Elucidation of the mechanisms of activation of chemical carcinogens is central to understanding the process of cancer initiation by chemicals and in designing preventive strategies. A powerful approach to this problem is to identify carcinogen-DNA adducts. Metabolic activation of polycyclic aromatic hydrocarbons (PAH) can be understood in terms of two main mechanisms: one-electron oxidation to form intermediate radical cations and monooxygenation to produce bay-region diol epoxides. The overall objective of this research is to demonstrate that these mechanisms of activation occur in vitro and in vivo by identifying DNA adducts formed with the potent carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) and several related PAH. Primary emphasis will be placed on adducts formed by one-electron oxidation, but the analytical techniques employed will identify adducts formed by both mechanisms. The central hypothesis is that adducts formed by one-electron oxidation of DMBA contain a covalent bond between one of the methyl groups and DNA, whereas adducts formed by monooxygenation arise from reaction of a diol epoxide that binds to DNA at C-1. This comprehensive research approach is based on the fact that cytochrome P-450 can catalyze activation of chemicals by one- electron oxidation as well as monooxygenation. DNA adducts formed by DMBA (highly carcinogenic), 1,2,3,4-tetrahydro DMBA (highly carcinogenic despite its saturated angular benzo ring) 5-fluoro DMBA (weakly carcinogenic) and 9,10-dimethyl-anthracene (noncarcinogenic) will be analyzed by fast atom bombardment tandem mass spectrometry and fluorescence line-narrowing spectrometry (FLNS). Mechanistic studies of the PAH radical cation chemistry will be conducted by the UNMC and UN-L groups. Synthesis of adducts as well as biochemical and biological experiments will be conducted by the UNMC group. Mass spectrometric analysis of adduct structures will be conducted at UN-L, whereas fluorescence line- narrowing spectrometric analysis of nucleoside, DNA and globin adducts will be conducted at ISU. The studies will enable us to assess the roles of one-electron oxidation and monooxygenation in metabolic activation of DMBA. Furthermore, they provide a systematic framework to develop MS and FLNS techniques for resolving biological problems.
NIH ExPorter
NIH ExPorter