Our research is focused on the biochemical toxicology of dietary and environmental genotoxicants, as well as endogenous electrophiles that damage protein and DNA. We have conducted extensive research on the metabolism and bioactivation of carcinogenic aromatic amines (AAs) and heterocyclic aromatic amines (HAAs), which are formed tobacco smoke and in well-done cooked meats, and aristolochic acids, nitrophenanthrenes present in some traditional medicinal herbs. The biotransformation of these compounds generates an array of metabolites including reactive and reactive toxic, metabolites that are responsible for their carcinogenicity in animal models and humans. These reactive species lead to the formation of covalent modifications of proteins and DNA, known as adducts, that can impair normal cellular functions; DNA adducts can induce mutations that ultimately may lead to cancer. Our long-term objectives are to understand the etiological roles of these chemicals, and implement chemical markers and state-of-the-art mass spectrometry methods for use in molecular epidemiology studies that seek to understand the origin of human cancer for which an environmental cause is suspected.

We have used human cell lines and human primary cells to investigate the metabolism of carcinogenic AAs and HAAs, and their ability to form DNA adducts in humans. By quantifying DNA adducts in cell systems and human organs by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) and relating adduct formation to the activities of metabolic enzymes, we can identify enzyme pathways involved in genotoxicity and interindividual susceptibilities to the carcinogenicity of these genotoxicants.

We develop robust and sensitive analytical methods to biomonitor AA and HAA exposures at ultra-trace levels in human biospecimens employing liquid chromatography/mass spectrometry. We have developed assays to quantify biomarkers in humans: (1) HAAs in naturally colored hair and hair after permanent dye treatment; (2) HAA and AA metabolites in urine; (3) serum albumin and hemoglobin adducts of HAAs and AAs; (4) DNA adducts of HAAs and AAs in the white blood cells; and (5) DNA adducts in freshly frozen and formalin fixed paraffin embedded tissues. Several of these biomarkers are being employed in human cohorts. Our goal is to see if differences in dietary habits or inter-individual difference metabolism of HAAs, AAs, and their ensuing DNA adducts, can be employed to better understand the cancer risk posed by these ubiquitous genotoxicants.

Fresh frozen biopsy samples are often difficult to obtain for DNA adduct biomarker research. However, formalin-fixed paraffin embedded (FFPE) tissues with clinical diagnosis of disease are routinely archived. We have developed novel methods to completely reverse DNA cross-links, which permits measurements of DNA adducts for multiple classes of carcinogens. We have extended this technology and adapted a rapid throughput technology used in genomics to recover DNA to measure DNA adducts of AAs, HAAs, polycyclic aromatic hydrocarbons, N-nitroso compounds in FFPE prostate, bladder, and lung.

Hair represents another non-invasive tissue specimen that can be used to assess chemical exposures. In contrast to urine and many blood markers, the accumulation of toxicants in hair represents a long-term biomarker that can integrate exposures over a time period of months. We have developed methods to measure HAAs in naturally colored hair and hair after permanent dye treatment. Our goal is to extend this methodology to screen hair for a variety of dietary and environmental toxicants.

We are developing novel data-independent and data-dependent multistage mass spectrometry scanning methods to measure genotoxicants in the bladder and DNA adducts in exfoliated cells in urine that may contribute to genitourinary cancers. Novel biomarkers under development are urinary serum albumin adducts as a non-invasive method to characterize reactive electrophiles in the urine that may contribute to bladder cancer.

Novel scanning approaches, by ion trap and high-resolution accurate mass measurement Orbitrap MS, are under development to screen human biospecimens for a variety of DNA lesions formed with carcinogens present in the diet and environment, and endogenous electrophiles formed under pathological conditions, such as inflammation and oxidative stress. These screening methods are expected to provide a better understanding of the major exogenous chemicals in the environment and endogenous ones that damage DNA that may lead to the onset of cancer.