title: Anti-CEA antibody fragments labeled with [(18)F]AlF for PET imaging of CEA-expressing tumors.
abstract: A facile and rapid method to label peptides with (18)F based on chelation of [(18)F]AlF has been developed recently. Since this method requires heating to 100 °C, it cannot be used to label heat-sensitive proteins. Here, we used a two-step procedure to prepare (18)F-labeled heat-labile proteins using the [(18)F]AlF method based on hot maleimide conjugation. 1,4,7-Triazacyclononae-1,4-diacetate (NODA) containing a methyl phenylacetic acid group (MPA) functionalized with N-(2-aminoethyl)maleimide (EM) was used as a ligand which was labeled with [(18)F]AlF and then conjugated to the humanized anti-CEA antibody derivatives hMN-14-Fab', hMN-14-(scFv)2 (diabody), and a Dock-and-Lock engineered dimeric fragment hMN-14 Fab-AD2 at room temperature. The in vivo tumor targeting characteristics of the (18)F-labeled antibody derivatives were determined by PET imaging of mice with s.c. xenografts. NODA-MPAEM was radiolabeled with [(18)F]AlF at a specific activity of 29-39 MBq/nmol and a labeling efficiency of 94 ± 2%. The labeling efficiencies of the maleimide conjugation ranged from 70% to 77%, resulting in [(18)F]AlF-labeled hMN14-Fab', hMN14-Fab-AD2, or hMN14-diabody with a specific activity of 15-17 MBq/nmol. The radiolabeled conjugates were purified by gel filtration. For biodistribution and microPET imaging, antibody fragments were injected intravenously into BALB/c nude mice with s.c. CEA-expressing LS174T xenografts (right flank) and CEA-negative SK-RC-52 xenografts (left flank). All [(18)F]AlF-labeled conjugates showed specific uptake in the LS174T xenografts with a maximal tumor uptake of 4.73% ID/g at 4 h after injection. Uptake in CEA-negative SK-RC-52 xenografts was significantly lower. Tumors were clearly visualized on microPET images. Using a [(18)F]AlF-labeled maleimide functionalized chelator, antibody fragments could be radiofluorinated within 4 h at high specific activity. Here, we translated this method to preclinical PET imaging studies and showed feasibility of [(18)F]AlF-fluorinated hMN-14-Fab', [(18)F]AlF-hMN-14-Fab-AD2, and [(18)F]AlF-hMN-14-diabody for microPET imaging of CEA-expressing colonic cancer.
authors.affiliation: Department of Nuclear Medicine, Radboud University Medical Center , Nijmegen, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Lütje
authors.forename: G M
authors.initials: GM
authors.lastname: Franssen
authors.forename: R M
authors.initials: RM
authors.lastname: Sharkey
authors.forename: P
authors.initials: P
authors.lastname: Laverman
authors.forename: E A
authors.initials: EA
authors.lastname: Rossi
authors.forename: D M
authors.initials: DM
authors.lastname: Goldenberg
authors.forename: W J G
authors.initials: WJ
authors.lastname: Oyen
authors.forename: O C
authors.initials: OC
authors.lastname: Boerman
authors.forename: W J
authors.initials: WJ
authors.lastname: McBride
mesh_terms: D017607:Aluminum Compounds; D000818:Animals; D002272:Carcinoembryonic Antigen / Q000737:chemistry*; D045744:Cell Line, Tumor; D005260:Female; D005459:Fluorides; D005462:Fluorine Radioisotopes; D064593:Heterografts; D006801:Humans; D007128:Immunoglobulin Fragments / Q000737:chemistry; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009369:Neoplasms / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography
chemical_list: D017607:Aluminum Compounds; D002272:Carcinoembryonic Antigen; D005462:Fluorine Radioisotopes; D007128:Immunoglobulin Fragments; D005459:Fluorides; C032311:aluminum fluoride