title: p-Isothiocyanatobenzyl-desferrioxamine: a new bifunctional chelate for facile radiolabeling of monoclonal antibodies with zirconium-89 for immuno-PET imaging.
abstract: OBJECTIVE
  Immuno-PET is an emerging imaging tool for the selection of high potential antibodies (mAbs) for imaging and therapy. The positron emitter zirconium-89 ((89)Zr) has attractive characteristics for immuno-PET with intact mAbs. Previously, we have described a multi-step procedure for stable coupling of (89)Zr to mAbs via the bifunctional chelate (BFC) tetrafluorophenol-N-succinyldesferal (TFP-N-sucDf). To enable widespread use of (89)Zr-immuno-PET, we now introduce the novel BFC p-isothiocyanatobenzyl-desferrioxamine B (Df-Bz-NCS) and compare its performance in (89)Zr-immuno-PET with the reference BFC TFP-N-sucDf.
  
  
  METHODS
  Three mAbs were premodified with Df-Bz-NCS and labeled with (89)Zr at different pHs to assess the reaction kinetics and robustness of the radiolabeling. Stability of both (89)Zr-Df-Bz-NCS- and (89)Zr-N-sucDf-conjugates was evaluated in different buffers and human serum. Comparative biodistribution and PET studies in tumor-bearing mice were undertaken.
  
  
  RESULTS
  The selected conjugation conditions resulted in a chelate:mAb substitution ratio of about 1.5:1. Under optimal radiolabeling conditions (pH between 6.8-7.2), the radiochemical yield was >85% after 60 min incubation at room temperature, resulting in radioimmunoconjugates with preserved integrity and immunoreactivity. The new radioimmunoconjugate was very stable in serum for up to 7 days at 37 degrees C, with <5% (89)Zr release, and was equally stable compared to the reference conjugate when stored in the appropriate buffer at 4 degrees C. In biodistribution and imaging experiments, the novel and the reference radioimmunoconjugates showed high and similar accumulation in tumors in nude mice.
  
  
  CONCLUSIONS
  The novel Df-Bz-NCS BFC allows efficient and easy preparation of optimally performing (89)Zr-labeled mAbs, facilitating further exploration of (89)Zr-immuno-PET as an imaging tool.
authors.affiliation: Department of Otolaryngology/Head and Neck Surgery, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Lars R
authors.initials: LR
authors.lastname: Perk
authors.forename: Maria J W D
authors.initials: MJ
authors.lastname: Vosjan
authors.forename: Gerard W M
authors.initials: GW
authors.lastname: Visser
authors.forename: Marianne
authors.initials: M
authors.lastname: Budde
authors.forename: Paul
authors.initials: P
authors.lastname: Jurek
authors.forename: Garry E
authors.initials: GE
authors.lastname: Kiefer
authors.forename: Guus A M S
authors.initials: GA
authors.lastname: van Dongen
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000493:pharmacokinetics*; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000378:metabolism*; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000737:chemistry*; D003676:Deferoxamine / Q000031:analogs & derivatives* / Q000737:chemistry; D005260:Female; D006801:Humans; D017879:Isothiocyanates / Q000737:chemistry*; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009928:Organ Specificity; D049268:Positron-Emission Tomography / Q000379:methods*; D016719:Radioimmunodetection / Q000379:methods; D011868:Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution; D015040:Zirconium / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: C549125:4-isothiocyanatobenzyl-desferrioxamine; D000911:Antibodies, Monoclonal; D002614:Chelating Agents; D017879:Isothiocyanates; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D015040:Zirconium; D003676:Deferoxamine