title: Monoclonal antibodies recognising the cluster 2 antigen associated with human small cell lung cancer mediate the toxic effects of ricin A chain in an indirect assay of immunotoxin cytotoxicity.
abstract: Monoclonal antibodies (Mabs) submitted to the Second International Workshop on Small Cell Lung Cancer Antigens were screened for their ability to mediate the toxic effects of ricin A chain against the NCI-H69 cell line in an indirect assay of immunotoxin cytotoxicity. Cluster 1 Mabs, recognising the neural cell adhesion molecule, mediated little or no cytotoxic effect in combination with screening agent, ricin A chain linked to an antibody Fab' fragment recognising either mouse or rat Mabs. In contrast, cluster 2 Mabs, recognising an epithelial tumour-associated antigen, generally mediated potent cytotoxic effects with the screening agent, inhibiting the incorporation of 3H-leucine by NCI-H69 cells by between 90% and 99%. Measurements of Mab binding to the NCI-H69 cell line by indirect immunofluorescence and flow cytometry indicated that the cluster 2 Mabs generally bound in higher amounts than the cluster 1 Mabs suggesting that the cluster 1 Mabs were ineffective in the screen because they did not bind to the cells in sufficient amounts. However, Mabs recognising antigens other than cluster 1 bound to NCI-H69 cells in amounts similar to those of the cluster 2 Mabs yet did not mediate potent cytotoxic effects in the indirect assay suggesting that the cluster 2 antigen may be internalised in a fashion favouring the delivery of ricin A chain to the cytosol.
authors.affiliation: Drug Targeting Laboratory, Institute of Cancer Research, Sutton, Surrey, UK.
authors.forename: E J
authors.initials: EJ
authors.lastname: Derbyshire
authors.forename: E J
authors.initials: EJ
authors.lastname: Wawrzynczak
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000951:Antigens, Neoplasm / Q000276:immunology; D018288:Carcinoma, Small Cell / Q000628:therapy*; D003602:Cytotoxicity, Immunologic; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D007132:Immunoglobulin Isotypes; D000922:Immunotoxins / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000628:therapy*; D012276:Ricin / Q000494:pharmacology*
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D007132:Immunoglobulin Isotypes; D000922:Immunotoxins; D012276:Ricin