Application of toxicogenomics to determine mechanism of tumor modulation by dietary indole phytochemicals in hepatocellular carcinoma

Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM), a primary I3C derivative in vivo, are known chemopreventive agents available as dietary supplements. I3C was found to suppress or enhance tumors in several animal models. Chemoprotection is attributed to the ability of indoles to alter carcinogen metabolism effectively blocking initiation. However, mechanisms for enhancement are unknown. In rainbow trout, I3C promotes hepatocarcinogenesis at concentrations that differentially activated estrogen receptor (ER) or aryl hydrocarbon receptor (AhR)-mediated responses. The relative importance of these pathways was evaluated using toxicogenomics in juvenile trout exposed to I3C and DIM compared to ER and AhR agonists, 17beta-estradiol (E2) and beta-naphthoflavone. I3C and DIM acted transcriptionally similar to E2 by correlation analysis indicating I3C promotes hepatocarcinogenesis through estrogenic mechanisms in trout and suggesting DIM may be a more potent tumor promoter.; The ability of DIM to enhance hepatocarcinogenesis was evaluated in trout initiated with aflatoxin B1 compared to E2. Tumor incidence was significantly elevated in initiated trout fed 400 ppm DIM. To evaluate the mechanism of promotion, hepatic gene expression profiles were examined in animals on promotional diets during the course of tumorigenesis and in hepatocellular carcinomas (HCCs) using a trout 70-mer oligonucleotide array. DIM altered gene expression profiles similar to E2 at all timepoints measured. Expression profiles in trout HCC were similar to transcriptional changes reported in human and rodent HCC further supporting the validity of the trout tumor model. Further, transcription in HCCs from DIM and E2 treatments indicated decreased invasive potential compared to control HCCs. These findings confirm importance of estrogenic signaling in the mechanism of indoles and indicate a possible dual effect that enhances tumor incidence and decreases potential for metastasis.; The estrogenic response of DIM in trout liver was characterized by measuring its in vitro biological activity, its ability to bind to ER and its potential for metabolism to estrogenic metabolites. The results support the role of DIM as a potent estrogen in trout liver that may require metabolism for ligand-dependent activation of ER or activation of extracellular signaling pathways for ligand-independent activation of ER. It is likely that multiple mechanisms are involved for DIM estrogenic activity.