title: Targeting of HER2-expressing tumors using 111In-ABY-025, a second-generation affibody molecule with a fundamentally reengineered scaffold.
abstract: Overexpression of the human epidermal growth factor receptor type 2 (HER2) in breast carcinomas predicts response to trastuzumab therapy. Affibody molecules based on a nonimmunoglobulin scaffold have demonstrated a high potential for in vivo molecular imaging of HER2-expressing tumors. The reengineering of the molecular scaffold has led to a second generation of optimized Affibody molecules that have a surface distinctly different from the parental protein domain from staphylococcal protein A. Compared with the parental molecule, the new tracer showed a further increased melting point, stability, and overall hydrophilicity and was more amenable to chemical peptide synthesis. The goal of this study was to assess the potential effects of this extensive reengineering on HER2 targeting, using ABY-025, a DOTA-conjugated variant of the novel tracer.
  
  
  METHODS
  (111)In-ABY-025 was compared with previously evaluated parent HER2-binding Affibody tracers in vitro and in vivo. The in vivo behavior was further evaluated in mice bearing SKOV-3 xenografts, rats, and cynomolgus macaques (Macaca fascicularis).
  
  
  RESULTS
  (111)In-ABY-025 bound specifically to HER2 in vitro and in vivo. Direct comparison with the previous generation of HER2-binding tracers showed that ABY-025 retained excellent targeting properties. Rapid blood clearance was shown in mice, rats, and macaques. A highly specific tumor uptake of 16.7 +/- 2.5 percentage injected activity per gram of tissue was seen at 4 h after injection. The tumor-to-blood ratio was 6.3 at 0.5 h and 88 at 4 h and increased up to 3 d after injection. gamma-camera imaging of tumors was already possible at 0.5 h after injection. Furthermore, the repeated intravenous administration of ABY-025 did not induce antibody formation in rats.
  
  
  CONCLUSIONS
  The biodistribution of (111)In-ABY-025 was in remarkably good agreement with the parent tracers, despite profound reengineering of the nonbinding surface. The molecule displayed rapid blood clearance in all species investigated and excellent targeting capacity in tumor-bearing mice, leading to high tumor-to-organ-ratios and high-contrast imaging shortly after injection.
authors.affiliation: Division of Nuclear Medicine, Department of Medical Sciences, Uppsala University, Uppsala, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Ahlgren
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.forename: Helena
authors.initials: H
authors.lastname: Wållberg
authors.forename: Monika
authors.initials: M
authors.lastname: Hansson
authors.forename: Mattias
authors.initials: M
authors.lastname: Sandström
authors.forename: Richard
authors.initials: R
authors.lastname: Lewsley
authors.forename: Anders
authors.initials: A
authors.lastname: Wennborg
authors.forename: Lars
authors.initials: L
authors.lastname: Abrahmsén
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
authors.forename: Joachim
authors.initials: J
authors.lastname: Feldwisch
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D015902:Gamma Cameras; D006801:Humans; D007120:Immunochemistry; D007205:Indium Radioisotopes; D007553:Isotope Labeling; D008252:Macaca fascicularis; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D010446:Peptide Fragments / Q000737:chemistry / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D013205:Staphylococcal Protein A / Q000737:chemistry; D014018:Tissue Distribution
chemical_list: D000596:Amino Acids; D007205:Indium Radioisotopes; D010446:Peptide Fragments; D019275:Radiopharmaceuticals; D018719:Erb-b2 Receptor Tyrosine Kinases; D013205:Staphylococcal Protein A; C549680:ABY-025; C508053:ERBB2 protein, human