title: Imaging of HER3-expressing xenografts in mice using a (99m)Tc(CO) 3-HEHEHE-Z HER3:08699 affibody molecule.
abstract: OBJECTIVE
  Human epidermal growth factor receptor type 3 (HER3) is a transmembrane receptor tyrosine kinase belonging to the HER (ErbB) receptor family. Membranous expression of HER3 is associated with trastuzumab resistance in breast cancer and the transition to androgen independence in prostate cancer. Imaging of HER3 expression in malignant tumors may provide important diagnostic information that can influence patient management. Affibody molecules with low picomolar affinity to HER3 were recently selected. The aim of this study was to investigate the feasibility of HER3 imaging using radiolabeled Affibody molecules.
  
  
  METHODS
  A HER3-binding Affibody molecule, Z08699, with a HEHEHE-tag on N-terminus was labeled with (99m)Tc(CO)3 using an IsoLink kit. In vitro and in vivo binding specificity and the cellular processing of the labeled binder were evaluated. Biodistribution of (99m)Tc(CO)3-HEHEHE-Z08699 was studied over time in mice bearing HER3-expressing xenografts.
  
  
  RESULTS
  HEHEHE-Z08699 was labeled with (99m)Tc(CO)3 with an isolated yield of >80 % and a purity of >99 %. Binding of (99m)Tc(CO)3-HEHEHE-Z08699 was specific to BT474 and MCF7 (breast cancer), and LS174T (colon cancer) cells. Cellular processing showed rapid binding and relatively quick internalization of the receptor/Affibody molecule complex (70 % of cell-associated radioactivity was internalized after 24 h). The tumor targeting was receptor mediated and the excretion was predominantly renal. Receptor-mediated uptake was also found in the liver, lung, stomach, intestine, and salivary glands. At 4 h pi, tumor-to-blood ratios were 7 ± 3 for BT474, and 6 ± 2 for LS174T xenografts. LS174T tumors were visualized by microSPECT 4 h pi.
  
  
  CONCLUSIONS
  The results of this study suggest the feasibility of HER3-imaging in malignant tumors using Affibody molecules.
authors.affiliation: Preclinical PET Platform, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden, anna.orlova@pet.medchem.uu.se.
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.forename: Magdalena
authors.initials: M
authors.lastname: Malm
authors.forename: Maria
authors.initials: M
authors.lastname: Rosestedt
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Varasteh
authors.forename: Ken
authors.initials: K
authors.lastname: Andersson
authors.forename: Ram Kumar
authors.initials: RK
authors.lastname: Selvaraju
authors.forename: Mohamed
authors.initials: M
authors.lastname: Altai
authors.forename: Hadis
authors.initials: H
authors.lastname: Honarvar
authors.forename: Joanna
authors.initials: J
authors.lastname: Strand
authors.forename: Stefan
authors.initials: S
authors.lastname: Ståhl
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
authors.forename: John
authors.initials: J
authors.lastname: Löfblom
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D004355:Drug Stability; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D015609:Organotechnetium Compounds / Q000737:chemistry* / Q000493:pharmacokinetics; D020893:Receptor, ErbB-3 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D015609:Organotechnetium Compounds; D011993:Recombinant Fusion Proteins; C581292:ERBB3 protein, human; D020893:Receptor, ErbB-3