The principal focus of our research is determination of how cancer is initiated by carcinogens, such as polycyclic aromatic hydrocarbons (PAHs). PAHs are most potent class of carcinogens prevalent in urban environments. They are produced by combustion of organic matter and commonly occur in cigarette smoke, automobile exhaust, and fried and charbroiled meats. PAHs have been classified as human carcinogens by the World Health Organization.

Our earlier investigations showed that PAHs are activated by cytochrome P-450 enzymes to diol epoxide metabolites that react with DNA to form adducts, leading to mutations and ultimately to tumor induction. Methods for syntheses of the (+) and (-)anti- and syn-diol epoxides of benzo[a]pyrene (BP) and other PAH carcinogens were devised in our laboratories. And the molecular structures of the adducts formed by the PAH diol epoxide metabolites with DNA were determined in studies conducted in collaboration with Weinstein at Columbia University and Geacintov at NYU. The findings stimulated an outpouring of research, and it is now generally accepted that the diol epoxide path is importantly involved in the initation of lung cancer in cigarette smokers as well as other cancers.

More recent studies being conducted in collaboration with Trevor Penning (Univ. Penn) have provided evidence for a second PAH activation pathway. This path entails aldo-keto reductase-mediated transformation of PAH dihydrodiols to PAH catechols that enter into redox cycles with O₂ to form PAH quinones and reactive oxygen species (ROS). The quinones react with DNA form stable and depurinated adducts, and the ROS cause extensive DNA damage. Syntheses of both types of adducts have been developed, making them availble for biological studies to determine their role in tumor induction. A third pathway of activation of PAH carcinogens was proposed by Ercole Cavalieri (Univ. Nebraska). It entails peroxidase-mediated formation of PAH radical-cations that react with DNA to form depurinated adducts. We have also recently devised efficient syntheses of these types of adducts.

Current studies are directed toward obtaining more direct evidence on the relative importance of these activation pathways for lung cancer. Most investigations of PAH carcinogenesis have been conducted with rodent cells as model systems. However, their relevance to human cancer is uncertain. In collaboration with Penning and Blair (Univ. Penn) we have initiated studies of the metabolism of PAH carcinogens in human bronchoalveolar H358 cells using a sensitive stable isotope dilution LC-MS-based analytical method developed by Dr. Blair. Initial experimental findings indicate that these cells afford a profile of metabolites that differs in significant respects from those of rodent cells. In this connection, we synthesized the ¹³C-labeled analogues of BP and its active metabolites (¹³C₂-BP, ¹³C₂-BP-7,8-diol, ¹³C₂-BP-7,8-dione, and ¹³C₂-BPDE) needed as standards for LC-MS analysis. Synthesis of the complete set ¹³C-labeled metabolites of BP and DBC, the most potent known PAH carcinogen, is under investigation.