Chemoprevention of chemically-induced mammary carcinogenesis by indole-3-carbinol. 
Indole-3-carbinol, a component of cruciferous vegetables, was evaluated for it efficacy in the prevention of chemically-induced mammary tumors using three different protocols.  Because this compound was unstable, it was administered by gavage rather than in the diet.  A preliminary dose range study revealed that dose levels of 100 and 50 mg/day, 5x/week, were not toxic to female Sprague-Dawley rats.  Initial studies in the DMBA model showed that administering indole-3-carbinol during the initiation and promotion phases were highly effective chemopreventive methods (91-96% reduction in cancer multiplicity).  Subsequent studies showed that the administration of indole-3-carbinol only during the initiation phase (7 days prior to until 7 days post DMBA) was also highly effective as a chemopreventive agent.  Determination of enzyme levels in the livers of animals treated long-term with indole-3-carbinol showed high levels of induction of various phase I and phase II drug metabolizing enzymes.  Finally, indole-3-carbinol when administered both prior to and after MNU (a direct acting carcinogen) caused a significant decrease (65%) in mammary tumor multiplicity.  These results support previous studies that indole-3-carbinol can prevent mammary carcinogenesis by direct and indirect acting carcinogens.  Therefore, indole-3-carbinol might be a good candidate for chemoprevention of breast cancer in women.