Characterization of new pancreatic cancer-reactive monoclonal antibodies directed against purified mucin

Although mucins have been found to be useful in the diagnosis of pancreatic cancer, the carbohydrate and peptide structures of pancreatic mucins are still not well characterized. Monoclonal antibodies were produced using mucins purified from xenografts of a human pancreatic cancer cell line as the immunogen. One of these, Ia3, reacted with almost all pancreatic, gastric, and colorectal carcinomas examined by immunoperoxidase staining, but with few normal tissues. Ia3 antigen was elevated in sera of 50.4% of individuals with gastrointestinal tumors, but its levels did not correlate with those of CA15-3, CA19-9, or DU-PAN-2. Serum Ia3 antigens migrated more slowly in sodium dodecyl sulfate-polyacrylamide gel electrophoresis than the polymorphic epithelial mucins recognized by DF3 or 115D8. Ia3 reacted only with native, and not with partially deglycosylated, pancreatic cancer xenograft mucins. Periodate or neuraminidase treatment destroyed this reactivity, but protease had little effect. The antigen recognized by another antibody, Nd2, was not detected in normal pancreatic, colonic, or gastric tissues but was present in approximately 60% of the pancreatic and gastric carcinomas examined. Nd2 reactivity with native and partially deglycosylated mucin was lost after pretreatment with protease and beta-mercaptoethanol. We conclude that, while Ia3 reacts with carbohydrates, Nd2 reactivity appears to be dependent on the integrity of the mucin protein core. The antigenic determinants of Ia3 and Nd2 are different from those of B72.3, CA19-9, DU-PAN-2, SPan-1, and several breast cancer mucin-directed antibodies. These results suggest that the malignancy-associated structures identified by Ia3 and Nd2 may provide new information on the carbohydrate and peptide structure of pancreatic cancer mucins.