A novel tumor-associated mucin of gastrointestinal carcinoma

Purpose: To identify a new tumor-associated antigen, a monoclonal antibody, SC142, was produced by immunizing mice with a stomach cancer cell line. Th e tumor specificity of mAb SC142 was studied by immunohistochemical stainin g, and the biochemical characteristics of this new gastrointestinal tumor-a ssociated antigen were also studied. Methods: The expression of SC142-react ive antigen was investigated in various cancers by immunohistochemical stai ning. The SC142-reactive antigen was characterized by immunoblotting, sodiu m metaperiodate treatment assay, O-glycanase digestion assay, and lectin bi nding assay. Results: The SC142-reactive antigen was highly expressed in 78 % of gastric cancers (29/37) and 87% of colon cancers (27/31). No normal co lon or stomach tissues remote from the tumor were positive for the antigen. The antibody also reacted with other tumors of epithelial origin such as l ung squamous cell cancer (2/4), breast ductal cancer (2/20), bladder transi tional cell carcinoma (4/6), and uterine cancer (3/16). Western blot analys is of the antigen revealed glycoprotein(s) which migrated as a smear rangin g from the origin of the gel to about the 80 kDa region. The reactivity of this antigen with SC142 was reduced by sodium metaperiodate treatment or O- glycanase digestion, but not by N-glycanase, suggesting that the epitope is an O-glycan. In lectin-binding assay, this antigen reacted only with wheat germ agglutinin but not with Ricinus communis agglutinin, Datura stramoniu m agglutinin, and Sambucus nigra agglutinin. Conclusions: Our findings indi cate that the antigen defined by SC142 is a tumor-associated antigen that c ould differentiate the gastrointestinal cancer cells from the normal cells. Therefore, SC142 may become a valuable tool for the immunohistochemical di agnosis and tumor immunoscintigraphy of the gastrointestinal cancer patient s.