Adaptation of mass spectrometry for the analysis of tumor antigens as applied to blood group glycolipids of a human gastric carcinoma.

Total neutral (nonacidic) glycolipid fractions have been isolated from a gastric adenocarcinoma and the surrounding normal gastric tissue removed at laparotomy of a Blood Group B human individual. Each glycolipid mixture was fractionated by silicic acid column chromatography into ten different partly purified glycolipid fractions. These fractions were analyzed by thin-layer chromatography and tested for Blood Group A and B activity. Blood group B activity was found in several fractions from both tumor and normal tissue. Two of the tumor glycolipid fractions reacted with some batches of commercial anti-A antisera, but other antisera tested did not react. No such Blood Group A reactivity was found in the fractions from the normal gastric tissue. The two Blood Group A-active tumor glycolipid fractions were methylated and methylated-reduced, and these two derivatives were analyzed by mass spectrometry. It was shown that these two fractions were mixtures of glycosphingolipids with five to nine sugars. The dominating glycosphingolipids were blood group Leb and B-like hexaglycosylceramides, a B-similar heptaglycosylceramide with an additional fucose, an H-like heptaglycosylceramide, and a Leb-like octaglycosylceramide. Evidence for small amounts of a Blood Group A-similar heptaglycosylceramide with an additional fucose was also found. The finding of a Blood Group A-similar glycolipid in a fraction which reacts with some anti-A antisera is the first chemical evidence for a heterolog blood group antigen in human cancer which has previously been found by histoimmunological techniques. The clinical significance of this finding is discussed in relation to diagnostic procedures and immunotherapy.