title: Tumor imaging using a picomolar affinity HER2 binding affibody molecule.
abstract: The detection of cell-bound proteins that are produced due to aberrant gene expression in malignant tumors can provide important diagnostic information influencing patient management. The use of small radiolabeled targeting proteins would enable high-contrast radionuclide imaging of cancers expressing such antigens if adequate binding affinity and specificity could be provided. Here, we describe a HER2-specific 6 kDa Affibody molecule (hereinafter denoted Affibody molecule) with 22 pmol/L affinity that can be used for the visualization of HER2 expression in tumors in vivo using gamma camera. A library for affinity maturation was constructed by re-randomization of relevant positions identified after the alignment of first-generation variants of nanomolar affinity (50 nmol/L). One selected Affibody molecule, Z(HER2:342) showed a >2,200-fold increase in affinity achieved through a single-library affinity maturation step. When radioiodinated, the affinity-matured Affibody molecule showed clear, high-contrast visualization of HER2-expressing xenografts in mice as early as 6 hours post-injection. The tumor uptake at 4 hours post-injection was improved 4-fold (due to increased affinity) with 9% of the injected dose per gram of tissue in the tumor. Affibody molecules represent a new class of affinity molecules that can provide small sized, high affinity cancer-specific ligands, which may be well suited for tumor imaging.
authors.affiliation: Affibody AB, Bromma, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.forename: Mikaela
authors.initials: M
authors.lastname: Magnusson
authors.forename: Tove L J
authors.initials: TL
authors.lastname: Eriksson
authors.forename: Martin
authors.initials: M
authors.lastname: Nilsson
authors.forename: Barbro
authors.initials: B
authors.lastname: Larsson
authors.forename: Ingmarie
authors.initials: I
authors.lastname: Höidén-Guthenberg
authors.forename: Charles
authors.initials: C
authors.lastname: Widström
authors.forename: Jörgen
authors.initials: J
authors.lastname: Carlsson
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
authors.forename: Stefan
authors.initials: S
authors.lastname: Ståhl
authors.forename: Fredrik Y
authors.initials: FY
authors.lastname: Nilsson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000235:genetics / Q000378:metabolism*; D000918:Antibody Specificity; D015374:Biosensing Techniques / Q000379:methods; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007150:Immunohistochemistry; D007457:Iodine Radioisotopes; D051379:Mice; D008807:Mice, Inbred BALB C; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009447:Neuroblastoma / Q000000981:diagnostic imaging* / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism; D011877:Radionuclide Imaging; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D000906:Antibodies; D007457:Iodine Radioisotopes; D018719:Erb-b2 Receptor Tyrosine Kinases