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Mechanistic relationships between DNA adducts, oncogene mutations, and lung tumorigenesis in strain A mice
1National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA. nesnow.stephen@epamail.epa.gov
Abstract:
This paper describes a series of studies on the lung tumorigenic activities of polycyclic aromatic hydrocarbons (PAHs) in strain A/J mice, their ability to form PAH-DNA adducts in lung tissues, and their ability to mutate the Ki-ras oncogene in PAH-induced tumors. Seven PAHs were studied: cyclopenta[cd]pyrene (CPP), benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), dibenz[a,h] anthracene (DBA), 5-methylchrysene (5MC), benz[j]aceanthrylene (B[j]A), and dibenzo[a,l]pyrene (DB[a,l]P). The dose-response data for the PAHs revealed 100-fold differences in tumor potency based on dose, with the order of activity DB[a,l]P, DBA > B[j]A > 5MC > CPP B[a]P > B[b]F. Large differences in tumor multiplicity were also observed between the PAHs. DNA adducts were measured by 32P-postlabeling techniques on DNA from lungs of mice treated with these PAH's. DB[a,l]P gave syn- and anti-fjord-region diol-epoxide adducts of dAdo and dGuo; DBA gave both bay-region diol-epoxide-dGuo and bisdihydrodiol-epoxide adducts; CPP gave cyclopenta-ring-dGuo adducts; B[j]A gave a mixture of cyclopenta-ring-dGuo and -dAdo adducts; 5MC gave anti-bay-region diol-epoxide-dGuo adducts; B[a]P gave bay-region diol-epoxide-dGuo adducts; and B[b]F gave 5-hydroxy-B[b]F-diol-epoxide-dGuo adducts. Ki-ras codon 12 and 61 mutation analysis of PAH induced tumors was performed using PCR and dideoxy sequencing methods. DB[a,l]P gave both codon 12 and codon 61 mutations. High proportions of codon 12 TGT mutations from B[a]P-, B[b]F- and 5MC-, induced tumors and CGT mutations from CPP- and B[j]A-induced tumors were observed. DBA produced no mutations in Ki-ras codons 12 or 61 by direct sequencing. The interrelationships between the tumorigenesis, DNA adduct, and oncogene mutation data are discussed.
Insights
This study investigated polycyclic aromatic hydrocarbons (PAHs) and their lung tumor-causing potential in mice. Different PAHs showed varying potencies, DNA adduct formation, and Ki-ras oncogene mutations, revealing distinct molecular mechanisms of lung carcinogenesis.
Area of Science:
- Environmental Toxicology
- Molecular Carcinogenesis
- Chemical Mutagenesis
Background:
- Polycyclic Aromatic Hydrocarbons (PAHs) are environmental pollutants known for their carcinogenic properties.
- Understanding the specific mechanisms by which different PAHs induce lung tumors is crucial for risk assessment.
Purpose of the Study:
- To investigate the lung tumorigenic activities of seven PAHs in A/J mice.
- To correlate PAH exposure with the formation of specific PAH-DNA adducts in lung tissue.
- To analyze mutations in the Ki-ras oncogene within PAH-induced tumors.
Main Methods:
- Administered seven PAHs to A/J mice and assessed dose-response tumor multiplicity.
- Quantified PAH-DNA adducts in lung tissue using 32P-postlabeling.
- Analyzed Ki-ras codon 12 and 61 mutations in tumors via PCR and dideoxy sequencing.
Main Results:
- Significant variations in tumor potency and multiplicity were observed among the seven PAHs, with Dibenzo[a,l]pyrene (DB[a,l]P) and Dibenz[a,h]anthracene (DBA) being the most potent.
- Specific PAH-DNA adducts were identified, correlating with the chemical structure of each PAH.
- Distinct mutation patterns in the Ki-ras oncogene (codon 12 and 61) were associated with specific PAHs, while DBA induced no detectable mutations.
Conclusions:
- PAH tumorigenicity in A/J mouse lungs is PAH-specific, influenced by dose, DNA adduct formation, and Ki-ras oncogene mutations.
- The study highlights the complex interplay between PAH exposure, DNA damage, and genetic alterations in lung cancer development.
- Different PAHs may utilize distinct molecular pathways to initiate lung tumorigenesis.