Novel O-glycan arrays to characterize human cancer-associated epithelial antigens

• Main Author: Gao, Chao
• Other Authors: Feizi, Ten
• Published: Imperial College London 2015
• Subjects: 610
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646924

Aberrantly expressed carbohydrates occur on cancer cells and are antigenic. This thesis is focused on studies to elucidate two elusive hybridoma-defined, cancer-associated carbohydrate antigens: a prostate cancer-associated antigen F77 and a broadly distributed epithelial cancer-associated antigen AE3. The key experiments performed are microarray analyses with mucin-type glycoproteins and generation of designer arrays, multidimensional chromatographies and mass spectrometry of O-glycomes. Antigen-positive sequences assigned are corroborated with focused arrays of natural and chemically synthetized oligosaccharides or glycolipids and products of glycosidase treatments. The F77 antigen is assigned as blood group H type 2 on a 6-linked branch of a poly-N-acetyllactosamine backbone (structure a). This sequence is shown to occur on O-glycans and on glycolipids. The F77 antibody can bind, with lower intensities, to the blood group A and B analogues of structure a. The minimum F77 antigenic sequence is shown to be a pentasaccharide (underlined in structure a). The close association of F77 antigen with prostate cancer is proposed to be a consequence of up-regulation of branching enzymes together with persistent expression of H antigen. This may account for the prevalence of F77 antigen in prostate cancers irrespective of the patient's ABO blood group status. There appear to be two distinct forms of AE3 antigen as evidenced by the ability of AE3 antibody to bind: (i) the O-glycan structure b, known as T antigen, which is joined by α-linkage to serine on mucin-type glycoproteins, and (ii) a sulphated glycolipid known as SM1a (structure c) in which 'T' sequence is joined by β-linkage to galactose. An O-glycan analogue of structure c (structure d), has not been reported so far. Chemo-enzymatic synthesis of structure d will shortly be attempted for antigenic analysis. With knowledge of details of these two antigens, the biosynthetic pathways, the biological functions and clinical applications can now be rationally pursued.