Purpose: Colorectal cancer is one of the most common forms of cancer, and the development of novel tools for detection and efficient treatment of metastases is needed. One promising approach is the use of radiolabeled antibodies for positron emission tomography (PET) imaging and radioimmunotherapy. Since carcinoembryonic antigen (CEA) is an important target in colorectal cancer, the CEA-specific M5A antibody has been extensively studied in subcutaneous xenograft models; however, the M5A antibody has not yet been tested in advanced models of liver metastases. The aim of this study was to investigate the (64)Cu-DOTA-labeled M5A antibody using PET in mice bearing CEA-positive liver metastases.
Procedures: Mice were injected intrasplenically with CEA-positive C15A.3 or CEA-negative MC38 cells and underwent micro-computed tomography (micro-CT) to monitor the development of liver metastases. After metastases were detected, PET/MRI scans were performed with (64)Cu-DOTA-labeled M5A antibodies. H&E staining, immunohistology, and autoradiography were performed to confirm the micro-CT and PET/MRI findings.
Results: PET/MRI showed that M5A uptake was highest in CEA-positive metastases. The %ID/cm(3) (16.5% ± 6.3%) was significantly increased compared to healthy liver tissue (8.6% ± 0.9%) and to CEA-negative metastases (5.5% ± 0.6%). The tumor-to-liver ratio of C15A.3 metastases and healthy liver tissue was 1.9 ± 0.7. Autoradiography and immunostaining confirmed the micro-CT and PET/MRI findings.
Conclusion: We show here that the (64)Cu-DOTA-labeled M5A antibody imaged by PET can detect CEA positive liver metastases and is therefore a potential tool for staging cancer, stratifying the patients or radioimmunotherapy.