title: Comparison of bifunctional chelates for (64)Cu antibody imaging.
abstract: OBJECTIVE
  Improved bifunctional chelates (BFCs) are needed to facilitate efficient (64)Cu radiolabeling of monoclonal antibodies (mAbs) under mild conditions and to yield stable, target-specific agents. The utility of two novel BFCs, 1-Oxa-4,7,10-triazacyclododecane-5-S-(4-isothiocyanatobenzyl)-4,7,10-triacetic acid (p-SCN-Bn-Oxo-DO3A) and 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-4-S-(4-isothiocyanatobenzyl)-3,6,9-triacetic acid (p-SCN-Bn-PCTA), for mAb imaging with (64)Cu were compared to the commonly used S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-tetraacetic acid (p-SCN-Bn-DOTA).
  
  
  METHODS
  The BFCs were conjugated to trastuzumab, which targets the HER2/neu receptor. (64)Cu radiolabeling of the conjugates was optimized. Receptor binding was analyzed using flow cytometry and radioassays. Finally, PET imaging and biodistribution studies were done in mice bearing either HER2/neu-positive or HER2/neu-negative tumors.
  
  
  RESULTS
  (64)Cu-Oxo-DO3A- and PCTA-trastuzumab were prepared at room temperature in >95% radiochemical yield (RCY) in <30 min, compared to only 88% RCY after 2 h for the preparation of (64)Cu-DOTA-trastuzumab under the same conditions. Cell studies confirmed that the immunoreactivity of the mAb was retained for each of the bioconjugates. In vivo studies showed that (64)Cu-Oxo-DO3A- and PCTA-trastuzumab had higher uptake than the (64)Cu-DOTA-trastuzumab at 24 h in HER2/neu-positive tumors, resulting in higher tumor to background ratios and better tumor images. By 40 h all three of the (64)Cu-BFC-trastuzumab conjugates allowed for clear visualization of the HER2/neu-positive tumors but not the negative control tumor.
  
  
  CONCLUSIONS
  The antibody conjugates of PCTA and Oxo-DO3A were shown to have superior (64)Cu radiolabeling efficiency and stability compared to the analogous DOTA conjugate. In addition, (64)Cu-PCTA and Oxo-DO3A antibody conjugates may facilitate earlier imaging with greater target to background ratios than the analogous (64)Cu-DOTA antibody conjugates.
authors.affiliation: MDS Nordion, Vancouver, BC, V6T 2A3, Canada. Cara.Ferreira@mdsinc.com
authors.forename: Cara L
authors.initials: CL
authors.lastname: Ferreira
authors.forename: Donald T T
authors.initials: DT
authors.lastname: Yapp
authors.forename: Sarah
authors.initials: S
authors.lastname: Crisp
authors.forename: Brent W
authors.initials: BW
authors.lastname: Sutherland
authors.forename: Sylvia S W
authors.initials: SS
authors.lastname: Ng
authors.forename: Martin
authors.initials: M
authors.lastname: Gleave
authors.forename: Corinne
authors.initials: C
authors.lastname: Bensimon
authors.forename: Paul
authors.initials: P
authors.lastname: Jurek
authors.forename: Garry E
authors.initials: GE
authors.lastname: Kiefer
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism*; D061067:Antibodies, Monoclonal, Humanized; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000737:chemistry*; D002722:Chlorobenzenes / Q000737:chemistry; D003301:Copper Radioisotopes / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry*; D006801:Humans; D017879:Isothiocyanates / Q000737:chemistry; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D049268:Positron-Emission Tomography; D015203:Reproducibility of Results; D000068878:Trastuzumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D002614:Chelating Agents; D002722:Chlorobenzenes; D003301:Copper Radioisotopes; D003432:Cross-Linking Reagents; D017879:Isothiocyanates; C037152:isothiocyanic acid; C031281:pentachloromethylthiobenzene; D000068878:Trastuzumab