SPECT- and Fluorescence Image–Guided Surgery Using a Dual-Labeled Carcinoembryonic Antigen–Targeting Antibody

Intraoperative visualization techniques promise to significantly improve the detection and resection of tumors. In this study, we used an anti–carcinoembryonic antigen (CEA) antibody (MN-14) tagged with both a radiolabel (¹¹¹In) and a fluorophore (IRDye 800CW) for radionuclide detection and intraoperative fluorescence imaging, respectively. Methods: For this purpose, we prepared and characterized the dual-labeled antibody ¹¹¹In-diethylenetriaminepentaacetic acid (DTPA)-MN-14-IRDye 800CW and performed 4 studies on mice with subcutaneous and intraperitoneal CEA–expressing tumors: a dose escalation study to determine the optimal MN-14 protein dose, a biodistribution study comparing dual-labeled MN-14 and radiolabeled MN-14, a study to determine the optimal time for SPECT and fluorescence imaging after injection of dual-labeled MN-14, and finally a SPECT and fluorescence image–guided surgery study using this dual-labeled antibody. Results: The optimal protein dose of dual-labeled MN-14 was 10 μg per mouse, yielding a tumor-to-blood ratio of 3.5 within 72 h. The biodistribution of ¹¹¹In-DTPA-MN-14-IRDye 800CW in mice with subcutaneous LS174T tumors showed tumor uptake after 3 d (19.7% ± 17.0% injected dose/g) comparable to that of ¹¹¹In-DTPA-MN-14 but higher accumulation in the liver. The optimal time for imaging after administration of the dual-labeled antibody was 2–3 d after injection. Finally, in mice with intraperitoneally growing LS174T tumor nodules that received ¹¹¹In-DTPA-MN-14-IRDye 800CW, intraperitoneal tumor nodules could be localized with SPECT imaging after 3 d and subsequently resected using fluorescence image–guided surgery. Conclusion: Thus, we showed the feasibility for assessment and image-guided resection of CEA antigen–expressing tumors using dual-labeled MN-14. Both radionuclide detection and fluorescence imaging may provide useful information to improve localization of tumors and radical excision of tumor tissue. Because humanized MN-14 (labetuzumab) is available for clinical use, translation to a clinical setting is the next step.