Prevention of experimental liver metastases by arabinogalactan

Polysaccharide conjugates surpass monosaccharide ligands in hepatospecific targeting - Synthesis and comparative in silico and in vitro assessment

Ligands with the polysaccharide headgroups have been recently reported by our group to possess enhanced interaction with asialoglycoprotein receptor (ASGPR) in silico as compared to ligands having galactose moieties. This enhanced interaction is a result of the polymer's backbone support in anchoring the ligand in a specific orientation within the bilayer. In this paper, we have attempted to provide an in vitro proof of concept by performing a comparative evaluation of polysaccharide and monosaccharide-based ligands. Docking was performed to understand interaction with ASGPR in silico. Agarose and galactose conjugates with behenic acid were synthesized, purified, and characterized to yield biocompatible hepatospecific ligands which were incorporated into nanoliposomes. Cellular internalization of these targeted liposomes was studied using confocal microscopy and flow cytometry. The toxicity potential was assessed in vivo. Results indicated that the polysaccharide-based ligand increased cellular uptake due to better interaction with the receptor as compared to ligand bearing a single galactose group. In addition to developing novel liver targeting ligands, the study also established proof of concept that has been suggested by earlier in silico investigations. The approach can be used to design targeting ligands and develop formulations with improved targeting efficacy.

Galectin-3 binds selectively to the terminal, non-reducing end of β(1→4)-galactans, with overall affinity increasing with chain length

Galactans are linear polysaccharides of β(1→4)-linked galactose residues. Although they can antagonize galectin function, the nature of their binding to galectins needs to be better defined to develop them as drugs. Here, we investigated interactions between galectin-3 (Gal-3) and a series of galactans ranging in weight average molecular weight from 670 to 7550 Da. 15N-1H HSQC NMR studies with 15N-labeled Gal-3 carbohydrate recognition domain (CRD) indicate that each of these galactans interacts primarily with residues in β-strands 4, 5 and 6 on the canonical, β-galactoside sugar binding S-face. Although these galactans also bind to full length Gal-3 (CRD plus N-terminal tail) to the same extent, it appears that binding to the S-face attenuates interactions between the CRD F-face and N-terminal tail, making interpretation of site-specific binding unclear. Following assignment of galactan 13C and 1H resonances using HSQC, HMBC and TOCSY experiments, we used 13C-1H HSQC data to demonstrate that the Gal-3 CRD binds to the terminal, non-reducing end of these galactans, regardless of their size, but with binding affinity increasing as the galactan chain length increases. Overall, our findings increase understanding as to how galactans interact with Gal-3 at the non-reducing, terminal end of galactose-containing polysaccharides as found on the cell surface.

Plant oligosaccharides - outsiders among elicitors?

This review substantiates the need to study the plant oligoglycome. The available information on oligosaccharins - physiologically active fragments of plant cell wall polysaccharides - is summarized. The diversity of such compounds in chemical composition, origin, and proved biological activity is highlighted. At the same time, plant oligosaccharides can be considered as outsiders among elicitors of various natures in research intensity of recent decades. This review discusses the reasons for such attitude towards these regulators, which are largely connected with difficulties in isolation and identification. Together with that, approaches are suggested whose potentials can be used to study oligosaccharins. The topics of oligosaccharide metabolism in plants, including the ways of formation, transport, and inactivation are presented, together with data on biological activity and interaction with plant hormones. The current viewpoints on the mode of oligosaccharin action - perception, signal transduction, and possible "targets" - are considered. The potential uses of such compounds in medicine, food industry, agriculture, and biotechnology are discussed.

Atomic force microscopy as a nanoscience tool in rational food design

Atomic force microscopy (AFM) is a nanoscience tool that has been used to provide new information on the molecular structure of food materials. As an imaging tool it has led to solutions to previously intractable problems in food science. This type of information can provide a basis for tailoring food structures to optimise functional behaviour. Such an approach will be illustrated by indicating how a basic understanding of the role of interfacial stability in complex foods systems can be extended to understand how such interfacial structures behave on digestion, and how this in turn suggests routes for the rational design of processed food structures to modify lipolysis and control fat intake. As a force transducer AFM can be used to probe interactions between food structures such as emulsion droplets at the colloidal level. This use of force spectroscopy will be illustrated through showing how it allows the effect of the structural modification of interfacial structures on colloidal interactions to be probed in model emulsion systems. Direct studies on interactions between colliding soft, deformable droplets reveal new types of interactions unique to deformable particles that can be exploited to manipulate the behaviour of processed or natural emulsion structures involved in digestion processes. Force spectroscopy can be adapted to probe specific intermolecular interactions, and this application of the technique will be illustrated through its use to test molecular hypotheses for the bioactivity of modified pectin molecules.

Inhibition of galectin-3 mediated cellular interactions by pectic polysaccharides from dietary sources

Pectic polysaccharides from dietary sources such as Decalepis hamiltonii--swallow root (SRPP), Hemidesmus indicus (HPP), Nigella sativa--black cumin (BCPP), Andrographis serpyllifolia-(APP), Zingiber officinale--ginger (GRPP) and, citrus pectin (CPP) were examined for galectin inhibitory activity. Inhibition of (a) galectin-3 of MDA-MB-231 cells induced hemagglutination of red blood cells; (b) galectin-3 mediated interaction between normal/metastatic human buccal cells (NBC)/(MBC) and; (c) invasion of MDA-MB-231 and MBC in the invasive chamber was assessed. Results indicated that SRPP inhibited hemagglutination at Minimum Inhibitory Concentration (MIC) of 1.86 microg ml(-1) equivalent of carbohydrate as apposed to those of BCPP (130 microg ml(-1)), APP (40 microg ml(-1)), HPP (40 microg ml(-1)) and CPP (25 microg ml(-1)). GRPP even at concentration >1-6 mg ml(-1) did not inhibit agglutination. Also SRPP showed approximately 15 and 2 fold potent anti hemagglutination activity relative to that of galectin-3 specific sugars-galactose (MIC-27.1 microg ml(-1)) and lactose (MIC-4.16 microg ml(-1)) respectively. Further, SRPP at 10 microg ml(-1) inhibited agglutination of NBC by galectin-3 of MDA-MB-231 cells. Modified swallow root pectic polysaccharide (MSRPP) of 50 kDa retained anti hemagglutination activity (MIC of 1.03 microg ml(-1)) and inhibited MDA-MB-231 and MBC invasion by 73 and 50% with an IC(50) of 136 and 200 microg ml(-1) respectively. Both SRPP and MSRPP induced apoptosis up to 80% at 100 microg ml(-1) concentration by activating approximately 2 and 8 folds of Caspase-3 activity. Sugar composition analysis and its correlation with the galectin inhibitory property indicated that pectic polysaccharides with higher arabinose and galactose content-arabinogalactan inhibited hemagglutination significantly.

Synthesis of poly(maleimide-co-2-ethylacrylic acid) and its properties of suppressing metastasis and growth of carcinoma

A series of copolymers is prepared using maleimide and 2-ethylacrylic acid as comonomer. This kind of copolymer shows low toxicity (LD50: 601-798 mg/kg) and significant curative effect on Lewis lung carcinoma and S180.

Synthesis of multivalent beta-lactosyl clusters as potential tumor metastasis inhibitors

A beta-lactosyl residue was linked to the amino groups of L-lysyl-L-lysine through spacer arms of three different lengths (C2, C4, and C9) to give trivalent beta-lactosyl clusters in order to increase the inhibitory activity of the beta-lactosyl group against tumor cell colonization. Thus, O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->4)-2,3, 6-tri-O-acetyl-glucopyranosyl trichloroacetimidate was treated with methyl or benzyl hydroxyethanoate, methyl or benzyl 4-hydroxybutanoate, and methyl 9-hydroxynonanoate, respectively, in the presence of trimethylsilyl trifluoromethanesulfonate to give the corresponding beta-lactosides. These were coupled to L-lysyl-L-lysine, after conversion to the N-hydroxysuccinimide esters, to yield the corresponding trivalent beta-lactosyl-L-lysyl-L-lysine conjugates in good yields. The beta-lactosyl group with a C4 spacer arm was also coupled similarly to poly(L-lysine) (M(r) 3800) to form a polyvalent beta-lactosyl cluster. Coinjection of the trivalent (with C2 and C4 spacer arms) and polyvalent beta-lactosyl clusters with the highly metastatic B16 murine melanoma cells inhibited the formation of lung colonies in C57/BL mice, whereas the trivalent cluster with a C9 spacer arm displayed no activity.

Lectins: mediators of adhesion for bacteria in infectious diseases and for tumor cells in metastasis

Adhesion of bacteria and adhesion of tumor cells have much in common, especially the participation of lectins in this process. In the future it might be possible to inhibit the metastatic process into the liver (e.g. during surgical operations of malignant tumors) and bacterial adherence to mucosal linings or plastic devices by blocking of adhesion molecules (lectins) with appropriate glycoconjugates. Initial clinical trials are very promising.

Glycosphingolipid expression on murine L1-fibrosarcoma cells: analysis of clonal in vivo and in vitro selected sublines with different lung colonisation potential

The patterns of acidic and neutral glycosphingolipids (GSLs) were examined in a syngeneic tumour system in Balb/c mice consisting of closely related cell lines with different colonisation potentials directed to the murine lungs (in vivo selected highly metastatic sublines of L1-fibrosarcoma cells and their WGA-resistant mutants with low metastatic potential). GSLs were analysed by high-performance thin-layer chromatography and structurally identified by fast atom bombardment mass spectrometry combined with compositional analyses and exo-glycosidase digestion. The results suggest that highly metastatic sublines L1-LM and L1-LM12 derived by in vivo selection from mouse fibrosarcoma cells (cell line L1) exhibit a drastic increase of polar ganglioside expression and a restriction to globo-series GSLs. Contrasting with this the low metastatic mutant cells (L1-LM13WGA) express a reduced portion of acidic GSLs and exhibit a shift to less polar ganglioside components. Total cellular and plasma membrane-integrated GSLs were demonstrated to exhibit largely identical patterns. Concomitant with a significant decrease in LacCer expression a substantial reduction of GM2 and a complete lack of GM3 expression can be assigned to the highly metastatic sublines of L1-cells. On the other hand, the more polar gangliosides GM1a and, to an even greater extent, GD1a (exceeding 70% of total gangliosides) accumulate on L1-LM and their clonal sublines. The shift to acidic GSLs of higher polarity is less pronounced on the low metastatic WGA-resistant mutant cells (L1-LM13WGA) showing a preponderance of GM1a. The portion of GD1a within the fractions of acidic GSLs does not correspond to the cellular activities of CMP-NeuAc/GM1 (alpha 2-3) sialyltransferase measured for high and low metastatic cell variants. Total sialic acid content of the various cell lines differs, but is not associated with the metastatic potential. Gangliosides on L1-cells exhibit a significant substitution of N-glycolyl for N-acetylneuraminic acid (13%) compared to their metastatic sublines and to mutant cells (less than 1%). A conversion of surface exposed GD1a to GM1a on membranes of metastatic cells by in situ treatment with Vibrio cholerae sialidase is associated with a significant reduction of tumour cell colonisation directed to the murine lungs.

Towards the development of antimicrobial drugs acting by inhibition of pathogen attachment to host cells: a need for polyvalency

The development of inhibitors of microbial attachment to target cells has been proposed recently as a possible novel approach to antimicrobial chemoprophylaxis and treatment. In this paper an attempt is made to contend that such artificial inhibitors must be polyvalent, i.e. capable of binding to the pathogen or its target by multiple bonds.

Pseudomonas aeruginosa lectins as a model for lectin production, properties, applications and functions

Pseudomonas aeruginosa is one of the most troublesome human pathogens in the antibiotic consuming era. It produces lectins and lectinoid adhesins as secondary metabolites. The production of these compounds is genetically determined and is highly sensitive to changing environmental conditions. These dictate the type of the lectin produced ["type" variation], the lectin level ["on-off" variation], and its localization ["in-out" variation]. PA-I [galactophilic] and PA-II [fucose and mannose-binding] P. aeruginosa lectins are sensitive to EDTA and exhibit biophysical properties, resembling those of classical plant lectins. They exert similar in vitro biological effects and have an equal applicative potential. Lectin deficient strains and mutants of P. aeruginosa may be used for studies on lectin role in "conditioning" the bacterium lytic and toxic activities in its attacks on cells or macromolecules. The Pseudomonas lectins confunction with lytic and toxic activities: We suggest that they serve the homing and "condition" the lytic enzyme optimal activity on cellular and macromolecular targets. Namely their role resembles that of "positioning sites" of lytic enzymes and "receptor-binding" domains of powerful microbial, plant and animal toxic or lytic systems [including immunoglobulins, which "condition" the lytic activities of complement and phagocytes], as well as certain hormones, which condition limited key lytic activities, and thereby trigger a cascade of metabolic reactions.

Inhibition of liver tumor cell colonization in two animal tumor models by lectin blocking with D-galactose or arabinogalactan

Repeated administration of the hepatic lectin blocking agents D-galactose or arabinogalactan completely prevented the settling of metastatic cells of sarcoma L-1 tumor in the liver of Balb/c mice and greatly reduced the colonization process of highly metastatic ESb lymphoma cells of the liver of DBA/2 mice. Therefore, when hepatic lectins were blocked with competitive glycoconjugates, tumor cell colonization of the liver could be prevented in two different model systems.

Mechanism of liver-specific metastatic tumor spread in a murine tumor model

Malignant tumors frequently show an organ-specific metastatic spread, the causes of which are still largely unknown. Using an experimental tumor model, a methylcholanthrene-induced pleomorphic myofibrosarcoma ER 15-P of the C57Bl6J mouse, we wanted to find out whether this phenomenon is due to an adaptation or to a selection of tumor cells. After i.v. injection of tumor cells from the primary ER 15-P into the tail vein of male mice, metastases were regularly found in the lungs, mediastinal lymph nodes, and brain, as well as in the liver and kidneys, and occasionally in the adrenals. The following experimental procedures were used to isolate a tumor cell line with a possible liver preference: (1) Tumor cells from the primary ER 15-P were injected into a mesenteric vein of male mice. Tumor cells from the resulting liver colonies were again injected into the portal system of one group of mice. In a second group, part of the same cell suspension was injected into the tail vein. This procedure was performed four times. (2) Tumor cells from the primary ER 15-P were applied into the tail vein of male mice. Tumor cells from the resulting liver metastases were reinjected directly into the tail vein. This experiment was repeated three times. (3) Tumor cells from the primary ER 15-P were injected into the tail vein of male mice. Tumor cells from liver metastases were then injected, first, into the portal system of one group of male mice, and thereafter into the tail vein of another group of animals. This experiment was repeated twice. The following results were obtained: (1) By a repeated adaptation of tumor cells from the primary ER 15-P to liver tissue, no tumor cell line could be isolated that would show a preferential metastatic spread to this organ after tail-vein injection. (2) Repeated i.v. passages of tumor cells from liver metastases into the tail vein led to the selection of a tumor cell line with a tendency to liver metastasis. (3) Tumor cells selected from liver metastases induced via tail-vein injection showed, after a prolonged stay in the liver and a successive i.v. passage into the tail vein, a marked specificity for this organ. These results indicate that the liver-specific spread of tumor cells in our model is based on the selection of a tumor cell line from the primary ER 15-P influenced by the hepatic microenvironment.

Modification of glycosylation by tunicamycin treatment inhibits lectin-mediated adhesion of Streptococcus pneumoniae to various tissues

Oligosaccharide moieties of cell surface glycoconjugates are thought to be involved in recognition events associated with infectious diseases. Treatment of Streptococcus pneumoniae (which exhibits well defined surface lectins) with subinhibitory concentrations of the antibiotic tunicamycin was found to block the protein glycosylation of the bacterial surfaces. Since bacterial lectins (adhesins) are in most cases glycoproteins and play an important role in the organ specificity of infectious diseases, adhesion of Streptococcus pneumoniae to frozen sections of lung, meninges and kidney (from Balb/c-mice) was almost totally lacking after inhibition of the biosynthesis of N-linked carbohydrate chains which are important for an adequate lectin function. Chemiluminescence measurements of human granulocyte stimulation yielded results suggesting a great importance of lectin-carbohydrate interactions in this process, too. These experimental data indicate that the presence of specific cell surface carbohydrates is required for a successful completion of the adhesion phase of pathogenic bacteria in infectious diseases and for the induction of granulocyte stimulation.

In vitro and in vivo inhibition of lectin mediated adhesion of Pseudomonas aeruginosa by receptor blocking carbohydrates

In vitro and in vivo experiments with Balb/c mice and Pseudomonas aeruginosa ATCC 27853 supported our hypothesis that bacterial lectins play an important role in the organotropy of infectious diseases. In vitro and in vivo adhesion of P. aeruginosa was mediated by N-acetylneuraminic acid (NANA) receptors. Blocking of the binding sites (lectins) on the bacterial surfaces with competitive specific carbohydrates (NANA) completely prevented the bacterial adhesion process in vitro. In vivo the number of adherent organisms in various organs decreased dramatically in the presence of NANA, whereas non-related carbohydrates (e.g. D-galactose) just showed negligible effects. Additionally, the application of NANA-treated organisms protected the animals from septicemia and death. Therefore, blocking of bacterial lectin receptors with specific carbohydrates might be of clinical relevance to prevent bacterial attachment to organ cells.

Lectin mediated adhesion of Streptococcus pneumoniae and its specific inhibition in vitro and in vivo

According to our hypothesis, bacterial lectins play an important role in the organotropy of infectious diseases which is analogous to the metastasis of tumor cells. As a model for proving this, we investigated the specific lectin of Streptococcus pneumoniae, which has N-acetyl-D-glucosamine/D-galactose (GlcNAc-Gal) specificity. In vitro, after incubation with Streptococcus pneumoniae, cryotome sections of various organs from Balb/c-mice showed remarkable quantitative differences of bacterial adhesion to the organ cells. Whereas lungs and meninges were closely settled with bacteria, attachment to other organs (e.g. liver, spleen, brain) was lacking. In vitro lectin-blocking by GlcNAc completely prevented the adherence of Streptococcus pneumoniae to lungs and meninges. Other non-related carbohydrates (e.g. D-mannose, D-xylose) showed no effect. During in vivo experiments with Balb/c-mice, intratracheal application of Streptococcus pneumoniae led to a diffuse settlement of the lung. However, bacterial lectin-blocking with intratracheal GlcNAc administration completely inhibited adhesion to the organ cells of the lung. Therefore blocking of bacterial adhesins with competitive specific monosaccharides can completely prevent bacterial adhesion processes, a fact, which opens therapeutical aspects.

Combined immunostimulation (Propionibacterium avidum KP 40) and anticoagulation (heparin) prevents metastatic lung and liver colonization in mice

The antineoplastic activity of Propionibacterium avidum KP-40 and its enhancement by anticoagulation with heparin was studied. In Balb/c mice syngeneic sarcoma L-1 exclusively caused tumor colonization of the lungs. After neuraminidase treatment the organotropism of this tumor was changed, with tumor nodules developing in lung and liver. After single systemic application of Propionibacterium avidum KP-40 the number of lung and liver colonies decreased evidently. Combination of this immunomodulating therapy with temporary anticoagulation resulted in further reduction of tumor colonies in lung and liver.

Prevention of experimental liver metastases by D-galactose

The metastasis of malignant tumors from a primary site to near and distant secondary sites is probably the most important event in the pathogenesis of cancer and it accounts for most cancer deaths. Whereas advances in the treatment of primary cancer have led to increased patient survival, metastatic cancers are still the most difficult group of diseases to treat successfully. As organ-characteristic lectins play an important role in the organ manifestation of metastatic islets, it might be possible (e.g. during surgical operations on malignant tumors) to block those organ-characteristic lectins with the appropriate receptor-bearing glycoconjugates in order to inhibit the metastatic spread. Recent experiments have demonstrated that neuraminidase treatment of tumor cells (mouse sarcoma-1) alters in vivo (Balb/c-mice) the organotropic distribution of metastases; instead of being found exclusively in the lung, they are found both in lung and liver. However, pre-injection and regular application of D-galactose--the same holds for arabinogalactan--prevents the setting of metastases in the liver but does not influence the metastatic process to the lung, whereas mannan--as a galactose-free control substance--does not alter the initial pattern of metastasis to lung and liver.

Inhibition of liver metastasis in mice by blocking hepatocyte lectins with arabinogalactan infusions and D-galactose

According to our hypothesis, organ-specific lectins (e.g., the D-galactose-specific hepatic binding protein) play an important role in the organ location of metastatic malignant cells. The rapid clearance and uptake by the liver of tritiated alpha 1-acid-(asialo)glycoprotein from the circulation of Balb/c mice was markedly delayed after preinjection of D-galactose or arabinogalactan. The preinjection (1 h) and regular application (for 3 days after tumor cell inoculation in Balb/c mice) of the receptor blocking agents D-galactose and arabinogalactan prevented the settling of sarcoma L-1 tumor in the liver completely, but did not influence the settling in the lung. Other galactans, dextrans, and phosphate-buffered saline showed no effect. Therefore, when lectins were blocked with competitive-specific glycoconjugates, colonization was prevented.