Selectinminus signCarbohydrate Interactions: From Natural Ligands to Designed Mimics

Growing impact of sialic acid-containing glycans in future drug discovery

In nature, almost all cells are covered with a complex array of glycan chain namely sialic acids or nuraminic acids, a negatively charged nine carbon sugars which is considered for their great therapeutic importance since long back. Owing to its presence at the terminal end of lipid bilayer (commonly known as terminal sugars), the well-defined sialosides or sialoconjugates have served pivotal role on the cell surfaces and thus, the sialic acid-containing glycans can modulate and mediate a number of imperative cellular interactions. Understanding of the sialo-protein interaction and their roles in vertebrates in regard of normal physiology, pathological variance, and evolution has indeed a noteworthy journey in medicine. In this tutorial review, we present a concise overview about the structure, linkages in chemical diversity, biological significance followed by chemical and enzymatic modification/synthesis of sialic acid containing glycans. A more focus is attempted about the recent advances, opportunity, and more over growing impact of sialosides and sialoconjugates in future drug discovery and development.

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.

Carbohydrate-based drugs launched during 2000-2021

Carbohydrates are fundamental molecules involved in nearly all aspects of lives, such as being involved in formating the genetic and energy materials, supporting the structure of organisms, constituting invasion and host defense systems, and forming antibiotics secondary metabolites. The naturally occurring carbohydrates and their derivatives have been extensively studied as therapeutic agents for the treatment of various diseases. During 2000 to 2021, totally 54 carbohydrate-based drugs which contain carbohydrate moities as the major structural units have been approved as drugs or diagnostic agents. Here we provide a comprehensive review on the chemical structures, activities, and clinical trial results of these carbohydrate-based drugs, which are categorized by their indications into antiviral drugs, antibacterial/antiparasitic drugs, anticancer drugs, antidiabetics drugs, cardiovascular drugs, nervous system drugs, and other agents.

Supramolecular polymerization of sulfated dendritic peptide amphiphiles into multivalent L-selectin binders

The synthesis of a sulfate-modified dendritic peptide amphiphile and its self-assembly into one-dimensional rod-like architectures in aqueous medium is reported. The influence of the ionic strength on the supramolecular polymerization was probed via circular dichroism spectroscopy and cryogenic transmission electron microscopy. Physiological salt concentrations efficiently screen the charges of the dendritic building block equipped with eight sulfate groups and trigger the formation of rigid supramolecular polymers. Since multivalent sulfated supramolecular structures mimic naturally occurring L-selectin ligands, the corresponding affinity was evaluated using a competitive SPR binding assay and benchmarked to an ethylene glycol-decorated supramolecular polymer.

Quantification of binding affinity of glyconanomaterials with lectins

Carbohydrate-mediated interactions are involved in many cellular activities including immune responses and infections. These interactions are relatively weak, and as such, cells employ multivalency, i.e., the presentation of multiple monovalent carbohydrate ligands within a close proximity, for cooperative binding thus drastically enhanced binding affinity. In the past two decades, the field of glyconanomaterials has emerged where nanomaterials are used as multivalent scaffolds to present multiple copies of carbohydrate ligands on the nanomaterial surface. At the core of glyconanomaterial research is the ability to control and modulate multivalency through ligand display. For the quantitative evaluation of multivalency, the binding affinity must be determined. Quantification of the binding parameters provides insights for not only the fundamental glyconanomaterial-lectin interactions, but also the rational design of effective diagnostics and therapeutics. Several methods have been developed to determine the binding affinity of glyconanomaterials with lectins, including fluorescence competitive assays in solution or on microarrays, Förster resonance energy transfer, fluorescence quenching, isothermal titration calorimetry, surface plasmon resonance spectroscopy, quartz crystal microbalance and dynamic light scattering. This Feature Article discusses each of these techniques, as well as how each technique is applied to determine the binding affinity of glyconanomaterials with lectins, and the data analysis. Although the results differed depending on the specific method used, collectively, they showed that nanomaterials as multivalent scaffolds could amplify the binding affinity of carbohydrate-lectin interactions by several orders of magnitude, the extent of which depending on the structure of the carbohydrate ligand, the ligand density, the linker length and the particle size.

Receptor targeting drug delivery strategies and prospects in the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA), a chronic inflammatory disease, is characterized by cartilage damage, bone tissue destruction, morphological changes in synovial fluids, and synovial joint inflammation. The inflamed synovial tissue has potential for passive and active targeting because of enhanced permeability and retention effect and the existence of RA synovial macrophages and fibroblasts that selectively express surface receptors such as folate receptor β, CD44 and integrin αVβ. Although there are numerous interventions in RA treatment, they are not safe and effective. Therefore, it is important to develop new drug or drug delivery systems that specifically targets inflamed/swollen joints but attenuates other possible damages to healthy tissues. Recently some receptors such as toll-like receptors (TLRs), the nucleotide-binding oligomerization domain-like receptors, and Fc-γ receptor have been identified in synovial tissue and immune cells that are involved in induction or suppression of arthritis. Analysis of the TLR pathway has moreover suggested new insights into the pathogenesis of RA. In the present paper, we have reviewed drug delivery strategies based on receptor targeting with novel ligand-anchored carriers exploiting CD44, folate and integrin αVβ as well as TLRs expressed on synovial monocytes and macrophages and antigen presenting cells, for possible active targeting in RA. TLRs could not only open a new horizon for developing new drugs but also their antagonists or humanized monoclonal antibodies that block TLRS specially TLR4 and TLR9 signaling could be used as targeting agents to antigen presenting cells and dendritic cells. As a conclusion, common conventional receptors and multifunctional ligands that arte involved in targeting receptors or developing nanocarriers with appropriate ligands for TLRs can provide profoundly targeting drug delivery systems for the effective treatment of RA.

Synthesis of Sialyl LewisX Glycomimetics Bearing a Bicyclic 3- O,4- C-Fused Galactopyranoside Scaffold

Reported herein is the synthesis of sialyl Lewis^X analogues bearing a trans-bicyclo[4.4.0] dioxadecane-modified 3- O,4- C-fused galactopyranoside scaffold that locks the carboxylate pharmacophore in either the axial or equatorial position. This novel series of bicyclic galactopyranosides are prepared through a stereocontrolled intramolecular cyclization reaction that has been evaluated both experimentally and by density functional theory calculations. The cyclization precursors are obtained from β-d-galactose pentaacetate in a nine-step sequence featuring a highly diastereoselective equatorial alkynylation and Cu(I) catalyzed formation of the acetylenic α-ketoester moiety. Preliminary biological evaluations indicate improved activity as P-selectin antagonists for the axially configured analogues as compared to their equatorial counterparts.

Identification of two highly promiscuous thermostable sugar nucleotidylyltransferases for glycorandomization

Glycorandomization is a process that improves the efficacy of glycoconjugates by the addition of a diverse array of sugars to secondary metabolites and antibiotics of pharmaceutical importance. This process, which employs sugar nucleotidylyltransferases (SNTs) and glycosyl transferases (GTs) in tandem, would benefit by the employment of promiscuous enzymes, i.e. those with the ability to utilize diverse noncanonical substrates. As promiscuous GTs are available, here we set out to identify promiscuous SNTs. For this, we began with a detailed family-wide characterization of SNTs. Earlier, we had proposed that SNTs could be classified into two major groups - I and II. They share a common structural framework and utilize a similar catalytic mechanism. Subtle variations in the way two magnesium ions - MgA2+ and MgB2+ - are stabilized by metal ion coordination motifs led to their classification into diverse subgroups viz. I-A, I-B, I-C, II-A, and II-B. Based on this classification, here we investigate promiscuity across the entire family of SNTs. We study the utilization of several sugar phosphates and nucleotides by the various subgroups of SNTs to understand substrate specificity and promiscuity in these. We find that promiscuity is prevalent among SNTs; and in particular, in the thermophilic homologs. In principle, promiscuity profiling identified four new SNTs that can be employed for the production of sugar-nucleotide libraries. However, assaying for their ability to simultaneously utilize multiple substrates in a single-pot reaction, we find two thermophilic SNTs- TM^GA , an adenylyltransferase from Thermotoga maritima and PH^GT , a thymidylyltransferase from Pyrococcus horikoshii that are readily employable for the production of diverse sugar-nucleotides.

A toolbox approach for multivalent presentation of ligand-receptor recognition on a supramolecular scaffold

A supramolecular toolbox approach for multivalent ligand-receptor recognition was established based on β-cyclodextrin vesicles (CDVs). A series of bifunctional ligands for CDVs was synthesised. These ligands comprise on one side adamantane, enabling the functionalisation of CDVs with these ligands, and either mannose or sulphate group moieties on the other side for biological receptor recognition. The physicochemical properties of the host-guest complexes formed by β-cyclodextrin (β-CD) and adamantane were determined by isothermal titration calorimetry (ITC). Ligand-lectin interactions were investigated by surface plasmon resonance experiments (SPR) for the mannose ligands and the lectin Concanavalin A (ConA). Microscale thermophoresis (MST) measurements were applied for sulphate-dependent binding to L-selectin. In both cases, a multivalent affinity enhancement became apparent when the ligands were presented on the CDV scaffold. Furthermore, not only the clustering between our supramolecular mannosylated complex and Escherichia coli (E. coli), expressing the lectin FimH, was visualised by cryo-TEM, but also the competitive character to detach bound E. coli from a cell line, representing the uroepithelial cell surface, was demonstrated. In summary, a facile and effective supramolecular toolbox was established for various ligand-receptor recognition applications.

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

In order to translate nanotechnology into medical practice, magnetic nanoparticles (MNPs) have been presented as a class of non-invasive nanomaterials for numerous biomedical applications. In particular, MNPs have opened a door for simultaneous diagnosis and brisk treatment of diseases in the form of theranostic agents. This review highlights the recent advances in preparation and utilization of MNPs from the synthesis and functionalization steps to the final design consideration in evading the body immune system for therapeutic and diagnostic applications with addressing the most recent examples of the literature in each section. This study provides a conceptual framework of a wide range of synthetic routes classified mainly as wet chemistry, state-of-the-art microfluidic reactors, and biogenic routes, along with the most popular coating materials to stabilize resultant MNPs. Additionally, key aspects of prolonging the half-life of MNPs via overcoming the sequential biological barriers are covered through unraveling the biophysical interactions at the bio-nano interface and giving a set of criteria to efficiently modulate MNPs' physicochemical properties. Furthermore, concepts of passive and active targeting for successful cell internalization, by respectively exploiting the unique properties of cancers and novel targeting ligands are described in detail. Finally, this study extensively covers the recent developments in magnetic drug targeting and hyperthermia as therapeutic applications of MNPs. In addition, multi-modal imaging via fusion of magnetic resonance imaging, and also innovative magnetic particle imaging with other imaging techniques for early diagnosis of diseases are extensively provided.

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

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

Heparin Mimetics: Their Therapeutic Potential

Heparin mimetics are synthetic and semi-synthetic compounds that are highly sulfated, structurally distinct analogues of glycosaminoglycans. These mimetics are often rationally designed to increase potency and binding selectivity towards specific proteins involved in disease manifestations. Some of the major therapeutic arenas towards which heparin mimetics are targeted include: coagulation and thrombosis, cancers, and inflammatory diseases. Although Fondaparinux, a rationally designed heparin mimetic, is now approved for prophylaxis and treatment of venous thromboembolism, the search for novel anticoagulant heparin mimetics with increased affinity and fewer side effects remains a subject of research. However, increasingly, research is focusing on the non-anticoagulant activities of these molecules. Heparin mimetics have potential as anti-cancer agents due to their ability to: (1) inhibit heparanase, an endoglycosidase which facilitates the spread of tumor cells; and (2) inhibit angiogenesis by binding to growth factors. The heparin mimetic, PI-88 is in clinical trials for post-surgical hepatocellular carcinoma and advanced melanoma. The anti-inflammatory properties of heparin mimetics have primarily been attributed to their ability to interact with: complement system proteins, selectins and chemokines; each of which function differently to facilitate inflammation. The efficacy of low/non-anticoagulant heparin mimetics in animal models of different inflammatory diseases has been demonstrated. These findings, plus clinical data that indicates heparin has anti-inflammatory activity, will raise the momentum for developing heparin mimetics as a new class of therapeutic agent for inflammatory diseases.

Synthesis of 1D-glyconanomaterials by a hybrid noncovalent-covalent functionalization of single wall carbon nanotubes: a study of their selective interactions with lectins and with live cells

To take full advantage of the remarkable applications of carbon nanotubes in different fields, there is a need to develop effective methods to improve their water dispersion and biocompatibility while maintaining their physical properties. In this sense, current approaches suffer from serious drawbacks such as loss of electronic structure together with low surface coverage in the case of covalent functionalizations, or instability of the dynamic hybrids obtained by non-covalent functionalizations. In the present work, we examined the molecular basis of an original strategy that combines the advantages of both functionalizations without their main drawbacks. The hierarchical self-assembly of diacetylenic-based neoglycolipids into highly organized and compacted rings around the nanotubes, followed by photopolymerization leads to the formation of nanotubes covered with glyconanorings with a shish kebab-type topology exposing the carbohydrate ligands to the water phase in a multivalent fashion. The glyconanotubes obtained are fully functional, and able to establish specific interactions with their cognate receptors. In fact, by taking advantage of this selective binding, an easy method to sense lectins as a working model of toxin detection was developed based on a simple analysis of TEM images. Remarkably, different experimental settings to assess cell membrane integrity, cell growth kinetics and cell cycle demonstrated the cellular biocompatibility of the sugar-coated carbon nanotubes compared to pristine single-walled carbon nanotubes.

Synthesis of Carbohydrate Capped Silicon Nanoparticles and their Reduced Cytotoxicity, In Vivo Toxicity, and Cellular Uptake

The development of smart targeted nanoparticles (NPs) that can identify and deliver drugs at a sustained rate directly to cancer cells may provide better efficacy and lower toxicity for treating primary and advanced metastatic tumors. Obtaining knowledge of the diseases at the molecular level can facilitate the identification of biological targets. In particular, carbohydrate-mediated molecular recognitions using nano-vehicles are likely to increasingly affect cancer treatment methods, opening a new area in biomedical applications. Here, silicon NPs (SiNPs) capped with carbohydrates including galactose, glucose, mannose, and lactose are successfully synthesized from amine terminated SiNPs. The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] analysis shows an extensive reduction in toxicity of SiNPs by functionalizing with carbohydrate moiety both in vitro and in vivo. Cellular uptake is investigated with flow cytometry and confocal fluorescence microscope. The results show the carbohydrate capped SiNPs can be internalized in the cells within 24 h of incubation, and can be taken up more readily by cancer cells than noncancerous cells. Moreover, these results reinforce the use of carbohydrates for the internalization of a variety of similar compounds into cancer cells.

Discrete multiporphyrin pseudorotaxane assemblies from di- and tetravalent porphyrin building blocks

Two pairs of divalent and tetravalent porphyrin building blocks carrying the complementary supramolecular crown ether/secondary ammonium ion binding motif have been synthesized and their derived pseudorotaxanes have been studied by a combination of NMR spectroscopy in solution and ESI mass spectrometry in the gas phase. By simple mixing of the components the formation of discrete dimeric and trimeric (metallo)porphyrin complexes predominates, in accordance to binding stoichiometry, while the amount of alternative structures can be neglected. Our results illustrate the power of multivalency to program the multicomponent self-assembly of specific entities into discrete functional nanostructures.

Sulfonated Polyethylenimine for Photosensitizer Conjugation and Targeting

Polysulfonated macromolecules are known to bind selectins, adhesion membrane proteins which are broadly implicated in inflammation. Commercially available branched polyethylenimine (PEI) was reacted with chlorosulfonic acid to generate sulfonated PEI with varying degrees of sulfonation. Remaining unreacted amine groups were then used for straightforward conjugation with pyropheophoribide-a, a near-infrared photosensitizer. Photosensitizer-labeled sulfonated PEI conjugates inhibited blood coagulation and were demonstrated to specifically bind to cells genetically programmed to overexpress L-selectin (CD62L) or P-selectin (CD62P). In vitro, following targeting, selectin-expressing cells could be destroyed via photodynamic therapy.

Recent Developments in Synthetic Carbohydrate-Based Diagnostics, Vaccines, and Therapeutics

Glycans are everywhere in biological systems, being involved in many cellular events with important implications for medical purposes. Building upon a detailed understanding of the functional roles of carbohydrates in molecular recognition processes and disease states, glycans are increasingly being considered as key players in pharmacological research. On the basis of the important progress recently made in glycochemistry, glycobiology, and glycomedicine, we provide a complete overview of successful applications and future perspectives of carbohydrates in the biopharmaceutical and medical fields. This review highlights the development of carbohydrate-based diagnostics, exemplified by glycan imaging techniques and microarray platforms, synthetic oligosaccharide vaccines against infectious diseases (e.g., HIV) and cancer, and finally carbohydrate-derived therapeutics, including glycomimetic drugs and glycoproteins.

Sequential one-pot multienzyme (OPME) synthesis of lacto-N-neotetraose and its sialyl and fucosyl derivatives

A highly efficient sequential one-pot multienzyme (OPME) approach for the synthesis of lacto-N-neotetraose (LNnT) and its derivatives at preparative scale was reported.

Total synthesis of trifluorobutyryl-modified, globally protected sialyl Lewis x by a convergent [2+2] approach

Structural and quantitative changes in the expression of sialic acid residues on the surface of eukaryotic cells profoundly influence a broad range of biological processes including inflammation, antigen recognition, microbial attachment, and tumor metastasis. Uptake and incorporation of sialic acid analogues in mammalian cells enable structure-function studies and perturbation of specific recognition events. Our group has recently shown that a trifluorobutyryl-modified sialic acid metabolite diminishes the adhesion of mammalian cells to E and P-selectin, presumably by leading to the expression of fluorinated sLex epitopes on cell surfaces, and interfering with the sLex-selectin interactions that are well known in mediating tumor cell migration.1 For studies directed towards understanding the molecular basis of this reduced adhesion, chemical synthesis of trifluorobutyrylated sialyl Lewis x (C4F3--sLex) was crucial. We have developed a highly efficient [2+2] approach for the assembly of C4F3-sLex on a preparative scale that contains versatile protective groups allowing the glycan to be surface immobilized or solubilized as needed for biophysical studies to investigate selectin interactions. This strategy can, in principle, be used for preparation of other N-modified sLex analogues.

Preparation of biointeractive glycoprotein-conjugated hydrogels through metabolic oligosacchalide engineering

In the current study, synthetic hydrogels containing metabolically engineered glycoproteins of mammalian cells were prepared for the first time and selectin-mediated cell adhesion on the hydrogel was demonstrated. A culture of HL-60 cells was supplemented with an appropriate volume of aqueous solution of N-methacryloyl mannosamine (ManMA) to give a final concentration of 5 mM. The cells were then incubated for 3 days to deliver methacryloyl groups to the glycoproteins of the cells. A transparent hydrogel was formed via redox radical polymerization of methacryloyl functionalized glycoproteins with 2-methacryloyloxyethyl phosphorylcholine and a cross-linker. Conjugation of the glycoproteins into the hydrogel was determined using Coomassie brilliant blue (CBB) and periodic acid-Schiff (PAS) staining. The surface density of P-selectin glycoprotein ligand-1 (PSGL-1) on the hydrogels was also detected using gold-colloid-labeled immunoassay. Finally, selectin-mediated cell adhesion on hydrogels containing glycoproteins was demonstrated. Selectin-mediated cell adhesion is considered an essential step in the progression of various diseases; therefore, hydrogels having glycoproteins could be useful in therapeutic and diagnostic applications.

Chemoenzymatic synthesis of functional sialyl Lewis(x) mimetics with a heteroaromatic core

Functional mimetics of the sialyl Lewis(X) tetrasaccharide were prepared by the enzymatic sialylation of a 1,3-diglycosylated indole and a glycosyl azide, which was subsequently transformed into a 1,4-diglycosylated 1,2,3-triazole, by using the trans-sialidase of Trypanosoma cruzi. These compounds inhibited the binding of E-, L-, and P-selectin-coated nanoparticles to polyacrylamide-bound sialyl-Lewis(X) -containing neighboring sulfated tyrosine residues (sTyr/sLe(X) -PAA) at low or sub-millimolar concentrations. Except for E-selectin, the mimetics showed higher activities than the natural tetrasaccharide.

d-Glucose based bisacrylamide crosslinker: synthesis and study of homogeneous biocompatible glycopolymeric hydrogels

The ability of sugar pendants in glycopolymeric hydrogels to mimic that on the cell surface can be used as a reliable method for the site specific delivery of drugs.

Simultaneous determination of concanavalin A and peanut agglutinin by dual-color quantum dots

In this work, we designed a novel detection strategy to realize simultaneous determination of multiplex lectin by labeling glucosamine (G1) and galactosamine (G2) with different-colored semiconductor quantum dots (QDs). On the basis of the agglutination of the aminosugar-labeled QDs induced by the exclusive binding between the lectin and sugar on the QDs surfaces, the fluorescence emission of the QDs supernatant after centrifugation decreased with relevant lectin concentration [i.e., when concanavalin A (Con A) exists alone], only green color fluorescence emission from QDs-G1 supernatant decreased, so it is peanut agglutinin (PNA) and red color fluorescence emission from QDs-G2. Moreover, since QDs can be simultaneously excited with multiple fluorescence colors and have a larger Stokes shift than organic fluorophores, when both Con A and PNA are present in the sample, both of the green and red color fluorescence emission from QDs-G1 and QDs-G2 supernatant would decrease, thus realizing the simultaneous determination of Con A and PNA. The detection limits of Con A and PNA are 0.30 and 0.18 nM (3σ), respectively. Furthermore, the present detection method not only can determine the protein/lectins by fluorescence spectral method but also can realize visualization detection by UV lamp illumination. To the best of our knowledge, this is the first report of such analytical method in multiple and simultaneous lectin detection.

Avidity modulation of folate-targeted multivalent dendrimers for evaluating biophysical models of cancer targeting nanoparticles

We investigated two types of generation 5 polyamidoamine (PAMAM) dendrimers, each conjugated stochastically with a mean number of 5 or 10 methotrexate (MTX) ligands per dendrimer (G5-MTX5, G5-MTX10), for their binding to surface-immobilized folate binding protein (FBP) as a function of receptor density. The binding study was performed under flow by surface plasmon resonance spectroscopy. Two multivalent models were examined to simulate binding of the dendrimer to the receptor surface, showing that at relatively high receptor density, both dendrimer conjugates exhibit high avidity. However, upon reducing the receptor density by a factor of 3 and 13 relative to the high density level, the avidity of the lower-valent G5-MTX5 decreases by up to several orders of magnitude (KD = nM to μM), whereas the avidity of G5-MTX10 remains largely unaffected regardless of the density variation. Notably, on the 13-fold reduced FBP surface, G5-MTX5 displays binding kinetics similar to that of monovalent methotrexate, which is patently different from the still tight binding of the higher-valent G5-MTX10. Thus, the binding analysis demonstrates that avidity displayed by multivalent MTX conjugates varies in response to the receptor density and can be modulated for achieving tighter, more specific binding to the higher receptor density by modulation of ligand valency. We believe this study provides experimental evidence supportive of the mechanistic hypothesis of multivalent NP uptake to a cancer cell over a healthy cell where the diseased cell expresses the folate receptor at higher density.

Stabilization of branched oligosaccharides: Lewis(x) benefits from a nonconventional C-H···O hydrogen bond

Although animal lectins usually show a high degree of specificity for glycan structures, their single-site binding affinities are typically weak, a drawback which is often compensated in biological systems by an oligovalent presentation of carbohydrate epitopes. For the design of monovalent glycomimetics, structural information regarding solution and bound conformation of the carbohydrate lead represents a valuable starting point. In this paper, we focus on the conformation of the trisaccharide Le(x) (Gal[Fucα(1-3)]β(1-4)GlcNAc). Mainly because of the unfavorable tumbling regime, the elucidation of the solution conformation of Le(x) by NMR has only been partially successful so far. Le(x) was therefore attached to a (13)C,(15)N-labeled protein. (13)C,(15)N-filtered NOESY NMR techniques at ultrahigh field allowed increasing the maximal NOE enhancement, resulting in a high number of distance restraints per glycosidic bond and, consequently, a well-defined structure. In addition to the known contributors to the conformational restriction of the Le(x) structure (exoanomeric effect, steric compression induced by the NHAc group adjacent to the linking position of L-fucose, and the hydrophobic interaction of L-fucose with the β-face of D-galactose), a nonconventional C-H···O hydrogen bond between H-C(5) of L-fucose and O(5) of D-galactose was identified. According to quantum mechanical calculations, this C-H···O hydrogen bond is the most prominent factor in stabilization, contributing 40% of the total stabilization energy. We therefore propose that the nonconventional hydrogen bond contributing to a reduction of the conformational flexibility of the Le(x) core represents a novel element of the glycocode. Its relevance to the stabilization of related branched oligosaccharides is currently being studied.

Nanomolar E-selectin antagonists with prolonged half-lives by a fragment-based approach

Selectins, a family of C-type lectins, play a key role in inflammatory diseases (e.g., asthma and arthritis). However, the only millimolar affinity of sialyl Lewis(x) (sLe(x)), which is the common tetrasaccharide epitope of all physiological selectin ligands, has been a major obstacle to the development of selectin antagonists for therapeutic applications. In a fragment-based approach guided by NMR, ligands binding to a second site in close proximity to a sLe(x) mimic were identified. A library of antagonists obtained by connecting the sLe(x) mimic to the best second-site ligand via triazole linkers of different lengths was evaluated by surface plasmon resonance. Detailed analysis of the five most promising candidates revealed antagonists with K(D) values ranging from 30 to 89 nM. In contrast to carbohydrate-lectin complexes with typical half-lives (t(1/2)) in the range of one second or even less, these fragment-based selectin antagonists show t1/2 of several minutes. They exhibit a promising starting point for the development of novel anti-inflammatory drugs.

Carbohydrate microarrays

In the last decade, carbohydrate microarrays have been core technologies for analyzing carbohydrate-mediated recognition events in a high-throughput fashion. A number of methods have been exploited for immobilizing glycans on the solid surface in a microarray format. This microarray-based technology has been widely employed for rapid analysis of the glycan binding properties of lectins and antibodies, the quantitative measurements of glycan-protein interactions, detection of cells and pathogens, identification of disease-related anti-glycan antibodies for diagnosis, and fast assessment of substrate specificities of glycosyltransferases. This review covers the construction of carbohydrate microarrays, detection methods of carbohydrate microarrays and their applications in biological and biomedical research.

Glyconanosomes: disk-shaped nanomaterials for the water solubilization and delivery of hydrophobic molecules

Herein, we describe the first report on a new class of disk-shaped and quite monodisperse water-soluble nanomaterials that we named glyconanosomes (GNS). GNSs were obtained by sliding out the cylindrical structures formed upon self-organization and photopolymerization of glycolipid 1 on single-walled carbon nanotube (SWCNT) sidewalls. GNSs present a sheltered hydrophobic inner cavity formed by the carbonated tails, surrounded by PEG and lactose moieties. The amphiphilic character of GNSs allows the water solubility of insoluble hydrophobic cargos such as a perylene-bisimide derivative, [60]fullerene, or the anti-carcinogenic drug camptothecin (CPT). GNS/C60 inclusion complexes are able to establish specific interactions between peanut agglutinin (PNA) lectin and the lactose moiety surrounding the complexes, while CPT solubilized by GNS shows higher cytotoxicity toward MCF7-type breast cancer cells than CPT alone. Thus, GNS represents an attractive extension of nanoparticle-based drug delivery systems.