Chapter 13
Synthetic Glycopeptides for the Construction of Anticancer Vaccines
Downloaded by PENNSYLVANIA STATE UNIV on May 21, 2013 | http://pubs.acs.org Publication Date: July 2, 2008 | doi: 10.1021/bk-2008-0989.ch013
Horst Kunz, Sebastian Dziadek, Sven Wittrock, and Torsten Becker Institut fuer Organische Chemie, Johannes Gutenberg-Universitaet Mainz, 55099 Mainz, Germany
Glycopeptides of the tandem repeat region of the tumor -associated epithelial mucin MUC1 containing tumor -associated saccharide antigens have been synthesized and conjugated to carrier proteins or T-cell epitope peptides. The T, sialyl T , 2,6- and 2,3-sialyl Τ antigen amino acid building blocks were obtained by biomimetic syntheses starting from the monosaccharide T antigen conjugate. To synthesize the MUC1 glycopeptides solid-phase methods with varied anchors were applied. Conjugation of synthetic glycopeptides to bovine serum albumin were achieved by selective reactions at squaric esters. Solid-phase fragment condensation proved successful for constructions of MUC1 glycopeptide-T-cell epitope conjugates. Immunization of mice with a synthetic vaccine consisting of a MUC1 glycopeptide and a T-cell epitope from ovalbumin induced a specific immune response. The elicited antibody only reacted with the glycopeptide. Neither its peptide nor the glycan in a different peptide were recognized. This precise differentiation by antibodies induced by chemically pure vaccines is considered promising for the development of antitumor vaccines. N
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© 2008 American Chemical Society
In Carbohydrate-Based Vaccines; Roy, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
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Downloaded by PENNSYLVANIA STATE UNIV on May 21, 2013 | http://pubs.acs.org Publication Date: July 2, 2008 | doi: 10.1021/bk-2008-0989.ch013
Tumor-associated Saccharide Antigens - Early Experiments Membrane glycoproteins of epithelial cells play key roles in selective biological recognition processes in multicellular organisms. In many cases, the protein portions of these glycoproteins constitute the specific binding sites, for example, in integrin ligands like fibronectin or vitronectin which contain the RGD peptide binding motif (1). In other instances, the carbohydrate portions of glycoproteins are involved in these recognition phenomena as in the differentiation of blood groups (2). About 30 year ago, cell biological and biochemical investigations had shown that the glycan patterns of glycoproteins on tumor cells are distinctly altered compared to those present on normal cells (3,4). Springer et al. described glycoproteins from epithelial tumor cells carrying the Thomsen-Friedenreich antigen (T antigen) 1 as tumor-associated antigen (5). From cross reactivity of monoclonal antibodies induced by these T-antigen glycoproteins isolated from epithelial tumor cells, Springer and colleagues concluded, that these Τ antigen glycoproteins are structurally related to asialoglycophorin. On the basis of these structural informations, glycopeptides of the N-terminal portion of glycophorin of M blood group specificity have been synthesized and selectively coupled to bovine serum albumin to give a synthetic vaccine 2 (6). The assumption had been that an immune response selectively elicited against such a structural element present on tumor cells but not on normal cells might help to eradicate malignant cells without destroying healthy cells. Using the synthetic vaccine 2 (Figure 1), an antibody 82-A6 was induced in mice which actually exhibited affinity to epithelial tumor cells, but was not sufficiently tumor-selective (6,7). To understand this at first sight disappointing result, further immunological characterizations of the specificity of antibody 82-A6 were performed. This antibody did not show affinity to glycophorin itself. In glycophorin, the Τ antigen side chains as in 1 and 2 are covered by 2,3 - and 2,6-linked sialic acids. After removal of these sialic acid residues using N-acetyl-neuraminidases, the thus obtained asialoglycophorins 3 strongly reacted with the antibody 82-A6 (7) giving evidence of its specificity towards the Τ antigen structure 1 (5-7). On the basis of this specificity toward the saccharide antigen, a number of synthetic vaccines have been constructed by linking Τ (and T ) antigen serine or threonine conjugates to proteins (8,9,10). Glycophorin and asialoglycophorin 3, however, exist in two blood group specificities M and N , which differ in the 131 amino acids containing glycoproteins in only two amino acid positions. One of these positions is the N-terminal amino-acid which is a serine in M blood group specificity 3a, but a leucine N-blood specificity 3b. Surprisingly, antibody 82-A6 was distinctly more reactive towards asialoglycophorin of M specificity 3a, which has the aminoterminal sequence of the synthetic vaccine 2, than to asialoglycophorin of Ν specificity 3b. This N
In Carbohydrate-Based Vaccines; Roy, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
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