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

Advances in MUC1 resistance to chemotherapy in pancreatic cancer

The incidence of pancreatic cancer (PC), a highly fatal malignancy, is increasing every year. Chemotherapy is an important treatment for it in addition to surgery, yet most patients become resistant to chemotherapeutic agents within a few weeks of treatment initiation.​ MUC1 is a highly glycosylated transmembrane protein, and studies have shown that aberrantly glycosylated overexpression of MUC1 is involved in regulating the biology of chemoresistance in cancer cells. This article summarizes the mechanism of MUC1 in PC chemoresistance and reviews MUC1-based targeted therapies.

Divergent synthesis of amino acid-linked O-GalNAc glycan core structures

O-GalNAc glycans, also known as mucin-type O-glycans, are primary constituents of mucins on various mucosal sites of the body and also ubiquitously expressed on cell surface and secreted proteins. They have crucial roles in a wide range of physiological and pathological processes, including tumor growth and progression. In addition, altered expression of O-GalNAc glycans is frequently observed during different disease states. Research dedicated to unraveling the structure-function relationships of O-GalNAc glycans has led to the discovery of disease biomarkers and diagnostic tools and the development of O-glycopeptide-based cancer vaccines. Many of these efforts require amino acid-linked O-GalNAc core structures as building blocks to assemble complex O-glycans and glycopeptides. There are eight core structures (cores one to eight), from which all mucin-type O-glycans are derived. In this protocol, we describe the first divergent synthesis of all eight cores from a versatile precursor in practical scales. The protocol involves (i) chemical synthesis of the orthogonally protected precursor (3 days) from commercially available materials, (ii) chemical synthesis of five unique glycosyl donors (1-2 days for each donor) and (iii) selective deprotection of the precursor and assembly of the eight cores (2-4 days for each core). The procedure can be adopted to prepare O-GalNAc cores linked to serine, threonine and tyrosine, which can then be utilized directly for solid-phase glycopeptide synthesis or chemoenzymatic synthesis of complex O-glycans. The procedure empowers researchers with fundamental organic chemistry skills to prepare gram scales of any desired O-GalNAc core(s) or all eight cores concurrently.

Non-Natural MUC1 Glycopeptide Homogeneous Cancer Vaccine with Enhanced Immunogenicity and Therapeutic Activity

Glycopeptides derived from the glycoprotein mucin-1 (MUC1) have shown potential as tumor-associated antigens for cancer vaccine development. However, their low immunogenicity and non-selective conjugation to carriers present significant challenges for the clinical efficacy of MUC1-based vaccines. Here, we introduce a novel vaccine candidate based on a structure-guided design of an artificial antigen derived from MUC1 glycopeptide. This engineered antigen contains two non-natural amino acids and has an α-S-glycosidic bond, where sulfur replaces the conventional oxygen atom linking the peptide backbone to the sugar N-acetylgalactosamine. The glycopeptide is then specifically conjugated to the immunogenic protein carrier CRM197 (Cross-Reactive Material 197), a protein approved for human use. Conjugation involves selective reduction and re-bridging of a disulfide in CRM197, allowing the attachment of a single copy of MUC1. This strategy results in a chemically defined vaccine while maintaining both the structural integrity and immunogenicity of the protein carrier. The vaccine elicits a robust Th1-like immune response in mice and generates antibodies capable of recognizing human cancer cells expressing tumor-associated MUC1. When tested in mouse models of colon adenocarcinoma and pancreatic cancer, the vaccine is effective both as a prophylactic and therapeutic use, significantly delaying tumor growth. In therapeutic applications, improved outcomes were observed when the vaccine was combined with an anti-programmed cell death protein 1 (anti-PD-1) checkpoint inhibitor. Our strategy reduces batch-to-batch variability and enhances both immunogenicity and therapeutic potential. This site-specific approach disputes a prevailing dogma where glycoconjugate vaccines require multivalent display of antigens.

Immunotherapy for HPV negative head and neck squamous cell carcinoma

Head and neck cancer (HNSCC) is the 8th most common cancer in the UK, with incidence increasing due to lifestyle factors such as tobacco and alcohol abuse. HNSCC is an immune-suppressive disease characterised by impaired cytokine secretion and dysregulation of immune infiltrate. As such, immunotherapy is a potential treatment option, with therapeutic cancer vaccination demonstrating the greatest potential. The success of cancer vaccination is dependent on informed antigen selection: an ideal antigen must be either tumour-specific or tumour-associated, as well as highly immunogenic. Stratification of the patient population for antigen expression and validated biomarkers are also vital. This review focuses on the latest developments in immunotherapy, specifically the development of therapeutic vaccines, and highlights successes, potential drawbacks and areas for future development. Immunotherapy approaches considered for HNSCC include monoclonal antibodies (mAb), Oncolytic viral (OV) therapies, Immune Checkpoint Inhibitors (ICIs) and cancer vaccines.

Multifunctional Lipidated Protein Carrier with a Built-In Adjuvant as a Universal Vaccine Platform Potently Elevates Immunogenicity of Weak Antigens

Weak antigens represented by MUC1 are poorly immunogenic, which greatly constrains the development of relevant vaccines. Herein, we developed a multifunctional lipidated protein as a carrier, in which the TLR1/2 agonist Pam3CSK4 was conjugated to the N-terminus of MUC1-loaded carrier protein BSA through pyridoxal 5'-phosphate-mediated transamination reaction. The resulting Pam3CSK4-BSA-MUC1 conjugate was subsequently incorporated into liposomes, which biomimics the membrane structure of tumor cells. The results indicated that this lipidated protein carrier significantly enhanced antigen uptake by APCs and obviously augmented the retention of the vaccine at the injection site. Compared with the BSA-MUC1 and BSA-MUC1 + Pam3CSK4 groups, Pam3CSK4-BSA-MUC1 evoked 22- and 11-fold increases in MUC1-specific IgG titers. Importantly, Pam3CSK4-BSA-MUC1 elicited robust cellular immunity and significantly inhibited tumor growth. This is the first time that lipidated protein was constructed to enhance antigen immunogenicity, and this universal carrier platform exhibits promise for utilization in various vaccines, holding the potential for further clinical application.

Development of Glycosylation-Modified DPPA-1 Compounds as Innovative PD-1/PD-L1 Blockers: Design, Synthesis, and Biological Evaluation

In the context of peptide drug development, glycosylation plays a pivotal role. Accordingly, L-type peptides were synthesized predicated upon the PD-1/PD-L1 blocker DPPA-1. Subsequent glycosylation resulted in the production of two distinct glycopeptides, D-glu-LPPA-1 and D-gal-LPPA-1, by using D-glucose (D-glu) and D-galactose (D-gal), respectively, during glycosylation. Both glycopeptides significantly inhibited the interaction between PD-1 and PD-L1, and the measured half maximal inhibitory concentrations (IC50s) were 75.5 μM and 101.9 μM for D-glu-LPPA-1 and D-gal-LPPA-1, respectively. Furthermore, D-gal-LPPA-1 displayed a pronounced ability to restore T-cell functionality. In an MC38 tumor-bearing mouse model, D-gal-LPPA-1 demonstrated a significant inhibitory effect. Notably, D-gal-LPPA-1 substantially augmented the abundance and functionality of CD8+ T cells in the tumor microenvironment. Additionally, in the lymph nodes and spleens, D-gal-LPPA-1 significantly increased the proportion of CD8+ T cells secreting interferon-gamma (IFN-γ). These strong findings position D-gal-LPPA-1 as a potent enhancer of the antitumor immune response in MC38 tumor-bearing mice, underscoring its potential as a formidable PD-1/PD-L1 blocking agent.

Structure-Guided Approach for the Development of MUC1-Glycopeptide-Based Cancer Vaccines with Predictable Responses

Mucin-1 (MUC1) glycopeptides are exceptional candidates for potential cancer vaccines. However, their autoantigenic nature often results in a weak immune response. To overcome this drawback, we carefully engineered synthetic antigens with precise chemical modifications. To be effective and stimulate an anti-MUC1 response, artificial antigens must mimic the conformational dynamics of natural antigens in solution and have an equivalent or higher binding affinity to anti-MUC1 antibodies than their natural counterparts. As a proof of concept, we have developed a glycopeptide that contains noncanonical amino acid (2S,3R)-3-hydroxynorvaline. The unnatural antigen fulfills these two properties and effectively mimics the threonine-derived antigen. On the one hand, conformational analysis in water shows that this surrogate explores a landscape similar to that of the natural variant. On the other hand, the presence of an additional methylene group in the side chain of this analog compared to the threonine residue enhances a CH/π interaction in the antigen/antibody complex. Despite an enthalpy-entropy balance, this synthetic glycopeptide has a binding affinity slightly higher than that of its natural counterpart. When conjugated with gold nanoparticles, the vaccine candidate stimulates the formation of specific anti-MUC1 IgG antibodies in mice and shows efficacy comparable to that of the natural derivative. The antibodies also exhibit cross-reactivity to selectively target, for example, human breast cancer cells. This investigation relied on numerous analytical (e.g., NMR spectroscopy and X-ray crystallography) and biophysical techniques and molecular dynamics simulations to characterize the antigen-antibody interactions. This workflow streamlines the synthetic process, saves time, and reduces the need for extensive, animal-intensive immunization procedures. These advances underscore the promise of structure-based rational design in the advance of cancer vaccine development.

Development of synthetic, self-adjuvanting, and self-assembling anticancer vaccines based on a minimal saponin adjuvant and the tumor-associated MUC1 antigen

The overexpression of aberrantly glycosylated tumor-associated mucin-1 (TA-MUC1) in human cancers makes it a major target for the development of anticancer vaccines derived from synthetic MUC1-(glyco)peptide antigens. However, glycopeptide-based subunit vaccines are weakly immunogenic, requiring adjuvants and/or additional immunopotentiating approaches to generate optimal immune responses. Among these strategies, unimolecular self-adjuvanting vaccine constructs that do not need coadministration of adjuvants or conjugation to carrier proteins emerge as a promising but still underexploited approach. Herein, we report the design, synthesis, immune-evaluation in mice, and NMR studies of new, self-adjuvanting and self-assembling vaccines based on our QS-21-derived minimal adjuvant platform covalently linked to TA-MUC1-(glyco)peptide antigens and a peptide helper T-cell epitope. We have developed a modular, chemoselective strategy that harnesses two distal attachment points on the saponin adjuvant to conjugate the respective components in unprotected form and high yields via orthogonal ligations. In mice, only tri-component candidates but not unconjugated or di-component combinations induced significant TA-MUC1-specific IgG antibodies able to recognize the TA-MUC1 on cancer cells. NMR studies revealed the formation of self-assembled aggregates, in which the more hydrophilic TA-MUC1 moiety gets exposed to the solvent, favoring B-cell recognition. While dilution of the di-component saponin-(Tn)MUC1 constructs resulted in partial aggregate disruption, this was not observed for the more stably-organized tri-component candidates. This higher structural stability in solution correlates with their increased immunogenicity and suggests a longer half-life of the construct in physiological media, which together with the enhanced antigen multivalent presentation enabled by the particulate self-assembly, points to this self-adjuvanting tri-component vaccine as a promising synthetic candidate for further development.

Convergent chemoenzymatic synthesis of O-GalNAc rare cores 5, 7, 8 and their sialylated forms

All O-GalNAc glycans are derived from 8 cores with 2 or 3 monosaccharides linked via α- or β-glycosidic bonds. While chemical and chemoenzymatic syntheses of β-linked cores 1-4 and 6 and derived glycans have been well developed, the preparation of α-linked rare cores 5, 7, and 8 is challenging due to the presence of this 1,2-cis linkage. Meanwhile, the biosynthesis and functional roles of these structures are poorly understood. Herein, we synthesize 3 α-linked rare cores with exclusive α-configuration from a versatile precursor through multifaceted chemical modulations. Efficient regioselective α2-6sialylion of the rare cores was then achieved by Photobacterium damselae α2-6sialyltransferase-catalyzed reactions. These structures, together with β-linked cores 1-4 and 6, and their sialylated forms, were fabricated into a comprehensive O-GalNAc core microarray to profile the binding of clinically important GalNAc-specific lectins. It is found that only Tn, (sialyl-)core 5, and core 7 are the binders of WFL, VVL, and SBA, while DBA only recognized (sialyl-)core 5, and Jacalin is the only lectin that binds core 8. In addition, activity assays of human α-N-acetylgalactosaminide α2-6sialyltransferases (ST6GalNAcTs) towards the cores suggested that ST6GalNAc1 may be involved in the biosynthesis of previously identified sialyl-core 5 and sialyl-core 8 glycans. In conclusion, we provide efficient routes to access α-linked O-GalNAc rare cores and derived structures, which are valuable tools for functional glycomics studies of mucin O-glycans.

Niosomes as Biocompatible Scaffolds for the Multivalent Presentation of Tumor-Associated Antigens (TACAs) to the Immune System

Fully synthetic tumor-associated carbohydrate antigen (TACA)-based vaccines are a promising strategy to treat cancer. To overcome the intrinsic low immunogenicity of TACAs, the choice of the antigens' analogues and multivalent presentation have been proved to be successful. Here, we present the preparation, characterization, and in vitro screening of niosomes displaying multiple copies of the mucin antigen TnThr (niosomes-7) or of TnThr mimetic 1 (niosomes-2). Unprecedentedly, structural differences, likely related to the carbohydrate portions, were observed for the two colloidal systems. Both niosomal systems are stable, nontoxic and endowed with promising immunogenic properties.

Breast Cancer Vaccine Containing a Novel Toll-like Receptor 7 Agonist and an Aluminum Adjuvant Exerts Antitumor Effects

Mucin 1 (MUC1) has received increasing attention due to its high expression in breast cancer, in which MUC1 acts as a cancer antigen. Our group has been committed to the development of small-molecule TLR7 (Toll-like receptor 7) agonists, which have been widely investigated in the field of tumor immunotherapy. In the present study, we constructed a novel tumor vaccine (SZU251 + MUC1 + Al) containing MUC1 and two types of adjuvants: a TLR7 agonist (SZU251) and an aluminum adjuvant (Al). Immunostimulatory responses were first verified in vitro, where the vaccine promoted the release of cytokines and the expression of costimulatory molecules in mouse BMDCs (bone marrow dendritic cells) and spleen lymphocytes. Then, we demonstrated that SZU251 + MUC1 + Al was effective and safe against a tumor expressing the MUC1 antigen in both prophylactic and therapeutic schedules in vivo. The immune responses in vivo were attributed to the increase in specific humoral and cellular immunity, including antibody titers, CD4⁺, CD8⁺ and activated CD8⁺ T cells. Therefore, our vaccine candidate may have beneficial effects in the prevention and treatment of breast cancer patients.

Preclinical Assessment of Immunogenicity and Protectivity of Novel ROR1 Fusion Proteins in a Mouse Tumor Model

The receptor tyrosine kinase-like orphan receptor 1 (ROR1) is a new tumor associated antigen (TAA) which is overexpressed in several hematopoietic and solid malignancies. The present study aimed to produce and evaluate different fusion proteins of mouse ROR1 (mROR1) to enhance immunogenicity and protective efficacy of ROR1. Four ROR1 fusion proteins composed of extracellular region of mROR1, immunogenic fragments of TT as well as Fc region of mouse IgG2a were produced and employed to immunize Balb/C mice. Humoral and cellular immune responses and anti-tumor effects of these fusion proteins were evaluated using two different syngeneic murine ROR1+ tumor models. ROR1-specific antibodies were induced in all groups of mice. The levels of IFN-γ, IL-17 and IL-22 cytokines in culture supernatants of stimulated splenocytes were increased in all groups of immunized mice, particularly mice immunized with TT-mROR1-Fc fusion proteins. The frequency of ROR1-specific CTLs was higher in mice immunized with TT-mROR1-Fc fusion proteins. Finally, results of tumor challenge in immunized mice showed that immunization with TT-mROR1-Fc fusion proteins completely inhibited ROR1+ tumor cells growth in two different syngeneic tumor models until day 120 post tumor challenge. Our preclinical findings, for the first time, showed that our fusion proteins could be considered as a potential candidate vaccine for active immunotherapy of ROR1-expressing malignancies.

Mining the Immunopeptidome for Antigenic Peptides in Cancer

Although harnessing the immune system for cancer therapy has shown success, response to immunotherapy has been limited. The immunopeptidome of cancer cells presents an opportunity to discover novel antigens for immunotherapy applications. These neoantigens bind to MHC class I and class II molecules. Remarkably, the immunopeptidome encompasses protein post-translation modifications (PTMs) that may not be evident from genome or transcriptome profiling. A case in point is citrullination, which has been demonstrated to induce a strong immune response. In this review, we cover how the immunopeptidome, with a special focus on PTMs, can be utilized to identify cancer-specific antigens for immunotherapeutic applications.

Integrated Chemoenzymatic Approach to Streamline the Assembly of Complex Glycopeptides in the Liquid Phase

Glycosylation of proteins is a complicated post-translational modification. Despite the significant progress in glycoproteomics, accurate functions of glycoproteins are still ambiguous owing to the difficulty in obtaining homogeneous glycopeptides or glycoproteins. Here, we describe a streamlined chemoenzymatic method to prepare complex glycopeptides by integrating hydrophobic tag-supported chemical synthesis and enzymatic glycosylations. The hydrophobic tag is utilized to facilitate peptide chain elongation in the liquid phase and expeditious product separation. After removal of the tag, a series of glycans are installed on the peptides via efficient glycosyltransferase-catalyzed reactions. The general applicability and robustness of this approach are exemplified by efficient preparation of 16 well-defined SARS-CoV-2 O-glycopeptides, 4 complex MUC1 glycopeptides, and a 31-mer glycosylated glucagon-like peptide-1. Our developed approach will open up a new range of easy access to various complex glycopeptides of biological importance.

Alum Adjuvant and Built-in TLR7 Agonist Synergistically Enhance Anti-MUC1 Immune Responses for Cancer Vaccine

The tumor-associated antigen mucin 1 (MUC1) is an attractive target of antitumor vaccine, but its weak immunogenicity is a big challenge for the development of vaccine. In order to enhance immune responses against MUC1, herein, we conjugated small molecular toll-like receptor 7 agonist (TLR7a) to carrier protein BSA via MUC1 glycopeptide to form a three-component conjugate (BSA-MUC1-TLR7a). Furthermore, we combined the three-component conjugate with Alum adjuvant to explore their synergistic effects. The immunological studies indicated that Alum adjuvant and built-in TLR7a synergistically enhanced anti-MUC1 antibody responses and showed Th1-biased immune responses. Meanwhile, antibodies elicited by the vaccine candidate effectively recognized tumor cells and induced complement-dependent cytotoxicity. In addition, Alum adjuvant and built-in TLR7a synergistically enhanced MUC1 glycopeptide-specific memory CD8+ T-cell immune responses. More importantly, the vaccine with the binary adjuvant can significantly inhibit tumor growth and prolong the survival time of mice in the tumor challenge experiment. This novel vaccine construct provides an effective strategy to develop antitumor vaccines.

Glycoconjugate Nanoparticle-Based Systems in Cancer Immunotherapy: Novel Designs and Recent Updates

For many years, cell-surface glycans (in particular, Tumor-Associated Carbohydrate Antigens, TACAs) have been the target of both passive and active anticancer immunotherapeutic design. Recent advances in immunotherapy as a treatment for a variety of malignancies has revolutionized anti-tumor treatment regimens. Checkpoint inhibitors, Chimeric Antigen Receptor T-cells, Oncolytic virus therapy, monoclonal antibodies and vaccines have been developed and many approvals have led to remarkable outcomes in a subset of patients. However, many of these therapies are very selective for specific patient populations and hence the search for improved therapeutics and refinement of techniques for delivery are ongoing and fervent research areas. Most of these agents are directed at protein/peptide epitopes, but glycans-based targets are gaining in popularity, and a handful of approved immunotherapies owe their activity to oligosaccharide targets. In addition, nanotechnology and nanoparticle-derived systems can help improve the delivery of these agents to specific organs and cell types based on tumor-selective approaches. This review will first outline some of the historical beginnings of this research area and subsequently concentrate on the last 5 years of work. Based on the progress in therapeutic design, predictions can be made as to what the future holds for increasing the percentage of positive patient outcomes for optimized systems.