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Photoscan Localization of GW-39 Tumors in Hamsters Using Radiolabeled Anticarcinoembryonic Antigen Immunoglobulin G

Departments of Pathology and Radiation Medicine, University of Kentucky Medical Center, Lexington, Kentucky 40506, and Department of Biochemical Nutrition, Hoffmann-LaRoche, Inc., Nutley, New Jersey 07110

Photoscans and organ radioactivity were assessed in hamsters bearing cheek pouch grafts of a carcinoembryonic antigen (CEA)-producing human colonic carcinoma, GW-39; a human sarcoma, H.S.1; and a hamster amelanotic melanoma, A.Mel.3. The animals were given injections of 10 to 50 µCi ¹²⁵I-labeled heterospecific anti-CEA immunoglobulin G (IgG) or normal IgG. The photoscans showed an increased uptake of radioactivity over the tumors and frequently over the areas of the thorax and urinary bladder, regardless of the tumor or the radiolabeled IgG preparation used. Even normal hamsters receiving either radiolabeled preparation showed an increased accretion of radioactivity over the thoracic region. A specific tumor localization, however, was demonstrated in animals bearing small (<200 mg) GW-39 tumors and given injections of radiolabeled anti-CEA IgG. In fact, even GW-39 tumors of merely 70 mg were visualized in the hamster by administering radiolabeled anti-CEA IgG and scanning 6 to 8 days later.

The radioactivity recovered from GW-39 tumors borne in hamsters given injections of radiolabeled anti-CEA IgG revealed an increase of 7.5 to 20 times that recovered from other tissues. A slightly increased uptake of either the specific or nonspecific radiolabeled preparation was seen in the other, non-CEA-producing tumors studied, which was sufficiently increased over background radiation to permit visualization of the tumors by photoscanning, especially when the neoplasms were large and vascular. Evidently radiolabeled nonantibody components of heterospecific IgG can be localized in certain tumors and normal tissues by photoscanning. Nevertheless, tumor localization due to an antigen-antibody reaction, as we have found in CEA-producing GW-39 tumors treated with an anti-CEA antibody preparation, permits photoscan visualization of tumors too small to be demonstrated by radiolabeled normal IgG. It thus appears that CEA is a suitable tumor target for radioantibody by photoscanning.

Received 8/ 6/73. Accepted 10/18/73.

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