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Carmelo Rizzo

Professor of Chemistry

Chemistry and Biology of DNA Damage.

Covalent modification of DNA by electrophiles is generally accepted as the initial event in chemical carcinogenesis. If these modifications are not repaired, they can compromise the fidelity of DNA replication leading to mutations and possibly cancer. To properly study the biological processing of pre-mutagenic DNA lesions, oligonucleotides containing structurally defined carcinogen adducts are required. Our laboratory develops synthetic strategies for the site-specific incorporation of nucleotides that are chemically modified by carcinogens into DNA. Once synthesized, the structure, replication and repair of the carcinogen-modified oligonucleotides are examined. Many of these studies are preformed in collaboration with other laboratories on Vanderbilt's campus and elsewhere.

One specific project includes the preparation of the C8-deoxyguanosine adduct of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). IQ is a member of a family of highly mutagenic heterocyclic amines found in cooked meats. We found that the C8-IQ adduct adopts different conformations depending on the sequence of the adducted oligonucleotide and we have hypothesized that this sequence-dependent conformation plays an important role in the biological processing of the lesion. This hypothesis will be tested using in vitro and in vivo systems. The adduction of IQ with DNA also gives a minor N2-adduct of deoxyguanosine, which has not been extensively studied. We have recently completed a synthesis of the N2-adduct and have incorporated it into oligonucleotides.

A second major project in our lab involves DNA adducts derived from endogneous sources such as lipid peroxidation. Examples of such reactive electrophiles include alpha,beta-unsaturated aldehydes (acrolein, crotonaldehyde, and 4-hydroxynonenal), 2,3-epoxyaldehydes and dicarbonyl species (malondialdehyde and 4-oxo-2-nonenal). Although these compounds are chemically simple, they react with DNA in a complex and diverse manner. We recently demonstrated that alpha,beta-unsaturated aldehydes can form inter- and intra-strand DNA crosslinks, which are a very severe but largely unstudied form of DNA damage. The crosslinking chemistry is highly dependent on the stereochemistry of the DNA adduct. In collaboration with other laboratories, we are studying the mechanism of the DNA crosslinking reaction and the biological processing of the DNA crosslinks.

Modern mass spectrometry and NMR are integral parts to all of our studies on DNA damage. We have convenient and open access to superb analytical facilities on Vanderbilt campus. Our laboratory is affiliated with the Vanderbilt Center in Molecular Toxicology, Vanderbilt Institute of Chemical Biology, and the Vanderbilt-Ingram Cancer Center .