Synthesis and immunological evaluation of N-acyl modified Globo H derivatives as anticancer vaccine candidates

Stereoconvergent and Chemoenzymatic Synthesis of Tumor-Associated Glycolipid Disialosyl Globopentaosylceramide for Probing the Binding Affinity of Siglec-7

Disialosyl globopentaosylceramide (DSGb5) is a tumor-associated complex glycosphingolipid. However, the accessibility of structurally well-defined DSGb5 for precise biological functional studies remains challenging. Herein, we describe the first total synthesis of DSGb5 glycolipid by an efficient chemoenzymatic approach. A Gb5 pentasaccharide-sphingosine was chemically synthesized by a convergent and stereocontrolled [2 + 3] method using an oxazoline disaccharide donor to exclusively form β-anomeric linkage. After investigating the substrate specificity of different sialyltransferases, regio- and stereoselective installment of two sialic acids was achieved by two sequential enzyme-catalyzed reactions using α2,3-sialyltransferase Cst-I and α2,6-sialyltransferase ST6GalNAc5. A unique aspect of the approach is that methyl-β-cyclodextrin-assisted enzymatic α2,6-sialylation of glycolipid substrate enables installment of the challenging internal α2,6-linked sialoside to synthesize DSGb5 glycosphingolipid. Surface plasmon resonance studies indicate that DSGb5 glycolipid exhibits better binding affinity for Siglec-7 than the oligosaccharide moiety of DSGb5. The binding results suggest that the ceramide moiety of DSGb5 facilitates its binding by presenting multivalent interactions of glycan epitope for the recognition of Siglec-7.

Stereoselective Synthesis of Sialyl Lewisa Antigen and the Effective Anticancer Activity of Its Bacteriophage Qβ Conjugate as an Anticancer Vaccine

Sialyl Lewisa (sLea ), also known as cancer antigen 19-9 (CA19-9), is a tumor-associated carbohydrate antigen. The overexpression of sLea on the surface of a variety of cancer cells makes it an attractive target for anticancer immunotherapy. However, sLea -based anticancer vaccines have been under-explored. To develop a new vaccine, efficient stereoselective synthesis of sLea with an amine-bearing linker was achieved, which was subsequently conjugated with a powerful carrier bacteriophage, Qβ. Mouse immunization with the Qβ-sLea conjugate generated strong and long-lasting anti-sLea IgG antibody responses, which were superior to those induced by the corresponding conjugate of sLea with the benchmark carrier keyhole limpet hemocyanin. Antibodies elicited by Qβ-sLea were highly selective toward the sLea structure, could bind strongly with sLea -expressing cancer cells and human pancreatic cancer tissues, and kill tumor cells through complement-mediated cytotoxicity. Furthermore, vaccination with Qβ-sLea significantly reduced tumor development in a metastatic cancer model in mice, demonstrating tumor protection for the first time by a sLea -based vaccine, thus highlighting the significant potential of sLea as a promising cancer antigen.

Stereoselective Synthesis of Sialyl Lewisa Antigen and the Effective Anticancer Activity of Its Bacteriophage Qβ Conjugate as an Anticancer Vaccine

Sialyl Lewisa (sLea ), also known as cancer antigen 19-9 (CA19-9), is a tumor-associated carbohydrate antigen. The overexpression of sLea on the surface of a variety of cancer cells makes it an attractive target for anticancer immunotherapy. However, sLea -based anticancer vaccines have been under-explored. To develop a new vaccine, efficient stereoselective synthesis of sLea with an amine-bearing linker was achieved, which was subsequently conjugated with a powerful carrier bacteriophage, Qβ. Mouse immunization with the Qβ-sLea conjugate generated strong and long-lasting anti-sLea IgG antibody responses, which were superior to those induced by the corresponding conjugate of sLea with the benchmark carrier keyhole limpet hemocyanin. Antibodies elicited by Qβ-sLea were highly selective toward the sLea structure, could bind strongly with sLea -expressing cancer cells and human pancreatic cancer tissues, and kill tumor cells through complement-mediated cytotoxicity. Furthermore, vaccination with Qβ-sLea significantly reduced tumor development in a metastatic cancer model in mice, demonstrating tumor protection for the first time by a sLea -based vaccine, thus highlighting the significant potential of sLea as a promising cancer antigen.

Cancer Vaccines Based on Fluorine-Modified KH-1 Elicit Robust Immune Response

KH-1 is a tumor-associated carbohydrate antigen (TACA), which serves as a valuable target of antitumor vaccines for cancer immunotherapies. However, most TACAs are thymus-independent antigens (TD-Ag), and they tend to induce immunological tolerance, leading to their low immunogenicity. To overcome these problems, some fluorinated derivatives of the KH-1 antigen were designed, synthesized, and conjugated to the carrier protein CRM197 to form glycoconjugates, which were used for immunological studies with Freund's adjuvant. The results showed that fluorine-modified N-acyl KH-1 conjugates can induce higher titers of antibodies, especially IgG, which can recognize KH-1-positive cancer cells and can eliminate cancer cells through complement-dependent cytotoxicity (CDC). The trifluoro-modified KH-1-TF-CRM197 showed great potential as an anticancer vaccine candidate.

Glycosylation Alterations in Cancer Cells, Prognostic Value of Glycan Biomarkers and Their Potential as Novel Therapeutic Targets in Breast Cancer

Although we are lately witnessing major improvements in breast cancer treatment and patient outcomes, there is still a significant proportion of patients not receiving efficient therapy. More precisely, patients with triple-negative breast cancer or any type of metastatic disease. Currently available prognostic and therapeutic biomarkers are not always applicable and oftentimes lack precision. The science of glycans is a relatively new scientific approach to better characterize malignant transformation and tumor progression. In this review, we summarize the most important information about glycosylation characteristics in breast cancer cells and how different glycoproteins and enzymes involved in glycosylation could serve as more precise biomarkers, as well as new therapeutic targets.

Structure Guided Design of Bacteriophage Qβ Mutants as Next Generation Carriers for Conjugate Vaccines

Vaccines are critical tools to treat and prevent diseases. For an effective conjugate vaccine, the carrier is crucial, but few carriers are available for clinical applications. In addition, a drawback of current protein carriers is that high levels of antibodies against the carrier are induced by the conjugate vaccine, which are known to interfere with the immune responses against the target antigen. To overcome these challenges, we obtained the near atomic resolution crystal structure of an emerging protein carrier, i.e., the bacteriophage Qβ virus like particle. On the basis of the detailed structural information, novel mutants of bacteriophage Qβ (mQβ) have been designed, which upon conjugation with tumor associated carbohydrate antigens (TACAs), a class of important tumor antigens, elicited powerful anti-TACA IgG responses and yet produced lower levels of anticarrier antibodies as compared to those from the wild type Qβ-TACA conjugates. In a therapeutic model against an aggressive breast cancer in mice, 100% unimmunized mice succumbed to tumors in just 12 days even with chemotherapy. In contrast, 80% of mice immunized with the mQβ-TACA conjugate were completely free from tumors. Besides TACAs, to aid in the development of vaccines to protect against COVID-19, the mQβ based conjugate vaccine has been shown to induce high levels of IgG antibodies against peptide antigens from the SARS-CoV-2 virus, demonstrating its generality. Thus, mQβ is a promising next-generation carrier platform for conjugate vaccines, and structure-based rational design is a powerful strategy to develop new vaccine carriers.

Glycoconjugates: Synthesis, Functional Studies, and Therapeutic Developments

Glycoconjugates are major constituents of mammalian cells that are formed via covalent conjugation of carbohydrates to other biomolecules like proteins and lipids and often expressed on the cell surfaces. Among the three major classes of glycoconjugates, proteoglycans and glycoproteins contain glycans linked to the protein backbone via amino acid residues such as Asn for N-linked glycans and Ser/Thr for O-linked glycans. In glycolipids, glycans are linked to a lipid component such as glycerol, polyisoprenyl pyrophosphate, fatty acid ester, or sphingolipid. Recently, glycoconjugates have become better structurally defined and biosynthetically understood, especially those associated with human diseases, and are accessible to new drug, diagnostic, and therapeutic developments. This review describes the status and new advances in the biological study and therapeutic applications of natural and synthetic glycoconjugates, including proteoglycans, glycoproteins, and glycolipids. The scope, limitations, and novel methodologies in the synthesis and clinical development of glycoconjugates including vaccines, glyco-remodeled antibodies, glycan-based adjuvants, glycan-specific receptor-mediated drug delivery platforms, etc., and their future prospectus are discussed.

Recent advances and future perspectives on carbohydrate-based cancer vaccines and therapeutics

Carbohydrates are abundantly expressed on the surface of both eukaryotic and prokaryotic cells, often as post translational modifications of proteins. Glycoproteins are recognized by the immune system and can trigger both innate and humoral responses. This feature has been harnessed to generate vaccines against polysaccharide-encapsulated bacteria such as Streptococcus pneumoniae, Hemophilus influenzae type b and Neisseria meningitidis. In cancer, glycosylation plays a pivotal role in malignancy development and progression. Since glycans are specifically expressed on the surface of tumor cells, they have been targeted for the discovery of anticancer preventive and therapeutic treatments, such as vaccines and monoclonal antibodies. Despite the various efforts made over the last years, resulting in a series of clinical studies, attempts of vaccination with carbohydrate-based candidates have proven unsuccessful, primarily due to the immune tolerance often associated with these glycans. New strategies are thus deployed to enhance carbohydrate-based cancer vaccines. Moreover, lessons learned from glycan immunobiology paved the way to the development of new monoclonal antibodies specifically designed to recognize cancer-bound carbohydrates and induce tumor cell killing. Herein we provide an overview of the immunological principles behind the immune response towards glycans and glycoconjugates and the approaches exploited at both preclinical and clinical level to target cancer-associated glycans for the development of vaccines and therapeutic monoclonal antibodies. We also discuss gaps and opportunities to successfully advance glycan-directed cancer therapies, which could provide patients with innovative and effective treatments.

Synthesis of Azido-Globo H Analogs for Immunogenicity Evaluation

Globo H (GH) is a tumor-associated carbohydrate antigen (TACA), and GH conjugations have been evaluated as potential cancer vaccines. However, like all carbohydrate-based vaccines, low immunogenicity is a major issue. Modifications of the TACA increase its immunogenicity, but the systemic modification on GH is challenging and the synthesis is cumbersome. In this study, we synthesized several azido-GH analogs for evaluation, using galactose oxidase to selectively oxidize C6-OH of the terminal galactose or N-acetylgalactosamine on lactose, Gb3, Gb4, and SSEA3 into C6 aldehyde, which was then transformed chemically to the azido group. The azido-derivatives were further glycosylated to azido-GH analogs by glycosyltransferases coupled with sugar nucleotide regeneration. These azido-GH analogs and native GH were conjugated to diphtheria toxoid cross-reactive material CRM197 for vaccination with C34 adjuvant in mice. Glycan array analysis of antisera indicated that the azido-GH glycoconjugate with azide at Gal-C6 of Lac (1-CRM197) elicited the highest antibody response not only to GH, SSEA3, and SSEA4, which share the common SSEA3 epitope, but also to MCF-7 cancer cells, which express these Globo-series glycans.