REFINEMENT OF AN INDIRECT IMMUNOTOXIN ASSAY OF MONOCLONAL-ANTIBODIES RECOGNIZING THE HUMAN SMALL-CELL LUNG-CANCER CLUSTER-2 ANTIGEN

Monoclonal antibodies (Mabs) from the Second International Workshop on Small Cell Lung Cancer (SCLC) Antigens that recognise the cluster 2 SCLC-associated antigen mediated potent and selective cytotoxic effects in an indirect assay of immunotoxin cytotoxicity. In this assay, the NCI-H69 cell line was treated with each Mab at 4-degrees-C, washed to remove unbound Mab, and then incubated at 37-degrees-C in the presence of a fixed concentration, 1 x 10(-8) M, of the screening agent, sheep anti-mouse IgG-ricin A chain. The use of a fixed high concentration of screening agent led to a 300-fold overestimate of the potency of a cluster 2-directed immunotoxin, MOC-31-ricin A chain. In contrast, when the concentration of the screening agent was identical to the Mab concentration, a precise match to immunotoxin potency was obtained. MOC-31-ricin A chain selectivity inhibited the incorporation of [H-3]leucine by the NCI-H69, SW2 and GLC-8 SCLC cell lines by 50% at a concentration between 3 x 10(-11) m and 3 x 10(-10) m, and by the NCI-H125 lung adenocarcinoma cell line at 7 x 10(-11) m, but exerted no selective toxic effects upon human lung and non-lung tumour cell lines lacking surface expression of the cluster 2 antigen

REFINEMENT OF AN INDIRECT IMMUNOTOXIN ASSAY OF MONOCLONAL-ANTIBODIES RECOGNIZING THE HUMAN SMALL-CELL LUNG-CANCER CLUSTER-2 ANTIGEN

Monoclonal antibodies (Mabs) from the Second International Workshop on Small Cell Lung Cancer (SCLC) Antigens that recognise the cluster 2 SCLC-associated antigen mediated potent and selective cytotoxic effects in an indirect assay of immunotoxin cytotoxicity. In this assay, the NCI-H69 cell line was treated with each Mab at 4-degrees-C, washed to remove unbound Mab, and then incubated at 37-degrees-C in the presence of a fixed concentration, 1 x 10(-8) M, of the screening agent, sheep anti-mouse IgG-ricin A chain. The use of a fixed high concentration of screening agent led to a 300-fold overestimate of the potency of a cluster 2-directed immunotoxin, MOC-31-ricin A chain. In contrast, when the concentration of the screening agent was identical to the Mab concentration, a precise match to immunotoxin potency was obtained. MOC-31-ricin A chain selectivity inhibited the incorporation of [H-3]leucine by the NCI-H69, SW2 and GLC-8 SCLC cell lines by 50% at a concentration between 3 x 10(-11) m and 3 x 10(-10) m, and by the NCI-H125 lung adenocarcinoma cell line at 7 x 10(-11) m, but exerted no selective toxic effects upon human lung and non-lung tumour cell lines lacking surface expression of the cluster 2 antigen