[Lectins and the organotropy of metastasis]

Hepatocellular injury inhibits lectin-mediated tumor colonization into BALB/c-mice livers

Acute (hepatitis) and chronic (cirrhosis) liver injuries were experimentally induced in BALB/c-mice by administration of D-galactosamine and carbon tetrachloride, respectively. In both experimental liver diseases the incidence of hepatic tumor colonization of sarcoma L-1 was significantly reduced as compared to non-treated control animals. Thus, it seems that either dysfunction or loss of organ-characteristic lectins (galactosyl-specific hepatic lectins) prevented liver colonization. Histochemical staining of liver sections from D-galactosamine or carbon tetrachloride-treated mice with appropriate galactose-containing (neo)glycoproteins supported this hypothesis, since the lectin-dependent binding was greatly reduced as compared to sections from non-treated animals.

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.

[Tumor lectinology--status and perspectives of clinical application]

A detailed knowledge of the mechanisms of molecular recognition is a prerequisite to rationally improved diagnostic and therapeutic procedures in diseases. In addition to sequences of amino acids, carbohydrate structures apparently store biological information that is thought to be relevant for physiologically important processes. Such ligands, namely the carbohydrate part of cellular glycoconjugates, can be recognized by specific endogenous binding proteins like lectins. If their presence can be reliably ascertained and correlated to the clinical course of the disease, e.g. in oncology, lectinology may help to define a yet undisclosed role for this class of proteins in tumor progression and spread.

Blocking of lectin-like adhesion molecules on pulmonary cells inhibits lung sarcoma L-1 colonization in BALB/c-mice

Adhesion and inhibition experiments with pulmonary cells of BALB/c-mouse origin and syngeneic sarcoma L-1 cells indicated that L-fucose specific lectin-like adhesion molecules, presumably situated on pulmonary cell surfaces are (at least partly) responsible for the specificity of this cell-cell interaction. Addition of specific sugars and glycoconjugates (L-fucose and fucoidan, respectively) to the incubation medium evidently inhibited the adhesion process as quantified using radiolabelled tumor cells. Unspecific carbohydrates (e.g. D-galactose) did not affect the cellular interaction. In vivo, repeated administration of fucoidan (but not of unspecific glycoconjugates) significantly inhibited the settling of metastatic sarcoma L-1 cells in the lungs of BALB/c-mice. Therefore, when lectin-like adhesion molecules on pulmonary cells were blocked with competitive glycoconjugates, tumor cell colonization of the lung could be significantly inhibited.

Lectin binding sites in normal and phenobarbitale/halothane treated rat liver. A histochemical study

The content of carbohydrate residues of both normal and phenobarbitale-halothane-hypoxia exposed rat liver has been examined by means of lectin histochemistry. Eight biotinylated lectins specific to galactose, N-acetyl-galactosamine, N-acetyl-glucosamine, fucose and mannose were applied to paraffin sections of rat liver at light microscopic level. The most distinct binding was observed at the structures of the "perisinusoidal functional unit": Kupffer cells are bound by S-WGA, SBA and PNA. Bile canaliculi display binding sites for RCA I and WGA. Cytoplasm of hepatocytes appears lectin-negative, except for PSA. The enhanced reaction of S-WGA, PNA and SBA after the preincubation of the sections with neuraminidase indicates the occurrence of sialic acid in Kupffer cells. The phenobarbitale-halothane-hypoxia exposed rat liver shows centrolobular degeneration of hepatocytes with a diminished amount of hepatocyte and Kupffer cells as well. The lectin binding pattern of sinusoidal walls, membranes of hepatocytes and bile canaliculi remains the same compared to that of normal rat liver. This finding suggests that at least the carbohydrate content of membranes in the liver resists severe destruction under phenobarbitale-halothane-hypoxia. It is assumed that there exists a connection between intact carbohydrate residues and the regeneration of liver parenchyma.

Characterization and biological implications of membrane lectins in tumor, lymphoid and myeloid cells

Complex carbohydrates and sugar receptors at the surface of eukaryotic cells are involved in recognition phenomena. Membrane lectins have been characterized, using biochemical, biological and cytological methods. Their biological activities have been assessed using labeled glycoproteins or neoglycoproteins. Specific glycoproteins or neoglycoproteins have been used to inhibit their binding capacity in both in vitro and in vivo experiments. In adults, lymphoid and myeloid cells as well as tumor cells grow in a given organ and eventually migrate and home in another organ; these phenomena are known as the homing process or metastasis, respectively. In specific cases, membrane lectins of endothelial cells recognize cell surface glycoconjugates of lymphocytes or tumor cells, while membrane lectins of lymphocytes and of tumor cells recognize glycoconjugates of extracellular matrices or of non-migrating cells. Therefore, membrane lectins are involved in cell-cell recognition phenomena. Membrane lectins are also involved in endocytosis and intracellular traffic of glycoconjugates. This property has been demonstrated not only in hepatocytes, fibroblasts, macrophages and histiocytes but also in tumor cells, monocytes, thyrocytes, etc. Upon endocytosis, membrane lectins are present in endosomes, whose luminal pH rapidly decreases. In cells such as tumor cells or macrophages, endosomes fuse with lysosomes; it is therefore possible to target cytotoxic drugs or activators, by binding them to specific glycoconjugates or neoglycoproteins through a linkage specifically hydrolyzed by lysosomal enzymes. In cells such as monocytes, the delivery of glycoconjugates to lysosomes is not active; in this case, it would be preferable to use an acid-labile linkage. Cell surface membrane lectins are developmentally regulated; they are present at given stages of differentiation and of malignant transformation. Cell surface membrane lectins usually bind glycoconjugates at neutral pH but not in acidic medium: their ligand is released in acidic specialized organelles; the internalized ligand may be then delivered into lysosomes, while the membrane lectin is recycled. Some membrane lectins, however, do bind their ligand in relatively acidic medium as in the case of thyrocytes. The presence of cell surface membrane lectins which recognize specific sugar moieties opens the way to interesting applications: for instance, isolation of cell subpopulations such as human suppressor T cells, targeting of anti-tumor or anti-viral drugs, targeting of immunomodulators or biological response modifiers.

Lectin histochemistry on mucous substances of the taste buds and adjacent epithelia of different vertebrates

In the present study carbohydrate residues in taste buds (TBs) and adjacent epithelial formations of a teleostean fish, a frog and the rabbit were detected by means of lectin histochemistry. Biotinylated lectins from Pisum sativum (PSA), Arachis hypogaea (PNA), Dolichos biflorus (DBA), Triticum vulgaris (WGA and succinylated WGA), Glycine max (SBA) and Ulex europaeus (UEA I) have been applied. The lectins were bound to an avidin-biotin-peroxidase-complex (ABC) and visualized by diaminobenzidine/H2O2. Most intensive reactivity was observed at the taste disc cells of the frog with DBA, S-WGA and SBA. PNA did not bind to the TBs of any of the animals tested. As shown in SBA preparations, sialic acid is present in a nonacylated and an acylated form in the mucosa of the frog's tongue. The TBs of the fish possess all the sugars we looked for except for the disaccharide D-galactose-(1-3)-beta-D-N-acetyl-galactosamine (Gal/GalNAc) and sialic acid. The TBs of the rabbit contain GalNAc, as detected with DBA, but not with SBA; and fucose (Fuc), mannose (Man) and N-acetyl-glucosamine (GlcNAc). As revealed by preincubation of the tissue sections with neuraminidase in TB cells of the rabbit, sialic acid masks Gal/GalNAc and GalNAc. These lectin-binding characteristics show that in the TBs of some selected representatives which belong to different vertebrate classes exist different mucous substances. These substances possess different binding characteristics to specific sugars, and this is possibly of particular interest to chemoreception phenomena.

The influence of the microenvironment of liver-specific tumor cell colonization in a murine tumor model

Malignant tumors often show an organ-specific metastatic spread. Some cells of the primary apparently bear an affinity for growing in the microenvironment of certain organs. After i.v. injection of myofibrosarcoma cells from the primary ER 15-P into the tail vein of male C57/Bl6J mice, metastases developed in various organs. A tumor cell line (ER 15-Me3) isolated from liver metastases of the primary was found to colonize preferentially to the liver. To find out whether the liver specificity of the tumor cell line ER 15-Me3 depended on the hepatic microenvironment, tumor cells from this line were transplanted i.m. into the thighs of mice once (ER 15-Me3 i.m.1) or 5 times (ER 15-Me3 i.m.5), and then injected into the tail vein of mice. A part of the 5-times passaged tumor cell line was also injected into the mesenteric vein (ER 15-Me3 i.m.5-Me1) prior to reinjection into the tail vein.

RESULTS

After i.v. administration of tumor cells from the first i.m. passage of the tumor cell line (ER 15-Me3 i.m.1) into the tail vein, the liver-specific metastatic behavior of tumor cells remained stable. Following the i.v. injection of tumor cells from the 5th i.m. transplant generation of the tumor cell line (ER 15-Me3 i.m.5) into the tail vein, organ distribution was similar to that of the primary. After only 1 mesenteric vein passage of the 5-times i.m. transplanted line ER 15-Me3 i.m.5-Me1 followed by i.v. injection into the tail vein, did tumor cells regain their liver-specific colonizing potential. Thus, the liver-specific tumor cell line seems to contain a small number of other tumor cell populations from the unselected primary. In the muscle, these tumor cells have a growth advantage over the liver-specific cells, while the latter will grow better in the liver. This indicates that the microenvironment may be one important factor influencing the organ-specific metastatic pattern of tumor cells.

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.

Endogenous galactoside-binding lectins: a new class of functional tumor cell surface molecules related to metastasis

The formation of secondary tumors by circulating cancer cells (blood-borne metastasis) correlates with an increased tendency of the cells to form emboli by aggregation with other tumor cells or with host cells. Although it is evident that cell-cell recognition and adhesion are mediated by cell surface components, the identity of these molecules is only now being unraveled. Over the last decade an increasing number of studies have demonstrated the presence of endogenous carbohydrate-binding proteins on the surface of various normal cells, and it has been proposed that such lectin-like molecules might be involved in intercellular adhesion. We have shown that various tumor cell lines contain endogenous galactose-specific lectins. Lectin activity was detected at the cell surface by the binding of asialofetuin. This glycoprotein also enhanced the aggregation of the tumor cells. After purification by affinity chromatography on immobilized asialofetuin the lectin activity was associated with two proteins of Mr 14,500 and 34,000. By using polyclonal and monoclonal antilectin antibodies in conjunction with various immunologic techniques we have demonstrated that the endogenous lectins are present on the surface of different tumor cells. Quantitation of cell surface lectins by flow cytometric analyses of antilectin antibody binding revealed that among related tumor cells those exhibiting a higher metastatic potential expressed more lectin on their surface. The binding of monoclonal antilectin antibodies to metastatic cells decreased asialofetuin-induced homotypic aggregation in vitro and suppressed the ability of the cells to form lung metastases after intravenous injection in the tail vein of syngeneic mice. These results strongly implicate the tumor cell surface lectins in cell adhesion and metastasis. We propose that such lectins can increase the ability of tumor cells that enter the blood stream to form aggregates with other tumor cells, or to adhere to host cells or the extracellular matrix and thereby increase their metastatic potential. Other contributing components to tumor cell-host cell interactions are cell surface carbohydrate-binding proteins that have been detected on lymphocytes, platelets, macrophages, hepatocytes, and endothelial cells. These lectin-like molecules might recognize and bind carbohydrates expressed on the surface of tumor cells and enhance emboli formation and organ colonization.

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.

Differential expression of endogenous sugar-binding proteins (lectins) in murine tumor model systems with metastatic capacity

In order to investigate possible differences in sugar binding activities of strongly versus weakly metastatic tumors, sugar-binding molecules (endogenous lectins) of murine tumor cells differing in metastatic capacity were analyzed by affinity chromatography on supports with immobilized sugars or glycoproteins and compared. After elution with specific sugar in the absence of Ca2+-ions, the proteins were separated by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. In comparison to a weakly metastatic subline (Eb) spontaneous strongly metastatic variants (ESb) of a murine lymphoma contained additional sugar receptors for N-acetylglucosamine (Mr 30 kDa) and maltose (Mr 64 kDa, 62 kDa, 54 kDa and 32 kDa), and lacked one sugar receptor for myoinositol (Mr 85 kDa), N-acetylglucosamine (Mr 23 kDa) and maltose (Mr 22 kDa), respectively. The strongly metastatic variant ESb expressed the common beta-galactoside-specific lectin to a higher extent and receptors for myo-inositol, melibiose and mannan to a lower extent. In another model system derived from the murine mastocytoma cell line P 815 X 2A, biochemical analysis of the liver-metastasizing variant P 815 X 2B revealed additional characteristic N-acetylgalactosamine- and maltose-specific binding proteins. This variant had reduced amounts of receptors for beta-galactosides and fucose in comparison to the parental clone. In a third tumor system a similar qualitative difference was disclosed: a metastatic variant derived from spleen metastases displayed a sugar receptor profile with 5 additional beta-galactoside-binding proteins when compared to its parental clone 6-6#3 + F, which is a virally transformed fibroblast line. The results show that metastatic variants of 3 murine tumor models consisting of lymphomas, mastocytomas and sarcomas are characterized by qualitative and quantitative alterations in the profiles of sugar-binding proteins.

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.