title: Pretargeted immuno-PET of CEA-expressing intraperitoneal human colonic tumor xenografts: a new sensitive detection method.
abstract: BACKGROUND
  In this study, pretargeted immuno-positron-emission tomography [PET] with a bispecific monoclonal anti-carcinoembryonic antigen [CEA] (CEACAM5) × anti-hapten antibody (bispecific monoclonal antibody [bsmAb]) and a small (1.5 kD) peptide labeled with 68Ga was compared to fludeoxyglucose [18F-FDG]-PET for detecting intraperitoneal [i.p.] CEA-expressing human colonic tumor xenografts in nude mice.
  
  
  METHODS
  Two groups of female BALB/c nude mice were inoculated with LS174T human colonic tumor cells i.p. One group received 5 MBq 18F-FDG, and the other received intravenous injections of the bsmAb, followed 16 h later with 5 MBq of 68Ga-labeled peptide. One hour after the radiolabeled peptide or FDG was given, micro-PET/computed tomography images were acquired. Thereafter, the uptake of the 68Ga or 18F in dissected tissue was determined.
  
  
  RESULTS
  Within 1 h, high uptake of the 68Ga-labeled peptide in the tumor lesions (23.4 ± 7.2% ID/g) and low background activity levels were observed (e.g., tumor-to-intestine ratio, 58 ± 22). This resulted in a clear visualization of all intra-abdominal tumor lesions ≥ 10 μL and even some tumors as small as 5 μL (2 mm diameter). 18F-FDG efficiently localized in the tumors (8.7 ± 3.1% ID/g) but also showed physiological uptake in various normal tissues (e.g., tumor-to-intestine ratio, 3.9 ± 1.1).
  
  
  CONCLUSIONS
  Pretargeted immuno-PET with bsmAb and a 68Ga-labeled peptide could be a very sensitive imaging method for imaging colonic cancer, disclosing occult lesions.
authors.affiliation: Dept, of Nuclear Medicine, Radboud University Nijmegen Medical Centre, 6500 HB, Nijmegen, 9101, The Netherlands. r.schoffelen@nucmed.umcn.nl.
authors.forename: Rafke
authors.initials: R
authors.lastname: Schoffelen
authors.forename: Winette Ta
authors.initials: WT
authors.lastname: van der Graaf
authors.forename: Robert M
authors.initials: RM
authors.lastname: Sharkey
authors.forename: Gerben M
authors.initials: GM
authors.lastname: Franssen
authors.forename: William J
authors.initials: WJ
authors.lastname: McBride
authors.forename: Chien-Hsing
authors.initials: CH
authors.lastname: Chang
authors.forename: Peter
authors.initials: P
authors.lastname: Laverman
authors.forename: David M
authors.initials: DM
authors.lastname: Goldenberg
authors.forename: Wim Jg
authors.initials: WJ
authors.lastname: Oyen
authors.forename: Otto C
authors.initials: OC
authors.lastname: Boerman