Glycan Antagonists and Inhibitors: A Fount for Drug Discovery

ABSTRACT

Glycans, the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids, represent a relatively unexploited area for drug development compared with other macromolecules. This review describes the major classes of glycans synthesized by animal cells, their mode of assembly, and available inhibitors for blocking their biosynthesis and function. Many of these agents have proven useful for studying the biological activities of glycans in isolated cells, during embryological development, and in physiology. Some are being used to develop drugs for treating metabolic disorders, cancer, and infection, suggesting that glycans are excellent targets for future drug development.     

L-selectin interactions with novel mono- and multisulfated Lewisx sequences in comparison with the potent ligand 3'-sulfated Lewisa.

The cell adhesion molecule L-selectin binds to 3'-sialyl-Lewis (Le)x and -Lea and to 3'-sulfo-Lex and -Lea sequences. The binding to 3'-sialyl-Lex is strongly affected by the presence of 6-O-sulfate as found on oligosaccharides of the counter receptor, GlyCAM-1; 6-O-sulfate on the N-acetylglucosamine (6-sulfation) enhances, whereas 6-O-sulfate on the galactose (6'-sulfation) virtually abolishes binding. To extend knowledge on the specificity of L-selectin, we have investigated interactions with novel sulfo-oligosaccharides based on the Lex pentasaccharide sequence. We observe that, also with 3'-sulfo-Lex, the 6-sulfation enhances and 6'-sulfation suppresses L-selectin binding. The 6'-sulfation without 3'-sialyl or 3'-sulfate gives no binding signal with L-selectin. Where the 6-sulfo,3'-sialyl-Lex is on an extended di-N-acetyllactosamine backbone, additional 6-O-sulfates on the inner galactose and inner N-acetylglucosamine do not influence the binding. Although binding to the 6,3'-sulfo-Lex and 6-sulfo, 3'-sialyl-Lex sequences is comparable, the former is a more effective inhibitor of L-selectin binding. This difference is most apparent when L-selectin is in paucivalent form (predominantly di- and tetramer) rather than multivalent. Indeed, as inhibitors of the paucivalent L-selectin, the 3'-sulfo-Lex series are more potent than the corresponding 3'-sialyl-Lex series. Thus, for synthetic strategies to design therapeutic oligosaccharide analogs as antagonists of L-selectin binding, those based on the simpler 3'-sulfo-Lex (and also the 3'-sulfo-Lea) would seem most appropriate.     

Capillary zone electrophoresis for the determination of atovaquone in serum

A rapid and simple capillary zone electrophoresis (CZE) method has been developed for the determination of atovaquone in serum. The drug was extracted from equine serum–chloroform (1:3, v/v) at greater than 80% recovery and assayed in buffer containing 25 mM sodium borate (pH 9.1) and 25% acetonitrile. A 100 μm I.D. fused-silica capillary was used and the detection was by UV-diode array at 254 nm; the migration time was approximately 8 min. Intra- and inter-assay variabilities were less than 7.8% and 5.8%, respectively, and the accuracy of the assay (expressed as % bias) ranged from 4.5 to −5.2%. The working assay range was from 2 to 100 μg/ml. This sensitivity could be increased by concentrating during the extraction procedure. Replacement of acetonitrile with 75 mM surfactant 3-(dimethyldodecylammonio)propanesulfonate gave similar sensitivity and provided an additional option to facilitate the separation of atovaquone on multiple-drug samples.     

Mitogenic effects of transforming growth factor type e on epithelial and fibroblastic cells--comparison with other growth factors

Transforming growth factor type-e (TGFe) is a novel TGF which was first described as a growth factor possibly involved in autocrine stimulation of anchorage-independent growth of carcinoma cells. Its later identification in normal tissues, plasma, and platelets suggested a role for TGFe in normal cell growth. This study shows that TGFe stimulates both anchorage-dependent and -independent growth of epithelial and fibroblastic cells of nonneoplastic origin. The mitogenic activity of TGFe in monolayer is slightly less than that of basic fibroblast growth factor, equipotent to that of epidermal growth factor, and greater than that of IGF-1. TGFe acts as a progression factor for both AKR-2B and Balb-3T3 cells. TGFe is also a potent mitogen for normal human epidermal keratinocytes and may therefore play a role in epidermal growth and regeneration.     

Force-induced melting of DNA—evidence for peeling and internal melting from force spectra on short synthetic duplex sequences

Overstretching of DNA occurs at about 60–70 pN when a torsionally unconstrained double-stranded DNA molecule is stretched by its ends. During the transition, the contour length increases by up to 70% without complete strand dissociation. Three mechanisms are thought to be involved: force-induced melting into single-stranded DNA where either one or both strands carry the tension, or a B-to-S transition into a longer, still base-paired conformation. We stretch sequence-designed oligonucleotides in an effort to isolate the three processes, focusing on force-induced melting. By introducing site-specific inter-strand cross-links in one or both ends of a 64 bp AT-rich duplex we could repeatedly follow the two melting processes at 5 mM and 1 M monovalent salt. We find that when one end is sealed the AT-rich sequence undergoes peeling exhibiting hysteresis at low and high salt. When both ends are sealed the AT sequence instead undergoes internal melting. Thirdly, the peeling melting is studied in a composite oligonucleotide where the same AT-rich sequence is concatenated to a GC-rich sequence known to undergo a B-to-S transition rather than melting. The construct then first melts in the AT-rich part followed at higher forces by a B-to-S transition in the GC-part, indicating that DNA overstretching modes are additive.