title: Direct comparison of 111In-labelled two-helix and three-helix Affibody molecules for in vivo molecular imaging.
abstract: OBJECTIVE
  Radiolabelled Affibody molecules have demonstrated a potential for visualization of tumour-associated molecular targets. Affibody molecules (7 kDa) are composed of three alpha-helices. Recently, a smaller two-helix variant of Affibody molecules (5.1 kDa) was developed. The aim of this study was to compare two- and three-helix HER2-targeting Affibody molecules directly in vivo.
  
  
  METHODS
  The three-helix Affibody molecule ABY-002 and the two-helix Affibody molecule PEP09239 were labelled with (111)In at the N-termini via DOTA chelator. Tumour-targeting properties were directly compared at 1 and 4 h after injection in mice bearing SKOV-3 xenografts with high HER2 expression and LS174T xenografts with low HER2 expression.
  
  
  RESULTS
  The dissociation constants (K(D)) for HER2 binding were 78 pM for the three-helix Affibody molecule and 2.1 nM for the two-helix Affibody molecule. (111)In-PEP09239 cleared more rapidly from the blood. In xenografts with high HER2 expression, the uptake of (111)In-ABY-002 was significantly higher than that of (111)In-PEP09239. The tumour-to-blood ratio was higher for (111)In-PEP09239 at 4 h after injection, while there was no significant difference in other tumour-to-organ ratios. The tumour uptake of (111)In-ABY-002 was eightfold higher than that of (111)In-PEP09239 in xenografts with low expression. Tumour-to-blood ratios were equal in this case, but other tumour-to-organ ratios were appreciably higher for the three-helix variant.
  
  
  CONCLUSIONS
  For tumours with high HER2 expression, two-helix HER2-targeting Affibody molecules can provide higher tumour-to-blood ratio at the cost of lower tumour uptake. In the case of low expression, both tumour uptake and tumour-to-organ ratios are appreciably higher for three-helix than for two-helix HER2-targeting Affibody molecules.
authors.affiliation: Division of Molecular Biotechnology, School of Biotechnology, KTH Royal Institute of Technology, Stockholm, Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rosik
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.forename: Jennie
authors.initials: J
authors.lastname: Malmberg
authors.forename: Mohamed
authors.initials: M
authors.lastname: Altai
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Varasteh
authors.forename: Mattias
authors.initials: M
authors.lastname: Sandström
authors.forename: Amelie Eriksson
authors.initials: AE
authors.lastname: Karlström
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D005260:Female; D006801:Humans; D007205:Indium Radioisotopes; D007553:Isotope Labeling; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics
chemical_list: D007205:Indium Radioisotopes; D018719:Erb-b2 Receptor Tyrosine Kinases; D011993:Recombinant Fusion Proteins; C508053:ERBB2 protein, human