Effects of tetramethoxystilbene on hormone-resistant breast cancer cells: biological and biochemical mechanisms of action

The Aryl Hydrocarbon Receptor and Its Crosstalk: A Chemopreventive Target of Naturally Occurring and Modified Phytochemicals

The aryl hydrocarbon receptor (AhR) is an environmentally sensitive transcription factor (TF) historically associated with carcinogenesis initiation via the activation of numerous carcinogens. Nowadays, the AhR has been attributed to multiple endogenous functions to maintain cellular homeostasis. Moreover, crosstalk, often reciprocal, has been found between the AhR and several other TFs, particularly estrogen receptors (ERs) and nuclear factor erythroid 2-related factor-2 (Nrf2). Adequate modulation of these signaling pathways seems to be an attractive strategy for cancer chemoprevention. Several naturally occurring and synthetically modified AhR or ER ligands and Nrf2 modulators have been described. Sulfur-containing derivatives of glucosinolates, such as indole-3-carbinol (I3C), and stilbene derivatives are particularly interesting in this context. I3C and its condensation product, 3,3'-diindolylmethane (DIM), are classic examples of blocking agents that increase drug-metabolizing enzyme activity through activation of the AhR. Still, they also affect multiple essential signaling pathways in preventing hormone-dependent cancer. Resveratrol is a competitive antagonist of several classic AhR ligands. Its analogs, with ortho-methoxy substituents, exert stronger antiproliferative and proapoptotic activity. In addition, they modulate AhR activity and estrogen metabolism. Their activity seems related to a number of methoxy groups introduced into the stilbene structure. This review summarizes the data on the chemopreventive potential of these classes of phytochemicals, in the context of AhR and its crosstalk modulation.

Induction of synergistic apoptosis by tetramethoxystilbene and nutlin-3a in human cervical cancer cells

2,4,3',5'-Tetramethoxystilbene (TMS) is a selective inhibitor of cytochrome P450 1B1 to block the conversion from estradiol to 4-OH-estradiol. Several studies suggested that TMS may act as a potent anti-cancer agent for hormone-related cancer including cervical cancer. Nutlin-3a is a cis-imidazoline analog that interferes with the interaction between mouse double minute 2 homolog (MDM2) and the tumor suppressor p53. The purpose of the study was to compare the cytotoxic effect of TMS and nutlin-3a treatment individually and in combination in HeLa cells. To assess the potential synergistic effects between TMS and nutlin-3a, low concentrations of TMS and nutlin-3a were simultaneously treated in HeLa cells. Based on cell viability, apoptosis assays, and the increase in cleaved caspase-3 and poly (ADP-ribose) polymerase cleavage, it was demonstrated that the combination with TMS and nutlin-3a exerts a synergistic effect on cancer cell death. Isobologram analysis of HeLa cells noted synergism between TMS and nutlin-3a. The combined treatment increased the expression of mitochondrial pro-apoptotic factors such as Bax and Bak, and decreased the expression of the XIAP. In addition, combination treatment significantly enhanced the translocation of AIF to the nucleus in HeLa cells. In conclusion, the results demonstrate that the combination of TMS and nutlin-3a induces synergistic apoptosis in HeLa cells, suggesting the possibility that this combination can be applied as a novel therapeutic strategy for cervical cancer.

CYP1B1 Augments the Mesenchymal, Claudin-Low, and Chemoresistant Phenotypes of Triple-Negative Breast Cancer Cells

Cytochrome P4501B1 (CYP1B1) is elevated in breast cancer. Studies indicate a relationship between CYP1B1 and aggressive cancer phenotypes. Here, we report on in vitro studies in triple-negative breast cancer cell lines, where knockdown (KD) of CYP1B1 was used to determine the influence of its expression on invasive cell phenotypes. CYP1B1 KD in MDA-MB-231 cells resulted in the loss of mesenchymal morphology, altered expression of epithelial-mesenchymal genes, and increased claudin (CLDN) RNA and protein. CYP1B1 KD cells had increased cell-to-cell contact and paracellular barrier function, a reduced rate of cell proliferation, abrogation of migratory and invasive activity, and diminished spheroid formation. Analysis of clinical breast cancer tumor samples revealed an association between tumors exhibiting higher CYP1B1 RNA levels and diminished overall and disease-free survival. Tumor expression of CYP1B1 was inversely associated with CLDN7 expression, and CYP1B1HI/CLDN7LOW identified patients with lower median survival. Cells with CYP1B1 KD had an enhanced chemosensitivity to paclitaxel, 5-fluorouracil, and cisplatin. Our findings that CYP1B1 KD can increase chemosensitivity points to therapeutic targeting of this enzyme. CYP1B1 inhibitors in combination with chemotherapeutic drugs may provide a novel targeted and effective approach to adjuvant or neoadjuvant therapy against certain forms of highly metastatic breast cancer.

Cytochrome P450 1B1 Overexpression in Cervical Cancers: Cross-sectional Study

Background

Current standard treatments for patients with recurrent cervical cancer are not very effective and are associated with severe toxicity. Recently, the rational approach for the discovery of new therapies for cervical cancer is based on the alterations in the molecular biology of cancer cells. One of the emerging molecular changes in cancer cells is the aberrant expression of cytochrome P450 1B1 (CYP1B1). This unique enzyme has been reported to be selectively overexpressed in several cancers.

Objective

The aim of this study was to examine CYP1B1 expression in cervical cancers and to assess the enzyme’s relationship with several clinicopathological features.

Methods

Immunohistochemistry was performed to examine CYP1B1 expression in 100 patient samples with cervical cancer and 10 patient samples with normal healthy cervical tissues.

Results

CYP1B1 was expressed in the majority of the cervical cancer samples (91/100, 91.0%) but not in normal healthy cervical samples. The difference in the expression of CYP1B1 between healthy and tumorous cervical tissues was significant (P=.01). Moreover, the frequency of CYP1B1 expression was found to be significantly higher in patients with advanced grades of the disease (P=.03) and in patients having metastasis to the lymph nodes (P=.01). Surprisingly, there was a significantly higher expression of CYP1B1 in patients with a high prevalence of human papilloma virus 16/18 (P=.04).

Conclusions

The differential profile of CYP1B1 expression between cervical cancer tissues and normal cervical tissues suggests that CYP1B1 may be used as a target for future therapeutic exploitations.

GPER is involved in the regulation of the estrogen-metabolizing CYP1B1 enzyme in breast cancer

The cytochrome P450 1B1 (CYP1B1) is a heme-thiolate monooxygenase involved in both estrogen biosynthesis and metabolism. For instance, CYP1B1 catalyzes the hydroxylation of E2 leading to the production of 4-hydroxyestradiol that may act as a potent carcinogenic agent. In addition, CYP1B1 is overexpressed in different tumors including breast cancer. In this scenario, it is worth mentioning that CYP1B1 expression is triggered by estrogens through the estrogen receptor (ER)α in breast cancer cells. In the present study, we evaluated whether the G protein estrogen receptor namely GPER may provide an alternate route toward the expression and function of CYP1B1 in ER-negative breast cancer cells, in main players of the tumor microenvironment as cancer associated fibroblasts (CAFs) that were obtained from breast cancer patients, in CAFs derived from a cutaneous metastasis of an invasive mammary ductal carcinoma and in breast tumor xenografts. Our results show that GPER along with the EGFR/ERK/c-Fos transduction pathway can lead to CYP1B1 regulation through the involvement of a half-ERE sequence located within the CYP1B1 promoter region. As a biological counterpart, we found that both GPER and CYP1B1 mediate growth effects in vitro and in vivo. Altogether, our data suggest that estrogens in ER-negative cell contexts may engage the alternate GPER signaling toward CYP1B1 regulation. Estrogen-CYP1B1 landscape via GPER should be taken into account in setting novel pharmacological approaches targeting breast cancer development.

Chemoprevention of Colorectal Cancer by Artocarpin, a Dietary Phytochemical from Artocarpus heterophyllus

Artocarpus heterophyllus is an evergreen tree distributed in tropical regions, and its fruit (jackfruit) is well-known as the world's largest tree-borne fruit. Although A. heterophyllus has been widely used in folk medicines against inflammation, its potential in cancer chemoprevention remains unclear. Herein we identified artocarpin from A. heterophyllus as a promising colorectal cancer chemopreventive agent by targeting Akt kinase. Phenotypically, artocarpin exhibited selective cytotoxicity against human colon cancer cells. Artocarpin impaired the anchorage-independent growth capability, suppressed colon cancer cell growth, and induced a G1 phase cell cycle arrest which was followed by apoptotic as well as autophagic cell death. Mechanistic studies revealed that artocarpin directly targeted Akt 1 and 2 kinase activity evidenced by in vitro kinase assay, ex vivo binding assay as well as Akt downstream cellular signal transduction. Importantly, oral administration of artocarpin attenuated colitis-associated colorectal tumorigenesis in mice. Taken together, artocarpin, a bioactive component of A. heterophyllus, might merit investigation as a potential colorectal cancer chemopreventive agent.

Anticancer Activity of Stilbene-Based Derivatives

Stilbene is an abundant structural scaffold in nature, and stilbene-based compounds have been widely reported for their biological activity. Notably, (E)-resveratrol and its natural stilbene-containing derivatives have been extensively investigated as cardioprotective, potent antioxidant, anti-inflammatory, and anticancer agents. Starting from its potent chemotherapeutic activity against a wide variety of cancers, the stilbene scaffold has been subject to synthetic manipulations with the aim of obtaining new analogues with improved anticancer activity and better bioavailability. Within the last decade, the majority of new synthetic stilbene derivatives have demonstrated significant anticancer activity against a large number of cancer cell lines, depending on the type and position of substituents on the stilbene skeleton. This review focuses on the structure-activity relationship of the key compounds containing a stilbene scaffold and describes how the structural modifications affect their anticancer activity.

Potential role of CYP1B1 in the development and treatment of metabolic diseases

Cytochrome P450 1B1 (CYP1B1), a member of CYP superfamily, is expressed in liver and extrahepatic tissues carries out the metabolism of numerous xenobiotics, including metabolic activation of polycyclic aromatic hydrocarbons. Surprisingly, CYP1B1 was also shown to be important in regulating endogenous metabolic pathways, including the metabolism of steroid hormones, fatty acids, melatonin, and vitamins. CYP1B1 and nuclear receptors including peroxisome proliferator-activated receptors (PPARs), estrogen receptor (ER), and retinoic acid receptors (RAR) contribute to the maintenance of the homeostasis of these endogenous compounds. Many natural flavonoids and synthetic stilbenes show inhibitory activity toward CYP1B1 expression and function, notably isorhamnetin and 2,4,3',5'-tetramethoxystilbene. Accumulating evidence indicates that modulation of CYP1B1 can decrease adipogenesis and tumorigenesis, and prevent obesity, hypertension, atherosclerosis, and cancer. Therefore, it may be feasible to consider CYP1B1 as a therapeutic target for the treatment of metabolic diseases.

Tubulin-interactive stilbene derivatives as anticancer agents

Microtubules are dynamic polymers that occur in eukaryotic cells and play important roles in cell division, motility, transport and signaling. They form during the process of polymerization of α- and β-tubulin dimers. Tubulin is a significant and heavily researched molecular target for anticancer drugs. Combretastatins are natural cis-stilbenes that exhibit cytotoxic properties in cultured cancer cells in vitro. Combretastatin A-4 (3′-hydroxy-3,4,4′, 5-tetramethoxy-cis-stilbene; CA-4) is a potent cytotoxic cis-stilbene that binds to β-tubulin at the colchicine-binding site and inhibits tubulin polymerization. The prodrug CA-4 phosphate is currently in clinical trials as a chemotherapeutic agent for cancer treatment. Numerous series of stilbene analogs have been studied in search of potent cytotoxic agents with the requisite tubulin-interactive properties. Microtubule-interfering agents include numerous CA-4 and transresveratrol analogs and other synthetic stilbene derivatives. Importantly, these agents are active in both tumor cells and immature endothelial cells of tumor blood vessels, where they inhibit the process of angiogenesis. Recently, computer-aided virtual screening was used to select potent tubulin-interactive compounds. This review covers the role of stilbene derivatives as a class of antitumor agents that act by targeting microtubule assembly dynamics. Additionally, we present the results of molecular modeling of their binding to specific sites on the α- and β-tubulin heterodimer. This has enabled the elucidation of the mechanism of stilbene cytotoxicity and is useful in the design of novel agents with improved anti-mitotic activity. Tubulin-interactive agents are believed to have the potential to play a significant role in the fight against cancer.

Estrogen metabolism within the lung and its modulation by tobacco smoke

Although estrogen and the enzymes responsible for its metabolism have been detected within the lung, the ability of this tissue to metabolize estrogen has not been demonstrated previously. The goal of this study was to characterize the profile of estrogen metabolites within the murine lung and to determine the effect of tobacco smoke exposure on metabolite levels. Use of liquid chromatography-tandem mass spectrometry led to the detection of three estrogens (E1, E2 and E3) and five estrogen metabolites (2-OHE1, 4-OHE1, 4-OHE2, 2-OMeE1 and 2-OMeE2) within the perfused lung, with 4-OHE1 being the most abundant species. Levels of 4-OHEs, carcinogenic derivatives produced primarily by cytochrome P450 1B1 (Cyp1b1), were 2-fold higher in females than males. Deletion of Cyp1b1 in females led to a dramatic reduction (21-fold) in 4-OHEs, whereas levels of 2-OHE1 and the putative protective estrogen metabolite 2-OMeE2 were increased (2.4- and 5.0-fold, respectively) (P = 0.01). Similar quantitative differences in estrogen metabolite levels were observed between Cyp1b1 null and wild-type males. Exposure of female mice to tobacco smoke for 8 weeks (2h per day, 5 days per week) increased the levels of 4-OHE1 (4-fold) and 2-OHE2 (2-fold) within the lung while reducing the total concentration of 2-OMeEs to 70% of those of unexposed controls. These data suggest that tobacco smoke accelerates the production of 4-OHEs within the lung; carcinogenic metabolites that could potentially contribute to lung tumor development. Thus, inhibition of CYP1B1 may represent a promising strategy for the prevention and treatment of lung cancer.

Solid-phase chemical synthesis and in vitro biological evaluation of novel 2β-piperazino-(20R)-5α-pregnane-3α,20-diol N-derivatives as anti-leukemic agents

The steroid nucleus is an interesting scaffold for the development of new therapeutic agents. Within the goal of identifying anticancer agents, new pregnane derivatives were prepared by using a sequence of liquid and solid-phase reactions. After we dehydrated epi-allopregnanolone in one step with diethylaminosulfur trifluoride and generated a 2,3α-epoxide, the regio- and stereo-selective aminolysis of this epoxide enabled us to obtain a 2β-piperazino-pregnane, whose secondary amine was protected as N-Fmoc-derivative. Using the difference in reactivity between OHs 3 and 20, we linked the pregnane nucleus-selectively on the polystyrene diethylbutylsilane resin via the OH in position 20. We next achieved in parallel the coupling of an amino acid (1st level of diversity) and the coupling of a carboxylic acid (2nd level of diversity) to generate two libraries of pregnane derivatives. The compounds inhibited the HL-60 leukemia cell growth and the most potent were three compounds (PD, LPC-37 and LPC-48) with a l-proline as first level of diversity and a cyclohexyl-carbonyl, a naphthalene-2-carbonyl or a 3-acetylbenzoyl as second level of diversity. LPC-48 efficiently inhibited HL-60 cell proliferation with IC(50) value of 1.9 μM and exhibited a low toxicity on normal peripheral blood lymphocytes (IC(50)=31 μM). These results encouraged us to further evaluate the biological activity of these new aminosteroids by investigating their preliminary mechanism of action.

Resveratrol analogue 3,4,4',5-tetramethoxystilbene inhibits growth, arrests cell cycle and induces apoptosis in ovarian SKOV-3 and A-2780 cancer cells

In the screening studies, cytotoxicity of 12 methylated resveratrol analogues on 11 human cancer cell lines was examined. The most active compound 3,4,4'5-tetramethoxystilbene (DMU-212) and two ovarian cancer cell lines A-2780 (IC(50)=0.71 μM) and SKOV-3 (IC(50)=11.51 μM) were selected for further investigation. To determine the mechanism of DMU-212 cytotoxicity, its ability to induce apoptosis was examined. DMU-212 arrested cell cycle in the G2/M or G0/G1 phase which resulted in apoptosis of both cell lines. The expression level of 84 apoptosis-related genes was investigated. In SKOV-3 cells DMU-212 caused up-regulation of pro-apoptotic Bax, Apaf-1 and p53 genes, specific to intrinsic pathway of apoptosis, and a decrease in Bcl-2 and Bcl 2110 mRNA expressions. Conversely, in A-2780 cells an increased expression of pro-apoptotic genes Fas, FasL, TNF, TNFRSF10A, TNFRSF21, TNFRSF16 specific to extracellular mechanism of apoptosis was observed. There are no data published so far regarding the receptor mediated apoptosis induced by DMU-212. The activation of caspase-3/7 was correlated with decreased TRAF-1 and BIRC-2 expression level in A-2780 cells exposed to DMU-212. DMU-212 caused a decrease in CYP1A1 and CYP1B1 mRNA levels in A-2780 by 50% and 75%, and in SKOV-3 cells by 15% and 45%, respectively. The protein expression was also reduced in both cell lines. It is noteworthy that the expression of CYP1B1 protein was entirely inhibited in A-2780 cells treated with DMU-212. It can be suggested that different CYP1B1 expression patterns in either ovarian cell line may affect their sensitivity to cytotoxic activity of DMU-212.

The resveratrol analogue, 2,3',4,5'-tetramethoxystilbene, does not inhibit CYP gene expression, enzyme activity and benzo[a]pyrene-DNA adduct formation in MCF-7 cells exposed to benzo[a]pyrene

Exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs) induces cytochrome P450 (CYP) 1A1 and 1B1 enzymes, which biotransform PAHs resulting in the formation of DNA adducts. We hypothesised that 2,3',4,5'-tetramethoxystilbene (TMS), an analogue of resveratrol and a potent CYP1B1 inhibitor, may inhibit r7, t8, t9-trihydroxy-c-10-(N(2)deoxyguanosyl)-7,8,9,10-tetrahydro-benzo[a]pyrene (BPdG) adduct formation in cells exposed to benzo[a]pyrene (BP). To address this, MCF-7 cells were cultured for 96 h in the presence of 1 μM BP, 1 μM BP + 1 μM TMS or 1 μM BP + 4 μM TMS. Cells were assayed at 2-12 h intervals for: BPdG adducts by r7, t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA chemiluminescence immunoassay; CYP1A1 and 1B1 gene expression changes by relative real-time polymerase chain reaction; and CYP1A1/1B1 enzyme activity by ethoxyresorufin-O-deethylase (EROD) assay. Whereas maximal BPdG levels were similar for all exposure groups, the times at which the maxima were reached increased by 16 and 24 h with the addition of 1 and 4 μM TMS, respectively. The maximal expression of CYP1A1 and CYP1B1 occurred at 16, 24 and 48 h, but the maximal level for EROD-specific activity was reached at 24, 48 and 60 h, in cells exposed to 1 μM BP, 1 μM BP + 1 μM TMS or 1 μM BP + 4 μM TMS, respectively. The area under the curve from 4 to 96 h of exposure (AUC(4-)(96 h)) for BPdG adduct formation was not increased in the presence of TMS, but for CYP1A1 and CYP1B1 expression fold increase AUC(4-)(96 h) and EROD-specific activity AUC(4-)(96 h), there were significant (P < 0.05) increases in the presence of 4 μM TMS. Therefore, during 96 h of exposure in MCF-7 cells, the combination of BP plus TMS caused a slowing of BP biotransformation, with an increase in CYP1A1 and CYP1B1 expression and EROD activity, and a slowing, but no change in magnitude of BPdG formation.

Role of DDR1 in the gelatinases secretion induced by native type IV collagen in MDA-MB-231 breast cancer cells

Discoidin domain receptors (DDRs) are receptor tyrosine kinases that get activated by collagens in its native triple-helical form. In mammalian cells, DDR family consists of two members, namely DDR1 and DDR2, which mediates migration and proliferation of several cell types. DDR1 is activated by native type IV collagen and overexpressed in human breast cancer. Type IV collagen is the main component of basement membrane (BM), and the ability to degrade and penetrate BM is related with an increased potential for invasion and metastasis. Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that collectively are capable of degrading all components of the extracellular matrix, including the BM. In breast cancer cells, denatured type IV collagen induces MMP-9 secretion and invasion. However, the role of DDR1 in the regulation of gelatinases (MMP-2 and -9) secretion and invasion in breast cancer cells remains to be studied. We demonstrate here that native type IV collagen induces MMP-2 and -9 secretions and invasion through a DDR1 and Src-dependent pathway, together with an increase of MMP-2 and -9-cell surface levels. MMP-2 and -9 secretions require PKC kinase activity, epidermal growth factor receptor (EGFR) activation, arachidonic acid (AA) production and AA metabolites in MDA-MB-231 breast cancer cells. In summary, our data demonstrate, for the first time, that DDR1 mediates MMP-2 and -9 secretions and invasion induced by native type IV collagen in MDA-MB-231 breast cancer cells.

Tetra-methoxystilbene modulates ductal growth of the developing murine mammary gland

Extensive data suggest that estradiol contributes to the development of breast cancer by acting as a mitogen and exerting direct genotoxic effects after enzymatic conversion to 4-hydroxyestradiol (4-OHE2) via cytochrome P450 1B1 (CYP1B1). The mammary gland, ovary, and uterus all express CYP1B1. Overexpression of this enzyme has been associated with an increased risk of breast cancer and blockade might reduce this carcinogenic effect. For this reason, we conducted systematic in vitro and in vivo studies of a CYP1B1 inhibitor, TMS (2,3',4,5'-tetramethoxystilbene). We found that TMS blocked the enzymatic conversion of radiolabeled estradiol to both 2-hydroxyestradiol (2-OHE2) and 4-OHE2, but did not inhibit Cyp1b1 message formation. In vivo studies using mass spectrometry showed that TMS inhibited formation of 2-OHE2 and 4-OHE2 and the resulting estrogen-DNA adducts. To examine its biologic actions in vivo, we investigated whether TMS could block the hyperplastic changes that occur in the developing breast of aromatase-transfected mice. We found that TMS induced a significant reduction of ductal structures in mice less than 6 months in age. In older mice, no reduction in breast morphology occurred. These latter studies uncovered unexpected estrogen agonistic actions of TMS at high doses, including a paradoxical stimulation of breast ductal structures and the endometrium. These studies suggest that the enzyme inhibitory properties of TMS, as well as the effects on developing breast, could implicate a role for TMS in breast cancer prevention, but only in low doses and on developing breast.

Anticancer effect of (E)-2-hydroxy-3',4,5'-trimethoxystilbene on breast cancer cells by mitochondrial depolarization

BACKGROUND

TMS (2,3',4,5'-tetramethoxystilbene), a stilbene analog derived from rhapontigenin, was previously demonstrated to induce apoptosis in hormone-resistant breast cancer cells. Therefore, this study investigated the anticancer effect of a new stilbene analog, HTMS ((E)-2-hydroxy-3',4,5'-trimethoxystilbene), and its mechanism in various breast cancer cell lines.

MATERIALS AND METHODS

The effect of HTMS on cell proliferation of MDA-MB-231, MCF-7, and LTED cells was evaluated using MTT assays. Cell apoptosis was detected by FITC-annexin V staining and flow cytometry analysis, changes in mitochondrial potential were determined by fluorescence microscopy using TMRE staining, and the expression of cleaved PARP and release of cytochrome c were assessed by Western blot analysis.

RESULTS

HTMS significantly decreased the cell viability of various types of breast cancer cells in a dose- and time-dependent manner, characterized by G2/M arrest of the cell cycle and the induction of apoptosis. In particular, HTMS disturbed the mitochondrial membrane potential, causing a release of cytochrome c during apoptosis. Furthermore, HTMS was superior to TMS in inhibiting cancer cell growth in a pilot comparison study.

CONCLUSION

HTMS is an effective apoptotic agent for breast cancer cells, making it a candidate therapeutic agent for the treatment of breast cancer.

2,3',4,4',5'-Pentamethoxy-trans-stilbene, a resveratrol derivative, inhibits colitis-associated colorectal carcinogenesis in mice

BACKGROUND AND PURPOSE

Resveratrol, a naturally occurring polyphenolic antioxidant, has been shown to exhibit chemoprophylactic effects on cancer development. Previously, we reported that 2,3',4,4',5'-pentamethoxy-trans-stilbene (PMS), a methoxylated resveratrol derivative, exerted a highly potent anti-proliferative effect on human colon cancer cells as compared with its parent compound. In the present study, the chemopreventive effect of PMS was evaluated in a mouse model of colitis-associated colon carcinogenesis.

EXPERIMENTAL APPROACH

Seven-week-old Balb/c mice were injected i.p. with 10 mg.kg(-1) azoxymethane (AOM). After 1 week, 3% dextran sodium sulphate (DSS) was administered in the drinking water for 7 days followed by 14 days of tap water for recovery, and this cycle was repeated twice.

KEY RESULTS

Intragastric administration of PMS (25, 50 mg.kg(-1) body weight) for 16 weeks significantly reduced the multiplicity of colonic neoplasms by 15% and 35% (P < 0.01) respectively. Moreover, PMS at 50 mg.kg(-1) inhibited colon cancer cell proliferation and promoted apoptosis. Such changes were accompanied by reduction of Akt (protein kinase B) phosphorylation, inactivation of beta-catenin and down-regulation of inducible nitric oxide synthase. In parallel, in vitro studies also demonstrated that PMS inhibited proliferation and induced apoptosis in the murine colon adenocarcinoma cell line Colon26 with concomitant inhibition of Akt phosphorylation and inactivation of beta-catenin.

CONCLUSIONS AND IMPLICATIONS

PMS effectively suppressed colon carcinogenesis in an AOM/DSS animal model and may merit further clinical investigation as a chemoprophylactic agent against colitis-associated colon cancer in humans.

TMS, a chemically modified herbal derivative of resveratrol, induces cell death by targeting Bax

Breast cancer recurrence after an initial favorable response to treatment is a major concern for patients who receive hormonal therapies. Additional therapies are necessary to extend the time of response, and ideally, these therapies should exhibit minimal toxicity. Our study described herein focuses on a non-toxic pro-apoptotic agent, TMS (2,4,3',5'-tetramethoxystilbene), which belongs to the Resveratrol family of stilbenes. Prior study demonstrated that TMS was more effective than Resveratrol for inducing apoptosis. Additionally, TMS was effective for invoking death of relapsing breast cancer cells. As TMS was effective for reducing tumor burden, we sought to determine the mechanism by which it achieved its effects. Microarray analysis demonstrated that TMS treatment increased tubulin genes as well as stress response and pro-apoptotic genes. Fractionation studies uncovered that TMS treatment causes cleavage of Bax from the p21 form to a truncated p18 form which is associated with the induction of potent apoptosis. Co-localization analysis of immunofluorescent studies showed that Bax moved from the cytosol to the mitochondria. In addition, the pro-apoptotic proteins Noxa and Bim (EL, L, and S) were increased upon TMS treatment. Cell lines reduced for Bax, Bim, and Noxa are compromised for TMS-mediated cell death. Electron microscopy revealed evidence of nuclear condensation, formation of apoptotic bodies and DAPI staining showed evidence of DNA fragmentation. TMS treatment was able to induce both caspase-independent and caspase-dependent death via the intrinsic death pathway.

Oleic acid promotes migration on MDA-MB-231 breast cancer cells through an arachidonic acid-dependent pathway

An association between dietary fatty, obesity and an increased risk of developing breast cancer has been suggested. In breast cancer cells, free fatty acids (FFAs) mediate biological effects including cell proliferation and ERK1/2 activation. However, the contribution of FFAs to tumor progression and metastasis through the regulation of cell migration has not been studied. We demonstrated here that stimulation on MDA-MB-231 breast cancer cells with oleic acid (OA) promotes an increase in focal adhesion kinase (FAK) phosphorylation, as revealed by site-specific antibodies that recognize the phosphorylation state of FAK at tyrosine-397 (Tyr-397), Tyr-577 and in vitro kinase assays. OA also promotes the migration of MDA-MB-231 cells. Treatment with Gi/Go proteins, phospholipase C (PLC), lipoxygenases (LOXs) and Src inhibitor prevents FAK phosphorylation and cell migration. In summary, our findings delineate a new signal transduction pathway, where OA mediates the production of arachidonic acid (AA), and then AA metabolites mediate FAK phosphorylation and cell migration in MDA-MB-231 breast cancer cells.

2,3',4,4',5'-Pentamethoxy-trans-stilbene, a resveratrol derivative, is a potent inducer of apoptosis in colon cancer cells via targeting microtubules

Resveratrol, a naturally occurring polyphenolic antioxidant, is a compound holding promise for cancer chemoprevention. Previous studies suggest that 2,3',4,5'-tetramethoxy-trans-stilbene (TMS) and 3,4,4',5,-tetramethoxy-trans-stilbene (MR-4), both of which are derivatives of resveratrol, are potent apoptosis-inducing agents with clinical potential. In this study, we chemically synthesized 2,3',4,4',5'-pentamethoxy-trans-stilbene (PMS), the hybrid molecule of TMS and MR-4, and determined its effects on colon cancer growth. When compared with its parent compounds, PMS displayed more potent in vitro anti-mitogenic effect on colon cancer cells (Caco-2, HT-29 and SW1116). Moreover, PMS inhibited tumor growth in vivo in a colon cancer xenograft model. In this connection, PMS strongly induced apoptosis in HT-29 cells as evidenced by increased PARP cleavage, DNA fragmentation, and accumulation of sub-G(1) population. Further mechanistic analysis revealed that PMS enhanced the polymerization of microtubules, which was followed by G(2)/M mitotic arrest and caspase-dependent apoptosis. The activation of caspases-3, -7, -8, and -9 was involved in PMS-induced apoptosis with concomitant down-regulation of the pro-survival PI3K/Akt signaling. Collectively, these data suggest that PMS is a potent inducer of apoptosis via targeting microtubules and may merit investigation as a potential chemoprophylactic and therapeutic agent for colon cancer.

Arachidonic acid promotes FAK activation and migration in MDA-MB-231 breast cancer cells

Arachidonic acid (AA) is a common dietary n-6 polyunsaturated fatty acid that is present in an esterified form in cell membrane phospholipids, and it might be present in the extracellular microenvironment. In particular, AA promotes MAPK activation and mediates the adhesion of MDA-MB-435 breast cancer cells to type IV collagen. However, the signal transduction pathways mediated by AA have not been studied in detail. Our results demonstrate that stimulation of MDA-MB-231 breast cancer cells with AA promotes an increase in the phoshorylation of Src and FAK, as revealed by site-specific antibodies that recognized the phosphorylation state of Src at Tyr-418, and of FAK at tyrosine-397 and in vitro kinase assays. In addition, AA also induces an increase in the migration of MDA-MB-231 cells. In contrast, AA does not induce phosphorylation of FAK and an increase in cell migration of non-tumorigenic epithelial cells MCF10A. Inhibition of Gi/Go proteins, LOX and Src activity prevent FAK activation and cell migration. In conclusion, our results demonstrate, for the first time, that Gi/Go proteins, LOX and Src play an important role in FAK activation and cell migration induced by AA in MDA-MB-231 breast cancer cells.

Resveratrol analog trans 3,4,5,4'-tetramethoxystilbene (DMU-212) mediates anti-tumor effects via mechanism different from that of resveratrol

PURPOSE

Resveratrol is a well-known chemopreventive and chemotherapeutic agent. Among all of the resveratrol analogs synthesized, 3,4,5,4'-tetramethoxystilbene (DMU-212) shows high activity and selectivity against various cancer cell types. The objective of this study is to investigate why DMU-212 has higher anti-tumor activity than resveratrol.

METHODS

The effects of DMU-212 and resveratrol on cell viability, cell cycle, Stat3 activation, and microtubule dynamic were investigated and compared using MTT assay, cell cycle analysis, Western blot, tubulin polymerization assay, respectively, in MDA-MB-435 and MCF-7 human breast cancer cells.

RESULTS

Compared to resveratrol, DMU-212 exerted a significantly higher growth inhibition in both cell lines. Further studies demonstrated that DMU-212 acted via different mechanisms from resveratrol. First, DMU-212 induced predominantly G2/M arrest whereas resveratrol induced G0/G1 arrest in both cell lines. Correlating with these findings, resveratrol induced more dramatic changes in the expression of Cyclin D1 compared to DMU-212. Second, DMU-212 induced apoptosis and reduced the expression of multiple anti-apoptotic proteins more appreciably than resveratrol. Third, while both agents inhibited Stat3 phosphorylation, treatments of DMU-212 but not resveratrol led to a significant increase in tubulin polymerization. The higher sensitivity to DMU-122 in MDA-MB-435 correlated with the more prominent effects seen in these parameters in this cell line, as compared to MCF7.

CONCLUSION

Compared to resveratrol, the novel stilbene derivative, DMU-212, had higher anti-tumor effects, which are likely owing to its modulation of multiple cellular targets.