Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and they pose a cancer threat tohumans as they are products of activities in a modern society. Alternant bay and fjord region PAHs aremetabolized to 4 isomeric diol epoxides that are potent DNA alkylating agents. Reaction of these diolepoxides with cellular DNA results in the formation of 16 nucleoside adducts; 8 isomers fromdeoxyadenosine (dA) and correspondingly 8 from deoxyguanosine (dG). The isomeric diol epoxides havemarkedly different tumorigenicities that implies differences in intracellular recognition, replication and repairthe individual diol epoxide-nucleoside adducts. Thus, an understanding of the structural differences in theindividual diol epoxide-DNA lesions in relation to the biological responses is expected to provide a betterbasis for understanding chemical carcinogenesis at the molecular level. The proposed studies are on twotopologically different structural paradigms; the bay region represented by benzo[a]pyrene (BaP) and thefjord region represented by benzo[c]phenanthrene (BcPh) the DNA adducts of which are expected to elicitmarkedly different structural properties.
One aim of the project is to complete delineation of novel,unequivocal synthesis of all diol epoxide-nucleoside adducts of these two PAHs. The methods that soevolve will potentially have general applicability for studies with any bay or fjord region PAH diol epoxide.The adducts will be incorporated into suitable DNA sequences (primarily human N-ras for the dA adductsand c-Ki-ras for the dG) for comparative studies within the individual sequence contexts. These include: 7mstudies with normal and mismatched complementary strands, and temperature-dependent CD studies of theduplexes. The proposed synthesis encompasses ample flexibility to allow for the modification of anysequence or the incorporation of MeC adjacent to the dG adducts. Thus sequence context effects can alsobe probed. In-house collaboration will be the NMR structural evaluations of the modified duplexes. Externalcollaborations are also planned for UvrABC repair experiments and single molecule studies on protein-DNAcomplexes. This concerted synthesis and structural evaluation is anticipated to contribute to a greater globalunderstanding of the causative effects in PAH carcinogenesis.
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