Synthetic glycopeptides for the development of tumour-selective vaccines

The Development of Vaccines from Synthetic Tumor-Associated Mucin Glycopeptides and their Glycosylation-Dependent Immune Response

Tumor-associated carbohydrate antigens are overexpressed as altered-self in most common epithelial cancers. Their glycosylation patterns differ from those of healthy cells, functioning as an ID for cancer cells. Scientists have been developing anti-cancer vaccines based on mucin glycopeptides, yet the interplay of delivery system, adjuvant and tumor associated MUC epitopes in the induced immune response is not well understood. The current state of the art suggests that the identity, abundancy and location of the glycans on the MUC backbone are all key parameters in the cellular and humoral response. This review shares lessons learned by us in over two decades of research in glycopeptide vaccines. By bridging synthetic chemistry and immunology, we discuss efforts in designing synthetic MUC1/4/16 vaccines and focus on the role of glycosylation patterns. We provide a brief introduction into the mechanisms of the immune system and aim to promote the development of cancer subunit vaccines.

A Synthetic MUC1 Glycopeptide Bearing βGalNAc-Thr as a Tn Antigen Isomer Induces the Production of Antibodies against Tumor Cells

This study presents the synthesis of the novel protected O-glycosylated amino acid derivatives 1 and 2, containing βGalNAc-SerOBn and βGalNAc-ThrOBn units, respectively, as mimetics of the natural Tn antigen (αGalNAc-Ser/Thr), along with the solid-phase assembly of the glycopeptides NHAcSer-Ala-Pro-Asp-Thr[αGalNAc]-Arg-Pro-Ala-Pro-Gly-BSA (3-BSA) and NHAcSer-Ala-Pro-Asp-Thr[βGalNAc]-Arg-Pro-Ala-Pro-Gly-BSA (4-BSA), bearing αGalNAc-Thr or βGalNAc-Thr units, respectively, as mimetics of MUC1 tumor mucin glycoproteins. According to ELISA tests, immunizations of mice with βGalNAc-glycopeptide 4-BSA induced higher sera titers (1:320 000) than immunizations with αGalNAc-glycopeptide 3-BSA (1:40 000). Likewise, flow cytometry assays showed higher capacity of the obtained anti-glycopeptide 4-BSA antibodies to recognize MCF-7 tumor cells. Cross-recognition between immunopurified anti-βGalNAc antibodies and αGalNAc-glycopeptide and vice versa was also verified. Lastly, molecular dynamics simulations and surface plasmon resonance (SPR) showed that βGalNAc-glycopeptide 4 can interact with a model antitumor monoclonal antibody (SM3). Taken together, these data highlight the improved immunogenicity of the unnatural glycopeptide 4-BSA, bearing βGalNAc-Thr as Tn antigen isomer.

A marine analgesic peptide, Contulakin-G, and neurotensin are distinct agonists for neurotensin receptors: uncovering structural determinants of desensitization properties

Neurotensin receptors have been studied as molecular targets for the treatment of pain, schizophrenia, addiction, or cancer. Neurotensin (NT) and Contulakin-G, a glycopeptide isolated from a predatory cone snail Conus geographus, share a sequence similarity at the C-terminus, which is critical for activation of neurotensin receptors. Both peptides are potent analgesics, although affinity and agonist potency of Contulakin-G toward neurotensin receptors are significantly lower, as compared to those for NT. In this work, we show that the weaker agonist properties of Contulakin-G result in inducing significantly less desensitization of neurotensin receptors and preserving their cell-surface density. Structure-activity relationship (SAR) studies suggested that both glycosylation and charged amino acid residues in Contulakin-G or NT played important roles in desensitizing neurotensin receptors. Computational modeling studies of human neurotensin receptor NTS1 and Contulakin-G confirmed the role of glycosylation in weakening interactions with the receptors. Based on available SAR data, we designed, synthesized, and characterized an analog of Contulakin-G in which the glycosylated amino acid residue, Gal-GalNAc-Thr10, was replaced by memantine-Glu10 residue. This analog exhibited comparable agonist potency and weaker desensitization properties as compared to that of Contulakin-G, while producing analgesia in the animal model of acute pain following systemic administration. We discuss our study in the context of feasibility and safety of developing NT therapeutic agents with improved penetration across the blood-brain barrier. Our work supports engineering peptide-based agonists with diverse abilities to desensitize G-protein coupled receptors and further emphasizes opportunities for conotoxins as novel pharmacological tools and drug candidates.

Antibodies against mucin-based glycopeptides affect Trypanosoma cruzi cell invasion and tumor cell viability

This study describes the synthesis of glycopeptides NHAc[βGal]-(Thr)2 -[αGalNAc]-(Thr)2 -[αGlcNAc]-(Thr)2 Gly-OVA (1-OVA) and NHAc[βGal-αGalNAc]-(Thr)3 -[αLacNAc]-(Thr)3 -Gly-OVA (2-OVA) as mimetics of both T. cruzi and tumor mucin glycoproteins. These glycopeptides were obtained by solid-phase synthesis, which involved the prior preparation of the protected glycosyl amino acids αGlcNAc-ThrOH (3), αGalNAc-ThrOH (4), βGal-ThrOH (5), αLacNAc-ThrOH (6), and βGal-αGalNAc-ThrOH (7) through glycosylation reactions. Immunizations of mice with glycopeptides 1-OVA and 2-OVA induced high antibody titers (1:16 000), as verified by ELISA tests, whereas flow cytometry assays showed the capacity of the obtained anti-glycopeptides 1-OVA and 2-OVA antibodies to recognize both T. cruzi and MCF-7 tumor cells. In addition, antisera induced by glycopeptides 1-OVA and 2-OVA were also able to inhibit T. cruzi fibroblast cell invasion (70 %) and to induce antibody-mediated cellular cytotoxicity (ADCC) against MCF-7 cells, with 50 % reduction of cell viability.

Design and synthesis of multifunctional gold nanoparticles bearing tumor-associated glycopeptide antigens as potential cancer vaccines

The development of vaccines against specific types of cancers will offer new modalities for therapeutic intervention. Here, we describe the synthesis of a novel vaccine construction prepared from spherical gold nanoparticles of 3-5 nm core diameters. The particles were coated with both the tumor-associated glycopeptides antigens containing the cell-surface mucin MUC4 with Thomsen Friedenreich (TF) antigen attached at different sites and a 28-residue peptide from the complement derived protein C3d to act as a B-cell activating "molecular adjuvant". The synthesis entailed solid-phase glycopeptide synthesis, design of appropriate linkers, and attachment chemistry of the various molecules to the particles. Attachment to the gold surface was mediated by a novel thiol-containing 33 atom linker which was further modified to be included as a third "spacer" component in the synthesis of several three-component vaccine platforms. Groups of mice were vaccinated either with one of the nanoplatform constructs or with control particles without antigen coating. Evaluation of sera from the immunized animals in enzyme immunoassays (EIA) against each glycopeptide antigen showed a small but statistically significant immune response with production of both IgM and IgG isotypes. Vaccines with one carbohydrate antigen (B, C, and E) gave more robust responses than the one with two contiguous disaccharides (D), and vaccine E with a TF antigen attached to threonine at the 10th position of the peptide was selected for IgG over IgM suggesting isotype switching. The data suggested that this platform may be a viable delivery system for tumor-associated glycopeptide antigens.

A new murine IgG1 anti-Tn monoclonal antibody with in vivo anti-tumor activity

The Tn antigen (GalNAc α-O-Ser/Thr) is heterogeneously synthesized by a variety of tumors and contains an epitope defined by lectins and antibodies as a cluster of αGalNAc carbohydrates synthesized within a peptide sequence, which is rich in serine and/or threonine. The Tn antigen has been utilized as a target in vaccine experiments and also used as a biomarker for prognosis of different cancer forms. In this paper, we present a new monoclonal antibody, GOD3-2C4, with the clear hallmarks of an anti-Tn antibody. It was generated through somatic cell hybridization after immunization of a mouse with a tumor cell line and a Tn carrying mucin. The antibody recognizes synthetic Tn antigen and binds breast, colon, lung, ovarian and pancreas cancer. The GOD3-2C4 antibody has antibody-dependent cellular cytotoxicity activity against Jurkat cells in vitro, and for the first time, it can be shown that an anti-Tn antibody has a significant in vivo effect on a human cancer cell line grown as a xenograft in severe combined immunodeficiency mice.

Synthesis of MUC1 Peptide and Glycopeptide Dendrimers

Several dendrimers possessing multiple copies of peptides and glycopeptides belonging to the MUC1 eicosapeptide tandem repeat sequence have been prepared. Fmoc-strategy solid-phase peptide synthesis was used to construct the peptides and glycopeptides, which were conjugated to suitably functionalized dendrimer cores using the copper-catalyzed azide-alkyne cycloaddition reaction to produce multivalent peptide and glycopeptide dendrimers.

Glycopeptide dendrimers, part III: a review. Use of glycopeptide dendrimers in immunotherapy and diagnosis of cancer and viral diseases

Glycopeptide dendrimers containing different types of tumor associated-carbohydrate antigens (T(N), TF, sialyl-T(N), sialyl-TF, sialyl-Le(x), sialyl-Le(a) etc.) were used in diagnosis and therapy of different sorts of cancer. These dendrimeric structures with incorporated T-cell epitopes and adjuvants can be used as antitumor vaccines. Best results were obtained with multiantigenic vaccines, containing, e.g. five or six different TAAs. The topic of TAAs and their dendrimeric forms at molecular level are reviewed, including structure, syntheses, and biological activities. Use of glycopeptide dendrimers as antiviral vaccines against HIV and influenza is also described. Their syntheses, physico-chemical properties, and biological activities are given with many examples.

Monosaccharide-based water-soluble fluorescent tags

Monosaccharides are fluorescently labeled under microwave irradiation by N-(coumarin-3-carbonyl)benzotriazole 4. 1,2:3,4-di- O-isopropylidene-alpha- d-galactopyranose 9 gives 12 (90%), 1,2:5,6-di- O-isopropylidene- d-glucose 10 gives 13 (89%), 2,3:5,6-di- O-isopropylidene-alpha- d-mannofuranose 11 gives 14 (65%) (all by O-acylation) and 2,3,4,5-tetra- O-pivaloyl-beta- d-galactopyranosylamine 15 gives 16 (60%) (by N-acylation). Similarly, the coumarin-containing activated lysine derivatives 7 and 8 afford the l-lysine-scaffold based coumarin labeled sugars 17, 18a, b, and 19 (67-85%) which, after removal of the diisopropylidene groups, provide water-soluble fluorescent derivatives.

Chemoselective Assembly and Immunological Evaluation of Multiepitopic Glycoconjugates Bearing Clustered Tn Antigen as Synthetic Anticancer Vaccines

In this paper we investigated the use of regioselectively addressable functionalized templates (RAFTs) as new scaffolds for the design of anticancer vaccine candidates. We report the synthesis of well-defined multiepitopic RAFT scaffolds and their immunological evaluation. These conjugates exhibit clustered Tn analogue as tumor-associated carbohydrate antigen (TACA, B-cell epitope) and the CD4+ helper T-cell peptide from the type 1 poliovirus. The saccharidic and peptidic epitopes were both synthesized separately and combined regioselectively to the RAFT core using a sequential oxime bond formation strategy. B- and T-antigenicity and immunogenicity of the vaccine candidates were investigated in vitro and in vivo. These studies clearly demonstrate that the saccharidic part of the conjugates is recognized by Tn-specific monoclonal antibodies. Moreover, the antibodies elicited by immunization of mice with our vaccine candidates recognize the native form of Tn epitope expressed on human tumor cells. Together with oxime ligation technique, these results suggest that the RAFT scaffold provides a promising and suitable tool for engineering potent synthetic anticancer vaccine.

Influence of sialic acid removal on MUC1 antigenic reactivity in head and neck carcinoma

To investigate the influence of sialic acid removal on MUC1 peptidic and carbohydrate epitope reactivity in head and neck squamous cell carcinoma (HNSCC), tumor samples belonging to 24 HNSCC patients were studied by standard immunohistochemistry (IHC) with and without desialylation with 0.1 U/ml neuraminidase. From each tumor sample, subcellular fractions were obtained and analyzed by SDS-PAGE and Western blotting (WB). Three monoclonal antibodies (MAbs) were used: C595 MAb directed to MUC1 protein core, an anti-Tn hapten MAb, and an anti-sTn hapten MAb; a comparative analysis between desialylated and sialylated samples was performed. By IHC without neuraminidase treatment, 19 of 24 samples reacted with anti-MUC1 peptidic epitope, while Tn hapten was not detected and sTn was found in 1 of 24 cases. Desialylation increased either the number of reacting cells or the intensity of the reaction with C595 and anti-Tn MAbs, and some negative samples became positive. On the other hand, sTn expression decreased with desialylation. By WB, several bands from >200 to 25 kDa were found; desialylation increased high-molecular-weight bands, diminishing the detection of low-molecular-weight ones. The use of desialylation is a suitable treatment that contributes to the exposure of MUC1-associated epitopes, which may be related to the spreading of HNSCC.

Expression of peanut agglutinin-binding mucin-type glycoprotein in human esophageal squamous cell carcinoma as a marker

Background

The TF (Thomson – Friedenreich) blood group antigen behaves as an onco-foetal carcinoma-associated antigen, showing increased expression in malignancies and its detection and quantification can be used in serologic diagnosis mainly in adenocarcinomas. This study was undertaken to analyze the sera and tissue level detectable mucin-type glycoprotein (TF-antigen) by Peanut agglutinin (PNA) and its diagnostic index in serum as well tissues of human esophageal squamous cell carcinoma as marker.

Results

We examined 100 patients for serological analysis by Enzyme Linked Lectin Assay (ELISA) and demonstrated a sensitivity of 87.5%, specificity of 90% and a positive predictive value of 95%. The immuno-histochemical localization of TF antigen by Fluorescence Antigen Technique (FAT) in 25 specimens of normal esophageal squamous epithelium specimens and 92 specimens with different grades of, allowed a quicker and more precise identification of its increased expression and this did not correlate with gender and tumor size. There was a positive correlation between membrane bound TF antigen expression with different histological progression, from well differentiated to poorly differentiated, determined by PNA binding. Specimens showed morphological changes and a pronounced increase in PNA binding in Golgi apparatus, secretory granules of the cytosol of well differentiated and an increased cell membrane labeling in moderately and poorly differentiated, when compared with ESCC and normal tissues.

Conclusion

The authors propose that the expression of TF-antigen in human may play an important role during tumorigenesis establishing it as a chemically well-defined carcinoma-associated antigen. Identification of the circulating TF-antigen as a reactive form and as a cryptic form in the healthy individuals, using PNA-ELLA and Immunohistochemical analysis of TF antigen by FAT is positively correlated with the different histological grades as a simple and cost-effective method for the early diagnosis of ESCC. The present study reveals that, during tumorigenesis, an aberrant glycosylation takes place in Golgi apparatus leading to over secretion of TF antigen into the cytoplasm along with mucin granules and later into cell membrane. We suggest that the further characterization of TF antigen may unravel pathogenetic aspects of this silent disease.