Benzo[b]fluoranthene: Tumorigenicity in strain A/J mouse lungs, DNA adducts and mutations in the Ki-ras oncogene

The polycyclic aromatic hydrocarbon benzo[b]fluoranthene (B[b]F) is a pervasive constituent of environmental combustion products, We sought to examine the lung tumorigenic activity of B[b]F in strain A/J mice, to study the relationship between formation and decay of B[b]F-DNA adducts and to examine mutations in the Ki-ras proto-oncogene in DNA from B[b]F-induced tumors, Mice were given i.p. injections of 0, 10, 50, 100 or 200 mg/kg body wt and lung adenomas were scored after 8 months, B[b]F induced significant numbers of mouse lung adenomas in a dose-related fashion, with the highest dose (200 mg/kg) yielding 6.95 adenomas/mouse, with 100% of the mice exhibiting an adenoma, In mice given tricaprylin, the vehicle control, there were 0.60 adenomas/mouse, with 55% of the mice exhibiting an adenoma, Based on dose, B[b]F was less active than benzo[a]pyrene. DNA adducts were analyzed qualitatively and quantitatively by P-32-post-labeling in lungs of strain A/J mice 1, 3, 5, 7, 14 and 21 days after i.p. injection, Maximal levels of adduction occurred 5 days after treatment with the 200 mg/kg dose group, producing 1230 amol B[b]F-DNA adducts/mu g DNA, The major B[b]F-DNA adduct was identified by co-chromatography as trans-9,10-dihydroxy-anti-11,12-epoxy-5-hydroxy-9,10,11,12-tetra-hydro-B[b]F-deoxyguanosine. Approximately 86% of the tumors had a mutation in codon 12 of the Ki-ras oncogene, as determined by direct DNA sequencing of PCR-amplified exon 1 and single-stranded conformation polymorphism analysis, Analysis of the Ki-ms mutation spectrum in 25 of 29 B[b]F-induced tumors revealed the predominant mutation to be a G-->T transversion in the first or second base of codon 12, congruous with the DNA adduct data, Our data are consistent with previous reports in mouse skin implicating a phenolic diol epoxide as the proximate carcinogenic form of B[b]F that binds to guanine.