Specific detection of sialyl Lewis X determinant carried on the mucin GlcNAcβ1→6GalNAcα 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 NeuAc alpha 2-->Gal beta 1-->4 (Fuc alpha 1-->3) GlcNAc beta 1-->6GalNAc alpha 1-->R, the sialyl Lewis X on the mucin GlcNAc beta 1-->6 GalNAc alpha structure, The antibody was not reactive to the conventional sialyl Lewis X determinants on straight and/or branched polylactosamine structures including Ne uAc alpha 2-->3Gal beta 1-->4 (Fuc alpha 1-->3) GlcNAc beta 1-->3 Gal beta 1-->4Glc beta 1-->R and NeuAc alpha 2-3Gal beta 1-->4(Fuc alpha 1-->3) GlcNAc beta 1-->6Gal beta 1-->4 Glc beta 1-->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 GrlcNAc beta 1-->6GalNAc alpha 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. (C) 1998 Academic Press.