Towards a fully synthetic MUC1-based anticancer vaccine: efficient conjugation of glycopeptides with mono-, di-, and tetravalent lipopeptides using click chemistry

Rational Design of T-Cell- and B-Cell-Based Therapeutic Cancer Vaccines

Cancer vaccines provide an efficient strategy to enhance tumor-specific immune responses by redeploying immune systems. Despite the approval of the first cancer vaccine (Sipuleucel-T) by the U.S. Food and Drug Administration in 2010, most therapeutic cancer vaccines fail in clinical trials. Basically, tumor-specific immune responses rely on not only T-cell but also B-cell immunity, which indicates that cancer vaccines should leverage both arms of the adaptive immune system. For example, CD8⁺ T cells activated by antigen-presenting cells (APCs) recognize and directly kill tumor cells via peptide-bound major histocompatibility complex (pMHC). B cells recognize antigen with no need of pMHC and require CD4⁺ T cells for sufficient activation and antibody generation, enabling antibody-mediated nondirect killing on tumor cells. Considering the different mechanisms of T-cell and B-cell activation, the rational design of therapeutic cancer vaccines should consider several factors, including antigen selection and recognition, immune activation, vaccine delivery, and repeatable vaccination, which can be advanced by chemical strategies.In this Account, we summarize our recent contributions to the development of effective T-cell- and B-cell-based therapeutic cancer vaccines. For T-cell-based vaccines, we focus on adjuvants as the key component for controllable APC activation and T-cell priming. Not only synthetic molecular agonists of pattern recognition receptors (PRRs) but also adjuvant nanomaterials were explored to satisfy diversiform vaccine designs. For example, a type of natural cyclic dinucleotide (CDN) that was chemically modified with fluorination and ipsilateral phosphorothioation to activate the stimulator of interferon gene (STING) was found to mediate antitumor responses. It retains structural similarity to the parent CDN scaffold but possesses increased stability, cellular uptake, and immune activation for antitumor treatment. It also facilitates facile conjugation with other agonists, which not only enhances APC-targeting delivery but also balances cellular and humoral antitumor responses. We also explored the intrinsic properties of nanomaterials that allow them to serve as adjuvants. A black phosphorus nanosheet-based nanovaccine was constructed and found to strongly potentiate antigen-specific T-cell antitumor immune responses through multiple immune-potentiating properties, leading to a highly integrated nanomaterial-based adjuvant design. For B-cell-based vaccines, multicomponent and multivalent strategies were applied to improve the immunogenicity. A multicomponent linear vaccine conjugate coordinates helper T (Th) cells and APCs to proliferate and differentiates B cells for enhanced antitumor immunoglobulin G antibody responses. To further improve antigen recognition, clustered designs on a multivalent epitope were applied by generating various structures, including branched lysine-based peptides, natural multivalent scaffold molecules, and self-assembled nanofibers. We also engineered nano- and microvaccine systems to optimize systemic and localized vaccination. A multilayer-assembled nanovaccine successfully integrated antigens and multiple agonists to modulate APC activation. A DNA hydrogel contributed to the control of APC's immune behaviors, including cell recruitment, activation, and migration, and induced robust antitumor responses as an all-in-one designable platform. In this Account, by summarizing strategies for both T-cell- and B-cell-based vaccine design, we not only compare the differences but also address the intrinsic uniformity between such vaccine designs and further discuss the potential of a combined T-cell- and B-cell-based vaccine, which highlights the applicability and feasibility of chemical strategies.

Glycosylation in Renal Cell Carcinoma: Mechanisms and Clinical Implications

Renal cell carcinoma (RCC) is one of the most prevalent malignant tumors of the urinary system, accounting for around 2% of all cancer diagnoses and deaths worldwide. Clear cell RCC (ccRCC) is the most prevalent and aggressive histology with an unfavorable prognosis and inadequate treatment. Patients' progression-free survival is considerably improved by surgery; however, 30% of patients develop metastases following surgery. Identifying novel targets and molecular markers for RCC prognostic detection is crucial for more accurate clinical diagnosis and therapy. Glycosylation is a critical post-translational modification (PMT) for cancer cell growth, migration, and invasion, involving the transfer of glycosyl moieties to specific amino acid residues in proteins to form glycosidic bonds through the activity of glycosyltransferases. Most cancers, including RCC, undergo glycosylation changes such as branching, sialylation, and fucosylation. In this review, we discuss the latest findings on the significance of aberrant glycans in the initiation, development, and progression of RCC. The potential biomarkers of altered glycans for the diagnosis and their implications in RCC have been further highlighted.

Built-in adjuvants for use in vaccines

Vaccine refers to biological products that are produced using various pathogenic microorganisms for inoculation. The goal of vaccination is to induce a robust immune response against a specific antigen, thus preventing the organism from getting infected. In vaccines, adjuvants have been widely employed to enhance immunity against specific antigens. An ideal adjuvant should be stable, biodegradable, and low cost, not induce system rejection and promote an immune response. Various adjuvant components have been investigated across diverse applications. Typically, adjuvants are employed to meet the following objectives: (1) to improve the effectiveness of immunization with vaccines for specific populations, such as newborns and the elderly; (2) enhance the immunogenicity of highly purified or recombinant antigens; (3) allow immunization with a smaller dose of the vaccine, reducing drug dosage. In the present review, we primarily focus on chemically synthesized compounds that can be used as built-in adjuvants. We elaborate the classification of these compounds based on the induced immune activation mechanism and summarize their application in various vaccine types.

Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

TLR2 Agonistic Small Molecules: Detailed Structure-Activity Relationship, Applications, and Future Prospects

Toll-like receptors (TLRs) are the pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) in microbial species. Among the various TLRs, TLR2 has a special place due to its ability to sense the widest repertoire of PAMPs owing to its heterodimerization with either TLR1 or TLR6, broadening its ligand diversity against pathogens. Various scaffolds are reported to activate TLR2, which include naturally occurring lipoproteins, synthetic lipopeptides, and small heterocyclic molecules. We described a detailed SAR in TLR2 agonistic scaffolds and also covered the design and chemistry for the conjugation of TLR2 agonists to antigens, carbohydrates, polymers, and fluorophores. The approaches involved in delivery of TLR2 agonists such as lipidation of antigen, conjugation to polymers, phosphonic acids, and other linkers to achieve surface adsorption, liposomal formulation, and encapsulating nanoparticles are elaborated. The crystal structure analysis and computational modeling are also included with the structural features that facilitate TLR2 activation.

Altered glycosylation in cancer: A promising target for biomarkers and therapeutics

Glycosylation is a well-regulated cell and microenvironment specific post-translational modification. Several glycosyltransferases and glycosidases orchestrate the addition of defined glycan structures on the proteins and lipids. Recent advances and systemic approaches in glycomics have significantly contributed to a better understanding of instrumental roles of glycans in health and diseases. Emerging research evidence recognized aberrantly glycosylated proteins as the modulators of the malignant phenotype of cancer cells. The Cancer Genome Atlas has identified alterations in the expressions of glycosylation-specific genes that are correlated with cancer progression. However, the mechanistic basis remains poorly explored. Recent researches have shown that specific changes in the glycan structures are associated with 'stemness' and epithelial-to-mesenchymal transition of cancer cells. Moreover, epigenetic changes in the glycosylation pattern make the tumor cells capable of escaping immunosurveillance mechanisms. The deciphering roles of glycans in cancer emphasize that glycans can serve as a source for the development of novel clinical biomarkers. The ability of glycans in intervening various stages of tumor progression and the biosynthetic pathways involved in glycan structures constitute a promising target for cancer therapy. Advances in the knowledge of innovative strategies for identifying the mechanisms of glycan-binding proteins are hoped to hold great potential in cancer therapy. This review discusses the fundamental role of glycans in regulating tumorigenesis and tumor progression and provides insights into the influence of glycans in the current tactics of targeted therapies in the clinical setting.

Chemical Strategies to Boost Cancer Vaccines

Personalized cancer vaccines (PCVs) are reinvigorating vaccine strategies in cancer immunotherapy. In contrast to adoptive T-cell therapy and checkpoint blockade, the PCV strategy modulates the innate and adaptive immune systems with broader activation to redeploy antitumor immunity with individualized tumor-specific antigens (neoantigens). Following a sequential scheme of tumor biopsy, mutation analysis, and epitope prediction, the administration of neoantigens with synthetic long peptide (SLP) or mRNA formulations dramatically improves the population and activity of antigen-specific CD4+ and CD8+ T cells. Despite the promising prospect of PCVs, there is still great potential for optimizing prevaccination procedures and vaccine potency. In particular, the arduous development of tumor-associated antigen (TAA)-based vaccines provides valuable experience and rational principles for augmenting vaccine potency which is expected to advance PCV through the design of adjuvants, delivery systems, and immunosuppressive tumor microenvironment (TME) reversion since current personalized vaccination simply admixes antigens with adjuvants. Considering the broader application of TAA-based vaccine design, these two strategies complement each other and can lead to both personalized and universal therapeutic methods. Chemical strategies provide vast opportunities for (1) exploring novel adjuvants, including synthetic molecules and materials with optimizable activity, (2) constructing efficient and precise delivery systems to avoid systemic diffusion, improve biosafety, target secondary lymphoid organs, and enhance antigen presentation, and (3) combining bioengineering methods to innovate improvements in conventional vaccination, "smartly" re-educate the TME, and modulate antitumor immunity. As chemical strategies have proven versatility, reliability, and universality in the design of T cell- and B cell-based antitumor vaccines, the union of such numerous chemical methods in vaccine construction is expected to provide new vigor and vitality in cancer treatment.

Synthesis of a Self-Adjuvanting MUC1 Vaccine via Diselenide-Selenoester Ligation-Deselenization

Access to lipopeptide-based vaccines for immunological studies remains a significant challenge owing to the amphipathic nature of the molecules, which makes them difficult to synthesize and purify to homogeneity. Here, we describe the application of a new peptide ligation technology, the diselenide-selenoester ligation (DSL), to access self-adjuvanting glycolipopeptide vaccines. We show that rapid ligation of glyco- and lipopeptides is possible via DSL in mixed organic solvent-aqueous buffer and, when coupled with deselenization chemistry, affords rapid and efficient access to a vaccine candidate possessing a MUC1 glycopeptide epitope and the lipopeptide adjuvant Pam₂Cys. This construct was shown to elicit MUC1-specific antibody and cytotoxic T lymphocyte responses in the absence of any other injected lipids or adjuvants. The inclusion of the helper T cell epitope PADRE both boosted the antibody response and resulted in elevated cytokine production.

Recent Advances in Toll Like Receptor-Targeting Glycoconjugate Vaccines

Many malignant cell surface carbohydrates resulting from abnormal glycosylation patterns of certain diseases can serve as antigens for the development of vaccines against these diseases. However, carbohydrate antigens are usually poorly immunogenic by themselves, thus they need to be covalently coupled with immunologically active carrier molecules to be functional. The most well established and commonly used carriers are proteins. In recent years, the use of toll-like receptor (TLR) ligands to formulate glycoconjugate vaccines has gained significant attention because TLR ligands can serve not only as carrier molecules but also as built-in adjuvants to form fully synthetic and self-adjuvanting conjugate vaccines, which have several advantages over carbohydrate-protein conjugates and formulated mixtures with external adjuvants. This article reviews recent progresses in the development of conjugate vaccines based on TLR ligands. Two major classes of TLR ligands, lipopeptides and lipid A derivatives will be covered with more focus on monophosohoryl lipid A (MPLA) and related analogs, which are TLR4 ligands demonstrated to be able to provoke T cell-dependent, adaptive immune responses. Corresponding conjugate vaccines have shown promising application potentials to multiple diseases including cancer.

Self-assembly of Fluorescent Dehydroberberine Enhances Mitochondria-Dependent Antitumor Efficacy

Selective imaging and inducing mitochondrial dysfunction in tumor cells using mitochondria-targeting probes has become as a promising approach for cancer diagnosis and therapy. Here, we report the design of a fluorescent berberine analog, dehydroberberine (DH-BBR), as a new mitochondria-targeting probe capable of self-assembling into monodisperse organic nanoparticles (DTNPs) upon integration with a lipophilic counter anion, allowing for enhanced fluorescence imaging and treatment of tumors in living mice. X-ray crystallography revealed that the self-assembly process was attributed to a synergy of different molecular interactions, including π-π stacking, O⋅⋅⋅π interaction and electrostatic interaction between DH-BBR and counter anions. We demonstrated that DTNPs could efficiently enter tumor tissue following intravenous injection and enhance mitochondrial delivery of DH-BBR via an electrostatic interaction driven anion exchange process. Selective accumulation in the mitochondria capable of emitting strong fluorescence and causing mitochondrial dysfunction was achieved, enabling efficient inhibition of tumor growth in living mice. This study demonstrates promise for applying lipophilic anions to control molecular self-assembly and tune antitumor activity of mitochondria-targeting probes, which can facilitate to improve cancer treatment in vivo.

Peptide Lipidation - A Synthetic Strategy to Afford Peptide Based Therapeutics

Peptide and protein aberrant lipidation patterns are often involved in many diseases including cancer and neurological disorders. Peptide lipidation is also a promising strategy to improve pharmacokinetic and pharmacodynamic profiles of peptide-based drugs. Self-adjuvanting peptide-based vaccines commonly utilise the powerful TLR2 agonist Pam_nCys lipid to stimulate adjuvant activity. The chemical synthesis of lipidated peptides can be challenging hence efficient, flexible and straightforward synthetic routes to access homogeneous lipid-tagged peptides are in high demand. A new technique coined Cysteine Lipidation on a Peptide or Amino acid (CLipPA) uses a 'thiol-ene' reaction between a cysteine and a vinyl ester and offers great promise due to its simplicity, functional group compatibility and selectivity. Herein a brief review of various synthetic strategies to access lipidated peptides, focusing on synthetic methods to incorporate a Pam_nCys motif into peptides, is provided.

Toll-like Receptor Agonist Conjugation: A Chemical Perspective

Toll-like receptors (TLRs) are vital elements of the mammalian immune system that function by recognizing pathogen-associated molecular patterns (PAMPs), bridging innate and adaptive immunity. They have become a prominent therapeutic target for the treatment of infectious diseases, cancer, and allergies, with many TLR agonists currently in clinical trials or approved as immunostimulants. Numerous studies have shown that conjugation of TLR agonists to other molecules can beneficially influence their potency, toxicity, pharmacokinetics, or function. The functional properties of TLR agonist conjugates, however, are highly dependent on the ligation strategy employed. Here, we review the chemical structural requirements for effective functional TLR agonist conjugation. In addition, we provide similar analysis for those that have yet to be conjugated. Moreover, we discuss applications of covalent TLR agonist conjugation and their implications for clinical use.

Carbohydrate-based vaccines for oncotherapy

Cancer is still one of the most serious threats to human worldwide. Aberrant patterns of glycosylation on the surface of cancer cells, which are correlated with various cancer development stages, can differentiate the abnormal tissues from the healthy ones. Therefore, tumor-associated carbohydrate antigens (TACAs) represent the desired targets for cancer immunotherapy. However, these carbohydrate antigens may not able to evoke powerful immune response to combat with cancer for their poor immunogenicity and immunotolerance. Different approaches have been developed to address these problems. In this review, we want to summarize the latest advances in TACAs based anticancer vaccines.

Synthesis and Immunological Evaluation of a Multicomponent Cancer Vaccine Candidate Containing a Long MUC1 Glycopeptide

A fully synthetic MUC1-based cancer vaccine was designed and chemically synthesized containing an endogenous helper T-epitope (MHC class II epitope). The vaccine elicited robust IgG titers that could neutralize cancer cells by antibody-dependent cell-mediated cytotoxicity (ADCC). It also activated cytotoxic T-lymphocytes. Collectively, the immunological data demonstrate engagement of helper T-cells in immune activation. A synthetic methodology was developed for a penta-glycosylated MUC1 glycopeptide, and antisera of mice immunized by the new vaccine recognized such a structure. Previously reported fully synthetic MUC1-based cancer vaccines that elicited potent immune responses employed exogenous helper T-epitopes derived from microbes. It is the expectation that the use of the newly identified endogenous helper T-epitope will be more attractive, because it will activate cognate CD4+ T-cells that will provide critical tumor-specific help intratumorally during the effector stage of tumor rejection and will aid in the generation of sustained immunological memory.

Synthesis and Evaluation of GM2-Monophosphoryl Lipid A Conjugate as a Fully Synthetic Self-Adjuvant Cancer Vaccine

An efficient method was developed for the synthesis of a GM2 derivative suitable for the conjugation with various biomolecules. This GM2 derivative was covalently linked to keyhole limpet hemocyanin (KLH) and monophosphoryl lipid A (MPLA) to form novel therapeutic cancer vaccines. Immunological evaluations of the resultant conjugates in mice revealed that they elicited robust GM2-specific overall and IgG antibody responses. Moreover, the GM2-MPLA conjugate was disclosed to elicit strong immune responses without the use of an adjuvant, proving its self-adjuvant property. The antisera of both conjugates showed strong binding and mediated similarly effective complement-dependent cytotoxicity to GM2-expressing cancer cell line MCF-7. Based on these results, it was concluded that both GM2-MPLA and GM2-KLH are promising candidates as therapeutic cancer vaccines, whereas fully synthetic GM2-MPLA, which has homogeneous and well-defined structure and self-adjuvant property, deserves more attention and studies.

Self-Assembled Nano-Immunostimulant for Synergistic Immune Activation

Immunotherapy has become one of the most promising therapies for the treatment of diseases. Synthetic immunostimulants and nanomaterial immunostimulant systems are indispensable for the activation of the immune system in cancer immunotherapy. Herein, a strategy for preparing self-assembled nano-immunostimulants (SANIs) for synergistic immune activation is reported. Three immunostimulants self-assemble into nanoparticles through electrostatic interactions. SANIs showed strong synergistic immunostimulation in macrophages. SANIs could also induce a strong antitumor immune response to inhibit tumor growth in mice and act as an efficient adjuvant of antitumor vaccines. Therefore, SANIs may be generally applied in cancer immunotherapy. This novel SANI strategy provides a new way for the development of both immunostimulants and -suppressants.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Protein glycosylation in cancers and its potential therapeutic applications in neuroblastoma

Glycosylation is the most complex post-translational modification of proteins. Altered glycans on the tumor- and host-cell surface and in the tumor microenvironment have been identified to mediate critical events in cancer pathogenesis and progression. Tumor-associated glycan changes comprise increased branching of N-glycans, higher density of O-glycans, generation of truncated versions of normal counterparts, and generation of unusual forms of terminal structures arising from sialylation and fucosylation. The functional role of tumor-associated glycans (Tn, sTn, T, and sLe^a/x) is dependent on the interaction with lectins. Lectins are expressed on the surface of immune cells and endothelial cells or exist as extracellular matrix proteins and soluble adhesion molecules. Expression of tumor-associated glycans is involved in the dysregulation of glycogenes, which mainly comprise glycosyltransferases and glycosidases. Furthermore, genetic and epigenetic mechanisms on many glycogenes are associated with malignant transformation. With better understanding of all aspects of cancer-cell glycomics, many tumor-associated glycans have been utilized for diagnostic, prognostic, and therapeutic purposes. Glycan-based therapeutics has been applied to cancers from breast, lung, gastrointestinal system, melanomas, and lymphomas but rarely to neuroblastomas (NBs). The success of anti-disialoganglioside (GD2, a glycolipid antigen) antibodies sheds light on glycan-based therapies for NB and also suggests the possibility of protein glycosylation-based therapies for NB. This review summarizes our understanding of cancer glycobiology with a focus of how protein glycosylation and associated glycosyltransferases affect cellular behaviors and treatment outcome of various cancers, especially NB. Finally, we highlight potential applications of glycosylation in drug and cancer vaccine development for NB.

Cu-Catalyzed Click Reaction in Carbohydrate Chemistry

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

Multi-component self-assembled anti-tumor nano-vaccines based on MUC1 glycopeptides

Novel multi-component self-assembled nano-vaccines containing both Pam₃CSK₄ and CpG were developed based on the strategy of electrostatic interaction.

Pathobiological implications of mucin glycans in cancer: Sweet poison and novel targets

Mucins are large glycoproteins expressed on the epithelia that provide a protective barrier against harsh insults from toxins and pathogenic microbes. These glycoproteins are classified primarily as being secreted and membrane-bound; both forms are involved in pathophysiological functions including inflammation and cancer. The high molecular weight of mucins is attributed to their large polypeptide backbone that is extensively covered by glycan moieties that modulate the function of mucins and, hence, play an important role in physiological functions. Deregulation of glycosylation machinery during malignant transformation results in altered mucin glycosylation. This review describes the functional implications and pathobiological significance of altered mucin glycosylation in cancer. Further, this review delineates various factors such as glycosyltransferases and tumor microenvironment that contribute to dysregulation of mucin glycosylation during cancer. Finally, this review discusses the scope of mucin glycan epitopes as potential diagnostic and therapeutic targets.

Multi-stimuli-responsive chiral organogels based on peptide derivatives

A series of chiral aryl amide compounds bearing peptide pendants have been investigated as low molecular weight gelators. A mechanistic study reveals that complementary hydrogen bonding from peptide pendants is the main driving force for the formation of organogels. This new class of organogels can exhibit multi-stimuli-responsive behavior upon applying (1) thermal, (2) pH, (3) enantiomeric purity, and (4) fluoride anion stimuli. Enantiomeric purity as a new external stimulus displays sensitive stimuli-responsiveness; only 0.02 equiv. of the enantiomer can completely disassemble the gel aggregate. They will serve as excellent smart materials with potential applications in chiral sensors, recognition, and separation.

Linear synthesis and immunological properties of a fully synthetic vaccine candidate containing a sialylated MUC1 glycopeptide

A strategy for the linear synthesis of a sialylated glycolipopeptide cancer vaccine candidate has been developed using a strategically designed sialyl-Tn building block and microwave-assisted solid-phase peptide synthesis. The glycolipopeptide elicited potent humoral and cellular immune responses. T-cells primed by such a vaccine candidate could be restimulated by tumor-associated MUC1.

Strategy for Designing a Synthetic Tumor Vaccine: Multi-Component, Multivalency and Antigen Modification

Synthetic tumor vaccines have been proven to be promising for cancer immunotherapy. However, the limitation of the specificity and efficiency of the synthetic tumor vaccines need further improvements. To overcome these difficulties, additional tumor-associated targets need to be identified, and optimized structural designs of vaccines need to be elaborated. In this review, we summarized the main strategies pursued in the design of synthetic tumor vaccines, such as multi-component, multivalency, antigen modification and other possible ways to improve the efficiency of synthetic tumor vaccines.

Solid-phase peptide synthesis: an overview focused on the preparation of biologically relevant peptides

Tailor-made design preparation of complex peptide sequence including posttranslational modifications, fluorescent labels, unnatural amino acids are of exceptional value for biological studies of several important diseases. The possibility to obtain these molecules in sufficient amounts in relative short time is thanks to the solid-phase approach.

Direct peptide lipidation through thiol-ene coupling enables rapid synthesis and evaluation of self-adjuvanting vaccine candidates

A radical lipidation: Application of a novel thiol-ene lipidation enables the one-step synthesis of self-adjuvanting antigenic peptides as vaccine candidates. The resultant monoacyl lipopeptides are shown to activate monocytes in a robust manner.

'Multicopy multivalent' glycopolymer-stabilized gold nanoparticles as potential synthetic cancer vaccines

Mucin-related carbohydrates are overexpressed on the surface of cancer cells, providing a disease-specific target for cancer immunotherapy. Here, we describe the design and construction of peptide-free multivalent glycosylated nanoscale constructs as potential synthetic cancer vaccines that generate significant titers of antibodies selective for aberrant mucin glycans. A polymerizable version of the Tn-antigen glycan was prepared and converted into well-defined glycopolymers by Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization. The polymers were then conjugated to gold nanoparticles, yielding 'multicopy-multivalent' nanoscale glycoconjugates. Immunological studies indicated that these nanomaterials generated strong and long-lasting production of antibodies that are selective to the Tn-antigen glycan and cross-reactive toward mucin proteins displaying Tn. The results demonstrate proof-of-concept of a simple and modular approach toward synthetic anticancer vaccines based on multivalent glycosylated nanomaterials without the need for a typical vaccine protein component.

Synthesis and immunological evaluation of a MUC1 glycopeptide incorporated into l-rhamnose displaying liposomes

MUC1 variable number tandem repeats (VNTRs) conjugated to tumor-associated carbohydrate antigens (TACAs) have been shown to break self-tolerance in humanized MUC1 transgenic mice. Therefore, we hypothesize that a MUC1 VNTR TACA-conjugate can be successfully formulated into a liposome-based anticancer vaccine. The immunogenicity of the vaccine should be further augmented by incorporating surface-displayed l-rhamnose (Rha) epitopes onto the liposomes to take advantage of a natural antibody-dependent antigen uptake mechanism. To validate our hypothesis, we synthesized a 20-amino-acid MUC1 glycopeptide containing a GalNAc-O-Thr (Tn) TACA by SPPS and conjugated it to a functionalized Toll-like receptor ligand (TLRL). An l-Rha-cholesterol conjugate was prepared using tetra(ethylene glycol) (TEG) as a linker. The liposome-based anticancer vaccine was formulated by the extrusion method using TLRL-MUC1-Tn conjugate, Rha-TEG-cholesterol, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in a total lipid concentration of 30 mM. The stability, homogeneity, and size characterization of the liposomes was evaluated by SEM and DLS measurements. The formulated liposomes demonstrated positive binding with both anti-Rha and mouse anti-human MUC1 antibodies. Groups of female BALB/c mice were immunized and boosted with a rhamnose-Ficoll (Rha-Ficoll) conjugate formulated with alum as adjuvant to generate the appropriate concentration of anti-Rha antibodies in the mice. Anti-Rha antibody titers were >25-fold higher in the groups of mice immunized with the Rha-Ficoll conjugate than the nonimmunized control groups. The mice were then immunized with the TLRL-MUC1-Tn liposomal vaccine formulated either with or without the surface displaying Rha epitopes. Sera collected from the groups of mice initially immunized with Rha-Ficoll and later vaccinated with the Rha-displaying TLRL-MUC1-Tn liposomes showed a >8-fold increase in both anti-MUC1-Tn and anti-Tn antibody titers in comparison to the groups of mice that did not receive Rha-Ficoll. T-cells from BALB/c mice primed with a MUC1-Tn peptide demonstrated increased proliferation to the Rha-liposomal vaccine in the presence of antibodies isolated from Rha-Ficoll immunized mice compared to nonimmune mice, supporting the proposed effect on antigen presentation. The anti-MUC1-Tn antibodies in the vaccinated mice serum recognized MUC1 on human leukemia U266 cells. Because this vaccine uses separate rhamnose and antigenic epitope components, the vaccine can easily be targeted to different antigens or epitopes by changing the peptide without having to change the other components.

The development of synthetic antitumour vaccines from mucin glycopeptide antigens

Based on important cell-biological and biochemical results concerning the structural difference between membrane glycoproteins of normal epithelial cells and epithelial tumour cells, tumour-associated glycopeptide antigens have been chemically synthesised and structurally confirmed. Glycopeptide structures of the tandem repeat sequence of mucin MUC1 of epithelial tumour cells constitute the most promising tumour-associated antigens. In order to generate a sufficient immunogenicity of these endogenous structures, usually tolerated by the immune system, these synthetic glycopeptide antigens were conjugated to immune stimulating components: in fully synthetic two-component vaccines either with T-cell peptide epitopes or with Toll-like receptor2 lipopeptide ligands or in three-component vaccines with both these stimulants. Alternatively, the synthetic glycopeptide antigens were coupled to immune stimulating carrier proteins. In particular, MUC1 glycopeptide conjugates with Tetanus toxoid proved to be efficient vaccines inducing very strong immune responses in mice. The antibodies elicited with the fully synthetic vaccines showed selective recognition of the tumour-associated glycopeptides as was shown by neutralisation and micro-array binding experiments. After booster immunisations, most of the immune responses showed the installation of an immunological memory. Immunisation with fully synthetic three-component vaccines induced immune reactions with therapeutic effects in terms of reduction of the tumour burden in mice or in killing of tumour cells in culture, while MUC1 glycopeptide-Tetanus toxoid vaccines elicited antibodies in mice which recognised tumour cells in human tumour tissues. The results achieved so far are considered to be promising for the development of an active immunisation against tumours.

Multivalent glyco(cyclo)peptides

Because of the importance of carbohydrate-protein interactions in biological processes, the development of glycoclusters and glycodendrimers capable of mimicking the multivalent display of carbohydrates at the cell surface has become a major field of research over the last decade. Among the large variety of scaffolds that are now available, peptides and cyclopeptides are widely used for the multivalent presentation of glycans. This review will provide an overview of the most recent advances in the preparation and utilization of linear glycopeptides and glycocyclopeptides in glycobiology.

Synthetic glycopeptides and glycoproteins with applications in biological research

Over the past few years, synthetic methods for the preparation of complex glycopeptides have been drastically improved. The need for homogenous glycopeptides and glycoproteins with defined chemical structures to study diverse biological phenomena further enhances the development of methodologies. Selected recent advances in synthesis and applications, in which glycopeptides or glycoproteins serve as tools for biological studies, are reviewed. The importance of specific antibodies directed to the glycan part, as well as the peptide backbone has been realized during the development of synthetic glycopeptide-based anti-tumor vaccines. The fine-tuning of native chemical ligation (NCL), expressed protein ligation (EPL), and chemoenzymatic glycosylation techniques have all together enabled the synthesis of functional glycoproteins. The synthesis of structurally defined, complex glycopeptides or glyco-clusters presented on natural peptide backbones, or mimics thereof, offer further possibilities to study protein-binding events.

A totally synthetic, self-assembling, adjuvant-free MUC1 glycopeptide vaccine for cancer therapy

In the development of vaccines for epithelial tumors, the key targets are MUC1 proteins, which have a variable number of tandem repeats (VNTR) bearing tumor-associated carbohydrate antigens (TACAs), such as Tn and STn. A major obstacle in vaccine development is the low immunogenicity of the short MUC1 peptide. To overcome this obstacle, we designed, synthesized, and evaluated several totally synthetic self-adjuvanting vaccine candidates with self-assembly domains. These vaccine candidates aggregated into fibrils and displayed multivalent B-cell epitopes under mild conditions. Glycosylation of Tn antigen on the Thr residue of PDTRP sequence in MUC1 VNTR led to effective immune response. These vaccines elicited a high level antibody response without any adjuvant and induced antibodies that recognized human breast tumor cells. These vaccines appeared to act through a T-cell independent pathway and were associated with the activation of cytotoxic T cells. These fully synthetic, molecularly defined vaccine candidates had several features that hold promise for anticancer therapy.

Natural and Induced Humoral Responses to MUC1

MUC1 is a membrane-tethered mucin expressed on the ductal cell surface of glandular epithelial cells. Loss of polarization, overexpression and aberrant glycosylation of MUC1 in mucosal inflammation and in adenocarcinomas induces humoral immune responses to the mucin. MUC1 IgG responses have been associated with a benefit in survival in patients with breast, lung, pancreatic, ovarian and gastric carcinomas. Antibodies bound to the mucin may curb tumor progression by restoring cell-cell interactions altered by tumor-associated MUC1, thus preventing metastatic dissemination, as well as counteracting the immune suppression exerted by the molecule. Furthermore, anti-MUC1 antibodies are capable of effecting tumor cell killing by antibody-dependent cell-mediated cytotoxicity. Although cytotoxic T cells are indispensable to achieve anti-tumor responses in advanced disease, abs to tumor-associated antigens are ideally suited to address minimal residual disease and may be sufficient to exert adequate immune surveillance in an adjuvant setting, destroying tumor cells as they arise or maintaining occult disease in an equilibrium state. Initial evaluation of MUC1 peptide/glycopeptide mono and polyvalent vaccines has shown them to be immunogenic and safe; anti-tumor responses are scarce. Progress in carbohydrate synthesis has yielded a number of sophisticated substrates that include MUC1 glycopeptide epitopes that are at present in preclinical testing. Adjuvant vaccination with MUC1 glycopeptide polyvalent vaccines that induce strong humoral responses may prevent recurrence of disease in patients with early stage carcinomas. Furthermore, prophylactic immunotherapy targeting MUC1 may be a strategy to strengthen immune surveillance and prevent disease in subjects at hereditary high risk of breast, ovarian and colon cancer.