Probing the Lactose·GM3 Carbohydrate−Carbohydrate Interaction with Glycodendrimers

Research Status of Dendrimer Micelles in Tumor Therapy for Drug Delivery

Dendrimers are a family of polymers with highly branched structure, well-defined composition, and extensive functional groups, which have attracted great attention in biomedical applications. Micelles formed by dendrimers are ideal nanocarriers for delivering anticancer agents due to the explicit study of their characteristics of particle size, charge, and biological properties such as toxicity, blood circulation time, biodistribution, and cellular internalization. Here, the classification, preparation, and structure of dendrimer micelles are reviewed, and the specific functional groups modified on the surface of dendrimers for tumor active targeting, stimuli-responsive drug release, reduced toxicity, and prolonged blood circulation time are discussed. In addition, their applications are summarized as various platforms for biomedical applications related to cancer therapy including drug delivery, gene transfection, nano-contrast for imaging, and combined therapy. Other applications such as tissue engineering and biosensor are also involved. Finally, the possible challenges and perspectives of dendrimer micelles for their further applications are discussed.

Potential Dental Biofilm Inhibitors: Dynamic Combinatorial Chemistry Affords Sugar-Based Molecules that Target Bacterial Glucosyltransferase

We applied dynamic combinatorial chemistry (DCC) to find novel ligands of the bacterial virulence factor glucosyltransferase (GTF) 180. GTFs are the major producers of extracellular polysaccharides, which are important factors in the initiation and development of cariogenic dental biofilms. Following a structure‐based strategy, we designed a series of 36 glucose‐ and maltose‐based acylhydrazones as substrate mimics. Synthesis of the required mono‐ and disaccharide‐based aldehydes set the stage for DCC experiments. Analysis of the dynamic combinatorial libraries (DCLs) by UPLC‐MS revealed major amplification of four compounds in the presence of GTF180. Moreover, we found that derivatives of the glucose‐acceptor maltose at the C1‐hydroxy group act as glucose‐donors and are cleaved by GTF180. The synthesized hits display medium to low binding affinity (K_D values of 0.4–10.0 mm) according to surface plasmon resonance. In addition, they were investigated for inhibitory activity in GTF‐activity assays. The early‐stage DCC study reveals that careful design of DCLs opens up easy access to a broad class of novel compounds that can be developed further as potential inhibitors.

Diversiform and Transformable Glyco-Nanostructures Constructed from Amphiphilic Supramolecular Metallocarbohydrates through Hierarchical Self-Assembly: The Balance between Metallacycles and Saccharides

During the past decade, self-assembly of saccharide-containing amphiphilic molecules toward bioinspired functional glycomaterials has attracted continuous attention due to their various applications in fundamental and practical areas. However, it still remains a great challenge to prepare hierarchical glycoassemblies with controllable and diversiform structures because of the complexity of saccharide structures and carbohydrate-carbohydrate interactions. Herein, through hierarchical self-assembly of modulated amphiphilic supramolecular metallocarbohydrates, we successfully prepared various well-defined glyco-nanostructures in aqueous solution, including vesicles, solid spheres, and opened vesicles depending on the molecular structures of metallocarbohydrates. More attractively, these glyco-nanostructures can further transform into other morphological structures in aqueous solutions such as worm-like micelles, tubules, and even tupanvirus-like vesicles (TVVs). It is worth mentioning that distinctive anisotropic structures including the opened vesicles (OVs) and TVVs were rarely reported in glycobased nano-objects. This intriguing diversity was mainly controlled by the subtle structural trade-off of the two major components of the amphiphiles, i.e., the saccharides and metallacycles. To further understand this precise structural control, molecular simulations provided deep physical insights on the morphology evolution and balancing of the contributions from saccharides and metallacycles. Moreover, the multivalency of glyco-nanostructures with different shapes and sizes was demonstrated by agglutination with a diversity of sugar-binding protein receptors such as the plant lectins Concanavalin A (ConA). This modular synthesis strategy provides access to systematic tuning of molecular structure and self-assembled architecture, which undoubtedly will broaden our horizons on the controllable fabrication of biomimetic glycomaterials such as biological membranes and supramolecular lectin inhibitors.

Self-assembly of bacteria cellulose hydrogels carrying multiple carbohydrate appendages to visualize carbohydrate-carbohydrate interactions

Nata de coco was chemically modified to afford the bacterial cellulose hydrogels carrying terminal alkynes. The resultant hydrogels were then converted into hydrogels carrying lactosides or those carrying α-2,3-sialyllactosides by the Cu⁺-catalyzed alkyne-azide cyclization. The stable homo association of the hydrogels carrying lactosides was observed in an aqueous solution containing Ca²⁺, thereby demonstrating the Ca²⁺-mediated lactoside-lactoside interactions. Ca²⁺ also stabilized the hetero associations among the hydrogels carrying lactosides and those carrying α-2,3-sialyllactosides, thereby also demonstrating the Ca²⁺-induced interactions between the lactosides and the α-2,3-sialyllactosides. The sizes of these hydrogels were of the order of ca. 5 mm, and their associations could thus be readily monitored with the naked eye.

Preparation of Non-Surface-Active Langmuir Trough Subphases from Milk

Milk polar lipid interfacial behavior continues to be analyzed using Langmuir trough experiments, but the reported Langmuir trough subphases commonly used are not fully representative of milk. A method to transform liquids of biological origin, such as milk, into appropriate Langmuir trough subphases does not currently exist, which hinders the applicability of Langmuir trough experiments to nature. Here, a procedure to manufacture milk-derived Langmuir trough subphases with insignificant amounts of surfactants from bovine milk is presented. Ultrafiltration is used to remove the bulk of protein surfactants from milk followed by the creation of solvent-induced emulsions that remove trace proteins and lipids from collected skim milk permeates. Change in surface tension upon compression of resulting washed permeates from the surfactant removal process was ≤0.1 mN/m, terming the permeates non-surface-active (NSA). NSA permeates (72.4 ± 0.2 mN/m) had a surface tension similar to that of ultrapure water (72.6 ± 0.1 mN/m), but their pH, conductivity, percent total solids, Brix percentage, alkalinity, and hardness were not the same, with NSA permeates being more compositionally similar to skim milk than water. The lift-off points of milk ganglioside GM3 monolayer surface pressure-area isotherms spread on NSA permeates and ultrapure water subphases were significantly different when compared for the same sample, indicating that surface tension measurements obtained on ultrapure water are not the same as with NSA milk permeate. Overall, surfactants were removed from bovine milk without the addition of exogenous compounds, allowing for the production of a NSA solution derived from milk that can be used in the Langmuir trough experiment to more realistically resemble the natural environment of milk polar lipids. The procedure described here was able to produce NSA solutions for other dairy beverages aside from milk, indicating that it can be applicable to other biological fluids.

Synthesis of Glycosylated Metal Complexes for Probing Carbohydrate-Carbohydrate Interactions

Densely packed carbohydrate clusters on cell surfaces play essential roles in varieties of bioprocesses. Little information has been, however, accumulated so far concerning their structural/functional details. In this chapter, we discuss artificial systems to investigate carbohydrate-carbohydrate interactions within/between the carbohydrate cluster(s). Among such artificial systems, much attention will be especially placed on glycosylated tris-bipyridine ferrous complexes for monitoring not only carbohydrate-carbohydrate interactions within the glycocluster but also their resultant conformational changes.

Synthesis and conformational analysis of poly(phenylacetylene)s with serinol-tethered carbohydrate appendages

We synthesized phenylacetylenes containing β-lactoside, β-cellobioside, or β-maltoside, and polymerized them to produce the corresponding poly (phenylacetylene)s. In these poly (phenylacetylene)s, the pendent carbohydrates were tethered to the mainchains by serinol spacers. Because similar glycosyl serinol units are found in the natural glycosphingolipids in cell membranes, the densely packed carbohydrate clusters along the poly (phenylacetylene) mainchains act as molecular mimics of cell surface glycoclusters. We analyzed the conformation of the glycosylated poly (phenylacetylene)s using circular dichroism spectroscopy, and found that the spatial carbohydrate packing within the glycoclusters changed on the addition of salts.

Triggerable Multivalent Glyconanoparticles for Probing Carbohydrate-Carbohydrate Interactions

Carbohydrate-carbohydrate interactions are proposed to be biologically significant but have lower affinities than the well-studied carbohydrate-protein interactions. Here we introduce multivalent glyconanostructures where the surface expression of lactose can be triggered by an external stimulus, and a gold nanoparticle core enables colorimetric signal outputs to probe binding. Macromolecular engineering of a responsive polymer "gate" enables the lactose moieties to be presented only when an external stimulus is present, mimicking how nature uses enzymes to dynamically regulate glycan expression. Two different carbohydrate-carbohydrate interactions are investigated using this tool.

Synthesis, characterization, optical and electrochemical properties and antibacterial activity of novel BODIPY glycoconjugated dendrimers

A new class of novel BODIPY glycoconjugated dendrimers with optical, electrochemical and antibacterial properties is reported.

Analysis of Carbohydrate-Carbohydrate Interactions Using Sugar-Functionalized Silicon Nanoparticles for Cell Imaging

Protein-carbohydrate binding depends on multivalent ligand display that is even more important for low affinity carbohydrate-carbohydrate interactions. Detection and analysis of these low affinity multivalent binding events are technically challenging. We describe the synthesis of dual-fluorescent sugar-capped silicon nanoparticles that proved to be an attractive tool for the analysis of low affinity interactions. These ultrasmall NPs with sizes of around 4 nm can be used for NMR quantification of coupled sugars. The silicon nanoparticles are employed to measure the interaction between the cancer-associated glycosphingolipids GM3 and Gg3 and the associated kD value by surface plasmon resonance experiments. Cell binding studies, to investigate the biological relevance of these carbohydrate-carbohydrate interactions, also benefit from these fluorescent sugar-capped nanoparticles.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Glycodendrimers and Modified ELISAs: Tools to Elucidate Multivalent Interactions of Galectins 1 and 3

Multivalent protein-carbohydrate interactions that are mediated by sugar-binding proteins, i.e., lectins, have been implicated in a myriad of intercellular recognition processes associated with tumor progression such as galectin-mediated cancer cellular migration/metastatic processes. Here, using a modified ELISA, we show that glycodendrimers bearing mixtures of galactosides, lactosides, and N-acetylgalactosaminosides, galectin-3 ligands, multivalently affect galectin-3 functions. We further demonstrate that lactose functionalized glycodendrimers multivalently bind a different member of the galectin family, i.e., galectin-1. In a modified ELISA, galectin-3 recruitment by glycodendrimers was shown to directly depend on the ratio of low to high affinity ligands on the dendrimers, with lactose-functionalized dendrimers having the highest activity and also binding well to galectin-1. The results depicted here indicate that synthetic multivalent systems and upfront assay formats will improve the understanding of the multivalent function of galectins during multivalent protein carbohydrate recognition/interaction.

Dendritic glycopolymers based on dendritic polyamine scaffolds: view on their synthetic approaches, characteristics and potential for biomedical applications

The potential of dendritic glycopolymers based on dendritic polyamine scaffolds for biomedical applications is presented and compared with that of the structurally related anti-adhesive dendritic glycoconjugates.

Synthesis, photophysical, electrochemical and laser properties of anthracene conjugated glycodendrimers with triazole as a bridging unit

Blue light emitting glycodendrimers 1, 2 and 3 were successfully synthesized by click reaction and the higher generation glycodendrimers showed enhanced optical, photophysical, laser and electrochemical properties.

Multivalent scaffolds induce galectin-3 aggregation into nanoparticles

Galectin-3 meditates cell surface glycoprotein clustering, cross linking, and lattice formation. In cancer biology, galectin-3 has been reported to play a role in aggregation processes that lead to tumor embolization and survival. Here, we show that lactose-functionalized dendrimers interact with galectin-3 in a multivalent fashion to form aggregates. The glycodendrimer–galectin aggregates were characterized by dynamic light scattering and fluorescence microscopy methodologies and were found to be discrete particles that increased in size as the dendrimer generation was increased. These results show that nucleated aggregation of galectin-3 can be regulated by the nucleating polymer and provide insights that improve the general understanding of the binding and function of sugar-binding proteins.

Role of galactosylceramide and sulfatide in oligodendrocytes and CNS myelin: formation of a glycosynapse

The two major glycosphingolipids of myelin, galactosylceramide (GalC) and sulfatide (SGC), interact with each other by trans carbohydrate-carbohydrate interactions in vitro. They face each other in the apposed extracellular surfaces of the multilayered myelin sheath produced by oligodendrocytes and could also contact each other between apposed oligodendrocyte processes. Multivalent galactose and sulfated galactose, in the form of GalC/SGC-containing liposomes or silica nanoparticles conjugated to galactose and galactose-3-sulfate, interact with GalC and SGC in the membrane sheets of oligodendrocytes in culture. This interaction causes transmembrane signaling, loss of the cytoskeleton and clustering of membrane domains, similar to the effects of cross-linking by anti-GalC and anti-SGC antibodies. These effects suggest that GalC and SGC could participate in glycosynapses, similar to neural synapses or the immunological synapse, between GSL-enriched membrane domains in apposed oligodendrocyte membranes or extracellular surfaces of mature myelin. Formation of such glycosynapses in vivo would be important for myelination and/or oligodendrocyte/myelin function.

Characterization of multivalent lactose quantum dots and its application in carbohydrate-protein interactions study and cell imaging

We have previously reported a facile and convenient method for the preparation of a new type of lactose-CdSeS/ZnS quantum dots conjugates (Lac-QDs) that exhibit biocompatibility, noncytotoxicity and specificity to leukocytes. In order to further study the carbohydrate-protein interactions, a series of Lac-QDs with different lactose densities and a PEGylated (n=3) lactose-QDs conjugate (LacPEG-QDs) with more flexible sugar ligands were prepared. The amount of the sugar molecules on QDs can be determined by NMR, which was in agreement with the results from TGA determination. The formula of the conjugates was determined with ICP-OES. The interactions between the conjugated QDs and the PNA protein were measured using SPR, which revealed that higher lactose density favored binding affinity under the same concentration, and Lac-QDs exhibit higher affinity than LacPEG-QDs. We further used a solid phase assay to assess the anti-adhesion activity of Lac-QDs and LacPEG-QDs on the cell level. The results showed that Lac-QDs had stronger activity in preventing THP1 from adhering to HUVEC than LacPEG-QDs, which was consistent with the SPR results. We reasoned that decrease in the conformational entropy induced by appropriate restriction of sugar flexibility could enhance the binding affinity of glyco-QDs, which implies that entropy change may be the main contributor to the interaction between high valent glyco-QDs and protein. The fabrication of lactose on QDs provides a fluorescent multivalent carbohydrate probe that can be used as mimics of glycoprotein for the study of carbohydrate-protein interactions and cell imaging.

Two-dimensional supramolecular assemblies involving neoglycoplipids: Self-organization and insertion properties into Langmuir monolayers

In nature, interfacial molecular recognition and chirality are of fundamental significance for the construction of biological assemblies. Lipid monolayers at liquid interface can be used as biomimetic models for studying molecular interactions in such assemblies. In this article, we will focus on the use of Langmuir monolayers for studying self-organization and insertion properties of several neoglycolipids. Two types of glycolipids have been considered, one in the context of the analysis of glycoconjugates of biological relevance, and one dealing with the ability of some glycoprobes to insert into a monolayer in relation with their efficiency for serving as membrane imaging systems.

Design and creativity in synthesis of multivalent neoglycoconjugates

From the authors' opinion, this chapter constitutes a modest extension of the seminal and inspiring contribution of Stowell and Lee on neoglycoconjugates published in this series [C. P. Stowell and Y. C. Lee, Adv. Carbohydr. Chem. Biochem., 37 (1980) 225-281]. The outstanding progresses achieved since then in the field of the "glycoside cluster effect" has witnessed considerable creativity in the design and synthetic strategies toward a vast array of novel carbohydrate structures and reflects the dynamic activity in the field even since the recent chapter by the Nicotra group in this series [F. Nicotra, L. Cipolla, F. Peri, B. La Ferla, and C. Radaelli, Adv. Carbohydr. Chem. Biochem., 61 (2007) 353-398]. Beyond the more classical neoglycoproteins and glycopolymers (not covered in this work) a wide range of unprecedented and often artistically beautiful multivalent and monodisperse nanostructures, termed glycodendrimers for the first time in 1993, has been created. This chapter briefly surveys the concept of multivalency involved in carbohydrate-protein interactions. The topic is also discussed in regard to recent steps undertaken in glycobiology toward identification of lead candidates using microarrays and modern analytical tools. A systematic description of glycocluster and glycodendrimer synthesis follows, starting from the simplest architectures and ending in the most complex ones. Presentation of multivalent glycostructures of intermediate size and comprising, calix[n]arene, porphyrin, cyclodextrin, peptide, and carbohydrate scaffolds, has also been intercalated to better appreciate the growing synthetic complexity involved. A subsection describing novel all-carbon-based glycoconjugates such as fullerenes and carbon nanotubes is inserted, followed by a promising strategy involving dendrons self-assembling around metal chelates. The chapter then ends with those glycodendrimers that have been prepared using commercially available dendrimers possessing varied functionalities, or systematically synthesized using either divergent or convergent strategies.