Work carried out in our laboratory has demonstrated that human cytochrome P4501A2 efficiently metabolizes the dietary heterocyclic amines (HCAs) and other environmental agents to carcinogenic and mutagenic agents. The P4501A2 directed oxidative metabolism of dietary HCAs found in cooked meat as well as N-nitrosamines that are generated in the condensation of smoke derived from nicotine are known carcinogens, and have been implicated in human cancers of the colon and respiratory tract, respectively. It is appreciated that under normal states of homeostasis, formation of these oxidative products usually leads to additional metabolism by the UDP- glucuronosyltransferases (UGTs). In past years, our laboratory and others have been successful in identifying most tissues. Using methods that we have developed, it has been demonstrated that the UGT1A locus is dramatically down-regulated in human hepatocellular carcinoma. This observation ha sled us to propose that an imbalance in the expression patterns of tissue specific UGTs may contribute to the carcinogenic process initiated by specific P450 oxidation reactions. In addition, preliminary results have demonstrated that it is possible to express the UGTs in significant abundance through baculovirus directed expression in insect Sf9 cells. It is the intention of this application to examine the contribution of specific human UGTs to catalyze the glucuronidation of dietary and tobacco generated carcinogens. In conjunction with our collaborators, we are hopeful that it will be possible to specifically PhlQ, lQ, and MelQx. In addition, the P4501A2 generated hydroxylated metabolites of the N-nitrosamine-4-(methylnitrosamino)-1-(3-pyridyl)-1- butane (NNK), a tobacco smoke generated lung carcinogen, will be examined for its ability to be glucuronidated by the UGTs. If successful, additional experiments will be developed to examine the contribution of glucuronidation in the prevention of P4501A2 generated mutagens, as examined with bacterial and cellular genotoxicity assays. We are hopeful that it will be possible to identify the UGTs that participate in the glucuronidation of these hazardous dietary and environmental agents, and coupled with the oxidation of these compounds by P4501A2, provide evidence that the UGTs serve a cellular defense role.
