3,3’-Diindolylmethane (DIM) is a major condensation product (metabolite) of indole-3-carbinol, a potential anticancer component of cruciferous Brassica vegetables such as cabbage and broccoli. Both compounds have shown experimental cancer preventive efficacy in breast, prostate and cervical cancer models. The purpose of this study was to assess the toxicity of DIM in Beagle dogs following 4 weeks of daily oral capsule treatment at target doses of 0, 25 (low dose), 120 (mid dose) and 450 mg/kg/day (high dose). No mortalities occurred, but a male and a female in the high dose group were moribund sacrificed on days 19 and 26, respectively. Unusual thinness was seen in 2 other males and 3 other females in this group. Clinical signs included vomit in run, decreased activity, dehydration and pale gums in the high dose group. Food consumption was decreased in the high dose group, but moderately so in the mid dose group females. Total body weight gain reduction was observed in the high dose group males (14.5%↓) and females (24.6%↓). Serum total bilirubin levels were elevated in high dose group males, and high and mid dose group females. Elevated serum ALT, AST and ALKP values in one high dose group female and histopathologic lesions also in the liver suggested hepatocellular injury and cholestasis. DIM-induced anemia, more pronounced in the high dose group females than males, was accompanied by a dose-dependent compensatory increase in percentage of reticulocytes. No treatment-related changes were seen in ophthalmologic, electrocardiographic and urinalysis parameters and organ weights except moderate thymic atrophy in the high dose group. The tmax for DIM occurred between 2 - 4.5 hr. The systemic exposure of DIM increased in a dose-dependent fashion. The mean AUC0-24 values for the low, mid and high dose groups were 835, 2382 and 4271 ng-hr/mL, respectively for males, and 981, 1202 and 8034 ng-hr/mL, respectively, for females. Females were more sensitive to the toxic effects of DIM. Overall, toxic responses to oral treatment of DIM in dogs included several signs of toxicity related to body weight gain reduction, reduced food consumption, hepatoxicity, anemia, thymic atrophy, hematopoietic hyperplasia in sternal bone marrow and mild kidney damage [histopathologic renal lesions and mild changes in serum electrolyte levels (hypocalcemia and hyperchloremia)] seen predominantly in the high dose group. Under the conditions of this study, based on the purity of DIM, the No Observed Adverse Effect Level (NOAEL) was 21 mg/kg/day. (Supported by NCI Contract no. N01-CN-95132).

[Proc Amer Assoc Cancer Res, Volume 45, 2004]