TUMOR LABELING IN-VIVO USING CYANINE-CONJUGATED MONOCLONAL-ANTIBODIES

Far-red-emitting cyanine fluorochromes have many properties desirable for in vivo imaging: absorption and emission at wavelengths where bloo d and tissue are relatively transparent, high quantum yields, and good solubility even at high molar ratios of fluorochrome to antibody. Pot entially, conjugation by multiple linkages should minimize hydrolysis in vivo. We conjugated two tumor-targeting monoclonal antibodies: anti -SSEA-1 (IgM, kappa) at ratios of 1.2-35 mel dye/mol antibody and 9.2. 27 (IgG(2a), kappa) at 0.6-6 mol dye/mol antibody, using the cyanine f luorochromes Cy3.18, Cy5.18, and Cy5.5.18. Nude mice were inoculated u sing the SSEA-1-expressing MH-15 teratocarcinoma or the 9.2.27 antigen -expressing SK-MEL-2 melanoma to give tumors at several sites. Conjuga ted antibody was injected, and mice were imaged immediately after inje ction and at appropriate intervals thereafter using a standard camera lens, dissecting microscope, or endoscopes. Images were acquired using either an image-intensified video camera or cooled CCD cameras. Immed iately after injection, major blood vessels and the heart, liver, and kidneys were readily visualized. After 1 day, tumor-targeting antibody conjugates were concentrated in tumors and there was little circulati ng conjugate; however, the bladder and kidneys were still visible. Tum ors labeled by specific antibody were the most fluorescent tissues at 2 days after injection, but non-specific antibody conjugates did not c oncentrate in the tumors. The small intestine was weakly visualized by both specific and non-specific antibody conjugates. These data suppor t the possibility of visualizing tumor metastasis by optical means, in cluding currently available endoscopes.