Chemoenzymatic synthesis and immunological evaluation of sialyl-Thomsen-Friedenreich (sTF) antigen conjugate to CRM197

sTF (sialyl-Thomsen-Friedenreich) is a type of tumor-associated carbohydrate antigens (TACAs) and is highly expressed in various human malignancies. To validate if sTF could be a valuable molecular target for future cancer vaccine development, in this work the sTF antigen was prepared by adopting a strategy combining chemical and enzymatic methods, and then was covalently conjugated to a carrier protein, CRM197. The preliminary immunological evaluation, performed on BALB/c mice, revealed that the sTF-CRM197 conjugate elicited high titers of specific IgG antibodies. FACS experiments showed that the antisera induced by sTF-CRM197 conjugate could specifically recognize and bind to sTF-positive cancer cells T-47D. Furthermore, the conjugate mediated effective and specific antibody-mediated complement-dependent cytotoxicity (CDC).

A bispecific, crosslinking lectibody activates cytotoxic T cells and induces cancer cell death

BACKGROUND

Aberrant glycosylation patterns play a crucial role in the development of cancer cells as they promote tumor growth and aggressiveness. Lectins recognize carbohydrate antigens attached to proteins and lipids on cell surfaces and represent potential tools for application in cancer diagnostics and therapy. Among the emerging cancer therapies, immunotherapy has become a promising treatment modality for various hematological and solid malignancies. Here we present an approach to redirect the immune system into fighting cancer by targeting altered glycans at the surface of malignant cells. We developed a so-called "lectibody", a bispecific construct composed of a lectin linked to an antibody fragment. This lectibody is inspired by bispecific T cell engager (BiTEs) antibodies that recruit cytotoxic T lymphocytes (CTLs) while simultaneously binding to tumor-associated antigens (TAAs) on cancer cells. The tumor-related glycosphingolipid globotriaosylceramide (Gb3) represents the target of this proof-of-concept study. It is recognized with high selectivity by the B-subunit of the pathogen-derived Shiga toxin, presenting opportunities for clinical development.

METHODS

The lectibody was realized by conjugating an anti-CD3 single-chain antibody fragment to the B-subunit of Shiga toxin to target Gb3⁺ cancer cells. The reactive non-canonical amino acid azidolysine (AzK) was inserted at predefined single positions in both proteins. The azido groups were functionalized by bioorthogonal conjugation with individual linkers that facilitated selective coupling via an alternative bioorthogonal click chemistry reaction. In vitro cell-based assays were conducted to evaluate the antitumoral activity of the lectibody. CTLs, Burkitt´s lymphoma-derived cells and colorectal adenocarcinoma cell lines were screened in flow cytometry and cytotoxicity assays for activation and lysis, respectively.

RESULTS

This proof-of-concept study demonstrates that the lectibody activates T cells for their cytotoxic signaling, redirecting CTLs´ cytotoxicity in a highly selective manner and resulting in nearly complete tumor cell lysis-up to 93%-of Gb3⁺ tumor cells in vitro.

CONCLUSIONS

This research highlights the potential of lectins in targeting certain tumors, with an opportunity for new cancer treatments. When considering a combinatorial strategy, lectin-based platforms of this type offer the possibility to target glycan epitopes on tumor cells and boost the efficacy of current therapies, providing an additional strategy for tumor eradication and improving patient outcomes.

Tumor-associated O-glycans of MUC1: Carriers of the glyco-code and targets for cancer vaccine design

The transformation from normal to malignant phenotype in human cancers is associated with aberrant cell-surface glycosylation. It has frequently been reported that MUC1, the heavily glycosylated cell-surface mucin, is altered in both, expression and glycosylation pattern, in human carcinomas of the epithelium. The presence of incomplete or truncated glycan structures, often capped by sialic acid, commonly known as tumor-associated carbohydrate antigens (TACAs), play a key role in tumor initiation, progression, and metastasis. Accumulating evidence suggests that expression of TACAs is associated with tumor escape from immune defenses. In this report, we will give an overview of the oncogenic functions of MUC1 that are exerted through TACA interactions with endogenous carbohydrate-binding proteins (lectins). These interactions often lead to creation of a pro-tumor microenvironment, favoring tumor progression and metastasis, and tumor evasion. In addition, we will describe current efforts in the design of cancer vaccines with special emphasis on synthetic MUC1 glycopeptide vaccines. Analysis of the key factors that govern structure-based design of immunogenic MUC1 glycopeptide epitopes are described. The role of TACA type, position, and density on observed humoral and cellular immune responses is evaluated.

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.

The Synthesis and Biological Characterization of Acetal-Free Mimics of the Tumor-Associated Carbohydrate Antigens

Carcinomas express unique carbohydrates, known as tumor-associated carbohydrate antigens (TACAs), on their surface. These are potential targets for anticancer vaccines; however, to date, no such vaccine has reached the clinic. One factor that may complicate the success of this effort is the lability of the glycosidic bond. Acetal-free carbohydrates are analogues that lack the glycosidic linkage by replacing either the endo or exo oxygen with a methylene. This chapter summarizes the seminal syntheses of the mucin TACAs, provides an overview of common techniques for the synthesis of carbasugars and C-glycosides, reviews the syntheses published to date of acetal-free TACA analogues, and provides an overview of their observed biological activity. We conclude by offering a summation of the challenges remaining to the field biologically and the potential that acetal-free TACAs have of answering several basic questions in carbohydrate immunology.

Granular cell tumor of the esophagus with elevated preoperative serum carbohydrate antigen 19-9: a case report

A 59-year-old Japanese man was admitted to our hospital for treatment of a submucosal tumor of the esophagus detected by upper gastrointestinal endoscopy and computed tomography (CT). Endoscopic examination revealed a submucosal tumor in the esophagus 35 cm from the incisor teeth. Biopsy of the lesions identified granular cell tumor. CT indicated a projecting and slightly enhanced homogenous mass measuring 2.0 × 1.5 cm in the esophagus below the tracheal bifurcation. Serum tumor marker studies revealed elevated carbohydrate antigen (CA) 19-9. Therefore, the tumor was considered to have malignant potential, and surgical resection was performed. The final pathologic diagnosis was a benign granular cell tumor, positive for S-100 protein. The patient was doing well with normal CA 19-9 levels and no recurrence more than 5 years after surgery. To the best of our knowledge, this is the first report of a granular cell tumor with elevated serum CA 19-9.

Synthesis and cell-selective antitumor properties of amino acid conjugated tumor-associated carbohydrate antigen-coated gold nanoparticles

The Thomsen Friedenreich antigen (TFag) disaccharide is a tumor-associated carbohydrate antigen (TACA) found primarily on carcinoma cells and rarely expressed in normal tissue. The TFag has been shown to interact with Galectin-3 (Gal-3), one in a family of β-galactoside binding proteins. Galectins have a variety of cellular functions, and Gal-3 has been shown to be the sole galectin with anti-apoptotic activity. We have previously prepared gold nanoparticles (AuNP) coated with the TFag in various presentations as potential anti-adhesive therapeutic tools or antitumor vaccine platforms. Here we describe the synthesis of TFag-glycoamino acid conjugates attached to gold nanoparticles through a combined alkane/PEG linker, where the TFag was attached to either a serine or threonine amino acid. Particles were fully characterized by a host of biophysical techniques, and along with a control particle carrying hydroxyl-terminated linker units, were evaluated in both Gal-3 positive and negative cell lines. We show that the particles bearing the saccharides selectively inhibited tumor cell growth of the Gal-3 positive cells significantly more than the Gal-3 negative cells. In addition, the threonine-attached TF particles were more potent than the serine-attached constructs. These results support the use of AuNP as antitumor therapeutic platforms, targeted against cell lines that express specific lectins that interact with TFag.