4-Ipomeanol (IPO) is a potent pulmonary toxin which is metabolically activated by cytochrome P450 enzymes in Clara cells of the lung. 4- Methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) is a tobacco-specific nitrosamine which is a potent pulmonary carcinogen and is also metabolically activated by cytochrome P450 enzymes in Clara cells. It is believed to be important in tobacco-induced lung cancer. The structures of IPO and NNK are similar. Our hypothesis is that non-toxic structural analogues of IPO could be competitive inhibitors of NNK metabolic activation in the lung and could therefore inhibit its tumorigenicity. Our preliminary results demonstrate that this is the case. We propose to extend our preliminary studies as follows: 1. Synthesize 14C-labelled 4-hydroxy-1-phenyl-1-pentanone (HPP), 7- hydroxy-1-phenyl-1-octanone (HPO) and 4-hydroxy-1-(2-thiophenyl)-1- pentanone (HTP). While all three compounds inhibited NNK metabolism in vitro by pulmonary microsomes, only HPP and HPO inhibited NNK tumorigenicity. We will study the metabolism and distribution of [14C]HPP, HPO, and HTP in A/J mice to gain insights on the mechanism of inhibition of NNK tumorigenicity. 2. Determine the effects of the IPO analogues on the formation and persistence of O6-methylguanine in the lung of A/J mice treated with NNK. This miscoding DNA adduct is critical in NNK tumorigenesis in A/J mice. 3. Synthesize other analogues of IPO and test them in vitro and in vivo as inhibitors of NNK metabolic activation. Carry out bioassays of the promising analogues as inhibitors of NNK tumorigenesis. These promising analogues will also be synthesized in labelled form. 4. Determine the ability of IPO and its analogues to inhibit NNK metabolism in Clara cells and other pulmonary cell types, and in microsomes prepared from cells transfected with cDNAs encoding human cytochromes P450. Examine the metabolism of the labelled analogues in these systems. The results of this study will lead to the development of new mechanism based inhibitors of NNK tumorigenesis and will further our understanding of the structural features associated with effective metabolism by cytochrome P450 enzymes present in the lung.
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