Anti-CEA Antibody Fragments Labeled with [18F]AlF for PET Imaging of CEA-Expressing Tumors

• Published in: Bioconjugate chemistry Vol. 25; no. 2; pp. 335 - 341
• Main Authors: Lütje, S, Franssen, G. M, Sharkey, R. M, Laverman, P, Rossi, E. A, Goldenberg, D. M, Oyen, W. J. G, Boerman, O. C, McBride, W. J
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 19.02.2014; Amer Chemical Soc
• Subjects: Aluminum Compounds; Animals; Biochemical Research Methods; Biochemistry & Molecular Biology; Carcinoembryonic Antigen - chemistry; Cell Line, Tumor; Cells; Chemistry; Chemistry, Multidisciplinary; Chemistry, Organic; Female; Fluorides; Fluorine Radioisotopes; Gene expression; Heterografts; Humans; Immunoglobulin Fragments - chemistry; Life Sciences & Biomedicine; Mice; Mice, Inbred BALB C; Mice, Nude; Neoplasms - diagnostic imaging; Physical Sciences; Positron-Emission Tomography; Rodents; Science & Technology; Tomography; Tumors; F-18; RESOLUTION; XENOGRAFTS
• ISSN: 1043-1802; 1520-4812
• DOI: 10.1021/bc4004926

A facile and rapid method to label peptides with 18F based on chelation of [18F]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 18F-labeled heat-labile proteins using the [18F]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 [18F]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 18F-labeled antibody derivatives were determined by PET imaging of mice with s.c. xenografts. NODA-MPAEM was radiolabeled with [18F]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 [18F]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 [18F]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 [18F]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 [18F]AlF-fluorinated hMN-14-Fab′, [18F]AlF-hMN-14-Fab-AD2, and [18F]AlF-hMN-14-diabody for microPET imaging of CEA-expressing colonic cancer.