Detection of Micrometastases Using SPECT/Fluorescence Dual-Modality Imaging in a CEA-Expressing Tumor Model

Abstract

Intraoperative dual-modality imaging can help the surgeon distinguish tumor from normal tissue. This technique may prove particularly valuable if small tumors need to be removed that are difficult to detect with the naked eye. The humanized anticarcinoembryonic antigen (anti-CEA) monoclonal antibody, labetuzumab, can be used as a tumor-targeting agent in colorectal cancer, since CEA is overexpressed in approximately 95% of colorectal cancer. Dual-labeled labetuzumab, labeled with both a near-infrared fluorescent dye (IRDye800CW) and a radioactive label ( 111 In), can be used as a tracer for dual-modality imaging. This study aimed to assess whether dualmodality imaging using 111 In-diethylenetriaminepentaacetic acid (DTPA)-labetuzumab-IRDye800CW can detect pulmonary micrometastases in a mouse model. Methods: Pulmonary GW-39 human colonic carcinoma microcolonies were induced in athymic BALB/c mice by intravenous injection of 100 mL of a GW-39 cell suspension. After 1, 2, 3, and 4 wk of tumor growth, dual-modality imaging was performed 3 d after intravenous injection of 111 In-DTPA-labetuzumabIRDye800CW (10 mg, 25 MBq). Small-animal SPECT images and optical images were acquired, and image-guided surgery was performed. Finally, the biodistribution of the dual-labeled tracer was determined. Formalin-fixed sections of the lungs were analyzed using fluorescence imaging, autoradiography, and immunohistochemistry. Results: Submillimeter pulmonary tumor colonies could be visualized with both small-animal SPECT and fluorescence imaging from the first week of tumor growth, before they became visible to the naked eye. Furthermore, dual-modality imaging could be used to guide resection of tumors. Mean uptake (percentage injected dose per gram) of the dual-labeled tracer in tumors was 17.2 6 5.4 and 16.5 6 4.4 at weeks 3 and 4, respectively. Immunohistochemical analysis of the tumorous lungs showed that the distribution of the radioactive and fluorescent signal colocalized with CEA-expressing tumors. Conclusion: Dualmodality imaging after injection of 111 In-labetuzumab-IRDye800CW can be used to detect submillimeter CEA-expressing pulmonary tumors before they become visible to the naked eye, supporting the added value of this technique in the resection of small tumors.

New Developments in Dual-Labeled Molecular Imaging Agents

“…Several strategies have been used to dual-label mAbs, with the most straightforward approach involving the formation of amide bonds between the side chains of lysine residues within the protein and activated ester analogs of dyes and chelators. This method was used by Hekman et al to dual-label the anticarcinoembryonic antigen (CEA) mAb labetuzumab with 111 In (via diethylenetriaminepentaacetic acid [DTPA] conjugation) and IRDye800 (Ex/Em, 778/794 nm) for imageguided resection of CEA-overexpressing intraperitoneal tumors in a model (10). Since many tumors are grossly identifiable during surgery, the efficacy of dual-labeled agents is related to their ability to detect very small tumors that could be missed by the naked eye.…”

Improved antibody-guided surgery with a near-infrared dye on a PEGylated linker for CEA-positive tumors

“…Alternative FGS approaches using anti-CEA mAbs are ongoing by several groups. 34,35 SMG-101 an anti-CEA-IR700 conjugate in a phase 1 study shows feasibility to detect in CEA-expressing pancreatic cancer primary and metastases. 35 However, this probe shows a TBR of 3.5 using a 30-μg dose in animal models and TBR's between 1 and 1.5 in patients.…”

Intraoperatieve detectie van het heldercellig niercelcarcinoom met 111In-girentuximab-IRDye800CW: proof-of-principlestudie

“…De detectie van kleine hoeveelheden achtergebleven tumorweefsel is afhankelijk van meerdere factoren, zoals de vascularisatie van de tumor, antigeenexpressie, het achtergrondsignaal en de locatie van de tumor. Recentelijk hebben wij in een diermodel aangetoond dat micrometastasen die kleiner waren dan 1 mm gedetecteerd konden worden met dual-modality imaging [39]. Van Driel et al hebben laten zien dat het NIR-fluorescentiecamerasysteem dat in de huidige studie gebruikt is, in staat is om laesies ter grootte van 1 mm 3 te detecteren [40].…”