The authors describe the immunochemical detection, biochemical characterization, and tissue distribution of neuroendocrine antigens recognized by three newly developed monoclonal antibodies (MoAb) obtained after immunization of mice with the variant small cell lung cancer (SCLC) cell line NCI-H82. RNL-1 was reactive with neuroendocrine tissues similar to the SCLC cluster-1 MoAb, known to recognize N-CAM. Antibodies RNL-2 and RNL-3 are directed against different epitopes on the same proteinaceous complex. Both MoAb recognize an intracellularly located, water-soluble antigen which has a subunit composition with a protein triplet ranging in molecular weight between 44 and 45 kilodaltons (kD) next to a component of approximately 30 kD. The antibodies RNL-2 and RNL-3 reacted with a subset of neuroendocrine tissues and neuroendocrine neoplasms. In lung cancer both antibodies reacted only with some SCLC and carcinoids and not with nonneuroendocrine lung carcinomas. The potential diagnostic applicability of antibodies RNL-1, RNL-2, and RNL-3 is discussed.
The intermediate filament protein (IFP) characteristics of a panel of lung cancer cell lines including adenocarcinoma (two cell lines) and small cell lung cancer (SCLC, three classic and three variant cell lines) were examined using one- and two-dimensional gel electrophoretic techniques, immunocytochemical techniques and immunoblotting assays. A panel of 28 monoclonal and polyclonal antibodies to the five different types of IFP were used. The results of our studies indicate that these human lung adenocarcinoma, classic SCLC and variant SCLC cell lines can be differentiated on the basis of their pattern of IFP. The main conclusions from this study can be summarized as follows. The two adenocarcinoma cell lines contain cytokeratins 7, 8, 18, and sometimes 19, next to vimentin intermediate filament (IF). The three classic-type SCLC cell lines contain only cytokeratin IFs but not vimentin IF or neurofilaments (NFs). Cytokeratin polypeptides 7, 8, 18 and 19 could be detected. All three variant-type SCLC cell lines do not contain detectable amounts of cytokeratins. In contrast, two out of three variant SCLC cell lines contain neurofilament proteins. All three variant-type SCLC cell lines contain vimentin IF. Using immunoblotting assays with monoclonal and polyclonal antibodies to defined NF proteins the presence of the 68 X 10(3) Mr and the 160 X 10(3) Mr NF polypeptide could be demonstrated in two variant SCLC cell lines. As patients with SCLC-variant phenotype have a poorer prognosis after cytotoxic therapy than patients with ‘pure’ SCLC, the use of antibodies to IFP in staining fresh lung tumours, especially anaplastic ones, may differentiate the two subtypes of SCLC. Such a distinction would have a major impact on therapy selections and may be of prognostic importance.
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