The abnormal glycans expressed on the surface of tumor cells, known as tumor-associated carbohydrate antigens, increase the chance to develop carbohydrate-based anticancer vaccines. However, carbohydrate antigens pose certain difficulties, and the major drawback is their weak immunogenicity. To tackle this problem, numerous structurally modified STn antigens were designed and synthesized in this work. These synthetic antigens were screened in vitro by using competitive ELISA method, and the antigens with positive response were conjugated to the protein carrier for vaccination. The vaccination results on mice showed that some fluorine-containing modifications on the STn antigen can significantly increase the anti-STn IgG titers and improve the ratios of anti-STn IgG/IgM. The antisera can recognize the tumor cells expressing the native STn antigen.

Development of an effective vaccine to target tumor associated carbohydrate antigens, aberrantly expressed on the cell surface of various carcinomas, is an appealing approach toward cancer immunotherapy. However, a major problem of carbohydrate antigens is their poor immunogenicity. Immunization with modified-carbohydrate antigens could improve the immunogenicity and induce cross reaction with the native carbohydrate antigens. In this study, we investigated the antitumor ability of three fluoro-substituted sialyl-Tn (STn) analogues (2, 3, 4) coupled to KLH (keyhole limpet hemocyanin) and studied the mechanism of tumor immunotherapy of the vaccines in a murine model of colon cancer. Vaccination with 4-KLH, in which the two N-acetyl groups of STn are substituted with N-fluoroacetyl groups, could remarkably prolong the survival of tumor-bearing mouse and resulted in a significant reduction in tumor burden of lungs compared with STn-KLH (1-KLH). The vaccine 4-KLH could provoke stronger cytotoxic T lymphocytes immune response, T helper (Th) cell-mediated immune response and an earlier-stage Th1 immune response than 1-KLH, thus breaking immune tolerance and generating a therapeutic response. The 4-KLH vaccine induced strong tumor-specific anti-STn antibodies which could mediate complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity against human tumor cells. Moreover, in the absence of adjuvant, 4-KLH still elicited stronger immune responses than 1-KLH. Our data suggested that 4-KLH is superior in tumor prevention. The strategic hapten fluorination may be a potential approach applicable to the vaccines development for the cancer immunotherapy.

It is well known that tumor cells express some aberrant glycans, termed tumor-associated carbohydrate antigens (TACAs). TACAs are good targets for the development of carbohydrate-based anticancer vaccines. However, one of the major problems is that carbohydrate antigens possess a weak immunogenicity. To tackle this problem, a number of unnatural N-modified S-linked STn analogues were designed and prepared. Reaction of the modified STn disaccharides with bifunctional adipic acid p-nitrophenyl diester provided the corresponding activated esters, which was followed by the conjugation with keyhole limpet hemocyanin (KLH), affording the corresponding protein conjugates. The immunological properties of these glycoconjugates were evaluated in a mouse model. The results showed that the modified glycoconjugates stimulated the production of IgG antibodies that are capable of recognizing the naturally occurring STn antigen, helping the discovery of carbohydrate-based anticancer vaccine candidates.

Tumor cells often display aberrant levels and patterns of cell surface glycosylation, which provides a potential opportunity to develop carbohydrate-based anticancer vaccines for cancer immunotherapy. However, one of the most addressed challenges in this field is the low efficiency of the carbohydrate vaccination due to poor immunogenicity of carbohydrate antigens. In this article, a number of structure-modified GM3 antigen analogues were designed and chemically synthesized. The modified GM3 antigens were conjugated to protein carriers for vaccination. The vaccination results on mice show that the modification on the GM3 antigen could improve the efficiency of the vaccination, and in particular, two glycoconjugates (3-KLH and 8-KLH) elicited higher titers of anti-GM3 antibodies than the unmodified GM3-protein conjugate (2-KLH) did.