Targets for indole-3-carbinol in cancer prevention

Water extracts of cabbage and kale inhibit ex vivo H(2)O(2)-induced DNA damage but not rat hepatocarcinogenesis

The chemopreventive potential of water extracts of the Brassica vegetables cabbage and kale was evaluated by administering their aqueous extracts in drinking water ad libitum to Wistar rats submitted to Ito's hepatocarcinogenesis model (CB group and K group, respectively - 14 rats per group). Animals submitted to this same model and treated with water were used as controls (W group - 15 rats). Treatment with the vegetable extracts did not inhibit (P > 0.05) placental glutathione S-transferase-positive preneoplastic lesions (PNL). The number of apoptotic bodies did not differ (P > 0.05) among the experimental groups. Ex vivo hydrogen peroxide treatment of rat livers resulted in lower (P < 0.05) DNA strand breakage in cabbage- (107.6 +/- 7.8 microm) and kale- (110.8 +/- 10.0 microm) treated animals compared with control (120.9 +/- 12.7 microm), as evaluated by the single cell gel (comet) assay. Treatment with cabbage (2 +/- 0.3 microg/g) or kale (4 +/- 0.2 microg/g) resulted in increased (P < 0.05) hepatic lutein concentration compared with control (0.5 +/- 0.07 microg/g). Despite the absence of inhibitory effects of cabbage and kale aqueous extracts on PNL, these Brassica vegetables presented protection against DNA damage, an effect possibly related to increased hepatic lutein concentrations. However, it must be pointed out that the cause-effect relationship between lutein levels and protection is hypothetical and remains to be demonstrated.

{2-[1-(3-Methoxycarbonylmethyl-1H-indol-2-yl)-1-methyl-ethyl]-1H-indol-3-yl}-acetic acid methyl ester (MIAM): its anti-cancer efficacy and intercalation mechanism identified via multi-model systems

{2-[1-(3-Methoxycarbonylmethyl-1H-indol-2-yl)-1-methyl-ethyl]-1H-indol-3-yl}-acetic acid methyl ester (MIAM) was provided as a DNA-intercalator. For the comprehensive evaluation of this new intercalator, an assay system consisting of cell, S180 mouse, healthy mouse, spectrum, non-spectrum, and gel electrophoresis models was constructed. On the cell (S180, K562, MCF-7, HeLa and HepG2) models, MIAM selectively inhibited the viability of HeLa. On the S180 mouse model, 0.89, 8.9, 89 and 890 μmol kg(-1) of MIAM dose-dependently inhibited the tumor growth. Even at a dose of 890 μmol kg(-1), MIAM did not damage the treated S180 mice. The safety of MIAM was supported by a high spleen index and an obvious increase of body weight of the treated S180 mice. On the healthy mouse model the LD(50) value of MIAM is higher than 890 μmol kg(-1). The ultraviolet (UV), fluorescence, circular dichroism (CD), relative viscosity, melting curve, and gel electrophoresis assays of DNA with or without MIAM consistently supported an intercalation mechanism for MIAM.

Effect of 4-methoxyindole-3-carbinol on the proliferation of colon cancer cells in vitro, when treated alone or in combination with indole-3-carbinol

Consumption of cruciferous vegetables and cancer prevention seem to be positively associated. We present an easy two-step synthesis for 4-methoxyindole-3-carbinol (4MeOI3C), the expected breakdown product of 4-methoxyglucobrassicin during ingestion. 4MeOI3C inhibited the proliferation of human colon cancer cells DLD-1 and HCT 116 with IC(50) values of 116 microM and 96 microM, respectively, after 48 h in vitro, and is therefore a more potent inhibitor than indole-3-carbinol (I3C). 4MeOI3C and I3C combined in different molar ratios inhibited proliferation in a nearly additive to slightly synergistic manner. Proliferation was inhibited by 100 microM 4MeOI3C after 48 h without affecting cell cycle phase distribution, indicating an overall-slowdown effect on the cell cycle. However, 200 microM 4MeOI3C caused a very high level of cell death and an accumulation of living cells in the G(0)/G(1) phase, indicating a concentration-dependent mode of action. We conclude that 4MeOI3C might play a role in the cancer preventive effect of cruciferous vegetables.

Direct inhibition of elastase activity by indole-3-carbinol triggers a CD40-TRAF regulatory cascade that disrupts NF-kappaB transcriptional activity in human breast cancer cells

Treatment of highly tumorigenic MDA-MB-231 human breast cancer cells with indole-3-carbinol (I3C) directly inhibited the extracellular elastase-dependent cleavage of membrane-associated CD40, a member of the tumor necrosis factor (TNF) receptor superfamily. CD40 signaling has been implicated in regulating cell survival, apoptosis, and proliferation, as well as in sensitizing breast cancer cells to chemotherapy, and is therefore an important potential target of novel breast cancer treatments. The I3C-dependent accumulation of full-length unprocessed CD40 protein caused a shift in CD40 signaling through TNF receptor-associated factors (TRAF), including the TRAF1/TRAF2 positive regulators and TRAF3 negative regulator of NF-kappaB transcription factor activity. Because TRAF1 is a transcriptional target gene of NF-kappaB, I3C disrupted a positive feedback loop involving these critical cell survival components. siRNA ablation of elastase expression mimicked the I3C inhibition of CD40 protein processing and G(1) cell cycle arrest, whereas siRNA knockdown of TRAF3 and the NF-kappaB inhibitor IkappaB prevented the I3C-induced cell cycle arrest. In contrast, siRNA knockdown of PTEN had no effect on the I3C control of NF-kappaB activity, showing the importance of CD40 signaling in regulating this transcription factor. Our study provides the first direct in vitro evidence that I3C directly inhibits the elastase-mediated proteolytic processing of CD40, which alters downstream signaling to disrupt NF-kappaB-induced cell survival and proliferative responses. Furthermore, we have established a new I3C-mediated antiproliferative cascade that has significant therapeutic potential for treatment of human cancers associated with high levels of elastase and its CD40 membrane substrate.

1-Benzyl-indole-3-carbinol is a novel indole-3-carbinol derivative with significantly enhanced potency of anti-proliferative and anti-estrogenic properties in human breast cancer cells

Indole-3-carbinol (I3C), a natural autolysis product of a gluccosinolate present in Brassica vegetables such as broccoli and cabbage, has anti-proliferative and anti-estrogenic activities in human breast cancer cells. A new and significantly more potent I3C analogue, 1-benzyl-I3C was synthesized, and in comparison to I3C, this novel derivative displayed an approximate 1000-fold enhanced potency in suppressing the growth of both estrogen responsive (MCF-7) and estrogen-independent (MDA-MB-231) human breast cancer cells (I3C IC(50) of 52 microM, and 1-benzyl-I3C IC(50) of 0.05 microM). At significantly lower concentrations, 1-benzyl-I3C induced a robust G1 cell cycle arrest and elicited the key I3C-specific effects on expression and activity of G1-acting cell cycle genes including the disruption of endogenous interactions of the Sp1 transcription factor with the CDK6 promoter. Furthermore, in estrogen responsive MCF-7 cells, with enhanced potency 1-benzyl-I3C down-regulated production of estrogen receptor-alpha protein, acts with tamoxifen to arrest breast cancer cell growth more effectively than either compound alone, and inhibited the in vivo growth of human breast cancer cell-derived tumor xenografts in athymic mice. Our results implicate 1-benzyl-I3C as a novel, potent inhibitor of human breast cancer proliferation and estrogen responsiveness that could potentially be developed into a promising therapeutic agent for the treatment of indole-sensitive cancers.

Indole-3-carbinol triggers aryl hydrocarbon receptor-dependent estrogen receptor (ER)alpha protein degradation in breast cancer cells disrupting an ERalpha-GATA3 transcriptional cross-regulatory loop

We have established in human breast cancer cells that indole-3-carbinol (I3C), a promising anti-cancer phytochemical from Brassica vegetables, ablates ERα expression by stimulating the Rbx-1 E3 ligase mediated degradation of ERα protein and disruption of a cross-regulatory positive feedback loop involving ERα and the GATA3 transcription factor.

Estrogen receptor (ER)α is a critical target of therapeutic strategies to control the proliferation of hormone-dependent breast cancers. Preferred clinical options have significant adverse side effects that can lead to treatment resistance due to the persistence of active estrogen receptors. We have established the cellular mechanism by which indole-3-carbinol (I3C), a promising anticancer phytochemical from Brassica vegetables, ablates ERα expression, and we have uncovered a critical role for the GATA3 transcription factor in this indole-regulated cascade. I3C-dependent activation of the aryl hydrocarbon receptor (AhR) initiates Rbx-1 E3 ligase-mediated ubiquitination and proteasomal degradation of ERα protein. I3C inhibits endogenous binding of ERα with the 3′-enhancer region of GATA3 and disrupts endogenous GATA3 interactions with the ERα promoter, leading to a loss of GATA3 and ERα expression. Ectopic expression of GATA3 has no effect on I3C-induced ERα protein degradation but does prevent I3C inhibition of ERα promoter activity, demonstrating the importance of GATA3 in this I3C-triggered cascade. Our preclinical results implicate I3C as a novel anticancer agent in human cancers that coexpress ERα, GATA3, and AhR, a combination found in a large percentage of breast cancers but not in other critical ERα target tissues essential to patient health.

Inhibitory effects of andrographolide on migration and invasion in human non-small cell lung cancer A549 cells via down-regulation of PI3K/Akt signaling pathway

Lung cancer is the leading cause of death among cancers worldwide and non-small cell lung cancer (NSCLC) comprises more than 80% of lung cancer cases. Treatment options for patients with advanced NSCLC have evolved in the last decade with the advent of novel biological agents. Andrographolide, a diterpenoid lactone isolated from a traditional herbal medicine Andrographis paniculata, is known to have the potential to be developed as a chemotherapeutic agent. In order to understand the anti-cancer properties of andrographolide, we examined its effect on migration and invasion in human NSCLC A549 cells. The results of wound-healing assay and in vitro transwell assay revealed that andrographolide inhibited dose-dependently the migration and invasion of A549 cells under non-cytotoxic concentrations. Molecular data showed that the effect of andrographolide in A549 cells might be mediated via sustained inactivation of phosphatidylinositol 3-kinase (PI3K)/Akt signal involved in the up-regulation of matrix metalloproteinases (MMPs). Our results showed that andrographolide exerted an inhibitory effect on the activity and the mRNA and protein levels of MMP-7, but not MMP-2 or MMP-9. The andrographolide-inhibited MMP-7 expression or activity appeared to occur via activator protein-1 (AP-1) because of its DNA binding activity was suppressed by andrographolide. Additionally, the transfection of Akt over-expression vector (Akt1 cDNA) to A549 cells could result in an increase expression of MMP-7 concomitantly with a marked induction on cell invasion. These findings suggested that the inhibition on MMP-7 expression by andrographolide may be through suppression on PI3K/Akt/AP-1 signaling pathway, which in turn led to the reduced invasiveness of the cancer cells.

Minireview: modulation of hormone receptor signaling by dietary anticancer indoles

Indole-3-carbinol and its diindole condensation product 3-3'-diindolylmethane are dietary phytochemicals that have striking anticarcinogenic properties in human cancer cells. Molecular, cellular, physiological, and clinical studies have documented that both indole-3-carbinol and 3-3'-diindolylmethane have potent endocrine modulating activities through a myriad of mechanisms. The focus of this review is to discuss the evidence that directly links the anticancer actions of these two indole compounds to the control of steroid receptor and growth factor receptor signaling.

Dietary chemopreventive phytochemicals: too little or too much?

There is a large body of evidence that the consumption of fruit and vegetables can decrease the risk of cancer. However, the link between diet and health is extremely complex. Some dietary phytochemicals seem to offer protection in an exposure-related manner and many molecular targets and signaling pathways affected by phytochemicals have been discovered. Although in vitro studies have contributed significantly to our understanding, quite a number use concentrations orders of magnitude greater than those achievable in humans or toxic to normal tissues (exemplified by toxic concentrations of indole-3-carbinol, epigallocatechin-3-gallate, curcumin, and genistein for breast cells). Such studies may produce results that are physiologically irrelevant, thus hindering predictions of efficacy. Here, we argue for careful consideration to be given to the in vitro experimental conditions under which dietary phytochemicals are investigated. Design features, such as the use of appropriate nontoxic concentrations, extended treatment times, three-dimensional cultures, primary tumor cultures, and comparison of susceptibility of various cancer subtypes, should improve our understanding of their molecular targets. This in turn would facilitate predictions as to their potential usefulness in the clinic.

OSU-A9, a potent indole-3-carbinol derivative, suppresses breast tumor growth by targeting the Akt-NF-kappaB pathway and stress response signaling

The molecular heterogeneity of human tumors challenges the development of effective preventive and therapeutic strategies. To overcome this issue, a rational approach is the concomitant targeting of clinically relevant cellular abnormalities with combination therapy or a potent multi-targeted agent. OSU-A9 is a novel indole-3-carbinol derivative that retains the parent compound's ability to perturb multiple components of oncogenic signaling, but provides marked advantages in chemical stability and antitumor potency. Here, we show that OSU-A9 exhibits two orders of magnitude greater potency than indole-3-carbinol in inducing apoptosis in various breast cancer cell lines with distinct genetic abnormalities, including MCF-7, MDA-MB-231 and SKBR3, with the half maximal inhibitory concentration in the range of 1.2-1.8 microM vis-à-vis 200 microM for indole-3-carbinol. This differential potency was paralleled by OSU-A9's superior activity against multiple components of the Akt-nuclear factor-kappa B (NF-kappaB) and stress response signaling pathways. Notable among these were the increased estrogen receptor (ER)-beta/ERalpha expression ratio, reduced expression of HER2 and CXCR4 and the upregulation of aryl hydrocarbon receptor expression and its downstream target NF-E2 p45-regulated factor (Nrf2). Non-malignant MCF-10A cells were resistant to OSU-A9's antiproliferative effects. Daily oral administration of OSU-A9 at 25 and 50 mg/kg for 49 days significantly inhibited MCF-7 tumor growth by 59 and 70%, respectively, without overt signs of toxicity or evidence of induced hepatic biotransformation enzymes. In summary, OSU-A9 is a potent, orally bioavailable inhibitor of the Akt-NF-kappaB signaling network, targeting multiple aspects of breast tumor pathogenesis and progression. Thus, its translational potential for the treatment or prevention of breast cancer warrants further investigation.

Aryl hydrocarbon receptor suppresses intestinal carcinogenesis in ApcMin/+ mice with natural ligands

Intestinal cancer is one of the most common human cancers. Aberrant activation of the canonical Wnt signaling cascade, for example, caused by adenomatous polyposis coli (APC) gene mutations, leads to increased stabilization and accumulation of beta-catenin, resulting in initiation of intestinal carcinogenesis. The aryl hydrocarbon receptor (AhR) has dual roles in regulating intracellular protein levels both as a ligand-activated transcription factor and as a ligand-dependent E3 ubiquitin ligase. Here, we show that the AhR E3 ubiquitin ligase has a role in suppression of intestinal carcinogenesis by a previously undescribed ligand-dependent beta-catenin degradation pathway that is independent of and parallel to the APC system. This function of AhR is activated by both xenobiotics and natural AhR ligands, such as indole derivatives that are converted from dietary tryptophan and glucosinolates by intestinal microbes, and suppresses intestinal tumor development in Apc(Min/+) mice. These findings suggest that chemoprevention with naturally-occurring and chemically-designed AhR ligands can be used to successfully prevent intestinal cancers.

Aryl hydrocarbon receptor suppresses intestinal carcinogenesis in ApcMin/+ mice with natural ligands

Intestinal cancer is one of the most common human cancers. Aberrant activation of the canonical Wnt signaling cascade, for example, caused by adenomatous polyposis coli (APC) gene mutations, leads to increased stabilization and accumulation of beta-catenin, resulting in initiation of intestinal carcinogenesis. The aryl hydrocarbon receptor (AhR) has dual roles in regulating intracellular protein levels both as a ligand-activated transcription factor and as a ligand-dependent E3 ubiquitin ligase. Here, we show that the AhR E3 ubiquitin ligase has a role in suppression of intestinal carcinogenesis by a previously undescribed ligand-dependent beta-catenin degradation pathway that is independent of and parallel to the APC system. This function of AhR is activated by both xenobiotics and natural AhR ligands, such as indole derivatives that are converted from dietary tryptophan and glucosinolates by intestinal microbes, and suppresses intestinal tumor development in Apc(Min/+) mice. These findings suggest that chemoprevention with naturally-occurring and chemically-designed AhR ligands can be used to successfully prevent intestinal cancers.

Indole-3-carbinol inhibits MDA-MB-231 breast cancer cell motility and induces stress fibers and focal adhesion formation by activation of Rho kinase activity

Indole-3-carbinol (I3C), a phytochemical derived from cruciferous vegetables such as broccoli and Brussels sprouts, has potent antiproliferative effects in human breast cancer cells and has been shown to decrease metastatic spread of tumors in experimental animals. Using chemotaxis and fluorescent-bead cell motility assays, we demonstrated that I3C significantly decreased the in vitro migration of MDA-MB-231 cells, a highly invasive breast cancer cell line. Immunofluorescence staining of the actin cytoskeleton revealed that concurrent with the loss of cell motility, I3C treatment significantly increased stress fiber formation. Furthermore, I3C induced the localization of the focal adhesion component vinculin and tyrosine-phosphorylated proteins to the cell periphery, which implicates an indole-dependent enhancement of focal adhesions within the outer boundary of the cells. Coimmunoprecipitation analysis of focal adhesion kinase demonstrated that I3C stimulated the dynamic formation of the focal adhesion protein complex without altering the total level of individual focal adhesion proteins. The RhoA-Rho kinase pathway is involved in stress fiber and focal adhesion formation, and I3C treatment stimulated Rho kinase enzymatic activity and cofilin phosphorylation, which is a downstream target of Rho kinase signaling, but did not increase the level of active GTP-bound RhoA. Exposure of MDA-MB-231 cells to the Rho kinase inhibitor Y-27632, or expression of dominant negative RhoA ablated the I3C induced formation of stress fibers and of peripheral focal adhesions. Expression of constitutively active RhoA mimicked the I3C effects on both processes. Taken together, our data demonstrate that I3C induces stress fibers and peripheral focal adhesions in a Rho kinase-dependent manner that leads to an inhibition of motility in human breast cancer cells.

Andrographolide could inhibit human colorectal carcinoma Lovo cells migration and invasion via down-regulation of MMP-7 expression

Andrographolide (Andro), a diterpenoid lactone isolated from a traditional herbal medicine Andrographis paniculata, is known to possess multiple pharmacological activities. In our previous study, Andro had been shown to have potent anti-cancer activity against human colorectal carcinoma Lovo cells by inhibiting cell-cycle progression. To further investigate the mechanism for the anti-cancer properties of Andro, it was used to examine the effect on migration and invasion of Lovo cells. The results of wound-healing assay and in vitro transwell assay revealed that Andro inhibited dose-dependently the migration and invasion of Lovo cells under non-cytotoxic concentrations. Using zymographic assay and RT-PCR, the results revealed that Andro diminished the activity and the mRNA and protein levels of MMP-7, but not MMP-2 or MMP-9. The down-regulation of MMP-7 appeared to be via the inactivation of activator protein-1 (AP-1) since the treatment with Andro suppressed the nuclear protein level of AP-1, which was accompanied by a decrease in DNA-binding level of the factor. Taken together, these results indicated that Andro reduces the MMP-7-mediated cellular events in Lovo cells, and provided a new mechanism for its anti-cancer activity.

Anti-adult T-cell leukemia/lymphoma effects of indole-3-carbinol

Background

Adult T-cell leukemia/lymphoma (ATLL) is a malignancy derived from T cells infected with human T-cell leukemia virus type 1 (HTLV-1), and it is known to be resistant to standard anticancer therapies. Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables such as cabbage, broccoli and Brussels sprout, is a promising chemopreventive agent as it is reported to possess antimutagenic, antitumorigenic and antiestrogenic properties in experimental studies. The aim of this study was to determine the potential anti-ATLL effects of I3C both in vitro and in vivo.

Results

In the in vitro study, I3C inhibited cell viability of HTLV-1-infected T-cell lines and ATLL cells in a dose-dependent manner. Importantly, I3C did not exert any inhibitory effect on uninfected T-cell lines and normal peripheral blood mononuclear cells. I3C prevented the G₁/S transition by reducing the expression of cyclin D1, cyclin D2, Cdk4 and Cdk6, and induced apoptosis by reducing the expression of XIAP, survivin and Bcl-2, and by upregulating the expression of Bak. The induced apoptosis was associated with activation of caspase-3, -8 and -9, and poly(ADP-ribose) polymerase cleavage. I3C also suppressed IκBα phosphorylation and JunD expression, resulting in inactivation of NF-κB and AP-1. Inoculation of HTLV-1-infected T cells in mice with severe combined immunodeficiency resulted in tumor growth. The latter was inhibited by treatment with I3C (50 mg/kg/day orally), but not the vehicle control.

Conclusion

Our preclinical data suggest that I3C could be potentially a useful chemotherapeutic agent for patients with ATLL.

Indole-3-carbinol inhibits Sp1-induced matrix metalloproteinase-2 expression to attenuate migration and invasion of breast cancer cells

Indole-3-carbinol (I3C), a major indole metabolite in cruciferous vegetables, has been shown to inhibit invasion of breast cancer cells. This study addressed the effect of I3C on the expression of matrix metalloproteinases (MMPs) and clarified the underlying mechanism. Migration, invasion, and MMP-2 activity of MCF-7 breast cancer cells were dose-dependently inhibited by I3C. In addition, the MMP-2 mRNA level was also reduced by I3C. Promoter deletion and mutation analysis suggested that I3C inhibited MMP-2 gene transcription via the -85/-7 bp promoter region and the Sp1 transcription factor binding site located within the -72/-64 bp promoter region was important for the inhibition. Chromatin immunoprecipitation assay confirmed that Sp1 proteins constitutively bound to this consensus sequence in vivo and that the binding was attenuated by I3C. In addition, I3C inhibited the extracellular signal-regulated kinase (ERK) signaling pathway in MCF-7 cells. The results suggest that I3C inhibits MMP-2 expression by blocking the ERK/Sp1-mediated gene transcription to attenuate migration and invasion of breast cancer cells.

High-throughput screening for analysis of in vitro toxicity

The influence of combinatorial chemistry and high-throughput screening (HTS) technologies in the pharmaceutical industry during the last 10 years has been enormous. However, the attrition rate of drugs in the clinic due to toxicity during this period still remained 40-50%. The need for reduced toxicity failure led to the development of early toxicity screening assays. This chapter describes the state of the art for assays in the area of genotoxicity, cytotoxicity, carcinogenicity, induction of specific enzymes from phase I and II metabolism, competition assays for enzymes of phase I and II metabolism, embryotoxicity as well as endocrine disruption and reprotoxicity. With respect to genotoxicity, the full Ames, Ames II, Vitotox, GreenScreen GC, RadarScreen, and non-genotoxic carcinogenicity assays are discussed. For cytotoxicity, cellular proliferation, calcein uptake, oxygen consumption, mitochondrial activity, radical formation, glutathione depletion as well as apoptosis are described. For high-content screening (HCS), the possibilities for analysis of cytotoxicity, micronuclei, centrosome formation and phospholipidosis are examined. For embryotoxicity, endocrine disruption and reprotoxicity alternative assays are reviewed for fast track analysis by means of nuclear receptors and membrane receptors. Moreover, solutions for analyzing enzyme induction by activation of nuclear receptors, like AhR, CAR, PXR, PPAR, FXR, LXR, TR and RAR are given.

The dietary phytochemical indole-3-carbinol is a natural elastase enzymatic inhibitor that disrupts cyclin E protein processing

Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables, such as broccoli, cabbage, and Brussels sprouts, induces a G(1) cell-cycle arrest of human breast cancer cells, although the direct cellular targets that mediate this process are unknown. Treatment of highly invasive MDA-MB-231 breast cancer cells with I3C shifted the stable accumulation of cyclin E protein from the hyperactive lower-molecular-mass 35-kDa form that is associated with cancer cell proliferation and poor clinical outcomes to the 50-kDa cyclin E form that typically is expressed in normal mammary tissue. An in vitro cyclin E processing assay, in combination with zymography, demonstrated that I3C, but not its natural dimer, 3,3'-diindolylmethane, disrupts proteolytic processing of the 50-kDa cyclin E into the lower-molecular-mass forms by direct inhibition of human neutrophil elastase enzymatic activity. Analysis of elastase enzyme kinetics using either cyclin E or N-methoxysuccinyl-Ala-Ala-Pro-Val-p-nitroanalide as substrates demonstrated that I3C acts as a noncompetitive inhibitor of elastase activity with an inhibitory constant of approximately 12 microM. Finally, siRNA ablation of neutrophil elastase protein production in MDA-MB-231 cells mimicked the I3C-disrupted processing of the 50-kDa cyclin E protein and the indole-induced cell-cycle arrest. Taken together, our results demonstrate that elastase is the first identified specific target protein for I3C and that the direct I3C inhibition of elastase enzymatic activity implicates the potential use of this indole, or related compounds, in targeted therapies of human breast cancers where high elastase levels are correlated with poor prognosis.

Potential role of tryptophan derivatives in stress responses characterized by the generation of reactive oxygen and nitrogen species

To face physicochemical and biological stresses, living organisms evolved endogenous chemical responses based on gas exchange with the atmosphere and on formation of nitric oxide (NO(*)) and oxygen derivatives. The combination of these species generates a complex network of variable extension in space and time, characterized by the nature and level of the reactive oxygen (ROS) and nitrogen species (RNS) and of their organic and inorganic scavengers. Among the latter, this review focusses on natural 3-substituted indolic structures. Tryptophan-derived indoles are unsensitive to NO(*), oxygen and superoxide anion (O(2)(*-)), but react directly with other ROS/RNS giving various derivatives, most of which have been characterized. Though the detection of some products like kynurenine and nitroderivatives can be performed in vitro and in vivo, it is more difficult for others, e.g., 1-nitroso-indolic compounds. In vitro chemical studies only reveal the strong likelihood of their in vivo generation and biological effects can be a sign of their transient formation. Knowing that 1-nitrosoindoles are NO donors and nitrosating agents indicating they can thus act both as mutagens and protectors, the necessity for a thorough evaluation of indole-containing drugs in accordance with the level of the oxidative stress in a given pathology is highlighted.

Synergistic action of dietary phyto-antioxidants on survival and proliferation of ovarian cancer cells

OBJECTIVES

A number of herbal dietary antioxidant supplements containing Indole-3 Carbinol (I3C) and Resveratrol (RE) have been established as anti-proliferative agents in cancer. These compounds have both similar as well as unique molecular targeting profiles. The purpose of this study is to analyze their mechanism of action when used individually and in combination in ovarian cancer.

METHODS

SK-OV-3 ovarian cancer cells were treated with various doses of I3C, RE or I3C+RE. AlamarBlue dye assay was used to examine cell growth and proliferation. Cell cycle and apoptosis were analyzed by flow cytometry. Western blot was performed to determine the expression of the genes associated with cell cycle and apoptosis. CA-125, a functional marker of ovarian cancer, and nitric oxide, were analyzed by ELISA.

RESULTS

I3C or RE inhibited cell proliferation, and caused cell contraction and apoptosis. Analysis of apoptosis-associated genes revealed an inhibition of Retinoblastoma protein (Rb) and Survivin (SVV) gene expression. This was accompanied by elevation of p21, a tumor suppressor. Cell cycle was inhibited at both G1 and G2/M by individual treatments, and accentuated by a combination. AlamarBlue assay revealed a clear synergistic action of I3C+RE. CA125 was inhibited by either I3C or RE treatments. In contrast, basal nitric oxide production was inhibited by I3C and I3C+RE but not RE alone.

CONCLUSIONS

This is the first evidence demonstrating the effects of I3C on ovarian cancer cells and its synergism with RE. Based on this model, our data indicate that combinations of compounds with different targeting properties will be more effective in chemoprevention and/or chemotherapy of ovarian and possibly other cancers.

Inhibition of cell-cycle progression in human colorectal carcinoma Lovo cells by andrographolide

In recent years, attention has been focused on the anti-cancer properties of pure components, an important role in the prevention of disease. Andrographolide (Andro), the major constituent of Andrographis paniculata (Burm. F.) Nees plant, is implicated towards its pharmacological activity. To investigate the mechanism basis for the anti-tumor properties of Andro, Andro was used to examine its effect on cell-cycle progression in human colorectal carcinoma Lovo cells. The data from cell growth experiment showed that Andro exhibited the anti-proliferation effect on Lovo cells in a time- and dose-dependent manner. This event was accompanied the arrest of the cells at the G1-S phase by Andro at the tested concentrations of 0-30 microM. Cellular uptake of Andro and Andro was confirmed by capillary electrophoresis analysis and the intracellular accumulation of Andro (0.61+/-0.07 microM/mg protein) was observed when treatment of Lovo cells with Andro for 12h. In addition, an accumulation of the cells in G1 phase (15% increase for 10 microM of Andro) was observed as well as by the association with a marked decrease in the protein expression of Cyclin A, Cyclin D1, Cdk2 and Cdk4. Andro also inducted the content of Cdk inhibitor p21 and p16, and the phosphorylation of p53. Further immunoprecipitation studies found that, in response to the treatment, the formation of Cyclin D1/Cdk4 and Cyclin A/Cdk2 complexes had declined, preventing the phosphorylation of Rb and the subsequent dissociation of Rb/E2F complex. These results suggested Andro can inhibit Lovo cell growth by G1-S phase arrest, and was exerted by inducing the expression of p53, p21 and p16 that, in turn, repressed the activity of Cyclin D1/Cdk4 and/or Cyclin A/Cdk2, as well as Rb phosphorylation.

Indole-3-carbinol as a chemopreventive and anti-cancer agent

During the course of oncogenesis and tumor progression, cancer cells constitutively upregulate signaling pathways relevant to cell proliferation and survival as a strategy to overcome genomic instability and acquire resistance phenotype to chemotherapeutic agents. In light of this clinical and molecular heterogeneity of human cancers, it is desirable to concomitantly target these genetic abnormalities by using an agent with pleiotropic mode of action. Indole-3-carbinol and its metabolite 3,3'-diindoylmethane (DIM) target multiple aspects of cancer cell-cycle regulation and survival including Akt-NF kappa B signaling, caspase activation, cyclin-dependent kinase activities, estrogen metabolism, estrogen receptor signaling, endoplasmic reticulum stress, and BRCA gene expression. This broad spectrum of anti-tumor activities in conjunction with low toxicity underscores the translational value of indole-3-carbinol and its metabolites in cancer prevention/therapy. Furthermore, novel anti-tumor agents with overlapping underlying mechanisms have emerged via structural optimization of indole-3-carbinol and DIM, which may provide considerable therapeutic advantages over the parental compounds with respect to chemical stability and anti-tumor potency. Together, these agents might foster new strategies for cancer prevention and therapy.

The search for endogenous activators of the aryl hydrocarbon receptor

The primary design of this perspective is to describe the major ligand classes of the aryl hydrocarbon receptor (AHR). A grander objective is to provide models that may help define the physiological activator or "endogenous ligand" of the AHR. We present evidence supporting a developmental role for the AHR and propose mechanisms by which an endogenous ligand and consequent AHR activation might be important during normal physiology and development. From this vista, we survey the known xenobiotic, endogenous, dietary, and "unconventional" activators of the AHR, including, when possible, information about their induction potency, receptor binding affinity, and potential for exposure. In light of the essential function of the AHR in embryonic development, we discuss the candidacy of each of these compounds as physiologically important activators.

A potent indole-3-carbinol derived antitumor agent with pleiotropic effects on multiple signaling pathways in prostate cancer cells

Indole-3-carbinol has emerged as a promising chemopreventive agent due to its in vivo efficacy in various animal models. However, indole-3-carbinol exhibits weak antiproliferative potency and is unstable in acidic milieu. Thus, this study was aimed at exploiting indole-3-carbinol to develop potent antitumor agents with improved chemical stability. This effort culminated in OSU-A9 {[1-(4-chloro-3-nitrobenzenesulfonyl)-1H-indol-3-yl]-methanol}, which is resistant to acid-catalyzed condensation, and exhibits 100-fold higher apoptosis-inducing activity than the parent compound. Relative to indole-3-carbinol, OSU-A9 displays a striking qualitative similarity in its effects on the phosphorylation or expression of multiple signaling targets, including Akt, mitogen-activated protein kinases, Bcl-2 family members, survivin, nuclear factor-kappaB, cyclin D1, p21, and p27. The ability of OSU-A9 to concurrently modulate this broad range of signaling targets underscores its in vitro and in vivo efficacy in prostate cancer cells. Nevertheless, despite this complex mode of mechanism, normal prostate epithelial cells were less susceptible to the antiproliferative effect of OSU-A9 than PC-3 and LNCaP prostate cancer cells. Treatment of athymic nude mice bearing established s.c. PC-3 xenograft tumors with OSU-A9 at 10 and 25 mg/kg i.p. for 42 days resulted in a 65% and 85%, respectively, suppression of tumor growth. Western blot analysis of representative biomarkers in tumor lysates revealed significant reductions in the intratumoral levels of phosphorylated (p-) Akt, Bcl-xL, and RelA, accompanied by robust increases in p-p38 levels. In conclusion, the ability of OSU-A9 to target multiple aspects of cancer cell survival with high potency suggests its clinical value in prostate cancer therapy.

N-Alkoxy derivatization of indole-3-carbinol increases the efficacy of the G1 cell cycle arrest and of I3C-specific regulation of cell cycle gene transcription and activity in human breast cancer cells

Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables, such as cabbage, broccoli, and Brussels sprouts, induces a G1 cell cycle arrest of human breast cancer cells. Structure-activity relationships of I3C that mediate this anti-proliferative response were investigated using synthetic and natural I3C derivatives that contain substitutions at the indole nitrogen. Nitrogen substitutions included N-alkoxy substituents of one to four carbons in length, which inhibit dehydration and the formation of the reactive indolenine. Analysis of growth and cell cycle arrest of indole-treated human breast cancer cells revealed a striking increase in efficacy of the N-alkoxy I3C derivatives that is significantly enhanced by the presence of increasing carbon lengths of the N-alkoxy substituents. Compared to I3C, the half maximal growth arrest responses occurred at 23-fold lower indole concentration for N-methoxy I3C, 50-fold lower concentration for N-ethoxy I3C, 217-fold lower concentration for N-propoxy I3C, and 470-fold lower concentration for N-butoxy I3C. At these lower concentrations, each of the N-alkoxy substituted compounds induced the characteristic I3C response in that CDK6 gene expression, CDK6 promoter activity, and CDK2 specific enzymatic activity for its retinoblastoma protein substrate were strongly down-regulated. 3-Methoxymethylindole and 3-ethoxymethylindole were approximately as bioactive as I3C, whereas both tryptophol and melatonin failed to induce the cell cycle arrest, showing the importance of the C-3 hydroxy methyl substituent on the indole ring. Taken together, our study establishes the first I3C structure-activity relationship for cytostatic activities, and implicates I3C-based N-alkoxy derivatives as a novel class of potentially more potent experimental therapeutics for breast cancer.

EGFR and Src are involved in indole-3-carbinol-induced death and cell cycle arrest of human breast cancer cells

Indole-3-carbinol (I3C), a dietary chemopreventive compound, induced marked reduction in epidermal growth factor receptor (EGFR) prior to cell death in cells representing three breast cancer subtypes. Signalling pathways, linking these events were investigated in detail. I3C modulated tyrosine phosphorylation from 30 min in four cell lines. In MDA-MB-468 and HBL100 cells, it induced Src activation after 5 h. In MDA-MB-468 cells, I3C induced signalling between 4.5 and 7 h, which involved sequential activation of Src, EGFR, STAT-1 and STAT-3, followed by EGFR degradation. It also induced physical association between activated Src and EGFR. In MCF7 and MDA-MB-231 cells, I3C modulated expression of cell cycle-related proteins, p21Cip1, p27Kip1, cyclin E, cyclin D1 and CDK6, with upregulation of p21Cip1 and cyclin E being dependent on Src. Inhibition of EGFR by specific inhibitors PD153035 or ZD1839 increased susceptibility to I3C-induced apoptosis of MCF7, MDA-MB-468 and MDA-MB-231 cells. Inhibition of Src sensitized MDA-MB-468 and MDA-MB-231 cells to I3C, whereas overexpression of c-Src increased resistance to I3C in MDA-MB-468 and HBL100 cells. Modulation of Src in MDA-MB-468 cells influenced the basal level of EGFR expression and cell viability; the latter being positively correlated with EGFR activation levels. Therefore, EGFR and Src activities are essential for I3C-induced cell cycle arrest and death; however, I3C-induced pathways depend on specific features of breast cancer cells. The cancer types, which rely on 'EGFR addiction' or Src deregulation, are likely to be susceptible to I3C.

Gene expression analysis during tumor enhancement by the dietary phytochemical, 3,3'-diindolylmethane, in rainbow trout

Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM), a primary I3C derivative, are known dietary chemopreventive agents also available as supplements. However, I3C has been found to act as a tumor promoter in rat (multi-organ) and trout (liver) models. I3C and DIM were previously found to be estrogenic in trout liver based on toxicogenomic profiles. In this study, we compare the post-initiation effects of DIM and 17beta-estradiol (E2) on aflatoxin B(1) (AFB(1))-induced hepatocarcinogenesis in trout. Trout were initiated as embryos with AFB(1) and juvenile fish were fed diets containing 0, 120 or 400 p.p.m. DIM or 5 p.p.m. E2 for 18 weeks. Tumor incidence was determined at 13 months and found to be significantly elevated in AFB(1)-initiated trout fed either 400 p.p.m. DIM or 5 p.p.m. E2 compared with control animals. To evaluate the mechanism of tumor enhancement, hepatic gene expression profiles were examined in animals fed promotional diets during the course of tumorigenesis and in hepatocellular carcinomas (HCCs) of initiated animals. We demonstrate that DIM alters gene expression profiles similar to E2 in liver samples during tumorigenesis and in HCC tumors. Further, HCCs from animals on DIM and E2 promotional diets had a transcriptional signature indicating decreased invasive or metastatic potential compared with HCCs from control animals. Overall, these findings are the first to demonstrate tumor promotion by DIM. They confirm the importance of estrogenic signaling in the mechanism of promotion by dietary indoles in trout liver and indicate a possible dual effect that enhances tumor incidence and decreases potential for metastasis.

Combinations of tomato and broccoli enhance antitumor activity in dunning r3327-h prostate adenocarcinomas

The consumption of diets containing 5 to 10 servings of fruits and vegetables daily is the foundation of public health recommendations for cancer prevention, yet this concept has not been tested in experimental models of prostate cancer. We evaluated combinations of tomato and broccoli in the Dunning R3327-H prostate adenocarcinoma model. Male Copenhagen rats (n=206) were fed diets containing 10% tomato, 10% broccoli, 5% tomato plus 5% broccoli (5:5 combination), 10% tomato plus 10% broccoli (10:10 combination) powders, or lycopene (23 or 224 nmol/g diet) for approximately 22 weeks starting 1 month prior to receiving s.c. tumor implants. We compared the effects of diet to surgical castration (2 weeks before termination) or finasteride (5 mg/kg body weight orally, 6 d/wk). Castration reduced prostate weights, tumor areas, and tumor weight (62%, P<0.001), whereas finasteride reduced prostate weights (P<0.0001), but had no effect on tumor area or weight. Lycopene at 23 or 224 nmol/g of the diet insignificantly reduced tumor weights by 7% or 18%, respectively, whereas tomato reduced tumor weight by 34% (P<0.05). Broccoli decreased tumor weights by 42% (P<0.01) whereas the 10:10 combination caused a 52% decrease (P<0.001). Tumor growth reductions were associated with reduced proliferation and increased apoptosis, as quantified by proliferating cell nuclear antigen immunohistochemistry and the ApopTag assay. The combination of tomato and broccoli was more effective at slowing tumor growth than either tomato or broccoli alone and supports the public health recommendations to increase the intake of a variety of plant components.

Methyl-3-indolylacetate inhibits cancer cell invasion by targeting the MEK1/2-ERK1/2 signaling pathway

Epidemiologic studies have suggested an inverse correlation between dietary intake of cruciferous vegetables and cancer risk. It is thus of interest to investigate the anticancer potential of phytochemicals presented in cruciferous vegetables. In this study, methyl-3-indolylacetate (MIA), a cruciferous indole for which the bioactivity has not been previously reported, was found to significantly suppress the invasion of cancer cells stimulated by the 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Our data show that MIA pretreatments inhibited matrix metalloproteinase 9 (MMP-9) expression in a concentration-dependent manner, resulting in decreased MMP-9 activity. By using real-time reverse transcription-PCR, luciferase reporter gene assay, and electrophoretic mobility shift assay, we provided convincing evidence that MIA suppresses MMP-9 gene transcription via targeting the activator protein-1 signaling but not the nuclear factor-kappaB pathway. The TPA-induced mitogen-activated protein kinase (MAPK) activation cascade was also analyzed. Despite extensive activation of major MAPKs [c-Jun NH2-terminal kinase, p38, and extracellular signal-regulated kinase-1/2 (ERK1/2)] under TPA stimulation, only the ERK1/2 activation and its consequent nuclear translocation were found to be diminished by MIA. Interestingly, MIA did not affect the TPA-induced phosphorylation of either c-Raf or MAPK/ERK kinase-1/2 (MEK1/2), two upstream kinases of ERK. Moreover, using the in vitro kinase assay, MIA was shown to inhibit the kinase activity of MEK1/2, the upstream kinases of ERK, suggesting that MEK is the major molecular target of MIA. In conclusion, data from this study provided new insight into the anticancer potential of MIA, a cruciferous vegetable-derived indole compound.

Therapeutic intervention of experimental breast cancer bone metastasis by indole-3-carbinol in SCID-human mouse model

Several lines of experimental evidence have suggested that chemokine receptor CXCR4, a metastasis-promoting molecule, may play important roles in breast cancer bone metastasis. There is emerging evidence linking CXCR4 to matrix metalloproteinases (MMP) as well as their regulator nuclear factor-kappaB (NF-kappaB), a key transcription factor, which is known to activate metastasis-promoting molecules for many types of malignancies, including breast cancer. A recent study also showed that promoter region of CXCR4 has several NF-kappaB-binding sites, suggesting that there may be a cross-talk between CXCR4 and NF-kappaB. We have shown previously that indole-3-carbinol (I3C), a natural compound present in vegetables of the genus Brassica, can inhibit NF-kappaB in breast cancer cells. However, there are no reports in the literature showing any effect of I3C on CXCR4 expression in vitro and in vivo. We therefore examined whether I3C could inhibit bone metastasis of breast cancer by inhibiting CXCR4 and MMP-9 expression mediated via the inhibition of the NF-kappaB signaling pathway. Here, we have modified the severe combined immunodeficient (SCID)-human mouse model of experimental bone metastasis for use with the MDA-MB-231 breast cancer cell line. In this animal model, we found that I3C significantly inhibited MDA-MB-231 bone tumor growth, and our results were correlated with the down-regulation of NF-kappaB. Moreover, we found that I3C significantly inhibited the expression of multiple genes involved in the control of metastasis and invasion in vitro and in vivo, especially the expression of CXCR4 and MMP-9 along with pro-MMP-9, with concomitant decrease in Bcl-2 and increase in the proapoptotic protein Bax. From these results, we conclude that the CXCR4/NF-kappaB pathway is critical during I3C-induced inhibition of experimental breast cancer bone metastasis. These results also suggest that I3C could be a promising agent for the prevention and/or treatment of breast cancer bone metastasis in the future.

Comparison of growth inhibition profiles and mechanisms of apoptosis induction in human colon cancer cell lines by isothiocyanates and indoles from Brassicaceae

The isothiocyanates sulforaphane and PEITC (beta-phenethyl isothiocyanate) as well as the indoles indole-3-carbinol and its condensation product 3,3'-diindolylmethane are known to inhibit cancer cell proliferation and induce apoptosis. In this study, we compared the cell growth inhibitory potential of the four compounds on the p53 wild type human colon cancer cell line 40-16 (p53(+/+)) and its p53 knockout derivative 379.2 (p53(-/-)) (both derived from HCT116). Using sulforhodamin B staining to assess cell proliferation, we found that the isothiocyanates were strongly cytotoxic, whereas the indoles inhibited cell growth in a cytostatic manner. Half-maximal inhibitory concentrations of all four compounds in both cell lines ranged from 5-15 microM after 24, 48 and 72 h of treatment. Apoptosis induction was analyzed by immunoblotting of poly(ADP-ribose)polymerase (PARP). Treatment with sulforaphane (15 microM), PEITC (10 microM), indole-3-carbinol (10 microM) and 3,3'-diindolylmethane (10 microM) induced PARP cleavage after 24 and 48 h in both 40-16 and the 379.2 cell lines, suggestive of a p53-independent mechanism of apoptosis induction. In cultured 40-16 cells, activation of caspase-9 and -7 detected by Western blotting indicated involvement of the mitochondrial pathway. We detected time- and concentration-dependent changes in protein expression of anti-apoptotic Bcl-x(L) as well as pro-apoptotic Bax and Bak proteins. Of note is that for sulforaphane only, ratios of pro- to anti-apoptotic Bcl-2 family protein levels directly correlated with apoptosis induction measured by PARP cleavage. Taken together, we demonstrated that the glucosinolate breakdown products investigated in this study have distinct profiles of cell growth inhibition, potential to induce p53-independent apoptosis and to modulate Bcl-2 family protein expression in human colon cancer cell lines.

Critical role of pro-apoptotic Bcl-2 family members in andrographolide-induced apoptosis in human cancer cells

Andrographolide (Andro), a diterpenoid lactone isolated from a traditional herbal medicine Andrographis paniculata, is known to possess potent anti-inflammatory activity. In this study, Andro induced apoptosis in human cancer cells via activation of caspase 8 in the extrinsic death receptor pathway and subsequently with the participation of mitochondria. Andro triggered a caspase 8-dependent Bid cleavage, followed by a series of sequential events including Bax conformational change and mitochondrial translocation, cytochrome c release from mitochondria, and activation of caspase 9 and 3. Inhibition of caspase 8 blocked Bid cleavage and Bax conformational change. Consistently, knockdown of Bid protein using small interfering RNA (siRNA) technique suppressed Andro-induced Bax conformational change and apoptosis. In conclusion, the pro-apoptotic Bcl-2 family members (Bid and Bax) are the key mediators in relaying the cell death signaling initiated by Andro from caspase 8 to mitochondria and then to downstream effector caspases, and eventually leading to apoptotic cell death.

GSTP1 and GSTA1 polymorphisms interact with cruciferous vegetable intake in colorectal adenoma risk

The possible interplay between cruciferous vegetable consumption, functional genetic variations in glutathione S-transferases (GST) M1, T1, P1, and A1, and colorectal adenomas, was investigated in a Dutch case-control study. The GSTM1 and GSTT1 deletion polymorphisms, and the single nucleotide polymorphisms in GSTP1 (A313G) and in GSTA1 (C-69T) were assessed among 746 cases who developed colorectal adenomas and 698 endoscopy-based controls without any type of colorectal polyps. High and low cruciferous vegetable consumption was defined based on a median split in the control group. High consumption was slightly positively associated with colorectal adenomas [odds ratio (OR) 1.15; 95% confidence interval, 0.92-1.44]. For GSTP1, a positive association with higher cruciferous vegetable intake was only apparent in individuals with the low-activity GSTP1 genotype (GG genotype, OR 1.94; 95% confidence interval, 1.02-3.69). This interaction was more pronounced in men, with higher age and with higher meat intake. The GSTA1 polymorphism may have a modifying role as well: the OR for higher intake compared with lower intake was 1.57 (0.93-2.65) for individuals homozygous for the low expression variant (TT genotype). This seemed to be stronger with younger age and higher red meat intake. Cruciferous vegetable consumption and the combined GSTA1 and GSTP1 genotypes showed a statistically significant interaction (P = 0.034). The GSTM1 and GSTT1 genotypes did not seem to modify the association between cruciferous vegetable intake and colorectal adenomas. In conclusion, GSTP1 and GSTA1 genotypes might modulate the association between cruciferous vegetable intake and colorectal adenomas.

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.

Synergy among phytochemicals within crucifers: does it translate into chemoprotection?

The association between cruciferous vegetables and cancer prevention has been linked to glucosinolate derivatives. These phytochemicals enhance endogenous detoxification, leading to inactivation of potential carcinogens before initiation occurs. Two derivatives, indole-3-carbinol (I3C) and 1-cyano-2-hydroxy-3-butene (crambene) were shown in rats to induce a synergistic enhancement of detoxification enzyme activity. To follow up on these findings, a short-term carcinogenicity study using aflatoxin B1 (AFB(1)) was performed in which male F344 rats were fed diets supplemented with these 2 compounds alone or in combination. Groups included a negative control group (no AFB(1), crambene, or I3C), a crambene group (diet 0.150% crambene), an I3C group (diet 0.165% I3C), a high-dose group (diet 0.150% crambene, 0.165% I3C) a low-dose group (diet 0.030% crambene, 0.033% I3C), and a positive control group (AFB(1) treatment only). AFB(1) was administered after 2 wk of dietary pretreatment. Liver sections were scored for lesions including karyomegaly, apoptosis, and biliary hyperplasia and evaluated for expression of the preneoplastic marker glutathione S-transferase-pi (GSTP). I3C and crambene groups were protected against AFB(1) toxicity whereas the low-dose group was not. The high-dose group had scores close to those of the negative controls. For log(10) transformed 2- and 3-dimensional GSTP data, the high-dose group demonstrated synergistic reduction in GSTP-positive area and an additive reduction in GSTP-positive volume compared with the crambene and I3C groups. The low-dose group had no effect. In conclusion, high combination dietary doses of I3C and crambene demonstrated enhanced protection from AFB(1). Low combination doses, as might be realistically in the diet, were not effective.

Toxicogenomic profiling of the hepatic tumor promoters indole-3-carbinol, 17beta-estradiol and beta-naphthoflavone in rainbow trout

Indole-3-carbinol (I3C), from cruciferous vegetables, has been found to suppress or enhance tumors in several animal models. We previously reported that dietary I3C promotes hepatocarcinogenesis in rainbow trout (Oncorhynchus mykiss) at concentrations that differentially activated estrogen receptor (ER) or aryl hydrocarbon receptor (AhR)-mediated responses based on individual protein biomarkers. In this study, we evaluated the relative importance of these pathways as potential mechanisms for I3C on a global scale. Hepatic gene expression profiles were examined in trout after dietary exposure to 500 and 1500 ppm I3C and 3,3'-diindolylmethane (DIM), a major in vivo component of I3C, and were compared to the transcriptional signatures of two model hepatic tumor promoters: 17beta-estradiol (E2), an ER agonist, and beta-naphthoflavone, an AhR agonist. We demonstrate that I3C and DIM acted similar to E2 at the transcriptional level based on correlation analysis of expression profiles and clustering of gene responses. Of the genes regulated by E2 (fold change >or =2.0 or < or =0.50), most genes were regulated similarly by DIM (87-92%) and I3C (71%), suggesting a common mechanism of action. Of interest were upregulated genes associated with signaling pathways for cell growth and proliferation, vitellogenesis, and protein folding, stability, and transport. Other genes downregulated by E2, including those involved in acute-phase immune response, were also downregulated by DIM and I3C. Gene regulation was confirmed by qRT-PCR and Western blot. These data indicate I3C promotes hepatocarcinogenesis through estrogenic mechanisms in trout liver and suggest DIM may be an even more potent hepatic tumor promoter in this model.