EXPRESSION OF HUMAN TUMOR MUCIN-ASSOCIATED CARBOHYDRATE EPITOPES, INCLUDING SIALYLATED TN, AND LOCALIZATION OF MURINE MONOCLONAL-ANTIBODIESCC49 AND B72.3 IN A SYNGENEIC RAT COLON-CARCINOMA MODEL

Using immunohistochemical techniques and whole-cell enzyme-linked immu nosorbent assay, we have determined that monoclonal antibodies (mAbs) B72.3 and CC49, which are widely used in the diagnosis and treatment o f several human epithelial cancers, are expressed in a transplantable rat colon carcinoma cell line, K12-TRb. MAbs B72.3 and CC49 react with tumor-associated glycoprotein-72 (TAG-72) which is a carcinoma mucin molecule expressed in colon, breast, pancreatic, ovarian, lung, and ga stric cancers. The carbohydrate epitope for mAb B72.3 is sialylated Tn (sTn), whereas CC49 reacts with an unknown carbohydrate epitope. K12- TRb is a transplantable rat colon carcinoma cell line derived from a d imethylhydrazine tumor which grows as progressive tumors in syngeneic BD IX rats. We found that the carbohydrate epitopes for mAbs B72.3 and CC49, including sTn, were more tumor-restricted in the rat than in hu mans. The only binding these had mAbs to normal rat tissue was to smal l-intestinal mucosa. MAbs B72.3 and CC49 were radiolabeled with iodine -125 (I-125) and injected intravenously into BD IX rats containing sub cutaneously grown syngeneic K12-TRb tumors. Biodistribution experiment s were conducted by dissecting groups of three rats on days 2, 4, 7, a nd 14 after injection of radiolabeled mAbs. These experiments confirme d that mAbs B72.3 and CC49 localize to K12-TRb tumors in vivo, and tha t the higher affinity mAb CC49 localized better than mAb B72.3. Gamma- camera imaging of subcutaneous K12-TRb tumors was successfully perform ed using I-125-labeled mAb CC49. The importance of this model is that mAbs B72.3 and CC49, immunoconjugates of these mAbs, and vaccines cont aining their corresponding carbohydrate epitopes, including sTn, can b e studied in a relevant immunocompetent syngeneic rat colon carcinoma model.