Antitumour promoting activity of indole-3-carbinol in mouse skin carcinogenesis

Cultivar-Specific Changes in Primary and Secondary Metabolites in Pak Choi (Brassica Rapa, Chinensis Group) by Methyl Jasmonate

Glucosinolates, their hydrolysis products and primary metabolites were analyzed in five pak choi cultivars to determine the effect of methyl jasmonate (MeJA) on metabolite flux from primary metabolites to glucosinolates and their hydrolysis products. Among detected glucosinolates (total 14 glucosinolates; 9 aliphatic, 4 indole and 1 aromatic glucosinolates), indole glucosinolate concentrations (153-229%) and their hydrolysis products increased with MeJA treatment. Changes in the total isothiocyanates by MeJA were associated with epithiospecifier protein activity estimated as nitrile formation. Goitrin, a goitrogenic compound, significantly decreased by MeJA treatment in all cultivars. Changes in glucosinolates, especially aliphatic, significantly differed among cultivars. Primary metabolites including amino acids, organic acids and sugars also changed with MeJA treatment in a cultivar-specific manner. A decreased sugar level suggests that they might be a carbon source for secondary metabolite biosynthesis in MeJA-treated pak choi. The result of the present study suggests that MeJA can be an effective agent to elevate indole glucosinolates and their hydrolysis products and to reduce a goitrogenic compound in pak choi. The total glucosinolate concentration was the highest in "Chinese cabbage" in the control group (32.5 µmol/g DW), but indole glucosinolates increased the greatest in "Asian" when treated with MeJA.

Protective effects of indole-3-carbinol on cyclophosphamide-induced clastogenecity in mouse bone marrow cells

Indole-3-carbinol (I3C) is present in many cruciferous vegetables and is known to possess protective properties against chemically induced toxicity and carcinogenesis. In the present study, the antimutagenic potential of I3C has been evaluated using in vivo chromosomal aberration (CA) assay as a cytogenetic end point. Chromosomal analysis was carried out in mouse bone marrow cells following administration of I3C (5 mg/kg; i.p.) for 5 consecutive days. Cyclophosphamide (CP), a well known mutagen, was given at two dose levels of 25 mg/kg b.wt. and 100 mg/kg b.wt., respectively, 24 hours prior to the last dose of I3C. Two groups of five mice each were also injected with CP (25 or 100 mg/kg b.wt.) alone whereas for the vehicle control a group of mice was injected with normal saline only. The results revealed a significant inhibition in the frequencies of CP-induced CAs and aberrant cells in bone marrow cells of I3C-supplemented Swiss albino mice. The antimutagenic potential of I3C towards CP was also evident as the status of mitotic index (MI) was found to show an increment. This study revealed the antigenotoxic potential of I3C against CP- induced chromosomal mutations.

Cooperative antiproliferative signaling by aspirin and indole-3-carbinol targets microphthalmia-associated transcription factor gene expression and promoter activity in human melanoma cells

Antiproliferative signaling of combinations of the nonsteroidal anti-inflammatory drug acetylsalicylic acid (aspirin) and indole-3-carbinol (I3C), a natural indolecarbinol compound derived from cruciferous vegetables, was investigated in human melanoma cells. Melanoma cell lines with distinct mutational profiles were sensitive to different extents to the antiproliferative response of aspirin, with oncogenic BRAF-expressing G361 cells and wild-type BRAF-expressing SK-MEL-30 cells being the most responsive. I3C triggered a strong proliferative arrest of G361 melanoma cells and caused only a modest decrease in the proliferation of SK-MEL-30 cells. In both cell lines, combinations of aspirin and I3C cooperatively arrested cell proliferation and induced a G1 cell cycle arrest, and nearly ablated protein and transcript levels of the melanocyte master regulator microphthalmia-associated transcription factor isoform M (MITF-M). In melanoma cells transfected with a -333/+120-bp MITF-M promoter-luciferase reporter plasmid, treatment with aspirin and I3C cooperatively disrupted MITF-M promoter activity, which accounted for the loss of MITF-M gene products. Mutational analysis revealed that the aspirin required the LEF1 binding site, whereas I3C required the BRN2 binding site to mediate their combined and individual effects on MITF-M promoter activity. Consistent with LEF1 being a downstream effector of Wnt signaling, aspirin, but not I3C, downregulated protein levels of the Wnt co-receptor LDL receptor-related protein-6 and β-catenin and upregulated the β-catenin destruction complex component Axin. Taken together, our results demonstrate that aspirin-regulated Wnt signaling and I3C-targeted signaling pathways converge at distinct DNA elements in the MITF-M promoter to cooperatively disrupt MITF-M expression and melanoma cell proliferation.

Indole-3-carbinol (I3C) increases apoptosis, represses growth of cancer cells, and enhances adenovirus-mediated oncolysis

Epidemiological studies suggest that high intake of cruciferous vegetables is associated with a lower risk of cancer. Experiments have shown that indole-3-carbinol (I3C), a naturally occurring compound derived from cruciferous vegetables, exhibits potent anticarcinogenic properties in a wide range of cancers. In this study, we showed that higher doses of I3C (≥400 μM) induced apoptotic cancer cell death and lower doses of I3C (≤200 μM) repressed cancer cell growth concurrently with suppressed expression of cyclin E and its partner CDK2. Notably, we found that pretreatment with low doses of I3C enhanced Ad-mediated oncolysis and cytotoxicity of human carcinoma cells by synergistic upregulation of apoptosis. Thus, the vegetable compound I3C as a dietary supplement may benefit cancer prevention and improve Ad oncolytic therapies.

Attenuation of Carcinogenesis and the Mechanism Underlying by the Influence of Indole-3-carbinol and Its Metabolite 3,3'-Diindolylmethane: A Therapeutic Marvel

Rising evidence provides credible support towards the potential role of bioactive products derived from cruciferous vegetables such as broccoli, cauliflower, kale, cabbage, brussels sprouts, turnips, kohlrabi, bok choy, and radishes. Many epidemiological studies point out that Brassica vegetable protects humans against cancer since they are rich sources of glucosinolates in addition to possessing a high content of flavonoids, vitamins, and mineral nutrients. Indole-3-carbinol (I3C) belongs to the class of compounds called indole glucosinolate, obtained from cruciferous vegetables, and is well-known for tits anticancer properties. In particular, I3C and its dimeric product, 3,3'-diindolylmethane (DIM), have been generally investigated for their value against a number of human cancers in vitro as well as in vivo. This paper reviews an in-depth study of the anticancer activity and the miscellaneous mechanisms underlying the anticarcinogenicity thereby broadening its therapeutic marvel.

In vitro suppression of growth of murine WEHI-3 leukemia cells and in vivo promotion of phagocytosis in a leukemia mice model by indole-3-carbinol

Indole-3-carbinol (I3C), a potential anticancer substance, can be found in cruciferous (cabbage family) vegetables, mainly cauliflower and Chinese cabbage. However, the bioactivity of I3C on the apoptotic effects of murine leukemia WEHI-3 cells and promotion of immune responses in leukemia mice model are unclear. In this study, we investigated the effect of I3C on cell-cycle arrest and apoptosis in vitro and immunomodulation in vivo. I3C decreased the viable WEHI-3 cells and caused morphological changes in a concentration- and time-dependent manner. I3C also led to G0/G1 phase arrest, decreased the levels of cyclin A, cyclin D, and CDK2, and increased the level of p21(WAF1/CIP1). Flow cytometric analyses further proved that I3C promoted ROS and intracellular Ca(2+) production and decreased the levels of ΔΨ(m) in WEHI-3 cells. Cells after exposure to I3C for 24 h showed DNA fragmentation and chromatin condensation. Comet assay also indicated that I3C induced DNA damage in examined cells. I3C increased the levels of cytochrome c, FADD, GADD153, GRP78, and caspase-12 as well as induced activities of caspase-3, -8, and -9. Moreover, I3C attenuated NF-κB DNA binding activity in I3C-treated WEHI-3 cells as shown by EMSA and Western blotting analyses. In the in vivo study, we examined the effects of I3C on WEHI-3 leukemia mice. Results showed that I3C increased the level of T cells and decreased the level of macrophages. I3C also reduced the weights of liver and spleen, and it promoted phagocytosis by macrophages as compared to the nontreated leukemia mice group. On the basis of our results, I3C affects murine leukemia WEHI-3 cells both in vitro and in vivo.

3,3'-diindolylmethane induces activating transcription factor 3 (ATF3) via ATF4 in human colorectal cancer cells

3,3'-Diindolylmethane (DIM) is a major in vivo condensation product of indole-3-carbinol, which is present in cruciferous vegetables. Although these compounds have been widely implicated in antitumorigenic and proapoptotic properties in animal as well as in vitro models of cancer, the underlying cellular mechanisms regulated by DIM are only partially understood. Activating transcription factor 3 (ATF3) is a member of the ATF/c-AMP response element-binding (CREB) subfamily of the basic-region leucine zipper family and has been known to induce apoptosis in human colorectal cancer (CRC) cells. The present study was performed to elucidate the molecular mechanism of ATF3 induction by DIM in human CRC cells. The DIM treatment induced apoptosis and induced ATF3 gene expression at protein and messenger RNA levels. DIM increased ATF3 promoter activity, and the region of -84 to +34 within ATF3 promoter was responsible for promoter activation by DIM. This region contained an ATF binding site. Deletion and point mutation of the ATF binding site (-23 to -16) abolished ATF3 promoter activation by DIM, and overexpression of ATF4 enhanced ATF3 transactivation. Chromatin immunoprecipitation assay confirmed the binding of ATF4 in the ATF3 promoter. Inhibition of ATF4 expression by small interference RNA results in repression of DIM-induced ATF3 expression. The current study demonstrates that DIM stimulates ATF3 expression through ATF4-mediated pathway and subsequently induces apoptosis in human CRC cells.

Indole-3-carbinol prevents PTEN loss in cervical cancer in vivo

Indole-3-carbinol (I3C) is a phytochemical (derived from broccoli, cabbage, and other cruciferous vegetables) with proven anticancer efficacy including the reduction of cervical intraepithelial neoplasia (CIN) and its progression to cervical cancer. In a breast cancer cell line, I3C inhibited cell adhesion, spreading, and invasion associated with an upregulation of the tumor suppressor gene PTEN, suggesting that PTEN is important in inhibition of late stages in the development of cancer. The goal of this study was to determine the expression of PTEN during the development of cervical cancer and whether I3C affected expression of PTEN in vivo. We show diminished PTEN expression during the progression from low-grade to high-grade cervical dysplasia in humans and in a mouse model for cervical cancer, the K14HPV16 transgenic mice promoted with estrogen. The implication is that loss of PTEN function is required for this transition. Additionally, dietary I3C increased PTEN expression in the cervical epithelium of the transgenic mouse, an observation that suggests PTEN upregulation by I3C is one mechanism by which I3C inhibits development of cervical cancer.

Induction of G1 and G2/M cell cycle arrests by the dietary compound 3,3'-diindolylmethane in HT-29 human colon cancer cells

Background

3,3'-Diindolylmethane (DIM), an indole derivative produced in the stomach after the consumption of broccoli and other cruciferous vegetables, has been demonstrated to exert anti-cancer effects in both in vivo and in vitro models. We have previously determined that DIM (0 – 30 μmol/L) inhibited the growth of HT-29 human colon cancer cells in a concentration-dependent fashion. In this study, we evaluated the effects of DIM on cell cycle progression in HT-29 cells.

Methods

HT-29 cells were cultured with various concentrations of DIM (0 – 30 μmol/L) and the DNA was stained with propidium iodide, followed by flow cytometric analysis. [³H]Thymidine incorporation assays, Western blot analyses, immunoprecipitation and in vitro kinase assays for cyclin-dependent kinase (CDK) and cell division cycle (CDC)2 were conducted.

Results

The percentages of cells in the G1 and G2/M phases were dose-dependently increased and the percentages of cells in S phase were reduced within 12 h in DIM-treated cells. DIM also reduced DNA synthesis in a dose-dependent fashion. DIM markedly reduced CDK2 activity and the levels of phosphorylated retinoblastoma proteins (Rb) and E2F-1, and also increased the levels of hypophosphorylated Rb. DIM reduced the protein levels of cyclin A, D1, and CDK4. DIM also increased the protein levels of CDK inhibitors, p21^CIP1/WAF1 and p27^KIPI. In addition, DIM reduced the activity of CDC2 and the levels of CDC25C phosphatase and cyclin B1.

Conclusion

Here, we have demonstrated that DIM induces G1 and G2/M phase cell cycle arrest in HT-29 cells, and this effect may be mediated by reduced CDK activity.

Cruciferous vegetable intake and the risk of human cancer: epidemiological evidence

Over several decades a number of epidemiological studies have identified the inverse associations between cruciferous vegetables and the risk of several cancers, including gastric, breast, colo-rectal, lung, prostate, bladder and endometrial cancers, via plausible physiological mechanisms. Although retrospective case–control studies have consistently reported inverse associations between the risk of these cancers and the intake of cruciferous vegetables and isothiocyanate-containing plants, current prospective cohort studies have found these associations to be weaker and less consistent. Genetic variations affecting the metabolism of glucosinolate hydrolysis products may modulate the effects of cruciferous vegetable consumption on cancer risk, which may be one of the reasons for the discrepancies between retrospective and prospective studies. In addition, methodological issues such as measurement errors of dietary exposure, misclassification, recall bias, publication bias, confounding and study design should be carefully considered in interpreting the results of case–control and cohort studies and in drawing conclusions in relation to the potential effects of cruciferous vegetables on cancers. Although recent comprehensive reviews of numerous studies have purported to show the specific protective role of cruciferous vegetables, and particularly Brassicas, against cancer risk, the current epidemiological evidence suggests that cruciferous vegetable consumption may reduce the risk only of gastric and lung cancers. However, there is at present no conclusive evidence that the consumption of cruciferous vegetables attenuates the risk of all other cancers.

Activation of caspase-8 contributes to 3,3'-Diindolylmethane-induced apoptosis in colon cancer cells

3,3'-Diindolylmethane (DIM) is the major in vivo product of acid-catalyzed oligomerization of indole-3-carbinol, which is a promising anticancer agent present in cruciferous vegetables and has itself been reported to have anticarcinogenic properties. This study examined DIM-mediated regulation of apoptosis in the HCT116 (wild-type p53) and HT-29 (mutant p53) human colon cancer cell lines. DIM (0-30 micromol/L) substantially decreased the number of viable cells and induced apoptosis of HCT116 and HT-29 cells in a concentration-dependent manner. Western-blot analyses of total cell lysates revealed that DIM increased the activation of caspase-3, -7, -8, and -9 and enhanced poly(ADP-ribose) polymerase cleavage in both HCT116 and HT-29 cells. In addition, DIM increased the translocation of cytochrome c and Smac/Diablo from the mitochondria to the cytoplasm. In concert with the caspase-8 activation by DIM, increased levels of Fas and truncated Bid were observed. DIM did not affect the protein levels of p53, Bcl-2, Bax, or Fas ligand (FasL) in HCT116 cells. In HT-29 cells, however, DIM decreased Bcl-2 levels, although the protein levels of Bax or FasL were not affected. The caspase-8 inhibitor Z-IETD-FMK attenuated the DIM-induced apoptosis, indicating that increased activation of this enzyme contributed to the increase in p53-independent apoptosis that was observed in colon cancer cells. We have demonstrated that DIM induces apoptosis in colon cancer cells, providing insights into the mechanisms underlying its antitumorigenic activities.

Indole-3-carbinol mediated cell cycle arrest of LNCaP human prostate cancer cells requires the induced production of activated p53 tumor suppressor protein

Indole-3-carbinol (I3C), a dietary compound found naturally in cruciferous vegetables of the Brassica genus such as broccoli and brussels sprouts, induces a G1 growth arrest of human reproductive cancer cells. We previously reported that in LNCaP prostate cancer cells, I3C down-regulated cyclin-dependent kinase (CDK) 2 activity. In our current study, Western blotting and quantitative RT-PCR demonstrated that I3C treatment increased both the transcripts and protein levels of the CDK2 inhibitor p21(waf1/cip1) (p21). Transfection of luciferase reporter plasmids containing wild-type and mutated p21 promoter fragments revealed that I3C induced p21 gene transcription through a p53 DNA binding element. Oligonucleotide precipitation showed that I3C increased the level of activated p53 nuclear protein that is competent to bind its DNA target site on the p21 promoter. Ablation of p53 production using short interfering RNA (siRNA) prevented that the I3C induced G1 arrest and up-regulation of p21 expression. Western blots using p53 phospho-specific antibodies revealed that I3C treatment increased the levels of three phosphorylated forms of p53 (Ser15, Ser37, Ser392) that are known to contribute to p53 protein stability and greater transactivation potential. Taken together, our results establish that the I3C induced G1 arrest of human prostate cancer cells requires the induced production of the activated phosphorylated forms of p53, which stimulate transcription of the CDK2 inhibitor p21.

Ultraviolet radiation-induced non-melanoma skin cancer in the Crl:SKH1:hr-BR hairless mouse: augmentation of tumor multiplicity by chlorophyllin and protection by indole-3-carbinol

Over 1 million new cases of ultraviolet radiation-induced non-melanoma skin cancers (NMSC) per year now occur in the USA and the incidence of these diseases continues to increase. New preventative strategies are required. The hypothesis tested was that dietary administration of the putative cancer chemopreventatives sodium-copper-chlorophyllin (Chlor) or indole-3-carbinol (I3C) would inhibit UV-induced skin carcinogenesis in the Crl:SKH1:hr-BR hairless mouse. Groups of 20 mice were pre-fed isocaloric/isonutritive 20% corn-oil AIN-76a based diets that contained either Chlor (1.52 g%), I3C (5.08 g%) or no chemopreventative (control) for 2 weeks followed by exposure of their dorsal skin to a 10 week incremental, sub-erythemal, carcinogenic simulated solar UV exposure regime. Feeding was continued for the duration of the experiment. Matched non-UV exposed dietary groups were also included in the experimental design. The diets had no significant (p > 0.05) effect on body weight, feed consumption, cutaneous methanol-extractable UV photoprotective substances or on cutaneous UV-reflective characteristics. By day 180, UV-irradiated mice fed the Chlor had a significantly (p < 0.05) higher tumor multiplicity (33.6 +/- 4.72; mean +/- SEM) than UV-irradiated control animals (22.8 +/- 4.25). UV-irradiated mice fed I3C had a significantly (p < 0.001) lower tumor multiplicity (13.0 +/- 2.42) than that of both the UV-irradiated control and UV-irradiated Chlor-fed mice. The Chlor or I3C diets did not significantly (p > 0.05) affect UV-induced systemic suppression of contact hypersensitivity responses. These results demonstrate augmentation of the UV-induced cutaneous carcinogenic process by dietary chlorophyllin and protection from this carcinogenic process by indole-3-carbinol via mechanisms that do not involve changes in skin optical properties, modulation of photoimmunosuppression or caloric/nutrient effects.

Indole-3-carbinol inhibition of androgen receptor expression and downregulation of androgen responsiveness in human prostate cancer cells

Indole-3-carbinol (I3C), a naturally occurring compound found in vegetables of the Brassica genus, such as broccoli and cabbage, is a promising anticancer agent previously shown to induce a G(1) cell-cycle arrest in the cells of human lymph node carcinoma of prostate (LNCaP) through regulation of specific G(1)-acting cell-cycle components. Since the androgen receptor (AR) mediates proliferation and differentiation in the prostate and is expressed in nearly all human prostate cancers, the effects of I3C on AR expression and function were examined in LNCaP cells. Immunoblot and quantitative RT-PCR assays revealed that I3C inhibited the expression of AR protein and mRNA levels within 12 h of indole treatment. I3C downregulated the reporter activity of LNCaP cells transiently transfected with an AR promoter-luciferase plasmid, demonstrating that a unique response to I3C is the inhibition of AR promoter activity. In contrast to I3C, the natural I3C dimerization product 3,3'-diindolylmethane, which acts as an androgen antagonist, had no effect on AR expression. To determine the functional significance of the I3C-inhibited expression of AR, the AR-regulated prostate specific antigen (PSA) was utilized as a downstream indicator. I3C downregulated the expression of PSA transcripts and protein levels and inhibited PSA promoter activity, as well as that of a minimal androgen responsive element containing reporter plasmid. Expression of exogenous AR prevented the I3C disruption of androgen-induced PSA expression. Taken together, our results demonstrate that I3C represses AR expression and responsiveness in LNCaP cells as a part of its antiproliferative mechanism.

Indole-3-carbinol and 3,3'-diindolylmethane induce expression of NAG-1 in a p53-independent manner

Indole-3-carbinol (I3C), present in cruciferous vegetables, and its major in vivo product 3,3'-diindolylmethane (DIM), have been reported to suppress cancer development. However, the responsible molecular mechanisms are not fully understood. Nonsteroidal anti-inflammatory drug-activated gene-1 (NAG-1) is a TGF-beta superfamily gene associated with pro-apoptotic and anti-tumorigenic activities. The present study was performed to investigate whether I3C and DIM influence NAG-1 expression and to provide the potential molecular mechanism of their effects on anti-tumorigenesis. The I3C repressed cell proliferation and induced NAG-1 expression in a concentration-dependent manner. In addition, DIM increased the expression of NAG-1 as well as activating transcription factor 3 (ATF3), and the induction of ATF3 was earlier than that of NAG-1. The DIM treatment increased luciferase activity of NAG-1 in HCT-116 cells transfected with NAG-1 promoter construct. The results suggest that I3C represses cell proliferation through up-regulation of NAG-1 and that ATF3 may play a pivotal role in DIM-induced NAG-1 expression in human colorectal cancer cells. Furthermore, the mixture of I3C with resveratrol enhances NAG-1 expression, suggesting the synergistic effect of these two unrelated compounds on NAG-1 expression.

Pharmacokinetics and tissue disposition of indole-3-carbinol and its acid condensation products after oral administration to mice

Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM) are promising cancer chemopreventive agents in rodent models, but there is a paucity of data on their pharmacokinetics and tissue disposition. The disposition of I3C and its acid condensation products, DIM, [2-(indol-3-ylmethyl)-indol-3-yl]indol-3-ylmethane (LTr(1)), indolo[3,2b]carbazole (ICZ) and 1-(3-hydroxymethyl)-indolyl-3-indolylmethane (HI-IM) was studied, after oral administration of I3C (250 mg/kg) to female CD-1 mice. Blood, liver, kidney, lung, heart, and brain were collected between 0.25 and 24 h after administration and the plasma and tissue concentrations of I3C and its derivatives determined by high-performance liquid chromotography. I3C was rapidly absorbed, distributed, and eliminated from plasma and tissues, falling below the limit of detection by 1 h. Highest concentrations of I3C were detected in the liver where levels were approximately 6-fold higher than those in the plasma. Levels of DIM, LTr(1), and HI-IM were much lower, although they persisted in plasma and tissues for considerably longer. DIM and HI-IM were still present in the liver 24 h after I3C administration. Tissue levels of DIM and LTr(1) were found to be in equilibrium with plasma at almost every time point measured. In addition to acid condensation products of I3C, a major oxidative metabolite (indole-3-carboxylic acid) and a minor oxidative metabolite (indole-3-carboxaldehyde) were detected in plasma of mice after oral administration of I3C. ICZ was also tentatively identified in the liver of these mice. This study shows for the first time that, after oral administration to mice, I3C, in addition to its acid condensation products, is absorbed from the gut and distributed systemically into a number of well-perfused tissues, thus allowing the possibility for some pharmacological activity of the parent compound in vivo.

Indole-3-Carbinol (I3C) Inhibits Cyclin-dependent Kinase-2 Function in Human Breast Cancer Cells by Regulating the Size Distribution, Associated Cyclin E Forms, and Subcellular Localization of the CDK2 Protein Complex

Indole-3-carbinol (I3C), a dietary compound found in cruciferous vegetables, induces a robust inhibition of CDK2 specific kinase activity as part of a G1 cell cycle arrest of human breast cancer cells. Treatment with I3C causes a significant shift in the size distribution of the CDK2 protein complex from an enzymatically active 90 kDa complex to a larger 200 kDa complex with significantly reduced kinase activity. Co-immunoprecipitations revealed an increased association of both a 50 kDa cyclin E and a 75 kDa cyclin E immunoreactive protein with the CDK2 protein complex under I3C-treated conditions, whereas the 90 kDa CDK2 protein complexes detected in proliferating control cells contain the lower molecular mass forms of cyclin E. I3C treatment caused no change in the level of CDK2 inhibitors (p21, p27) or in the inhibitory phosphorylation states of CDK2. The effects of I3C are specific for this indole and not a consequence of the cell cycle arrest because treatment of MCF-7 breast cancer cells with either the I3C dimerization product DIM or the anti-estrogen tamoxifen induced a G1 cell cycle arrest with no changes in the associated cyclin E or subcellular localization of the CDK2 protein complex. Taken together, our results have uncovered a unique effect of I3C on cell cycle control in which the inhibition of CDK2 kinase activity is accompanied by selective alterations in cyclin E composition, size distribution, and subcellular localization of the CDK2 protein complex.

Chemopreventive Effect of Indole-3-Carbinol on Induction of Preneoplastic Altered Hepatic Foci

Indole-3-carbinol (I3C) is a cleavage product of glucobrassicanin, a natural compound present in a wide variety of plant food substances including members of the family Cruciferae. I3C is known to possess cancer-chemopreventive potential in various animal models. The present study reveals the protective effect of I3C on the development of diethylnitrosamine (DEN)-initiated and 2-acetylaminofluorene (AAF)-promoted preneoplastic, altered hepatic foci (AHF) in Wistar rats. I3C was given at dose levels of 0.5 and 1 mg/kg body weight for five consecutive days along with DEN and AAF. AHF were scored and analyzed by quantitative stereology using the Image Analysis System from frozen liver sections stained for positive and negative biological markers of AHF, that is, glutathione S-transferase (GST-P), gamma-glutamyl transpeptidase (GGT), glucose-6-phosphatase (G6Pase), adenosine triphosphatase (ATPase), and alkaline phosphatase (AlkPase). Results revealed the chemopreventive effect of I3C on the DEN-initiated AHF in Wistar rats. The expression of G6Pase, ATPase, and AlkPase was restored in the I3C-supplemented animal. Similarly the induced expression GST-P and GGT also decreased in the animals with I3C administration. The recovery of altered levels of these biomarkers was of comparatively higher magnitude in the animals given a higher dose of I3C (1 mg/kg body weight) in comparison with the animals given 0.5 mg/kg body weight dose of I3C, although no dose-dependence pattern was recorded in I3C-supplemented groups. These results thus suggest the chemopreventive effect of I3C in rat hepatocarcinogenesis by suppressing DEN- and AAF-induced AHF development.

Therapeutic activity of 3,3'-diindolylmethane on prostate cancer in an in vivo model

BACKGROUND

Prostate cancer (PC) is the second leading cancer-related death in men in Western countries. Hence, efficient anti-carcinogenic and therapeutic compounds against PC are badly needed. We have previously shown that 3,3'-diindolylmethane (DIM) has a suppressive effect on the growth of human breast and PC cell lines. The objective of this study was examination of the potential therapeutic effects of DIM in an in vivo model.

METHODS

TRAMP-C2, a mouse PC cell line, was injected into the flank of male C57BL/6 mice. When tumors appeared, mice were injected intraperitoneally with either corn oil (vehicle) or DIM (2.5, 5, or 10 mg per kg body weight) 3-times a week, for 3 weeks, and tumor volumes were measured bi-weekly with calibermeters. Later, the tumors were removed, their final weights and volumes were measured, and tumor sections were tested for histological studies.

RESULTS

DIM had a significant inhibitory effect, caused by diminished tumor growth. Histological examination of tumors from treated groups revealed apoptosis and decreased cell proliferation, compared with the controls. DIM didn't affect body weights or kidney and liver functioning.

CONCLUSIONS

The inhibitory action of DIM on tumor growth was demonstrated in vivo. Hence, this compound at the concentrations tested may offer an effective and non toxic therapeutic means against tumor growth in rodents, and may serve as a potential natural anti-carconigenic compound in humans.

Effect of common Brassica vegetables (Brussels sprouts and red cabbage) on the development of preneoplastic lesions induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in liver and colon of Fischer 344 rats

Aim of the present study was the investigation of effects of juices from commonly consumed Brassica vegetables (two cultivars of Brussels sprouts and two cultivars of red cabbage) on formation and development of preneoplastic lesions in colons (aberrant crypt foci, ACF) and livers (glutathione-S-transferase placental form, GST-P+) in male F344 rats. The foci were induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a widespread carcinogenic heterocyclic aromatic amine which is found in fried meats. Recently, we reported on pronounced protective effects in the two-organ foci model when the vegetable juices were given during the carcinogen treatment but several findings by other groups indicated that breakdown products of glucosinolates contained in Brassica vegetables cause tumour promotion in various organs of laboratory rodents. In the present study, the animals received the juices in the drinking water (5%) over a period of 20 days after treatment with IQ (100 mg/kg bw on 10 alternate days). To increase the foci yield (which facilitates the detection of modifying effects), the animals were fed with a modified (high fat, fibre free) AIN-76 diet. With exception of the sprout variety "Cyrus", all juices lowered the number of GST-P+ foci as well as the foci area in the liver, but none of these effects was statistically significant. In the colon, none of the juices had an impact on crypt multiplicity (number of crypts/focus), whereas the number of ACF was decreased; only with the sprout variety Maximus the protective effect was significant (reduction 49%). The present findings show that administration of vegetable juices to the animals after the carcinogen does not increase the number and size of IQ-induced preneoplastic lesions in liver and colon.

Dietary agent indole-3-carbinol protects female rats against the hepatotoxicity of the antitumor drug ET-743 (trabectidin) without compromising efficacy in a rat mammary carcinoma

ET-743, an experimental antitumor drug with promising activity in sarcoma, breast and ovarian carcinoma, is currently under phase 2 clinical evaluation. It is hepatotoxic in animals and patients. We tested the hypothesis that indole-3-carbinol (I3C), the hydrolysis product of glucosinolates occurring in cruciferous vegetables, may protect against ET-743-induced hepatotoxicity in the female Wistar rat, the animal species with the highest sensitivity toward the adverse hepatic effect of this drug. Hepatotoxicity was adjudged by measurement of plasma levels of bilirubin, alkaline phosphatase (ALP) and aspartate aminotransferase (AST) and by liver histopathology. The effect of I3C on the kinetics of ET-743 in rat plasma and liver was investigated by high-pressure liquid chromatography. The effect of I3C on the antitumor efficacy of ET-743 was explored in rats bearing the 13762 mammary carcinoma. ET-743 (40 microg/kg i.v.) alone caused an elevation of plasma bilirubin, ALP and AST levels and degeneration and patchy focal necrosis of bile duct epithelial cells. Addition of I3C to the diet (0.5%) for 6 days prior to ET-743 administration almost completely abolished manifestations of hepatotoxicity. In contrast, a dietary concentration of 0.1% I3C did not protect, nor did dietary diindolylmethane (0.2%), an acid-catalyzed condensation product of I3C. Ingestion by rats of I3C for 6 days prior to ET-743 (40 microg/kg i.v.) decreased plasma but not hepatic concentrations of ET-743 compared to animals that received ET-743 alone. I3C did not interfere with the antitumor efficacy of ET-743. The results suggest that ingestion of I3C may counteract the unwanted effect of ET-743 in the liver. I3C should be investigated as a hepatoprotectant in patients who receive ET-743 therapy.

Indole-3-carbinol induces a G1 cell cycle arrest and inhibits prostate-specific antigen production in human LNCaP prostate carcinoma cells

BACKGROUND

Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables, such as cabbage, broccoli, and Brussels sprouts, is a promising anticancer agent for certain reproductive tumor cells. The objective of the current study was to characterize the cell cycle effects of I3C in human prostate carcinoma cells.

METHODS

The incorporation of [(3)H]thymidine and flow cytometry of propidium iodide-stained nuclei were used to monitor I3C-regulated changes in prostate carcinoma cell proliferation and cell cycle progression. Western blotting was used to document expression changes in cell cycle components and prostate-specific antigen (PSA) levels. The enzymatic activities of cyclin-dependent kinases (CDK) were tested by in vitro protein kinase assays using the retinoblastoma protein as a substrate.

RESULTS

I3C suppressed the growth of LNCaP prostate carcinoma cells in a dose-dependent manner by inducing a G1 block in cell cycle progression. I3C selectively inhibited the expression of CDK6 protein and transcripts and strongly stimulated the production of the p16 CDK inhibitor. In vitro protein kinase assays revealed the striking inhibition by I3C of immunoprecipitated CDK2 enzymatic activity and the relatively minor down-regulation of CDK4 enzymatic activity. In LNCaP prostate carcinoma cells, I3C treatment inhibited production of PSA, whereas combinations of I3C and the androgen antagonist flutamide more effectively inhibited DNA synthesis and PSA levels compared with either agent alone.

CONCLUSIONS

The results of the current study demonstrated that I3C has a potent antiproliferative effect in LNCaP and other human prostate carcinoma cells. These findings implicate this dietary indole as a potential chemotherapeutic agent for controlling the growth of human prostate carcinoma cells.

Antigenotoxic potential of certain dietary constituents

The human diet contains a variety of compounds that exhibit chemopreventive effects towards an array of xenobiotics. In the present study, the antigenotoxic potential of selected dietary constituents including Diallyl sulfide (DAS), Indole-3-carbinol (I3C), Curcumin (CUR), and Black tea polyphenols (BTP) has been evaluated in the Salmonella typhimurium reverse mutation and mammalian in vivo cytogenetic assays. In addition, the anticlastogenic effect of the above dietary constituents was identified towards Benzo(a)pyrene (BaP) and cyclophosphamide- (CP) induced cytogenetic damage in mouse bone marrow cells. The induction of BaP and CP induced chromosomal aberrations, micronuclei formation, and sister chromatid exchanges (SCEs) were found to be inhibited in a dose-dependent manner by DAS, I3C, CUR, and BTP. Thus the study reveals the antimutagenic potential of these dietary compounds towards BaP- and CP-induced genotoxicity in microbial and mammalian test systems.

Indole-3-carbinol and 3-3'-diindolylmethane antiproliferative signaling pathways control cell-cycle gene transcription in human breast cancer cells by regulating promoter-Sp1 transcription factor interactions

Indole-3-carbinol (I3C), a compound that occurs naturally in Brassica vegetables such as cabbage and broccoli, can induce a G1 cell-cycle arrest of human MCF-7 breast cancer cells that is accompanied by the selective inhibition of cyclin-dependent kinase 6 (Cdk6) expression and stimulation of p21(Waf1/Cip1) gene expression. Construction and transfection of a series of promoter-reporter plasmids demonstrate that the indole-regulated changes in Cdk6 and p21(Waf1/Cip1) levels are due to specific effects on their corresponding promoters. Mutagenic analysis reveals that I3C signaling targets a composite transcriptional element in the Cdk6 promoter that requires both Sp1 and Ets transcription factors for transactivation function. Analysis of protein-DNA complexes formed with nuclear proteins isolated from I3C-treated and -untreated cells demonstrates that the Sp1 DNA element in the Cdk6 promoter interacts with an I3C-inhibited protein-protein complex that contains the Sp1 transcription factor. In indole-treated cells, a fraction of [(3)H]I3C was converted into its natural diindole product (3)H-labeled 3-3'-diindolylmethane ([(3)H]DIM), which accumulates in the nucleus; this suggests that DIM may have a role in the transcriptional activities of I3C. Mutagenic analysis of the p21(Waf1/Cip1) promoter reveals that in transfected breast cancer cells, DIM (as well as I3C) stimulates p21(Waf1/Cip1) transcription through an indole-responsive region of the promoter that contains multiple Sp1 consensus sequences. Furthermore, DIM treatment regulates the presence of a nuclear Sp1 DNA-binding activity. Our results demonstrate that both the Cdk6 and p21(Waf1/Cip1) promoters are newly defined downstream targets of the indole-signaling pathway, and that the observed transcriptional effects are due to a combination of the cellular activities of I3C and DIM.

Indole-3-carbinol and 3,3'-diindolylmethane induce apoptosis in human prostate cancer cells

Cruciferous vegetables contain glucobrassicin which, during metabolism, yields indole-3-carbinol (I3C). In a low pH environment I3C is converted into polymeric products, among which 3,3'-diindolylmethane (DIM) is the main one. The apoptotic effects of I3C and DIM were exhibited in human breast cancer cells. The objectives of this study were: (a) examination of the potential effects of I3C and DIM on the proliferation and induction of apoptosis in human prostate cancer cell lines with different p53 status; (b) to try to characterise the mechanism(s) involved in these effects. Our results indicate that both indole derivatives suppress the growth of these cells in a dose- and time-dependent manner, by inducing apoptosis. It appears that these indolic compounds may offer effective means against prostate cancer. Induction of apoptosis was p53-independent. Moreover, the indole derivatives employed did not affect the levels of bcl-2, bax and fasL.

Free radical-scavenging activity of indolic compounds in aqueous and ethanolic media

Indolic compounds are a broad family of substances present in microorganisms, plants and animals. They are mainly related with tryptophan metabolism, and present particularities that depend on their respective chemical structures. The most important members of the family are the plant hormone, indole-3-acetic acid, and the animal hormone, melatonin. An important characteristic of some indolic compounds is that they may be useful as chemical preventive agents against diseases such as cancer, oxidative stress, etc. For this reason, the possible antioxidant activities (free radical-scavenging activity) of several indoles were studied. The2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid /H(2)O(2)/HRP decoloration method was applied to determine both hydrophilic (in buffered media) and lipophilic (in organic media) antioxidant properties of the indolic compounds. Also, a study of the hydrophilic antioxidant activities of indoles at different pH values (between 4.5 and 8.5) was made. Finally, their possible role as diet plant antioxidants is discussed.

Modulation of vinca-alkaloid induced P-glycoprotein expression by indole-3-carbinol

The over-expression of mdr-1 gene transcript P-glycoprotein (P-gp), responsible for multiple drug resistance, is one of the major obstacles in cancer chemotherapy. In the present study, indole-3-carbinol (I3C), a well-known chemopreventive agent present in cruciferous vegetables, has been evaluated for its potential to modulate the over-expression of P-gp induced by vinblastine or vincristine, which are known inducers of mdr-1 gene. The results revealed that I3C significantly reversed the over-expression of P-gp in vinca-alkaloid induced drug resistance as evident by Western blotting using monoclonal antibody (clone JSB1). Quantization of immunostained tissue sections using image analysis technique revealed that vinblastine/ vincristine induced overexpression of P-gp was effectively reversed by I3C. The present investigation suggests that I3C can significantly inhibit the P-gp over-expression and may have utility as a dietary adjuvant in the treatment of cancer for the reversal of multiple drug resistance.

Growth-inhibitory effects of the chemopreventive agent indole-3-carbinol are increased in combination with the polyamine putrescine in the SW480 colon tumour cell line

BACKGROUND

Many tumours undergo disregulation of polyamine homeostasis and upregulation of ornithine decarboxylase (ODC) activity, which can promote carcinogenesis. In animal models of colon carcinogenesis, inhibition of ODC activity by difluoromethylornithine (DFMO) has been shown to reduce the number and size of colon adenomas and carcinomas. Indole-3-carbinol (I3C) has shown promising chemopreventive activity against a range of human tumour cell types, but little is known about the effect of this agent on colon cell lines. Here, we investigated whether inhibition of ODC by I3C could contribute to a chemopreventive effect in colon cell lines.

METHODS

Cell cycle progression and induction of apoptosis were assessed by flow cytometry. Ornithine decarboxylase activity was determined by liberation of CO2 from 14C-labelled substrate, and polyamine levels were measured by HPLC.

RESULTS

I3C inhibited proliferation of the human colon tumour cell lines HT29 and SW480, and of the normal tissue-derived HCEC line, and at higher concentrations induced apoptosis in SW480 cells. The agent also caused a decrease in ODC activity in a dose-dependent manner. While administration of exogenous putrescine reversed the growth-inhibitory effect of DFMO, it did not reverse the growth-inhibition following an I3C treatment, and in the case of the SW480 cell line, the effect was actually enhanced. In this cell line, combination treatment caused a slight increase in the proportion of cells in the G2/M phase of the cell cycle, and increased the proportion of cells undergoing necrosis, but did not predispose cells to apoptosis. Indole-3-carbinol also caused an increase in intracellular spermine levels, which was not modulated by putrescine co-administration.

CONCLUSION

While indole-3-carbinol decreased ornithine decarboxylase activity in the colon cell lines, it appears unlikely that this constitutes a major mechanism by which the agent exerts its antiproliferative effect, although accumulation of spermine may cause cytotoxicity and contribute to cell death. The precise mechanism by which putrescine enhances the growth inhibitory effect of the agent remains to be elucidated, but does result in cells undergoing necrosis, possibly following accumulation in the G2/M phase of the cell cycle.

Dietary factors in the prevention and treatment of nonmelanoma skin cancer and melanoma

BACKGROUND

The endogenous antioxidant system of the skin scavenges reactive oxygen species and combats ultraviolet induced oxidative skin damage. Supporting this cutaneous defense system with topical or oral antioxidants may provide a successful strategy for the treatment and prevention of skin cancer.

OBJECTIVE

Review evidence regarding treatment and prevention of melanoma and nonmelanoma skin cancers through dietary and topical antioxidants, vitamins, and herbal supplements.

METHODS

Literature review.

RESULTS

Review of the literature demonstrates that the administration of synthetic retinoids has not proved beneficial for otherwise healthy patients with nonmelanoma skin cancer. Selenium supplementation has reduced the incidence of several internal malignancies but not of nonmelanoma skin cancer. Synergistic use of beta-carotene with vitamins C and E has demonstrated prophylaxis against reactive oxygen radicals involved in nonmelanoma skin cancer and reduced sunburn reactions significantly. 1,25-dihydroxyvitamin D3 analog CB1093 has demonstrated promise as a therapeutic agent in the regression of the early stages of melanoma in specific cell lines.

CONCLUSION

Delivery of exogenous antioxidants in combination appears to be a more successful strategy for enhancing the cutaneous antioxidant system than the administration of isolated antioxidants alone. Vitamin D analogs may have a role in the medical therapy of melanoma. However, avoiding exposure to ultraviolet light appears to be the only true panacea against the development of melanoma and NMSC.

Bcl-2 family-mediated apoptotic effects of 3,3'-diindolylmethane (DIM) in human breast cancer cells

3,3'-Diindolylmethane (DIM) is a major in vivo derivative of the putative anticancer agent indole-3-carbinol (I3C), which is present in vegetables of the Brassica genus. At concentrations above 10 microM, DIM inhibited DNA synthesis and cell proliferation in both estrogen receptor replete (MCF-7) and deficient (MDA-MB-231) human breast cancer cells in a concentration- and time-dependent manner. These antiproliferative effects were accompanied by characteristic indications of programmed cell death in both cell lines, including externalization of phosphatidylserine, chromatin condensation, and DNA fragmentation. Furthermore, Western and Northern blot analyses, as well as coimmunoprecipitation assays, revealed that in both MCF-7 and MDA-MB-231 cells, DIM treatment decreased total transcript and protein levels of the apoptosis inhibitory protein Bcl-2, and the amount of Bcl-2 bound to the pro-apoptotic protein Bax. DIM treatment also caused an increase in Bax protein levels, but did not affect the level of Bax that was bound to Bcl-2. As a functional test of the role of Bcl-2 down-regulation in the DIM-induced apoptotic response, ectopic expression of Bcl-2 in MCF-7 cells was shown to attenuate the apoptotic effect of DIM. These results demonstrate that DIM can induce apoptosis in breast cancer cells independent of estrogen receptor status by a process that is mediated by the modulated expression of the Bax/Bcl-2 family of apoptotic regulatory factors.

Development of a multi-organ rat model for evaluating chemopreventive agents: efficacy of indole-3-carbinol

Indole-3-carbinol (I-3-C) is among the most widely and popularly known antiestrogens. Due to its putative chemopreventive action, I-3-C is being marketed to the general public in health food establishments. Although it has been demonstrated to prevent cancer in animal bioassays, I-3-C also acts as a promoter in the liver and colon. Because of this potential dual biological activity, it is important to investigate both the inhibitory and promotional activities of I-3-C in multi-organ tumorigenesis animal models. 7,12-Dimethylbenz[a]anthracene, aflatoxin B1 and azoxymethane were used to initiate mammary, liver and colon carcinogenesis, respectively in female Sprague-Dawley rats. The rats were fed continuously on a diet containing I-3-C for 25 weeks after initiation. I-3-C treatment was begun one week after the last carcinogen treatment had been administered. I-3-C treatment resulted in a delay in latency of mammary tumor formation, but did not alter tumor incidence or multiplicity among survivors. In the colon, the protocol produced a 40% decrease in aberrant colon crypt foci. However, in the liver, it strongly-induced GST-P foci in carcinogen-treated (a four-fold increase in volume percent foci) and in the vehicle controls (a 69-fold increase). These data support previous findings in other rodent and fish tumor models that I-3-C both inhibits and promotes carcinogenesis. The results of this study clearly demonstrate that I-3-C is not an appropriate chemoprotective agent for human use, in spite of its effects in the breast and colon in this rat animal model.

Indole-3-carbinol inhibits CDK6 expression in human MCF-7 breast cancer cells by disrupting Sp1 transcription factor interactions with a composite element in the CDK6 gene promoter

Indole-3-carbinol (I3C), a compound naturally occurring in Brassica vegetables, can induce a G(1) cell cycle arrest of human MCF-7 breast cancer cells that is accompanied by the selective inhibition of cyclin-dependent kinase 6 (CDK6) expression. Reverse transcriptase-polymerase chain reaction analysis of CDK6 mRNA decay rates revealed that I3C had no effect on CDK6 transcript stability. We report the first identification and functional characterization of the CDK6 promoter in order to determine whether I3C inhibits CDK6 transcription. In MCF-7 cells stably transfected with CDK6 promoter-linked luciferase reporter plasmids, I3C inhibited CDK6 promoter activity in an I3C-specific response that was not a consequence of the growth-arrested state of the cells. Deletion analysis revealed a 167-base pair I3C-responsive region of the CDK6 promoter between -805 and -638. Site-specific mutations within this region revealed that both Sp1 and Ets-like sites, which are spaced 5 base pairs apart, were necessary for I3C responsiveness in the context of the CDK6 promoter. Electrophoretic mobility shift analysis of protein-DNA complexes formed with nuclear proteins isolated from I3C-treated and -untreated cells, in combination with supershift assays using Sp1 antibodies, demonstrated that the Sp1-binding site in the CDK6 promoter forms a specific I3C-responsive DNA-protein complex that contains the Sp1 transcription factor. Taken together, our results suggest that I3C down-regulates CDK6 transcription by targeting Sp1 at a composite DNA site in the CDK6 promoter.

The micronutrient indole-3-carbinol: implications for disease and chemoprevention

This review provides a historical perspective for the development of indole-3-carbinol (I-3-C) as a chemopreventive or therapeutic agent. Early experiments in animal models clearly showed that feeding cruciferous vegetables reduced the incidence of chemical carcinogenesis. Excitement was generated by the finding that these vegetables contained a high content of indole-containing compounds, and I-3-C could by itself inhibit neoplasia. The mechanism of action was linked primarily to the ability of I-3-C and derived substances to induce mixed-function oxidases and phase II antioxidant enzymes by binding and activating the aryl hydrocarbon receptor. Most of the literature on chemoprotection by dietary indole compounds relates to this mechanism of action. Other mechanisms, however, are notable for this class of compounds, including their ability to act as radical and electrophile scavengers; the various ascorbate conjugates of I-3-C (ascorbigens) may be important in this regard. Exciting recent findings have demonstrated that I-3-C and its reaction products can affect cellular signaling pathways, regulate the cell cycle, and decrease tumor cell properties related to metastasis. It does not appear that I-3-C per se is the primary active compound in chemoprotection or chemoprevention. Rather, I-3-C and ascorbate provide the parent compounds for the formation of a myriad of nonenzymatic reaction products that have strong biological potency. We conclude with our thoughts regarding the current status and future directions for the use of I-3-C and related compounds.

3,3'-diindolylmethane, a major condensation product of indole-3-carbinol, is a potent estrogen in the rainbow trout

Indole-3-carbinol (I3C), a compound found in Brassica vegetables has been widely studied for its chemopreventive properties. I3C has been shown to block tumor initiation and promotion; however, it also acts as a tumor promoter. I3C and some of its acid condensation products, particularly 3,3'-diindolylmethane (I33'), have exhibited antiestrogenic properties. We report that I33' acts as an estrogen in the rainbow trout liver in vitro and in vivo by inducing vitellogenin (Vg), a well-characterized biomarker for estrogens. Precision-cut liver slices from male rainbow trout, Oncorhynchus mykiss, were incubated at 14 degrees C for 96 h in media containing I3C, I33', or a mixture of I3C acid condensation products (RXN) (0-250 microM). I33' and RXN increased Vg levels in rainbow trout liver slices by over 300- and 20-fold, respectively, vs vehicle. The efficacy of I33' induction of Vg was comparable to 17 beta-estradiol (E(2)) with 2500-fold less potency. I33' and E(2) cotreatment resulted in additive Vg induction. Tamoxifen completely inhibited I33'-induced Vg induction, suggesting that Vg induction by I33' is entirely through the estrogen receptor. In vivo, juvenile male rainbow trout were fed I3C, RXN (0-2000 mg/kg), or I33' (0-250 mg/kg) for 2 weeks. At 2000 mg/kg, I3C induced Vg by over 100,000-fold compared to controls, which was comparable to 5 mg/kg 17 beta-estradiol (the dose resulting in maximum induction). I33' was five times as potent as I3C with equal efficacy. The potency of RXN was only 5% of I3C. Again, I33' and E(2) cotreatment resulted in additive Vg induction. I33' may have accounted for Vg increases observed in trout fed I3C as it is present in liver after oral dosing at concentrations (70 microM) expected to maximally induce Vg. In trout, results in vitro and in vivo document that I33' is estrogenic, consistent with our hypothesis that I3C promotes liver cancer in trout by estrogenic pathways.