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

Abstract

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 [D2xB6D2F(1)]F(2) 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 [D2xB6D2F(1)]F(2) 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 [D2xB6D2F(1)]F(2) mice. SSCP analysis of the tumor suppressor gene p16Ink4a showed a 6% incidence of point mutations, consistent with that found in [D2xB6D2F(1)]F(2) mice. No mutations were found in exon 1beta 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 BALB/c mice are treated with MC, BHT does not appear to significantly promote the formation of lung tumors following transplacental exposure to MC, possibly due to the rapid growth and cell proliferation in the developing organism. Strain-dependent differences in the Ki-ras mutational spectrum may be associated with their differential susceptibility to lung tumor initiation.

CRM1-dependent p53 nuclear accumulation in lung lesions of a bitransgenic mouse lung tumor model

“…Whether these are due to differences intrinsic to the host or a result of differences in the effects of different rAs mutations remains to be determined. several laboratories have demonstrated mutation-specific effects of different mutagenic rAs alleles on lung tumorigenesis in a variety of murine and cell culture models (26)(27)(28)(29)(30)(31)(32)(33)(34). on the other hand, the data of p53 and crM1 alterations after curcumin treatment in the present study cannot exclude the possible protective effects of curcumin at the molecular levels against lung tumor progression.…”

3-Metilkolantren ve bütil hidroksitoluenle uyarılmış rat akciğer dokularında p-53 ekson 8 geni mutasyon analizi

“…Kimyasal karsinogenezde kullanılan ajanlardan 3-MC; bakterilere mutajenik, kemik iliğine klastojenik olup, hayvanlarda DNA eklentisini uyardığı bildirilmiştir [21][22][23]. Cyp-450 gen ekspresyonunu artırarak kanser gelişiminde rol oynadığı bilinmektedir.…”

“…Burada MC'in transplasental karsinojenik etki göstermekte olduğu da vurgulanmıştır. Bu da bize daha anne karnındayken karşılaşılan kimyasalların, doğumdan sonra ne derece önem kazandığını göstermektedir [23].…”

Farelerde 3-Metilkolantren İle İndüklenen Fibrosarkoma Üzerine Sisteaminin Etkileri: Genotoksisitenin Araştırılması

“…Yapılan in vivo araştırmalarda 3-MC'nin 40 mg/ Kg dozda intraperitonal olarak bir kez enjekte edilmesiyle 6 saat içerisinde Cyp1A gen transkripsiyon oranında 179 kez artışa neden olduğu belirlenmiştir. Yine Cyp 2C11 geninde transkripsiyon oranında kontrole göre %51 oranında redüklenmeye neden olduğu gösterilmiştir [28][29][30][31] .…”