Beat Ernst

From carbohydrate leads to glycomimetic drugs

Carbohydrates are the most abundant natural products. Besides their role in metabolism and as structural building blocks, they are fundamental constituents of every cell surface, where they are involved in vital cellular recognition processes. Carbohydrates are a relatively untapped source of new drugs and therefore offer exciting new therapeutic opportunities. Advances in the functional understanding of carbohydrate–protein interactions have enabled the development of a new class of small-molecule drugs, known as glycomimetics. These compounds mimic the bioactive function of carbohydrates and address the drawbacks of carbohydrate leads, namely their low activity and insufficient drug-like properties. Here, we examine examples of approved carbohydrate-derived drugs, discuss the potential of carbohydrate-binding proteins as new drug targets (focusing on the lectin families) and consider ways to overcome the challenges of developing this unique class of novel therapeutics.

Carbohydrates in Chemistry and Biology

= Abstract Carbohydrate Chemistry and Glycobiology have witnessed a rapid expansion during the last few years with the development of numerous new, imaginative and efficient syntheses which provide further insight into structures and biological interactions of glycoconjugates. Glycosylation reactions are widely used in the synthesis of pharmaceuticals and bio-active compounds. In biology and medicine oligosaccharides play a central role in immunostimulation, cancer or allergic responses. Glycoscience is a very instructive example of how one common topic of interest stimulates both chemistry and biology to collectively open scientific frontiers. This synergy is made visible in this work. Three leading experts in the fields of Glycochemistry and Glycobiology have invited numerous renowned authors to provide a comprehensive overview of the recent advances and findings in Glycoscience. This four-volume handbook presents an integrated and cutting-edge view, and covers all chemical aspects, such as syntheses and analysis of carbohydrates and oligosaccharides, as well as the biological role and activity of oligosaccharides and carbohydrate/protein interactions.

GMI-1070, a novel pan-selectin antagonist, reverses acute vascular occlusions in sickle cell mice

Leukocyte adhesion in the microvasculature influences blood rheology and plays a key role in vaso-occlusive manifestations of sickle cell disease. Notably, polymorphonuclear neutrophils (PMNs) can capture circulating sickle red blood cells (sRBCs) in inflamed venules, leading to critical reduction in blood flow and vaso-occlusion. Recent studies have suggested that E-selectin expression by endothelial cells plays a key role by sending activating signals that lead to the activation of Mac-1 at the leading edge of PMNs, thereby allowing RBC capture. Thus, the inhibition of E-selectin may represent a valuable target in this disease. Here, we have tested the biologic properties of a novel synthetic pan-selectin inhibitor, GMI-1070, with in vitro assays and in a humanized model of sickle cell vaso-occlusion analyzed by intravital microscopy. We have found that GMI-1070 predominantly inhibited E-selectin-mediated adhesion and dramatically inhibited sRBC-leukocyte interactions, leading to improved microcirculatory blood flow and improved survival. These results suggest that GMI-1070 may represent a valuable novel therapeutic intervention for acute sickle cell crises that should be further evaluated in a clinical trial.

FimH antagonists for the oral treatment of urinary tract infections: from design and synthesis to in vitro and in vivo evaluation.

Urinary tract infection (UTI) by uropathogenic Escherichia coli (UPEC) is one of the most common infections, particularly affecting women. The interaction of FimH, a lectin located at the tip of bacterial pili, with high mannose structures is critical for the ability of UPEC to colonize and invade the bladder epithelium. We describe the synthesis and the in vitro/in vivo evaluation of α-D-mannosides with the ability to block the bacteria/host cell interaction. According to the pharmacokinetic properties, a prodrug approach for their evaluation in the UTI mouse model was explored. As a result, an orally available, low molecular weight FimH antagonist was identified with the potential to reduce the colony forming units (CFU) in the urine by 2 orders of magnitude and in the bladder by 4 orders of magnitude. With FimH antagonist, the great potential for the effective treatment of urinary tract infections with a new class of orally available antiinfectives could be demonstrated.

Oligohis-tags: mechanisms of binding to Ni2+-NTA surfaces.

Since immobilized metal ion affinity chromatography (IMAC) was first reported, several modifications have been developed. Among them, Ni2+ immobilized by chelation with nitrilotriacetic acid (NTA) bound to a solid support has become the most common method for the purification of proteins carrying either a C‐ or N‐terminal histidine (His) tag. Despite its broad application in protein purification, only little is known about the binding properties of the His‐tag, and therefore almost no thermodynamic and kinetic data are available. In this study, we investigated the binding mechanism of His‐tags to Ni2+‐NTA. Different series of oligohistidines and mixed oligohistidines/oligoalanines were synthesized using automated solid‐phase peptide synthesis (SPPS). Binding to Ni2+‐NTA was analyzed both qualitatively and quantitatively with surface plasmon resonance (SPR) using commercially available NTA sensor chips from Biacore. The hexahistidine tag shows an apparent equilibrium dissociation constant (KD) of 14 ± 1 nM and thus the highest affinity of the peptides synthesized in this study. Furthermore, we could demonstrate that two His separated by either one or four residues are the preferred binding motifs within hexahis tag. Finally, elongation of these referred motifs decreased affinity, probably due to increased entropy costs upon binding. Copyright

EUROCarbDB: An open-access platform for glycoinformatics.

The EUROCarbDB project is a design study for a technical framework, which provides sophisticated, freely accessible, open-source informatics tools and databases to support glycobiology and glycomic research. EUROCarbDB is a relational database containing glycan structures, their biological context and, when available, primary and interpreted analytical data from high-performance liquid chromatography, mass spectrometry and nuclear magnetic resonance experiments. Database content can be accessed via a web-based user interface. The database is complemented by a suite of glycoinformatics tools, specifically designed to assist the elucidation and submission of glycan structure and experimental data when used in conjunction with contemporary carbohydrate research workflows. All software tools and source code are licensed under the terms of the Lesser General Public License, and publicly contributed structures and data are freely accessible. The public test version of the web interface to the EUROCarbDB can be found at http://www.ebi.ac.uk/eurocarb.

Peripheral lipopolysaccharide administration transiently affects expression of brain-derived neurotrophic factor, corticotropin and proopiomelanocortin in mouse brain.

Peripheral inflammation induced by intraperitoneal (i.p.) injection of Lipopolysaccharide (LPS) is known to cause functional impairments in the brain affecting memory and learning. One of mechanisms may be the interference with neurotrophin (NT) expression and function. In the current study we administered a single, high dose of LPS (3mg/kg, i.p.) into mice and investigated changes in brain-derived neurotrophic factor (BDNF) gene expression within 1-6 days after LPS injection. Crude synaptosomes were isolated from brain tissue and subjected to Western-blot analyses. We found transient reductions in synaptosomal proBDNF- and BDNF protein expression, with a maximal decrease at day 3 as compared to saline injected controls. The time course of reduction of BDNF mRNA in whole brain extracts parallels the decrease in protein levels in synaptosomes. LPS effects in the central nervous system (CNS) are known to crucially involve the activation of the hypothalamic-pituitary-adrenal (HPA) axis. We analysed the time course of corticotropin releasing hormone (CRH)- and proopiomelanocortin (POMC) mRNA expression. As observed for BDNF-, CRH- and POMC mRNA levels are also significantly reduced on day 3 indicating a comparable time course. These results suggest that peripheral inflammation causes a reduction of trophic supply in the brain, including BDNF at synaptic sites. The mechanisms involved could be a negative feedback of the activated HPA axis.

Trivalent, Gal/GalNAc-containing ligands designed for the asialoglycoprotein receptor.

A series of novel, fluorescent ligands designed to bind with high affinity and specificity to the asialoglycoprotein receptor (ASGP-R) has been synthesized and tested on human liver cells. The compounds bear three non-reducing, beta-linked Gal or GalNAc moieties linked to flexible spacers for an optimal spatial interaction with the binding site of the ASGP-R. The final constructs were selectively endocytosed by HepG2 cells derived from parenchymal liver cells-the major human liver cell type-in a process that was visualized with the aid of fluorescence microscopy. Furthermore, the internalization was analyzed with flow cytometry, which showed the process to be receptor-mediated and selective. The compounds described in this work could serve as valuable tools for studying hepatic endocytosis, and are suited as carriers for site-specific drug delivery to the liver.

Antiadhesion Therapy for Urinary Tract Infections—A Balanced PK/PD Profile Proved To Be Key for Success

The initial step for the successful establishment of urinary tract infections (UTIs), predominantly caused by uropathogenic Escherichia coli, is the adhesion of bacteria to urothelial cells. This attachment is mediated by FimH, a mannose-binding adhesin, which is expressed on the bacterial surface. To date, UTIs are mainly treated with antibiotics, leading to the ubiquitous problem of increasing resistance against most of the currently available antimicrobials. Therefore, new treatment strategies are urgently needed, avoiding selection pressure and thereby implying a reduced risk of resistance. Here, we present a new class of highly active antimicrobials, targeting the virulence factor FimH. When the most potent representative, an indolinylphenyl mannoside, was administered in a mouse model at the low dosage of 1 mg/kg (corresponding to approximately 25 μg/mouse), the minimal therapeutic concentration to prevent UTI was maintained for more than 8 h. In a treatment study, the colony-forming units in the bladder could be reduced by almost 4 orders of magnitude, comparable to the standard antibiotic treatment with ciprofloxacin (8 mg/kg, sc).

Preparation of glycosyl halides under neutral conditions

Abstract The anomeric hydroxyl group of various furanose and pyranose hemiacetals can be replaced by a fluorine, chlorine, bromine or iodine atom under neutral conditions using haloenamines.