Small Molecules Targeting Human N-Acetylmannosamine Kinase

Small Molecules Targeting Human UDP-GlcNAc 2-Epimerase

Uridine diphosphate N-acetylglucosamine 2-epimerase (GNE) is a key enzyme in the sialic acid biosynthesis pathway. Sialic acids are primarily terminal carbohydrates on glycans and play fundamental roles in health and disease. In search of effective GNE inhibitors not based on a carbohydrate scaffold, we performed a high-throughput screening campaign of 68,640 drug-like small molecules against recombinant GNE using a UDP detection assay. We validated nine of the primary actives with an orthogonal real-time NMR assay and verified their IC50 values in the low micromolar to nanomolar range manually. Stability and solubility studies revealed three compounds for further evaluation. Thermal shift assays, analytical size exclusion, and interferometric scattering microscopy demonstrated that the GNE inhibitors acted on the oligomeric state of the protein. Finally, hydrogen-deuterium exchange mass spectrometry (HDX-MS) revealed which sections of GNE were shifted upon the addition of the inhibitors. In summary, we have identified three small molecules as GNE inhibitors with high potency in vitro, which serve as promising candidates to modulate sialic acid biosynthesis in more complex systems.

Racemases and epimerases operating through a 1,1-proton transfer mechanism: reactivity, mechanism and inhibition

Racemases and epimerases catalyse changes in the stereochemical configurations of chiral centres and are of interest as model enzymes and as biotechnological tools. They also occupy pivotal positions within metabolic pathways and, hence, many of them are important drug targets. This review summarises the catalytic mechanisms of PLP-dependent, enolase family and cofactor-independent racemases and epimerases operating by a deprotonation/reprotonation (1,1-proton transfer) mechanism and methods for measuring their catalytic activity. Strategies for inhibiting these enzymes are reviewed, as are specific examples of inhibitors. Rational design of inhibitors based on substrates has been extensively explored but there is considerable scope for development of transition-state mimics and covalent inhibitors and for the identification of inhibitors by high-throughput, fragment and virtual screening approaches. The increasing availability of enzyme structures obtained using X-ray crystallography will facilitate development of inhibitors by rational design and fragment screening, whilst protein models will facilitate development of transition-state mimics.

Effects of Zinc Oxide Nanoparticles in HUVEC: Cyto- and Genotoxicity and Functional Impairment After Long-Term and Repetitive Exposure in vitro

Purpose

The present study focuses on threshold levels for cytotoxicity after long-term and repetitive exposure for HUVEC as a model for the specific microvascular endothelial system. Furthermore, possible genotoxic effects and functional impairment caused by ZnO NPs in HUVEC are elucidated.

Methods

Thresholds for cytotoxic effects are determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Annexin V assay. To demonstrate DNA damage, single-cell microgel electrophoresis (comet) assay is performed after exposure to sub-cytotoxic concentrations of ZnO NPs. The proliferation assay, dot blot assay and capillary tube formation assay are also carried out to analyze functional impairment.

Results

NPs showed to be spherical in shape with an average size of 45–55 nm. Long-term exposure as well as repetitive exposure with ZnO NPs exceeding 25 µg/mL lead to decreased viability in HUVEC. In addition, DNA damage was indicated by the comet assay after long-term and repetitive exposure. Twenty-four hours after long-term exposure, the proliferation assay does not show any difference between negative control and exposed cells. Forty-eight hours after exposure, HUVEC show an inverse concentration-related ability to proliferate. The dot blot assay provides evidence that ZnO NPs lead to a decreased release of VEGF, while capillary tube formation assay shows restriction in the ability of HUVEC to build tubes and meshes as a first step in angiogenesis.

Conclusion

Sub-cytotoxic concentrations of ZnO NPs lead to DNA damage and functional impairment in HUVEC. Based on these data, ZnO NPs may affect neo-angiogenesis. Further investigation based on tissue cultures is required to elucidate the impact of ZnO NPs on human cell systems.

Sialic acid as a target for the development of novel antiangiogenic strategies

Sialic acid is associated with glycoproteins and gangliosides of eukaryotic cells. It regulates various molecular interactions, being implicated in inflammation and cancer, where its expression is regulated by sialyltransferases and sialidases. Angiogenesis, the formation of new capillaries, takes place during inflammation and cancer, and represents the outcome of several interactions occurring at the endothelial surface among angiogenic growth factors, inhibitors, receptors, gangliosides and cell-adhesion molecules. Here, we elaborate on the evidences that many structures involved in angiogenesis are sialylated and that their interactions depend on sialic acid with implications in angiogenesis itself, inflammation and cancer. We also discuss the possibility to exploit sialic acid as a target for the development of novel antiangiogenic drugs.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

The benefits of in silico modeling to identify possible small-molecule drugs and their off-target interactions

The research into the use of small molecules as drugs continues to be a key driver in the development of molecular databases, computer-aided drug design software and collaborative platforms. The evolution of computational approaches is driven by the essential criteria that a drug molecule has to fulfill, from the affinity to targets to minimal side effects while having adequate absorption, distribution, metabolism, and excretion (ADME) properties. A combination of ligand- and structure-based drug development approaches is already used to obtain consensus predictions of small molecule activities and their off-target interactions. Further integration of these methods into easy-to-use workflows informed by systems biology could realize the full potential of available data in the drug discovery and reduce the attrition of drug candidates.