The major focus of these studies is to identify critical target genes and alterations in biochemical pathways which are involved in cell transformation. Some of the biological endpoints being examined include DNA adduct formation, gene expression, and oncogene activation. Activation of the K-ras proto-oncogene appears to be one step in the development of mouse lung tumors. In order to identify other factors involved in tumor progression, epithelial cell lines are being developed from these murine tumors. The expression of growth factors, proto-oncogenes, and proteases are being characterized in these cell lines as well as solid tumors. Preliminary data indicates that gene expression in these murine tumors is similar to that observed in human lung tumors. Subtractive cDNA cloning will also be employed using cell lines or benign and malignant tumors to identify specific proteins whose expression or suppression may be involved in the progression from benign to malignant to a fully metastatic phenotype. Although activation of the K-ras gene has been associated with the induction of lung tumors in the A/J and C3H mouse following treatment with 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), this gene is not activated in lung tumors induced in the rat by this carcinogen. The nude mouse tumorigenicity assay is being employed to attempt the detection of novel transforming genes in NNK-induced rat lung tumors. The progression of pulmonary neoplasia has been characterized in the A/J mouse. The role of the type II cell as a progenitor for pulmonary neoplasia is suggested by ultrastructural findings and supported further by the fact that an activated K-ras oncogene is detected in approximately 90% of hyperplasias and contains the same activating mutation present in the carcinomas induced in this mouse strain by NNK. Since a significant number of human pulmonary cancers are thought to arise from type II cells and 30 to 40% of these neoplasms contain an activated K-ras gene, the identification of metabolic factors involved in cell transformation in this murine model could further our understanding of the development of human lung cancer.
