title: Comparison of the octadentate bifunctional chelator DFO*-pPhe-NCS and the clinically used hexadentate bifunctional chelator DFO-pPhe-NCS for89Zr-immuno-PET.
abstract: OBJECTIVE
  All clinical89Zr-immuno-PET studies are currently performed with the chelator desferrioxamine (DFO). This chelator provides hexadentate coordination to zirconium, leaving two coordination sites available for coordination with, e.g., water molecules, which are relatively labile ligands. The unsaturated coordination of DFO to zirconium has been suggested to result in impaired stability of the complex in vivo and consequently in unwanted bone uptake of89Zr. Aiming at clinical improvements, we report here on a bifunctional isothiocyanate variant of the octadentate chelator DFO* and the in vitro and in vivo comparison of its89Zr-DFO*-mAb complex with89Zr-DFO-mAb.
  
  
  METHODS
  The bifunctional chelator DFO*-pPhe-NCS was prepared from previously reported DFO* and p-phenylenediisothiocyanate. Subsequently, trastuzumab was conjugated with either DFO*-pPhe-NCS or commercial DFO-pPhe-NCS and radiolabeled with Zr-89 according to published procedures. In vitro stability experiments were carried out in saline, a histidine/sucrose buffer, and blood serum. The in vivo performance of the chelators was compared in N87 tumor-bearing mice by biodistribution studies and PET imaging.
  
  
  RESULTS
  In 0.9 % NaCl89Zr-DFO*-trastuzumab was more stable than89Zr-DFO-trastuzumab; after 72 h incubation at 2-8 °C 95 % and 58 % intact tracer were left, respectively, while in a histidine-sucrose buffer no difference was observed, both products were ≥ 92 % intact. In vivo uptake at 144 h post injection (p.i.) in tumors, blood, and most normal organs was similar for both conjugates, except for skin, liver, spleen, ileum, and bone. Tumor uptake was 32.59 ± 11.95 and 29.06 ± 8.66 % ID/g for89Zr-DFO*-trastuzumab and89Zr-DFO-trastuzumab, respectively. The bone uptake was significantly lower for89Zr-DFO*-trastuzumab compared to89Zr-DFO-trastuzumab. At 144 h p.i. for89Zr-DFO*-trastuzumab and89Zr-DFO-trastuzumab, the uptake in sternum was 0.92 ± 0.16 and 3.33 ± 0.32 % ID/g, in femur 0.78 ± 0.11 and 3.85, ± 0.80 and in knee 1.38 ± 0.23 and 8.20 ± 2.94 % ID/g, respectively. The uptake in bone decreased from 24 h to 144 h p.i. about two fold for the DFO* conjugate, while it increased about two fold for the DFO conjugate.
  
  
  CONCLUSIONS
  Zr-DFO*-trastuzumab showed superior in vitro stability and in vivo performance when compared to89Zr-DFO-trastuzumab. This makes the new octadentate DFO* chelator a candidate successor of DFO for future clinical89Zr-immuno-PET.
authors: Department of Radiology & Nuclear Medicine, VU University Medical Center, De Boelelaan 1085, loc. Radionuclide Center, 1081HV, Amsterdam, The Netherlands. d.vugts@vumc.nl.
authors: Danielle J
authors: DJ
authors: Vugts
authors: Department of Radiology & Nuclear Medicine, VU University Medical Center, De Boelelaan 1085, loc. Radionuclide Center, 1081HV, Amsterdam, The Netherlands.
authors: Chris
authors: C
authors: Klaver
authors: Department of Radiology & Nuclear Medicine, VU University Medical Center, De Boelelaan 1085, loc. Radionuclide Center, 1081HV, Amsterdam, The Netherlands.
authors: Claudia
authors: C
authors: Sewing
authors: Department of Radiology & Nuclear Medicine, VU University Medical Center, De Boelelaan 1085, loc. Radionuclide Center, 1081HV, Amsterdam, The Netherlands.
authors: Alex J
authors: AJ
authors: Poot
authors: Department of Radiology & Nuclear Medicine, VU University Medical Center, De Boelelaan 1085, loc. Radionuclide Center, 1081HV, Amsterdam, The Netherlands.
authors: Kevin
authors: K
authors: Adamzek
authors: Department of Chemistry, University of Zurich, Zurich, Switzerland.
authors: Seraina
authors: S
authors: Huegli
authors: Department of Chemistry, University of Zurich, Zurich, Switzerland.
authors: Cristina
authors: C
authors: Mari
authors: Department of Radiology & Nuclear Medicine, VU University Medical Center, De Boelelaan 1085, loc. Radionuclide Center, 1081HV, Amsterdam, The Netherlands.
authors: Gerard W M
authors: GWM
authors: Visser
authors: Division of Radiopharmaceutical Chemistry, University of Basel Hospital, Basel, Switzerland.
authors: Ibai E
authors: IE
authors: Valverde
authors: Department of Chemistry, University of Zurich, Zurich, Switzerland. gilles.gasser@chem.uzh.ch.
authors: Gilles
authors: G
authors: Gasser
authors: ETH Zurich, Institute of Pharmaceutical Sciences, Vladimir-Prelog Weg 4, CH-8093, Zurich, Switzerland. t.mindt@gmx.ch.|Ludwig Boltzmann Institute for Applied Diagnostics, General Hospital of Vienna, Vienna, Austria. t.mindt@gmx.ch.
authors: Thomas L
authors: TL
authors: Mindt
authors: Department of Radiology & Nuclear Medicine, VU University Medical Center, De Boelelaan 1085, loc. Radionuclide Center, 1081HV, Amsterdam, The Netherlands.
authors: Guus A M S
authors: GAMS
authors: van Dongen
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000737:chemistry; D003676:Deferoxamine / Q000737:chemistry*; D004355:Drug Stability; D005260:Female; D007553:Isotope Labeling / Q000379:methods; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000276:immunology*; D009928:Organ Specificity; D049268:Positron-Emission Tomography / Q000379:methods*; D011868:Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D000068878:Trastuzumab / Q000276:immunology*; D015040:Zirconium / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: D002614:Chelating Agents; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D015040:Zirconium; D003676:Deferoxamine; D000068878:Trastuzumab
keywords: 89Zr; DFO; DFO*; Immuno-PET; Monoclonal antibodies