Biomedical subjects

Stephen Safe

Publications and source records attributed to Stephen Safe.

At least 19 recordsLinked to original sources

PubMed2007

Differential activation of wild-type estrogen receptor alpha and C-terminal deletion mutants by estrogens, antiestrogens and xenoestrogens in breast cancer cells.

17beta-Estradiol (E2), diethylstilbestrol (DES) and several synthetic (or xenoestrogenic) compounds induced transactivation in MCF-7 or MDA-MB-231 cells transfected with wild-type estrogen receptor alpha (ERalpha) and a construct (pERE(3)) containing three tandem estrogen responsive elements (EREs) linked to a luciferase gene. In contrast, the antiestrogens ICI 182,780 and 4-hydroxytamoxifen (4-OHT) were inactive in this assay. We have investigated the effects of these compounds and several structurally-diverse estrogenic compounds on transactivation in cells transfected with pERE(3) and wild-type ERalpha, mutant ERalpha (1-553), and ERalpha (1-537) containing deletions of amino acids 595-554 and 595-538, respectively. These constructs were used to develop an in vitro assay to distinguish between different structural classes of estrogenic compounds. The results obtained using these constructs were highly cell context- and structure-dependent. Neither E2- nor diethylstilbestrol-induced transactivation in MCF-7 (or MDA-MB-231) cells transfected with pERE(3)/ERalpha (1-537) due to partial deletion of helix 12; however, octylphenol and nonlylphenol, resveratrol (a phytoestrogen), kepone and 2',3',4',5'-tetrachloro-4-biphenylol were "estrogenic" in MCF-7 cells transfected with pERE(3)/ERalpha (1-537). Moreover, the structure-dependent estrogenic activities of several synthetic estrogens (xenoestrogens) in MDA-MB-231 cells were different than those observed in MCF-7 cells. These results demonstrate that the estrogenic activity of many synthetic compounds do not require activation function 2 (AF-2) of ERalpha and are mechanistically different from E2. These data suggest that xenoestrogens are selective ER modulators (SERMs).

Breast Neoplasms↗

PubMed2006

1,1-bis(3'-indolyl)-1-(p-substitutedphenyl)methanes inhibit growth, induce apoptosis, and decrease the androgen receptor in LNCaP prostate cancer cells through peroxisome proliferator-activated receptor gamma-independent pathways.

1,1-bis(3'-indolyl)-1-(p-substitutedphenyl)methanes (C-DIMs) containing para-trifluoromethyl, t-butyl, and phenyl groups are a novel class of peroxisome proliferator-activated receptor (PPAR)gamma agonists. In LNCaP prostate cancer cells, these compounds induce PPARgamma-dependent transactivation, inhibit cell proliferation, and induce apoptosis. In addition, these PPARgamma agonists modulate a number of antiproliferative and proapoptotic responses, including induction of p27, activating transcription factor 3, and nonsteroidal anti-inflammatory drug-activated gene-1 and down-regulation of cyclin D1 and caveolin-1. Moreover, the PPARgamma antagonist 2-chloro-5-nitrobenzanilide (GW9662) does not inhibit these effects. The C-DIM compounds also abrogate androgen receptor (AR)-mediated signaling and decrease prostate-specific antigen (PSA) and AR protein expression, and these responses were PPARgamma-independent. The effects of C-DIMs on AR and PSA were due to decreased AR and PSA mRNA expression in LNCaP cells. Thus, this series of methylene-substituted diindolylmethane derivatives simultaneously activate multiple pathways in LNCaP cells, including ablation of androgen-responsiveness and down-regulation of caveolin-1. Both of these responses are associated with activation of proapoptotic pathways in this cell line.

Apoptosis↗

PubMed2006

17beta-estradiol (E2) induces cdc25A gene expression in breast cancer cells by genomic and non-genomic pathways.

Cdc25A is a potent tyrosine phosphatase that catalyzes specific dephosphorylation of cyclin/cyclin-dependent kinase (cdk) complexes to regulate G1 to S-phase cell cycle progression. Cdc25A mRNA levels are induced by 17beta-estradiol (E2) in ZR-75 breast cancer cells, and deletion analysis of the cdc25A promoter identified the -151 to -12 region as the minimal E2-responsive sequence. Subsequent mutation/deletion analysis showed that at least three different cis-elements were involved in activation of cdc25A by E2, namely, GC-rich Sp1 binding sites, CCAAT motifs that bind NF-Y, and E2F sites that bind DP/E2F1 proteins. Studies with inhibitors and dominant negative expression plasmids show that E2 activates cdc25A expression through activation of genomic ERalpha/Sp1 and E2F1 and cAMP-dependent activation of NF-YA. Thus, both genomic and non-genomic pathways of estrogen action are involved in induction of cdc25A in breast cancer cells.

Base Composition↗

PubMed2006

The 2005 World Health Organization reevaluation of human and Mammalian toxic equivalency factors for dioxins and dioxin-like compounds.

In June 2005, a World Health Organization (WHO)-International Programme on Chemical Safety expert meeting was held in Geneva during which the toxic equivalency factors (TEFs) for dioxin-like compounds, including some polychlorinated biphenyls (PCBs), were reevaluated. For this reevaluation process, the refined TEF database recently published by Haws et al. (2006, Toxicol. Sci. 89, 4-30) was used as a starting point. Decisions about a TEF value were made based on a combination of unweighted relative effect potency (REP) distributions from this database, expert judgment, and point estimates. Previous TEFs were assigned in increments of 0.01, 0.05, 0.1, etc., but for this reevaluation, it was decided to use half order of magnitude increments on a logarithmic scale of 0.03, 0.1, 0.3, etc. Changes were decided by the expert panel for 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.3), 1,2,3,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.03), octachlorodibenzo-p-dioxin and octachlorodibenzofuran (TEFs = 0.0003), 3,4,4',5-tetrachlorbiphenyl (PCB 81) (TEF = 0.0003), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) (TEF = 0.03), and a single TEF value (0.00003) for all relevant mono-ortho-substituted PCBs. Additivity, an important prerequisite of the TEF concept was again confirmed by results from recent in vivo mixture studies. Some experimental evidence shows that non-dioxin-like aryl hydrocarbon receptor agonists/antagonists are able to impact the overall toxic potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds, and this needs to be investigated further. Certain individual and groups of compounds were identified for possible future inclusion in the TEF concept, including 3,4,4'-TCB (PCB 37), polybrominated dibenzo-p-dioxins and dibenzofurans, mixed polyhalogenated dibenzo-p-dioxins and dibenzofurans, polyhalogenated naphthalenes, and polybrominated biphenyls. Concern was expressed about direct application of the TEF/total toxic equivalency (TEQ) approach to abiotic matrices, such as soil, sediment, etc., for direct application in human risk assessment. This is problematic as the present TEF scheme and TEQ methodology are primarily intended for estimating exposure and risks via oral ingestion (e.g., by dietary intake). A number of future approaches to determine alternative or additional TEFs were also identified. These included the use of a probabilistic methodology to determine TEFs that better describe the associated levels of uncertainty and "systemic" TEFs for blood and adipose tissue and TEQ for body burden.

Animals↗

PubMed2006

The role of xenoestrogenic compounds in the development of breast cancer.

Lifetime exposure to endogenous steroidal estrogens is an established risk factor for breast cancer, and exposures to other estrogenic and antiestrogenic compounds might also modify the risk of breast cancer. It has been hypothesized that synthetic estrogenic industrial pollutants such as organochlorine compounds and plant-derived estrogenic compounds also modify breast cancer risks; however, recent studies show that levels of organochlorine pollutants are similar in breast cancer patients and controls. There is evidence that synthetic and plant-derived estrogens are selective estrogen receptor modulators, which implies that these compounds can induce tissue-specific, time- and dose-dependent estrogenic or antiestrogenic responses. Therefore, the effects of synthetic or plant-derived estrogens on the incidence of breast cancer depend on both the levels and the timing of exposure to these compounds, particularly during stages of mammary gland development that are extremely sensitive to hormone levels.

Breast Neoplasms↗

PubMed2006

Tolfenamic acid and pancreatic cancer growth, angiogenesis, and Sp protein degradation.

BACKGROUND: Sp1, Sp3, and Sp4 are transcription factors that regulate cell proliferation and vascular endothelial growth factor (VEGF) expression and are overexpressed in many cancer cell lines. For some cancers, Sp1 overexpression is associated with poor survival. Cyclooxygenase inhibitors decrease Sp1 expression in cancer cells, and therefore different structural classes of nonsteroidal anti-inflammatory drugs (NSAIDs) were screened for their ability to decrease levels of Sp1, Sp3, and Sp4 and to decrease pancreatic tumor growth and metastasis in an in vivo model. METHODS: Levels of Sp1, Sp3, Sp4, and VEGF proteins in pancreatic cancer cell lines were assessed by immunoblot analysis. mRNA was assessed by reverse transcription-polymerase chain reaction. Panc-1 pancreatic cancer cells transfected with VEGF promoter constructs were used to assess VEGF promoter activation. Pancreatic tumor weight and size and liver metastasis were assessed in an orthotopic mouse model of pancreatic cancer (groups of 10 mice). Protein expression in tumors was assessed immunohistochemically. RESULTS: Tolfenamic acid and structurally related biaryl derivatives induced degradation of Sp1, Sp3, and Sp4 in pancreatic cancer cells. Tolfenamic acid also inhibited VEGF mRNA and protein expression in pancreatic cancer cells; this inhibition was associated with the decreased Sp-dependent activation of the VEGF promoter. In the mouse model for pancreatic cancer, treatment with tolfenamic acid (50 mg/kg of body weight), compared with control treatment, statistically significantly decreased tumor growth and weight (P = .005), liver metastasis (P = .027), and levels of Sp3 and VEGF (P = .009) and Sp1 and Sp4 (P = .006) proteins in tumors. For example, tumors from mice treated with tolfenamic acid (50 mg/kg) had statistically significantly lower VEGF levels (45%, 95% confidence interval = 39% to 51%; P = .009) than tumors from control mice. CONCLUSIONS: Tolfenamic acid is a new antipancreatic cancer NSAID that activates degradation of transcription factors Sp1, Sp3, and Sp4; reduces VEGF expression; and decreases tumor growth and metastasis.

Animals↗

PubMed2006

Molecular mechanism of inhibitory aryl hydrocarbon receptor-estrogen receptor/Sp1 cross talk in breast cancer cells.

The trifunctional carbamoylphosphate synthetase/aspartate transcarbamyltransferase/dihydroorotase (CAD) gene is hormone responsive in MCF-7 and ZR-75 breast cancer cells, and this response is inhibited by the aryl hydrocarbon receptor (AhR) agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Estrogen-dependent induction of CAD mRNA and reporter gene activity in cells transfected with constructs (pCAD) containing hormone-responsive GC-rich CAD promoter inserts involves estrogen receptor alpha (ERalpha)/Sp1 interactions with these proximal GC-rich motifs. TCDD also inhibits hormone-induced transactivation in MCF-7 and ZR-75 cells transfected with pCAD constructs. The mechanism of inhibitory AhR-ERalpha/Sp1 cross talk was further investigated by chromatin immunoprecipitation (ChIP), and the results show that ERalpha/Sp1 and the AhR are constitutively bound to the CAD gene promoter and only minor changes are observed after treatment with 17beta-estradiol, TCDD, or their combination. However, examination of interactions of these transcription factors by fluorescence resonance energy transfer shows that E2 enhances ERalpha-Sp1 interactions, whereas cotreatment with TCDD significantly decreases interaction of these proteins. These results suggest that inhibitory AhR-ERalpha/Sp1 cross talk is due, in part, to enhanced association of AhR and ERalpha (also determined by fluorescence resonance energy transfer), which coordinately dissociates ER and Sp1 and decreases ERalpha/Sp1-mediated transactivation, whereas remaining associated with the CAD promoter. This represents a novel interaction between two ligand activated receptors where one receptor inhibits activation of the second receptor.

Animals↗

PubMed2006

Structure-dependent Ah receptor agonist activities of chlorinated biphenylenes.

Polychlorinated biphenylenes (PCBP) have been identified as combustion by-products that bind the aryl hydrocarbon receptor (AhR) and exhibit 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like activity. This study investigates the Ah-responsiveness of 2,3,6,7-tetrachlorobiphenylene (2,3,6,7-CBP), 2,3,6-CBP, 2,3-CBP and 2-CBP in breast cancer cells. MCF-7 or ZR-75 cells were treated with different concentrations (1-100 nM) of the compounds alone to determine their activity as inducers of CYP1A1 protein expression or luciferase activity in cells transfected with a construct (pDRE(3)) containing three tandem dioxin responsive elements (DREs) linked to a luciferase reporter gene. In both assays, the order of potency was 2,3,6,7-CBP>2,3,6-CBP>2,3-CBP approximately 2-CBP, and 2,3,6,7-CBP and TCDD were equipotent. Similar results were also observed in an antiestrogenic assay in MCF-7 cells, confirming the high AhR agonist activity of 2,3,6,7-CBP in breast cancer cells.

Blotting, Western↗

PubMed2006

Regulation of vascular endothelial growth factor receptor-2 expression in pancreatic cancer cells by Sp proteins.

Vascular endothelial growth factor receptor-2 (VEGFR2/KDR) is an important mediator of angiogenesis, and VEGFR2 mRNA is expressed in several pancreatic cancer cell lines. Deletion analysis of the VEGFR2 promoter in Panc-1, AsPC-1, and MiaPaCa-2 pancreatic cancer cells shows that the proximal region of the promoter is primarily responsible for VEGFR2 expression, and two GC-rich sites at -58 and -44 are critical elements in all three cell lines. Panc-1, AsPC-1, and MiaPaCa-2 cells also express Sp1, Sp3, and Sp4 proteins which bind to the GC-rich region of the VEGFR2 promoter in electrophoretic mobility shift and chromatin immunoprecipitation assays. RNA interference with small inhibitory RNAs for Sp1, Sp3, and Sp4 decreases VEGFR2 mRNA and reporter gene activity in transfection assays, confirming that VEGFR2 expression in pancreatic cancer cells is regulated by Sp proteins. These results suggest that VEGFR2 cannot only be targeted by receptor tyrosine kinase inhibitors but also by drugs that downregulate Sp proteins or block Sp-dependent transactivation.

Cell Line, Tumor↗

PubMed2006

Vascular endothelial growth factor receptor-2 expression is induced by 17beta-estradiol in ZR-75 breast cancer cells by estrogen receptor alpha/Sp proteins.

Vascular endothelial growth factor receptor-2 kinase insert domain receptor (VEGFR2/KDR) is critical for angiogenesis, and VEGFR2 mRNA and protein are expressed in ZR-75 breast cancer cells and induced by 17beta-estradiol (E2). Deletion analysis of the VEGFR2 promoter indicates that the proximal GC-rich region is required for both basal and hormone-induced transactivation, and mutation of one or both of the GC-rich motifs at -58 and -44 results in loss of transactivation. Electrophoretic mobility shift and chromatin immunoprecipitation assays show that Sp1, Sp3, and Sp4 proteins bind the GC-rich region of the VEGFR2 promoter. Results of the chromatin immunoprecipitation assay also demonstrate that ERalpha is constitutively bound to the VEGFR2 promoter and that these interactions are not enhanced after treatment with E2, whereas ERalpha binding to the region of the pS2 promoter containing an estrogen-responsive element is enhanced by E2. RNA interference studies show that hormone-induced activation of the VEGFR2 promoter constructs requires Sp3 and Sp4 but not Sp1, demonstrating that hormonal activation of VEGFR2 involves a nonclassical mechanism in which ERalpha/Sp3 and ERalpha/Sp4 complexes activate GC-rich sites where Sp proteins but not ERalpha bind DNA. These results show for the first time that Sp3 and Sp4 cooperatively interact with ERalpha to activate VEGFR2 and are in contrast to previous results showing that several hormone-responsive genes are activated by ERalpha/Sp1 in breast cancer cell lines.

Base Sequence↗

PubMed2006

Effects of benzo-a-pyrene on oxytocin-induced Ca2+ oscillations in myometrial cells.

Benzo-a-pyrene (BaP) is a polycyclic aromatic hydrocarbon that exists as a major environmental pollutant. The effect of this carcinogen/mutagen upon myometrial Ca(2+) signaling in a human myometrial cell line (PHM1) was examined. Exposure of cells to BaP did not alter basal Ca(2+) levels or the inositol(1,4,5) trisphosphate-releasable Ca(2+) pool. However, BaP significantly decreased the initial oxytocin-induced Ca(2+) transient and the frequency of oxytocin-induced Ca(2+)oscillations as well as delayed their onset. To determine the specific effects of BaP, pharmacologic agents that target intracellular Ca(2+) homeostasis mechanisms were used. Genistein (a non-specific tyrosine kinase inhibitor) and AG1478 (an epidermal growth factor receptor blocker) markedly reduced the oxytocin-induced Ca(2+) oscillations in control, but had no effect in BaP treated cells. Addition of epidermal growth factor or serum before or after oxytocin restored the Ca(2+) oscillations in BaP treated cells to a level similar to control cells, while the K(+) channel blocker tetraethylammonium chloride, partially restored the Ca(2+) response. These data suggest that the tyrosine kinase pathway, which is part of the G-protein coupled receptor pathway response to oxytocin in PHM1 cells, is a target of BaP action and that EGF or serum can restore the oxytocin-induced Ca(2+) oscillations.

Adult↗

PubMed2006

3-Methylcholanthrene and other aryl hydrocarbon receptor agonists directly activate estrogen receptor alpha.

3-Methylcholanthrene (3MC) is an aryl hydrocarbon receptor (AhR) agonist, and it has been reported that 3MC induces estrogenic activity through AhR-estrogen receptor alpha (ER alpha) interactions. In this study, we used 3MC and 3,3',4,4',5-pentachlorobiphenyl (PCB) as prototypical AhR ligands, and both compounds activated estrogen-responsive reporter genes/gene products (cathepsin D) in MCF-7 breast cancer cells. The estrogenic responses induced by these AhR ligands were inhibited by the antiestrogen ICI 182780 and by the transfection of a small inhibitory RNA for ER alpha but were not affected by the small inhibitory RNA for AhR. These results suggest that 3MC and PCB directly activate ER alpha, and this was confirmed in a competitive ER alpha binding assay and in a fluorescence resonance energy transfer experiment in which PCB and 3MC induced CFP-ER alpha/YFP-ER alpha interactions. In a chromatin immunoprecipitation assay, PCB and 3MC enhanced ER alpha (but not AhR) association with the estrogen-responsive region of the pS2 gene promoter. Moreover, in AhR knockout mice, 3MC increased uterine weights and induced expression of cyclin D1 mRNA levels. These results show that PCB and 3MC directly activate ER alpha-dependent transactivation and extend the number of ligands that activate both AhR and ER alpha.

Animals↗

PubMed2006

Activation of kinase pathways in MCF-7 cells by 17beta-estradiol and structurally diverse estrogenic compounds.

17beta-Estradiol (E2) activates non-genomic pathways in MCF-7 cells, and this study investigates the effects of structurally-diverse estrogenic compounds on activation of mitogen-activated protein kinase (MAPK), phosphatidylinositol-3-kinase (PI3-K), protein kinase C (PKC), PKA, and calcium calmodulin-dependent kinase IV (CaMKIV). Activation of kinases was determined by specific substrate phosphorylation and transactivation assays that were diagnostic for individual kinases. The compounds investigated in this study include E2, diethylstilbestrol (DES), the phytoestrogen resveratrol, and the following synthetic xenoestrogens, bisphenol-A (BPA), nonylphenol, octylphenol, endosulfan, kepone, 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), and 2',3',4',5'-tetrachloro-4-biphenylol (HO-PCB-Cl(4)). With the exception of resveratrol, all the compounds activated PI3-K and MAPK. Activation of PKC by the xenoestrogens was structure-dependent since resveratrol, kepone and HO-PCB-Cl(4) were inactive and only minimal activation of PKA was observed. CaMKIV was activated only by E2 and DES, and HO-PCB-Cl(4) was a potent inhibitor of CaMKIV-dependent activity. These results demonstrate that activation of estrogen receptor-alpha-mediated non-genomic pathways by estrogenic compounds in MCF-7 cells is structure-dependent and can result in activation or inhibition of kinase activities.

Benzhydryl Compounds↗

PubMed2006

Inhibition of bladder tumor growth by 1,1-bis(3'-indolyl)-1-(p-substitutedphenyl)methanes: a new class of peroxisome proliferator-activated receptor gamma agonists.

1,1-Bis(3'-indolyl)-1-(p-substitutedphenyl)methanes containing p-trifluoromethyl (DIM-C-pPhCF3), p-t-butyl (DIM-C-pPhtBu), and phenyl (DIM-C-pPhC6H5) substituents have been identified as a new class of peroxisome proliferator-activated receptor gamma (PPARgamma) agonists that exhibit antitumorigenic activity. The PPARgamma-active C-DIMs have not previously been studied against bladder cancer. We investigated the effects of the PPARgamma-active C-DIMs on bladder cancer cells in vitro and bladder tumors in vivo. In this study, the PPARgamma-active compounds inhibited the proliferation of KU7 and 253J-BV bladder cancer cells, and the corresponding IC50 values were 5 to 10 and 1 to 5 micromol/L, respectively. In the less responsive KU7 cells, the PPARgamma agonists induced caveolin-1 and p21 expression but no changes in cyclin D1 or p27; in 253J-BV cells, the PPARgamma agonists did not affect caveolin-1, cyclin D1, or p27 expression but induced p21 protein. In KU7 cells, induction of caveolin-1 by each of the PPARgamma agonists was significantly down-regulated after cotreatment with the PPARgamma antagonist GW9662. DIM-C-pPhCF3 (60 mg/kg thrice a week for 4 weeks) inhibited the growth of implanted KU7 orthotopic and s.c. tumors by 32% and 60%, respectively, and produced a corresponding decrease in proliferation index. Treatment of KU7 cells with DIM-C-pPhCF3 also elevated caveolin-1 expression by 25% to 30%, suggesting a role for this protein in mediating the antitumorigenic activity of DIM-C-pPhCF3 in bladder cancer.

Animals↗

PubMed2006

1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methanes inhibit colon cancer cell and tumor growth through PPARgamma-dependent and PPARgamma-independent pathways.

1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methanes containing p-trifluoromethyl, t-butyl, and phenyl [1,1-bis(3'-indolyl)-1-(p-phenyl)methane (DIM-C-pPhC(6)H(5))] substituents induce peroxisome proliferator-activated receptor gamma (PPARgamma)-mediated transactivation in SW480 colon cancer cells. These PPARgamma-active compounds also inhibit cell proliferation and modulate some cell cycle proteins. At concentrations from 2.5 to 7.5 micromol/L, the PPARgamma agonists induce caveolin-1 and phosphorylation of Akt and cotreatment with the PPARgamma antagonist GW9662 inhibited the induction response. In contrast, higher concentrations (10 micromol/L) of 1,1-bis(3'-indolyl)-1-(p-substituted phenyl)methanes containing 1,1-bis(3'-indolyl)-1-(p-trifluoromethyl)methane and DIM-C-pPhC(6)H(5) induce apoptosis, which is PPARgamma independent. This was accompanied by loss of caveolin-1 induction but induction of proapoptotic nonsteroidal anti-inflammatory drug activated gene-1. In athymic nude mice bearing SW480 cell xenografts, DIM-C-pPhC(6)H(5) inhibits tumor growth at doses of 20 and 40 mg/kg/d and immunohistochemical staining of the tumors showed induction of apoptosis and nonsteroidal anti-inflammatory drug activated gene-1 expression. Thus, the indole-derived PPARgamma-active compounds induce both receptor-dependent and receptor-independent responses in SW480 cells, which are separable over a narrow range of concentrations. This dual mechanism of action enhances their antiproliferative and anticancer activities.

Animals↗

PubMed2006

1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methanes inhibit ovarian cancer cell growth through peroxisome proliferator-activated receptor-dependent and independent pathways.

1,1-Bis(3'-indolyl)-1-(p-t-butylphenyl)methane (DIM-C-pPhtBu) is a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, and treatment of SKOV3 ovarian cancer cells with this compound (5 micromol/L) inhibits cell proliferation, whereas up to 15 micromol/L rosiglitazone had no effect on cell growth. DIM-C-pPhtBu also inhibits G0-G1 to S phase cell cycle progression and this is linked, in part, to PPARgamma-dependent induction of the cyclin-dependent kinase inhibitor p21. DIM-C-pPhtBu induces PPARgamma-independent down-regulation of cyclin D1 and we therefore further investigated activation of receptor-independent pathways. DIM-C-pPhtBu also induced apoptosis in SKOV3 cells and this was related to induction of glucose-related protein 78, which is typically up-regulated as part of the unfolded protein response during endoplasmic reticulum (ER) stress. Activation of ER stress was also observed in other ovarian cancer cell lines treated with DIM-C-pPhtBu. In addition, DIM-C-pPhtBu induced CCAAT/enhancer binding protein homologous protein through both ER stress and c-jun NH2-terminal kinase-dependent pathways, and CCAAT/enhancer binding protein homologous protein activated death receptor 5 and the extrinsic pathway of apoptosis. These results show that DIM-C-pPhtBu inhibits growth and induces apoptosis in ovarian cancer cells through both PPARgamma-dependent and PPARgamma-independent pathways, and this complex mechanism of action will be advantageous for future clinical development of these compounds for treatment of ovarian cancer.

Animals↗

PubMed2006

Aryl hydrocarbon receptor agonists directly activate estrogen receptor alpha in MCF-7 breast cancer cells.

The aryl hydrocarbon receptor (AhR) binds with high affinity to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related halogenated aromatics, but also binds with lower affinity to structurally diverse exogenous and endogenous chemicals. One study reported that 3-methylcholanthrene (3MC) activated the estrogen receptor (ER) through the AhR, which acts as co-regulatory protein, whereas a recent report showed that 3MC directly bound and activated ERalpha. This study also shows that the AhR agonists benzo[a]pyrene, 3,3',4,4'-tetrachlorobiphenyl, chrysin, 6-methyl-1,3,8-trichlorodibenzofuran, and 3,3'-diindolylmethane also induce ERalpha-dependent transactivation. Moreover, in chromatin immunoprecipitation assays, these compounds induce binding of AhR and ERalpha to the CYP1A1 and pS2 gene promoters, which is consistent with their activities as both selective AhR modulators (SAhRMs) and selective ER modulators (SERMs).

Benzo(a)pyrene↗

PubMed2005

3,3'-diindolylmethane (DIM) and its derivatives induce apoptosis in pancreatic cancer cells through endoplasmic reticulum stress-dependent upregulation of DR5.

3,3'-Diindolylmethane (DIM), ring-substituted DIMs and 1,1-bis(3'-indolyl)-1-(p-substitutedphenyl)methanes (C-DIMs) inhibit growth of Panc-1 and Panc-28 pancreatic cancer cells. Although DIMs (diarylmethanes) and selected C-DIMs (triarylmethanes), such as the p-t-butyl derivative (DIM-C-pPhtBu), activate the aryl hydrocarbon receptor and peroxisome proliferator-activated receptor gamma, respectively, this study shows that both DIM and DIM-C-pPhtBu induce common receptor-independent pathways. Both DIM and DIM-C-pPhtBu increased endoplasmic reticulum (ER) staining and ER calcium release in Panc-1 cells, and this was accompanied by increased expression of glucose related protein 78 and C/EBP homologous transcription factor (CHOP/GADD153) proteins. Similar results were observed after treatment with thapsigargin (Tg), a prototypical inducer of ER stress. The subsequent downstream effects of DIM/DIM-C-pPhtBu- and Tg-induced ER stress included CHOP-dependent induction of death receptor DR5 and subsequent cleavage of caspase 8, caspase 3, Bid and PARP. Activation of both receptor-dependent and receptor-independent (ER stress) pathways by DIM and DIM-C-pPhtBu in pancreatic cancer cells enhances the efficacy and potential clinical importance of these compounds for cancer chemotherapeutic applications.

Anticarcinogenic Agents↗