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Role of carbohydrates in cancer
4th LTBW Abstracts/Lung
Cancer IO (1994) 347-373
These findings indicate that GRP may be a mitogen for the bronchial epithelium. Bronchial epithelial cells express message for the GRP and neuromedin B receptors, and a mitogenic response was demonstrated in eight of 13 cultures. Three out of three cultures from COPD patients showed a positive response to bombesin and/or GRP. Non-small cell carcinomas also express receptors for GRP, and a non-small cell carcinoma cell line was induced to express a GRP-like protein when adapted to serum-free conditions. These findings also provide further evidence for the plasticity of the differentiation features of lung tumors, and for a common precursor cell for both small cell and non-small cell lung carcinoma. Role of carbohydrates in cancer Singhal AK. The Biomembrane Institute & University of Washington Seattle, WA 98119.
Development of cancer is always associated with abnormal expression of cell surface carbohydrates. These diverse group of carbohydrate antigens including blood group antigens and gangliosides may be expressed either on glycosphingolipids or glycoproteins. Recent studies have indicated that these membrane carbohydrates are involved in cell-cell and cellsubstratum interactions. Certain gangliosides and their metabolites also modulate trans-membrane signal transduction by either up- or down-regulating various receptor kinases. Membrane Carbohydrate antigens expressed on mucin type glycoproteins have also been found to elicit cellular immune responses. Metastatic tumor cells migrate to the secondary sites by binding to the blood vessel endothelial cells. Recent studies showed that this binding is mediated by the interaction of blood group carbohydrates, sialylated Lex (SLeX) and its isomer SLe” expressed on metastatic tumor cells to the E- and P-Selectin molecules expressed on activated blood vessel endothelial cells. The tumor cells subsequently degrade capillary walls, migrate into tissues and establish metastatic deposits. The antibodies to these carbohydrate structures as well as carbohydrate analogs that may block this endothelial cell interaction are being considered as potential anti-metastatic drugs. Similar to the selectin-carbohydrate interaction, evidence is emerging that carbohydrate-carbohydrate interaction may also be an early and critical event in this tumor cell interaction. Exogenous addition of ganglioside GM3 strongly downregulates EGF receptor kinase and this inhibitory effect is more pronounced in the presence of lyso-phosphatidyl choline. Metabolites of GM3, namely, lyso-GM3 and sphingosine have been shown to be strong inhibitors of protein kinase C. Through this mechanism, a chemical derivative of sphingosine, trimethyl sphingosine (TMS) was found to block platelet activation and subsequent aggregation caused by tumor cells. Platelet aggregation is thought to be prominently involved in the metastatic process. TMS also down-regulates the expression of P-Selectin on activated endothelial cells and platelets and was found to significantly reduce metastatic deposits of B16 melanoma in lungs of C57 black mice. A block in carbohydrate chain elongation of O-glycosylated mucins results in specific accumulation of core structure, Tn (GalNac ol-O-Serinelthreonine) in large percentage of human
371
adenocarcinomas. Multivalent Tn antigen was found to induce a specific CD4+ T cell stimulation in mice. Active specific immunotherapy with the Tn antigen was effective in preventing growth of syngeneic tumors in mice. Therefore, certain carbohydrate antigens presented in a specific configuration may provide potential for a tumor vaccine. Monoelonal antiImrIy treatment of small cell lung cancer Stahel RA. Division of Oncology, Department of Medicine, University Hospital, CH-8091 Ziirich. Switzerland. Target antigens: The molecular nature of potential target
structures in the membrane of small cell lung cancer (SCLC) has been elucidated for three glycoproteins, including cluster-l antigen or the neural cell adhesion molecule NCAM cluster-2 antigen consisting of 40-kDa panepithetial transmembrane molecule, and cluster-w4 antigen. The latter, a 45-kDa highly glycosylated surface molecule of only 31 to 35 amino acids anchored in the membrane by glycosylphosphoinositol linkage has recently been shown to be identical to the leukocyte activation antigen CD24 and to be hyperexpressed in small cell lung cancer on the RNA and protein level. Using synthetic peptides we have been able to localise the epitope of cluster-w4 antibodies and several other CD24 antibodies to a three amino acid region of the core protein close to the phosphoinositol anchor. In addition to a uniform expression in all small cell lung cancer, the three antigens described have each selective expression in normal tissues, including neuroendocrine tissues for NCAM and CD24, and panepithelial expression for cluster-2 antigen. On white blood cells, NCAM expression is found in a moderate proportion of peripheral blood mononuclear cells and CD24 on pre-B cells and a proportion of granulocytes. Recently we have identified a monoclonal antibody reacting with NCAM transfectants which in contrast to other NCAM antibodies examined does not react with peripheral mononuclear cells or lymphoid tissues and thus might be of advantage for immunotargeting. The other two glycoprotein antigens, cluster-5 and cluster-5A antigen, have not yet been cloned. In regards of tissue expression, these antigens, in cone to the antigens described above, are only strongly expressed in half of the samples of SCLC, a potential disadvantage in regard to immunotargeting. However, there virtual lack of expression in normal tissues might be of advantage if immunoconjuates with highly toxic substances are considered. Preclinical studies with immunotoxins: Plant and bacterial toxins which are some of the most cytotoxic substances known, They act by irreversibly arresting the synthesis of protein in cells. To construct active immunotoxins, the toxin must be modified so that its interactions with cellular receptors are diminished or abolished. As a consequence, toxin entry is mediated by antibody binding. With ricin this can be accomplished through removal of the B chain (ricin A chain immunotoxins) or blockage of the galactose binding site with high affinity ligands (blocked ricin immunotoxins). With Pseudomonas exotoxin A (PE), this modification occurs when the antibody is coupled to the domain I, which interferes with its binding to the PE receptor, or when domain I is genetically deleted and the antibody is coupled to domain II. Because toxins act within the cell, surface antigens that naturally enter cells by endocytosis
Cancer IO (1994) 347-373
These findings indicate that GRP may be a mitogen for the bronchial epithelium. Bronchial epithelial cells express message for the GRP and neuromedin B receptors, and a mitogenic response was demonstrated in eight of 13 cultures. Three out of three cultures from COPD patients showed a positive response to bombesin and/or GRP. Non-small cell carcinomas also express receptors for GRP, and a non-small cell carcinoma cell line was induced to express a GRP-like protein when adapted to serum-free conditions. These findings also provide further evidence for the plasticity of the differentiation features of lung tumors, and for a common precursor cell for both small cell and non-small cell lung carcinoma. Role of carbohydrates in cancer Singhal AK. The Biomembrane Institute & University of Washington Seattle, WA 98119.
Development of cancer is always associated with abnormal expression of cell surface carbohydrates. These diverse group of carbohydrate antigens including blood group antigens and gangliosides may be expressed either on glycosphingolipids or glycoproteins. Recent studies have indicated that these membrane carbohydrates are involved in cell-cell and cellsubstratum interactions. Certain gangliosides and their metabolites also modulate trans-membrane signal transduction by either up- or down-regulating various receptor kinases. Membrane Carbohydrate antigens expressed on mucin type glycoproteins have also been found to elicit cellular immune responses. Metastatic tumor cells migrate to the secondary sites by binding to the blood vessel endothelial cells. Recent studies showed that this binding is mediated by the interaction of blood group carbohydrates, sialylated Lex (SLeX) and its isomer SLe” expressed on metastatic tumor cells to the E- and P-Selectin molecules expressed on activated blood vessel endothelial cells. The tumor cells subsequently degrade capillary walls, migrate into tissues and establish metastatic deposits. The antibodies to these carbohydrate structures as well as carbohydrate analogs that may block this endothelial cell interaction are being considered as potential anti-metastatic drugs. Similar to the selectin-carbohydrate interaction, evidence is emerging that carbohydrate-carbohydrate interaction may also be an early and critical event in this tumor cell interaction. Exogenous addition of ganglioside GM3 strongly downregulates EGF receptor kinase and this inhibitory effect is more pronounced in the presence of lyso-phosphatidyl choline. Metabolites of GM3, namely, lyso-GM3 and sphingosine have been shown to be strong inhibitors of protein kinase C. Through this mechanism, a chemical derivative of sphingosine, trimethyl sphingosine (TMS) was found to block platelet activation and subsequent aggregation caused by tumor cells. Platelet aggregation is thought to be prominently involved in the metastatic process. TMS also down-regulates the expression of P-Selectin on activated endothelial cells and platelets and was found to significantly reduce metastatic deposits of B16 melanoma in lungs of C57 black mice. A block in carbohydrate chain elongation of O-glycosylated mucins results in specific accumulation of core structure, Tn (GalNac ol-O-Serinelthreonine) in large percentage of human
371
adenocarcinomas. Multivalent Tn antigen was found to induce a specific CD4+ T cell stimulation in mice. Active specific immunotherapy with the Tn antigen was effective in preventing growth of syngeneic tumors in mice. Therefore, certain carbohydrate antigens presented in a specific configuration may provide potential for a tumor vaccine. Monoelonal antiImrIy treatment of small cell lung cancer Stahel RA. Division of Oncology, Department of Medicine, University Hospital, CH-8091 Ziirich. Switzerland. Target antigens: The molecular nature of potential target
structures in the membrane of small cell lung cancer (SCLC) has been elucidated for three glycoproteins, including cluster-l antigen or the neural cell adhesion molecule NCAM cluster-2 antigen consisting of 40-kDa panepithetial transmembrane molecule, and cluster-w4 antigen. The latter, a 45-kDa highly glycosylated surface molecule of only 31 to 35 amino acids anchored in the membrane by glycosylphosphoinositol linkage has recently been shown to be identical to the leukocyte activation antigen CD24 and to be hyperexpressed in small cell lung cancer on the RNA and protein level. Using synthetic peptides we have been able to localise the epitope of cluster-w4 antibodies and several other CD24 antibodies to a three amino acid region of the core protein close to the phosphoinositol anchor. In addition to a uniform expression in all small cell lung cancer, the three antigens described have each selective expression in normal tissues, including neuroendocrine tissues for NCAM and CD24, and panepithelial expression for cluster-2 antigen. On white blood cells, NCAM expression is found in a moderate proportion of peripheral blood mononuclear cells and CD24 on pre-B cells and a proportion of granulocytes. Recently we have identified a monoclonal antibody reacting with NCAM transfectants which in contrast to other NCAM antibodies examined does not react with peripheral mononuclear cells or lymphoid tissues and thus might be of advantage for immunotargeting. The other two glycoprotein antigens, cluster-5 and cluster-5A antigen, have not yet been cloned. In regards of tissue expression, these antigens, in cone to the antigens described above, are only strongly expressed in half of the samples of SCLC, a potential disadvantage in regard to immunotargeting. However, there virtual lack of expression in normal tissues might be of advantage if immunoconjuates with highly toxic substances are considered. Preclinical studies with immunotoxins: Plant and bacterial toxins which are some of the most cytotoxic substances known, They act by irreversibly arresting the synthesis of protein in cells. To construct active immunotoxins, the toxin must be modified so that its interactions with cellular receptors are diminished or abolished. As a consequence, toxin entry is mediated by antibody binding. With ricin this can be accomplished through removal of the B chain (ricin A chain immunotoxins) or blockage of the galactose binding site with high affinity ligands (blocked ricin immunotoxins). With Pseudomonas exotoxin A (PE), this modification occurs when the antibody is coupled to the domain I, which interferes with its binding to the PE receptor, or when domain I is genetically deleted and the antibody is coupled to domain II. Because toxins act within the cell, surface antigens that naturally enter cells by endocytosis