Pattern of endogenous lectins of a human sarcoma (Ewing's sarcoma) reveals differences to human normal tissues and tumors of epithelial and germ cell origin

Isolation and characterization of galactose-specific carbohydrate-binding protein from Guerin tumor cells

Carbohydrate-binding protein with specificity towards galactose was isolated from Guerin tumor cells. This protein had molecular weight of 51 kDa in dissociating and reducing conditions. It was phosphorylated, but not glycosylated, having two isoforms with pIs corresponding to 7.3 and 7.9. We found predominantly cytoplasmic and nuclear, but not plasma membrane, localization of the isolated protein. Oxidative conditions and presence of the ligand are required for the protein to oligomerize. Probing of the carbohydrate-binding domain with sugar derivatives showed that hydroxyl groups at C3, C4 and C6 positions of galactose, as well as at C3 and C6 positions of the glucose part of NAcLactosamine are involved in ligand binding. Tyrosine, tryptophan and histidine amino acids were found to participate in binding of the galactose ligand. N-linked multivalent macromolecular ligands, containing up to four antennae, bound to the isolated protein with positive cooperativity. Affinity for NAcLactosamine, as measured by its I(50) value, was 7918-times higher than that for galactose. Binding of galactose to the combining site was enthalpically driven, dH=-32.16 (kJ mol(-1)), with K(d) in the micromolar range, 32.25 x 10(4) mol(-1).

Ewing's sarcoma. A retrospective study of histological and immunohistochemical factors and their relation to prognosis

Histological and immunohistochemical features of 87 patients with conventionally diagnosed Ewing's sarcoma were studied retrospectively on routinely processed material and evaluated with regard to prognostic significance. 74% were convincingly positive when stained for vimentin, 13% were doubtful, and 13% were negative. A varying degree of positivity for neuron-specific enolase (NSE) was found in 15%; these cases all co-expressed vimentin. A single tumour contained scattered cytokeratin-positive cells. Positivity for the leukocyte common antigen (LCA) could be demonstrated in three cases; these were excluded from the statistical analysis of prognostic factors. Growth pattern, soft tissue invasion, monomorphic or dimorphic cell population, and PAS-, NSE- or vimentin-positivity did not influence survival significantly. However, prognosis was increasingly poor with increasing degree of necrosis: median survival was 28 months for grade I necrosis (less than 10%), 16 months for grade II (10-50%), and 11 months for grade III (greater than 50%), p less than 0.0005. A mitosis count of less than 1 per high-powerfield (HPF) was correlated to a median survival of 26 months, greater than or equal to 1 per HPF to 12 months, p less than 0.05. The findings indicate some degree of heterogeneity in Ewing's sarcoma which may be related to primitive peripheral neuroectodermal tumours (PNETs), or be a true blastoma. In future trials, diagnostic criteria (including immunohistochemistry) should be clearly defined and materials should be large enough to allow for stratification according to prognostic factors.

Endogenous lectins as mediators of tumor cell adhesion

Endogenous carbohydrate-binding proteins have been found in various normal tissues and cells. Although lectins with different sugar-binding specificities have been described, the most prevalent ones are those that bind beta-galactosides. The ability of some normal and malignant cells to bind exogenous carbohydrate-containing ligands suggested that lectinlike activity is associated with the cell surface and that carbohydrate-binding proteins might mediate intercellular recognition and adhesion. We found that extracts of various cultured murine and human tumor cells exhibit a galactoside-inhibitable hemagglutinating activity. This activity was associated with two proteins of molecular weights of 34,000 and 14,500 daltons, which were purified by affinity chromatography by using immobilized asialofetuin. That these lectins are present on the cell surface was indicated by the binding of monoclonal antilectin antibodies to the surface of various tumor cells and by the immunoprecipitation of 125I-labeled lectins from solubilized cell-surface iodinated cells by polyclonal antilectin antibodies. That these cell surface lectins are functional was demonstrated by the ability of the galactose-terminating asialofetuin to enhance cell aggregation and of asialofetuin glycopeptides to block this homotypic aggregation as well as to suppress cell attachment to substratum, and by the inhibition of both asialofetuin-induced cell aggregation and cell attachment to substratum by the binding of monoclonal antilectin antibodies to the cell surface. These findings implicate cell surface lectins as mediators of cell-cell and cell-substratum adhesion. Some of these cellular interactions might be important determinants of tumor cell growth and metastasis.

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.

Targeting of neoglycoprotein-drug conjugates to cultured human embryonal carcinoma cells

Fluorescent neoglycoproteins were used to screen for the presence and sugar specificities of cell surface lectins in two human embryonal carcinoma cell lines. Efficient labeling correlated with extent of lectin-mediated uptake of neoglycoproteins, as measured by inhibition of DNA synthesis by drug-neoglycoprotein conjugates. These conjugates contain covalently linked carbohydrate moieties on the carriers to render them accessible to the membrane lectins, most effectively galactosides and alpha-glucosides. They furthermore contain chemically linked cytotoxic drugs (etoposide, cis-diamminedichloroplatinum II and methotrexate) which are intracellularly released after lysosomal breakdown of the carrier, as indicated by the effect of leupeptin. Sugars can confer a greater than 10-fold increase in cytotoxic capacity to the nonglycosylated carrier-drug conjugate, nearly reaching the level of toxicity of the freely diffusible drug. Two different neoglycoproteins, reacting with independently targeted membrane lectins, were shown to be useful in a model for combination chemotherapy. These results therefore suggest potential usefulness of custom-made glycosylated carriers in the targeting of therapeutic agents to human embryonal carcinoma cells.

Carbohydrate-binding proteins of tumor lines with different growth properties. II. Changes in their pattern in clones of transformed rat fibroblasts of differing metastatic potential

A tumor model system of clones of myeloproliferative sarcoma virus (MPV)-transformed rat fibroblasts (NRK) with different growth properties and metastatic potential was studied. The relationship between metastatic behavior and composition of carbohydrate-binding proteins (lectins) was analyzed by affinity chromatography. The metastatic variant differs qualitatively from its parental clone in the presence of galactoside-binding proteins at apparent molecular weight of 42 kDa. The alpha-glucosyl-binding proteins at apparent molecular weights of 67 kDa and 53 kDa and a galactoside-binding protein of apparent molecular weight of 34 kDa, however, are not detectable in the metastatic variant in comparison to its parental clone. In this respect the parental clone shows closer resemblance to the clone 5-8#1 with different growth properties and low metastatic potential than to its own metastatic variant. Furthermore, only the parental clone has a melibiose- and a mannan-binding protein of an apparent molecular weight of 64 kDa and 14 kDa, respectively. Rosette formation as model system for intercellular interaction reveals differences in the inhibition pattern with sugar between the two clones 5-8#1 and 5-20#20, whereas the metastatic variant 5-20#20 (s) exhibits drastically reduced capability to form rosettes. Initial experiments demonstrate the feasibility of drug targeting to transformed fibroblasts via carbohydrate-binding proteins.

Localization of endogenous lectins in normal human breast, benign breast lesions and mammary carcinomas

Specific antisera against three mammalian beta-galactoside-specific lectins of apparent molecular weights 14.5 kDa, 18 kDa and 29 kDa have been used to localize these lectins in normal breast, and in benign and malignant mammary lesions. In normal breast tissue discrete localization of two lectins (Mrs 14.5 kDa and 18 kDa) was demonstrated in fibroblasts, smooth muscle cells, myoepithelial cells and capillary endothelium. Extracellular localization of one lectin (Mr 14.5 kDa) in collagen was apparent. The third lectin (Mr 29 kDa) labelled preferentially luminal cells and their secretory product. Two benign tumours (an analyzed fibroadenoma and a papilloma) revealed strong staining with two lectins (Mrs 18 kDa and 29 kDa). Of the 24 mammary carcinomas examined, the lectin (Mr 14.5 kDa) was expressed by only occasional tumour cells, the lectin (Mr 18 kDa) occurred in many tumour cells and the lectin (Mr 29 kDa) labelled tumour cells in nearly all cases. The expression of these beta-galactoside-specific endogenous lectins therefore appears to be regulated differently in normal breast compared with mammary tumours.