Carbohydrate-specific cell adhesion directly to glycosphingolipids separated on thin-layer chromatography plates

Molecular Docking, G-QSAR Studies, Synthesis and Anticancer Screening of Some New 2-Phenazinamines as Bcr-Abl Tyrosine Kinase Inhibitors

BACKGROUND

The computational studies on 2-phenazinamines with their protein targets have been carried out to design compounds with potential anticancer activity. This strategy of designing compounds possessing selectivity over specific tyrosine kinase has been achieved through G-QSAR and molecular docking studies.

METHODS

The objective of this research has been to design newer 2-phenazinamine derivatives as Bcr-Abl tyrosine kinase inhibitors by G-QSAR, molecular docking studies followed by wet lab studies along with evaluation of their anticancer potential. Computational chemistry was done by using VLife MDS 4.3 and Autodock 4.2 followed by wet lab experiments for synthesizing 2- phenazinamine derivatives. The chemical structures of ligands in 2D were drawn by employing Chemdraw 2D Ultra 8.0 and were converted into 3D. These were optimised by using semiempirical method called MOPAC. The protein structure was retrieved from RCSC protein data bank as PDB file. The binding interactions of protein and ligands were done by using PYMOL. The molecular properties of the designed compounds were predicted in silico by using Osiris property explorer. Later, we synthesized novel 13 2-phenazinamine derivatives by treating parent compound with various aldehydes in the presence of dicyclohexylcarbodiimide (DCC) and urea to afford 2-(2-chlorophenyl)-3-(phenazin-2-yl) thiazolidin-4-one and another series of derivatives synthesized with different aldehydes in the presence of p-toluylsulphonic acid, diphydropyridine and benzene sulfonyl chloride to afford benzenesulfonyl-N-(2-chlorobenzyl)-phenazin-2-amine. All the derivatives were tested for invitro anticancer activity on K562 human chronic myelogenous leukemia cell line by employing MTT assay method.

RESULTS

The developed G-QSAR models were found to be statistically significant with respect to training (r2=0.8074), cross-validation (q2=0.6521), and external validation (pred_r2=0.5892). The best developed G-QSAR model suggested that the XlogP values of phenazinamine derivatives were found to be highly influential in determining biological activity. The standard drug was found to exhibit binding energy - 6.79 kcal/mol and the derivatives 5b and 6c exhibited binding energy of - 7.46 and - 8.51; respectively.

CONCLUSION

Compounds 5b, 6c were observed to possess good lipophilicity and were found to exhibit better activity than other compounds in the series, although less than standard doxorubicin. The synthesis of these 2-phenazinamine derivatives (5a-m) is reported to be obtained from 2,4- dinitrodiphenylamine by applying appropriate synthetic route. Compounds 5b and 6c showed better cytotoxic activity against K562 cancer cell line when compared to other compounds of the series, although less than standard doxorubicin.

Glycolipid-mediated cell-cell recognition in inflammation and nerve regeneration

Cell surface complex carbohydrates have emerged as key recognition molecules, mediating physiological interactions between cells. Typically, glycans on one cell surface are engaged by complementary carbohydrate binding proteins (lectins) on an apposing cell, initiating appropriate cellular responses. Although many cell surface lectins have been identified in vertebrates, only a few of their endogenous carbohydrate ligands have been established. Each major class of cell surface glycans-glycoproteins, glycolipids, and proteoglycans-has been implicated as physiologically relevant lectin ligands. The current minireview focuses on findings that implicate glycosphingolipids as especially important molecules in cell-cell recognition in two different systems: the recognition of human leukocytes by E-selectin on the vascular endothelium during inflammation and the recognition of nerve cell axons by myelin-associated glycoprotein in myelin-axon stabilization and the regulation of axon regeneration.

Sialic acid specificity of myelin-associated glycoprotein binding

Myelin-associated glycoprotein (MAG), a nervous system cell adhesion molecule, is an I-type lectin that binds to sialylated glycoconjugates, including gangliosides bearing characteristic structural determinants (Yang, L. J.-S., Zeller, C. B., Shaper, N. L., Kiso, M., Hasegawa, A., Shapiro, R. E., and Schnaar, R. L. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 814-818). Two cell adhesion systems, COS-1 monkey kidney fibroblasts transiently transfected to express MAG and Chinese hamster ovary (CHO) cells stably transfected to express MAG, were used to probe the structural specificity of MAG-ganglioside binding. Both cell types bound to the same gangliosides: GQ1b alpha (IV3NeuAc,III6NeuAc,II3(NeuAc)2Gg4Cer) > GT1b = GD1a > GM3 > GM1, GD1b, and GQ1b (the latter do not support adhesion). Binding was enhanced by pretreatment of MAG-expressing cells with neuraminidase. MAG-expressing Chinese hamster ovary cells bound directly to gangliosides resolved on thin layer chromatograms, allowing detection of MAG binding species in a mixture. The simplest ganglioside ligand for MAG was GM3 bearing N-acetylneuraminic acid, whereas GM3 bearing N-glycolylneuraminic acid did not support adhesion. Chemical modifications of N-acetylneuraminic acid residues (on GD1a) abrogated MAG binding. Mild periodate oxidation of sialic acids to their corresponding seven-carbon (or eight-carbon) sialic acid aldehydes abolished MAG binding, as did further conversion to the corresponding primary alcohols. Eliminating the anionic charge by ethyl esterification, amidation, or reduction also abolished MAG-mediated cell adhesion. These data demonstrate that MAG-ganglioside binding is highly specific and defines key carbohydrate structural determinants for MAG-mediated cell adhesion to gangliosides.

Gliolectin is a novel carbohydrate-binding protein expressed by a subset of glia in the embryonic Drosophila nervous system

Interactions between embryonic neural cells generate the specific patterns of connectivity observed in nervous systems. Cell surface carbohydrates have been proposed to function in cellular recognition events guiding such interactions. Carbohydrate-binding proteins (lectins) that recognize specific oligosaccharide ligands in embryonic neural tissue provide a molecular mechanism for carbohydrate-mediated cell-cell interactions in neural development. Therefore, we have screened an embryonic Drosophila melanogaster cDNA library, expressed in COS1 cells, for carbohydrate-binding activity. COS1 cells expressing putative Drosophila lectins were identified and recovered based on their adhesion to immobilized preparations of neutral and zwitterionic glycolipids extracted from Drosophila embryos. We have identified an endogenous lectin expressed during Drosophila embryogenesis. The cloned lectin, designated ‘gliolectin’, possesses a novel protein sequence with a calculated molecular mass of 24,993. When expressed in Drosophila S2 cells, the lectin mediates heterophilic cellular aggregation. In embryos, gliolectin is expressed by a subset of glial cells found at the midline of the developing nervous system. Expression is highest during the formation of the Drosophila embryonic axonal commissures, a process requiring midline glial cell funcion. Immunoprecipitation with a monoclonal antibody against gliolectin yields a protein of Mr=46,600 from Drosophila embryonic membranes, suggesting that post-translational modification of gliolectin is extensive. Epitope- tagged chimericproteins composed of the amino terminal one-half of gliolectin and the Fc region of human IgG bind a small subset of the total glycolipids extracted from Drosophila embryos, demonstrating that the lectin activity of gliolectin can discriminate between oligosaccharide structures. The presence of gliolectin in the developing Drosophila embryonic nervous system further supports a role for cell surface carbohydrates in cell-cell recognition and indicates that the molecular diversity of animal lectins is not yet completely defined.

Monosialogangliosides of human myelogenous leukemia HL60 cells and normal human leukocytes. 2. Characterization of E-selectin binding fractions, and structural requirements for physiological binding to E-selectin

E-selectin binding gangliosides were isolated from myelogenous leukemia HL60 cells, and the E-selectin binding pattern was compared with that of human neutrophils as described in the preceding paper in this issue. The binding fractions were identified as monosialogangliosides having a series of unbranched polylactosamine cores. Structures of fractions 12-3, 13-1, 13-2, and 14, which showed clear binding to E-selectin under the conditions described in the preceding paper, were characterized by functional group analysis by application of monoclonal antibodies, 1H-NMR, FAB-MS, and electrospray mass spectrometry with collision-induced dissociation of permethylated fractions. Fractions 12-3, 13-1, and 13-2 were characterized by the presence of a major ganglioside with the following structure: NeuAc alpha 2-->3Gal beta 1-->4 GlcNAc beta 1-->3Gal beta 1-->4(Fuc alpha 1-->3) GlcNAc beta 1-->3Gal beta 1-->4(Fuc alpha 1-->3)-GlcNAc beta 1-->3Gal beta 1-->4GlcNAc beta 1-->3 Gal beta 1-->4 Glc beta Cer. Fractions 12-3 and 13-2 contained, in addition, small quantities (10-15%) of extended SLex with internally fucosylated structures: NeuAc alpha 2-->3 Gal beta 1-->4-(Fuc alpha 1-->3) GlcNAc beta 1-->3 Gal beta 1-->4(Fuc alpha 1-->3) GlcNAc beta 1-->3 Gal beta 1-->4 (+/- Fuc alpha 1-->3)GlcNA c beta 1-->3 Gal beta beta 1-->4GlcNAc beta 1-->3 Gal beta 1-->Glc Beta Cer. Fraction 13-1, showing stronger E-selectin binding activity than 12-3 and 13-2, contained only a trace quantity (< 1%) of SLex. Fraction 14, which also showed clear binding to E-selectin, was characterized by the presence of the following structures, in addition to two internally monofucosylated structures (XX and XXI, Table 2, text): NeuAc alpha 2-->3Gal beta 1-->4GlcNAc beta 1-->3Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc beta 1-->3 Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc beta 1-->3Gal beta 1-->4 GlcNAc beta 1-->3 Gal beta 1-->4 GlcNAc beta 1-->3 Gal beta 1-->4 Glc beta Cer; andNeuAc alpha 2-->3Gal beta 1-->4GlcNAc beta 1-->3 Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc beta 1-->3Gal beta 1-->4GlcNAc beta 1-->3Gal beta 1-->4 (Fuc alpha 1--3)-GlcNAc beta 1-->3Gal beta 1-->4GlcNAc beta 1-->3Gal beta 1--4Glc beta Cer. SLex determinant was completely absent. Thus, the E-selectin binding epitope in HL60 cells is carried by unbranched terminally alpha 2-->3 sialylated polylactosamine having at least 10 monosaccharide units (4 N-acetyllactosamine units) with internal multiple fucosylation at GlcNAc. These structures are hereby collectively called "myeloglycan". Monosialogangliosides from normal human neutrophils showed an essentially identical pattern of gangliosides with selectin binding property. Myeloglycan, rather than SLex, provides a major physiological epitope in E-selectin-dependent binding of leukocytes and HL60 cells.

Monosialogangliosides of human myelogenous leukemia HL60 cells and normal human leukocytes. 1. Separation of E-selectin binding from nonbinding gangliosides, and absence of sialosyl-Le(x) having tetraosyl to octaosyl core

Previous studies suggested that sialosyl-Le(x) (SLex) is a ligand expressed in human neutrophils and myelogenous leukemia HL60 cells which binds to E-selectin and possibly P-selectin. However, clear data on structures of carbohydrate epitopes in these cells were lacking. A systematic study was therefore initiated, employing a large quantity of HL60 cells (> or = 1200 mL packed) and human leukocytes (approximately 100 mL packed). Gangliosides were extracted, followed by extensive fractionation and examination of the E- and P-selectin binding ability of each fraction. The following results were of particular interest: (i) Only monosialogangliosides having a polylactosamine core with > 10 monosaccharide units (or > 4 N-acetyllactosamine units) showed E-selectin binding under static conditions with thin-layer chromatography overlay technique employing 32P-labeled E-selectin-expressing CHO cells. (ii) Sulfate groups were not detectable in the binding fractions, and di- and trisialoganglioside fractions did not show E-selectin binding under these conditions. (iii) None of the fractions showed P-selectin binding under a similar assay system using 32P-labeled P-selectin-expressing CHO cells. (iv) Major gangliosides of HL60 cells were structures I-XI (shown in Table 1 of text), none of which showed E-selectin binding under the above conditions. (v) SLex gangliosides having tetraosyl to octaosyl ceramide core, which are the major gangliosides of epithelial tumors (shown in Table 2), were completely absent from HL60 cells and neutrophils. Isolation and chemical characterization of ganglioside structures I-XI are described in this paper.

High-resolution thin-layer chromatography of gangliosides

In this review an updated overview of current improvements on thin-layer chromatography (TLC) of gangliosides over the past decade is provided. Basic general techniques and special advice is given for successful separation of glycosphingolipids. New approaches concerning continuous and multiple development, and several preparative TLC methods are also included. Emphasis is placed on TLC immunostaining and related techniques, i.e. practical applications of carbohydrate-specific antibodies, toxins and bacteria, viruses, lectins and eukaryotic cells. Thus, this review on ganglioside TLC summarizes its power as an analytical tool for a wide range of purposes.

Carbohydrate recognition in the peripheral nervous system: a calcium-dependent membrane binding site for HNK-1 reactive glycolipids potentially involved in Schwann cell adhesion

The carbohydrate determinants recognized by the HNK-1 antibody are potential cell-cell recognition ligands in the peripheral nervous system (PNS). The HNK-1 reactive sulfoglucuronylneolacto (SGNL) glycolipids specifically support Schwann cell adhesion, suggesting the presence of a cell surface receptor specific for SGNL-oligosaccharides. We directly probed PNS membranes for receptors complementary to SGNL determinants using a synthetic radioligand consisting of radioiodinated serum albumin derivatized with multiple SGNL-oligosaccharides. A high-affinity, saturable, calcium-dependent binding site for this ligand was found in PNS myelin membranes. Binding activity was carbohydrate-specific (most potently inhibited by SGNL-lipids compared to other glycolipids) and PNS-specific (absent from comparable central nervous system membranes). The SGNL-specific binding activity on PNS membranes reported here may be involved in peripheral myelination or myelin stabilization.

A quantitative microassay of carbohydrate-mediated cell adhesion to glycoconjugates immobilized on polystyrene plates

A microadhesion assay that allows the quantitative determination of carbohydrate-mediated cell adhesion to glycoconjugates immobilized on 96-well polystyrene plates has been developed. After dislodging nonadherent cells by centrifugation, specifically bound cells are quantified by colorimetric analysis of a blue formazan product generated from the dye 3-(4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide by enzymatic reduction. Carbohydrate specificity of the cell adhesion was demonstrated by inhibition analyses and the general applicability of the assay was proved with indicator cells of three different origins: mouse fibrosarcoma cells, Chang liver cells, and human breast carcinoma cells (MDA-MB 231).

Polyisobutylmethacrylate modifies glycolipid binding specificity of verotoxin 1 in thin-layer chromatogram overlay procedures

Verotoxins (or Shiga-like toxins) are a family of closely related toxins elaborated by Escherichia coli. At least three toxins have been described, VT1, VT2, and SLTII, in addition to Shiga toxin itself, and all bind to globotriaosyl ceramide, Gb3. Some discrepancies exist in the literature regarding the binding of the toxins to Gb4 as monitored by TLC overlay procedures. These procedures are widely used to investigate the specificity of carbohydrate-binding ligands. Polyisobutylmethacrylate, PIBM, is generally used in TLC overlay procedures to prevent silica loss and orient carbohydrate moieties for the binding of various ligands to glycolipids. We now report that pretreatment of chromatograms with PIBM modifies binding of VT1 to include Gb4 and decreases binding to Gb3 and the P1 glycolipid. We suggest that PIBM can alter the conformation of the glycolipid oligosaccharide, and therefore caution is advised in analysis of ligand binding to glycolipids after treatment with this compound.

Complex carbohydrates in drug development

Recent advances in carbohydrate chemistry and biochemistry afford the opportunity to develop bioactive complex carbohydrates, per se , as drugs or as lead compounds in drug development. Complex carbohydrates are unique among biopolymers in their inherent potential to generate diverse molecular structures. While proteins vary only in the linear sequence of their monomer constituents, individual monosaccharides can combine at any of several sites on each carbohydrate ring, in linear or branched arrays, and with varied stereochemistry at each linkage bond. This chapter addresses some salient features of mammalian glycoconjugate structure and biosynthesis, and presents examples of the biological activities of complex carbohydrates. The chapter presents selected examples that will provide an accurate introduction to their pharmacological potential. In addition to their independent functions, oligosaccharides can modify the activities of proteins to which they are covalently attached. Many glycoprotein enzymes and hormones require glycosylation for expression and function. The chapter discusses the ancillary role of carbohydrates that is of great importance to the use of engineered glycoproteins as pharmaceuticals.

The resolution into molecular species on desorption of glycolipids from thin-layer chromatograms, using combined thin-layer chromatography and fast-atom-bombardment mass spectrometry

Using a specially designed, motorised t.l.c.-f.a.b.-m.s. probe with continuous desorption and scanning over a moving t.l.c. plate, it was shown that glycolipids with identical carbohydrate sequences were well resolved into molecular species with differences in long-chain base and fatty acid. There was no serious diffusion of the glycolipids into the matrix. The technique is demonstrated for sulphatides (one and two sugar residues) isolated from human kidney, GM3 ganglioside isolated from human malignant melanoma, and chemically modified gangliotetraosylceramide from mouse intestine. T.l.c.-f.a.b.m.s. is convenient for sequencing and composition analysis of receptor-active glycolipids, the biological activity of which can be monitored in parallel by overlay on the t.l.c. plate with proteins, viruses, bacteria, or animal cells.

Carbohydrate ligands for endothelial-leukocyte adhesion molecule 1

The acute inflammatory response requires that circulating leukocytes bind to and penetrate the vascular wall to access the site of injury. Several receptors have been implicated in this interaction, including a family of putative carbohydrate-binding proteins. We report here the identification of an endogenous carbohydrate ligand for one of these receptors, endothelial-leukocyte adhesion molecule 1 (ELAM-1). Radiolabeled COS cells transfected with a plasmid containing the cDNA for ELAM-1 were used as probes to screen glycolipids extracted from human leukocytes. COS cells transfected with this plasmid adhered to a subset of sialylated glycolipids resolved on TLC plates or adsorbed on polyvinyl chloride microtiter wells. Adhesion to these glycolipids required calcium but was not inhibited by heparin, chondroitin sulfate, keratan sulfate, or yeast phosphomannan. Monosaccharide composition, linkage analysis, and fast atom bombardment mass spectrometry of the glycolipids indicate that the ligands for ELAM-1 are terminally sialylated lactosylceramides with a variable number of N-acetyllactosamine repeats and at least one fucosylated N-acetylglucosamine residue.

Carbohydrate-mediated cell adhesion to glycoproteins immobilized on nitrocellulose

A method that allows the estimation of carbohydrate-mediated cell adhesion to glycoproteins and polysaccharides immobilized to a nitrocellulose matrix is described. Specificity of adhesion by indicator cells (Chang liver) has been verified using glycoconjugates with defined carbohydrate structure. Two independent receptor systems with beta-galactose or alpha-fucose specificity, respectively, have been demonstrated by this method to occur on Chang liver cells. The method is also applicable for other indicator cells like murine fibrosarcoma cells and has been used for the analysis of dot-blots and Western blots of glycoproteins.

A sensitive method to quantitate gangliosides of the gangliotetraose series directly on chromatograms using peroxidase conjugated cholera toxin

A method is described whereby ganglioside GM1 can be quantitated directly on thin-layer chromatograms using cholera toxin subunit B conjugated to horseradish peroxidase and visualized with chloronaphthol. Overlay and color development were performed after separating gangliosides on nano-TLC plates, and fixing with polyisobutylmethacrylate. Absolute quantitation was realized using a Shimadzu CS-9000 integrating spectrodensitometer, scanning at 580 nm. A correlation coefficient of 0.98 was obtained in a linear range of detection from 10(-11) to 10(-16) moles. Statistical analysis revealed good reproducibility and over 99% of the added gangliosides remained with the chromatogram during all overlay and washing procedures. By comparison, standard chemical visualization by resorcinol-HCl was linear in the nanomole range with a detection limit of only 10(-10) moles. Since the carbohydrate portion of gangliosides immobilized in this manner is susceptible to the action of enzymes including neuraminidase, this technique can be applied to all structures of the gangliotetraose series.