DOSE-DEPENDENT RAS MUTATION SPECTRA IN N-NITROSODIETHYLAMINE INDUCED MOUSE-LIVER TUMORS AND 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE INDUCED MOUSE LUNG-TUMORS

In a previous study, the spectrum of H-ras mutations detected in B6C3F 1 mouse liver tumors induced by 5, 50 or 150 Amol/kg body wt of N-nitr osodiethylamine (NDEA) was similar to that in spontaneous B6C3F1 mouse liver tumors, suggesting that activation of the H-ras gene in NDEA-in duced mouse liver tumors may not be the direct result of the chemical interaction with the H-ras gene. In the present study, mutations in th e H-ras oncogene from B6C3F1 mouse liver tumors induced by 5 or 50 mum ol/kg body wt of NDEA were characterized by DNA amplification with pol ymerase chain reaction (PCR), single-strand conformation polymorphism (SSCP) and direct sequence analysis. Twenty-one of 66 NDEA-induced B6C 3F1 mouse liver tumors contained activated H-ras gene with 2 of 21 hav ing a CG to AT transversion at the first base of codon 61, 17 of 21 ha ving AT to GC transition and 2 of 21 having an AT to TA transversion a t the second base of codon 61 in the H-ras gene. The predominant mutat ion, AT to GC transition (17/21, 81%) is consistent with the formation of O4-ethylthymine adduct, and is distinct from the predominant CG to AT transversion (50%) at the first base of codon 61 detected in H-ras gene from NDEA-induced B6C3F1 mouse fiver tumors in a previous study by Stowers et al. Mutations in the K-ras oncogene from 59 A/J mouse lu ng tumors induced by 0.53 mmol/kg body wt of 4-(methylnitrosamino)-1-( 3-pyridyl)-1-butanone (NNK) were also characterized by using the above mentioned methods. Forty-six of 59 NNK-induced A/J mouse lung tumors contained activated K-ras genes. All 46 (100%) of the activated K-ras gene had GC to AT transitions at the second base of codon 12. The same mutation was observed in 70% (7/10) of the K-ras oncogene from A/J lu ng tumors induced by 4.8 mmol/kg body wt (given in 21 doses) of NNK. T hese data suggest that other factors in addition to genotoxic effect m ight be involved in the induction of rodent tumors by some carcinogens when given at higher doses. Therefore, further studies to compare the dose-dependent differences in the profile of ras mutations induced by chemical carcinogens may help to assess human cancer risk. Mutation(s ) in exons 5-8 of the p53 gene was not found in these NDEA-induced mou se liver tumors and NNK-induced mouse lung tumors.