Increased frequency of K-ras mutations in lung neoplasms from female B6C3F1 mice exposed to ozone for 24 or 30 months

Abstract

The National Toxicology Program recently completed long-term ozone inhalation studies in B6C3F1 mice and F344/N rats. Mice and rats were exposed to 0, 0.5 or 1.0 p.p.m. ozone by inhalation for 24 or 30 months. There was an increased incidence of lung neoplasms in B6C3F1 mice. However, there was no evidence of carcinogenicity in F344/N rats. The objectives of this study were to (i) evaluate benign and malignant lung neoplasms from B6C3F1 mice for mutations in the K-ras gene at codons 12, 13 and 61, (ii) determine if the frequency and spectra of K-ras mutations were unique for ozone-induced lung neoplasms, (iii) determine if specific K-ras mutations were associated with the size and morphological patterns of lung neoplasms or ozone exposure concentrations and (iv) screen lung neoplasms by immunohistochemical methods for the p53 protein. K-ras mutations were detected by single-strand conformation analysis and identified by direct sequencing of polymerase chain reaction-amplified DNA isolated from formalin-fixed, paraffin-embedded neoplasms. K-ras mutations were detected in 73% of ozone-induced neoplasms, as compared with 33% of lung neoplasms from controls. The predominant mutations consisted of A-->T transversions at codon 61 (8/19) and G-->T transversions at codon 12 (7/19). Specific K-ras mutations in lung neoplasms were not associated with various morphological patterns. Our data suggests that ozone may cause direct and/or indirect DNA damage in the K-ras proto-oncogene of B6C3F1 mice.

High Frequency of Ras Mutations in Forestomach and Lung Tumors of B6C3F1 Mice Exposed to 1-Amino-2,4-dibromoanthraquinone for 2 Years

“…In ADBAQ-induced lung tumors, A to T transversions (6/23, 26%) and A to G transitions (5/23, 22%) were identied in K-ras codon 61 ( Table 4). The K-ras codon 61 CTA mutation was considered to be chemical speci c since this mutation has not been detected previously in 82 spontaneous lung tumors of B6C3F 1 mice (7,11,25) or in lung tumors from concurrent control mice (Table 4). When K-ras mutation pro les were compared in lung tumors from mice exposed to 10,000 or 20,000 ppm ADBAQ, most of the codon 61 A T mutations were observed in the high dosage groups.…”

Selective mutation of K-ras by N-ethylnitrosourea shifts from codon 12 to codon 61 during fetal mouse lung maturation

“…Ozone caused lung tumors in mice, with a high frequency of K-ras mutations including G to T transversion in codon 12 (Sills et al, 1995). Alveolar type II cells in rat lungs exposed intratracheally to inorganic particles, resulting in neutrophil and macrophage in®ltration, showed a large increase in HPRT mutations (Driscoll et al, 1997).…”

Products of ozonized arachidonic acid potentiate the formation of DNA single strand breaks in cultured human lung cells

“…Reports concerning rodents chronically exposed to 0, have reported an increase in lung tumors in some studies but not others [Werthamer et al, 1970;Last et al, 19871. One study has reported an 0,-induced increase in lung tumors when urethane was co-administered, suggesting O3 may act as a co-carcinogen [Hassett et al, 19851. Recent reports from the National Toxicology Program have shown that B6C3F1 mice, but not Fischer 344 rats, exposed to 1.0 ppm 0, for 24 or 30 months had an increase in lung neoplasms, suggesting the carcinogenicity of 0, exposure alone [Sills et al, 1995;Boorman et al, times, solution additives (e.g., metal chelators), fatty acid types, fatty acid concentrations, and/or different reaction mechanisms. For example, we utilized only 37°C in our exposures while others have reported using lower temperatures.…”