Human tumor-associated Le(a)-Le(x) hybrid carbohydrate antigen IV3(Gal beta 1-->3[Fuc alpha 1-->4]GlcNAc)III3FucnLc4 defined by monoclonal antibody 43-9F: enzymatic synthesis, structural characterization, and comparative reactivity with various antibodies.

Two Le(a)-cross-reacting monoclonal antibodies (mAbs) were previously established which define complex tumor-associated carbohydrate antigens. The first mAb, 43-9F, was raised against human squamous cell lung carcinoma and shows preferential reactivity with various human cancers over normal cells. Its tumor cell binding activity is best inhibited by a milk oligosaccharide characterized as Le(a)-Le(x) [Mårtensson, S., et al. (1988) Cancer Res. 48, 2125], Gal beta 1-->3[Fuc alpha 1-->4] GlcNAc beta 1-->3Gal beta 1-->4]Fuc alpha 1-->3]-GlcNAc beta 1-->3Gal beta 1-->4Glc (1). The second mAb, ST-421, was raised against human gastric cancer xenograft in nude mice and found to have strong tumor growth-suppressing activity in nude mice. The epitope recognized by ST-421 was chemically identified as Le(a)-Le(a), Gal beta 1-->3 [Fuc alpha 1-->4]GlcNAc beta 1-->3Gal beta 1-->3-[Fuc alpha 1-->4] GlcNAc beta 1-->3Gal beta 1-->4Glc (2) [Stroud, M.R., et al. (1991) J. Biol. Chem. 266, 8439]. Both 43-9F and ST-421 cross-react with Le(a). Identification of the 43-9F antigen as structure 1 (Le(a)-Le(x)) is tentative since it was not based on isolation and chemical characterization of antigen from tumor cells or tissues. We therefore synthesized structure 1 starting from sialyl-nor-hexaosylceramide (VI3NeuAcnLc6), with sequential enzymatic hydrolysis by sialidase and beta-galactosidase followed by addition of beta 1-->3Gal with beta 1-->3 galactosyltransferase. This yielded the hybrid type 1/type 2 chain core structure IV3-(Gal beta 1-->3GlcNAc)nLc4, which was fucosylated with alpha 1-->3/4 fucosyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS)