Membrane-associated glycoprotein (gp 160) identified on human lung tumors by a monoclonal antibody

Abstract

A monoclonal antibody (5E8) has been used to identify and structurally characterize a previously unreported macromolecule present on the surface of human lung tumors. This antibody was derived from a hybrid clone that was produced using spleen cells of mice immunized with a surgically excised squamous cell carcinoma. Using immunofluorescence, the 5E8 antibody was observed to stain many different human lung tumor cell lines and surgically excised human lung tumors including squamous cell carcinomas, adenocarcinomas, alveolar carcinomas, and a portion of the large cell tumors tested. With few exceptions, notably the basal layer of the skin, little or no detectable staining of 5E8 to normal human tissues (lung, brain, kidney, heart, stomach, breast, erythrocytes, or lymphocytes) was observed. The 5E8 antibody was used to immunoprecipitate detergent lysates of biosynthetically labeled or surface radioiodinated lung tumors. Analysis of the immunoprecipitates by sodium dodecyl sulfate gel electrophoresis revealed a major band and a faster migrating second minor band. The molecular weights of these two proteins were estimated to be 160,000 and 120,000, respectively. The addition of a reducing agent to the gels did not alter the migration pattern of the immunoprecipitated macromolecules. The removal of a terminal carbohydrate, sialic acid, did not restrict the binding of 5E8 to the tumor-associated antigen. However, labeling studies using galactose oxidase and tritiated borohydride revealed the presence of galactose on the immunoprecipitated protein. This major Mr 160,000 glycoprotein that was identified on two different human lung tumor cell lines was also found on a human large cell tumor tissue obtained by surgical biopsy. The 5E8 antibody and the Mr 160,000 glycoprotein that it recognizes represent two very useful components with which to test several new antibody-mediated drug delivery systems in the treatment of human lung tumors. The tumor-associated glycoprotein also represents a potential analyte for a diagnostic or prognostic immunoassay for lung cancer.