Development and characterization of monoclonal antibody to T-antigen: (gal beta1-3GalNAc-alpha-O)

Exosomal Thomsen-Friedenreich Glycoantigen: A New Liquid Biopsy Biomarker for Lung and Breast Cancer Diagnoses

Exosomes are nanosized extracellular vesicles released by cells to transport biomolecules such as proteins and RNAs for intercellular communication. Exosomes play important roles in cancer development and metastasis; therefore, they have emerged as potential liquid biopsy biomarkers for cancer screening, diagnosis, and management. Many exosome cargos, including proteins, RNAs, and lipids, have been extensively investigated as biomarkers for cancer liquid biopsy. However, carbohydrates, an important type of biomolecule, have not yet been explored for this purpose. In this study, we reported a new exosomal carbohydrate biomarker, α-linked Thomsen-Friedenreich glycoantigen (TF-Ag-α; Galβ1-3GalNAc-α). To translate our discovery into clinical settings, we developed a surface plasmon resonance-based assay which utilized a unique mAb, JAA-F11, with high specificity to measure the levels of exosomal TF-Ag-α in blood. To the best of our knowledge, we are the first to demonstrate that exosomes carry TF-Ag-α. We detected exosomal TF-Ag-α in as low as 10 μL serum samples from patients with cancer, but in contrast, levels were negligible in those from normal controls. With a total of 233 patients with cancer and normal controls, we showed that exosomal TF-Ag-α detected lung cancer (n = 60) and breast cancer (n = 95) from normal controls (n = 78) with ≥95% and ≥97% accuracy, respectively. These results demonstrated that exosomal TF-Ag-α is a potential liquid biopsy biomarker for cancer diagnosis.

SIGNIFICANCE

Exosomes or small extracellular vesicles have emerged as potent biomarkers of cancer liquid biopsy. We discovered a new exosomal carbohydrate marker, TF-Ag-α (Galβ1-3GalNAc-α), and showed that exosomal TF-Ag-α detected both lung and breast cancers with >95% accuracy. Our findings demonstrated that exosomal TF-Ag-α is a promising liquid biopsy biomarker for cancer screening and early detection.

Therapeutic efficacy of the humanized JAA-F11 anti-Thomsen-Friedenreich antibody constructs H2aL2a and H3L3 in human breast and lung cancer xenograft models

The Thomsen-Friedenreich antigen (TF-Ag-α) is found on ~85% of human carcinomas but is cryptic on normal tissue. The humanized highly specific hJAA-F11-H2aL2a and -H3L3 antibodies target TF-Ag-α without binding to TF-Ag-beta (found on surface glycolipids of some normal cells). The relative affinity of H3L3 is 17 times that of H2aL2a, which would seem to favor superior efficacy, however, increased affinity can result in less tumor penetration. To assess the potential therapeutic efficacy of these antibodies, four human cancer- mouse xenograft models were treated with H2aL2a and H3L3. The tumor xenograft models used were human non-small cell lung cancer, H520, and small cell lung cancer, HTB171 in nude mice and human triple negative breast cancer, MDA-MB-231 and HCC1806 in SCID mice. H2aL2a significantly decreased tumor growth in both breast and both lung cancer models. H2aL2a showed statistically equal or better efficacy than H3L3 and has superior production capabilities. These results suggest that H2aL2a may be superior as a naked antibody, as an antibody drug conjugate or as a radiolabeled antibody, however the higher affinity of H3L3 may lead to better efficacy in bi-specific therapies in which the binding is decreased due to the presence of only one TF-Ag-α binding site.

Targeting Tumor Glycans for Cancer Therapy: Successes, Limitations, and Perspectives

Simple Summary

Aberrant glycosylation is a common feature of many cancers, and it plays crucial roles in tumor development and biology. Cancer progression can be regulated by several physiopathological processes controlled by glycosylation, such as cell–cell adhesion, cell–matrix interaction, epithelial-to-mesenchymal transition, tumor proliferation, invasion, and metastasis. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs), which are suitable for selective cancer targeting, as well as novel antitumor immunotherapy approaches. This review summarizes the strategies developed in cancer immunotherapy targeting TACAs, analyzing molecular and cellular mechanisms and state-of-the-art methods in clinical oncology.

Abstract

Aberrant glycosylation is a hallmark of cancer and can lead to changes that influence tumor behavior. Glycans can serve as a source of novel clinical biomarker developments, providing a set of specific targets for therapeutic intervention. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs) suitable for selective cancer-targeting therapy. The best characterized TACAs are truncated O-glycans (Tn, TF, and sialyl-Tn antigens), gangliosides (GD2, GD3, GM2, GM3, fucosyl-GM1), globo-serie glycans (Globo-H, SSEA-3, SSEA-4), Lewis antigens, and polysialic acid. In this review, we analyze strategies for cancer immunotherapy targeting TACAs, including different antibody developments, the production of vaccines, and the generation of CAR-T cells. Some approaches have been approved for clinical use, such as anti-GD2 antibodies. Moreover, in terms of the antitumor mechanisms against different TACAs, we show results of selected clinical trials, considering the horizons that have opened up as a result of recent developments in technologies used for cancer control.

Targeting cancer metastasis with antibody therapeutics

Cancer metastasis, the spread of disease from a primary to a distal site through the circulatory or lymphatic systems, accounts for over 90% of all cancer related deaths. Despite significant progress in the field of cancer therapy in recent years, mortality rates remain dramatically higher for patients with metastatic disease versus those with local or regional disease. Although there is clearly an urgent need to develop drugs that inhibit cancer spread, the overwhelming majority of anticancer therapies that have been developed to date are designed to inhibit tumor growth but fail to address the key stages of the metastatic process: invasion, intravasation, circulation, extravasation, and colonization. There is growing interest in engineering targeted therapeutics, such as antibody drugs, that inhibit various steps in the metastatic cascade. We present an overview of antibody therapeutic approaches, both in the pipeline and in the clinic, that disrupt the essential mechanisms that underlie cancer metastasis. These therapies include classes of antibodies that indirectly target metastasis, including anti-integrin, anticadherin, and immune checkpoint blocking antibodies, as well as monoclonal and bispecific antibodies that are specifically designed to interrupt disease dissemination. Although few antimetastatic antibodies have achieved clinical success to date, there are many promising candidates in various stages of development, and novel targets and approaches are constantly emerging. Collectively, these efforts will enrich our understanding of the molecular drivers of metastasis, and the new strategies that arise promise to have a profound impact on the future of cancer therapeutic development. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Aberrant glycosylation patterns on cancer cells: Therapeutic opportunities for glycodendrimers/metallodendrimers oncology

Despite exciting discoveries and progresses in drug design against cancer, its cure is still rather elusive and remains one of the humanities major challenges in health care. The safety profiles of common small molecule anti-cancer therapeutics are less than at acceptable levels and limiting deleterious side-effects have to be urgently addressed. This is mainly caused by their incapacity to differentiate healthy cells from cancer cells; hence, the use of high dosage becomes necessary. One possible solution to improve the therapeutic windows of anti-cancer agents undoubtedly resides in modern nanotechnology. This review presents a discussion concerning multivalent carbohydrate-protein interactions as this topic pertains to the fundamental aspects that lead glycoscientists to tackle glyconanoparticles. The second section describes the detailed properties of cancer cells and how their aberrant glycan surfaces differ from those of healthy cells. The third section briefly describes the immune systems, both innate and adaptative, because the numerous displays of cell surface protein receptors necessitate to be addressed from the multivalent angles, a strength full characteristic of nanoparticles. The next chapter presents recent advances in glyconanotechnologies, including glycodendrimers in particular, as they apply to glycobiology and carbohydrate-based cancer vaccines. This was followed by an overview of metallodendrimers and how this rapidly evolving field may contribute to our arsenal of therapeutic tools to fight cancer. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Temporal and molecular dynamics of human metastatic breast carcinoma cell adhesive interactions with human bone marrow endothelium analyzed by single-cell force spectroscopy

Bone is a common site of metastasis for breast cancer and the mechanisms of metastasis are not fully elucidated. The purpose of our study was to characterize temporal and molecular dynamics of adhesive interactions between human breast cancer cells (HBCC) and human bone marrow endothelium (HBME) with piconewton resolution using atomic force microscopy (AFM). In adhesion experiments, a single breast cancer cell, MDA-MB-231 (MB231) or MDA-MB-435 (MB435) was attached to the AFM cantilever and brought into contact with a confluent HBME monolayer for different time periods (0.5 to 300 sec). The forces required to rupture individual molecular interactions and completely separate interacting cells were analyzed as measures of cell-cell adhesion. Adhesive interactions between HBME and either MB231 or MB435 cells increased progressively as cell-cell contact time was prolonged from 0.5 to 300 sec due to the time-dependent increase in the number and frequency of individual adhesive events, as well as to the involvement of stronger ligand-receptor interactions over time. Studies of the individual molecule involvement revealed that Thomsen-Friedenreich antigen (TF-Ag), galectin-3, integrin-β1, and integrin-α3 are all contributing to HBCC/HBME adhesion to various degrees in a temporally defined fashion. In conclusion, cell-cell contact time enhances adhesion of HBCC to HBME and the adhesion is mediated, in part, by TF-Ag, galectin-3, integrin-α3, and integrin-β1.

Preclinical Analysis of JAA-F11, a Specific Anti-Thomsen-Friedenreich Antibody via Immunohistochemistry and In Vivo Imaging

The tumor specificity of JAA-F11, a novel monoclonal antibody specific for the Thomsen-Friedenreich cancer antigen (TF-Ag-alpha linked), has been comprehensively studied by in vitro immunohistochemical (IHC) staining of human tumor and normal tissue microarrays and in vivo biodistribution and imaging by micro-positron emission tomography imaging in breast and lung tumor models in mice. The IHC analysis detailed herein is the comprehensive biological analysis of the tumor specificity of JAA-F11 antibody performed as JAA-F11 is progressing towards preclinical safety testing and clinical trials. Wide tumor reactivity of JAA-F11, relative to the matched mouse IgG3 (control), was observed in 85% of 1269 cases of breast, lung, prostate, colon, bladder, and ovarian cancer. Staining on tissues from breast cancer cases was similar regardless of hormonal or Her2 status, and this is particularly important in finding a target on the currently untargetable triple-negative breast cancer subtype. Humanization of JAA-F11 was recently carried out as explained in a companion paper "Humanization of JAA-F11, a Highly Specific Anti-Thomsen-Friedenreich Pancarcinoma Antibody and In Vitro Efficacy Analysis" (Neoplasia 19: 716-733, 2017), and it was confirmed that humanization did not affect chemical specificity. IHC studies with humanized JAA-F11 showed similar binding to human breast tumor tissues. In vivo imaging and biodistribution studies in a mouse syngeneic breast cancer model and in a mouse-human xenograft lung cancer model with humanized 124I- JAA-F11 construct confirmed in vitro tumor reactivity and specificity. In conclusion, the tumor reactivity of JAA-F11 supports the continued development of JAA-F11 as a targeted cancer therapeutic for multiple cancers, including those with unmet need.

Cell surface Thomsen-Friedenreich proteome profiling of metastatic prostate cancer cells reveals potential link with cancer stem cell-like phenotype

The tumor-associated Thomsen-Friedenreich glycoantigen (TF-Ag) plays an important role in hematogenous metastasis of multiple cancers. The LTQ Orbitrap LC-MS/MS mass spectrometry analysis of cell surface TF-Ag proteome of metastatic prostate cancer cells reveals that several cell surface glycoproteins expressing this carbohydrate antigen in prostate cancer (CD44, α2 integrin, β1 integrin, CD49f, CD133, CD59, EphA2, CD138, transferrin receptor, profilin) are either known as stem cell markers or control important cancer stem-like cell functions. This outcome points to a potential link between TF-Ag expression and prostate cancer stem-like phenotype. Indeed, selecting prostate cancer cells for TF-Ag expression resulted in the enrichment of cells with stem-like properties such as enhanced clonogenic survival and growth, prostasphere formation under non-differentiating and differentiating conditions, and elevated expression of stem cell markers such as CD44 and CD133. Further, the analysis of the recent literature demonstrates that TF-Ag is a common denominator for multiple prostate cancer stem-like cell populations identified to date and otherwise characterized by distinct molecular signatures. The current paradigm suggests that dissemination of tumor cells with stem-like properties to bone marrow that occurred before surgery and/or radiation therapy is largely responsible for disease recurrence years after radical treatment causing a massive clinical problem in prostate cancer. Thus, developing means for destroying disseminated prostate cancer stem-like cells is an important goal of modern cancer research. The results presented in this study suggest that multiple subpopulation of putative prostate cancer stem-like cells characterized by distinct molecular signatures can be attacked using a single target commonly expressed on these cells, the TF-Ag.

Humanization of JAA-F11, a Highly Specific Anti-Thomsen-Friedenreich Pancarcinoma Antibody and InVitro Efficacy Analysis

JAA-F11 is a highly specific mouse monoclonal to the Thomsen-Friedenreich Antigen (TF-Ag) which is an alpha-O-linked disaccharide antigen on the surface of ~80% of human carcinomas, including breast, lung, colon, bladder, ovarian, and prostate cancers, and is cryptic on normal cells. JAA-F11 has potential, when humanized, for cancer immunotherapy for multiple cancer types. Humanization of JAA-F11, was performed utilizing complementarity determining regions grafting on a homology framework. The objective herein is to test the specificity, affinity and biology efficacy of the humanized JAA-F11 (hJAA-F11). Using a 609 target glycan array, 2 hJAA-F11 constructs were shown to have excellent chemical specificity, binding only to TF-Ag alpha-linked structures and not to TF-Ag beta-linked structures. The relative affinity of these hJAA-F11 constructs for TF-Ag was improved over the mouse antibody, while T20 scoring predicted low clinical immunogenicity. The hJAA-F11 constructs produced antibody-dependent cellular cytotoxicity in breast and lung tumor lines shown to express TF-Ag by flow cytometry. Internalization of hJAA-F11 into cancer cells was also shown using a surface binding ELISA and confirmed by immunofluorescence microscopy. Both the naked hJAA-F11 and a maytansine-conjugated antibody (hJAA-F11-DM1) suppressed in vivo tumor progression in a human breast cancer xenograft model in SCID mice. Together, our results support the conclusion that the humanized antibody to the TF-Ag has potential as an adjunct therapy, either directly or as part of an antibody drug conjugate, to treat breast cancer, including triple negative breast cancer which currently has no targeted therapy, as well as lung cancer.

Endothelial integrin α3β1 stabilizes carbohydrate-mediated tumor/endothelial cell adhesion and induces macromolecular signaling complex formation at the endothelial cell membrane

Blood borne metastatic tumor cell adhesion to endothelial cells constitutes a critical rate-limiting step in hematogenous cancer metastasis. Interactions between cancer associated carbohydrate Thomsen-Friedenreich antigen (TF-Ag) and endothelium-expressed galectin-3 (Gal-3) have been identified as the leading molecular mechanism initiating tumor/endothelial cell adhesion in several types of cancer. However, it is unknown how these rather weak and transient carbohydrate/lectin mediated interactions are stabilized. Here, using Western blot and LC tandem mass spectrometry analyses of pull-downs utilizing TF-Ag loaded gold nanoparticles, we identified Gal-3, endothelial integrin α3β1, Src kinase, as well as 5 additional molecules mapping onto focal adhesion pathway as parts of the macromolecular complexes formed at the endothelial cell membranes downstream of TF-Ag/Gal-3 interactions. In a modified parallel flow chamber assay, inhibiting α3β1 integrin greatly reduced the strength of tumor/endothelial cell interactions without affecting the initial cancer cell adhesion. Further, the macromolecular complex induced by TF-Ag/Gal-3/α3β1 interactions activates Src kinase, p38, and ERK1/2, pathways in endothelial cells in a time- and α3β1-dependent manner. We conclude that, following the initial metastatic cell attachment to endothelial cells mediated by TF-Ag/Gal-3 interactions, endothelial integrin α3β1 stabilizes tumor/endothelial cell adhesion and induces the formation of macromolecular signaling complex activating several major signaling pathways in endothelial cells.

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.

Preclinical studies with JAA-F11 anti-Thomsen-Friedenreich monoclonal antibody for human breast cancer

ABSTRACT: 

Aim: The Thomsen-Friedenreich antigen (TF-Ag) is a disaccharide hidden on normal cells, but selectively exposed on the surface of breast, colon, prostate and bladder cancer cells. JAA-F11, a highly specific monoclonal antibody to TF-Ag, reduces metastasis and prolongs survival in a mouse model. In addition,124I-JAA-F11 localizes 4T1 tumors in mice. These studies continue translation of JAA-F11 to human breast cancer. Materials & methods & results: Of the 41 human breast cancer cell lines tested, 78% were positive for reactivity with JAA-F11 by whole-cell enzyme immunoassay and positivity occurred unrelated to estrogen, progesterone or HER2 receptor status. JAA-F11 inhibited the growth rate of the human cancer cell lines tested. At 1 h, approximately 80% of JAA-F11 internalized in the three cell lines tested. 124I-JAA-F11 specifically imaged human triple-negative tumors in mice by microPET. Conclusion: The results highlight the potential that humanized JAA-F11 may have for immunotherapy and drug conjugate therapy in breast cancer patients.

Presentation, presentation, presentation! Molecular-level insight into linker effects on glycan array screening data

Changes in cell-surface glycan patterns are markers of the presence of many different disease and cancer types, offering a relatively untapped niche for glycan-targeting reagents and therapeutics in diagnosis and treatment. Of paramount importance for the success of any glycan-targeting reagent is the ability to specifically recognize the target among the plethora of different glycans that exist in the human body. The preeminent technique for defining specificity is glycan array screening, in which a glycan-binding protein (GBP) can be simultaneously screened against multiple glycans. Glycan array screening has provided unparalleled insight into GBP specificity, but data interpretation suffers from difficulties in identifying false-negative binding arising from altered glycan presentation, associated with the linker used to conjugate the glycan to the surface. In this work, we model the structure and dynamics of the linkers employed in the glycan arrays developed by the Consortium for Functional Glycomics. The modeling takes into account the physical presence and surface polarity of the array, and provides a structure-based rationalization of false-negative results arising from the so-called “linker effect.” The results also serve as a guide for interpreting glycan array screening data in a biological context; in particular, we show that attempts to employ natural amino acids as linkers may be prone to unexpected artifacts compromising glycan recognition.

Computational screening of the human TF-glycome provides a structural definition for the specificity of anti-tumor antibody JAA-F11

Recombinant antibodies are of profound clinical significance; yet, anti-carbohydrate antibodies are prone to undesirable cross-reactivity with structurally related-glycans. Here we introduce a new technology called Computational Carbohydrate Grafting (CCG), which enables a virtual library of glycans to be assessed for protein binding specificity, and employ it to define the scope and structural origin of the binding specificity of antibody JAA-F11 for glycans containing the Thomsen-Friedenreich (TF) human tumor antigen. A virtual library of the entire human glycome (GLibrary-3D) was constructed, from which 1,182 TF-containing human glycans were identified and assessed for their ability to fit into the antibody combining site. The glycans were categorized into putative binders, or non-binders, on the basis of steric clashes with the antibody surface. The analysis employed a structure of the immune complex, generated by docking the TF-disaccharide (Galβ1-3GalNAcα) into a crystal structure of the JAA-F11 antigen binding fragment, which was shown to be consistent with saturation transfer difference (STD) NMR data. The specificities predicted by CCG were fully consistent with data from experimental glycan array screening, and confirmed that the antibody is selective for the TF-antigen and certain extended core-2 type mucins. Additionally, the CCG analysis identified a limited number of related putative binding motifs, and provided a structural basis for interpreting the specificity. CCG can be utilized to facilitate clinical applications through the determination of the three-dimensional interaction of glycans with proteins, thus augmenting drug and vaccine development techniques that seek to optimize the specificity and affinity of neutralizing proteins, which target glycans associated with diseases including cancer and HIV.

Sugar-binding proteins from fish: selection of high affinity "lambodies" that recognize biomedically relevant glycans

Glycan-binding proteins are important for a wide variety of basic research and clinical applications, but proteins with high affinity and selectivity for carbohydrates are difficult to obtain. Here we describe a facile and cost-effective strategy to generate monoclonal lamprey antibodies, called lambodies, that target glycan determinants. We screened a library of yeast surface-displayed (YSD) lamprey variable lymphocyte receptors (VLR) for clones that can selectively bind various biomedically important glycotopes. These glycoconjugates included tumor-associated carbohydrate antigens (Tn and TFα), Lewis antigens (LeA and LeX), N-glycolylneuraminic acid, targets of broadly neutralizing HIV antibodies (poly-Man9 and the HIV gp120), and the glycoproteins asialo-ovine submaxillary mucin (aOSM) and asialo-human glycophorin A (aGPA). We isolated clones that bind each of these targets in a glycan-dependent manner and with very strong binding constants, for example, 6.2 nM for Man9 and 44.7 nM for gp120, determined by surface plasmon resonance (SPR). One particular lambody, VLRB.aGPA.23, was shown by glycan array analysis to be selective for the blood group H type 3 trisaccharide (BG-H3, Fucα1-2Galβ1-3GalNAcα), aGPA, and TFα (Galβ1-3GalNAcα), with affinity constants of 0.2, 1, and 8 nM, respectively. In human tissue microarrays this lambody selectively detected cancer-associated carbohydrate antigens in 14 different types of cancers. It stained 27% of non-small cell lung cancer (NSCLC) samples in a pattern that correlated with poor patient survival. Lambodies with exquisite affinity and selectivity for glycans may find myriad uses in glycobiology and biomedical research.

Glycodendrimers: versatile tools for nanotechnology

Combining nanotechnology with glycobiology has triggered an exponential growth of research activities in the design of novel functional bionanomaterials (glyconanotechnology). More specifically, recent synthetic advances towards the tailored and versatile design of glycosylated nanoparticles namely glyconanoparticles, considered as synthetic mimetics of natural glycoconjugates, paved the way toward diverse biomedical applications. The accessibility of a wide variety of these structured nanosystems, in terms of shapes, sizes, and organized around stable nanoparticles have readily contributed to their development and applications in nanomedicine. In this context, glycosylated gold-nanoparticles (GNPs), glycosylated quantum dots (QDs), fullerenes, single-wall natotubes (SWNTs), and self-assembled glycononanoparticles using amphiphilic glycopolymers or glycodendrimers have received considerable attention to afford powerful imaging, therapeutic, and biodiagnostic devices. This review will provide an overview of the most recent syntheses and applications of glycodendrimers in glycoscience that have permitted to deepen our understanding of multivalent carbohydrate-protein interactions. Together with synthetic breast cancer vaccines, inhibitors of bacterial adhesions to host tissues including sensitive detection devices, these novel bionanomaterials are finding extensive relevance.

Cancer vaccines and carbohydrate epitopes

Tumor-associated carbohydrate antigens (TACA) result from the aberrant glycosylation that is seen with transformation to a tumor cell. The carbohydrate antigens that have been found to be tumor-associated include the mucin related Tn, Sialyl Tn, and Thomsen-Friedenreich antigens, the blood group Lewis related Lewis(Y), Sialyl Lewis(X) and Sialyl Lewis(A), and Lewis(X) (also known as stage-specific embryonic antigen-1, SSEA-1), the glycosphingolipids Globo H and stage-specific embryonic antigen-3 (SSEA-3), the sialic acid containing glycosphingolipids, the gangliosides GD2, GD3, GM2, fucosyl GM1, and Neu5GcGM3, and polysialic acid. Recent developments have furthered our understanding of the T-independent type II response that is seen in response to carbohydrate antigens. The selection of a vaccine target antigen is based on not only the presence of the antigen in a variety of tumor tissues but also on the role this antigen plays in tumor growth and metastasis. These roles for TACAs are being elucidated. Newly acquired knowledge in understanding the T-independent immune response and in understanding the key roles that carbohydrates play in metastasis are being applied in attempts to develop an effective vaccine response to TACAs. The role of each of the above mentioned carbohydrate antigens in cancer growth and metastasis and vaccine attempts using these antigens will be described.

The Thomsen-Friedenreich antigen and alphaGal-specific human IgG glycoforms: concanavalin A reactivity and relation to survival of cancer patients

Glycan structures of IgG strongly influence the affinity for Fcgamma receptors and antibody effector functions. However, no particular attention has been paid yet to the glycosylation of tumor antigen-specific IgG. The objectives of this study were (i) to investigate the concanavalin A lectin (ConA) reactivity of human anti-Thomsen-Friedenreich (TF) and anti-alphaGal specific IgG in gastric cancer patients and healthy controls and (ii) to evaluate whether the ConA-reactivity of anti-TF and anti-alphaGal specific IgG is associated with the survival rate of patients with cancer. Total IgG was purified from the sera of patients with gastric cancer and healthy blood donors. The anti-TF and anti-alphaGal glycotope specific IgG were detected with ELISA using synthetic saccharide-polyacrylamide conjugates as antigen. In parallel plate, the ConA reactivity of the anti-TF or anti-alphaGal IgG was determined and the ConA index was calculated. Results show that serum anti-TF specific IgG antibodies of patients with cancer contain significantly higher content of ConA positive IgG glycoform compared to IgG of controls. No correlation between the ConA reactivity of anti-TF IgG and anti-alphaGal IgG was observed. High level of anti-TF IgG ConA reactivity was associated with a significantly lower survival rate of patients with gastric cancer.

In vivo tumor cell adhesion in the pulmonary microvasculature is exclusively mediated by tumor cell--endothelial cell interaction

BACKGROUND

Metastasis formation is the leading cause of death among colon cancer patients. We established a new in-situ model of in vivo microscopy of the lung to analyse initiating events of metastatic tumor cell adhesion within this typical metastatic target of colon cancer.

METHODS

Anaesthetized CD rats were mechanically ventilated and 106 human HT-29LMM and T84 colon cancer cells were injected intracardially as single cell suspensions. Quantitative in vivo microscopy of the lung was performed in 10 minute intervals for a total of 40 minutes beginning with the time of injection.

RESULTS

After vehicle treatment of HT-29LMM controls 15.2 +/- 5.3; 14.2 +/- 7.5; 11.4 +/- 5.5; and 15.4 +/- 6.5 cells/20 microscopic fields were found adherent within the pulmonary microvasculature in each 10 minute interval. Similar numbers were found after injection of the lung metastasis derived T84 cell line and after treatment of HT-29LMM with unspecific mouse control-IgG. Subsequently, HT-29LMM cells were treated with function blocking antibodies against beta1-, beta4-, and alphav-integrins wich also did not impair tumor cell adhesion in the lung. In contrast, after hydrolization of sialylated glycoproteins on the cells' surface by neuraminidase, we observed impairment of tumor cell adhesion by more than 50% (p < 0.05). The same degree of impairment was achieved by inhibition of P- and L-selectins via animal treatment with fucoidan (p < 0.05) and also by inhibition of the Thomson-Friedenreich (TF)-antigen (p < 0.05).

CONCLUSIONS

These results demonstrate that the initial colon cancer cell adhesion in the capillaries of the lung is predominantly mediated by tumor cell - endothelial cell interactions, possibly supported by platelets. In contrast to reports of earlier studies that metastatic tumor cell adhesion occurs through integrin mediated binding of extracellular matrix proteins in liver, in the lung, the continuously lined endothelium appears to be specifically targeted by circulating tumor cells.

Development, characterization, and immunotherapeutic use of peptide mimics of the Thomsen-Friedenreich carbohydrate antigen

The tumor-associated carbohydrate Thomsen-Friedenreich antigen (TF-Ag; Galbeta1-3GalNAcalpha-O-Ser/Thr) is overexpressed on the cell surface of several types of tumor cells, contributing to cancer cell adhesion and metastasis to sites containing TF-Ag-binding lectins. A highly specific immunoglobulin G(3) monoclonal antibody (Ab) developed to TF-Ag (JAA-F11) impedes TF-Ag binding to vascular endothelium, blocking a primary metastatic step and providing a survival advantage. In addition, in patients, even low levels of antibodies to TF-Ag seem to improve prognosis; thus, it is expected that vaccines generating antibodies toward TF-Ag would be clinically valuable. Unfortunately, vaccinations with protein conjugates of carbohydrate tumor-associated Ags have induced clinically inadequate immune responses. However, immunization using peptides that mimic carbohydrate Ags such as Lewis has resulted in both Ab and T-cell responses. Here, we tested the hypothesis that vaccinations with unique TF-Ag peptide mimics may generate immune responses to TF-Ag epitopes on tumor cells, useful for active immunotherapy against relevant cancers. Peptide mimics of TF-Ag were selected by phage display biopanning using JAA-F11 and rabbit anti-TF-Ag Ab and were analyzed in vitro to confirm TF-Ag peptide mimicry. In vitro, TF-Ag peptide mimics bound to TF-Ag-specific peanut agglutinin and blocked TF-Ag-mediated rolling and stable adhesion of cancer cells to vascular endothelium. In vivo, the immunization with TF-Ag-mimicking multiple antigenic peptides induced TF-Ag-reactive Ab production. We propose that this novel active immunotherapy approach could decrease tumor burden in cancer patients by specifically targeting TF-Ag-positive cancer cells and blocking metastasis.

Development and characterization of antibodies to carbohydrate antigens

Antibodies to carbohydrate antigens are critical for the study of bacteria, tumors, blood groups, and cell-cell adhesion interactions; for the analysis of viral, hormone, and toxin receptors; and, finally, for analysis of the glycosylation of recombinant proteins. However, antibodies to carbohydrate structures are more difficult to develop because of the T-cell-independent response to carbohydrates. This can result in the production of low affinity and difficult to work with IgM antibodies to these molecules. Screening technologies that include IgM antibodies can cause selections of antibodies with low-affinity binding sites because of the net avidity enhancement. Unfortunately, the low-affinity binding site can also have a similar affinity for unwanted structures. Production of antibodies using cellular extracts can result in antibodies that react with multiple related structures, and therefore the resultant bioassays have sensitivity or specificity problems. Protein conjugates of saccharides for the production of polyclonal and monoclonal antibodies to carbohydrate structures can be used to solve these problems. For monoclonal antibody development to oligosaccharides, mapping with closely related saccharides allows the determination of the areas of the saccharide to which the antibody binds so that conclusions can be made concerning which saccharide structures will cross-react. Determination of the reactivity of the produced antibodies with related saccharide structures is essential prior to utilization.

Mouse monoclonal antibodies to pneumococcal C-polysaccharide backbone show restricted usage of VH-DH-JH gene segments and share the same kappa chain

The immunization of BALB/c mice with heat-killed cells of Streptococcus mitis SK598 allowed the rescue of mouse monoclonal antibodies (mAbs) reactive with the pneumococcal cell wall C-polysaccharide backbone. We report for the first time the genetic and molecular characterization of these mAbs, which altogether reflect a typical thymus-independent type 2 immune response. They were isotype-diverse (IgM, IgG1, IgG2b and IgG3). They made use of restricted and scarcely mutated VH-DH-JH combinations, and the same kappa chain, essentially in germ line configuration. Interestingly, this light chain was also found making up part of an anti-phosphorylcholine mAb. These mAbs were not inhibited by phosphorylcholine and related compounds, nor N-acetylneuraminic acid (NANA), nor the Forssman disaccharide; some of them showed limited reactivity with the meningococcal C polysaccharide. Their CDR-H3s do not show any recognizable patterns resembling those found in antibodies to bacterial polysaccharides that have already been characterized.

Jaa-f11: extending the life of mice with breast cancer

JAA-F11 antibody (Ab) is a monoclonal Ab that is specific for the Thomsen-Friedenreich antigen, Galbeta1-3GalNAcalpha (TF-Ag). TF-Ag, discovered in the late 1920s, is a tumor-associated carbohydrate Ag of many clinically widespread carcinomas. In a mouse model, JAA-F11 Ab significantly extended median survival time of animals with metastatic 4T1 breast tumors and caused > 50% inhibition of lung metastasis. (124)Iodine labeled JAA-F11 Ab in in vivo micro positron emission tomography showed tumor specificity in a mouse breast tumor model, with no preferential uptake by any other organ. Human cancer cell adhesion to vascular endothelium was also blocked by JAA-F11. Structural specificity of the Ab was shown with glycan array analysis and indicated that this Ab, unlike many other Abs to TF-Ag, will not bind to a related glycolipid on natural killer cells, kidney or spleen. Patients with higher levels of naturally occurring anti-TF-Ag Ab appear to have a better prognosis, indicating that passive transfer of JAA-F11 or active immunization, resulting in production of anti-TF-Ag Ab, would clinically be beneficial for the patient.

Tumor immunolocalization using 124 I-iodine-labeled JAA-F11 antibody to Thomsen-Friedenreich alpha-linked antigen

Clinical immunolocalization has been attempted by others with an anti-Thomsen-Friedenreich antigen (TF-Ag) mAb that bound both alpha- and beta-linked TF-Ag. In this report, 124 I-labeled mAb JAA-F11 specific for alpha-linked TF-Ag showed higher tumor specificity in in vivo micro-positron emission tomography (micro-PET) of the mouse mammary adenocarcinoma line, 4T1, showing no preferential uptake by the kidney. Labeled product remained localized in the tumor for at least 20 days. Glycan array analysis showed structural specificity of the antibody.

Inhibition of spontaneous breast cancer metastasis by anti-Thomsen-Friedenreich antigen monoclonal antibody JAA-F11

Thomsen-Friedenreich antigen (TF-Ag) is expressed in many carcinomas, including those of the breast, colon, bladder, and prostate. TF-Ag is important in adhesion and metastasis and as a potential immunotherapy target. We hypothesized that passive transfer of JAA-F11, an anti-TF-Ag monoclonal antibody, may create a survival advantage for patients with TF-Ag-expressing tumors by cytotoxicity, blocking of tumor cell adhesion, and inhibition of metastasis. This was tested using in vitro models of tumor cell growth; cytotoxicity assays; in vitro, ex vivo, and in vivo models of cancer metastasis; and, finally, in vivo effects in mice with metastatic breast cancer. Unlike some anti-TF-Ag antibodies, JAA-F11 did not enhance breast carcinoma cell growth. JAA-F11 did not induce the killing of 4T1 tumor cells through complement-dependent cytotoxicity or apoptotic mechanisms. However, JAA-F11 blocked the stages of metastasis that involve the adhesion of human breast carcinoma cells to human endothelial cells (human umbilical vein endothelial cells and human bone marrow endothelial cells 60) in in vitro static adhesion models, in a perfused ex vivo model, and in murine lung vasculature in an in vivo metastatic deposit formation assay. JAA-F11 significantly extended the median survival time of animals bearing metastatic 4T1 breast tumors and caused a > 50% inhibition of lung metastasis.

Immune response to Thomsen-Friedenreich disaccharide and glycan engineering

Cancer-associated mucins show frequent alterations of their oligosaccharide chain profile, with a switch to unmask normally cryptic O-glycan backbone and core regions. Epithelial tumour cells typically show overexpression of the uncovered Gal(beta)1-3GalNAc(alpha)-O-Ser/Thr (Core 1) structure, known as the T antigen or the Thomsen-Friedenreich antigen, the oligosaccharide chain of which is called the Thomsen-Friedenreich disaccharide (TFD). T antigen expression has been associated with immunosuppression, metastasis dissemination, and the proliferation of cancer cells. Several different strategies have been used to trigger a specific immune response to TFD. Natural T antigen and synthetic TFD residues have low immunodominance. In the T antigen, flexibility of the glycosidic bond reduces the immunogenicity of the sugar residue. Enhanced rigidity should favour certain glycan conformations and thereby improve TFD immunotargeting. We propose the term 'glycan engineering' for this approach. Such engineering of TFD should reduce the flexibility of its glycan moiety and thereby enhance its stability, rigidity and immunogenicity.

Mechanical entrapment is insufficient and intercellular adhesion is essential for metastatic cell arrest in distant organs

In this report, we challenge a common perception that tumor embolism is a size-limited event of mechanical arrest, occurring in the first capillary bed encountered by blood-borne metastatic cells. We tested the hypothesis that mechanical entrapment alone, in the absence of tumor cell adhesion to blood vessel walls, is not sufficient for metastatic cell arrest in target organ microvasculature. The in vivo metastatic deposit formation assay was used to assess the number and location of fluorescently labeled tumor cells lodged in selected organs and tissues following intravenous inoculation. We report that a significant fraction of breast and prostate cancer cells escapes arrest in a lung capillary bed and lodges successfully in other organs and tissues. Monoclonal antibodies and carbohydrate-based compounds (anti-Thomsen-Friedenreich antigen antibody, anti-galectin-3 antibody, modified citrus pectin, and lactulosyl-l-leucine), targeting specifically beta-galactoside-mediated tumor-endothelial cell adhesive interactions, inhibited by >90% the in vivo formation of breast and prostate carcinoma metastatic deposits in mouse lung and bones. Our results indicate that metastatic cell arrest in target organ microvessels is not a consequence of mechanical trapping, but is supported predominantly by intercellular adhesive interactions mediated by cancer-associated Thomsen-Friedenreich glycoantigen and beta-galactoside-binding lectin galectin-3. Efficient blocking of beta-galactoside-mediated adhesion precludes malignant cell lodging in target organs.

Effective combinatorial strategy to increase affinity of carbohydrate binding by peptides

The Thomsen-Friedenreich antigen, a carcinoma-associated disaccharide involved in carcinoma cell homotypic aggregation and increased metastatic potential, has clinical value as a prognostic indicator and a marker of metastasized cells. Hence, it can reasonably be predicted that antigen-binding macromolecules are valuable clinical in vivo diagnostic/therapeutic targeting agents. Recently, we have selected first-generation antigen-binding peptides from a random peptide bacteriophage display library and have applied combinatorial affinity maturation to select functionally-maturated peptides, which target cultured carcinoma cells and inhibit carcinoma cell aggregation. In the current study we hypothesize that a targeted search of sequence space surrounding the antigen-binding consensus sequence will select unpredictable amino acid sequences in the non-consensus portions of the peptides, leading to increased affinity for the carbohydrate and greater solubility in physiological buffers. This comprehensive in vitro analysis demonstrates that preferential evolution of the amino-terminal sequence of the peptides occurred, which correlated, in structure/function studies, with the acquisition of maturated function. The maturated peptides are more soluble than the earlier peptides. Studies of peptide binding to the disaccharide indicate that two maturated peptides (P-30-1, F03) have higher affinity for the antigen and bind with higher intensity to the surface of cultured human carcinoma cells than the first-generation peptides. The results support our hypothesis that affinity maturation can improve carbohydrate binding by peptides and have theoretical importance as the first report of maturation of carbohydrate-binding affinity in a small, soluble peptide.

Evidence of porcine and human endothelium activation by cancer-associated carbohydrates expressed on glycoproteins and tumour cells

It is well established that after metastatic cancer cells escape the primary tumour and enter the circulation, their interactions with microvascular endothelium of a target organ constitute an essential rate-limiting step in haematogenous cancer metastasis. However, the physiological and biochemical processes supporting neoplastic cell arrest and retention in the microcirculation are still poorly understood. In this study, we present experimental evidence that microvascular endothelium of metastasis-prone tissues undergoes activation in response to desialylated cancer-associated carbohydrate structures such as Thomsen-Friedenreich (TF) antigen (Galbeta1-3GalNAc) expressed on circulating glycoproteins and neoplastic cells. The metastasis-associated endothelium activation, manifested by marked increase in endothelial cell surface galectin-3 expression, causes gradual decrease in cancer cell velocities (from 72 x 10(2)+/- 33 x 10(2) microm s-1 to 7.6 x 10(2)+/- 1.9 x 10(2) microm s-1, mean +/-s.d.) accompanied by a corresponding increase in the percentage of rolling cells (from 3.3%+/- 1.2% to 24.3%+/- 3.6%, mean +/-s.d.), and results in human breast and prostate carcinoma cell arrest and retention in the microvasculature. This process, which could be of high importance in haematogenous cancer metastasis, was inhibited efficiently by an anti-TF antigen function-blocking antibody. Carbohydrate-mediated endothelial activation could be a process of physiological significance as it probably occurs in the interactions between a variety of circulating constituents and the vessel wall.

Expression of tumor-associated Thomsen-Friedenreich antigen (T Ag) in Helicobacter pylori and modulation of T Ag specific immune response in infected individuals

We tested the hypothesis that the gastric cancer associated bacteria, Helicobacter pylori (H. pylori) express the cancer-related Thomsen-Friedenreich (T) antigen. We also analysed whether infection with H. pylori alters the amount of natural anti-T antibodies in the patients' sera. Cell surface membrane extracts of H. pylori NCTC 11637 strain and clinical isolates of H. pylori (n = 13) were analysed by immunoblotting and cell-ELISA with five different T antigen-specific monoclonal antibodies (MAbs). Two major protein bands of approximately 68 kDa and 58 kDa were immunostained on blots of H. pylori extracts with T specific MAbs but not immunostained with unrelated MAb. The specificity was shown in that immunostaining was blocked with peanut agglutinin (PNA) and rabbit antiserum to T antigen. The binding of T specific MAb to the 58 kDa protein band was also blocked by rabbit antiserum against heat shock proteins of H. pylori. The relative expression of T antigen-related proteins differed among H. pylori strains, with 68 kD associated T antigen expression higher in patients with more severe pathology. The level of IgG antibody to T epitope in patients with gastric cancer (n = 66) and normal blood donors (n = 62) were compared and the level of anti-T Ab in gastric cancer patients was significantly lower than that in normal blood donors. A significant positive correlation between T specific antibody in serum and H. pylori IgG antibody level was found in H. pylori-infected normal blood donors (P < 0.001), but this correlation was not found in H. pylori-infected cancer patients. In summary, the cancer related T epitope is expressed in H. pylori and modulation of T antigen-specific immune response in H. pylori-infected individuals suggests that H. pylori infection may alter natural immune mechanisms against cancer.

Glycodendrimers: novel glycotope isosteres unmasking sugar coding. case study with T-antigen markers from breast cancer MUC1 glycoprotein

Glycodendrimers are relatively novel synthetic biomacromolecules that are made of biologically relevant carbohydrate ligands constructed at the periphery of a wide range of highly functionalized and repetitive scaffolds having varied molecular weights and structures. They were aimed to fill the gap between glycopolymers, having generally dispersed higher molecular weight, and small glycoclusters, in the study of multivalent carbohydrate protein interactions. In a way, glycodendrimers, with their spheroidal or dendritic (wedge) type structures, were initially designed as bioisosteres of cell surface multiantennary glycans. Taken as a curiosity and elegant molecules at their beginning, they are now considered as potent inhibitors of microbial adhesins. They have also been shown to play some roles in signal transduction and in receptor cross-linking. This brief report will describe advances that have been made toward the syntheses of a range of glycodendrimers bearing the immunodominant T-antigen disaccharide [beta-D-Gal-(1-3)-alpha-D-GalNAc] found on malignant cells of carcinomas, particularly related to breast cancer. This antigen, usually cryptic on healthy tissues, is greatly increased on cancer cells as a result of aberrant glycosylation. It is considered to be an important cancer marker. The high incidence of these carcinomas to invade other tissues such as lymph nodes, lung, and liver by metastasis was one of the arguments raised to generate T-antigen dendrimers that might have the potential to block the receptor sites following surgery. The synthesis of the T-antigen disaccharide will be briefly described, followed by the elaboration of neoglycoproteins and glycopolymers used to raise monoclonal antibodies against the T-antigen and for screening purpose, respectively. Scaffolds made of poly(amidoamine) (PAMAM), poly(propylene imine), N,N'-bis(acrylamido)acetic acid, and finally hyperbranched L-lysine were used to construct relatively small glycodendrimers bearing T-antigen moieties. Few glycodendrimers were also linked to fluorescein and biotin probes to generate ligands that can be used to detect T-Ag receptor sites.

Influence of terminal residue on adjacent disaccharide immunogenicity

Aberrant O-glycosylation of cell surface mucin antigens is characteristic of epithelial cancer cells. For example, Thomsen-Friedenreich disaccharide (TFD) is a chemically well-defined carbohydrate antigen with a documented link to malignancy. There have been many attempts to improve immune response to carbohydrate antigens, for use in immunotherapy. As part of an alternative strategy to improve carbohydrate immunogenicity, we studied the influence of terminal benzyl (Bzl) or p-nitrophenyl (pNP) residue on immunogenicity of adjacent TFD. Mice immunized with keyhole limpets hemocyanin-TFD (KLH-TFD), KLH-TFD(alpha)Bzl, or KLH-TFD(alpha)pNP produced anti-KLH antibodies, which were analyzed by enzyme-linked immunosorbent assay (ELISA). KLH-TFD did not give significant anti-TFD antibody titer, confirming the poor immunogenicity of TFD. Immunization with KLH-TFD(alpha)Bzl and KLH-TFD(alpha)pNP raised antibody titers against TFD(alpha)Bzl and TFD(alpha)pNP, respectively. KLH-TFD(alpha)Bzl also gave higher anti-TFD antibody response, whereas KLH-TFD(alpha)pNP did not, indicating that terminal Bzl residue improves immune response to adjacent carbohydrate. Analysis of anti-TFD(alpha)Bzl or anti-TFD(alpha)pNP IgG antibodies by competitive ELISA, using carbohydrate-related antigens as inhibitors, demonstrated their high specificity to their respective antigens. Anti-TFD(alpha)pNP antibody was not inhibited by TFD, but was significantly inhibited by GalNAc(alpha)pNP. The fact that p-nitrophenol (pNPol) has more competitive ability that GalNAc indicates that terminal polar residue is the main target antigen. In contrast, anti-TFD(alpha)Bzl antibody was inhibited to a similar degree by GalNAc(alpha)Bzl and TFD, confirming the carbohydrate recognition by antibodies yielded by terminal non-polar modification of the immunogen.

Design and synthesis of water-soluble glycopolymers bearing breast tumor marker and enhanced lipophilicity for solid-phase assays

Water-soluble T-antigen containing glycopolymers [Gal beta(1,3)-GalNAc alpha) having a high degree of lipophilicity were synthesized from poly[N-(acryloxy)succinimide] (6-10) by amidation with an amine-ending T-antigen derivative (3) and various amines of increasing alkyl chain length (ammonia and methyl-, ethyl-, and propylamine). The enhanced lipophilicity was demonstrated by a solid-phase microtiter plate assay (ELISA) with mouse monoclonal antibody FAA-J11 (IgG3) and by a core 2-beta(1,6)-N-acetylglucoaminyltransferase using tritium-(3H-) labeled UDP-GlcNAc substrate. The new materials were thus useful in solid-phase high-throughput screening for drug discovery.

Synthesis and protein binding properties of T-antigen containing GlycoPAMAM dendrimers

Allyl O-(beta-D-galactopyranosyl)-(1-3)-2-acetamido-2-deoxy-alpha-D-galactopyranoside (8) was prepared in excellent yield from the corresponding galactosyl bromide (6, 7) and allyl 2-acetamido-4,6-benzylidene-2-deoxy-alpha-D-galactopyranoside (5) using Hg(CN)2 as a promoter. Compound 5 was obtained from N-acetylglucosamine 1 following sequential protecting group strategy and C-4 epimerization as a key step. Carboxylic acid functionalized T-antigen derivative 15, obtained by radical addition of 3-mercaptopropionic acid to allyl disaccharide 10, was conjugated to PAMAM dendritic cores 13-16 by an efficient amide coupling strategy using TBTU. GlycoPAMAM dendrimers having T-antigen residues with 4, 8, 16 and 32 valencies (17-20) were obtained in 73 to 99% yields. Their protein binding properties were demonstrated using peanut lectin from Arachis hypogaea and a mouse monoclonal IgG antibody. The higher valency conjugates generated stronger binding interactions indicating a cluster effect. The inhibitory potential of these glycoPAMAM conjugates toward antibody-coating antigen interactions was enhanced up to 3800 times over that of the monomeric T-antigen residue (10).

Simultaneous binding of mouse monoclonal antibody and streptavidin to heterobifunctional dendritic L-lysine core bearing T-antigen tumor marker and biotin

Thiolated T-antigen [Galbeta-(1-3)-GalNAcalpha, T-Ag] (6), derived in situ from thioacetate 5 was coupled to N-chloroacetylated glycylglycyl L-lysine dendritic cores (7-9) using high yielding substitution reactions to afford di- (10), tetra- (11), and octa-valent (12) glycodendrimers in good yields (76-86%). Heterobifunctional conjugate 14 was prepared as a biosensor from tetravalent conjugate 11 and biotin hydrazide 13 using TBTU strategy. In a solid-phase double sandwich enzyme linked immunosorbent assays (ELISA), biotinylated conjugate 14 was shown to bind to streptavidin used as a coating material. Mouse monoclonal anti T-Ag antibody (IgG3) and horseradish peroxydase-labeled goat anti mouse IgG, used for quantification, were found to bind T-Ag tetramer 14 immobilized on the surface of the streptavin layer. A typical saturation curve was observed for 14 while non-biotinylated tetramer 11 showed no binding in the entire concentration range. These results demonstrate the availability of both haptens toward the T-Ag antibody and streptavidin receptors.

Synthesis of N,N'-bis(acrylamido)acetic acid-based T-antigen glycodendrimers and their mouse monoclonal IgG antibody binding properties

Novel glycodendrimers based on N,N'-bis(acrylamido)acetic acid core with valencies between two and six were synthesized. The breast cancer-associated T-antigen carbohydrate marker, (beta-Gal-(1-3)-alpha-GalNAc-OR), was then conjugated by (i) 1,4-conjugate addition of thiolated T-antigen to the N-acrylamido dendritic cores and by (ii) amide bond formation between an acid derivative of the T-antigen and the polyamino dendrimers. The protein-binding ability of these new glycodendrimers was fully demonstrated by turbidimetric analysis and by enzyme-linked immunosorbent assay (ELISA) using peanut lectin from Arachis hypogaea and a mouse monoclonal antibody (MAb) FAA-J11 (IgG3). When tested as inhibitors of binding between MAb and a polymeric form of the T-antigen (T-antigen-co-polyacrylamide) used as a coating antigen, di- (17), tetra- (20), hexa- (21), and tetravalent (22) dendrimers showed IC(50) values of 174, 19, 48, and 18 nM, respectively. Two tetramers showed 120- to approximately 128-fold increased inhibitory properties over the monovalent antigen 6 used as a standard (IC(50) 2.3 mM). Heterobifunctional glycodendrimer bearing a biotin probe was also prepared for cancer cell labeling.

Chemoenzymatic synthesis of glycopolypeptides carrying alpha-Neu5Ac-(2-->3)-beta-D-Gal-(1-->3)-alpha-D-GalNAc, beta-D-Gal-(1-->3)-alpha-D-GalNAc, and related compounds and analysis of their specific interactions with lectins

Glycopolypeptide (1) carrying the beta-D-Gal-(1-->3)-alpha-D-GalNAc unit as a kind model of asialo-type mucin was synthesized through three steps: enzymatic synthesis of p-nitrophenyl disaccharide glycoside, reduction of the p-nitrophenyl group, and coupling of the amino group with the carboxyl group of poly(L-glutamic acid)s (PGA). In a similar manner, glycopolypeptides (2-7) carrying beta-D-Gal-(1-->3)-beta-D-GalNAc, beta-D-Gal-(1-->3)-beta-D-GlcNAc, beta-D-Gal-(1-->6)-alpha-D-GalNAc, beta-D-Gal-(1-->6)-beta-D-GalNAc, alpha-D-GalNAc, and beta-D-GalNAc, respectively, were synthesized as analogous polymers of polymer 1. Glycopolypeptides 8 and 9 as a mimic of sialo-type mucin were further prepared from polymers 1 and 2 as the acceptor of CMP-Neu5Ac by alpha2,3-(O)-sialyltransferase, respectively. Interactions of these glycopolypeptides with lectins were investigated with the double-diffusion test and the hemagglutination-inhibition assay and in terms of an optical biosensor based on surface plasmon resonance. Polymers 1 and 2 reacted strongly with peanut (Arachis hypogaea) agglutinin (PNA) and Agaricus bisporus agglutinin (ABA). On the other hand, polymers 8 and 9 through sialylation from polymers 1 and 2 reacted with ABA, but did not with PNA. Other polymers 3-7 did not show any reactivity for both the lectins. These results show that PNA acts precisely in an exo manner on the beta-D-Gal-(1-->3)-D-GalNAc sequence, while ABA acts in an endo manner. Polymers 6 and 7 substituted with GalNAc reacted strongly with soybean (Glycine max) agglutinin and Vicia villosa agglutinin B4, regardless of the configuration of the glycosidic linkage. The interaction of all polymers with Bauhinia purpurea agglutinin was much stronger than that of the corresponding sugars. Polymers 8 and 9 reacted with wheat germ (Triticum vulgaris) agglutinin (WGA), to which Neu5Ac residues are needed for binding, but polymers 1 and 2 did not. These sugar-substituted glycopolypeptides interacted specifically with the corresponding lectins. Furthermore, polymers 4-7 reacted with WGA, but the corresponding sugars did not. It suggests that the N-acetyl group along the PGA backbone has a cluster effect for WGA. The artificial glycopolypeptides were shown to be useful as tools and probes of carbohydrate recognition and modeling in the analysis of glycoprotein-lectin interactions.