Abstract 5282: Pretargeted immunoPET for imaging human colonic cancer in a mouse model

Abstract

Abstract Objective: Molecular imaging with pretargeting bispecific antibodies allows rapid and specific targeting of tumors for PET imaging. In this study, pretargeted immunoPET with a bispecific monoclonal anti-carcinoembryonic antigen (CEA; CEACAM5) × anti-hapten antibody (bsMAb) and a small (1.5 kD) peptide labeled with a short-lived positron-emitter 68Ga was compared to FDG for detection of intraperitoneal CEA-expressing human colonic tumor xenografts in nude mice. Methods: In BALB/c nude mice LS174T human colonic tumor cells were injected intraperitoneally. One group (n=5) received 5 MBq FDG i.v., and another group (n=5) received the bsMAb i.v. and 5 MBq of 68Ga-labeled peptide i.v. 16 h later. One hour after the injection of the peptide or FDG, PET/CT images were acquired. One day later the same procedure was repeated vice versa, and after microPET imaging the uptake of the 68Ga or 18F in dissected tissue was determined. Results: Within one hour, specific tumor targeting of 68Ga-labeled peptide (23.4 ± 7.2% ID/g) combined with the low background activity levels resulted in the clear visualization of the small intra-abdominal tumor lesions (1.5-5 mm). High tumor/background radioactivity concentration ratios were obtained (e.g. tumor/intestines 57.5 ± 22.4). FDG localized efficiently in the tumors (8.7 ± 3.1 % ID/g), but with physiological uptake in various normal tissues (ratio tumor/intestines 4.0 ± 0.9). Conclusion: Pretargeted immunoPET performs exceptionally well with short-lived radionuclides, and is a highly sensitive procedure for dectection of small tumor deposits that is also more specific than FDG-PET. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5282. doi:10.1158/1538-7445.AM2011-5282