and Characterization of ¹⁸F-Interleukin-8 Using a Cell-Free Translation System and 4-¹⁸F-Fluoro-L-Proline.
abstract: Macromolecules such as proteins are attracting increasing interest for molecular imaging. We previously proposed a novel strategy for preparing macromolecules labeled with a PET radionuclide, (11)C, using a cell-free translation system with (11)C-methionine. However, macromolecules tend to exhibit slower kinetics, thus requiring a longer scanning time. Here, we expand our strategy using (18)F, which has a longer half-life, with the cell-free translation system with 4-(18)F-fluoro-L-proline ((18)F-FPro). We evaluated (18)F-interleukin-8 ((18)F-IL-8) produced by this method in vitro and in vivo to provide a proof of concept of our strategy.
  
  
  METHODS
  We tested some fluorinated amino acids to be incorporated into a protein. Trans-(18)F-FPro was radiolabeled from the corresponding precursor. (18)F-IL-8 was produced using the cell-free translation system with trans-(18)F-FPro instead of natural L-proline with incubation at 37°C for 120 min. An in vitro binding assay of (18)F-IL-8 was performed using IL-8 receptor-expressing cells. After intravenous administration of (18)F-IL-8, in vivo PET imaging of IL-8 receptor-expressing xenograft-bearing mice was performed using a small-animal PET system.
  
  
  RESULTS
  FPro was identified as an amino acid incorporated into the protein. (18)F-IL-8 was successfully prepared using the cell-free translation system and trans-(18)F-FPro with the radiochemical yield of 1.5% (decay-corrected) based on trans-(18)F-FPro. In vitro binding assays of (18)F-IL-8 demonstrated its binding to IL-8 receptor. In vivo PET imaging demonstrated that (18)F-IL-8 clearly accumulated in IL-8 receptor-expressing xenografts in mice, unlike trans-(18)F-FPro.
  
  
  CONCLUSIONS
  (18)F-IL-8 produced by this method binds to IL-8 receptors in vitro, and (18)F-IL-8 PET clearly visualizes its target receptor-expressing xenograft in vivo. Therefore, this technique might be useful for labeling macromolecules and performing preclinical evaluations of proteins of interest in vitro and in vivo.
authors.affiliation: Division of Neuro-imaging, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Harada
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Japan.
authors.forename: Shozo
authors.initials: S
authors.lastname: Furumoto
authors.affiliation: Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan; and.
authors.forename: Takeo
authors.initials: T
authors.lastname: Yoshikawa
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ishikawa
authors.affiliation: Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan; and.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Shibuya
authors.affiliation: Division of Neuro-imaging, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan; and.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Okamura
authors.affiliation: Research Team for Neuroimaging, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
authors.forename: Kiichi
authors.initials: K
authors.lastname: Ishiwata
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Japan.
authors.forename: Ren
authors.initials: R
authors.lastname: Iwata
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Japan Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan; and yanai@med.tohoku.ac.jp.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Yanai
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001667:Binding, Competitive; D002474:Cell-Free System; D005462:Fluorine Radioisotopes; D057809:HEK293 Cells; D006801:Humans; D016209:Interleukin-8 / Q000737:chemistry* / Q000493:pharmacokinetics; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008813:Mice, Inbred ICR; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging; D011392:Proline / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis*; D053700:Receptors, Interleukin-8 / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D000596:Amino Acids; D005462:Fluorine Radioisotopes; D016209:Interleukin-8; D019275:Radiopharmaceuticals; D053700:Receptors, Interleukin-8; C431803:fluoro-proline; D011392:Proline
keywords: 18F; PET; cell-free protein synthesis; interleukin-8; non-natural amino acid