LEAPT: lectin-directed enzyme-activated prodrug therapy

Tumor selective self-assembled nanomicelles of carbohydrate-epothilone B conjugate for targeted chemotherapy

Epothilone B (Epo B) is a potent antitumor natural product with sub-nanomolar anti-proliferation action against several human cancer cells. However, poor selectivity to tumor cells and unacceptable therapeutic windows of Epo B and its analogs are the major obstacles to their development into clinical drugs. Herein, we present self-assembled nanomicelles based on an amphiphilic carbohydrate-Epo B conjugate that is inactive until converted to active Epo B within the tumor. Four Epo B-Rhamnose conjugates linked via two linkers containing a disulfide bond that is sensitive to GSH were synthesized. Conjugate 34 can self-assemble into nanomicelles with a high concentration of Rha on the surface, allowing for better tumor targeting. After internalization by cancer cells, the disulfide bond can be cleaved in the presence of high levels of GSH to release active Epo B, thereby exhibiting significant anticancer efficiency and selectivity in vitro and in vivo.

Biological properties of (1-4)-thio disaccharides

Thio sugars are carbohydrate derivatives in which one or more oxygen atoms have been replaced with sulfur. Thio sugars are effective inhibitors of glycosylases, have considerable therapeutic potential, and are used as drugs in the treatment of diabetes and infectious diseases. The development of this branch of carbohydrate chemistry would not be possible without the development of novel methods for its synthesis and the analysis of their biochemical properties. In this Review Article, we summarize our findings on the biological properties of a collection of thio sugars and their derivatives synthesized by the Witczak and Bielski team using their original methods based on the Michael addition of sugar thiols to levoglucosenone.

Biodegradable nanoemulsion-based bioorthogonal nanocatalysts for intracellular generation of anticancer therapeutics

Bioorthogonal catalysis mediated by transition metal catalysts (TMCs) provides controlled in situ activation of prodrugs through chemical reactions that do not interfere with cellular bioprocesses. The direct use of 'naked' TMCs in biological environments can have issues of solubility, deactivation, and toxicity. Here, we demonstrate the design and application of a biodegradable nanoemulsion-based scaffold stabilized by a cationic polymer that encapsulates a palladium-based TMC, generating bioorthogonal nanocatalyst "polyzymes". These nanocatalysts enhance the stability and catalytic activity of the TMCs while maintaining excellent mammalian cell biocompatibility. The therapeutic potential of these nanocatalysts was demonstrated through efficient activation of a non-toxic prodrug into an active chemotherapeutic drug, leading to efficient killing of cancer cells.

Alkynone β-trifluoroborates: A new class of amine-specific biocompatible click reagents

Amine-targeting reactions that work under biocompatible conditions or in water are green processes that are extremely useful for the synthesis of functional materials and biotherapeutics. Unfortunately, despite the usefulness of this reaction, there are very few good amine-specific click methods reported thus far. Here, we report an amine-specific click reagent using alkynone β-trifluoroborates as the electrophiles. These boron-containing alkynyl reagents exhibit extremely high chemoselectivity toward amines even in the presence of thiols. The resulting oxaboracycle products are bench-stable, displaying the reactivities of both organoborates and enaminones. Intrinsic advantages of this methodology include benign reaction conditions, operational simplicity, remarkable product stability, and excellent chemoselectivity, which satisfy the criteria of click chemistry and demonstrate the high potential in bioconjugation. Hence, this water-based chemical approach is also applicable to the modification of native amino acids, peptides, and proteins. Ultimately, the essential role of water during the reaction was elucidated.

Development and Recent Advances in Lysine and N-Terminal Bioconjugation for Peptides and Proteins

The demand for creation of protein diversity and regulation of protein function through native protein modification and post-translational modification has ignited the development of selective chemical modification methods for peptides and proteins. Chemical bioconjugation offers selective functionalization providing bioconjugates with desired properties and functions for diverse applications in chemical biology, medicine, and biomaterials. The amino group existing at the lysine residue and N-terminus of peptides and proteins has been extensively studied in bioconjugation because of its good nucleophilicity and high surface exposure. Herein, we review the development of chemical methods for modification of the amino groups on lysine residue and N-terminus featuring excellent selectivity, mild reaction conditions, short reaction time, high conversion, biocompatibility, and preservation of protein integrity. This review is organized based on the chemoselectivity and site-selectivity of the chemical bioconjugation reagents to the amino acid residues aiming to provide guidance for the selection of appropriate bioconjugation methods.

Applications of mannose-binding lectins and mannan glycoconjugates in nanomedicine

Glycosylated nanoparticles (NPs) have drawn a lot of attention in the biomedical field over the past few decades, particularly in applications like targeted drug delivery. Mannosylated NPs and mannan-binding lectins/proteins (MBL/MBP) are emerging as promising tools for delivery of drugs, medicines, and enzymes to targeted tissues and cells as nanocarriers, enhancing their therapeutic benefits while avoiding the adverse effects of the drug. The occurrence of plenty of lectin receptors and their mannan ligands on cell surfaces makes them multifaceted carriers appropriate for specific delivery of bioactive drug materials to their targeted sites. Thus, the present review describes the tethering of mannose (Man) to several nanostructures, like micelles, liposomes, and other NPs, applicable for drug delivery systems. Bioadhesion through MBL-like receptors on cells has involvements applicable to additional arenas of science, for example gene delivery, tissue engineering, biomaterials, and nanotechnology. This review also focuses on the role of various aspects of drug/antigen delivery using (i) mannosylated NPs, (ii) mannosylated lectins, (iii) amphiphilic glycopolymer NPs, and (iv) natural mannan-containing polysaccharides, with most significant applications of MBL-based NPs as multivalent scaffolds, using different strategies.

GRAPHICAL ABSTRACT

Mannosylated NPs and/or MBL/MBP are coming up as viable and versatile tools as nanocarriers to deliver drugs and enzymes precisely to their target tissues or cells. The presence of abundant number of lectin receptors and their mannan ligands on cell surfaces makes them versatile carriers suitable for the targeted delivery of bioactive drugs.

Exploring Glycan Binding Specificity of Odorranalectin by Alanine Scanning Library

Fluorescently labelled alanine scan analogues of odorranalectin (OL), a cyclic peptide that exhibits lectin like properties, were screened for binding BSA-conjugated monosaccharides using an enzyme-linked lectin assay (ELLA). Results revealed that Lys5, Phe7, Tyr9, Gly12, Leu14, and Thr17 were crucial for binding BSA-L-fucose, BSA-D-galactose and BSA-N-acetyl-D-galactosamine. Notably, Ala substitution of Ser3, Pro4, and Val13 resulted in higher binding affinities compared to the native OL. The obtained data also indicated that Arg8 plays an important role in differentiation of binding for BSA-L-fucose/D-galactose from BSA-N-acetyl-D-galactosamine. The thermodynamics of binding of the selected alanine analogues was evaluated by isothermal titration calorimetry. Low to moderate binding affinities were determined for the tetravalent MUC1 glycopeptide and asialofetuin, respectively, and high for the fucose rich polysaccharide, fucoidan. The thermodynamic profile of interactions with asialofetuin exhibits shift to an entropy-driven mechanism compared to the fucoidan, which displayed an enthalpyentropy compensation, typically associated with the carbohydratelectin recognition process.

Glycosylated 4-methylumbelliferone as a targeted therapy for hepatocellular carcinoma

BACKGROUND & AIMS

Reaching efficacious drug delivery to target cells/tissues represents a major obstacle in the current treatment of solid malignancies including hepatocellular carcinoma (HCC). In this study, we developed a pipeline to selective add complex-sugars to the aglycone 4-methylumbelliferone (4MU) to help their bioavailability and tumour cell intake.

METHODS

The therapeutic efficacy of sugar-modified rutinosyl-4-methylumbelliferone (4MUR) and 4MU were compared in vitro and in an orthotopic HCC model established in fibrotic livers. The mechanistic bases of its selective target to liver tumour cells were evaluated by the interaction with asialoglycoprotein receptor (ASGPR), the mRNA expression of hyaluronan synthases (HAS2 or HAS3) and hyaluronan deposition.

RESULTS

4MUR showed a significant antiproliferative effect on liver tumoural cells as compared to non-tumoural cells in a dose-dependent manner. Further analysis showed that 4MUR is incorporated mostly into HCC cells by interaction with ASGPR, a receptor commonly overexpressed in HCC cells. 4MUR-treatment decreased the levels of HAS2 and HAS3 and the cytoplasmic deposition of hyaluronan. Moreover, 4MUR reduced CFSC-2G activation, hence reducing the fibrosis. In vivo efficacy showed that 4MUR treatment displayed a greater tumour growth inhibition and increased survival in comparison to 4MU. 4MUR administration was associated with a significant reduction of liver fibrosis without any signs of tissue damage. Further, 60% of 4MUR treated mice did not present macroscopically tumour mass post-treatment.

CONCLUSION

Our results provide evidence that 4MUR may be used as an effective HCC therapy, without damaging non-tumoural cells or other organs, most probably due to the specific targeting.

Azaphilones as Activation-Free Primary-Amine-Specific Bioconjugation Reagents for Peptides, Proteins and Lipids

Residue-selective bioconjugation methods for biomolecules are highly sought to expand the scope of their biological and medical applications. Inspired by the mechanism of the generation of natural vinylogous γ-pyridones (vPDNs), we have developed a novel unique azaphilone-based, activation-free primary-amine-selective bioconjugation method for biomolecules. Our strategy allows facile functionalization of primary amine groups in peptides and proteins, including the clinically used therapeutic antibody trastuzumab, by generating a highly stable vPDN linkage. Excellent chemoselectivity toward primary amines also enables the azaphilone derivatives to specifically modify the lipid components of Gram-positive bacteria while bypassing Gram-negative bacteria and mammalian cells. The new method shows significant advantages including chemoselectivity, efficiency, flexibility and biocompatibility, and therefore provides a valuable addition to the current toolbox for biomolecule conjugation.

Immunomodulatory Lectin-like Peptides for Fish Erythrocytes-Targeting as Potential Antiviral Drug Delivery Platforms

One of the challenges of science in disease prevention is optimizing drug and vaccine delivery. Until now, many strategies have been employed in this sector, but most are quite complex and labile. To overcome these limitations, great efforts are directed to coupling drugs to carriers, either of natural or synthetic origin. Among the most studied cell carriers are antigen-presenting cells (APCs), however, red blood cells (RBCs) are positioned as attractive carriers in drug delivery due to their abundance and availability in the body. Furthermore, fish RBCs have a nucleus and have been shown to have a strong involvement in modulating the immune response. In this study, we evaluated the binding of three peptides to rainbow trout RBCs, two lectin-like peptides and another derived from Plasmodium falciparum membrane protein, in order to take advantage of this peptide-RBCs binding to generate tools to improve the specificity, efficacy, immunostimulatory effect, and safety of the antiviral therapeutic or prophylactic administration systems currently used.

Multitarget-directed therapeutics: (Urea/thiourea)2 derivatives of diverse heterocyclic-Lys conjugates

The synthesis of a new small library of molecules containing bis-urea/thiourea pendants in lysine conjugated to three different heterocycles is described. The heterocycles used in this study have benzisoxazole/piperazine/piperidine units. After a detailed antimicrobial, antioxidant, and anti-inflammatory evaluation, it was found that the most active compounds are 10, 11, 14, 15, 18, 19 and 10, 11, 19 and 8, 9, 12, 13, 16, 17, respectively. Further, it was observed that the presence of all three entities, that is, urea/thiourea, the substituent (OMe/F), as well as the heterocycle, is highly essential for exerting potent activity. Among the heterocycles, the presence of isoxazole seems to be highly beneficial for exerting good potency. In continuation, docking studies have revealed extraordinary binding efficiency for some of the active compounds. Given their potent biological results and docking score, some of the title compounds could be potential drug candidates for microbial-related diseases and provide a basis for future research into the development of molecules possessing multitask ability.

Glycoconjugation: An approach to cancer therapeutics

Cancer constitutes the second leading cause of death globally and is considered to have been responsible for an estimated 9.6 million fatalities in 2018. Although treatments against gastrointestinal tumors have recently advanced, those interventions can only be applied to a minority of patients at the time of diagnosis. Therefore, new therapeutic options are necessary for advanced stages of the disease. Glycosylation of antitumor agents, has been found to improve pharmacokinetic parameters, reduce side effects, and expand drug half-life in comparison with the parent compounds. In addition, glycosylation of therapeutic agents has been proven to be an effective strategy for their targeting tumor tissue, thereby reducing the doses of the glycodrugs administered to patients. This review focusses on the effect of the targeting properties of glycosylated antitumor agents on gastrointestinal tumors.

The flavonoid degrading fungus Acremonium sp. DSM 24697 produces two diglycosidases with different specificities

AbstractDiglycosidases hydrolyze the heterosidic linkage of diglycoconjugates, releasing the disaccharide and the aglycone. Usually, these enzymes do not hydrolyze or present only low activities towards monoglycosylated compounds. The flavonoid degrading fungus Acremonium sp. DSM 24697 produced two diglycosidases, which were termed 6-O-α-rhamnosyl-β-glucosidase I and II (αRβG I and II) because of their function of releasing the disaccharide rutinose (6-O-α-L-rhamnosyl-β-D-glucose) from the diglycoconjugates hesperidin or rutin. In this work, the genome of Acremonium sp. DSM 24697 was sequenced and assembled with a size of ~ 27 Mb. The genes encoding αRβG I and II were expressed in Pichia pastoris KM71 and the protein products were purified with apparent molecular masses of 42 and 82 kDa, respectively. A phylogenetic analysis showed that αRβG I grouped in glycoside hydrolase family 5, subfamily 23 (GH5), together with other fungal diglycosidases whose substrate specificities had been reported to be different from αRβG I. On the other hand, αRβG II grouped in glycoside hydrolase family 3 (GH3) and thus is the first GH3 member that hydrolyzes the heterosidic linkage of rutinosylated compounds. The substrate scopes of the enzymes were different: αRβG I showed exclusive specificity toward 7-O-β-rutinosyl flavonoids, whereas αRβG II hydrolyzed both 7-O-β-rutinosyl- and 3-O-β-rutinosyl- flavonoids. None of the enzymes displayed activity toward 7-O-β-neohesperidosyl- flavonoids. The recombinant enzymes also exhibited transglycosylation activities, transferring rutinose from hesperidin or rutin onto various alcoholic acceptors. The different substrate scopes of αRβG I and II may be part of an optimized strategy of the original microorganism to utilize different carbon sources.

Enzymatic rhamnosylation of anticancer drugs by an α-L-rhamnosidase from Alternaria sp. L1 for cancer-targeting and enzyme-activated prodrug therapy

The synthesis of rhamnosylated compounds has gained great importance since these compounds have potential therapeutic applications. The enzymatic approaches for glycosylation of bioactive molecules have been well developed; however, the enzymatic rhamnosylation has been largely hindered by lacking of the glycosyl donor for rhamnosyltransferases. Here, we employed an α-L-rhamnosidase from Alternaria sp. L1 (RhaL1) to perform one-step rhamnosylation of anticancer drugs, including 2'-deoxy-5-fluorouridine (FUDR), cytosine arabinoside (Ara C), and hydroxyurea (Hydrea). The key synthesis conditions including substrate concentrations and reaction time were carefully optimized, and the maximum yields of each rhamnosylated drugs were 57.7 mmol for rhamnosylated Ara C, 68.6 mmol for rhamnosylated Hydrea, and 42.2 mmol for rhamnosylated FUDR. It is worth pointing out that these rhamnosylated drugs exhibit little cytotoxic effects on cancer cells, but could efficiently restore cytotoxic activity when incubated with exogenous α-L-rhamnosidase, suggesting their potential applications in the enzyme-activated prodrug system. To evaluate the cancer-targeting ability of rhamnose moiety, the rhamnose-conjugated fluorescence dye rhodamine B (Rha-RhB) was constructed. The fluorescence probe Rha-RhB displayed much higher cell affinity and cellular internalization rate of oral cancer cell KB and breast cancer cell MDA-MB-231 than that of the normal epithelial cells MCF 10A, suggesting that the rhamnose moiety could mediate the specific internalization of rhamnosylated compounds into cancer cells, which greatly facilitated their applications for cancer-targeting drug delivery.

In vitro characterization of odorranalectin for peptide-based drug delivery across the blood-brain barrier

BACKGROUND

The use of siRNA-based gene silencing has been recently underscored as a potential therapeutic strategy for the treatment of neurological disorders. However, the stability of siRNA and other small molecule therapeutics is challenged by their intrinsic instability and limited passage across the blood-brain barrier (BBB). Based on these premises, our objective was to characterize/optimize odorranalectin (OL), a small non-immunogenic lectin-like peptide, as a carrier for targeted delivery across the BBB. For this purpose, 5(6)-carboxyfluorescein-conjugated OL and scramble peptide were synthesized, and then their BBB cellular internalization/trafficking and stability were characterized versus temperature, pH and serum content in the media in hCMEC/D3 cells as a model of BBB endothelium. Specifically, integrity of the internalized peptide in cell lysates was analyzed by LC/MS while cellular distribution and intracellular trafficking of OL was examined by fluorescence microscopy with early-late endosome (pHRodo Red^®) and lysosome (Lysotracker^®) markers.

RESULTS

Our data show that cellular uptake of OL increased linearly with the concentrations tested in this study at 37 °C and the uptake was two to threefolds higher when compared to scramble peptide. While there were no differences for scramble peptide, the uptake of OL decreased by 50% at 4 °C incubation (vs. 37 °C). No effects of pH were observed on endothelial uptake of OL. Immunofluorescence studies also indicated a significant cellular internalization of OL that remained intact (as evaluated by LC-MS/MS) and co-localized with endosomal, but not lysosome marker. Importantly, OL was found non-toxic to cells at all concentrations tested.

CONCLUSIONS

In summary, our data suggest the existence of a receptor-mediated transcytosis pathway for cellular uptake of OL at the BBB endothelium. However, in vivo studies will be needed to assess the siRNA loading capacity of OL and its trans-BBB transport efficiency for targeted delivery in the brain.

A novel Aspergillus oryzae diglycosidase that hydrolyzes 6-O-α-L-rhamnosyl-β-D-glucoside from flavonoids

α-L-Rhamnosyl-β-D-glucosidase (rutinosidase) hydrolyzes the glycosidic linkage between the disaccharide 6-O-α-L-rhamnosyl-β-D-glucoside (rutinose) and the aglycone. We identified a hypothetical protein (annotated as AO090012000917) encoded in the Aspergillus oryzae genome that exhibits sequence similarity with Aspergillus niger rutinosidase. The recombinant enzyme was expressed in Pichia pastoris GS115 and purified as a glyco-protein with apparent molecular mass of 65-75 kDa by SDS-PAGE. After N-deglycosylation, we observed a 42- and 40-kDa band, representing proteins before and after N-terminal signal peptide processing, respectively. Optimal enzymatic activity was observed at pH 4.0 and temperature of 45 °C. This enzyme is also significantly thermo-stable, with 90% activity retained after 1 h at 45 °C and 70% activity retained after 4 h, even at 50 °C. Biochemical characterization revealed that the enzyme has higher substrate specificity for 3-O-linked flavonoid β-rutinosides like rutin and kaempferol-3-O-rutinoside, than for 7-O-linked flavonoid β-rutinoside like hesperidin. However, no activity was found with naringin, diosmin, monoglycosylated chromogenic substrates, and polymeric laminarin substrate. Kinetic analyses showed that K _m value toward rutin was higher than those toward hesperidin and kaempferol-3-O-rutinoside. Meanwhile, k_cat value toward hesperidin was lower than those toward kaempferol-3-O-rutinoside and rutin. Overall, the catalytic efficiency (k_cat/K _m ) was highest for kaempferol-3-O-rutinoside.

Palladium-Mediated Arylation of Lysine in Unprotected Peptides

A mild method for the arylation of lysine in an unprotected peptide is presented. In the presence of a preformed biarylphosphine-supported palladium(II)-aryl complex and a weak base, lysine amino groups underwent C-N bond formation at room temperature. The process generally exhibited high selectivity for lysine over other amino acids containing nucleophilic side chains and was applicable to the conjugation of a variety of organic compounds, including complex drug molecules, with an array of peptides. Finally, this method was also successfully applied to the formation of cyclic peptides by macrocyclization.

Direct aqueous synthesis of cyanomethyl thioglycosides from reducing sugars; ready access to reagents for protein glycosylation

Unprotected carbohydrates can be directly converted into cyanooethyl thioglycosides, which in turn may be used for protein glycosylation, in a completely stereoselective manner by reaction with 2-chloro-1,3-dimethylimidazolinium chloride (DMC) and mercaptoacetonitrile in aqueous solution.

Carbohydrate-based materials for targeted delivery of drugs and genes to the liver

The insult to liver by toxic materials leads to cirrhosis, hepatitis and cancer. Upon administration, drugs accumulate in liver, which is systemically cleared by reticuloendothelial system. However, specific targeting of drugs to liver is a serious challenge. Specific delivery of molecules to hepatocytes is accomplished by targeting cell surface lectins, asialoglycoprotein receptors. Asialofetuin, N-acetyl glucosamine and galactose are high-affinity ligands of asialoglycoprotein receptors. The bioconjugation of drugs, fluorescent molecules and gene delivery vectors with lectin-targeting agents, and their delivery in liver hepatocytes, is discussed. Mannose and N-acetyl glucosamine conjugates are evaluated for their delivery to hepatic stellate and kupffer cells. The glycosylated gene and drug delivery vectors in clinical trials are outlined.

Delivery of chemically glycosylated cytochrome c immobilized in mesoporous silica nanoparticles induces apoptosis in HeLa cancer cells

Cytochrome c (Cyt c) is a small mitochondrial heme protein involved in the intrinsic apoptotic pathway. Once Cyt c is released into the cytosol, the caspase mediated apoptosis cascade is activated resulting in programmed cell death. Herein, we explore the covalent immobilization of Cyt c into mesoporous silica nanoparticles (MSN) to generate a smart delivery system for intracellular drug delivery to cancer cells aiming at affording subsequent cell death. Cyt c was modified with sulfosuccinimidyl-6-[3'-(2-pyridyldithio)-propionamido] hexanoate (SPDP) and incorporated into SH-functionalized MSN by thiol-disulfide interchange. Unfortunately, the delivery of Cyt c from the MSN was not efficient in inducing apoptosis in human cervical cancer HeLa cells. We tested whether chemical Cyt c glycosylation could be useful in overcoming the efficacy problems by potentially improving Cyt c thermodynamic stability and reducing proteolytic degradation. Cyt c lysine residues were modified with lactose at a lactose-to-protein molar ratio of 3.7 ± 0.9 using mono(lactosylamido)-mono(succinimidyl) suberate linker chemistry. Circular dichroism (CD) spectra demonstrated that part of the activity loss of Cyt c was due to conformational changes upon its modification with the SPDP linker. These conformational changes were prevented in the glycoconjugate. In agreement with the unfolding of Cyt c by the linker, a proteolytic assay demonstrated that the Cyt c-SPDP conjugate was more susceptible to proteolysis than Cyt c. Attachment of the four lactose molecules reversed this increased susceptibility and protected Cyt c from proteolytic degradation. Furthermore, a cell-free caspase-3 assay revealed 47% and 87% of relative caspase activation by Cyt c-SPDP and the Cyt c-lactose bioconjugate, respectively, when compared to Cyt c. This again demonstrates the efficiency of the glycosylation to improve maintaining Cyt c structure and thus function. To test for cytotoxicity, HeLa cells were incubated with Cyt c loaded MSN at different Cyt c concentrations (12.5, 25.0, and 37.5 μg/mL) for 24-72 h and cellular metabolic activity determined by a cell proliferation assay. While MSN-SPDP-Cyt c did not induced cell death, the Cyt c-lactose bioconjugate induced significant cell death after 72 h, reducing HeLa cell viability to 67% and 45% at the 25 μg/mL and 37.5 μg/mL concentrations, respectively. Confocal microscopy confirmed that the MSN immobilized Cyt c-lactose bioconjugate was internalized by HeLa cells and that the bioconjugate was capable of endosomal escape. The results clearly demonstrate that chemical glycosylation stabilized Cyt c upon formulation of a smart drug delivery system and upon delivery into cancer cells and highlight the general potential of chemical protein glycosylation to improve the stability of protein drugs.

Virus-like glycodendrinanoparticles displaying quasi-equivalent nested polyvalency upon glycoprotein platforms potently block viral infection

Ligand polyvalency is a powerful modulator of protein–receptor interactions. Host–pathogen infection interactions are often mediated by glycan ligand–protein interactions, yet its interrogation with very high copy number ligands has been limited to heterogenous systems. Here we report that through the use of nested layers of multivalency we are able to assemble the most highly valent glycodendrimeric constructs yet seen (bearing up to 1,620 glycans). These constructs are pure and well-defined single entities that at diameters of up to 32 nm are capable of mimicking pathogens both in size and in their highly glycosylated surfaces. Through this mimicry these glyco-dendri-protein-nano-particles are capable of blocking (at picomolar concentrations) a model of the infection of T-lymphocytes and human dendritic cells by Ebola virus. The high associated polyvalency effects (β>10⁶, β/N ~10²–10³) displayed on an unprecedented surface area by precise clusters suggest a general strategy for modulation of such interactions.

Host–pathogen relationships can be mediated by polyvalent glycan ligand–protein interactions. Here well-defined highly valent glycodendrimeric constructs are synthesized that can mimic pathogens, and can inhibit a model of infection by the Ebola virus.

Updates on naringinase: structural and biotechnological aspects

Naringinases has attracted a great deal of attention in recent years due to its hydrolytic activities which include the production of rhamnose, and prunin and debittering of citrus fruit juices. While this enzyme is widely distributed in fungi, its production from bacterial sources is less commonly known. Fungal naringinase are very important as they are used industrially in large amounts and have been extensively studied during the past decade. In this article, production of bacterial naringinase and potential biotechnological applications are discussed. Bacterial rhamnosidases are exotype enzymes that hydrolyse terminal non-reducing α-L-rhamnosyl groups from α-L-rhamnose containing polysaccharides and glycosides. Structurally, they are classified into family 78 of glycoside hydrolases and characterized by the presence of Asp567 and Glu841 in their active site. Optimization of fermentation conditions and enzyme engineering will allow the development of improved rhamnosidases for advancing suggested industrial applications.

Direct radiolabelling of proteins at cysteine using [18F]-fluorosugars

A strategy for the site-specific attachment of 2-deoxy-2-fluorosugars to cysteine and dehydroalanine tagged proteins is reported. When combined with thionation of fluorosugars, such as the widely available (18)F probe 2-deoxy-2-[(18)F]fluoroglucose ([(18)F]FDG), this methodology allows fast and direct access to site-specific [(18)F]FDG-labelled proteins.

Lectin-directed enzyme activated prodrug therapy (LEAPT): Synthesis and evaluation of rhamnose-capped prodrugs

The lectin-directed enzyme activated prodrug therapy (LEAPT) bipartite drug delivery system utilizes glycosylated enzyme, localized according to its sugar pattern, and capped prodrugs released by that enzyme. In this way, the sugar coat of a synthetic enzyme determines the site of release of a given drug. Here, prodrugs of doxorubicin and 5-fluorouracil capped by the nonmammalian l-rhamnosyl sugar unit have been efficiently synthesized and evaluated for use in the LEAPT system. Both are stable in blood, released by synthetically d-galactosylated rhamnosidase enzyme, and do not inhibit the uptake of the synthetic enzyme to its liver target. These results are consistent with their proposed mode of action and efficacy in models of liver cancer, and confirm modular flexibility in the drugs that may be used in LEAPT.

Analysis of the dispersity in carbohydrate loading of synthetic glycoproteins using MALDI-TOF mass spectrometry

Statistical correlation of mass spectrum peak broadening with product dispersity in protein conjugation reactions allows more detailed characterization of putative therapeutic conjugates.