title: Site-specific radiometal labeling and improved biodistribution using ABY-027, a novel HER2-targeting affibody molecule-albumin-binding domain fusion protein.
abstract: Because of their better penetration, smaller targeting proteins may be superior to antibodies for radioimmunotherapy of solid tumors. Therefore, Affibody molecules (6.5 kDa) have a potential for being suitable as targeted moiety for radiolabeled therapeutic proteins. Previous studies have demonstrated that a fusion of an Affibody molecule with an albumin-binding domain (ABD) provides a strong noncovalent binding to albumin in vivo. This strong noncovalent binding can be used for reduction of the renal uptake of the Affibody molecule while maintaining a size smaller than that of an antibody, which is important when using residualizing radionuclide labels conjugated to Affibody molecules. The goal of this study was to design and evaluate a new targeting Affibody-ABD fusion protein with improved biodistribution properties for radionuclide therapy.
  
  
  METHODS
  A novel Affibody-based construct, ZHER2:2891-ABD035-DOTA (ABY-027), was created by fusion of the reengineered HER2-binding Affibody molecule ZHER2:2891 to the N terminus of the high-affinity ABD035, and a maleimido-derivative of DOTA was conjugated at the C terminus of the construct. Binding and processing of (177)Lu-ABY-027 by HER2-expressing cells were evaluated in vitro. Targeting of HER2-expressing SKOV-3 xenografts was evaluated in BALB/C nu/nu mice and compared with targeting of previously reported ABD-(ZHER2:342)2.
  
  
  RESULTS
  The binding affinity (dissociation constant) of ABY-027 to HER2 (74 pM) was the same as for the parental ZHER2:2891 (76 pM). ABY-027 was stably labeled with (177)Lu and (111)In with preserved specific binding to HER2-expressing cells in vitro. In vivo receptor saturation experiments demonstrated that targeting of SKOV-3 xenografts in BALB/C nu/nu mice was HER2-specific. (177)Lu-ABY-027 demonstrated substantially (2- to 3-fold) lower renal and hepatic uptake than previously assessed HER2-specific Affibody-based albumin-binding agents. Tumor uptake of radiolabeled ABY-027 at 48 h after injection was 2-fold higher than that for previously reported ABD-(ZHER2:342)2.
  
  
  CONCLUSIONS
  An optimized molecular design of an ABD fusion protein resulted in an Affibody molecule construct with better properties for therapy. Fully preserved in vivo targeting of the fusion protein was shown in xenografted mice. Site-specific coupling of DOTA provides a uniform conjugate and creates the potential for labeling with a broad range of therapeutic radionuclides. The biodistribution of (177)Lu-ABY-027 in a murine model suggests it is more suitable for therapy than alternative approaches.
authors.affiliation: Preclinical PET Platform, Medicinal Chemistry, Uppsala University, Uppsala, Sweden. anna.orlova@pet.medchem.uu.se
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.forename: Andreas
authors.initials: A
authors.lastname: Jonsson
authors.forename: Daniel
authors.initials: D
authors.lastname: Rosik
authors.forename: Hans
authors.initials: H
authors.lastname: Lundqvist
authors.forename: Malin
authors.initials: M
authors.lastname: Lindborg
authors.forename: Lars
authors.initials: L
authors.lastname: Abrahmsen
authors.forename: Caroline
authors.initials: C
authors.lastname: Ekblad
authors.forename: Fredrik Y
authors.initials: FY
authors.lastname: Frejd
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
mesh_terms: D000418:Albumins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D045744:Cell Line, Tumor; D005260:Female; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D006801:Humans; D007553:Isotope Labeling; D008187:Lutetium / Q000627:therapeutic use*; D051379:Mice; D010051:Ovarian Neoplasms / Q000378:metabolism / Q000532:radiotherapy; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011868:Radioisotopes / Q000627:therapeutic use*; D011874:Radiometry; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics* / Q000627:therapeutic use; D013379:Substrate Specificity; D014018:Tissue Distribution
chemical_list: D000418:Albumins; D006573:Heterocyclic Compounds, 1-Ring; D008187:Lutetium; D011868:Radioisotopes; D018719:Erb-b2 Receptor Tyrosine Kinases; D011993:Recombinant Fusion Proteins; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; C508053:ERBB2 protein, human
keywords: 177Lu; HER2; affibody molecule; albumin; targeting therapy