Project: Research project

Project Details


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.
Effective start/end date3/1/932/28/94


  • National Cancer Institute

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