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 32P-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/microgram 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-ras 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.
Mass
M J
MJ
Biochemistry and Pathobiology Branch (MD-68), National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
Abu-Shakra
A
A
Roop
B C
BC
Nelson
G
G
Galati
A J
AJ
Stoner
G D
GD
Nesnow
S
S
Ross
J A
JA
D000818:Animals; D001483:Base Sequence; D018736:DNA Adducts; D017931:DNA Primers; D005449:Fluorenes / Q000633:toxicity*; D011905:Genes, ras; D008168:Lung / Q000187:drug effects*; D008175:Lung Neoplasms / Q000139:chemically induced / Q000235:genetics; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation
D018736:DNA Adducts; D017931:DNA Primers; D005449:Fluorenes; C006703:benzo(b)fluoranthene