Specific detection of sialyl Lewis X determinant carried on the mucin GlcNAcbeta1-->6GalNAcalpha core structure as a tumor-associated antigen

Sialyl Lewis X serves as a ligand for selectins and is proposed to be implicated in hematogenous metastasis of cancers. When a cultured human breast cancer cell line, MCF-7, which does not express sialyl Lewis X, was transfected with human fucosyltransferase VI cDNA, a strong expression of sialyl Lewis X was induced on transfectant cells. The transfectant cells were found to be also reactive to the antibody NCC-ST-439, which was initially raised against human gastric cancer cells and later was shown to recognize a tumor-associated carbohydrate antigen in breast, gastric, and colon cancers. This suggested that the antigen recognized by NCC-ST-439 is closely related to sialyl Lewis X. Subsequent studies indicated that NCC-ST-439 specifically reacts to NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->6GalNAcalpha1 -->R, the sialyl Lewis X on the mucin GlcNAcbeta1-->6 GalNAcalpha structure. The antibody was not reactive to the conventional sialyl Lewis X determinants on straight and/or branched polylactosamine structures including NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->3Galbeta1-->4 Glcbeta1-->R and NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->6Galbeta1-->4 Glcbeta1-->R. This was in clear contrast to most of the known anti-sialyl Lewis X antibodies, which do not discriminate internal structures carrying the sialyl Lewis X determinant. On the other hand, the newly generated monoclonal antibody GSC154-27 had a specificity completely the reverse of the specificity of NCC-ST-439 in that it was strongly reactive to the conventional sialyl Lewis X determinants in straight and branched polylactosamine structures, while far less reactive to the sialyl Lewis X determinant on the mucin GlcNAcbeta1-->6GalNAcalpha core structure. A set of these two antibodies would be useful in discriminating the molecular species of sialyl Lewis X expressed by malignant cells and in studying their functional significance.