title: [99mTc(CO)3]+-(HE)3-ZIGF1R:4551, a new Affibody conjugate for visualization of insulin-like growth factor-1 receptor expression in malignant tumours.
abstract: OBJECTIVE
  Radionuclide imaging of insulin-like growth factor type 1 receptor (IGF-1R) expression in tumours might be used for selection of patients who would benefit from IGF-1R-targeted therapy. We have previously shown the feasibility of IGF-1R imaging using the Affibody molecule (111)In-DOTA-His(6)-Z(IGF1R:4551). The use of (99m)Tc instead of (111)In should improve sensitivity and resolution of imaging, and reduce the dose burden to patients. We hypothesized that inclusion of a HEHEHE tag instead of a His(6) tag in Z(IGF1R:4551) would permit its convenient purification using IMAC, enable labelling with [(99m)Tc(CO)(3)](+), and improve its biodistribution.
  
  
  METHODS
  Z(IGF1R:4551) was expressed with a HEHEHE tag in the N terminus. The resulting (HE)(3)-Z(IGF1R:4551) construct was labelled with [(99m)Tc(CO)(3)](+). Targeting of IGF-1R-expressing cells using [(99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) was evaluated in vitro and in vivo.
  
  
  RESULTS
  (HE)(3)-Z(IGF1R:4551) was stably labelled with (99m)Tc with preserved specific binding to IGF-1R-expressing DU-145 prostate cancer cells in vitro. In mice, [(99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) accumulated in IGF-1R-expressing organs (pancreas, stomach, lung and salivary gland). [(99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) demonstrated 3.6-fold lower accumulation in the liver and spleen than (111)In-DOTA-Z(IGF1R:4551). In NMRI nu/nu mice with DU-145 prostate cancer xenografts, the tumour uptake was 1.32 ± 0.11 %ID/g and the tumour-to-blood ratio was 4.4 ± 0.3 at 8 h after injection. The xenografts were visualized using a gamma camera 6 h after injection.
  
  
  CONCLUSIONS
  (99m)Tc(CO)(3)](+)-(HE)(3)-Z(IGF1R:4551) is a promising candidate for visualization of IGF-1R expression in malignant tumours.
authors.affiliation: Preclinical PET Platform, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.forename: Camilla
authors.initials: C
authors.lastname: Hofström
authors.forename: Joanna
authors.initials: J
authors.lastname: Strand
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Varasteh
authors.forename: Mattias
authors.initials: M
authors.lastname: Sandstrom
authors.forename: Karl
authors.initials: K
authors.lastname: Andersson
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Gräslund
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D004355:Drug Stability; D015972:Gene Expression Regulation, Neoplastic; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D006801:Humans; D008297:Male; D051379:Mice; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D011877:Radionuclide Imaging; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000493:pharmacokinetics; D013667:Technetium
chemical_list: D006573:Heterocyclic Compounds, 1-Ring; D011993:Recombinant Fusion Proteins; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D013667:Technetium; D017526:Receptor, IGF Type 1