Synthesis of N-modified sTn analogs and evaluation of their immunogenicities by microarray-based immunoassay

Serum antibody screening using glycan arrays

Humans and other animals produce a diverse collection of antibodies, many of which bind to carbohydrate chains, referred to as glycans. These anti-glycan antibodies are a critical part of our immune systems' defenses. Whether induced by vaccination or natural exposure to a pathogen, anti-glycan antibodies can provide protection against infections and cancers. Alternatively, when an immune response goes awry, antibodies that recognize self-glycans can mediate autoimmune diseases. In any case, serum anti-glycan antibodies provide a rich source of information about a patient's overall health, vaccination history, and disease status. Glycan microarrays provide a high-throughput platform to rapidly interrogate serum anti-glycan antibodies and identify new biomarkers for a variety of conditions. In addition, glycan microarrays enable detailed analysis of the immune system's response to vaccines and other treatments. Herein we review applications of glycan microarray technology for serum anti-glycan antibody profiling.

Bioisosteres of Carbohydrate Functional Groups in Glycomimetic Design

The aberrant presentation of carbohydrates has been linked to a number of diseases, such as cancer metastasis and immune dysregulation. These altered glycan structures represent a target for novel therapies by modulating their associated interactions with neighboring cells and molecules. Although these interactions are highly specific, native carbohydrates are characterized by very low affinities and inherently poor pharmacokinetic properties. Glycomimetic compounds, which mimic the structure and function of native glycans, have been successful in producing molecules with improved pharmacokinetic (PK) and pharmacodynamic (PD) features. Several strategies have been developed for glycomimetic design such as ligand pre-organization or reducing polar surface area. A related approach to developing glycomimetics relies on the bioisosteric replacement of carbohydrate functional groups. These changes can offer improvements to both binding affinity (e.g., reduced desolvation costs, enhanced metal chelation) and pharmacokinetic parameters (e.g., improved oral bioavailability). Several examples of bioisosteric modifications to carbohydrates have been reported; this review aims to consolidate them and presents different possibilities for enhancing core interactions in glycomimetics.

Fluorine-modified sialyl-Tn-CRM197 vaccine elicits a robust immune response

Even though a vaccine that targets tumor-associated carbohydrate antigens on epithelial carcinoma cells presents an attractive therapeutic approach, relatively poor immunogenicity limits its development. In this study, we investigated the immunological activity of a fluoro-substituted Sialyl-Tn (F-STn) analogue coupled to the non-toxic cross-reactive material of diphtheria toxin197 (CRM197). Our results indicate that F-STn-CRM197 promotes a greater immunogenicity than non-fluorinated STn-CRM197. In the presence or absence of adjuvant, F-STn-CRM197 remarkably enhances both cellular and humoral immunity against STn by increasing antigen-specific lymphocyte proliferation and inducing a mixed Th1/Th2 response leading to production of IFN-γ and IL-4 cytokines, as well as STn-specific antibodies. Furthermore, antisera produced from F-STn-CRM197 immunization significantly recognizes STn-positive tumor cells and increases cancer cell lysis induced by antibody-dependent cell-mediated cytotoxicity (ADCC) or complement-dependent cytotoxicity (CDC) pathways. Our data suggest that this F-STn vaccine may be useful for cancer immunotherapy and possibly for prophylactic prevention of cancer.

Strategies for the Development of Glycomimetic Drug Candidates

Carbohydrates are a structurally-diverse group of natural products which play an important role in numerous biological processes, including immune regulation, infection, and cancer metastasis. Many diseases have been correlated with changes in the composition of cell-surface glycans, highlighting their potential as a therapeutic target. Unfortunately, native carbohydrates suffer from inherently weak binding affinities and poor pharmacokinetic properties. To enhance their usefulness as drug candidates, 'glycomimetics' have been developed: more drug-like compounds which mimic the structure and function of native carbohydrates. Approaches to improve binding affinities (e.g., deoxygenation, pre-organization) and pharmacokinetic properties (e.g., limiting metabolic degradation, improving permeability) have been highlighted in this review, accompanied by relevant examples. By utilizing these strategies, high-affinity ligands with optimized properties can be rationally designed and used to address therapies for novel carbohydrate-binding targets.

Stereoselective synthesis of a 9-O-sulfo Neu5Gc-capped O-linked oligosaccharide found on the sea urchin egg receptor

The first total synthesis of a serine bearing α2→5-O_glycolyl-linked oligoNeu5Gc found on sea urchin egg cell surfaces has been accomplished.

Syntheses and Immunological Evaluation of Self-Adjuvanting Clustered N-Acetyl and N-Propionyl Sialyl-Tn Combined with a T-helper Cell Epitope as Antitumor Vaccine Candidates

Sialyl-Tn (STn) is a tumor-associated carbohydrate antigen (TACA) rarely observed on healthy tissues. We synthesized two fully synthetic N-acetyl and N-propionyl STn trimer (triSTn) vaccines possessing a T-helper epitope and a TLR2 agonist, since the clustered STn antigens are highly expressed on many cancer cells. Immunization of both vaccines in mice induced the anti-triSTn IgG antibodies, which recognized triSTn-expressing cell lines PANC-1 and HepG2. The N-propionyl triSTn vaccine induced the triSTn-specific IgGs, while IgGs induced by the N-acetyl triSTn vaccine were less specific. These results illustrated that N-propionyl triSTn is a valuable unnatural TACA for anticancer vaccines.

Synthesis and immunological evaluation of N-acyl modified Tn analogues as anticancer vaccine candidates

Tumor-associated carbohydrate antigens (TACAs), which are aberrantly expressed on the surface of tumor cells, are important targets for anticancer vaccine development. Herein, several N-acyl modified Tn analogues were synthesized and conjugated with carrier protein CRM197. The immunological results of these glycoconjugates indicated that 6-CRM197 elicited higher titers of antibodies which cross-reacted with native Tn antigen than the unmodified 2-CRM197 did. The IFN-γ-producing frequency of lymphocytes in mice treated with 6-CRM197 was obviously increased, compared to that of mice vaccinated with 2-CRM197 (p=0.016), which was typically associated with the Th1 response. Moreover, the elicited antisera against antigen 6-CRM197 reacted strongly with the Tn-positive tumor cells, implying the potential of this glycoconjugate as an anticancer vaccine.

Synthesis and biological evaluation of a novel MUC1 glycopeptide conjugate vaccine candidate comprising a 4'-deoxy-4'-fluoro-Thomsen-Friedenreich epitope

The development of selective anticancer vaccines that provide enhanced protection against tumor recurrence and metastasis has been the subject of intense research in the scientific community. The tumor-associated glycoprotein MUC1 represents a well-established target for cancer immunotherapy and has been used for the construction of various synthetic vaccine candidates. However, many of these vaccine prototypes suffer from an inherent low immunogenicity and are susceptible to rapid in vivo degradation. To overcome these drawbacks, novel fluorinated MUC1 glycopeptide-BSA/TTox conjugate vaccines have been prepared. Immunization of mice with the 4’F-TF-MUC1-TTox conjugate resulted in strong immune responses overriding the natural tolerance against MUC1 and producing selective IgG antibodies that are cross-reactive with native MUC1 epitopes on MCF-7 human cancer cells.

Synthetic and immunological studies of N-acyl modified S-linked STn derivatives as anticancer vaccine candidates

N-Modified S-linked STn glycoconjugates significantly stimulated the production of IgG antibodies capable of recognizing the naturally occurring STn antigen.

Improvement of the immune efficacy of carbohydrate vaccines by chemical modification on the GM3 antigen

N-modified GM3 glycoconjugates improved the efficiency of the vaccination without the combination of metabolic oligosaccharide engineering technology.

Synthesis of sialic acid-containing saccharides

Sialic acids are a diverse family of negatively charged monosaccharides with a shared nine-carbon carboxylated backbone, and they often serve as the terminal positions of cell surface glycoproteins and glycolipids. Sialic acids play essential roles in mediating or modulating numerous pathological, biological, and immunological recognition events. Advances in synthesis have provided chemically well-defined and structurally homogeneous sialic acid-containing carbohydrates that are crucial for studying glycobiology. This review highlights recent innovations in the chemical and chemoenzymatic synthesis of difficult α-sialosides, with a particular focus on methods developed for α-selective sialylation in the synthesis of O-linked and S-linked oligosialic acids.

Recent advances in developing synthetic carbohydrate-based vaccines for cancer immunotherapies

Cancer cells can often be distinguished from healthy cells by the expression of unique carbohydrate sequences decorating the cell surface as a result of aberrant glycosyltransferase activity occurring within the cell; these unusual carbohydrates can be used as valuable immunological targets in modern vaccine designs to raise carbohydrate-specific antibodies. Many tumor antigens (e.g., GM2, Ley, globo H, sialyl Tn and TF) have been identified to date in a variety of cancers. Unfortunately, carbohydrates alone evoke poor immunogenicity, owing to their lack of ability in inducing T-cell-dependent immune responses. In order to enhance their immunogenicity and promote long-lasting immune responses, carbohydrates are often chemically modified to link to an immunogenic protein or peptide fragment for eliciting T-cell-dependent responses. This review will present a summary of efforts and advancements made to date on creating carbohydrate-based anticancer vaccines, and will include novel approaches to overcoming the poor immunogenicity of carbohydrate-based vaccines.

Enhancement of the immunogenicity of synthetic carbohydrate vaccines by chemical modifications of STn antigen

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.