Genetic Alterations in K‐ras and p53 Cancer Genes in Lung Neoplasms From B6C3F1 Mice Exposed to Cumene

Abstract

Cumene was evaluated for carcinogenicity in the 2-year NTP studies because of its high production volume and high potential for human exposure. Male and female B6C3F1 mice were exposed by whole-body inhalation to 0,125,250,500, or 1000 ppm cumene. The incidences of alveolar/bronchiolar adenomas and carcinomas in the treated groups were significantly greater than those of the controls. In the present study, we characterized the benign and malignant lung neoplasms from this bioassay for point mutations, in the K-ras and p53 cancer genes that are often mutated in human lung tumors. K-ras and p53 mutations were detected by cycle sequencing of PCR-amplified DNA, isolated from formalin-fixed, paraffin-embedded neoplasms. K-ras mutations were detected in 45 of 51 (87 %) of the cumene-induced lung neoplasms, and the predominant mutations were codon 12 G to T transversions, and codon 61 A to G transitions. P53 protein expression was detected by immunohistochemistry in 29 of 52 (56 %), and mutations were detected in 27 of 51 (52 %) of the cumene-induced lung neoplasms, with the predominant mutations being exon 5, codon 155 G to A transitions, and codon 133 C to T transitions. No p53 and one of 7 (14 %) K-ras mutation was detected in spontaneously occurring neoplasms. In addition, treated mouse lung carcinomas showed loss of heterozygosity (LOH) on chromosome 4 near p16 tumor suppressor gene (5/39, 13 %) and on chromosome 6 near K-ras gene (6/49, 12 %). No LOH was observed in spontaneous carcinomas (0/7) and in normal lung tissues (0/5) examined at both microsatellite markers. The patterns of mutations identified in the lung tumors suggest that DNA damage, and genomic instability may be the contributing factors to the mutation profile and development of lung cancer in these mice.