title: Direct site-specific radiolabeling of an Affibody protein with 4-[18F]fluorobenzaldehyde via oxime chemistry.
abstract: OBJECTIVE
  In this study, we introduce a methodology for preparing 18F-labeled Affibody protein, specifically 18F-Anti-HER2 dimeric Affibody (14 kDa), for in vivo imaging of HER2neu with positron emission tomography (PET).
  
  
  METHODS
  We have used 4-[18F]fluorobenzaldehyde as a synthon to prepare 18F-Anti-HER2 Affibody. Aminooxy-functionalized Affibody (Anti-HER2-ONH2) was incubated with 4-[18F]fluorobenzaldehyde in ammonium acetate buffer at pH 4 in the presence of methanol at 70 degrees C for 15 min. The resulting 18F-labeled Affibody molecule was evaluated as a PET probe in xenograft models expressing HER2.
  
  
  RESULTS
  We have successfully prepared 18F-Anti-HER2 dimeric Affibody (14 kDa), N-(4-[18F]fluorobenzylidine)oxime-Anti-HER2 Affibody, [18F]FBO-Anti-HER2, in 26-30% radiochemical yields (decay corrected). High-contrast small-animal PET images with relatively moderate tumor uptake (1.79 +/- 0.40% ID/g) were observed for the 18F-Anti-HER2 Affibody.
  
  
  CONCLUSIONS
  Site-specific 18F-labeled Affibody against HER2 has been synthesized via chemoselective oxime formation between an aminooxy-functionalized Affibody and 18F-fluorobenzaldehyde. The results have implications for radiolabeling of other affibodies and macromolecules and should also be important for advancing Affibody imaging with PET.
authors.affiliation: Molecular Imaging Program at Stanford, Department of Radiology and Bioengineering, Bio-X Program, Stanford University, 318 Campus Dr., Clark Center, E-150, Stanford, CA 94305, USA.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Namavari
authors.forename: Omayra
authors.initials: O
authors.lastname: Padilla De Jesus
authors.forename: Zhen
authors.initials: Z
authors.lastname: Cheng
authors.forename: Abhijit
authors.initials: A
authors.lastname: De
authors.forename: Ernest
authors.initials: E
authors.lastname: Kovacs
authors.forename: Jelena
authors.initials: J
authors.lastname: Levi
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
authors.forename: Joshua K
authors.initials: JK
authors.lastname: Hoerner
authors.forename: Hans
authors.initials: H
authors.lastname: Grade
authors.forename: Faisal A
authors.initials: FA
authors.lastname: Syud
authors.forename: Sanjiv S
authors.initials: SS
authors.lastname: Gambhir
mesh_terms: D000818:Animals; D001547:Benzaldehydes / Q000737:chemistry*; D045744:Cell Line, Tumor; D019281:Dimerization; D005240:Feasibility Studies; D005260:Female; D005462:Fluorine Radioisotopes; D006801:Humans; D007553:Isotope Labeling; D051379:Mice; D008819:Mice, Nude; D015394:Molecular Structure; D008970:Molecular Weight; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism; D010091:Oximes / Q000737:chemistry*; D049268:Positron-Emission Tomography / Q000379:methods; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011854:Radiochemistry; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012680:Sensitivity and Specificity; D020349:Surface Plasmon Resonance; D014018:Tissue Distribution; D023041:Xenograft Model Antitumor Assays
chemical_list: D001547:Benzaldehydes; D005462:Fluorine Radioisotopes; D009842:Oligopeptides; D010091:Oximes; D011506:Proteins; D019275:Radiopharmaceuticals; D018719:Erb-b2 Receptor Tyrosine Kinases; D011993:Recombinant Fusion Proteins