Aryl hydrocarbon receptor-mediated antiestrogenic and antitumorigenic activity of diindolylmethane.
Phytochemicals such as indole-3-carbinol (I3C) and sulforaphane are components of cruciferous vegetables which exhibit antitumorigenic activity associated with altered carcinogen metabolism and detoxification. Diindolylmethane (DIM) is a major acid-catalyzed metabolite of I3C formed in the gut that binds to the aryl hydrocarbon receptor (AhR) and treatment of MCF-7 human breast cancer cells with 10-50 microM DIM resulted in rapid formation of the nuclear AhR complex and induction of CYP1A1 gene expression was observed at concentrations >50 microM. Previous studies have demonstrated that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a high affinity AhR ligand, inhibits 17beta-estradiol (E2)-induced responses in MCF-7 cells and growth of E2-dependent 7,12-dimethylbenzanthracene (DMBA)-induced mammary tumors in female Sprague-Dawley rats. Results of this study show that like TCDD, DIM inhibits E2-induced proliferation of MCF-7 cells, reporter gene activity in cells transiently transfected with an E2-responsive plasmid (containing a frog vitellogenin A2 gene promoter insert) and down-regulates the nuclear estrogen receptor. Moreover, DIM (5 mg/kg every other day) also inhibits DMBA-induced mammary tumor growth in Sprague-Dawley rats and this was not accompanied by induction of hepatic CYP1A1-dependent activity. Thus, DIM represents a new class of relatively non-toxic AhR-based antiestrogens that inhibit E2-dependent tumor growth in rodents and current studies are focused on development of analogs for clinical treatment of breast cancer.
Department of Veterinary Physiology and Pharmacology, Texas A&M University, College Station 77843-4466, USA.
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Chen
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McDougal
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Wang
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D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D004965:Estrogen Antagonists / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007211:Indoles / Q000378:metabolism / Q000494:pharmacology*; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects* / Q000502:physiology; D014407:Tumor Cells, Cultured
D016588:Anticarcinogenic Agents; D004965:Estrogen Antagonists; D007211:Indoles; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; C016517:indole-3-carbinol; D019363:Cytochrome P-450 CYP1A1; C016392:3,3'-diindolylmethane