Post-initiation treatment of Indole-3-carbinol did not suppress N-methyl-N-nitrosourea induced mammary carcinogenesis in rats

The consumption of cruciferous vegetables (the Family of Cruciferae) such a s cabbage, broccoli and Brussels sprouts has been shown to have cancer chem opreventive effects in humans and experimental animals. Indole-3-carbinol ( I3C), one component of cruciferous vegetables, has been shown to exert canc er chemopreventive influence in liver, colon, and mammary tissue when given before or concurrent with exposure to a carcinogen. However in some report s, there has been evidence that consumption of I3C after carcinogen treatme nt might be associated with tumor promotion in some tissues. There have bee n no reports, to our knowledge, of post-initiation effects of I3C in the N- methyl-N-nitrosourea (MNU)-induced mammary tumor model in rats. Our studies were performed to examine this question. Ninety-six, 4-week-old female Spr ague-Dawley rats were randomly divided into five groups. The animals of gro ups 1, 2 and 3 received an intraperitoneal injection of MNU at the age of 5 0 days. The animals of groups 4 and 5 were injected with saline only at the same time. Animals of groups I and 2 were given diet containing 100 ppm an d 300 ppm I3C from week 1 until week 25 after MNU treatment. The animals of group 4 were given basal diet containing 300 ppm I3C without MNU treatment . All animals were killed at week 25. The incidences of mammary tumors in t he groups 1, 2 and 3 were 95.8% (23/24), 83.3% (20/24) and 82.4% (28/34), r espectively. The average number of tumors in the tumor bearing rats of the MNU and I3C 300 ppm group (group 2; 3.85 +/- 0.63) was higher than that in the MNU alone group (group 3; 2.46 +/- 0.31). These results represented tha t exposure to I3C after carcinogen treatment did not suppress development o f mammary tumors. (C) 2001 Elsevier Science Ireland Ltd. All rights reserve d.