A Stable Gold Nanoparticle-Based Vaccine for the Targeted Delivery of Tumor-Associated Glycopeptide Antigens

We have developed a novel antigen delivery system based on polysaccharide-coated gold nanoparticles (AuNPs) targeted to antigen-presenting cells (APCs) expressing Dectin-1. AuNPs were synthesized de novo using yeast-derived β-1,3-glucans (B13G) as the reductant and passivating agent in a microwave-catalyzed procedure, yielding highly uniform and serum-stable particles. These were further functionalized with both a peptide and a specific glycosylated form from the tandem repeat sequence of mucin 4 (MUC4), a glycoprotein overexpressed in pancreatic tumors. The glycosylated sequence contained the Thomsen–Friedenreich disaccharide, a pan-carcinoma, tumor-associated carbohydrate antigen (TACA), which has been a traditional target for antitumor vaccine design. These motifs were prepared with a cathepsin B protease cleavage site (Gly-Phe-Leu-Gly), loaded on the B13G-coated particles, and these constructs were examined for Dectin-1 binding, APC processing, and presentation in a model in vitro system and for immune responses in mice. We showed that these particles elicit strong in vivo immune responses through the production of both high-titer antibodies and priming of antigen-recognizing T-cells. Further examination showed that a favorable antitumor balance of expressed cytokines was generated, with limited expression of immunosuppressive Il-10. This system is modular in that any range of antigens can be conjugated to our particles and efficiently delivered to APCs expressing Dectin-1.

Chemical synthesis and immunological evaluation of entirely carbohydrate conjugate Globo H-PS A1

An anticancer, entirely carbohydrate conjugate, Globo H-polysaccharide A1 (Globo H-PS A1), was chemically prepared and immunologically evaluated in C57BL/6 mice. Tumor associated carbohydrate antigen Globo H hexasaccharide was synthesized in an overall 7.8% yield employing a convergent [3 + 3] strategy that revealed an anomeric aminooxy group used for conjugation to oxidized PS A1 via an oxime linkage. Globo H-PS A1, formulated with adjuvants monophosphoryl lipid A and TiterMax® Gold. After immunization an antigen specific immune response was observed in ELISA with anti-Globo H IgG/IgM antibodies. Specificity of the corresponding antibodies was determined by FACS showing cell surface binding to Globo H-positive cancer cell lines MCF-7 and OVCAR-5. The anti-Globo H antibodies also exhibited complement-dependent cellular cytotoxicity against MCF-7 and OVCAR-5 cells.

Enhanced Immune Response Against the Thomsen-Friedenreich Tumor Antigen Using a Bivalent Entirely Carbohydrate Conjugate

The Thomsen-Friedenreich (TF) antigen is a key target for the development of anticancer vaccines, and this ongoing challenge remains relevant due to the poor immunogenicity of the TF antigen. To overcome this challenge, we adopted a bivalent conjugate design which introduced both the TF antigen and the Thomsen-nouveau (Tn) antigen onto the immunologically relevant polysaccharide A1 (PS A1). The immunological results in C57BL/6 mice revealed that the bivalent, Tn-TF-PS A1 conjugate increased the immune response towards the TF antigen as compared to the monovalent TF-PS A1. This phenomenon was first observed with enzyme-linked immunosorbent assay (ELISA) where the bivalent conjugate generated high titers of IgG antibodies where the monovalent conjugate generated an exclusive IgM response. Fluorescence-activated cell sorting (FACS) analysis also revealed increased binding events to the tumor cell lines MCF-7 and OVCAR-5, which are consistent with the enhanced tumor cell lysis observed in a complement dependent cytotoxicity (CDC) assay. The cytokine profile generated by the bivalent construct revealed increased pro-inflammatory cytokines IL-17 and IFN-γ. This increase in cytokine concentration was matched with an increase in cytokine producing cells as observed by ELISpot. We hypothesized the mechanisms for this phenomenon to involve the macrophage galactose N-acetylgalactosamine specific lectin 2 (MGL2). This hypothesis was supported by using biotinylated probes and recombinant MGL2 to measure carbohydrate-protein interactions.

A Tumor-Selective Monoclonal Antibody from Immunization with a Tumor-Associated Mucin Glycopeptide

We have previously studied the generation of immune responses after vaccination with tumor-associated carbohydrate antigen (TACA)-containing glycopeptides from the tandem repeat (TR) sequence of MUC4, an aberrantly expressed mucin in pancreatic adenocarcinomas. A specific lead antigen from that study containing the Thomsen-Friedenreich TACA disaccharide facilitated the pursuit of a monoclonal antibody to this synthetic hapten. Initial evaluation of polyclonal antiserum resulting from immunization with a KLH conjugate of this glycopeptide into rabbits showed high titer antibodies by ELISA assays, and selective immunoreactivity with MUC4+ cells by western blot and flow cytometry techniques. Glycan microarray analysis showed an intriguing binding pattern where the antiserum showed near complete specificity for MUC4 TR glycopeptides and peptides, relative to all components on the array. Tissue staining also showed distinct tumor specificity to pancreatic tumor tissue in relation to normal pancreatic tissue, with a preference for more aggressive tumor foci. Based on this data, we produced a monoclonal antibody whose binding and reactivity profile was similar to that of the polyclonal serum, with the added benefit of being more specific for the N-terminal glycosylated peptide domain. This epitope represents a novel immunogen to potentially develop diagnostic antibodies or immunotherapies against various MUC4-positive cancers.

Production of a mouse monoclonal IgM antibody that targets the carbohydrate Thomsen-nouveau cancer antigen resulting in in vivo and in vitro tumor killing

The construction of a tumor-associated carbohydrate antigen-zwitterionic polysaccharide conjugate, Thomsen-nouveau-polysaccharide A1 (Tn-PS A1, where Tn = D-GalpNAc), has led to the development of a carbohydrate binding monoclonal antibody named Kt-IgM-8. Kt-IgM-8 was produced via hybridoma from Tn-PS A1 hyperimmunized Jackson Laboratory C57BL/6 mice, splenocytes and the murine myeloma cell line Sp2/0Ag14 with subsequent cloning on methyl cellulose semi-solid media. This in-house generated monoclonal antibody negates binding influenced from peptides, proteins, and lipids and preferentially binds monovalent Tn antigen as noted by ELISA, FACS, and glycan array technologies. Kt-IgM-8 demonstrated in vitro and in vivo tumor killing against the Michigan Cancer Foundation breast cell line 7 (MCF-7). In vitro tumor killing was observed using an LDH assay that measured antibody-induced complement-dependent cytotoxicity and these results were validated in an in vivo passive immunotherapy approach using an MCF-7 cell line-derived xenograft model. Kt-IgM-8 is effective in killing tumor cells at 30% cytotoxicity, and furthermore, it demonstrated approximately 40% reduction in tumor growth in the MCF-7 model.

Immunological evaluation of the entirely carbohydrate-based Thomsen-Friedenreich – PS B conjugate

PS B, a CD⁴⁺T-cell stimulating zwitterionic polysaccharide fromB. fragilis, was conjugated with aminooxy TF tumor antigen. Immunization revealed Ab specificity to TF. FACS revealed Ab binding to MCF-7 but not HCT-116 cells.

Synthesis of the tumor associative α-aminooxy disaccharide of the TF antigen and its conjugation to a polysaccharide immune stimulant

The α-aminooxy derivative of the Thomsen-Friedenriech tumor associated carbohydrate antigen has been synthesized in 11 steps utilizing a D-GalN3 acceptor carrying a pre-installed α-N-hydroxysuccinimidyl moiety. The natural α linkage was prepared in high selectivity employing a suitably protected D-GalN3-thioglycoside donor with N-hydroxysuccinimide. With access to α-TF-ONH2, the preparation of the TF-PS A1 vaccine candidate ensued smoothly through oxime bond formation.

Elucidating Structural Features of an Entirely Carbohydrate Cancer Vaccine Construct Employing Circular Dichroism and Fluorescent Labeling

The zwitterionic polysaccharide PS A1 from anaerobe Bacteroides fragilis ATCC 25285/NCTC 9343 is known to elicit a T-cell-dependent, major histocompatibility complex class II (MHCII) immune response through a correspondingly similar protein-antigen-based mechanism/pathway. The biological activity of PS A1 is known to arise from alternating charged motifs on adjacent monosaccharides comprising a tetrameric repeating oligomeric unit creating an alpha-helical secondary structure. However, we have learned that this alpha-helical structural characteristic may not play a role in immune activation. Paradoxically, our current knowledge of structure - activity relationships (SARs) with electrostatically charged polysaccharides has become more clearly defined, yet a lack of tools/probes for measuring dynamic structural changes hinders progress in carbohydrate-based vaccine development. Site- and region-specific structural modifications of PS A1, followed by conjugation with a known carbohydrate cancer antigen, the Thomsen-nouveau (Tn = alpha-D-GalNAc-OSer/Thr) antigen, does not alter antibody isotype switching ability and leads to specific IgG3 antibodies in C57BL/6 mice. Circular dichroism (CD) and studies using fluorescently labeled PS A1, described herein, reveal information pertaining to structure - activity relationships and the nature of Tn conjugation to chemically modified PS A1. The CD spectra of a Tn-PS A1 construct at 8.5 ≥ pH ≤ 3.5 illustrates complete loss of alpha-helical character while spectra obtained in the 3.6 ≤ pH ≥ 8.4 range denotes minimal alpha-helicity in comparison to naturally occurring PS A1. Temperatures exceeding 60 °C reveal complete loss of helical character. Two methods for Alexa Fluor488^® fluorescent labeling studies of chemically oxidized PS A1 have given rise to percent conjugation values (% loading) calculated to be on average 35 Tn molecules bound. Combined, our results argue that altering the structure of PS A1, without chemically modifying the electrostatic charge character, does not alter immune response/recognition in mice. These findings have important implications for the design of entirely carbohydrate-based vaccine constructs.

Design, synthesis, and X-ray analysis of a glycoconjugate bound to Mycobacterium tuberculosis antigen 85C

Tuberculosis (TB) is a global health threat with nearly 500 000 new cases of multidrug-resistant TB estimated to occur every year, so new drugs are desperately needed. A number of current antimycobacterial drugs work by interfering with the biosynthesis of key components of the mycolylarabinogalactan (mAG). In light of this observation, other enzymes involved in the synthesis of the mAG should also serve as targets for antimycobacterial drug development. One potential target is the Antigen 85 (Ag85) complex, a family of mycolyltransferases that are responsible for the transfer of mycolic acids from trehalose monomycolate (TMM) to the arabinogalactan. Virtual thiophenyl-arabinoside conjugates were docked to antigen Ag85C (PDB code: 1va5 ) using Glide. Compounds with good docking scores were synthesized by a Gewald synthesis followed by linking to 5-thioarabinofuranosides. The resulting thiophenyl-thioarabinofuranosides were assayed for inhibition of mycoyltransferase activity using a 4-methylumbelliferyl butyrate fluorescence assay. The conjugates showed K(i) values ranging from 18.2 to 71.0 μM. The most potent inhibitor was soaked into crystals of Mycobacterium tuberculosis antigen 85C and the structure of the complex determined. The X-ray structure shows the compound bound within the active site of the enzyme with the thiophene moiety positioned in the putative α-chain binding site of TMM and the arabinofuranoside moiety within the known carbohydrate-binding site as exhibited for the Ag85B-trehalose crystal structure. Unexpectedly, no specific hydrogen bonding interactions are being formed between the arabinofuranoside and the carbohydrate-binding site of the active site suggesting that the binding of the arabinoside within this structure is driven by shape complementarily between the arabinosyl moiety and the carbohydrate binding site.