Chemoenzymatic Synthesis of Galectin Binding Glycopolymers

CUREs for high-level Galectin-3 expression

Galectins are a large and diverse protein family defined by the presence of a carbohydrate recognition domain (CRD) that binds β-galactosides. They play important roles in early development, tissue regeneration, immune homeostasis, pathogen recognition, and cancer. In many cases, studies that examine galectin biology and the effect of manipulating galectins are aided by, or require the ability to express and purify, specific members of the galectin family. In many cases, E. coli is employed as a heterologous expression system, and galectin expression is induced with isopropyl β-galactoside (IPTG). Here, we show that galectin-3 recognizes IPTG with micromolar affinity and that as IPTG induces expression, newly synthesized galectin can bind and sequester cytosolic IPTG, potentially repressing further expression. To circumvent this putative inhibitory feedback loop, we utilized an autoinduction protocol that lacks IPTG, leading to significantly increased yields of galectin-3. Much of this work was done within the context of a course-based undergraduate research experience, indicating the ease and reproducibility of the resulting expression and purification protocols.

Lactose-Functionalized Carbosilane Glycodendrimers Are Highly Potent Multivalent Ligands for Galectin-9 Binding: Increased Glycan Affinity to Galectins Correlates with Aggregation Behavior

Galectins, the glycan binding proteins, and their respective carbohydrate ligands represent a unique fundamental regulatory network modulating a plethora of biological processes. The advances in galectin-targeted therapy must be based on a deep understanding of the mechanism of ligand-protein recognition. Carbosilane dendrimers, the well-defined and finely tunable nanoscaffolds with low toxicity, are promising for multivalent carbohydrate ligand presentation to target galectin receptors. The study discloses a synthetic method for two types of lactose-functionalized carbosilane glycodendrimers (Lac-CS-DDMs). Furthermore, we report their outstanding, dendritic effect-driven affinity to tandem-type galectins, especially Gal-9. In the enzyme-linked immunosorbent assay, the affinity of the third-generation multivalent dendritic ligand bearing 32 lactose units to Gal-9 reached nanomolar values (IC50 = 970 nM), being a 1400-fold more effective inhibitor than monovalent lactose for this protein. This demonstrates a game-changing impact of multivalent presentation on the inhibitory effect of a ligand as simple as lactose. Moreover, using DLS hydrodynamic diameter measurements, we correlated the increased affinity of the glycodendrimer ligands to Gal-3 and Gal-8 but especially to Gal-9 with the formation of relatively uniform and stable galectin/Lac-CS-DDM aggregates.

Catanionic Vesicles as a Facile Scaffold to Display Natural N-Glycan Ligands for Probing Multivalent Carbohydrate-Lectin Interactions

Multivalent interactions are a key characteristic of protein-carbohydrate recognition. Phospholipid-based liposomes have been explored as a popular platform for multivalent presentation of glycans, but this platform has been plagued by the instability of typical liposomal formulations in biological media. We report here the exploitation of catanionic vesicles as a stable lipid-based nanoparticle scaffold for displaying large natural N-glycans as multivalent ligands. Hydrophobic insertion of lipidated N-glycans into the catanionic vesicle bilayer was optimized to allow for high-density display of structurally diverse N-glycans on the outer membrane leaflet. In an enzyme-linked competitive lectin-binding assay, the N-glycan-coated vesicles demonstrated a clear clustering glycoside effect, with significantly enhanced affinity for the corresponding lectins including Sambucus nigra agglutinin (SNA), concanavalin A (ConA), and human galectin-3, in comparison with their respective natural N-glycan ligands. Our results showed that relatively low density of high-mannose and sialylated complex type N-glycans gave the maximal clustering effect for binding to ConA and SNA, respectively, while relatively high-density display of the asialylated complex type N-glycan provided maximal clustering effects for binding to human galectin 3. Moreover, we also observed a macromolecular crowding effect on the binding of ConA to high-mannose N-glycans when catanionic vesicles bearing mixed high-mannose and complex-type N-glycans were used. The N-glycan-coated catanionic vesicles are stable and easy to formulate with varied density of ligands, which could serve as a feasible vehicle for drug delivery and as potent inhibitors for intervening protein-carbohydrate interactions implicated in disease.

Targeting galectin-driven regulatory circuits in cancer and fibrosis

Galectins are a family of endogenous glycan-binding proteins that have crucial roles in a broad range of physiological and pathological processes. As a group, these proteins use both extracellular and intracellular mechanisms as well as glycan-dependent and independent pathways to reprogramme the fate and function of numerous cell types. Given their multifunctional roles in both tissue fibrosis and cancer, galectins have been identified as potential therapeutic targets for these disorders. Here, we focus on the therapeutic relevance of galectins, particularly galectin 1 (GAL1), GAL3 and GAL9 to tumour progression and fibrotic diseases. We consider an array of galectin-targeted strategies, including small-molecule carbohydrate inhibitors, natural polysaccharides and their derivatives, peptides, peptidomimetics and biological agents (notably, neutralizing monoclonal antibodies and truncated galectins) and discuss their mechanisms of action, selectivity and therapeutic potential in preclinical models of fibrosis and cancer. We also review the results of clinical trials that aim to evaluate the efficacy of galectin inhibitors in patients with idiopathic pulmonary fibrosis, nonalcoholic steatohepatitis and cancer. The rapid pace of glycobiology research, combined with the acute need for drugs to alleviate fibrotic inflammation and overcome resistance to anticancer therapies, will accelerate the translation of anti-galectin therapeutics into clinical practice.

Advanced high-affinity glycoconjugate ligands of galectins

Galectins are proteins of the family of human lectins. By binding terminal galactose units of cell surface glycans, they moderate biological and pathological processes such as cell signaling, cell adhesion, apoptosis, fibrosis, carcinogenesis, and metabolic disorders. The binding of monovalent glycans to galectins is usually relatively weak. Therefore, the presentation of carbohydrate ligands on multivalent scaffolds can efficiently increase and/or discriminate the affinity of the glycoconjugate to different galectins. A library of glycoclusters and glycodendrimers with various structural presentations of the common functionalized N-acetyllactosamine ligand was prepared to evaluate how the mode of presentation affects the affinity and selectivity to the two most abundant galectins, galectin-1 (Gal-1) and galectin-3 (Gal-3). In addition, the effect of a one- to two-unit carbohydrate spacer on the affinity of the glycoconjugates was determined. A new design of the biolayer interferometry (BLI) method with specific AVI-tagged constructs was used to determine the affinity to galectins, and compared with the gold-standard method of isothermal titration calorimetry (ITC). This study reveals new routes to low nanomolar glycoconjugate inhibitors of galectins of interest for biomedical research.

Multivalent glycosystems for human lectins

Human lectins are involved in a wide variety of biological processes, both physiological and pathological, which have attracted the interest of the scientific community working in the glycoscience field. Multivalent glycosystems have been employed as useful tools to understand carbohydrate-lectin binding processes as well as for biomedical applications. The review shows the different scaffolds designed for a multivalent presentation of sugars and their corresponding binding studies to lectins and in some cases, their biological activities. We summarise this research by organizing based on lectin types to highlight the progression in this active field. The paper provides an overall picture of how these contributions have furnished relevant information on this topic to help in understanding and participate in these carbohydrate-lectin interactions.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Nanoparticles To Study Lectins in Caenorhabditis elegans: Multivalent Galactose β1-4 Fucose-Functionalized Dendrimers Provide Protection from Oxidative Stress

Galectins are galactoside-binding lectins that are functional dimers or higher-order oligomers. Multivalent binding has been shown to augment the relatively low affinity of the galectins for their galactoside-binding partners, enabling the galectins to play an important role in the global remodeling of cells that occurs during the stress conditions of disease states, including heart disease and cancer. The presence of galectins in the nematode Caenorhabditis elegans and their galactoside-binding properties have been demonstrated, but the role of multivalent interactions for C. elegans galectins is unknown. Here, we describe the synthesis of Galβ1-4Fuc-functionalized poly(amidoamine) dendrimers and their utility in studies using C. elegans during oxidative stress. C. elegans were fed Galβ1-4Fuc-functionalized dendrimers and RNA interference to knock down lectins lec-1 and lec-10 while undergoing oxidative stress. C. elegans that were pretreated with the glycodendrimers were less susceptible to oxidative stress than untreated controls. Worms that were fed fluorescently tagged glycodendrimers and imaged indicated that the dendrimers are primarily present in the digestive tract of the worms, and uptake into the vulva and proximal gonads could also be observed in some instances. This study suggests that multivalently presented Galβ1-4Fuc can protect C. elegans from oxidative stress.

Multivalent glycans for biological and biomedical applications

Recognition of glycans by proteins plays a crucial role in a variety of physiological processes in cells and living organisms. In addition, interactions of glycans with proteins are involved in the development of diverse diseases, such as pathogen infection, inflammation and tumor metastasis. It is well-known that multivalent glycans bind to proteins much more strongly than do their monomeric counterparts. Owing to this property, numerous multivalent glycans have been utilized to elucidate glycan-mediated biological processes and to discover glycan-based biomedical agents. In this review, we discuss recent advances (2014-2020) made in the development and biological and biomedical applications of synthetic multivalent glycans, including neoglycopeptides, neoglycoproteins, glycodendrimers, glycopolymers, glyconanoparticles and glycoliposomes. We hope this review assists researchers in the design and development of novel multivalent glycans with predictable activities.

Long-Term Retarded Release for the Proteasome Inhibitor Bortezomib through Temperature-Sensitive Dendritic Glycopolymers as Drug Delivery System from Calcium Phosphate Bone Cement

For the local treatment of bone defects, highly adaptable macromolecular architectures are still required as drug delivery system (DDS) in solid bone substitute materials. Novel DDS fabricated by host-guest interactions between β-cyclodextrin-modified dendritic glycopolymers and adamantane-modified temperature-sensitive polymers for the proteasome inhibitor bortezomib (BZM) is presented. These DDS induce a short- and long-term (up to two weeks) retarded release of BZM from calcium phosphate bone cement (CPC) in comparison to a burst release of the drug alone. Different release parameters of BZM/DDS/CPC are evaluated in phosphate buffer at 37 °C to further improve the long-term retarded release of BZM. This is achieved by increasing the amount of drug (50-100 µg) and/or DDS (100-400 µg) versus CPC (1 g), by adapting the complexes better to the porous bone cement environment, and by applying molar ratios of excess BZM toward DDS with 1:10, 1:25, and 1:100. The temperature-sensitive polymer shells of BZM/DDS complexes in CPC, which allow drug loading at room temperature but are collapsed at body temperature, support the retarding long-term release of BZM from DDS/CPC. Thus, the concept of temperature-sensitive DDS for BZM/DDS complexes in CPC works and matches key points for a local therapy of osteolytic bone lesions.

Immunoprotective neo-glycoproteins: Chemoenzymatic synthesis of multivalent glycomimetics for inhibition of cancer-related galectin-3

Galectin-3 plays a crucial role in cancerogenesis; its targeting is a prospective pathway in cancer diagnostics and therapy. Multivalent presentation of glycans was shown to strongly increase the affinity of glycoconjugates to galectin-3. Further strengthening of interaction with galectin-3 may be accomplished using artificial glycomimetics with apt aryl substitutions. We established a new, as yet undescribed chemoenzymatic method to produce selective C-3-substituted N,N'-diacetyllactosamine glycomimetics and coupled them to human serum albumin. From a library of enzymes, only β-N-acetylhexosaminidase from Talaromyces flavus was able to efficiently synthesize the C-3-propargylated disaccharide. Various aryl residues were attached to the functionalized N,N'-diacetyllactosamine via click chemistry to assess the impact of the aromatic substitution. In ELISA-type assays with galectin-3, free glycomimetics exhibited up to 43-fold stronger inhibitory potency to Gal-3 than the lactose standard. Coupling to human serum albumin afforded multivalent neo-glycoproteins with up to 4209-fold increased inhibitory potency per glycan compared to the monovalent lactose standard. Surface plasmon resonance brought further information on the kinetics of galectin-3 inhibition. The potential of prepared neo-glycoproteins to target galectin-3 was demonstrated on colorectal adenocarcinoma DLD-1 cells. We investigated the uptake of neo-glycoproteins into cells and observed limited non-specific transport into the cytoplasm. Therefore, neo-glycoproteins primarily act as efficient scavengers of exogenous galectin-3 of cancer cells, inhibiting its interaction with the cell surface, and protecting T-lymphocytes against galectin-3-induced apoptosis. The present neo-glycoproteins combine the advantage of a straightforward synthesis, selectivity, non-toxicity, and high efficiency for targeting exogenous galectin-3, with possible application in the immunomodulatory treatment of galectin-3-overexpressing cancers.

Synthesis and Biopharmaceutical Applications of Sugar-Based Polymers: New Advances and Future Prospects

The rapid rise in research interest in carbohydrate-based polymers is undoubtedly due to the nontoxic nature of such materials in an in vivo environment and the versatile roles that the polymers can play in cellular functions. Such polymers have served as therapeutic tools for drug delivery, including antigens, proteins, and genes, as well as diagnostic devices. Our focus in the first half of this Review is on synthetic methods based on ring-opening polymerization and enzyme-catalyzed polymerization, along with controlled radical polymerization. In the second half of this Review, sugar-based polymers are discussed on the basis of their remarkable success in competitive receptor binding, as multifunctional nanocarriers of targeting inhibitors for cancer treatment, in genome-editing delivery, in immunotherapy based on endogenous antibody recruitment, and in treatment of respiratory diseases, including influenza A. Particular emphasis is put on the synthesis and biopharmaceutical applications of sugar-based polymers published in the most recent 5 years. A noticeable attribute of carbohydrate-based polymers is that the sugar-receptor interactions can be facilitated by the cooperative effect of multiple sugar units. Their diversified topology and structures will drive the development of new synthetic strategies and bring about important applications, including coronavirus-related drug therapy.

Synthesis of Galectin Inhibitors by Regioselective 3'-O-Sulfation of Vanillin Lactosides Obtained under Phase Transfer Catalysis

Vanillin-based lactoside derivatives were synthetized using phase-transfer catalyzed reactions from per-O-acetylated lactosyl bromide. The aldehyde group of the vanillin moiety was then modified to generate a series of related analogs having variable functionalities in the para- position of the aromatic residue. The corresponding unprotected lactosides, obtained by Zemplén transesterification, were regioselectively 3'-O-sulfated using tin chemistry activation followed by treatment with sulfur trioxide-trimethylamine complex (Men3N-SO3). Additional derivatives were also prepared from the vanillin's aldehyde using a Knoevenagel reaction to provide extended α, β-unsaturated carboxylic acid which was next reduced to the saturated counterpart.

Time-Dependent Fluorescence Spectroscopy to Quantify Complex Binding Interactions

Measuring the binding affinity for proteins that can aggregate or undergo complex binding motifs presents a variety of challenges. In this study, fluorescence lifetime measurements using intrinsic tryptophan fluorescence were performed to address these challenges and to quantify the binding of a series of carbohydrates and carbohydrate-functionalized dendrimers to recombinant human galectin-3. Collectively, galectins represent an important target for study; in particular, galectin-3 plays a variety of roles in cancer biology. Galectin-3 binding dissociation constants (K D) were quantified: lactoside (73 ± 4 μM), methyllactoside (54 ± 10 μM), and lactoside-functionalized G(2), G(4), and G(6)-PAMAM dendrimers (120 ± 58 μM, 100 ± 45 μM, and 130 ± 25 μM, respectively). The chosen examples showcase the widespread utility of time-dependent fluorescence spectroscopy for determining binding constants, including interactions for which standard methods have significant limitations.

Sequence-Defined Heteromultivalent Precision Glycomacromolecules Bearing Sulfonated/Sulfated Nonglycosidic Moieties Preferentially Bind Galectin-3 and Delay Wound Healing of a Galectin-3 Positive Tumor Cell Line in an In Vitro Wound Scratch Assay

Within this work, a new class of sequence-defined heteromultivalent glycomacromolecules bearing lactose residues and nonglycosidic motifs for probing glycoconjugate recognition in carbohydrate recognition domain (CRD) of galectin-3 is presented. Galectins, a family of β-galactoside-binding proteins, are known to play crucial roles in different signaling pathways involved in tumor biology. Thus, research has focused on the design and synthesis of galectin-targeting ligands for use as diagnostic markers or potential therapeutics. Heteromultivalent precision glycomacromolecules have the potential to serve as ligands for galectins. In this work, multivalency and the introduction of nonglycosidic motifs bearing either neutral, amine, or sulfonated/sulfated groups are used to better understand binding in the galectin-3 CRD. Enzyme-linked immunosorbent assays and surface plasmon resonance studies are performed, revealing a positive impact of the sulfonated/sulfated nonglycosidic motifs on galectin-3 binding but not on galectin-1 binding. Selected compounds are then tested with galectin-3 positive MCF 7 breast cancer cells using an in vitro would scratch assay. Preliminary results demonstrate a differential biological effect on MCF 7 cells with high galectin-3 expression in comparison to an HEK 293 control with low galectin-3 expression, indicating the potential for sulfonated/sulfated heteromultivalent glycomacromolecules to serve as preferential ligands for galectin-3 targeting.

Glycopolymers for Efficient Inhibition of Galectin-3: In Vitro Proof of Efficacy Using Suppression of T Lymphocyte Apoptosis and Tumor Cell Migration

The development of efficient galectin-3 (Gal-3) inhibitors draws attention in the field of anti-cancer therapy, especially due to the prominent role of extra- and intracellular Gal-3 in vital processes of cancerogenesis, such as immunosuppression, stimulation of tumor cells proliferation, survival, invasion, apoptotic resistance, and metastasis formation and progression. Here, by combining poly-LacNAc (Galβ4GlcNAc)-derived oligosaccharides with N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers, we synthesized multivalent glycopolymer inhibitors with a high potential to target extracellular and intracellular Gal-3. The inhibitory capabilities of the best conjugate in the studied series were in the nanomolar range proving the excellent Gal-3 inhibitory potential. Moreover, thorough investigation of the inhibitory effect in the biological conditions showed that the glycopolymers strongly inhibited Gal-3-induced apoptosis of T lymphocytes and suppressed migration and spreading of colorectal, breast, melanoma, and prostate cancer cells. In sum, the strong inhibitory activity toward Gal-3, combined with favorable pharmacokinetics of HPMA copolymers ensuring enhanced tumor accumulation via the enhanced permeability and retention effect, nominate the glycopolymers containing LacdiNAc-LacNAc (GalNAcβ4GlcNAcβ3Galβ4GlcNAc) tetrasaccharide as promising tools for preclinical in anti-cancer therapy evaluation.

Protein Aggregation Nucleated by Functionalized Dendritic Polyglycerols

Dendritic polyglycerols (dPGs) are emerging as important polymers for the study of biological processes due to their relatively low toxicity and excellent biocompatibility. The highly branched nature and high density of endgroups make the dPGs particularly attractive frameworks for the study of multivalent interactions such as multivalent protein-carbohydrate interactions. Here, we report the synthesis of a series of lactose functionalized dPGs with different hydrodynamic radii. A series of lactose functionalized dPGs bearing different densities of lactose functional groups was also synthesized. These lactose functionalized dPGs were used to study the templated aggregation of galectin-3, a galactoside binding protein that is overexpressed during many processes involved in cancer progression. Dynamic light scattering measurements revealed a direct correlation between the hydrodynamic radii of the lactose functionalized dPGs and the size of the galectin-3/lactose functionalized dPG aggregates formed upon mixing the lactose functionalized dPGs with galectin-3 in solution. These studies exposed the critical role of galectin-3's N-terminal domain in formation of galectin-3 multimers and also enabled comparisons of polymer templated aggregation using nonspecific interactions versus specific protein-carbohydrate binding interactions.