Up-regulation of miR-200 and let-7 by natural agents leads to the reversal of epithelial-to-mesenchymal transition in gemcitabine-resistant pancreatic cancer cells

Pancreatic cancer is the fourth most common cause of cancer death in the United States, and the aggressiveness of pancreatic cancer is in part due to its intrinsic and extrinsic drug resistance characteristics, which are also associated with the acquisition of epithelial-to-mesenchymal transition (EMT). Emerging evidence also suggests that the processes of EMT are regulated by the expression status of many microRNAs (miRNA), which are believed to function as key regulators of various biological and pathologic processes during tumor development and progression. In the present study, we compared the expression of miRNAs between gemcitabine-sensitive and gemcitabine-resistant pancreatic cancer cells and investigated whether the treatment of cells with "natural agents" [3,3'-diindolylmethane (DIM) or isoflavone] could affect the expression of miRNAs. We found that the expression of miR-200b, miR-200c, let-7b, let-7c, let-7d, and let-7e was significantly down-regulated in gemcitabine-resistant cells, which showed EMT characteristics such as elongated fibroblastoid morphology, lower expression of epithelial marker E-cadherin, and higher expression of mesenchymal markers such as vimentin and ZEB1. Moreover, we found that reexpression of miR-200 by transfection studies or treatment of gemcitabine-resistant cells with either DIM or isoflavone resulted in the down-regulation of ZEB1, slug, and vimentin, which was consistent with morphologic reversal of EMT phenotype leading to epithelial morphology. These results provide experimental evidence, for the first time, that DIM and isoflavone could function as miRNA regulators leading to the reversal of EMT phenotype, which is likely to be important for designing novel therapies for pancreatic cancer.

Acquisition of epithelial-mesenchymal transition phenotype of gemcitabine-resistant pancreatic cancer cells is linked with activation of the notch signaling pathway

Despite rapid advances in many fronts, pancreatic cancer (PC) remains one of the most difficult human malignancies to treat due, in part, to de novo and acquired chemoresistance and radioresistance. Gemcitabine alone or in combination with other conventional therapeutics is the standard of care for the treatment of advanced PC without any significant improvement in the overall survival of patients diagnosed with this deadly disease. Previous studies have shown that PC cells that are gemcitabine-resistant (GR) acquired epithelial-mesenchymal transition (EMT) phenotype, which is reminiscent of "cancer stem-like cells"; however, the molecular mechanism that led to EMT phenotype has not been fully investigated. The present study shows that Notch-2 and its ligand, Jagged-1, are highly up-regulated in GR cells, which is consistent with the role of the Notch signaling pathway in the acquisition of EMT and cancer stem-like cell phenotype. We also found that the down-regulation of Notch signaling was associated with decreased invasive behavior of GR cells. Moreover, down-regulation of Notch signaling by siRNA approach led to partial reversal of the EMT phenotype, resulting in the mesenchymal-epithelial transition, which was associated with decreased expression of vimentin, ZEB1, Slug, Snail, and nuclear factor-kappaB. These results provide molecular evidence showing that the activation of Notch signaling is mechanistically linked with chemoresistance phenotype (EMT phenotype) of PC cells, suggesting that the inactivation of Notch signaling by novel strategies could be a potential targeted therapeutic approach for overcoming chemoresistance toward the prevention of tumor progression and/or treatment of metastatic PC.

miR-146a suppresses invasion of pancreatic cancer cells

The aggressive course of pancreatic cancer is believed to reflect its unusually invasive and metastatic nature, which is associated with epidermal growth factor receptor (EGFR) overexpression and NF-kappaB activation. MicroRNAs (miRNA) have been implicated in the regulation of various pathobiological processes in cancer, including metastasis in pancreatic cancer and in other human malignancies. In this study, we report lower expression of miR-146a in pancreatic cancer cells compared with normal human pancreatic duct epithelial cells. Reexpression of miR-146a inhibited the invasive capacity of pancreatic cancer cells with concomitant downregulation of EGFR and the NF-kappaB regulatory kinase interleukin 1 receptor-associated kinase 1 (IRAK-1). Cellular mechanism studies revealed crosstalk between EGFR, IRAK-1, IkappaBalpha, NF-kappaB, and MTA-2, a transcription factor that regulates metastasis. Treatment of pancreatic cancer cells with the natural products 3,3'-diinodolylmethane (DIM) or isoflavone, which increased miR-146a expression, caused a downregulation of EGFR, MTA-2, IRAK-1, and NF-kappaB, resulting in an inhibition of pancreatic cancer cell invasion. Our findings reveal DIM and isoflavone as nontoxic activators of a miRNA that can block pancreatic cancer cell invasion and metastasis, offering starting points to design novel anticancer agents.

Epithelial to mesenchymal transition is mechanistically linked with stem cell signatures in prostate cancer cells

BACKGROUND

Current management of patients diagnosed with prostate cancer (PCa) is very effective; however, tumor recurrence with Castrate Resistant Prostate Cancer (CRPC) and subsequent metastasis lead to poor survival outcome, suggesting that there is a dire need for novel mechanistic understanding of tumor recurrence, which would be critical for designing novel therapies. The recurrence and the metastasis of PCa are tightly linked with the biology of prostate cancer stem cells or cancer-initiating cells that is reminiscent of the acquisition of Epithelial to Mesenchymal Transition (EMT) phenotype. Increasing evidence suggests that EMT-type cells share many biological characteristics with cancer stem-like cells.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we found that PCa cells with EMT phenotype displayed stem-like cell features characterized by increased expression of Sox2, Nanog, Oct4, Lin28B and/or Notch1, consistent with enhanced clonogenic and sphere (prostasphere)-forming ability and tumorigenecity in mice, which was associated with decreased expression of miR-200 and/or let-7 family. Reversal of EMT by re-expression of miR-200 inhibited prostasphere-forming ability of EMT-type cells and reduced the expression of Notch1 and Lin28B. Down-regulation of Lin28B increased let-7 expression, which was consistent with repressed self-renewal capability.

CONCLUSIONS/SIGNIFICANCE

These results suggest that miR-200 played a pivotal role in linking the characteristics of cancer stem-like cells with EMT-like cell signatures in PCa. Selective elimination of cancer stem-like cells by reversing the EMT phenotype to Mesenchymal-Epithelial Transition (MET) phenotype using novel agents would be useful for the prevention of tumor recurrence especially by eliminating those cells that are the "Root Cause" of tumor development and recurrence.

Metformin inhibits cell proliferation, migration and invasion by attenuating CSC function mediated by deregulating miRNAs in pancreatic cancer cells

Pancreatic cancer is the fourth leading cause of cancer-related deaths in the United States, which is, in part, due to intrinsic (de novo) and extrinsic (acquired) resistance to conventional therapeutics, suggesting that innovative treatment strategies are required for overcoming therapeutic resistance to improve overall survival of patients. Oral administration of metformin in patients with diabetes mellitus has been reported to be associated with reduced risk of pancreatic cancer and that metformin has been reported to kill cancer stem cells (CSC); however, the exact molecular mechanism(s) has not been fully elucidated. In the current study, we examined the effect of metformin on cell proliferation, cell migration and invasion, and self-renewal capacity of CSCs and further assessed the expression of CSC marker genes and microRNAs (miRNA) in human pancreatic cancer cells. We found that metformin significantly decreased cell survival, clonogenicity, wound-healing capacity, sphere-forming capacity (pancreatospheres), and increased disintegration of pancreatospheres in both gemcitabine-sensitive and gemcitabine-resistant pancreatic cancer cells. Metformin also decreased the expression of CSC markers,CD44, EpCAM,EZH2, Notch-1, Nanog and Oct4, and caused reexpression of miRNAs (let-7a,let-7b, miR-26a, miR-101, miR-200b, and miR-200c) that are typically lost in pancreatic cancer and especially in pancreatospheres. We also found that reexpression of miR-26a by transfection led to decreased expression of EZH2 and EpCAM in pancreatic cancer cells. These results clearly suggest that the biologic effects of metformin are mediated through reexpression of miRNAs and decreased expression of CSC-specific genes, suggesting that metformin could be useful for overcoming therapeutic resistance of pancreatic cancer cells.

Targeting miRNAs involved in cancer stem cell and EMT regulation: An emerging concept in overcoming drug resistance

Although chemotherapy is an important therapeutic strategy for cancer treatment, it fails to eliminate all tumor cells due to intrinsic or acquired drug resistance, which is the most common cause of tumor recurrence. Emerging evidence suggests an intricate role of cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT)-type cells in anticancer drug resistance. Recent studies also demonstrated that microRNAs (miRNAs) play critical roles in the regulation of drug resistance. Here we will discuss current knowledge regarding CSCs, EMT and the role of regulation by miRNAs in the context of drug resistance, tumor recurrence and metastasis. A better understanding of the molecular intricacies of drug-resistant cells will help to design novel therapeutic strategies by selective targeting of CSCs and EMT-phenotypic cells through alterations in the expression of specific miRNAs towards eradicating tumor recurrence and metastasis. A particular promising lead is the potential synergistic combination of natural compounds that affect critical miRNAs, such as curcumin or epigallocatechin-3-gallate (EGCG) with chemotherapeutic agents.

Shanghai trial of nifedipine in the elderly (STONE)

OBJECTIVE

To assess the effectiveness of nifedipine treatment in elderly hypertensives.

METHODS

A single-blind trial was conducted under the direction of the Shanghai Institute of Hypertension in 1632 subjects aged 60-79 years alternatively allocated to either nifedipine or placebo after a 4-week placebo run-in period between 1987 and 1990 with mean follow-up of 30 months. Clinical events and risk modification were analysed in collaboration with the University of Montreal. Seventy-four patients with severe hypertension were reallocated to active nifedipine treatment after placebo run-in.

RESULTS

Cox's proportional hazards model accounting for covariates demonstrated a highly significant decrease in the probability of events: 'original treatment assignment' analysis indicated that 77 events occurred in the placebo and 32 in the nifedipine group. Similar significances were achieved with 'actual treatment' or 'changes excluded' (excluding reallocated subjects) analyses. A significant reduction in relative risk was observed for strokes and severe arrhythmia with an overall decrease from 1.0 to 0.41 (95% confidence interval 0.27-0.61).

CONCLUSION

Nifedipine treatment diminished the number of severe clinical outcomes in elderly hypertensives significantly.

Cancer Stem Cells and Epithelial-to-Mesenchymal Transition (EMT)-Phenotypic Cells: Are They Cousins or Twins?

Cancer stem cells (CSCs) are cells within a tumor that possess the capacity to self-renew and maintain tumor-initiating capacity through differentiation into the heterogeneous lineages of cancer cells that comprise the whole tumor. These tumor-initiating cells could provide a resource for cells that cause tumor recurrence after therapy. Although the cell origin of CSCs remains to be fully elucidated, mounting evidence has demonstrated that Epithelial-to-Mesenchymal Transition (EMT), induced by different factors, is associated with tumor aggressiveness and metastasis and these cells share molecular characteristics with CSCs, and thus are often called cancer stem-like cells or tumor-initiating cells. The acquisition of an EMT phenotype is a critical process for switching early stage carcinomas into invasive malignancies, which is often associated with the loss of epithelial differentiation and gain of mesenchymal phenotype. Recent studies have demonstrated that EMT plays a critical role not only in tumor metastasis but also in tumor recurrence and that it is tightly linked with the biology of cancer stem-like cells or cancer-initiating cells. Here we will succinctly summarize the state-of-our-knowledge regarding the molecular similarities between cancer stem-like cells or CSCs and EMT-phenotypic cells that are associated with tumor aggressiveness focusing on solid tumors.

E-Cadherin gene promoter hypermethylation in primary human gastric carcinomas

BACKGROUND

E (epithelial)-cadherin, the cell adhesion molecule also considered a potential invasion/metastasis suppressor, is mutationally inactivated in nearly half of all undifferentiated-scattered (diffuse-type) gastric carcinomas. In addition, silencing of E-cadherin by CpG methylation within its promoter region has been reported in several gastric carcinoma cell lines. We investigated the methylation status of the E-cadherin promoter region in 53 primary human gastric carcinomas.

METHODS

Hypermethylation of the E-cadherin promoter was determined by utilizing methylation-specific polymerase chain reaction (PCR)-single-strand conformation polymorphism (MSP-SSCP) analysis followed by direct sequencing of PCR products. Expression of E-cadherin was studied by western blot analysis. All statistical tests were two-sided.

RESULTS

Hypermethylation of the E-cadherin promoter was evident in 27 (51%) of 53 primary gastric carcinomas examined by MSP-SSCP. It occurred more frequently in carcinomas of the undifferentiated-scattered type (in 15 [83%] of 18) than in other histologic subtypes (in 12 [34%] of 35) (P =.0011, Fisher's exact test), and it was present at similar rates in early (in six [60%] of 10) versus advanced (in 21 [49%] of 43) carcinomas (P =.73, Fisher's exact test). Methylation occurring at all cytosine-guanosine sequences (CpGs) near the transcriptional start site was confirmed in six of six tumors examined by bisulfite-DNA sequencing, including two early gastric carcinomas. In addition, loss or diminished expression of E-cadherin was confirmed by western blotting in four of the six tumor tissues demonstrating hypermethylation.

CONCLUSIONS

The E-cadherin promoter frequently undergoes hypermethylation in human gastric cancers, particularly those of the undifferentiated-scattered histologic subtype. E-cadherin promoter hypermethylation is associated with decreased expression and may occur early in gastric carcinogenesis.

The role of Notch signaling pathway in epithelial-mesenchymal transition (EMT) during development and tumor aggressiveness

The Notch signaling pathway maintains a balance between cell proliferation and apoptosis, and thus it is believed that Notch signaling pathways may play an important role in the development and progression of several malignancies. However, the functions of Notch signaling in EMT are largely unknown. This mini review describes the role of Notch signaling pathway in EMT, and cataloging how its deregulation is involved in EMT and tumor aggressiveness. Further attempts have been made to summarize the role of several chemopreventive agents that could be useful for targeted inactivation of Notch signaling, and thus it may cause reversal of EMT, which could become a novel approach for cancer prevention and treatment.

miR-200 regulates PDGF-D-mediated epithelial-mesenchymal transition, adhesion, and invasion of prostate cancer cells

MicroRNAs have been implicated in tumor progression. Recent studies have shown that the miR-200 family regulates epithelial-mesenchymal transition (EMT) by targeting zinc-finger E-box binding homeobox 1 (ZEB1) and ZEB2. Emerging evidence from our laboratory and others suggests that the processes of EMT can be triggered by various growth factors, such as transforming growth factor beta and platelet-derived growth factor-D (PDGF-D). Moreover, we recently reported that overexpression of PDGF-D in prostate cancer cells (PC3 PDGF-D cells) leads to the acquisition of the EMT phenotype, and this model offers an opportunity for investigating the molecular interplay between PDGF-D signaling and EMT. Here, we report, for the first time, significant downregulation of the miR-200 family in PC3 PDGF-D cells as well as in PC3 cells exposed to purified active PDGF-D protein, resulting in the upregulation of ZEB1, ZEB2, and Snail2 expression. Interestingly, re-expression of miR-200b in PC3 PDGF-D cells led to reversal of the EMT phenotype, which was associated with the downregulation of ZEB1, ZEB2, and Snail2 expression, and these results were consistent with greater expression levels of epithelial markers. Moreover, transfection of PC3 PDGF-D cells with miR-200b inhibited cell migration and invasion, with concomitant repression of cell adhesion to the culture surface and cell detachment. From these results, we conclude that PDGF-D-induced acquisition of the EMT phenotype in PC3 cells is, in part, a result of repression of miR-200 and that any novel strategy by which miR-200 could be upregulated would become a promising approach for the treatment of invasive prostate cancer.

Notch-1 induces epithelial-mesenchymal transition consistent with cancer stem cell phenotype in pancreatic cancer cells

Activation of Notch-1 is known to be associated with the development and progression of human malignancies including pancreatic cancer. Emerging evidence suggest that the acquisition of epithelial-mesenchymal transition (EMT) phenotype and induction of cancer stem cell (CSC) or cancer stem-like cell phenotype are interrelated and contributes to tumor recurrence and drug resistance. The molecular mechanism(s) by which Notch-1 contributes to the acquisition of EMT phenotype and CSC self-renewal capacity has not been fully elucidated. Here we show that forced over-expression of Notch-1 leads to increased cell growth, clonogenicity, migration and invasion of AsPC-1 cells. Moreover, over-expression of Notch-1 led to the induction of EMT phenotype by activation of mesenchymal cell markers such as ZEB1, CD44, EpCAM, and Hes-1. Here we also report, for the first time, that over-expression of Notch-1 leads to increased expression of miR-21, and decreased expression of miR-200b, miR-200c, let-7a, let-7b, and let-7c. Re-expression of miR-200b led to decreased expression of ZEB1, and vimentin, and increased expression of E-cadherin. Over-expression of Notch-1 also increased the formation of pancreatospheres consistent with expression of CSC surface markers CD44 and EpCAM. Finally, we found that genistein, a known natural anti-tumor agent inhibited cell growth, clonogenicity, migration, invasion, EMT phenotype, formation of pancreatospheres and expression of CD44 and EpCAM. These results suggest that the activation of Notch-1 signaling contributes to the acquisition of EMT phenotype, which is in part mediated through the regulation of miR-200b and CSC self-renewal capacity, and these processes could be attenuated by genistein treatment.

Curcumin analogue CDF inhibits pancreatic tumor growth by switching on suppressor microRNAs and attenuating EZH2 expression

The histone methyltransferase EZH2 is a central epigenetic regulator of cell survival, proliferation, and cancer stem cell (CSC) function. EZH2 expression is increased in various human cancers, including highly aggressive pancreatic cancers, but the mechanisms underlying for its biologic effects are not yet well understood. In this study, we probed EZH2 function in pancreatic cancer using diflourinated-curcumin (CDF), a novel analogue of the turmeric spice component curcumin that has antioxidant properties. CDF decreased pancreatic cancer cell survival, clonogenicity, formation of pancreatospheres, invasive cell migration, and CSC function in human pancreatic cancer cells. These effects were associated with decreased expression of EZH2 and increased expression of a panel of tumor-suppressive microRNAs (miRNA), including let-7a, b, c, d, miR-26a, miR-101, miR-146a, andmiR-200b, c that are typically lost in pancreatic cancer. Mechanistic investigations revealed that reexpression of miR-101 was sufficient to limit the expression of EZH2 and the proinvasive cell surface adhesion molecule EpCAM. In an orthotopic xenograft model of human pancreatic cancer, administration of CDF inhibited tumor growth in a manner associated with reduced expression of EZH2, Notch-1, CD44, EpCAM, and Nanog and increased expression of let-7, miR-26a, and miR-101. Taken together, our results indicated that CDF inhibited pancreatic cancer tumor growth and aggressiveness by targeting an EZH2-miRNA regulatory circuit for epigenetically controlled gene expression.

Down-regulation of Forkhead Box M1 Transcription Factor Leads to the Inhibition of Invasion and Angiogenesis of Pancreatic Cancer Cells

The Forkhead Box M1 (FoxM1) transcription factor has been shown to play important roles in regulating the expression of genes involved in cell proliferation, differentiation, and transformation. Overexpression of FoxM1 has been found in a variety of aggressive human carcinomas including pancreatic cancer. However, the precise role and the molecular mechanism of action of FoxM1 in pancreatic cancer remain unclear. To elucidate the cellular and molecular function of FoxM1, we tested the consequences of down-regulation and up-regulation of FoxM1 in pancreatic cancer cells, respectively. Using multiple cellular and molecular approaches such as 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, gene transfection, flow cytometry, real-time reverse transcription-PCR, Western blotting, migration, invasion, and angiogenesis assays, we found that down-regulation of FoxM1 inhibited cell growth, decreased cell migration, and decreased invasion of pancreatic cancer cells. FoxM1 down-regulation also decreased cell population in the S phase. Compared with control, FoxM1 small interfering RNA-transfected cells showed decreased expression of cyclin B, cyclin D1, and Cdk2, whereas p21 and p27 expression was increased. We also found that down-regulation of FoxM1 reduced the expression of matrix metalloproteinase-2 (MMP-2), MMP-9 and vascular endothelial growth factor, resulting in the inhibition of migration, invasion, and angiogenesis. These findings suggest that FoxM1 down-regulation could be a novel approach for the inhibition of pancreatic tumor progression.

NF-kappaB signaling pathway and its therapeutic implications in human diseases

The nuclear factor-kappaB (NF-kappaB) pathway is one of the most important cellular signal transduction pathways involved in both physiologic processes and disease conditions. It plays important roles in the control of immune function, inflammation, stress response, differentiation, apoptosis, and cell survival. Moreover, NF-kappaB is critically involved in the processes of development and progression of cancers. More importantly, recent studies have shown that NF-kappaB signaling also plays critical roles in the epithelial-mesenchymal transition (EMT) and cancer stem cells. Therefore, targeting of NF-kappaB signaling pathway could be a potent strategy for the prevention and/or treatment of human cancers and inflammatory diseases.

Over-expression of FoxM1 leads to epithelial-mesenchymal transition and cancer stem cell phenotype in pancreatic cancer cells

FoxM1 is known to play important role in the development and progression of many malignancies including pancreatic cancer. Studies have shown that the acquisition of epithelial-to-mesenchymal transition (EMT) phenotype and induction of cancer stem cell (CSC) or cancer stem-like cell phenotypes are highly inter-related, and contributes to drug resistance, tumor recurrence, and metastasis. The molecular mechanism(s) by which FoxM1 contributes to the acquisition of EMT phenotype and induction of CSC self-renewal capacity is poorly understood. Therefore, we established FoxM1 over-expressing pancreatic cancer (AsPC-1) cells, which showed increased cell growth, clonogenicity, and cell migration. Moreover, over-expression of FoxM1 led to the acquisition of EMT phenotype by activation of mesenchymal cell markers, ZEB1, ZEB2, Snail2, E-cadherin, and vimentin, which is consistent with increased sphere-forming (pancreatospheres) capacity and expression of CSC surface markers (CD44 and EpCAM). We also found that over-expression of FoxM1 led to decreased expression of miRNAs (let-7a, let-7b, let-7c, miR-200b, and miR-200c); however, re-expression of miR-200b inhibited the expression of ZEB1, ZEB2, vimentin as well as FoxM1, and induced the expression of E-cadherin, leading to the reversal of EMT phenotype. Finally, we found that genistein, a natural chemo-preventive agent, inhibited cell growth, clonogenicity, cell migration and invasion, EMT phenotype, and formation of pancreatospheres consistent with reduced expression of CD44 and EpCAM. These results suggest, for the first time, that FoxM1 over-expression is responsible for the acquisition of EMT and CSC phenotype, which is in part mediated through the regulation of miR-200b and these processes, could be easily attenuated by genistein.

Cellular signaling perturbation by natural products

Cancer cells are known to have alterations in multiple cellular signaling pathways and because of the complexities in the communication between multiple signaling networks, the treatment and the cure for most human malignancies is still an open question. Perhaps, this is the reason why specific inhibitors that target only one pathway have been typically failed in cancer treatment. However, the in vitro and in vivo studies have demonstrated that some natural products such as isoflavones, indole-3-carbinol (I3C), 3,3'-diindolylmethane (DIM), curcumin, (-)-epigallocatechin-3-gallate (EGCG), resveratrol, lycopene, etc, have inhibitory effects on human and animal cancers through targeting multiple cellular signaling pathways and thus these "natural agents" could be classified as multi-targeted agents. This is also consistent with the epidemiological studies showing that the consumption of fruits, soybean and vegetables is associated with reduced risk of several types of cancers. By regulating multiple important cellular signaling pathways including NF-kappaB, Akt, MAPK, Wnt, Notch, p53, AR, ER, etc, these natural products are known to activate cell death signals and induce apoptosis in pre-cancerous or cancer cells without affecting normal cells. Therefore, non-toxic "natural agents" harvested from the bounties of nature could be useful either alone or in combination with conventional therapeutics for the prevention of tumor progression and/or treatment of human malignancies.

Loss of let-7 up-regulates EZH2 in prostate cancer consistent with the acquisition of cancer stem cell signatures that are attenuated by BR-DIM

The emergence of castrate-resistant prostate cancer (CRPC) contributes to the high mortality of patients diagnosed with prostate cancer (PCa), which in part could be attributed to the existence and the emergence of cancer stem cells (CSCs). Recent studies have shown that deregulated expression of microRNAs (miRNAs) contributes to the initiation and progression of PCa. Among several known miRNAs, let-7 family appears to play a key role in the recurrence and progression of PCa by regulating CSCs; however, the mechanism by which let-7 family contributes to PCa aggressiveness is unclear. Enhancer of Zeste homolog 2 (EZH2), a putative target of let-7 family, was demonstrated to control stem cell function. In this study, we found loss of let-7 family with corresponding over-expression of EZH2 in human PCa tissue specimens, especially in higher Gleason grade tumors. Overexpression of let-7 by transfection of let-7 precursors decreased EZH2 expression and repressed clonogenic ability and sphere-forming capacity of PCa cells, which was consistent with inhibition of EZH2 3′UTR luciferase activity. We also found that the treatment of PCa cells with BR-DIM (formulated DIM: 3,3′-diindolylmethane by Bio Response, Boulder, CO, abbreviated as BR-DIM) up-regulated let-7 and down-regulated EZH2 expression, consistent with inhibition of self-renewal and clonogenic capacity. Moreover, BR-DIM intervention in our on-going phase II clinical trial in patients prior to radical prostatectomy showed upregulation of let-7 consistent with down-regulation of EZH2 expression in PCa tissue specimens after BR-DIM intervention. These results suggest that the loss of let-7 mediated increased expression of EZH2 contributes to PCa aggressiveness, which could be attenuated by BR-DIM treatment, and thus BR-DIM is likely to have clinical impact.

Implication of microRNAs in drug resistance for designing novel cancer therapy

Recently, microRNAs (miRNAs) have received increasing attention in the field of cancer research. miRNAs play important roles in many normal biological processes; however, the aberrant miRNA expression and its correlation with the development and progression of cancers is an emerging field. Therefore, miRNAs could be used as biomarkers for diagnosis of cancer and prediction of prognosis. Importantly, some miRNAs could regulate the formation of cancer stem cells and the acquisition of epithelial-mesenchymal transition, which are critically associated with drug resistance. Moreover, some miRNAs could target genes related to drug sensitivity, resulting in the altered sensitivity of cancer cells to anti-cancer drugs. Emerging evidences have also shown that knock-down or re-expression of specific miRNAs by synthetic anti-sense oligonucleotides or pre-miRNAs could induce drug sensitivity, leading to increased inhibition of cancer cell growth, invasion, and metastasis. More importantly, recent studies have shown that natural agents including isoflavone, 3,3'-diindolylmethane, and (-)-epigallocatechin-3-gallate altered miRNA expression profiles, leading to an increased sensitivity of cancer cells to conventional therapeutics. These emerging results suggest that specific targeting of miRNAs by different approaches could open new avenues for cancer treatment through overcoming drug resistance and thereby improve the outcome of cancer therapy.

Inhibition of angiogenesis and invasion by 3,3'-diindolylmethane is mediated by the nuclear factor-kappaB downstream target genes MMP-9 and uPA that regulated bioavailability of vascular endothelial growth factor in prostate cancer

Progression of prostate cancer is believed to be dependent on angiogenesis induced by tumor cells. 3,3'-Diindolylmethane (DIM) has been shown to repress neovascularization in a Matrigel plug assay and inhibit cell proliferation, migration, invasion, and capillary tube formation of cultured human umbilical vein endothelial cells. However, the molecular mechanism, by which DIM inhibits angiogenesis and invasion, has not been fully elucidated. Therefore, we sought to explore the molecular mechanism by which DIM inhibits angiogenesis and invasion, specifically by investigating the role of angiogenic factors secreted by prostate cancer cells which control all steps of angiogenesis. We found that BioResponse DIM (B-DIM), a formulated DIM with higher bioavailability, inhibited angiogenesis and invasion by reducing the bioavailability of vascular endothelial growth factor (VEGF) via repressing extracellular matrix-degrading proteases, such as matrix metalloproteinase (MMP)-9 and urokinase-type plasminogen activator (uPA), in human prostate cancer cells and reduced vascularity (angiogenesis) in vivo using Matrigel plug assay. We also found that B-DIM treatment inhibited DNA binding activity of nuclear factor-kappaB (NF-kappaB), which is known to mediate the expression of many NF-kappaB downstream target genes, including VEGF, IL-8, uPA, and MMP-9, all of which are involved in angiogenesis, invasion, and metastasis. Our data suggest that inhibition of NF-kappaB DNA binding activity by B-DIM contributes to the regulated bioavailability of VEGF by MMP-9 and uPA and, in turn, inhibits invasion and angiogenesis, which could be mechanistically linked with the antitumor activity of B-DIM as observed previously by our laboratory in a prostate cancer animal model.

Phosphoglucose isomerase/autocrine motility factor mediates epithelial-mesenchymal transition regulated by miR-200 in breast cancer cells

Phosphoglucose isomerase/autocrine motility factor (PGI/AMF) plays an important role in glycolysis and gluconeogenesis and is associated with invasion and metastasis of cancer cells. We have previously shown its role in the induction of epithelial-mesenchymal transition (EMT) in breast cancer cells, which led to increased aggressiveness; however, the molecular mechanism by which PGI/AMF regulates EMT is not known. Here we show, for the first time, that PGI/AMF overexpression led to an increase in the DNA-binding activity of NF-κB, which, in turn, led to increased expression of ZEB1/ZEB2. The microRNA-200s (miR-200s) miR-200a, miR-200b, and miR-200c are known to negatively regulate the expression of ZEB1/ZEB2, and we found that the expression of miR-200s was lost in PGI/AMF overexpressing MCF-10A cells and in highly invasive MDA-MB-231 cells, which was consistent with increased expression of ZEB1/ZEB2. Moreover, silencing of PGI/AMF expression in MDA-MB-231 cells led to overexpression of miR-200s, which was associated with reversal of EMT phenotype (i.e., mesenchymal-epithelial transition), and these findings were consistent with alterations in the relative expression of epithelial (E-cadherin) and mesenchymal (vimentin, ZEB1, ZEB2) markers and decreased aggressiveness as judged by clonogenic, motility, and invasion assays. Moreover, either reexpression of miR-200 or silencing of PGI/AMF suppressed pulmonary metastases of MDA-MB-231 cells in vivo, and anti-miR-200 treatment in vivo resulted in increased metastases. Collectively, these results suggest a role of miR-200s in PGI/AMF-induced EMT and thus approaches for upregulation of miR-200s could be a novel therapeutic strategy for the treatment of highly invasive breast cancer.

Anti-tumor activity of a novel compound-CDF is mediated by regulating miR-21, miR-200, and PTEN in pancreatic cancer

BACKGROUND

The existence of cancer stem cells (CSCs) or cancer stem-like cells in a tumor mass is believed to be responsible for tumor recurrence because of their intrinsic and extrinsic drug-resistance characteristics. Therefore, targeted killing of CSCs would be a newer strategy for the prevention of tumor recurrence and/or treatment by overcoming drug-resistance. We have developed a novel synthetic compound-CDF, which showed greater bioavailability in animal tissues such as pancreas, and also induced cell growth inhibition and apoptosis, which was mediated by inactivation of NF-κB, COX-2, and VEGF in pancreatic cancer (PC) cells.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study we showed, for the first time, that CDF could significantly inhibit the sphere-forming ability (pancreatospheres) of PC cells consistent with increased disintegration of pancreatospheres, which was associated with attenuation of CSC markers (CD44 and EpCAM), especially in gemcitabine-resistant (MIAPaCa-2) PC cells containing high proportion of CSCs consistent with increased miR-21 and decreased miR-200. In a xenograft mouse model of human PC, CDF treatment significantly inhibited tumor growth, which was associated with decreased NF-κB DNA binding activity, COX-2, and miR-21 expression, and increased PTEN and miR-200 expression in tumor remnants.

CONCLUSIONS/SIGNIFICANCE

These results strongly suggest that the anti-tumor activity of CDF is associated with inhibition of CSC function via down-regulation of CSC-associated signaling pathways. Therefore, CDF could be useful for the prevention of tumor recurrence and/or treatment of PC with better treatment outcome in the future.

Targeted regulation of PI3K/Akt/mTOR/NF-κB signaling by indole compounds and their derivatives: mechanistic details and biological implications for cancer therapy

Indole compounds, found in cruciferous vegetables, are potent anti-cancer agents. Studies with indole-3-carbinol (I3C) and its dimeric product, 3,3'-diindolylmethane (DIM) suggest that these compounds have the ability to deregulate multiple cellular signaling pathways, including PI3K/Akt/mTOR signaling pathway. These natural compounds are also effective modulators of downstream transcription factor NF-κB signaling which might help explain their ability to inhibit invasion and angiogenesis, and the reversal of epithelial-to-mesenchymal transition (EMT) phenotype and drug resistance. Signaling through PI3K/Akt/mTOR and NF-κB pathway is increasingly being realized to play important role in EMT through the regulation of novel miRNAs which further validates the importance of this signaling network and its regulations by indole compounds. Here we will review the available literature on the modulation of PI3K/Akt/mTOR/NF-κB signaling by both parental I3C and DIM, as well as their analogs/derivatives, in an attempt to catalog their anticancer activity.

Distinct methylation patterns of two APC gene promoters in normal and cancerous gastric epithelia

The adenomatous polyposis coli (APC) tumor suppressor gene is mutationally inactivated in both familial and sporadic forms of colorectal cancers. In addition, hypermethylation of CpG islands in the upstream portion of APC, a potential alternative mechanism of tumor suppressor gene inactivation, has been described in colorectal cancer. Because a subset of both gastric and colorectal cancers display the CpG island methylator phenotype, we hypothesized that epigenetic inactivation of APC was likely to occur in at least some gastric cancers. APC exhibits two forms of transcripts from exons 1A and 1B in the stomach. Therefore, we investigated CpG island methylation in the sequences upstream of exons 1A and 1B, i.e., promoters 1A and 1B, respectively. We evaluated DNAs from 10 gastric cancer cell lines, 40 primary gastric cancers, and 40 matching non-cancerous gastric mucosae. Methylated alleles of promoter 1A were present in 10 (100%) of 10 gastric cancer cell lines, 33 (82.5%) of 40 primary gastric cancers, and 39 (97.5%) of 40 noncancerous gastric mucosae. In contrast, promoter 1B was unmethylated in all of these same samples. APC transcripts from exon 1A were not expressed in nine of the 10 methylated gastric cancer cell lines, whereas APC transcripts were expressed from exon 1B. Thus, expression from a given promoter correlated well with its methylation status. We conclude that in contrast to the colon, methylation of promoter 1A is a normal event in the stomach; moreover, promoter 1B is protected from methylation in the stomach and thus probably does not participate in this form of epigenetic APC inactivation.