Domino and Intramolecular Rearrangement Reactions as Advanced Synthetic Methods in Glycosciences. Edited by Z. J. Witczak and R. Bielski .

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137584/1/anie201606642.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137584/2/anie201606642_am.pd

Recent Advances in Subunit Vaccine Carriers

The lower immunogenicity of synthetic subunit antigens, compared to live attenuated vaccines, is being addressed with improved vaccine carriers. Recent reports indicate that the physio-chemical properties of these carriers can be altered to achieve optimal antigen presentation, endosomal escape, particle bio-distribution, and cellular trafficking. The carriers can be modified with various antigens and ligands for dendritic cells targeting. They can also be modified with adjuvants, either covalently or entrapped in the matrix, to improve cellular and humoral immune responses against the antigen. As a result, these multi-functional carrier systems are being explored for use in active immunotherapy against cancer and infectious diseases. Advancing technology, improved analytical methods, and use of computational methodology have also contributed to the development of subunit vaccine carriers. This review details recent breakthroughs in the design of nano-particulate vaccine carriers, including liposomes, polymeric nanoparticles, and inorganic nanoparticles

Liposomal Fc Domain Conjugated to a Cancer Vaccine Enhances Both Humoral and Cellular Immunity

Targeted delivery of antigens to antigen-presenting cells (APCs) by utilizing natural anticarbohydrate antibodies is a promising approach for selective uptake and enhanced antigen presentation. Previously, we reported that in the presence of a natural antibody, anti-rhamnose antibody (anti-Rha), the bacterial sugar rhamnose conjugated with liposomal cancer antigen MUC1-Tn enhances antigen presentation by APCs such as dendritic cells by targeting Fc gamma receptors. The idea was to utilize the natural human anti-Rha antibodies present in human serum for targeted delivery of cancer-specific antigens. Recently, we found that the IgG3 antibody isotype was the most prevalent anti-Rha antibody generated in mice immunized with rhamnose-Ficoll (Rha-Ficoll) antigen. In this manuscript, we have conjugated the murine IgG3-Fc with a MUC1-containing cancer vaccine and compared the humoral and cellular immune response to this vaccine with one targeted via the human anti-Rha antibody and to the MUC1 vaccine alone. This Fc approach enhanced antibody production and T-cell proliferation almost to the same level as using the anti-Rha antibody. These results suggest that targeting Fc directly to dendritic cells can be an alternative approach to human anti-Rha for generating effective antigen-primed T-cells

Synthesis and Immunological Evaluation of a Single Molecular Construct MUC1 Vaccine Containing l-Rhamnose Repeating Units

A rhamnose targeting strategy for generating effective anticancer vaccines was successful in our previous studies. We showed that by utilizing natural anti-rhamnose antibodies, a rhamnose-containing vaccine can be targeted to antigen-presenting cells, such as dendritic cells. In this case, rhamnose (Rha) was linked directly to the liposomes bearing the antigen. However, in the current approach, we conjugated a multivalent Tri-Rha ligand with the antigen itself, making it a single component vaccine construct, unlike the previous two-component vaccine construct where Rha cholesterol and Mucin1 (MUC1) antigen were both linked separately to the liposomes. Synthesis required the development of a linker for coupling of the Rha-Ser residues. We compared those two systems in a mouse model and found increased production of anti-MUC1 antibodies and more primed antigen-specific CD4+ T cells in both of the targeted approaches when compared to the control group, suggesting that this one-component vaccine construct could be a potential design used in our MUC1 targeting mechanisms

Synthesis of Oligosaccharide Components of the Outer Core Domain of P. aeruginosa Lipopolysaccharide Using a Multifunctional Hydroquinone-Derived Reducing-End Capping Group

The synthesis of a trisaccharide (common to glycoform I and II) and a tetrasaccharide (common to glycoform I) from the outer core domain of Pseudomonas aeruginosa lipopolysaccharide (LPS) using a novel hydroquinone-based reducing-end capping group is reported. This multifunctional capping group was utilized as purification handle and was stable toward many common transformations in oligosaccharide synthesis. The access to outer-core LPS antigens with a TBDPS-protected hydroquinone (TPH) at the reducing end will be useful for glycan array and therapeutic glycoconjugate synthesis

Exploring Covalent Allosteric Inhibition of Antigen 85C from <i>Mycobacterium tuberculosis</i> by Ebselen Derivatives

Previous studies identified ebselen as a potent <i>in vitro</i> and <i>in vivo</i> inhibitor of the <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>) antigen 85 (Ag85) complex, comprising three homologous enzymes required for the biosynthesis of the mycobacterial cell wall. In this study, the <i>Mtb</i> Ag85C enzyme was cocrystallized with azido and adamantyl ebselen derivatives, resulting in two crystallographic structures of 2.01 and 1.30 Å resolution, respectively. Both structures displayed the anticipated covalent modification of the solvent accessible, noncatalytic Cys209 residue forming a selenenylsulfide bond. Continuous difference density for both thiol modifiers allowed for the assessment of interactions that influence ebselen binding and inhibitor orientation that were unobserved in previous Ag85C ebselen structures. The <i>k</i>_inact/<i>K</i>_I values for ebselen, adamantyl ebselen, and azido ebselen support the importance of observed constructive chemical interactions with Arg239 for increased <i>in vitro</i> efficacy toward Ag85C. To better understand the <i>in vitro</i> kinetic properties of these ebselen derivatives, the energetics of specific protein–inhibitor interactions and relative reaction free energies were calculated for ebselen and both derivatives using density functional theory. These studies further support the different <i>in vitro</i> properties of ebselen and two select ebselen derivatives from our previously published ebselen library with respect to kinetics and protein–inhibitor interactions. In both structures, the α9 helix was displaced farther from the enzyme active site than the previous Ag85C ebselen structure, resulting in the restructuring of a connecting loop and imparting a conformational change to residues believed to play a role in substrate binding specific to Ag85C. These notable structural changes directly affect protein stability, reducing the overall melting temperature by up to 14.5 °C, resulting in the unfolding of protein at physiological temperatures. Additionally, this structural rearrangement due to covalent allosteric modification creates a sizable solvent network that encompasses the active site and extends to the modified Cys209 residue. In all, this study outlines factors that influence enzyme inhibition by ebselen and its derivatives while further highlighting the effects of the covalent modification of Cys209 by said inhibitors on the structure and stability of Ag85C. Furthermore, the results suggest a strategy for developing new classes of Ag85 inhibitors with increased specificity and potency

Exploring Covalent Allosteric Inhibition of Antigen 85C from <i>Mycobacterium tuberculosis</i> by Ebselen Derivatives

Previous studies identified ebselen as a potent <i>in vitro</i> and <i>in vivo</i> inhibitor of the <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>) antigen 85 (Ag85) complex, comprising three homologous enzymes required for the biosynthesis of the mycobacterial cell wall. In this study, the <i>Mtb</i> Ag85C enzyme was cocrystallized with azido and adamantyl ebselen derivatives, resulting in two crystallographic structures of 2.01 and 1.30 Å resolution, respectively. Both structures displayed the anticipated covalent modification of the solvent accessible, noncatalytic Cys209 residue forming a selenenylsulfide bond. Continuous difference density for both thiol modifiers allowed for the assessment of interactions that influence ebselen binding and inhibitor orientation that were unobserved in previous Ag85C ebselen structures. The <i>k</i>_inact/<i>K</i>_I values for ebselen, adamantyl ebselen, and azido ebselen support the importance of observed constructive chemical interactions with Arg239 for increased <i>in vitro</i> efficacy toward Ag85C. To better understand the <i>in vitro</i> kinetic properties of these ebselen derivatives, the energetics of specific protein–inhibitor interactions and relative reaction free energies were calculated for ebselen and both derivatives using density functional theory. These studies further support the different <i>in vitro</i> properties of ebselen and two select ebselen derivatives from our previously published ebselen library with respect to kinetics and protein–inhibitor interactions. In both structures, the α9 helix was displaced farther from the enzyme active site than the previous Ag85C ebselen structure, resulting in the restructuring of a connecting loop and imparting a conformational change to residues believed to play a role in substrate binding specific to Ag85C. These notable structural changes directly affect protein stability, reducing the overall melting temperature by up to 14.5 °C, resulting in the unfolding of protein at physiological temperatures. Additionally, this structural rearrangement due to covalent allosteric modification creates a sizable solvent network that encompasses the active site and extends to the modified Cys209 residue. In all, this study outlines factors that influence enzyme inhibition by ebselen and its derivatives while further highlighting the effects of the covalent modification of Cys209 by said inhibitors on the structure and stability of Ag85C. Furthermore, the results suggest a strategy for developing new classes of Ag85 inhibitors with increased specificity and potency

Synthesis of a Liposomal MUC1 Glycopeptide-Based Immunotherapeutic and Evaluation of the Effect of l‑Rhamnose Targeting on Cellular Immune Responses

Generation of a CD8⁺ response to extracellular antigen requires processing of the antigen by antigen presenting cells (APC) and cross-presentation to CD8⁺ T cell receptors via MHC class I molecules. Cross-presentation is facilitated by efficient antigen uptake followed by immune-complex-mediated maturation of the APCs. We hypothesize that improved antigen uptake of a glycopeptide sequence containing a CD8⁺ T cell epitope could be achieved by delivering it on a liposome surface decorated with an immune complex-targeting ligand, an l-Rhamnose (Rha) epitope. We synthesized a 20-amino-acid glycopeptide TSAPDT­(GalNAc)­RPAPGSTAPPAHGV from the variable number tandem repeat region of the tumor marker MUC1 containing an N-terminal azido moiety and a tumor-associated α-<i>N</i>-acetyl galactosamine (GalNAc) at the immunogenic DTR motif. The MUC1 antigen was attached to Pam₃Cys, a Toll-like receptor-2 ligand via copper­(I)-catalyzed azido-alkyne cycloaddition (CuAAc) chemistry. The Rha-decorated liposomal Pam₃Cys-MUC1-Tn <b>4</b> vaccine was evaluated in groups of C57BL/6 mice. Some groups were previously immunized to generate anti-Rha antibodies. Anti-Rha antibody expressing mice that received the Rha liposomal vaccine showed higher cellular immunogenicity compared to the control group while maintaining a strong humoral response