Toxicity and Biosensing Properties of C8-Aryl-Deoxyguanosine Adducts

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Covalent modification of DNA by electrophiles is an initial step in chemical carcinogenesis. If these modifications are not repaired, they compromise the fidelity of DNA replication, leading to mutations and possibly cancer. Some modified DNA bases also play beneficial roles and serve as therapeutics, and sensors to detect light, pH or metal ions. Certain single-strand DNA oligonucleotides also act as nucleic acid ligands called aptamers that bind to molecular targets, such as proteins and small molecules, with high affinity and specificity. Replacement of the normal nucleobases with modified bases that add chemical diversity can enhance aptamer affinity for its molecular target. In this NSERC-funded research program our focus is on 2'-deoxyguanosine (dG) that has been modified at the C8-site by aryl residues. Part 1 of this grant focuses on the toxicology of C8-aryl-dG adducts in DNA substrates. Little is known about their toxicological properties (mutagenicity) and so experiments are designed to characterize how DNA polymerase enzymes process C8-aryl-dG adducts. C8-aryl-dG adducts are also prone to further oxidative processes that can lead to DNA cross-link formation. DNA cross-links can kill cells and are a therapeutic basis for many anticancer agents. Experiments will determine the oxidative reactivity of C8-aryl-dG adducts in the helical environment of DNA to characterize the potential of these lesions to induce DNA cross-link formation. Part 2 of this grant examines the biosensing properties of C8-aryl-dG adducts in various aptamer structures. Our goal is to incorporate C8-aryl-dG adducts into aptamers to enhance aptamer binding affinity to the molecular target and provide a fluorescent signal when the target binds to the modified aptamer. Aptamers have a wide range of applications in medicine and agriculture with biotechnology companies now specializing in aptamer synthesis and design. Expanding the chemistry of DNA for in vitro selection can enhance target binding and permit a wider range of targets to be selected. Chemically diverse C8-aryl-dG adducts that promote and provide turn-on emission upon target binding would be highly useful.