Extended type 1 chain glycosphingolipids: dimeric Lea (III4V4Fuc2Lc6) as human tumor-associated antigen

Glycolipid extracts from various human cancer tissues and cell lines showed the presence of a slow-migrating glycolipid component which was strongly reactive with monoclonal antibody (mAb) NCC-ST-421 (raised against human gastric adenocarcinoma) and weakly cross-reactive with anti-Lea mAbs. The slow-migrating glycolipid was isolated from human colonic adenocarcinoma cell line Colo205 grown in nude mice, and was purified by high-performance liquid chromatography followed by preparative thin-layer chromatography. Its structure was elucidated by sequential enzymatic degradation and thin-layer chromatography immunostaining of the degradation products with various mAbs, 1H NMR spectroscopy, positive-ion fast atom bombardment mass spectrometry, and methylation analysis. The major slow-migrating component reacting with mAb ST-421 was identified as dimeric Lea, with the structure as follows. [formula: see text] Antigens containing this structure and various analogous structures (including enzymatically synthesized Lea/Lex hybrid antigen) were tested with ST-421. While the mAb was equally reactive with dimeric Lea and Lea/Lex, only the former was chemically detectable as the slow-migrating glycolipid from the tumor extract. ST-421 showed less reactivity with simple Lea (III4FucLc4) or extended Lea (V4FucLc6, and/or IV3Gal beta 1----3[Fuc alpha 1----4]GlcNAcnLc4), and was not reactive with Lex/Lex (dimeric Lex). It was concluded, therefore, that the major tumor-associated slow-migrating glycolipid reacting with ST-421 has the dimeric Lea structure shown above. Since extension of lacto-series structure has been shown to be limited to type 2 chain in normal cells and tissues, extended elongation of type 1 chain as shown in this structure represents a novel tumor-associated epitope.