Carbohydrate-based vaccines with a glycolipid adjuvant for breast cancer

Development of Globo-H cancer vaccine

The development of anticancer vaccines requires the identification of unique epitope markers, preferably expressed exclusively on the surface of cancer cells. This Account describes the path of development of a carbohydrate-based vaccine for metastatic breast cancer, including the selection and synthesis of Globo-H as the target, the development of the vaccine conjugate and adjuvant design, the study of the immune response and consideration of class switch, and the analysis of Globo-H distribution on the surface of various cancer cells, cancer stem cells, and normal cells. The first synthesis of Globo-H was accomplished through the use of glycal chemistry; this approach delivered sufficient material for evaluation in phase I human trials. The development of a programmable one-pot synthesis method rendered the synthesis more practical and enabled the midstage proof-of-concept phase II trial and late-stage phase III trial. Finally, enzymatic synthesis of Globo-H coupled with cofactor regeneration was used for the late-stage multicenter trials and manufacture of the product. Along this path of development, it was discovered that the vaccine induced antibodies to target not only Globo-H, but also SSEA3 and SSEA4. Moreover, these three glycolipids were found to be uniquely expressed not only on the cell surface of breast cancer but on 15 additional cancer types, suggesting the broad application of this vaccine in cancer treatment and perhaps cancer prevention. In addition, a new glycolipid adjuvant was designed to target the CD1d receptor on dendritic cells and B cells for presentation to and activation of T cells to modulate the immune response and induce a class switch from IgM to IgG, thereby overcoming the common problem of carbohydrate-based vaccines that often induce mainly IgM antibodies. As demonstrated in this vaccine development, the chemical approach to the synthesis and conjugation of carbohydrate-based immunogens provides the flexibility for access to various structures and linkers to identify optimal compositions for development. The enzymatic method was then introduced to enable the practical synthesis of the vaccine candidate for clinical development and commercialization. Overall, this Account illustrates the path of development of a cancer vaccine, from selection of a unique glycan marker on breast cancer cells and the cancer stem cells as target to the use of chemistry in combination with immunology and cancer biology to enable the design and development of the Globo-H vaccine to target three specific glycan markers exclusively expressed on the cell surface of a number of different types of cancer.

Chemical Synthesis of the Tumor-Associated Globo H Antigen

A derivative of the tumor-associated globo H antigen, a complex hexasaccharide, was synthesized by a convergent and efficient [3+2+1] strategy using various glycosylation methods. All glycosylation reactions afforded good to excellent yields and outstanding stereoselectivity, including the installation of cis α-linked D-galactose and L-fucose. The longest linear sequence for this synthesis was 11 steps from a galactose derivative 11 to give an overall yield of 2.6%. The synthetic target had a free and reactive amino group at the glycan reducing end, facilitating its conjugation with other molecules for various applications.

Direct targeted glycation of the free sulfhydryl group of cysteine residue (Cys-34) of BSA. Mapping of the glycation sites of the anti-tumor Thomsen-Friedenreich neoglycoconjugate vaccine prepared by Michael addition reaction

We present in this manuscript the characterization of the exact glycation sites of the Thomsen-Friedenreich antigen-BSA vaccine (TF antigen:BSA) prepared using a Michael addition reaction between the saccharide antigen as an electrophilic acceptor and the nucleophilic thiol and L-Lysine ε-amino groups of BSA using different ligation conditions. Matrix laser desorption ionization time-of-flight mass spectrometry of the neoglycoconjugates prepared with TF antigen:protein ratios of 2:1 and 8:1, allowed to observe, respectively, the protonated molecules for each neoglycoconjugates: [M + H](+) at m/z 67,599 and 70,905. The measurements of these molecular weights allowed us to confirm exactly the carbohydrate:protein ratios of these two synthetic vaccines. These were found to be closely formed by a TF antigen:BSA ratios of 2:1 and 8:1, respectively. Trypsin digestion and liquid chromatography coupled with electrospray ionization mass spectrometry allowed us to identify the series of released glycopeptide and peptide fragments. De novo sequencing affected by low-energy collision dissociation tandem mass spectrometry was then employed to unravel the precise glycation sites of these neoglycoconjugate vaccines. Finally, we identified, respectively, three diagnostic and characteristic glycated peptides for the synthetic glycoconjugate possessing a TF antigen:BSA ratio 2:1, whereas we have identified for the synthetic glycoconjugate having a TF:BSA ratio 8:1 a series of 14 glycated peptides. The net increase in the occupancy sites of these neoglycoconjugates was caused by the large number of glycoforms produced during the chemical ligation of the synthetic carbohydrate antigen onto the protein carrier.

Affinity of monoclonal antibodies for Globo-series glycans

Globo-series glycans are human cell-surface carbohydrates that include stem-cell marker SSEA-4 and cancer-cell antigen Globo H. These two hexasaccharides differ only in their terminal saccharide: N-acetylneuraminic acid in SSEA-4 and L-fucose in Globo H. Herein, we evaluated the affinity of the monoclonal antibodies α-SSEA-4 and α-GH for the glycans SSEA-4 and Globo H. Using fluorescence polarization, we find that the two monoclonal antibodies have affinity for their cognate glycan in the low nanomolar range, and have negligible affinity for the non-cognate glycan. Using surface plasmon resonance, we find that each cognate affinity is ∼20-fold greater if the glycan is immobilized on a surface rather than free in solution. We conclude that the terminal saccharide plays a dominant role in the ability of monoclonal antibodies to recognize these Globo-series glycans and that the extraordinary specificity of these antibodies supports their use for identifying and sorting stem-cells (α-SSEA-4) and as an agent in cancer immunotherapy (α-GH).

Potent adjuvant effects of novel NKT stimulatory glycolipids on hemagglutinin based DNA vaccine for H5N1 influenza virus

H5N1 influenza virus is a highly pathogenic virus, posing a pandemic threat. Previously, we showed that phenyl analogs of α-galactosylceramide (α-GalCer) displayed greater NKT stimulation than α-GalCer. Here, we examined the adjuvant effects of one of the most potent analogs, C34, on consensus hemagglutinin based DNA vaccine (pCHA5) for H5N1 virus. Upon intramuscular electroporation of mice with pCHA5 with/without various α-GalCer analogs, C34-adjuvanted group developed the highest titer against consensus H5 and more HA-specific IFN-γ secreting CD8 cells (203±13.5) than pCHA5 alone (152.6±13.7, p<0.05). Upon lethal challenge of NIBRG-14 virus, C34-adjuvanted group (84.6%) displayed higher survival rate than pCHA5 only group (46.1%). In the presence of C34 as adjuvant, the antisera displayed broader and greater neutralizing activities against virions pseudotyped with HA of clade 1, and 2.2 than pCHA5 only group. Moreover, to simulate an emergency response to a sudden H5N1 outbreak, we injected mice intramuscularly with single dose of a new consensus H5 (pCHA5-II) based on 1192 full-length H5 sequences, with C34 as adjuvant. The latter not only enhanced the humoral immune response and protection against virus challenge, but also broadened the spectrum of neutralization against pseudotyped HA viruses. Our vaccine strategy can be easily implemented for any H5N1 virus outbreak by single IM injection of a consensus H5 DNA vaccine based on updated HA sequences using C34 as an adjuvant.

Current trends in cancer vaccines--a bioinformatics perspective

Cancer vaccine development is in the process of becoming reality in future, due to successful phase II/III clinical trials. However, there are still problems due to the specificity of tumor antigens and weakness of tumor associated antigens in eliciting an effective immune response. Computational models to assess the vaccine efficacy have helped to improve and understand what is necessary for personalized treatment. Further research is needed to elucidate the mechanisms of activation of antigen specific cytotoxic T lymphocytes, decreased TREG number functionality and antigen cascade, so that overall improvement in vaccine efficacy and disease free survival can be attained. T cell epitomic based in sillico approaches might be very effective for the design and development of novel cancer vaccines.

Stage-specific embryonic antigen-4 as a potential therapeutic target in glioblastoma multiforme and other cancers

Glioblastoma multiforme (GBM), the grade IV astrocytoma, is the most common and aggressive brain tumor in adults. Despite advances in medical management, the survival rate of GBM patients remains poor, suggesting that identification of GBM-specific targets for therapeutic development is urgently needed. Analysis of several glycan antigens on GBM cell lines revealed that eight of 11 GBM cell lines are positive for stage-specific embryonic antigen-4 (SSEA-4), and immunohistochemical staining confirmed that 38/55 (69%) of human GBM specimens, but not normal brain tissue, were SSEA-4(+) and correlated with high-grade astrocytoma. In addition, an SSEA-4-specific mAb was found to induce complement-dependent cytotoxicity against SSEA-4(hi) GBM cell lines in vitro and suppressed GBM tumor growth in mice. Because SSEA-4 is expressed on GBM and many other types of cancers, but not on normal cells, it could be a target for development of therapeutic antibodies and vaccines.

Glycotherapy: new advances inspire a reemergence of glycans in medicine

The beginning of the 20(th) century marked the dawn of modern medicine with glycan-based therapies at the forefront. However, glycans quickly became overshadowed as DNA- and protein-focused treatments became readily accessible. The recent development of new tools and techniques to study and produce structurally defined carbohydrates has spurred renewed interest in the therapeutic applications of glycans. This review focuses on advances within the past decade that are bringing glycan-based treatments back to the forefront of medicine and the technologies that are driving these efforts. These include the use of glycans themselves as therapeutic molecules as well as engineering protein and cell surface glycans to suit clinical applications. Glycan therapeutics offer a rich and promising frontier for developments in the academic, biopharmaceutical, and medical fields.

Synthesis of conjugation-ready zwitterionic oligosaccharides by chemoselective thioglycoside activation

A method to chemoselectively activate thioglycosides in the presence of thioethers is developed and applied in the total synthesis of repeating units of S. pneumoniae Sp1 and B. fragilis PS A1. Biochemical evaluation of these glycans is performed after conjugation to reporter moieties.

Efficient convergent synthesis of bi-, tri-, and tetra-antennary complex type N-glycans and their HIV-1 antigenicity

The structural diversity of glycoproteins often comes from post-translational glycosylation with heterogeneous N-glycans. Understanding the complexity of glycans related to various biochemical processes demands a well-defined synthetic sugar library. We report herein a unified convergent strategy for the rapid production of bi-, tri-, and tetra-antennary complex type N-glycans with and without terminal N-acetylneuraminic acid residues connected via the α-2,6 or α-2,3 linkages. Moreover, using sialyltransferases to install sialic acid can minimize synthetic steps through the use of shared intermediates to simplify the complicated procedures associated with conventional sialic acid chemistry. Furthermore, these synthetic complex oligosaccharides were compiled to create a glycan array for the profiling of HIV-1 broadly neutralizing antibodies PG9 and PG16 that were isolated from HIV infected donors. From the study of antibody PG16, we identified potential natural and unnatural glycan ligands, which may facilitate the design of carbohydrate-based immunogens and hasten the HIV vaccine development.

Effective sugar nucleotide regeneration for the large-scale enzymatic synthesis of Globo H and SSEA4

We report here the development of chemoenzymatic methods for the large-scale synthesis of cancer-associated antigens globopentaose (Gb5), fucosyl-Gb5 (Globo H), and sialyl-Gb5 (SSEA4) by using overexpressed glycosyltransferases coupled with effective regeneration of sugar nucleotides, including UDP-Gal, UDP-GalNAc, GDP-Fuc, and CMP-Neu5Ac. The enzymes used in the synthesis were first identified from different species through comparative studies and then overexpressed in E. coli and isolated for synthesis. These methods provide multigram quantities of products in high yield with only two or three purification steps and are suitable for the evaluation and development of cancer vaccines and therapeutics.

Synthesis of α-O- and α-S-glycosphingolipids related to Sphingomonous cell wall antigens using anomerisation

Analogues of glycolipids from Spingomonadacaece with O- and S- and SO2-linkages have been prepared using chelation induced anomerisation promoted by TiCl4. Included are examples of the anomerisation of intermediates with O- and S-glycosidic linkages as well as isomerisation of β-thioglycuronic acids (β-glycosyl thiols). The β-O-glucuronide and β-O-galacturonide precursors were efficiently prepared using benzoylated trichloroacetimidates. β-Glycosyl thiols were precursors to β-S-derivatives. Triazole containing mimics of the natural glycolipids were prepared using CuI promoted azide-alkyne cycloaddition reactions in THF. The glycolipid antigens are being evaluated currently for their effects on iNKT cells.

Nuclear reprogramming of luminal-like breast cancer cells generates Sox2-overexpressing cancer stem-like cellular states harboring transcriptional activation of the mTOR pathway

Energy metabolism plasticity enables stemness programs during the reprogramming of somatic cells to an induced pluripotent stem cell (iPSC) state. This relationship may introduce a new era in the understanding of Warburg's theory on the metabolic origin of cancer at the level of cancer stem cells (CSCs). Here, we used Yamanaka's stem cell technology in an attempt to create stable CSC research lines in which to dissect the transcriptional control of mTOR--the master switch of cellular catabolism and anabolism--in CSC-like states. The rare colonies with iPSC-like morphology, obtained following the viral transduction of the Oct4, Sox2, Klf4, and c-Myc (OSKM) stemness factors into MCF-7 luminal-like breast cancer cells (MCF-7/Rep), demonstrated an intermediate state between cancer cells and bona fide iPSCs. MCF-7/Rep cells notably overexpressed SOX2 and stage-specific embryonic antigen (SSEA)-4 proteins; however, other stemness-related markers (OCT4, NANOG, SSEA-1, TRA-1-60, and TRA-1-81) were found at low to moderate levels. The transcriptional analyses of OSKM factors confirmed the strong but unique reactivation of the endogenous Sox2 stemness gene accompanied by the silencing of the exogenous Sox2 transgene in MCF-7/Rep cells. Some but not all MCF-7/Rep cells acquired strong alkaline phosphatase (AP) activity compared with MCF-7 parental cells. SOX2-overexpressing MCF-7/Rep cells contained drastically higher percentages of CD44(+) and ALDEFLUOR-stained ALDH(bright) cells than MCF-7 parental cells. The overlap between differentially expressed mTOR signaling-related genes in 3 different SOX2-overexpressing CSC-like cell lines revealed a notable downregulation of 3 genes, PRKAA1 (which codes for the catalytic α 1 subunit of AMPK), DDIT4/REDD1 (a stress response gene that operates as a negative regulator of mTOR), and DEPTOR (a naturally occurring endogenous inhibitor of mTOR activity). The insulin-receptor gene (INSR) was differentially upregulated in MCF-7/Rep cells. Consistent with the downregulation of AMPK expression, immunoblotting procedures confirmed upregulation of p70S6K and increased phosphorylation of mTOR in Sox2-overexpressing CSC-like cell populations. Using an in vitro model of the de novo generation of CSC-like states through the nuclear reprogramming of an established breast cancer cell line, we reveal that the transcriptional suppression of mTOR repressors is an intrinsic process occurring during the acquisition of CSC-like properties by differentiated populations of luminal-like breast cancer cells. This approach may provide a new path for obtaining information about preventing the appearance of CSCs through the modulation of the AMPK/mTOR pathway.

Recent mechanistic insights on glycoconjugate vaccines and future perspectives

Vaccination is a key strategy for the control of various infectious diseases. Many pathogens, such as Streptococcus pneumoniae , Haemophilus influenzae type b (Hib), and Neisseria meningitidis produce on their surfaces dense and complex glycan structures, which represent an optimal target for eliciting carbohydrate specific antibodies able to confer protection against those bacteria. Glycoconjugates represent nowadays an important class of efficacious and safe commercial vaccines. It has been known for a long time that covalent linkage of poorly immunogenic carbohydrates to protein is fundamental to provide T cell epitopes for eliciting a memory response of the immune system against the saccharide. However, while the traditional mechanism of action of glycoconjugates has considered peptides generated from the carrier protein to be responsible of T cell help recruitment, only recently evidence of the active involvement of the carbohydrate part in determining the T cell help has been shown. In addition, zwitterionic polysaccharides have been proven to activate the adaptive immune system without further conjugation to protein. Progress in this interface area between chemistry and biology, in combination with novel synthetic and biosynthetic methods for the preparation of glycoconjugates, is opening new perspectives to clarify their mechanism of action and give new insights for the design of improved carbohydrate-based vaccines.

Immunization of fucose-containing polysaccharides from Reishi mushroom induces antibodies to tumor-associated Globo H-series epitopes

Carbohydrate-based vaccines have shown therapeutic efficacy for infectious disease and cancer. The mushroom Ganoderma lucidum (Reishi) containing complex polysaccharides has been used as antitumor supplement, but the mechanism of immune response has rarely been studied. Here, we show that the mice immunized with a l-fucose (Fuc)-enriched Reishi polysaccharide fraction (designated as FMS) induce antibodies against murine Lewis lung carcinoma cells, with increased antibody-mediated cytotoxicity and reduced production of tumor-associated inflammatory mediators (in particular, monocyte chemoattractant protein-1). The mice showed a significant increase in the peritoneal B1 B-cell population, suggesting FMS-mediated anti-glycan IgM production. Furthermore, the glycan microarray analysis of FMS-induced antisera displayed a high specificity toward tumor-associated glycans, with the antigenic structure located in the nonreducing termini (i.e., Fucα1-2Galβ1-3GalNAc-R, where Gal, GalNAc, and R represent, respectively, D-galactose, D-N-acetyl galactosamine, and reducing end), typically found in Globo H and related tumor antigens. The composition of FMS contains mainly the backbone of 1,4-mannan and 1,6-α-galactan and through the Fucα1-2Gal, Fucα1-3/4Man, Fucα1-4Xyl, and Fucα1-2Fuc linkages (where Man and Xyl represent d-mannose and d-xylose, respectively), underlying the molecular basis of the FMS-induced IgM antibodies against tumor-specific glycans.

Retinoic acid and α-galactosylceramide regulate the expression of costimulatory receptors and transcription factors responsible for B cell activation and differentiation

Mature naïve B cells possess a number of BCR coreceptors and other antigen receptors, including the MHC class I-like molecule CD1d, but little is known of the response of B cells to stimulation by the CD1d ligand, α-galactosylceramide (αGalCer). Previously, we showed that all-trans-retinoic acid (RA) increases the expression of CD1d and the magnitude of CD1d-mediated antibody production in vivo. Potential mechanisms could include changes in the expression of costimulatory molecules and transcription factors that regulate plasma cell formation. In the present study, we have used isolated purified B cells and in vivo studies to demonstrate that αGalCer and RA initiate a regulated expression of several genes essential for B cell activation and differentiation, such as Pax-5, Blimp-1, IRF-4 and activation-induced cytidine deaminase (Aid). Moreover, whereas αGalCer mainly increased the expression of Pax-5, CD40 and CD86 that are critical for B cell activation, RA predominantly increased CD138⁺ and Fas⁺-PNA⁺ B cells, which represent more advanced B cell differentiation. It is also noteworthy that αGalCer enriched a CD19hi subset of B cells, which represent B cells with more differentiated phenotype and higher potential for antibody production. In vivo, treatment with αGalCer enriched the CD19hi population, which, after sorting, produced more anti-TT IgG by ELISPOT assay. Together, our data demonstrate that RA and αGalCer can regulate B cell activation and differentiation at multiple levels in a complementary manner, facilitating the progress of B cells towards antibody secreting cells.