Effects of K‐ras Gene Mutations in the Development of Lung Lesions Induced by 4‐(N‐ Methyl‐N‐nitrosamino)‐1‐(3‐pyridyl)‐1‐butanone in A/J Mice

The relationship between the development of peripheral lung lesions induced by tobacco‐specific 4‐(N‐methyl‐N‐nitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK) and K‐ras gene mutation in A/J mice, and the correlations between histological alterations and the course of lung lesion development after NNK treatment and K‐ras gene mutation were investigated. The acquisition of a selective growth advantage by the lung lesions with mutations was also examined using immunohistochemical labeling with bromodeoxyuridine. Thirty female 5 weeks old A/J mice were each injected intraperitoneally with a single dose of NNK (100 mg/kg body weight) and subdivided into 6 groups according to the time after NNK treatment. The lung lesions were characterized histologically as alveolar/bronchiolar hyperplasia, adenoma and adenocarcinoma, and point mutations in codons 12 and 61 of the K‐ras gene were detected by polymerase chain reaction and restriction fragment length polymorphism (PCR‐RFLP) and dideoxy sequencing methods. K‐ras gene mutations were identified in 7 (58.3%) of 12 hyperplasias, 42 (75.0%) of 56 adenomas and 3 (75.0%) of 4 adenocarcinomas. The most frequent K‐ras gene mutation was a G‐to‐A transition at the second base of codon 12 and this accounted for 86.5% of all the mutations detected. Neither the frequency of activation of this gene nor the specific mutation was affected by the time after NNK treatment and there was no positive correlation between the proliferative activity of lung lesions and the presence of K‐ras gene mutations. Thus, K‐ras gene mutation is closely associated with the development of NNK‐induced peripheral lung lesions in A/J mice, but it plays no role in the selective growth advantage of these lesions.