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Carcinogenesis Advance Access published online on December 20, 2006
Carcinogenesis, doi:10.1093/carcin/bgl248
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Published by Oxford University Press 2006.

A Novel Synthetic Analogue of a Constituent of Isodon excisus Inhibits Transcription of CYP1A1, -1A2 and -1B1 by Preventing Activation of the Aryl Hydrocarbon Receptor

Pawel Sienkiewicz1, Henry P. Ciolino1, Benjamin J. Leslie2, Paul J. Hergenrother2, Keith Singletary3 and Grace Chao Yeh1,*

1 Cellular Defense and Carcinogenesis Section, Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute at Frederick, National Institutes of Health, Frederick, MD, USA 21702-1201
2 Department of Chemistry, University of Illinois, Urbana, IL
3 Department of Food Science and Human Nutrition, University of Illinois, Urbana, IL

* Corresponding author: Grace Chao Yeh, National Cancer Institute at Frederick, Bld. 538, Rm. 141, Frederick, MD, 21702, Tel: (301)846-5369. Fax: (301)846-6395. E-mail: yeh{at}ncifcrf.gov.

We investigated the effect of a novel synthetic analogue of a constituent from the Chinese medicinal herb Isodon excisus, 3-(3-methoxy-phenyl)-N-(3, 4, 5-trimethoxy-phenyl)-acrylamide (compound 343), on the carcinogen activation pathway mediated by the aryl hydrocarbon receptor (AhR) in human hepatoma HepG2 cells. We found that compound 343 inhibited the upregulation of CYP enzyme activity in cells treated with the AhR ligands and potent carcinogens dimethylbenzanthracene (DMBA) or 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). Compound 343 also inhibited the DMBA- or TCDD-induced increase in CYP1A1, 1A2 and 1B1 mRNA levels. Carcinogen-induced transcription of CYP genes was also suppressed by compound 343, as measured by a reporter gene controlled by the xenobiotic-response element. This was confirmed by measuring the amount of carcinogen-induced CYP1A1 heterogeneous nuclear RNA. Compound 343 blocked the DMBA- or TCDD-induced activation of the AhR DNA binding capacity for the xenobiotic responsive element, as measured by a chromatin immunoprecipitation assay. Compound 343 also inhibited CYP enzyme activity in microsomes isolated from DMBA- or TCDD-treated cells, as well as the activity of recombinant CYP1A1, 1A2 and 1B1, indicating that compound 343 directly inhibits CYP enzymes. These results indicate that compound 343 is a potent inhibitor of both carcinogen-induced CYP enzyme expression, as well as a direct inhibitor of CYP enzymes.

Key Words: Aryl Hydrocarbon Receptor • Cytochrome P450, DMBA • TCDD • HepG2 cells


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