Ligand-independent activation of estrogen receptor function by 3, 3'-diindolylmethane in human breast cancer cells

WITHDRAWN: The anti-cancer properties in parallel with toxic effects of indole-3-carbinol derivatives

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Normal human immune cells are sensitive to telomerase inhibition by Brassica-derived 3,3-diindolylmethane,partly mediated via ERα/β-AP1 signaling

SCOPE

Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM) from Brassica plants are regarded as promising anticancer phytochemicals. The enzyme telomerase is a very attractive target for cancer therapeutics; in normal cells such as lymphocytes, it plays a decisive role for cell maintenance. The effect of I3C and DIM on telomerase in normal human immune cells (PBMC) was studied compared to leukaemia cells (HL-60). Signalling of telomerase regulation via estrogen receptor (ER) was addressed.

METHODS AND RESULTS

Short-term treatment with I3C and DIM inhibited telomerase activity in leukaemia cells (>30 μM I3C; >3 μM DIM). In CD3/CD28 activated PBMC, inhibition was stronger, though (>3 μM I3C; >1 μM DIM). DIM long-term treatment resulted in DNA damage induction and proliferation inhibition in PBMC as determined by the comet assay and CFSE staining, respectively. A relevance of ERα/β-AP1 signaling for telomerase inhibition on enzyme activity, but not transcription level became evident indicating a nonclassical mode for ER regulation of telomerase by DIM.

CONCLUSION

Although desired in cancer cells, this study identified a potential adverse impact of I3C and DIM on telomerase action in normal human immune cells, partly mediated by an ER-dependent mechanism. These new findings should be considered for potential chronic high-dose chemoprevention strategies using these compounds.

A Possible Association of Diindolylmethane with Pulmonary Embolism and Deep Venous Thrombosis

Introduction. 3,3'-Diindolylmethane is available as a supplement in the United States for "cancer prevention" and "augmentation of physical fitness." A derivative of indole-3-carbinol found in plants, diindolylmethane, binds to receptors associated with the sex steroid pathways and has unclear effects on estrogen and androgen physiology. We present a patient who had been taking diindolylmethane and developed right lower extremity deep venous thrombosis and bilateral pulmonary embolism. Case Presentation. A 65-year-old man presented with swelling, erythema, and warmth of his right lower extremity for three to four weeks. He had been taking diindolylmethane one tablet daily for three to four months. Risk factors for venous thromboembolism included tobacco use, personal history of possible pulmonary embolism, body mass index, and age. Imaging studies found extensive deep venous thrombosis in his right lower extremity and bilateral pulmonary embolism with probable right middle lobe infarction. Follow-up imaging showed chronic deep venous thrombosis in his right lower extremity. Discussion. As suggested in this single case, patients who take diindolylmethane may be at greater risk for venous thromboembolism. Further reports and studies are necessary in order to elucidate this possible association. Clinicians should question patients about supplements in the setting of venous thromboembolism.

Synthesis of New 3-Heteroarylindoles as Potential Anticancer Agents

2-(3-(1H-Indol-3-yl)-5-(p-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)-4-substituted-5-(substituted diazenyl)thiazoles and 2-(1H-indol-3-yl)-9-substituted-4,7-disubstituted pyrido[3,2-e][1,2,4]triazolo[4,3-a]pyrimidin-5(7H)-ones were synthesized via reaction of hydrazonoyl halides with each of 3-(1H-indol-2-yl)-5-(p-tolyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide and 7-(1H-indol-3-yl)-2- thioxo-5-substituted-2,3-dihydropyrido[2,3-d]pyrimidin-4(1H)-ones, respectively. Also, hydrazonoyl halides were reacted with N’-(1-(1H-indol-3-yl)ethylidene)-2-cyanoacetohydrazide to afford 1,3,4-thiadiazole derivatives. Structures of the new synthesis were elucidated on the basis of elemental analysis, spectral data, and alternative synthetic routes whenever possible. Fifteen of the new compounds have been evaluated for their antitumor activity against the MCF-7 human breast carcinoma cell line. The results indicated that many of the tested compounds showed moderate to high anticancer activity when compared with doxorubicin as a reference drug.

Role of dietary bioactive natural products in estrogen receptor-positive breast cancer

Estrogen receptor (ER)-positive breast cancer, including luminal-A and -B, is the most common type of breast cancer. Extended exposure to estrogen is associated with an increased risk of breast cancer. Both ER-dependent and ER-independent mechanisms have been implicated in estrogen-mediated carcinogenesis. The ER-dependent pathway involves cell growth and proliferation triggered by the binding of estrogen to the ER. The ER-independent mechanisms depend on the metabolism of estrogen to generate genotoxic metabolites, free radicals and reactive oxygen species to induce breast cancer. A better understanding of the mechanisms that drive ER-positive breast cancer will help optimize targeted approaches to prevent or treat breast cancer. A growing emphasis is being placed on alternative medicine and dietary approaches toward the prevention and treatment of breast cancer. Many natural products and bioactive compounds found in foods have been shown to inhibit breast carcinogenesis via inhibition of estrogen induced oxidative stress as well as ER signaling. This review summarizes the role of bioactive natural products that are involved in the prevention and treatment of estrogen-related and ER-positive breast cancer.

Diindolylmethane, a naturally occurring compound, induces CYP3A4 and MDR1 gene expression by activating human PXR

Activation of human pregnane X receptor (hPXR)-regulated expression of cytochrome P450 3A4 (CYP3A4) and multidrug resistance protein 1 (MDR1) plays an important role in mediating adverse drug interactions. Given the common use of natural products as part of adjunct human health behavior, there is a growing concern about natural products for their potential to induce undesired drug interactions through the activation of hPXR-regulated CYP3A4 and MDR1. Here, we studied whether 3,3'-diindolylmethane (DIM), a natural health supplement, could induce hPXR-mediated regulation of CYP3A4 and MDR1 in human hepatocytes and intestinal cells. DIM, at its physiologically relevant concentrations, not only induced hPXR transactivation of CYP3A4 promoter activity but also induced gene expression of CYP3A4 and MDR1. DIM decreased intracellular accumulation of MDR1 substrate rhodamine 123, suggesting that DIM induces the functional expression of MDR1. Pharmacologic inhibition or genetic knockdown of hPXR resulted in attenuation of DIM induced CYP3A4 and MDR1 gene expression, suggesting that DIM induces CYP3A4 and MDR1 in an hPXR-dependent manner. Together, these results support our conclusion that DIM induces hPXR-regulated CYP3A4 and MDR1 gene expression. The inductive effects of DIM on CYP3A4 and MDR1 expression caution the use of DIM in conjunction with other medications metabolized and transported via CYP3A4 and MDR1, respectively.

Resolvin D2 supports MCF-7 cell proliferation via activation of estrogen receptor

Inflammation has been implicated in tumor initiation, angiogenesis, and metastasis, and linked to the development of more aggressive, therapy-resistant estrogen receptor (ER)-positive breast cancer. Resolvin D2 (RvD2) is a potent anti-inflammatory lipid mediator. As RvD2 may be synthesized within breast tumors by both tumor cells and the surrounding stroma cells and is present in plasma at bioactive concentrations, we sought to characterize the impact of RvD2 on cell processes underlying breast tumor growth and spread. Trypan-blue exclusion, transfection with estrogen response element (ERE) reporter, real-time quantitative polymerase chain reaction, competitive radioligand binding assays, Western blotting, and immunofluorescence were the techniques used. Unexpectedly, whereas RvD2 (10-1000 nM) supported the proliferation of the ER-positive breast tumor (MCF-7) cells, it did not affect the ER-negative MDA-MB-231 cell number. The proliferative effect of RvD2 in MCF-7 cells was attenuated by the ER antagonist ICI 182,780 (7α-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17β-diol). Furthermore, RvD2 increased ERE transcriptional activity in a number of ER-positive breast and ovarian tumor cell lines. This activation was also inhibited by ICI 182,780. RvD2 altered the expression of a subset of estrogen-responsive genes. Although binding experiments showed that RvD2 did not directly compete with [(3)H]17β-estradiol for ER binding, prior exposure of MCF-7 cells to RvD2 resulted in a significant reduction in the apparent cytosolic ER density. Confocal immunocytochemistry and Western blotting studies showed that RvD2 promoted nuclear localization of ERα. These observations indicate that RvD2 displays significant but indirect estrogenic properties and has the potential to play a role in estrogen-dependent breast cancer progression.

The role of estrogen receptor β in transplacental cancer prevention by indole-3-carbinol

In the present study, the efficacy of indole-3-carbinol (I3C), a key bioactive component of cruciferous vegetables, for prevention of cancer in offspring exposed in utero to the environmental carcinogen dibenzo[def,p]chrysene (DBC) was evaluated using an estrogen receptor β (ERβ) knockout mouse model. I3C was provided either through the maternal diet coincident with carcinogen exposure during pregnancy or directly to offspring postinitiation with DBC. I3C was effective at reducing T-cell acute lymphoblastic lymphoma/leukemia (T-ALL)-related mortality in offspring only if provided via the maternal diet, although a gender difference in the role of ERβ in mediating this response was evident. In female offspring, chemoprevention of T-ALL by maternal dietary I3C required expression of ERβ; survival in Esr2 wild-type and heterozygous female offspring was more than 90% compared with 66% in Esr2 null females. Alternatively, ERβ status did not significantly impact the transplacental chemoprevention by I3C in males. The possible role of ERβ in mediating lung carcinogenesis or chemoprevention by I3C was similarly complicated. Lung tumor incidence was unaltered by either dietary intervention, whereas lung tumor multiplicity was substantially reduced in Esr2 null females on the control diet and marginally lower in Esr2 null males exposed to I3C via the maternal diet compared with their wild-type and heterozygous counterparts. These findings suggest that I3C may act via ERβ to prevent or suppress DBC-initiated transplacental carcinogenesis but that the involvement of this receptor seems to differ depending on the cancer type and gender of the offspring.

Engineering glucosinolates in plants: current knowledge and potential uses

Glucosinolates (GSL) and their derivatives are well known for the characteristic roles they play in plant defense as signaling molecules and as bioactive compounds for human health. More than 130 GSLs have been reported so far, and most of them belong to the Brassicaceae family. Several enzymes and transcription factors involved in the GSL biosynthesis have been studied in the model plant, Arabidopsis, and in a few other Brassica crop species. Recent studies in GSL research have defined the regulation, distribution, and degradation of GSL biosynthetic pathways; however, the underlying mechanism behind transportation of GSLs in plants is still largely unknown. This review highlights the recent advances in the metabolic engineering of GSLs in plants and discusses their potential applications.

Synthesis and Preliminary Biological Study of Bisindolylmethanes Accessed by an Acid-Catalyzed Hydroarylation of Vinylindoles

An acid-catalyzed hydroarylation reaction of vinyl indoles is reported, which tolerates a wide range of heterocycles as the exogenous nucleophile such as indoles, pyrroles, and indolizines. The method rapidly accesses the biologically relevant bisindolylmethane scaffold in good to excellent yields. Evaluation of the biological activity of several synthesized analogues reveals cytotoxic activity against and selectivity for the MCF-7 breast cancer cell line.

Effects of stimulation and blockade of d(2) receptor on depression-like behavior in ovariectomized female rats

The aim of the present study was to explore the hedonic effects of D₂ receptor agonist, quinpirole and D₂ receptor antagonist, and sulpiride alone or in combination with a low dose of 17β-E₂-estradiol (17β-E₂) in the adult ovariectomized female rats (OVX). OVX rats of Wistar strain were used in all experiments. Two weeks after surgery rats were chronically treated with vehicle, a low dose of 17β-E₂ (5.0 μg/rat), quinpirole (0.1 mg/kg), sulpiride (10.0 mg/kg), quinpirole plus 17β-E₂, or sulpiride plus 17β-E₂ for 14 days before the forced swimming test. We found that sulpiride significantly decreased immobility time in the OVX females. A combination of sulpiride with a low dose of 17β-E₂ induced more profound decrease of immobility time in the OVX rats compared to the rats treated with sulpiride alone. On the contrary, quinpirole failed to modify depression-like behavior in the OVX rats. In addition, quinpirole significantly blocked the antidepressant-like effect of 17β-E₂ in OVX rats. Thus, the D₂ receptor antagonist sulpiride alone or in combination with a low dose of 17β-E₂ exerted antidepressant-like effect in OVX female rats, while the D₂ receptor agonist quinpirole produced depressant-like profile on OVX rats.

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.

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.

Estrogen receptor subtype- and promoter-specific modulation of aryl hydrocarbon receptor-dependent transcription

In this study, we examined the role of estrogen receptors (ER) in aryl hydrocarbon receptor (AHR)-dependent transactivation. Chromatin immunoprecipitation assays showed that AHR agonists differentially induced recruitment of ERalpha to the AHR target genes CYP1A1 and CYP1B1. Cotreatment with 17beta-estradiol significantly increased beta-naphthoflavone (BNF)- and 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced recruitment of ERalpha to CYP1A1, whereas 3,3'-diindolylmethane induced promoter occupancy of ERalpha at CYP1A1 that was unaffected by cotreatment with 17beta-estradiol. Cyclical recruitment of AHR and ERalpha to CYP1A1 was only observed in cells treated with BNF. Stable and subtype-specific knockdown of ERalpha or ERbeta using shRNA showed that suppression of ERalpha significantly reduced, whereas knockdown of ERbeta significantly enhanced, AHR agonist-induced Cyp1a1 expression in HC11 mouse mammary epithelial cells. AHR agonist-induced Cyp1b1 expression was reduced by ERbeta knockdown but unaffected by ERalpha knockdown. The siRNA-mediated knockdown of ERalpha in MCF-7 human breast cancer cells did not affect 2,3,7,8-tetrachlorodibenzo-p-dioxin-dependent regulation of CYP1A1 and CYP1B1 mRNA expression. In agreement with our in vitro findings in the HC11 cells, ERalpha knockout mice exhibit reduced BNF-dependent induction of Cyp1a1 mRNA. These results establish ligand- and promoter-specific influences on the cyclical recruitment patterns for AHR and show ER species-, subtype-, and promoter-specific modulation of AHR-dependent transcription.

Cancer chemotherapy with indole-3-carbinol, bis(3'-indolyl)methane and synthetic analogs

Indole-3-carbinol (I3C) conjugates are phytochemicals expressed in brassica vegetables and have been associated with the anticancer activities of vegetable consumption. I3C and its metabolite bis(3'-indolyl)methane (DIM) induce overlapping and unique responses in multiple cancer cell lines and tumors, and these include growth inhibition, apoptosis and antiangiogenic activities. The mechanisms of these responses are complex and dependent on cell context. I3C and/or DIM activate or inactivate multiple nuclear receptors, induce endoplasmic reticulum stress, decrease mitochondrial membrane potential, and modulate multiple signaling pathways including kinases. DIM has been used as a template to synthesize a series of 1,1-bis(3'indolyl)-1-(substituted aromatic)methanes (i.e. C-DIMs) which are also cytotoxic to cancer cells and tumors. Some of the effects of C-DIMs resemble those reported for DIM analogs; however, structure-activity studies with the aromatic ring has resulted in generation of highly unique receptor agonists. For example, p-trifluoromethylphenyl, p-t-butylphenyl and p-biphenyl analogs activate peroxisome proliferator-activated receptor gamma (PPARgamma), and p-methoxyphenyl and p-phenyl compounds activate nerve growth factor-induced-Balpha (NGFI-Balpha, Nur77) orphan nuclear receptor. The effects of C-DIMs on PPARgamma and Nur77 coupled with their receptor-independent activities has resulted in the development of a novel group of multi-targeted anticancer drugs with excellent potential for clinical treatment of cancer.

Dopaminergic activation of estrogen receptors induces fos expression within restricted regions of the neonatal female rat brain

Steroid receptor activation in the developing brain influences a variety of cellular processes that endure into adulthood, altering both behavior and physiology. Recent data suggests that dopamine can regulate expression of progestin receptors within restricted regions of the developing rat brain by activating estrogen receptors in a ligand-independent manner. It is unclear whether changes in neuronal activity induced by dopaminergic activation of estrogen receptors are also region specific. To investigate this question, we examined where the dopamine D1-like receptor agonist, SKF 38393, altered Fos expression via estrogen receptor activation. We report that dopamine D1-like receptor agonist treatment increased Fos protein expression within many regions of the developing female rat brain. More importantly, prior treatment with an estrogen receptor antagonist partially reduced D1-like receptor agonist-induced Fos expression only within the bed nucleus of the stria terminalis and the central amygdala. These data suggest that dopaminergic activation of estrogen receptors alters neuronal activity within restricted regions of the developing rat brain. This implies that ligand-independent activation of estrogen receptors by dopamine might organize a unique set of behaviors during brain development in contrast to the more wide spread ligand activation of estrogen receptors by estrogen.

3,3'-Diindolylmethane stimulates murine immune function in vitro and in vivo

3,3'-Diindolylmethane (DIM), a major condensation product of indole-3-carbinol, exhibits chemopreventive properties in animal models of cancer. Recent studies have shown that DIM stimulates interferon-gamma (IFN-gamma) production and potentiates the IFN-gamma signaling pathway in human breast cancer cells via a mechanism that includes increased expression of the IFN-gamma receptor. The goal of this study was to test the hypothesis that DIM modulates the murine immune function. Specifically, the effects of DIM were evaluated in a panel of murine immune function tests that included splenocyte proliferation, reactive oxygen species (ROS) generation, cytokine production and resistance to viral infection. DIM was found to induce proliferation of splenocytes as well as augment mitogen- and interleukin (IL)-2-induced splenocyte proliferation. DIM also stimulated the production of ROS by murine peritoneal macrophage cultures. Oral administration of DIM, but not intraperitoneal injection, induced elevation of serum cytokines in mice, including IL-6, granulocyte colony-stimulating factor (G-CSF), IL-12 and IFN-gamma. Finally, in a model of enteric virus infection, oral DIM administration to mice enhanced both clearance of reovirus from the GI tract and the subsequent mucosal IgA response. Thus, DIM is a potent stimulator of immune function. This property might contribute to the cancer inhibitory effects of this indole.

CXCR4 and CXCL12 down-regulation: a novel mechanism for the chemoprotection of 3,3'-diindolylmethane for breast and ovarian cancers

Cruciferous vegetables are thought to protect against numerous types of cancer. 3,3'-Diindolylmethane (DIM) is an acid-catalyzed product generated during the consumption of cruciferous vegetables and appears to be chemoprotective for breast cancer. The interaction between the chemokine receptor, CXCR4, and its unique ligand, CXCL12, is known to mediate the progression and metastasis of breast and other cancers. Organs to which these cancers metastasize secrete CXCL12, which binds to CXCR4 expressed on the surface of primary cancer cells. This process subsequently stimulates the invasive properties of the cancer cells and attracts them to the preferred organ sites of metastases. We have found that DIM down-regulates both CXCR4 and CXCL12 in MCF-7 and MDA-MB-231 breast cancer cells as well as in BG-1 ovarian cancer cells at the transcriptional level and in an estrogen-independent manner. We demonstrate that the potential of MDA-MB-231 and BG-1 cells for chemotaxis and invasion towards CXCL12, but not towards IL-6 or fetal bovine serum, respectively, is inhibited by DIM. Furthermore, we show that DIM down-regulates CXCR4 under hypoxia and CXCL12 under estradiol-inducing conditions. Our data suggest that one mechanism whereby DIM protects against breast, ovarian, and possibly other cancers is through the repression of CXCR4 and/or CXCL12, thereby lowering the invasive and metastatic potential of these cells.

Estrogen effects of Daldinia concentrica and Psathyrella efflorescens extracts in vitro

Daldinia concentrica and Psathyrella efflorescens are two fungi used in African traditional medicine. In the present study, their extracts were evaluated for their steroid activities in estrogen- or androgen-dependent cell lines using as endpoints steroid-dependent transcriptional activity and cell proliferation. Treatment of human breast cancer MCF-7 cells with 15 or 30 microg/ml of Daldinia concentrica or Psathyrellaefflorescens extracts in the absence of 17beta-estradiol (E2) significantly increased the transcriptional activity of an estrogen receptor (ER)-dependent reporter gene, in the same range as E2. Similar data were obtained in gonadotrope cell line alpha-T3-1. All the effects were prevented by the pure estrogen antagonist, ICI 182,780. In the absence of steroid addition, the two extracts induced cell proliferation of ER-dependent MCF-7 and Ishikawa Var-I cell lines by approximately 100% of the E2 response. Combination treatments with E2 showed no competitive or additive effects in the two latter cell lines. Interestingly, the extracts had no androgen-like response in androgen receptor (AR)-positive and ER-negative MDA-MB231 cells, suggesting that fungi effects are estrogen specific and extracts are not toxic at used concentrations. Results provided evidence that Daldinia concentrica or Psathyrellaefflorescens extracts induce estrogen-like effects in ER-positive cell lines, which could be responsible of the effects observed in vivo.

3,3'-diindolylmethane reduces levels of HIF-1alpha and HIF-1 activity in hypoxic cultured human cancer cells

3,3'-diindolylmethane (DIM) is a chemopreventive and chemotherapeutic phytochemical derived from the metabolism of indoles found at high concentrations in cruciferous vegetables. We have previously shown that DIM exhibits anti-angiogenic properties in cultured vascular endothelial cells and in Matrigel plug assays in rodents. In the present study, we demonstrate that DIM reduces the level of hypoxia-inducible factor (HIF)-1alpha in hypoxic tumor cell lines, as well as HIF-1 transcriptional activity as measured by a reporter assay. Moreover, DIM inhibited the expression of HIF-1-responsive endogenous genes, resulting in the reduced expression of key hypoxia responsive factors, VEGF, furin, enolase-1, glucose transporter-1 and phosphofructokinase. DIM reduced the level of HIF-1alpha in hypoxic cells by increasing the rate of the prolylhydroxylase- and proteasome-mediated degradation of HIF-1alpha, and by decreasing the rate of HIF-1alpha transcription. Using enzyme kinetics studies, we established that DIM interacts with the oligomycin-binding site on the F0 transmembrane component of mitochondrial F1F0-ATPase. The contributions of the resulting increases in levels of ROS and O2 in hypoxic cells to the inhibitory effects of DIM on HIF-1alpha expression are discussed. These studies are the first to show that DIM can decrease the accumulation and activity of the key angiogenesis regulatory factor, HIF-1alpha, in hypoxic tumor cells.

Co-planar 3,3',4,4',5-pentachlorinated biphenyl and non-co-planar 2,2',4,6,6'-pentachlorinated biphenyl differentially induce recruitment of oestrogen receptor alpha to aryl hydrocarbon receptor target genes

In the present study we examined the ability of 3,3',4,4',5-pentachlorinated biphenyl [PCB126 (polychlorinated biphenyl 126)], a prototypical AHR (aryl hydrocarbon receptor) agonist, and 2,2',4,6,6'-PCB (PCB104), which does not activate AHR, to induce the recruitment of ERalpha (oestrogen receptor alpha) to CYP1A1 (cytochrome P4501A1 gene) and CYP1B1 promoters in T-47D human breast cancer cells and other cell lines. PCB126 treatment strongly induced CYP1A1 and CYP1B1 mRNA expression that was unaffected by co-treatment with E2 (17beta-oestradiol). PCB104 failed to induce changes in either CYP1A1 or CYP1B1 expression levels. ChIP (chromatin immunoprecipitation) assays show that PCB126, but not PCB104, increased the promoter occupancy by ERalpha to CYP1A1 and CYP1B1 promoters. Co-treatment with PCB126+E2 significantly enhanced the promoter occupancy of ERalpha at CYP1A1, whereas co-treatment with PCB126+4-hydroxytamoxifen or ICI182,780 did not. Competitive binding studies revealed that neither PCB126 nor PCB104 bound to ERalpha. HEK-293 cells (human embryonic kidney-293 cells) stably transfected with ERalpha showed significantly higher PCB126-induced CYP1A1 expression compared with empty vector controls, whereas no increase was observed in cells stably transfected with ERalpha lacking its N-terminal AF1 (activation function-1) domain (ERalphaDeltaAF1). Despite no increase in AHR-mediated gene expression, ChIP assays revealed that ERalphaDeltaAF1 was present at CYP1A1 and CYP1B1 promoters. HC11 mouse mammary cells stably expressing shRNA (small-hairpin RNA) against ERalpha showed an 8-fold reduction in PCB126-dependent Cyp1a1 expression. Our results provide further evidence that AHR agonists induce ERalpha promoter occupancy at AHR target genes through indirect activation of ERalpha, and support a role for ERalpha in AHR transactivation.

Predicting the physiological relevance of in vitro cancer preventive activities of phytochemicals

There is growing interest in the ability of phytochemicals to prevent chronic diseases, such as cancer and heart disease. However, some of these agents have poor bioavailability and many of the in-depth studies into their mechanisms of action have been carried out in vitro using doses which are unachievable in humans. In order to optimize the design of chemopreventive treatment, it is important to determine which of the many reported mechanisms of action are clinically relevant. In this review we consider the physiologically achievable doses for a few of the best studied agents (indole-3-carbinol, diindolylmethane, curcumin, epigallocatechin-3-gallate and resveratrol) and summarize the data derived from studies using these low concentrations in cell culture. We then cite examples of in vitro effects which have been observed in vivo. Finally, the ability of agent combinations to act synergistically or antagonistically is considered. We conclude that each of the compounds shows an encouraging range of activities in vitro at concentrations which are likely to be physiologically relevant. There are also many examples of in vivo studies which validate in vitro observations. An important consideration is that combinations of agents can result in significant activity at concentrations where any single agent is inactive. Thus, for each of the compounds reviewed here, in vitro studies have provided useful insights into their mechanisms of action in humans. However, data are lacking on the full range of activities at low doses in vitro and the benefits or otherwise of combinations in vivo.

Interplay of genes regulated by estrogen and diindolylmethane in breast cancer cell lines

Diindolylmethane (DIM), a biologically active congener of indole-3-carbinol (I3C) derived from cruciferous vegetables, is a promising agent for the prevention of estrogen-sensitive cancers. Both DIM and estrogen affect transcription of genes by binding receptors, such as aryl hydrocarbon receptor (AhR) or estrogen receptors (ER). Gene regulation by DIM and estradiol (E2) can be very complex. While DIM typically binds the AhR, this complex can directly associate with the ER, recruit co-activators that bind to estrogen-responsive promoters, and activate transcription. Alternately, DIM can bind the ER directly. In this study, we have analyzed gene expression using microarray profiling and quantitative real time-polymerase chain reaction in MCF7 breast cancer cells treated with E2 (1 nM) or DIM (25 microM) alone or in combination for 16 h. The interplay of E2 and DIM was reflected in the expression of a subset of genes (<90) in which the combination of E2 and DIM acted either additively or antagonistically to alter gene expression.

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.

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.

Estrogenic effect of procymidone through activation of MAPK in MCF-7 breast carcinoma cell line

Procymidone modifies sexual differentiation in vitro and induces estrogenic activity in primary cultured rainbow trout hepatocytes, as shown by an increase in the contents of vitellogenin and heat shock proteins. Since this dicarboximide fungicide is found in human tissues, it was considered of interest to investigate its ability to induce endocrine damage in the MCF-7 human cell line. The mechanism of this estrogenic action was also evaluated. Procymidone 100 microM stimulated cell growth from day 3 up to day 12 and raised the level of pS2 on day 3. Although procymidone does not bind the estrogen receptor (ER), the antiestrogen ICI 182780 inhibited its effect on cell growth and pS2 content, suggesting that the ER is involved indirectly in these effects. In exploring the mechanism of ER indirect activation we found that the antibody against c-Neu receptor (9G6) did not modify procymidone's effects on cell growth and pS2 expression. Thus, procymidone does not bind the c-Neu membrane receptor, excluding this indirect ER activation pathway. We also found that procymidone induced mitogen-activated protein kinase (MAPK) at 15 and 30 min, and that PD 98059, a MAPK (Erk1/2) inhibitor, prevented procymidone's effects on cell growth and pS2, indicating that MAPK activation is responsible for procymidone ER activation. The production of reactive oxygen species (ROS) with these times and elimination of the phenomenon by alpha-tocopherol (alpha-T), a ROS scavenger, is proof that oxygen free-radical production is at the basis of the MAPK activation by procymidone.

Synthetic dimer of indole-3-carbinol: second generation diet derived anti-cancer agent in hormone sensitive prostate cancer

BACKGROUND

Cruciferous vegetables have been found to have anti-prostate cancer effects. The active compounds mediating these effects include indoles such as indole-3-carbinol (I3C) and isothiocyanates. I3C is unstable having tissue tropic effects and clinical utility has been partly addressed by the synthesis of a more stable dimer diindolylmethane (DIM).

METHODS

Anti-proliferative activity was measured by XTT assay and cytosolic proteins quantitated by Western blot analysis.

RESULTS

DIM (IC(50) 50 microM) is a better anti-proliferative agent than I3C (IC(50) 150 microM) in androgen dependent LNCaP cells, inhibits DNA synthesis, and growth of R1881 stimulated LNCaP cells. Androgen receptor (AR), cyclin D1, and cdk4, induced by R1881, are downregulated by DIM. DIM downregulates phosphorylated Akt and phosphatidyl inositol 3-kinase and downstream inhibition of cyclin D1 and cdk4.

CONCLUSION

These studies provide evidence that DIM is a second-generation chemopreventive agent with a viable cellular target and has clinical potential as an anti-prostate cancer chemopreventive.

Serum free BG-1 cell proliferation assay: A sensitive method for determining organochlorine pesticide estrogen receptor activation at the nanomolar range

Most xenobiotic estrogeniety assay methods rely on direct agonist action on the estrogen receptor (ER) to approximate activation potential. Such methods do have drawbacks since some ER activating pesticides are weak or non-agonistic in ligand-binding assays. This study discusses a method that detects pesticide estrogenic actions regardless of ER ligand binding ability. Using a serum-free BG-1 ovarian cell culture model, we investigated the ability of several organochlorine (OC) pesticides to stimulate known estrogenic actions. We observed concentration dependent ER mediated cell proliferation in BG-1 cells using heptachlor epoxide (HE), beta-hexachlorohexane (beta-HCH), and endosulfan (Endo). In addition, we observed upregulation of the ERE-dependent proteins progesterone receptor and PS2. Gel-shift/EMSA studies for ERE binding further supported these OC's ERE activating abilities. All of these effects were abolished using ICI 164,384(ICI). Using the same culture conditions, we tested the blocking action of growth factor antibodies for erbB2(9G6) and insulin-like growth factor (IGF-Ab) receptors and discovered they inhibited BG-1 proliferation (9G6: HE and beta-HCH/ IGF-Ab: Endo.) This experiment confirms the existence of a possible cross-talk between ER and growth factor receptors in OC ligand-dependent activation and also validates this sensitive method for determining both ligand-dependent and independent estrogenic activity of selected pesticides.

Using salmonid microarrays to understand the dietary modulation of carcinogenesis in rainbow trout

The highlighted article in this issue by Tilton et al. (2005a) is an innovative approach to evaluate the modulation of estrogen receptor (ER) and aryl hydrocarbon (Ah)-receptor pathways as mechanisms underlying indole-3-carbinol (I3C) tumor promotion in rainbow trout (Onchorhynchus mykiss). I3C and its major in vivo component 3,3'-diindolylmethane (DIM) are potent tumor promoters that appear to target both of the aforementioned receptor pathways. However, the relative importance of I3C modulation of ER and AhR-dependent pathways in the promotion of rainbow trout hepatocarcinogenesis has not been established. Previously, researchers within this group reported that I3C promotes aflatoxin B1 (AFB1)-induced trout hepatocarcinogenesis post-initiation at low concentrations in the diet that induce the expression of vitellogenin, a downstream marker for the activation of ER-dependent pathways in fish. Furthermore, the promotional effects of I3C on AFB1 hepatocarcinogenesis in rainbow trout occur at concentrations that differentially induce vitellogenin, but not CYP1A expression. Interestingly, higher I3C concentrations induce the expression of both CYP1A and vitellogenin. Thus, the relative induction of vitellogenin and CYP1A expression, which are respective markers for activation of fish ER and AhR-mediated gene expression, suggest that these pathways may be important for tumor promotion by dietary I3C in trout. Understanding the complexities of I3C-mediated tumor promotion is essential from several perspectives. For example, there is the obvious need to increase our basic understanding of dietary modulation of carcinogenesis. In addition, I3C also exhibits significant antioxidant and cancer chemoprotective effects under certain experimental conditions and in certain models which have led to its recent marketing as a dietary supplement, as well as its development as a possible chemopreventive agent in humans.

Activation and potentiation of interferon-gamma signaling by 3,3'-diindolylmethane in MCF-7 breast cancer cells

3,3'-Diindolylmethane (DIM), a natural autolytic product in plants of the Brassica genus, including broccoli, cauliflower, and Brussels sprouts, exhibits promising cancer protective activities, especially against mammary neoplasia in animal models. We observed previously that DIM induced a G(1) cell-cycle arrest and strong induction of cell-cycle inhibitor p21 expression and promoter activity in both estrogen-responsive and -independent breast cancer cell lines. We showed recently that DIM up-regulates the expression of interferon gamma (IFNgamma) in human MCF-7 breast cancer cells. This novel effect may contribute to the anticancer effects of DIM because IFNgamma plays an important role in preventing the development of primary and transplanted tumors. In this study, we observed that DIM activated the IFNgamma signaling pathway in human breast cancer cells. DIM activated the expression of the IFNgamma receptor (IFNGR1) and IFNgamma-responsive genes p56- and p69-oligoadenylate synthase (OAS). In cotreatments with IFNgamma, DIM produced an additive activation of endogenous p69-OAS and of an OAS-Luc reporter and a synergistic activation of a GAS-Luc reporter. DIM synergistically augmented the IFNgamma induced phosphorylation of signal transducer and activator of transcription factor 1, further evidence of DIM activation of the IFNgamma pathway. DIM and IFNgamma produced an additive inhibition of cell proliferation and a synergistic increase in levels of major histocompatibility complex class-1 (MHC-1) expression, accompanied by increased levels of mRNAs of MHC-1-associated proteins and transporters. These results reveal novel immune activating and potentiating activities of DIM in human tumor cells that may contribute to the established effectiveness of this dietary indole against various tumors types.

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.

Targets for indole-3-carbinol in cancer prevention

Mounting preclinical and clinical evidence indicate that indole-3-carbinol (I3C), a key bioactive food component in cruciferous vegetables, has multiple anticarcinogenic and antitumorigenic properties. Evidence that p21, p27, cyclin-dependent kinases, retinoblastoma, Bax/Bcl-2, cytochrome P-450 1A1 and GADD153 are targets for I3C already exists. Modification of nuclear transcription factors including Sp1, estrogen receptor, nuclear factor kappaB and aryl hydrocarbon receptor may represent a common site of action to help explain downstream cellular responses to dietary I3C and, ultimately, to its anticancer properties. While the current information is intriguing, future I3C research needs to focus on why these changes in nuclear transcription factors occur and how they relate to phenotypic responses and the quantity and duration of exposure to I3C and its dimer 3,3'-diindolylmethane.

Mechanisms of action and antiproliferative properties of Brassica oleracea juice in human breast cancer cell lines

Cruciferous vegetables are an important source of compounds that may be useful for chemoprevention. In this study, we evaluated the antiproliferative activity of juice obtained from leaves of several varieties of Brassica oleracea on both estrogen receptor (ER)-positive (ER+; MCF-7 and BT474) and ER-negative (ER-; MDA-MB-231 and BT20) human breast cancer cell lines. The effect of juice on cell proliferation was evaluated on DNA synthesis and on cell cycle-related proteins. Juice markedly reduced DNA synthesis, evaluated by [3H]thymidine incorporation, starting from low concentrations (final concentration 5-15 mL/L), and this activity was independent of ER. All cauliflower varieties tested suppressed cell proliferation in a dose-dependent manner. Cell growth inhibition was accompanied by significant cell death at the higher juice concentrations, although no evidence of apoptosis was found. Interestingly, the juice displayed a preferential activity against breast cancer cells compared with other mammalian cell lines investigated (ECV304, VERO, Hep2, 3T3, and MCF-10A) (P < 0.01). At the molecular level, the inhibition of proliferation was associated with significantly reduced CDK6 expression and an increased level of p27 in ER+ cells but not in ER- cells, whereas a common feature in all cell lines was significantly decreased retinoblastoma protein phosphorylation. These results suggest that the edible part of Brassica oleracea contains substances that can markedly inhibit the growth of both ER+ and ER- human breast cancer cells, although through different mechanisms. These results suggest that the widely available cruciferous vegetables are potential chemopreventive agents.

DIM stimulates IFNgamma gene expression in human breast cancer cells via the specific activation of JNK and p38 pathways

3,3'-Diindolylmethane (DIM) is a promising anticancer agent derived from Brassica vegetables, but the mechanisms of DIM action are largely unknown. We have shown that DIM can upregulate the expression and stimulate the secretion of interferon-gamma (IFNgamma) in the human MCF-7 breast cancer cell line. This novel effect may provide important clues to explain the anticancer effects of DIM because it is well known that IFNgamma plays an important role in preventing the development of primary and transplanted tumors. Utilizing promoter deletions, we show here that the region between -108 and -36 bp in the IFNgamma promoter, which contains two conserved and essential regulatory elements, is required for DIM-induced IFNgamma expression. DIM activates both JNK and p38 pathways, induces the phosphorylation of c-Jun and ATF-2, and increases the binding of the homodimer or heterodimer of c-Jun/ATF-2 to the proximal AP-1.CREB-ATF-binding element. Moreover, studies with specific enzyme inhibitors showed that up-stream Ca2+-dependent kinase(s) is required for the inducing effects of DIM in MCF-7 cells. These results establish that DIM-induced IFNgamma expression in human breast tumor cells is mediated by activation of both JNK and p38 pathways, which is ultimately dependent on intracellular calcium signaling.

Effects of analogs of indole-3-carbinol cyclic trimerization product in human breast cancer cells

5,6,11,12,17,18-Hexahydrocyclonona[1,2-b:4,5-b*:7,8-b**]triindole (CTr) is a major digestive product of indole-3-carbinol (I3C) from Brassica vegetables and exhibits strong estrogenic activities. CTr increases proliferation of estrogen-dependent breast tumor cells, binds with strong affinity for the estrogen receptor-alpha (ERalpha), and activates expression of estrogen (E(2))-dependent genes. To begin to examine the structural features that determine the biological activity of CTr, we prepared and studied the effects of two analogs, 9,18-dihydro-12H-[1,2,5]trithionino[3,4-b:6,7-b*:9,8-b**]triindole (S(3)CTr) and 5,6,11,12,17,18-hexahydro-5,11,17-trimethylcyclonona[1,2-b:4,5-b*:7,8-b**]triindole (Me(3)CTr). N-Methylation of CTr completely ablated the estrogenic activities of CTr. In the dose range in which CTr was clearly estrogenic, Me(3)CTr exhibited no detectable effect on cell growth, ERalpha binding to E(2), or ERalpha-responsive gene expression. S(3)CTr showed mixed ERalpha agonist activities. It bound to the ERalpha and activated receptor binding with DNA, weakly activated expression of transfected E(2)-responsive reporter gene constructs, and strongly inhibited the E(2)-induced activation of these reporter constructs. S(3)CTr activated aryl hydrocarbon receptor (AhR)-mediated pathways, consistent with the moderately strong binding affinity of S(3)CTr for the AhR. Comparisons of the conformational characteristics among CTr and its two analogs indicated that the estrogenic effects of CTr are highly sensitive to apparently minor structural modifications, and further supported the hypothesis for a central role of hydrogen bonding around the nitrogen atom in CTr binding to the ligand binding site of ERalpha.

Inhibition of Nuclear Translocation of Nuclear Factor-κB Contributes to 3,3′-Diindolylmethane-Induced Apoptosis in Breast Cancer Cells

Dietary indole-3-carbinol (I3C), a natural compound present in vegetables of the genus Brassica, showed clinical benefits and caused apoptosis in breast cancer cells. Our laboratory and others have shown that I3C induces apoptosis in breast cancer cells mediated by inactivation of Akt and nuclear factor-κB (NF-κB) pathway. 3,3′-Diindolylmethane (DIM), a major in vivo acid-catalyzed condensation product of I3C, also showed some benefit in breast cancer. However, the precise molecular mechanism(s) by which DIM induces apoptosis in breast cancer cells has not been fully elucidated. Hence, we investigated whether DIM-induced apoptosis of breast cancer cells could also be mediated by inactivation of Akt and NF-κB. We found that DIM induces apoptotic processes in MCF10A derived malignant (MCF10CA1a) cell lines but not in nontumorigenic parental MCF10A cells. DIM specifically inhibits Akt kinase activity and abrogates the epidermal growth factor–induced activation of Akt in breast cancer cells, similar to those observed for I3C. We also found that DIM reduces phosphorylation of IκBα, an inhibitor of NF-κB. Our confocal microscopy study clearly showed that DIM blocks the translocation of p65, a subunit of NF-κB to the nucleus. DNA binding analysis and transfection studies with IκB kinase cDNA revealed that overexpression of IκB kinase mediates IκBα phosphorylation, which activates NF-κB, and this activation was completely abrogated by DIM treatment. Taken together, these results showed for the first time that the inactivation of Akt and NF-κB activity also plays important roles in DIM-induced apoptosis in breast cancer cells, which seems to be more relevant to in vivo situations.

Innovative agents in cancer prevention

There are many facets to cancer prevention: a good diet, weight control and physical activity, a healthy environment, avoidance of carcinogens such as those in tobacco smoke, and screening of populations at risk to allow early detection. But there is also the possibility of using drugs or naturally occurring compounds to prevent initiation of, or to suppress, tumour growth. Only a few such agents have been used to date in the clinic with any success, and these include non-steroidal anti-inflammatory drugs for colon, finasteride for prostate and tamoxifen or raloxifene for breast tumours. An ideal chemopreventive agent would restore normal growth control to a preneoplastic or cancerous cell population by modifying aberrant signalling pathways or inducing apoptosis (or both) in cells beyond repair. Characteristics for such an agent include selectivity for damaged or transformed cells, good bioavailability and more than one mechanism of action to foil redundancy or crosstalk in signalling pathways. As more research effort is being targeted towards this area, the distinction between chemotherapeutic and chemopreventive agents is blurring. Chemotherapeutic drugs are now being designed to target over- or under-active signalling molecules within cancer cells, a philosophy which is just as relevant in chemoprevention. Development of dietary agents is particularly attractive because of our long-standing exposure to them, their relative lack of toxicity, and encouraging indications from epidemiology. The carcinogenic process relies on the cell's ability to proliferate abnormally, evade apoptosis, induce angiogenesis and metastasise to distant sites. In vitro studies with a number of different diet-derived compounds suggest that there are molecules capable of modulating each of these aspects of tumour growth. However, on the negative side many of them have rather poor bioavailability. The challenge is to uncover their multiple mechanisms of action in order to predict their efficacy, to learn how to use them effectively in combination, and in some cases to redesign them to improve potency or bioavailability. These ideas are illustrated by dietary agents such as indole-3-carbinol (I3C), epigallocatechin gallate (EGCG), curcumin and resveratrol, all of which appear to have a number of different molecular targets, impinging on several signalling pathways. Ultimately it may be possible not only to suppress tumours and to extend quality of life by administering appropriate diet-derived molecules, but also to refine the definition of a cancer chemopreventive diet.

Herbs or natural products that decrease cancer growth part one of a four-part series

PURPOSE/OBJECTIVES

To provide evidence-based research information about 31 herbs and natural products that have shown potential in early research to decrease cancer growth or as adjuncts with cancer treatment.

DATA SOURCES

Names of herbs and natural products with potential to decrease cancer growth have been selected from listings in the Natural Medicines Comprehensive Database and Lawrence Review of Natural Products-Monograph System. Information about these herbs has been found in evidence-based studies cited in references.

DATA SYNTHESIS

In preliminary studies, 31 herbs and natural products appear to have potential for cancer treatment.

CONCLUSIONS

This preliminary evidence may be useful to healthcare professionals and patients with cancer.

IMPLICATIONS FOR NURSING

The information in this article is designed to provide quick access for healthcare professionals working in clinical oncology. Oncology nurses who have this information can become resources for patients and other healthcare professionals.

Estrogenic activity of procymidone in rainbow trout (Oncorhynchus mykiss) hepatocytes: a possible mechanism of action

It is known that procymidone modifies sexual differentiation in vivo and in vitro, and that it induces vitellogenin (Vtg) synthesis in primary cultured rainbow trout hepatocytes. The aim of this study was to evaluate the mechanism underlying this latter in vitro estrogenic action. The cells were treated for 24 h with procymidone 150 microM (with 17beta-estradiol [E2] 20 microM as a positive control) combined with an estrogen receptor (ER) antagonist (tamoxifen 20 microM or ICI 182,780 1 microM) or, given the drug toxic action on the production of reactive oxygen species (ROS), a free radical scavenger (alpha-tocopherol 30 microM). The results from ELISA experiments provided evidence that procymidone Vtg-induction is inhibited by ER antagonists and by alpha-tocopherol suggesting that both ER and ROS are involved in this effect. The ROS detection revealed that the treatment with alpha-tocopherol and tamoxifen completely prevented ROS induction by procymidone, that was not inhibited by ICI 182,780. In exploring the mechanism mediating these events and its timing, we found that procymidone induced mitogen-activated protein kinase (MAPK) at 30 and 60 min, and that this effect was blocked by co-treatment with alpha-tocopherol. In summary, the results of the study clearly support the idea that the estrogenic activity of procymidone in primary cultured trout hepatocytes is mediated by ROS production, and that this activity is similar to that of the ligand-independent ER activation involving MAPK.

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.

Plant-derived 3,3'-Diindolylmethane is a strong androgen antagonist in human prostate cancer cells

3,3'-Diindolylmethane (DIM) is a major digestive product of indole-3-carbinol, a potential anticancer component of cruciferous vegetables. Our results indicate that DIM exhibits potent antiproliferative and antiandrogenic properties in androgen-dependent human prostate cancer cells. DIM suppresses cell proliferation of LNCaP cells and inhibits dihydrotestosterone (DHT) stimulation of DNA synthesis. These activities were not produced in androgen-independent PC-3 cells. Moreover, DIM inhibited endogenous PSA transcription and reduced intracellular and secreted PSA protein levels induced by DHT in LNCaP cells. Also, DIM inhibited, in a concentration-dependent manner, the DHT-induced expression of a prostate-specific antigen promoter-regulated reporter gene construct in transiently transfected LNCaP cells. Similar effects of DIM were observed in PC-3 cells only when these cells were co-transfected with a wild-type androgen receptor expression plasmid. Using fluorescence imaging with green fluorescent protein androgen receptor and Western blot analysis, we demonstrated that DIM inhibited androgen-induced androgen receptor (AR) translocation into the nucleus. Results of receptor binding assays indicated further that DIM is a strong competitive inhibitor of DHT binding to the AR. Results of structural modeling studies showed that DIM is remarkably similar in conformational geometry and surface charge distribution to an established synthetic AR antagonist, although the atomic compositions of the two substances are quite different. Taken together with our published reports of the estrogen agonist activities of DIM, the present results establish DIM as a unique bifunctional hormone disrupter. To our knowledge, DIM is the first example of a pure androgen receptor antagonist from plants.