An anti-CEA antibody with affinity for cancerous lesions and labeled with ICG-sulfo-OSu can therefore be imaged using this infrared fluorescence endoscope. Specific antibodies tagged with ICG-sulfo-OSu can label cancer cells and can generate a strong enough fluorescent signal to detect small cancers when examined with an infrared fluorescence endoscope.

The anti-MUC1 antibody stained gastrointestinal cancer cells well, and nearly specific infrared fluorescence in cancer tissues was observed using the labeled anti-MUC1 antibody. The ICG-sulfo-OSu-labeled anti-MUC1 antibody has possible usefulness for the screening of cancer via infrared fluorescence endoscopy.

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Object An indocyanine green derivative (ICG-sulfo-OSu) was used as the labeling substance for monoclonal antibody, and a fluorescence imaging system appropriate for ICG-sulfo-OSu excitable by infrared rays (IR) was developed. The goal of this study was to demonstrate antibody labeling at the tissue level using this new imaging system. Materials and Methods ICG-sulfo-OSu labeled mouse anti-human carcinoembryonic antigen (CEA) monoclonal antibody, a newly developed imaging system, and an infrared ray microscope were employed in this experiment. Paraffin sections of humancolon cancer previously proven to have cross-reactivity to anti-CEA antibody were examined. Results Positive staining was seen as a brownish discoloration of oxidized 3,3'-diaminobenzidine tetrahydrochloride (DAB) in sections that reacted with ICG-sulfoOSu-labeled anti-CEA antibody, and the fluorescence was well-matched with the oxidized DABpositive sites. Conclusion Specific antibodies labeled with ICG-sulfo-OSu have significant affinity to cancer cells and seem to reflect sufficient amounts of fluorescence by IR to be useful in a system for the endoscopic detection of micro cancers using the immunohistochemical staining method. (Internal Medicine 38: 537-542, 1999)