Strain-dependent lung tumor formation in mice transplacentally exposed to 3-methylcholanthrene and post-natally exposed to butylated hydroxytoluene

• Published in: Carcinogenesis (New York) 1999-11, Vol.20 (11), p.2159-2165
• Main Authors: Gressani, Kiersten M., Leone-Kabler, Sandra, O'Sullivan, M.Gerard, Case, L.Douglas, Malkinson, Alvin M., Miller, Mark Steven
• Format: Article
• Language: English
• Subjects: 3-methylcholanthrene; 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; allele-specific oligonucleotide hybridization; Animals; ASO; Base Sequence; BHT; Biological and medical sciences; butylated hydroxytoluene; Butylated Hydroxytoluene - administration & dosage; Carcinogenesis, carcinogens and anticarcinogens; Chemical agents; CYP1A1; cytochrome P4501A1; DNA Primers; Female; Genes, Tumor Suppressor; K-ras gene; Lung Neoplasms - chemically induced; Lung Neoplasms - genetics; Maternal-Fetal Exchange; Medical sciences; Methylcholanthrene - administration & dosage; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Inbred DBA; Mutagens - administration & dosage; NNK; PAH; polycyclic aromatic hydrocarbon; Pregnancy; single strand conformation polymorphism; Species Specificity; SSCP; Tumors
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/20.11.2159

The carcinogenic effects of in utero exposure to 3-methylcholanthrene (MC) have been demonstrated in the tumor-resistant C57BL/6 (B6) and DBA (D2) strains of mice. In this study, we determined the effects of in utero exposure to MC in BALB/c mice, a strain which demonstrates greater susceptibility to lung tumor induction, and compared our findings with those previously found in [D2×B6D2F1]F2 mice. In addition, we assessed the molecular pathogenesis of the chemically induced tumors and examined the effects of the putative lung tumor promoter butylated hydroxytoluene (BHT) in BALB/c mice. BALB/c mice were treated on day 17 of gestation with 5, 15 or 45 mg/kg MC and 6 weeks after birth with BHT for 6 consecutive weeks. Mice were killed at 6 months of age. Ki-ras, p16Ink4a and p19ARF gene loci were amplified from paraffin-embedded lung tumor tissue and screened for the presence of point mutations via allele-specific oligonucleotide hybridization and single strand conformation polymorphism (SSCP) analyses. Ki-ras point mutations were found in 56% (20/36) of BALB/c lung tumors, with 33% (2/6) of the hyperplasias, 58% (10/19) of the adenomas and 73% (8/11) of the carcinomas exhibiting point mutations at this gene locus. Similar incidences of Ki-ras mutations were previously found following transplacental exposure of [D2×B6D2F1]F2 mice to MC and treatment of adult A/J mice with urethane. Interestingly, a strain-dependent difference was observed in the mutational spectrum. Sixty-two and 38% of the lung lesions in BALB/c mice exhibited G→C and G→T transversions, respectively, in contrast to the 13 and 84% incidences previously observed in [D2×B6D2F1]F2 mice. SSCP analysis of the tumor suppressor gene p16Ink4a showed a 6% incidence of point mutations, consistent with that found in [D2×B6D2F1]F2 mice. No mutations were found in exon 1β of the p19ARF gene of either strain. BHT, a lung tumor promoter in adult mice, had no statistically significant effects on either tumor incidence, tumor multiplicity or the mutational spectrum produced in the Ki-ras gene by in utero MC treatment. However, though not significant, there was an observable trend in increased tumor multiplicity in mice co-treated with BHT. These data demonstrate the transplacental carcinogenic effect of MC in BALB/c mice and show that mutagenic damage to Ki-ras is a critical early event mediating murine lung tumorigenesis in both the tumor-sensitive and tumor-resistant strains. Unlike what occurs when adult