By dual labeling a targeting moiety with both nuclear and optical probes, the ability for noninvasive imaging and intraoperative guidance may be possible. Herein, the ability to detect metastasis in an immunocompetent animal model of human epidermal growth factor receptor 2 (HER-2)-positive cancer metastases using positron emission tomography (PET) and near-infrared (NIR) fluorescence imaging is demonstrated. METHODS: (64Cu-DOTA)n-trastuzumab-(IRDye800)m was synthesized, characterized, and administered to female Balb/c mice subcutaneously inoculated with highly metastatic 4T1.2neu/R breast cancer cells. (64Cu-DOTA)n-trastuzumab-(IRDye800)m (150 µg, 150 µCi, m = 2, n = 2) was administered through the tail vein at weeks 2 and 6 after implantation, and PET/computed tomography and NIR fluorescence imaging were performed 24 hours later. Results were compared with the detection capabilities of F-18 fluorodeoxyglucose (18FDG-PET). RESULTS: Primary tumors were visualized with 18FDG and (64Cu-DOTA)n-trastuzumab-(IRDye800)m, but resulting metastases were identified only with the dual-labeled imaging agent. 64Cu-PET imaging detected lung metastases, whereas ex vivo NIR fluorescence showed uptake in regions of lung, skin, skeletal muscle, and lymph nodes, which corresponded with the presence of cancer cells as confirmed by histologic hematoxylin and eosin stains. In addition to detecting the agent in lymph nodes, the high signal-to-noise ratio from NIR fluorescence imaging enabled visualization of channels between the primary tumor and the axillary lymph nodes, suggesting a lymphatic route for trafficking cancer cells. Because antibody clearance occurs through the liver, we could not distinguish between nonspecific uptake and liver metastases. CONCLUSION: (64Cu-DOTA)n-trastuzumab-(IRDye800)m may be an effective diagnostic imaging agent for staging HER-2-positive breast cancer patients and intraoperative resection.
This work is supported in parts by R01 CA112679-15 (E.M.S.-M.), U54 13640401 (E.M.S.-M.), the Texas STAR Award program, and Department of Defense predoctoral fellowship award BC073377 (L.S.). Cu-64 provided by Washington University, St. Louis, MO, was partially funded by National Cancer Instimte grant R24 CA86307.
