PEGylated Fluorescent Anti-carcinoembryonic Antigen Antibody Labels Colorectal Cancer Tumors in Orthotopic Mouse Models

Colorectal cancer (CRC) patients often develop liver metastasis. However, curative resection of liver metastasis is not always possible due to poor visualization of tumor margins. The present study reports the characterization of a humanized anti-carcinoembryonic antigen monoclonal antibody conjugated to a PEGylated near-infrared dye, that targets and brightly labels human CRC tumors in metastatic orthotopic mouse models. The hT84.66-M5A (M5A) monoclonal antibody was conjugated with a polyethylene glycol (PEG) chain that incorporated a near infrared (NIR) IR800 dye to establish M5A-IR800 Sidewinder (M5A-IR800-SW). Nude mice with CRC orthotopic primary tumors and liver metastasis both developed from a human CRC cell line, were injected with M5A-IR800-SW and imaged with the Pearl Trilogy Imaging System. M5A-IR800-SW targeted and brightly labeled CRC tumors, both in primary-tumor and liver-metastasis models. M5A-IR800-SW at 75 μg exhibited highly-specific tumor labeling in a primary-tumor orthotopic model with a median tumor-to-background ratio of 9.77 and in a liver-metastasis orthotopic model with a median tumor-to-background ratio of 7.23 at 96 h. The precise labeling of the liver metastasis was due to lack of hepatic accumulation of M5A-IR800-SW in the liver. M5A-IR800-SW provided bright and targeted NIR images of human CRC in orthotopic primary-tumor and liver-metastasis mouse models. The results of the present study suggest the clinical potential of M5A-IR800-SW for fluorescence-guided surgery including metastasectomies for CRC. The lack of hepatic NIR signal is of critical importance to allow for precise labeling of liver tumors.