title: Feasibility of Affibody-Based Bioorthogonal Chemistry-Mediated Radionuclide Pretargeting.
abstract: Affibody molecules constitute a new class of probes for radionuclide tumor targeting. The small size of Affibody molecules is favorable for rapid localization in tumors and clearance from circulation. However, high renal reabsorption of Affibody molecules prevents the use of residualizing radiometals, including several promising low-energy β- and α-emitters, for radionuclide therapy. We tested a hypothesis that Affibody-based pretargeting mediated by a bioorthogonal interaction between trans-cyclooctene (TCO) and tetrazine would provide higher accumulation of radiometals in tumor xenografts than in the kidneys.
  
  
  METHODS
  TCO was conjugated to the anti-human epidermal growth factor receptor 2 (HER2) Affibody molecule Z2395. DOTA-tetrazine was labeled with (111)In and (177)Lu. In vitro pretargeting was studied in HER2-expressing SKOV-3 and BT474 cell lines. In vivo studies were performed on BALB/C nu/nu mice bearing SKOV-3 xenografts.
  
  
  RESULTS
  (125)I-Z2395-TCO bound specifically to HER2-expressing cells in vitro with an affinity of 45 ± 16 pM. (111)In-tetrazine bound specifically and selectively to Z2395-TCO pretreated cells. In vivo studies demonstrated HER2-specific (125)I-Z2395-TCO accumulation in xenografts. TCO-mediated (111)In-tetrazine localization was shown in tumors, when the radiolabeled tracer was injected 4 h after an injection of Z2395-TCO. At 1 h after injection, the tumor uptake of (111)In-tetrazine and (177)Lu-tetrazine was approximately 2-fold higher than the renal uptake. Pretargeting provided more than a 56-fold reduction of renal uptake of (111)In in comparison with direct targeting.
  
  
  CONCLUSIONS
  The feasibility of Affibody-based bioorthogonal chemistry-mediated pretargeting was demonstrated. The use of pretargeting provides a substantial reduction of radiometal accumulation in kidneys, creating preconditions for palliative radionuclide therapy.
authors.affiliation: Institute for Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Altai
authors.affiliation: Division of Protein Technology, School of Biotechnology, KTH Royal Institute of Technology, Stockholm, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Perols
authors.affiliation: Institute for Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Tsourma
authors.affiliation: Department of Medicinal Chemistry, Preclinical PET Platform, Uppsala University, Uppsala, Sweden.
authors.forename: Bogdan
authors.initials: B
authors.lastname: Mitran
authors.affiliation: Institute for Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Hadis
authors.initials: H
authors.lastname: Honarvar
authors.affiliation: Tagworks Pharmaceuticals, Eindhoven, The Netherlands.
authors.forename: Marc
authors.initials: M
authors.lastname: Robillard
authors.affiliation: Tagworks Pharmaceuticals, Eindhoven, The Netherlands.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Rossin
authors.affiliation: Syncom, Groningen, The Netherlands; and.
authors.forename: Wolter
authors.initials: W
authors.lastname: ten Hoeve
authors.affiliation: Institute for Surgical Sciences, Radiology, Uppsala University, Uppsala, Sweden.
authors.forename: Mark
authors.initials: M
authors.lastname: Lubberink
authors.affiliation: Department of Medicinal Chemistry, Preclinical PET Platform, Uppsala University, Uppsala, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.affiliation: Division of Protein Technology, School of Biotechnology, KTH Royal Institute of Technology, Stockholm, Sweden.
authors.forename: Amelie Eriksson
authors.initials: AE
authors.lastname: Karlström
authors.affiliation: Institute for Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden Vladimir.tolmachev@igp.uu.se.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D016503:Drug Delivery Systems / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000532:radiotherapy; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009369:Neoplasms / Q000532:radiotherapy*; D011868:Radioisotopes / Q000627:therapeutic use; D019275:Radiopharmaceuticals / Q000008:administration & dosage* / Q000627:therapeutic use*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry; D015899:Tomography, Emission-Computed, Single-Photon; D023041:Xenograft Model Antitumor Assays
chemical_list: D011868:Radioisotopes; D019275:Radiopharmaceuticals; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human
keywords: affibody; engineered scaffold protein; radionuclide pretargeting; radionuclide therapy; tetrazine; trans-cyclooctene