K-ras mutations in lung tumors from A/J and A/J×TSG-p53 F1 mice treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and phenethyl isothiocyanate

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Abstract
The purpose of this study was to evaluate the effects of the loss of a p53 allele and phenethyl isothiocyanate (PEITC) pre-treatment on the tumorigenicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and K-ras mutation frequency in a hybrid mouse model. Male TSG-p53 ‘knock-out’ mice were bred with A/J female mice to produce (A/J×TSG-p53) F1 mice either homozygous (p53+/+) or heterozygous (p53+/−) for p53 alleles. These mice, together with female A/J mice, were treated at 6–8 weeks of age with NNK or dosed with PEITC prior to administration of NNK. The A/J mice treated with NNK had a 100% incidence of lung tumors, with 9.7 ± 3.4 tumors/mouse. A/J mice pre-treated with PEITC prior to NNK administration had 3.5 ± 2.1 lung tumors/animal, although the incidence remained at 100%. In (A/J×TSG-p53 F1 mice with either the p53(+/−) or p53(+/+) genotype PEITC pre-treatment significantly decreased tumor incidence (100 to 40 and 36%, respectively) and multiplicity (2.0 ± 0.5 to 0.5 ± 0.4 and 2.1 ± 0.5 to 0.5 ± 0.4, respectively), indicating that PEITC is an effective chemopreventive agent in both A/J mice and (A/J×TSG-p53) F1 mice. Analysis of lung tumor DNA from A/J mice treated with NNK or NNK/PEITC indicated that 15 of 17 (88%) and 20 of 23 (87%) of the tumors, respectively, contained G→A transitions at the second base of codon 12 in the K-ras gene. Similarly, in lung tumors from (A/J×TSG-p53) F1 mice treated with NNK or NNK/PEITC 29 of 30(96%) and 9 of 10 (90%), respectively contained G→A transitions at the second base of codon 12 of the K-ras gene. No mutations of the p53 gene were found in any of the tumors analyzed, suggesting minimal involvement of this gene in the development of lung adenomas. These data indicate that absence of a p53 allele in (A/J×TSG-p53) F1 mice does not alter the incidence or multiplicity of NNK-induced lung tumors and that PEITC inhibition of NNK tumorigenesis does not affect the frequency or spectrum of K-ras gene mutations found consistently with NNK carcinogenesis.