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

The molecular and cellular heterogeneity of pancreatic ductal adenocarcinoma

Current standard therapies for pancreatic ductal adenocarcinoma have failed to attenuate the aggressiveness of this disease or confer notable improvements in survival. Previous molecular research into pancreatic cancers, along with advances in sequencing technologies, have identified many altered genes in patients with pancreatic cancer and revealed the marked genetic heterogeneity of individual tumors. Thus, the lack of success of conventional empiric therapy can be partly attributed to the underlying heterogeneity of pancreatic tumors. The genetic alterations that have been detected in pancreatic cancer range from simple mutations at the level of base pairs to complex chromosomal structural changes and rearrangements. The identification of molecular changes that are unique to an individual patient's tumors, and the subsequent development of strategies to target the tumors in a personalized approach to therapeutics, is a necessary advance to improve therapy for patients with this disease.

Chemoresistance to 5-fluorouracil induces epithelial-mesenchymal transition via up-regulation of Snail in MCF7 human breast cancer cells

5-Fluorouracil (5-FU) is commonly used to treat breast cancer; however, it becomes increasingly ineffective with tumor progression. Epithelial-to-mesenchymal transition (EMT) is a process whereby cells acquire morphologic and molecular alterations facilitating tumor metastasis and progression. Emerging evidence associates chemoresistance with acquisition of EMT in cancer. However, it is not clear whether this phenomenon is involved in acquired resistance to 5-FU. Using a previously established in vitro cell model of 5-fluorouracil-resistant MCF7 cells (MCF7/5-FU), we assessed the cellular morphology, molecular changes, migration and invasion consistent with EMT. We found that silencing of Snail by stable RNA interference reversed the EMT and greatly abolished invasion behavior of MCF7/5-FU cells. We also showed that inhibition of Snail increased the sensitivity of 5-FU-resistant cells to 5-FU. Our study provided a new insight into EMT-like phenotypic changes associated with 5-FU resistance in MCF7 cells. We believed that down-regulation of Snail could be a potential novel therapeutic approach to overcoming chemoresistance and preventing metastasis during 5-FU chemotherapy.

Epithelial-mesenchymal transition and breast cancer: role, molecular mechanisms and clinical impact

Epithelial-mesenchymal transition (EMT) is defined by the loss of epithelial characteristics and the acquisition of a mesenchymal phenotype. In this process, cells acquire molecular alterations that facilitate dysfunctional cell-cell adhesive interactions and junctions. These processes may promote cancer cell progression and invasion into the surrounding microenvironment. Such transformation has implications in progression of breast carcinoma to metastasis, and increasing evidences support most tumors contain a subpopulation of cells with stem-like and mesenchymal features that is resistant to chemotherapy. This review focuses on the physiological and pathological role of EMT process, its molecular related network, its putative role in the metastatic process and its implications in response/resistance to the current and/or new approaching drugs in the clinical management of breast cancer.

Molecular pathogenesis of pancreatic cancer and clinical perspectives

Pancreatic cancer remains stubbornly resistant to many key cytotoxic chemotherapeutic agents and novel targeted therapies. The molecular heterogeneity of this cancer may account for therapy failures to date, although our growing arsenal of novel targeted agents could translate into patient survival. The main objectives of this review are to elucidate histological subtypes of pancreatic neoplasms that exhibit the characteristic of a gradual process of differentiation from benign entities to malignant ones. In addition, important genes, molecular abnormalities, and significant pathways of pancreatic cancer are analyzed and a potential clinical interpretation is presented (p16/cdkn2a, k-ras mutations, smad-4/tgf-/stat3, stk-11, braf, brca-2, neurotensin, mucs proteins, palb2, mitochondrial mutations, DNA mismatch repair genes, methylation, microrna expression, epithelial-to-mesenchymal transition, egfr mutations, the pi3k-akt-mtor pathway, the vegf pathway, heat shock proteins, cxcr4, the cox pathway, the src pathway, the hedgehog pathway, pancreatic stellate cells, a progression model, and molecular events in uncommon pancreatic tumors). Finally, future therapeutic directions are elucidated.

Molecular predictors of gemcitabine response in pancreatic cancer

Gemcitabine is one of the most used anti-neoplastic drugs with documented activity in almost all major localizations of cancer. In pancreatic cancer treatment, gemcitabine occupies a prominent place as a first line chemotherapy, partly because of the paucity of other efficacious chemotherapy options. In fact, only a minority of pancreatic cancer patients display a response or even stability of disease with the drug. There are currently no clinically applicable means of predicting which patient will derive a clinical benefit from gemcitabine although several proposed markers have been studied. These markers are proteins involved in drug up-take, activation and catabolism or proteins that define the ability of the cell to undergo apoptosis in response to the drug. Several of these markers are reviewed in this paper. We also briefly discuss the possible role of stem cells in drug resistance to gemcitabine.

MicroRNA 34c gene down-regulation via DNA methylation promotes self-renewal and epithelial-mesenchymal transition in breast tumor-initiating cells

Tumor-initiating cells (T-ICs), a subpopulation of cancer cells with stem cell-like properties, are related to tumor relapse and metastasis. Our previous studies identified a distinct profile of microRNA (miRNA) expression in breast T-ICs (BT-ICs), and the dysregulated miRNAs contribute to the self-renewal and tumorigenesis of these cells. However, the underlying mechanisms for miRNA dysregulation in BT-ICs remain obscure. In the present study, we demonstrated that the expression and function of miR-34c were reduced in the BT-ICs of MCF-7 and SK-3rd cells, a breast cancer cell line enriched for BT-ICs. Ectopic expression of miR-34c reduced the self-renewal of BT-ICs, inhibited epithelial-mesenchymal transition, and suppressed migration of the tumor cells via silencing target gene Notch4. Furthermore, we identified a single hypermethylated CpG site in the promoter region of miR-34c gene that contributed to transcriptional repression of miR-34c in BT-ICs by reducing DNA binding activities of Sp1. Therefore, miR-34c reduction in BT-ICs induced by a single hypermethylated CpG site in the promoter region promotes self-renewal and epithelial-mesenchymal transition of BT-ICs.

Computational analysis of expression of human embryonic stem cell-associated signatures in tumors

Background

The cancer stem cell model has been proposed based on the linkage between human embryonic stem cells and human cancer cells. However, the evidences supporting the cancer stem cell model remain to be collected. In this study, we extensively examined the expression of human embryonic stem cell-associated signatures including core genes, transcription factors, pathways and microRNAs in various cancers using the computational biology approach.

Results

We used the class comparison analysis and survival analysis algorithms to identify differentially expressed genes and their associated transcription factors, pathways and microRNAs among normal vs. tumor or good prognosis vs. poor prognosis phenotypes classes based on numerous human cancer gene expression data. We found that most of the human embryonic stem cell- associated signatures were frequently identified in the analysis, suggesting a strong linkage between human embryonic stem cells and cancer cells.

Conclusions

The present study revealed the close linkage between the human embryonic stem cell associated gene expression profiles and cancer-associated gene expression profiles, and therefore offered an indirect support for the cancer stem cell theory. However, many interest issues remain to be addressed further.

Contribution of epithelial-to-mesenchymal transition and cancer stem cells to pancreatic cancer progression

Pancreatic adenocarcinoma remains among the most lethal of human malignancies. Overall 5-y survival is less than 5%, and only 20% of patients presenting with localized disease amenable to surgical resection. Even in patients who undergo resection, long-term survival remains extremely poor. A major contributor to the aggressiveness of multiple cancers, and pancreatic cancer in particular, is the process of epithelial-to-mesenchymal transition (EMT). This review highlights the growing evidence of EMT in pancreatic cancer progression, focusing on the contribution of EMT to the development of cancer stem cells and on interaction of EMT with other pathways central to cancer progression, such as Hedgehog signaling, the K-ras oncogene, and transforming growth factor-beta (TGF-β). We will also discuss EMT-targeting agents currently in development and in clinical trials that may help to reduce the morbidity and mortality associated with pancreatic cancer.

The many faces of wnt and pancreatic ductal adenocarcinoma oncogenesis

Pancreatic ductal adenocarcinoma (PDAC) remains amongst the most lethal human cancers. PDAC is characterized by the tumor mass containing a paucity of malignant cells in association with a large desmoplastic reaction comprised of a variety of stromal components. Sporadic PDAC oncogenesis occurs as a result of the sequential acquisition of genetic aberrations occurring in core genetic pathways. Unfortunately, the average PDAC contains a large number of genetic aberrations that are not uniform between individual cancers. The interplay between the complex genetics and stromal component may represent a significant barrier to the development of effective therapy for this disease and ultimately be an important factor in PDAC lethality. The Wnt pathway has been identified as a one of the common pathways undergoing genetic alterations in PDAC. Wnt is a complex signal transduction pathway utilizing both a β-catenin dependent (canonical) and β-catenin independent (noncanonical) signals to affect a wide array of intracellular events. Wnt signal transduction is an integral component of pancreas organogenesis promoting the expansion and development of the exocrine pancreas. Pancreatic cancer may utilize the Wnt signaling pathway in concert with other signaling pathways such as notch during tumorigenesis. This review will focus on the role of Wnt signal transduction in pancreatic cancer biology.

Standard of care therapy for malignant glioma and its effect on tumor and stromal cells

Glioblastoma is the most common and deadly of the primary central nervous system tumors. Recent advances in molecular characterization have subdivided these tumors into at least three main groups. In addition, these tumors are cellularly complex with multiple stromal cell types contributing to the biology of the tumor and treatment response. Because essentially all glioma patients are treated with radiation, various chemotherapies and steroids, the tumor that finally kills them has been modified by these treatments. Most of the investigation of the effects of therapy on these tumors has focused on the glioma cells per se. However, despite the importance of the stromal cells in these tumors, little has been done to understand the effects of treatment on stromal cells and their contribution to disease. Understanding how current standard therapy affects the biology of the tumor and the tumor stroma may provide insight into the mechanisms that are important to the inhibition of tumor growth as well as the biology of recurrent tumors.

A NOTCH3-mediated squamous cell differentiation program limits expansion of EMT-competent cells that express the ZEB transcription factors

Zinc finger E-box-binding (ZEB) proteins ZEB1 and ZEB2 are transcription factors essential in TGF-β-mediated senescence, epithelial-to-mesenchymal transition (EMT), and cancer stem cell functions. ZEBs are negatively regulated by members of the miR-200 microRNA family, but precisely how tumor cells expressing ZEBs emerge during invasive growth remains unknown. Here, we report that NOTCH3-mediated signaling prevents expansion of a unique subset of ZEB-expressing cells. ZEB expression was associated with the lack of cellular capability of undergoing NOTCH3-mediated squamous differentiation in human esophageal cells. Genetic inhibition of the Notch-mediated transcriptional activity by dominant-negative Mastermind-like 1 (DNMAML1) prevented squamous differentiation and induction of Notch target genes including NOTCH3. Moreover, DNMAML1-enriched EMT-competent cells exhibited robust upregulation of ZEBs, downregulation of the miR-200 family, and enhanced anchorage-independent growth and tumor formation in nude mice. RNA interference experiments suggested the involvement of ZEBs in anchorage-independent colony formation, invasion, and TGF-β-mediated EMT. Invasive growth and impaired squamous differentiation were recapitulated upon Notch inhibition by DNMAML1 in organotypic three-dimensional culture, a form of human tissue engineering. Together, our findings indicate that NOTCH3 is a key factor limiting the expansion of ZEB-expressing cells, providing novel mechanistic insights into the role of Notch signaling in the cell fate regulation and disease progression of esophageal squamous cancers.

Loss of E-cadherin expression and outcome among patients with resectable pancreatic adenocarcinomas

Only a minority of patients who undergo surgical resection for pancreatic ductal adenocarcinoma are cured. Since patient outcome is not reliably predicted using pathological factors (tumor stage, differentiation, and resection margin status) alone, markers of tumor behavior are needed. One candidate predictor of pancreatic cancer outcome is E-cadherin status. CDH1 is a tumor suppressor gene encoding an important cell adhesion molecule (E-cadherin). The aim of this study was to determine if, among patients undergoing pancreaticoduodenectomy for pancreatic adenocarcinoma, loss of E-cadherin expression was an independent predictor of poor outcome. We examined patterns of loss of E-cadherin by immunohistochemistry in tissue microarrays of 329 surgically resected pancreatic ductal adenocarcinomas. E-cadherin expression was then correlated with outcome. Kaplan-Meier analysis and Cox proportional hazards regression modeling were used to assess the mortality risk. One hundred forty-one pancreatic adenocarcinomas (43%) had partial or complete loss of E-cadherin expression within the analyzed tissue cores. In most instances (134 cases, 41%), this loss was partial. Patients whose pancreatic adenocarcinomas had either complete loss (n=7; median survival, 5.5 months) or partial loss (n=134; 12.7 months) of E-cadherin expression had significantly worse median survival than those with uniformly intact E-cadherin expression (n=188; 18.5 months) by univariate (P=0.002) and multivariate (P=0.006) analyses. In subgroup analysis, patients with poorly differentiated cancers had a worse prognosis if their cancers had partial loss of E-cadherin expression (P=0.02). Among patients undergoing pancreaticoduodenectomy for pancreatic ductal adenocarcinoma, partial loss of tumoral E-cadherin expression is an independent predictor of poor outcome.

The two faces of FBW7 in cancer drug resistance

Chemotherapy is an important therapeutic approach for cancer treatment. However, drug resistance is an obstacle that often impairs the successful use of chemotherapies. Therefore, overcoming drug resistance would lead to better therapeutic outcomes for cancer patients. Recently, studies by our own and other groups have demonstrated that there is an intimate correlation between the loss of the F-box and WD repeat domain-containing 7 (FBW7) tumor suppressor and the incurring drug resistance. While loss of FBW7 sensitizes cancer cells to certain drugs, FBW7-/- cells are more resistant to other types of chemotherapies. FBW7 exerts its tumor suppressor function by promoting the degradation of various oncoproteins that regulate many cellular processes, including cell cycle progression, cellular metabolism, differentiation, and apoptosis. Since loss of the FBW7 tumor suppressor is linked to drug resistance, FBW7 may represent a novel therapeutic target to increase drug sensitivity of cancer cells to conventional chemotherapeutics. This paper thus focuses on the new functional aspects of FBW7 in drug resistance.

Nuclear factor-κB-dependent epithelial to mesenchymal transition induced by HIF-1α activation in pancreatic cancer cells under hypoxic conditions

BACKGROUND

Epithelial to mesenchymal transition (EMT) induced by hypoxia is one of the critical causes of treatment failure in different types of human cancers. NF-κB is closely involved in the progression of EMT. Compared with HIF-1α, the correlation between NF-κB and EMT during hypoxia has been less studied, and although the phenomenon was observed in the past, the molecular mechanisms involved remained unclear.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we report that hypoxia or overexpression of hypoxia-inducible factor-1α (HIF-1α) promotes EMT in pancreatic cancer cells. On molecular or pharmacologic inhibition of NF-κB, hypoxic cells regained expression of E-cadherin, lost expression of N-cadherin, and attenuated their highly invasive and drug-resistant phenotype. Introducing a pcDNA3.0/HIF-1α into pancreatic cancer cells under normoxic conditions heightened NF-κB activity, phenocopying EMT effects produced by hypoxia. Conversely, inhibiting the heightened NF-κB activity in this setting attenuated the EMT phenotype.

CONCLUSIONS/SIGNIFICANCE

These results suggest that hypoxia or overexpression of HIF-1α induces the EMT that is largely dependent on NF-κB in pancreatic cancer cells.

Expanding roles of ZEB factors in tumorigenesis and tumor progression

The ZEB family of transcription factors regulates key factors during embryonic development and cell differentiation but their role in cancer biology has only more recently begun to be recognized. Early evidence showed that ZEB proteins induce an epithelial-to-mesenchymal transition linking their expression with increased aggressiveness and metastasis in mice models and a wide range of primary human carcinomas. Reports over the last few years have found that ZEB proteins also play critical roles in the maintenance of cancer cell stemness, control of replicative senescence, tumor angiogenesis, overcoming of oncogenic addiction and resistance to chemotherapy. These expanding roles in tumorigenesis and tumor progression set ZEB proteins as potential diagnostic, prognostic and therapeutic targets.

Mechanism of the mesenchymal-epithelial transition and its relationship with metastatic tumor formation

Cancer metastasis consists of a sequential series of events, and the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are recognized as critical events for metastasis of carcinomas. A current area of focus is the histopathological similarity between primary and metastatic tumors, and MET at sites of metastases has been postulated to be part of the process of metastatic tumor formation. Here, we summarize accumulating evidence from experimental studies that directly supports the role of MET in cancer metastasis, and we analyze the main mechanisms that regulate MET or reverse EMT in carcinomas. Given the critical role of MET in metastatic tumor formation, the potential to effectively target the MET process at sites of metastasis offers new hope for inhibiting metastatic tumor formation.

Emerging pathways and future targets for the molecular therapy of pancreatic cancer

INTRODUCTION

Pancreatic cancer treatment remains a challenge for clinicians and researchers. Despite undisputable advances in the comprehension of the molecular mechanisms underlying cancer development and progression, early disease detection and clinical management of patients has made little, if any, progress in the past 20 years. Clinical development of targeted agents directed against validated pathways, such as the EGF/EGF receptor axis, the mutant KRAS protein, MMPs, and VEGF-mediated angiogenesis, alone or in combination with gemcitabine-based standard chemotherapy, has been disappointing.

AREAS COVERED

This review explores the preclinical rationale for clinical approaches aimed at targeting the TGF-β, IGF, Hedgehog, Notch and NF-κB signaling pathways, to develop innovative therapeutic strategies for pancreatic cancer.

EXPERT OPINION

Although some of the already clinically explored approaches (particularly EGFR and KRAS targeting) deserve further clinical consideration, by employing more innovative and creative clinical trial designs than the gemcitabine-targeted agent paradigm that has thus far invariably failed, the targeting of emerging and relatively unexplored signaling pathways holds great promise to increase our understanding of the complex molecular biology and to advance the clinical management of pancreatic cancer.

Comparative proteomic and radiobiological analyses in human lung adenocarcinoma cells

In clinic, many non-small cell lung cancer (NSCLC) patients receive radiation therapy after chemotherapy failure. However, whether the multidrug resistance (MDR) can elevate the radioresistance (RDR) remains unclear. To evaluate the MDR's effect on the RDR, screen MDR- and RDR-related proteins in human lung adenocarcinoma (HLA) cells and tissues A549, and A549/DDP cells after irradiation were analyzed by colony-forming assay and flow cytometry. Two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) were utilized to identify differentially expressed proteins (DEPs) between them. The value of D0, Dq, and SF2 increased, the mean percentage in G2 phase and apoptosis rate significantly decreased in A549/DDP cells compared with A549 cells. 40 DEP points were found, and among them 27 were identified through proteomics. Four up-regulated proteins (HSPB1, Vimentin, Cofilin-1, and Annexin A4) in MDR cells compared with non-MDR cells, were confirmed by Western blot. Immuno-histochemistry showed that they were also over-expressed in MDR tissues compared with non-MDR counterparts of HLA. These results proved that the MDR in HLA cells and tissues increased the RDR. HSPB1, Vimentin, Cofilin-1, and Annexin A4 are potential biomarkers for predicting HLA response to MDR and RDR, and novel treatment targets of HLA.

Molecular markers of epithelial-to-mesenchymal transition are associated with tumor aggressiveness in breast carcinoma

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) is a transient process occurring during developmental stages and carcinogenesis, characterized by phenotypic and molecular alterations, resulting in increased invasive and metastatic capabilities of cancer cells and drug resistance. Moreover, emerging evidence suggests that EMT is associated with increased enrichment of cancer stem-like cells in neoplastic tissues. We interrogated the molecular alterations occurring in breast cancer using proposed EMT markers such as E-cadherin, vimentin, epidermal growth factor receptor (EGFR), platelet-derived growth factor (PDGF) D, and nuclear factor κ B (NF-κ B) to decipher their roles in the EMT and breast cancer progression.

METHODS

Fifty-seven invasive ductal adenocarcinomas of the breast were assessed for the expression of E-cadherin, vimentin, EGFR, NF-κ B, and PDGF-D using immunohistochemical analysis. Tumors were categorized into three groups: A (ER+, and/or PR+, HER-2/neu-), B (ER+, and/or PR+, HER-2/neu+), and C (triple-negative: ER-, PR-, and HER-2/neu-). Immunostained slides were microscopically evaluated and scored using intensity (0, 1+, 2+, and 3+) and percentage of positive cells, and data were statistically analyzed.

RESULTS

Membranous E-cadherin was positive in all 57 cases (100%), whereas cytoplasmic E-cadherin was predominantly positive in groups B and C compared with group A (21%, 7%, and 0%, respectively). All group A cases were negative for vimentin and EGFR. There was statistically significant increased expression of vimentin (P < .0002), EGFR (P < .0001), and NF-κ B (P < .02) in triple-negative cases when compared with groups A and B.

CONCLUSIONS

Vimentin, EGFR, and NF-κ B were significantly increased in triple-negative tumors, which is consistent with the aggressiveness of these tumors. These markers could be useful as markers for EMT in breast cancers and may serve as predictive markers for designing customized therapy in the future.

Sorafenib inhibits the hepatocyte growth factor-mediated epithelial mesenchymal transition in hepatocellular carcinoma

The epithelial mesenchymal transition (EMT) has emerged as a pivotal event in the development of the invasive and metastatic potentials of cancer progression. Sorafenib, a VEGFR inhibitor with activity against RAF kinase, is active against hepatocellular carcinoma (HCC); however, the possible involvement of sorafenib in the EMT remains unclear. Here, we examined the effect of sorafenib on the EMT. Hepatocyte growth factor (HGF) induced EMT-like morphologic changes and the upregulation of SNAI1 and N-cadherin expression. The downregulation of E-cadherin expression in HepG2 and Huh7 HCC cell lines shows that HGF mediates the EMT in HCC. The knockdown of SNAI1 using siRNA canceled the HGF-mediated morphologic changes and cadherin switching, indicating that SNAI1 is required for the HGF-mediated EMT in HCC. Interestingly, sorafenib and the MEK inhibitor U0126 markedly inhibited the HGF-induced morphologic changes, SNAI1 upregulation, and cadherin switching, whereas the PI3 kinase inhibitor wortmannin did not. Collectively, these findings indicate that sorafenib downregulates SNAI1 expression by inhibiting mitogen-activated protein kinase (MAPK) signaling, thereby inhibiting the EMT in HCC cells. In fact, a wound healing and migration assay revealed that sorafenib completely canceled the HGF-mediated cellular migration in HCC cells. In conclusion, we found that sorafenib exerts a potent inhibitory activity against the EMT by inhibiting MAPK signaling and SNAI1 expression in HCC. Our findings may provide a novel insight into the anti-EMT effect of tyrosine kinase inhibitors in cancer cells.

RAD51 as a potential biomarker and therapeutic target for pancreatic cancer

Chemotherapy is a very important therapeutic strategy for cancer treatment. The failure of conventional and molecularly targeted chemotherapeutic regimes for the treatment of pancreatic cancer highlights a desperate need for novel therapeutic interventions. Chemotherapy often fails to eliminate all tumor cells because of intrinsic or acquired drug resistance, which is the most common cause of tumor recurrence. Overexpression of RAD51 protein, a key player in DNA repair/recombination has been observed in many cancer cells and its hyperexpression is implicated in drug resistance. Recent studies suggest that RAD51 overexpression contributes to the development, progression and drug resistance of pancreatic cancer cells. Here we provide a brief overview of the available pieces of evidence in support of the role of RAD51 in pancreatic tumorigenesis and drug resistance, and hypothesize that RAD51 could serve as a potential biomarker for diagnosis of pancreatic cancer. We discuss the possible involvement of RAD51 in the drug resistance associated with epithelial to mesenchymal transition and with cancer stem cells. Finally, we speculate that targeting RAD51 in pancreatic cancer cells may be a novel approach for the treatment of pancreatic cancer.

Silencing of hHS6ST2 inhibits progression of pancreatic cancer through inhibition of Notch signalling

Many of the ligands involved in developmental processes require HS (heparan sulfate) to modulate signal transduction. hHS6ST2 (human heparan sulfate D-glucosaminyl 6-O-sulfotransferase-2) is a Golgi-resident enzyme that usually acts on GlcA/IdoA(2S)-GlcNAc/NS disaccharide-6-sulfate modifications within the HS sequence. Emerging evidence indicates the importance of 6-O-sulfation in a number of developmental processes. However, any correlation with cancer-related events remains largely unexplored. In the present study, we found that hHS6ST2, but not other variants, was activated in human PC (pancreatic cancer). shRNA (short hairpin RNA)-mediated silencing of endogenous hHS6ST2 expression in the PC cell line PANC-1 inhibited cell invasion and migration. hHS6ST2 knockdown also resulted in markedly reduced tumorigenesis in immunocompromised mice. To specifically explore the molecular alterations resulting from depletion of hHS6ST2-generated 6-O-sulfation, we employed two-dimensional gel electrophoresis technology followed by nano-HPLC-ESI (electrospray ionization)-tandem MS to separate and identify total proteins from PC cells. Our data suggest that hHS6ST2 potentiates Notch signalling in PC cells. We also identified a role for hHS6ST2 in the growth and tumorigenicity of these cells which, at least in part, acts through Notch-mediated EMT (epithelial-mesenchymal transition) and angiogenesis. The results of the present study suggest that hHS6ST2 could be an attractive target for PC therapy.

Transcription factors that mediate epithelial-mesenchymal transition lead to multidrug resistance by upregulating ABC transporters

Development of multidrug resistance (MDR) is a major deterrent in the effective treatment of metastatic cancers by chemotherapy. Even though MDR and cancer invasiveness have been correlated, the molecular basis of this link remains obscure. We show here that treatment with chemotherapeutic drugs increases the expression of several ATP binding cassette transporters (ABC transporters) associated with MDR, as well as epithelial–mesenchymal transition (EMT) markers, selectively in invasive breast cancer cells, but not in immortalized or non-invasive cells. Interestingly, the mere induction of an EMT in immortalized and non-invasive cell lines increased their expression of ABC transporters, migration, invasion, and drug resistance. Conversely, reversal of EMT in invasive cells by downregulating EMT-inducing transcription factors reduced their expression of ABC transporters, invasion, and rendered them more chemosensitive. Mechanistically, we demonstrate that the promoters of ABC transporters carry several binding sites for EMT-inducing transcription factors, and overexpression of Twist, Snail, and FOXC2 increases the promoter activity of ABC transporters. Furthermore, chromatin immunoprecipitation studies revealed that Twist binds directly to the E-box elements of ABC transporters. Thus, our study identifies EMT inducers as novel regulators of ABC transporters, thereby providing molecular insights into the long-standing association between invasiveness and MDR. Targeting EMT transcription factors could hence serve as novel strategies to curb both metastasis and the associated drug resistance.

MiR-200b and miR-15b regulate chemotherapy-induced epithelial-mesenchymal transition in human tongue cancer cells by targeting BMI1

Chemotherapy has been reported to induce epithelial-mesenchymal transition (EMT) in tumor cells, which is a critical step in the process of metastasis leading to cancer spreading and treatment failure. However, the underlying mechanisms of chemotherapy-induced EMT remain unclear, and the involvement of microRNAs (miRNA) in this process is poorly understood. To address these questions, we established stable chemotherapy-resistant tongue squamous cell carcinoma (TSCC) cell lines CAL27-res and SCC25-res by exposing the parental CAL27 and SCC25 lines to escalating concentrations of cisplatin for 6 months. CAL27-res and SCC25-res cells displayed mesenchymal features with enhanced invasiveness and motility. MiRNA microarray illustrated that miR-200b and miR-15b were the most significantly downregulated microRNAs in CAL27-res cells. Ectopic expression of miR-200b and miR-15b with miRNA mimics effectively reversed the phenotype of EMT in CAL27-res and SCC25-res cells, and sensitized them to chemotherapy, but inhibition of miR-200b and miR-15b in the sensitive lines with anti-sense oligonucleotides induced EMT and conferred chemoresistance. Retrieving the expression of B lymphoma Mo-MLV insertion region 1 homolog (BMI1), a target for miR-200b and miR-15b, in the presence of the miRNA mimics by transfecting CAL27-res cells with pcDNA3.1-BMI1-carrying mutated seed sequences of miR-200b or miR-15b at its 3'-UTR recapitulated chemotherapy-induced EMT. In vivo, enforced miR-200b or miR-15b expression suppressed metastasis of TSCC xenografts established by CAL27-res cells. Clinically, reduced miR-200b or miR-15b expression was associated with chemotherapeutic resistance in TSCCs and poor patient survival. Our data suggest that reduced expression of miR-200b and miR-15b underscores the mechanisms of chemotherapy-induced EMT in TSCC, and may serve as therapeutic targets to reverse chemotherapy resistance in tongue cancers.

Overcoming drug resistance in pancreatic cancer

INTRODUCTION

Pancreatic cancer has the worst survival rate of all cancers. The current standard care for metastatic pancreatic cancer is gemcitabine, however, the success of this treatment is poor and overall survival has not improved for decades. Drug resistance (both intrinsic and acquired) is thought to be a major reason for the limited benefit of most pancreatic cancer therapies.

AREAS COVERED

Previous studies have indicated various mechanisms of drug resistance in pancreatic cancer, including changes in individual genes or signaling pathways, the influence of the tumor microenvironment, and the presence of highly resistant stem cells. This review summarizes recent advances in the mechanisms of drug resistance in pancreatic cancer and potential strategies to overcome this.

EXPERT OPINION

Increasing drug delivery efficiency and decreasing drug resistance is the current aim in pancreatic cancer treatment, and will also benefit the treatment of other cancers. Understanding the molecular and cellular basis of drug resistance in pancreatic cancer will lead to the development of novel therapeutic strategies with the potential to sensitize pancreatic cancer to chemotherapy, and to increase the efficacy of current treatments in a wide variety of human cancers.

Deconstructing the mechanisms and consequences of TGF-β-induced EMT during cancer progression

Transforming growth factor-β (TGF-β) is a potent pleiotropic cytokine that regulates mammalian development, differentiation, and homeostasis in essentially all cell types and tissues. TGF-β normally exerts anticancer activities by prohibiting cell proliferation and by creating cell microenvironments that inhibit cell motility, invasion, and metastasis. However, accumulating evidence indicates that the process of tumorigenesis, particularly that associated with metastatic progression, confers TGF-β with oncogenic activities, a functional switch known as the "TGF-β paradox." The molecular determinants governing the TGF-β paradox are complex and represent an intense area of investigation by researchers in academic and industrial settings. Recent findings link genetic and epigenetic events in mediating the acquisition of oncogenic activity by TGF-β, as do aberrant alterations within tumor microenvironments. These events coalesce to enable TGF-β to direct metastatic progression via the stimulation of epithelial-mesenchymal transition (EMT), which permits carcinoma cells to abandon polarized epithelial phenotypes in favor of apolar mesenchymal-like phenotypes. Attempts to deconstruct the EMT process induced by TGF-β have identified numerous signaling molecules, transcription factors, and microRNAs operant in mediating the initiation and resolution of this complex transdifferentiation event. In addition to its ability to enhance carcinoma cell invasion and metastasis, EMT also endows transitioned cells with stem-like properties, including the acquisition of self-renewal and tumor-initiating capabilities coupled to chemoresistance. Here, we review recent findings that delineate the pathophysiological mechanisms whereby EMT stimulated by TGF-β promotes metastatic progression and disease recurrence in human carcinomas.

Epigenetic markers for chemosensitivity and chemoresistance in pancreatic cancer--a review

Adjuvant first-line gemcitabine monochemotherapy presents a standard treatment for patients with advanced pancreatic adenocarcinoma and improves overall survival in chemosensitive patients. Nonetheless, 6-month progression-free survival remains below 15%, despite interdisciplinary approaches. The success of gemcitabine treatment is disappointing and-in the absence of reliable tumor markers--challenging to quantify. Epigenetic alterations have been recently identified to take on important roles in cancer development and possibly cancer treatment. In this context, microRNAs are becoming increasingly acknowledged as useful biomarkers for classifying cancers and providing information on their chemo- and radiosensitivity. This review illustrates the potential of genetic and epigenetic markers in the prediction of chemosensitivity in pancreatic cancer patients and in the monitoring of their response rates to adjuvant therapy.

Detecting and targeting mesenchymal-like subpopulations within squamous cell carcinomas

Curative eradication of all cells within carcinomas is seldom achievable with chemotherapy alone. This limitation may be partially attributable to tumor cell subpopulations with intrinsic resistance to current drugs. Within squamous cell carcinoma (SCC) cell lines, we previously characterized a subpopulation of mesenchymal-like cells displaying phenotypic plasticity and increased resistance to both cytotoxic and targeted agents. These mesenchymal-like (Ecad-lo) cells are separable from epithelial-like (Ecad-hi) cells based on loss of surface E-cadherin and expression of vimentin. Despite their long-term plasticity, both Ecad-lo and Ecad-hi subsets in short-term culture maintained nearly uniform phenotypes after purification. This stability allowed testing of segregated subpopulations for relative sensitivity to the cytotoxic agent cisplatin in comparison to salinomycin, a compound with reported activity against CD44(+)CD24(-) stem-like cells in breast carcinomas. Salinomycin showed comparable efficacy against both Ecad-hi and Ecad-lo cells in contrast to cisplatin, which selectively depleted Ecad-hi cells. An in vivo correlate of these mesenchymal-like Ecad-lo cells was identified by immunohistochemical detection of vimentin-positive malignant subsets across a part of direct tumor xenografts (DTXs) of advanced stage SCC patient samples. Cisplatin treatment of mice with established DTXs caused enrichment of vimentin-positive malignant cells in residual tumors, but salinomycin depleted the same subpopulation. These results demonstrate that mesenchymal-like SCC cells, which resist current chemotherapies, respond to a treatment strategy developed against a stem-like subset in breast carcinoma. Further, they provide evidence of mesenchymal-like subsets being well-represented across advanced stage SCCs, suggesting that intrinsic drug resistance in this subpopulation has high clinical relevance.

Activated K-ras and INK4a/Arf deficiency cooperate during the development of pancreatic cancer by activation of Notch and NF-κB signaling pathways

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death in the United States, suggesting that novel strategies for the prevention and treatment of PDAC are urgently needed. K-ras mutations are observed in >90% of pancreatic cancer, suggesting its role in the initiation and early developmental stages of PDAC. In order to gain mechanistic insight as to the role of mutated K-ras, several mouse models have been developed by targeting a conditionally mutated K-ras(G12D) for recapitulating PDAC. A significant co-operativity has been shown in tumor development and metastasis in a compound mouse model with activated K-ras and Ink4a/Arf deficiency. However, the molecular mechanism(s) by which K-ras and Ink4a/Arf deficiency contribute to PDAC has not been fully elucidated.

METHODOLOGY/PRINCIPAL FINDINGS

To assess the molecular mechanism(s) that are involved in the development of PDAC in the compound transgenic mice with activated K-ras and Ink4a/Arf deficiency, we used multiple methods, such as Real-time RT-PCR, western blotting assay, immunohistochemistry, MTT assay, invasion, EMSA and ELISA. We found that the deletion of Ink4a/Arf in K-ras(G12D) expressing mice leads to PDAC, which is in part mediated through the activation of Notch and NF-κB signaling pathways. Moreover, we found down-regulation of miR-200 family, which could also play important roles in tumor development and progression of PDAC in the compound transgenic mice.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that the activation of Notch and NF-κB together with the loss of miR-200 family is mechanistically linked with the development and progression of PDAC in the compound K-ras(G12D) and Ink4a/Arf deficient transgenic mice.

Notch signaling activated by replication stress-induced expression of midkine drives epithelial-mesenchymal transition and chemoresistance in pancreatic cancer

The incidence of pancreatic ductal adenocarcinoma (PDAC) nearly equals its mortality rate, partly because most PDACs are intrinsically chemoresistant and thus largely untreatable. It was found recently that chemoresistant PDAC cells overexpress the Notch-2 receptor and have undergone epithelial-mesenchymal transition (EMT). In this study, we show that these two phenotypes are interrelated by expression of Midkine (MK), a heparin-binding growth factor that is widely overexpressed in chemoresistant PDAC. Gemcitabine, the front-line chemotherapy used in PDAC treatment, induced MK expression in a dose-dependent manner, and its RNAi-mediated depletion was associated with sensitization to gemcitabine treatment. We identified an interaction between the Notch-2 receptor and MK in PDAC cells. MK-Notch-2 interaction activated Notch signaling, induced EMT, upregulated NF-κB, and increased chemoresistance. Taken together, our findings define an important pathway of chemoresistance in PDAC and suggest novel strategies for its clinical attack.

Cancer stem cells and chemosensitivity

Cancer lethality is mainly due to the onset of distant metastases and refractoriness to chemotherapy. Thus, the development of molecular targeted agents that can restore or increase chemosensitivity will provide valuable therapeutic options for cancer patients. Growing evidence indicates that a cellular subpopulation with stem cell-like features, commonly referred to as cancer stem cells (CSCs), is critical for tumor generation and maintenance. Recent advances in stem cell biology are revealing that this cellular fraction shares many properties with normal adult stem cells and is able to propagate the parental tumor in animal models. CSCs seem to be protected against widely used chemotherapeutic agents by means of different mechanisms, such as a marked proficiency in DNA damage repair, high expression of ATP-binding cassette drug transporters, and activation of PI3K/AKT and Wnt pathways. Moreover, microenvironmental stimuli such as those involved in the epithelial-mesenchymal transition and hypoxia indirectly contribute to chemoresistance by inducing in cancer cells a stem-like phenotype. Understanding how CSCs overcome chemotherapy-induced death stimuli, and integrating such knowledge into clinical research methodology, has become a priority in the process of identifying innovative therapeutic strategies aimed at improving the outcome of cancer patients.

Oncolytic virotherapy for pancreatic cancer

Within the past decade, many oncolytic viruses (OVs) have been studied as potential treatments for pancreatic cancer and some of these are currently under clinical trials. The applicability of certain OVs, such as adenoviruses, herpesviruses and reoviruses, for the treatment of pancreatic cancer has been intensively studied for several years, whereas the applicability of other more recently investigated OVs, such as poxviruses and parvoviruses, is only starting to be determined. At the same time, studies have identified key characteristics of pancreatic cancer biology that provide a better understanding of the important factors or pathways involved in this disease. This review aims to summarise the different replication-competent OVs proposed as therapeutics for pancreatic cancer. It also focuses on the unique biology of these viruses that makes them exciting candidate virotherapies for pancreatic cancer and discusses how they could be genetically manipulated or combined with other drugs to improve their efficacy based on what is currently known about the molecular biology of pancreatic cancer.

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.

Stem cells in squamous head and neck cancer

The initiation and metastasis of head and neck squamous cell carcinomas (HNSCC) and other cancers have recently been related to the presence of cancer stem cells (CSC). CSC are cancer initiating, sustaining and are mostly quiescent. Specific markers that vary considerably depending on tumor type or tissue of origin characterize putative CSC. Compared to the bulk tumor mass, CSC are less sensitive to chemo- and radiotherapy and may also have low immunogenicity. Therapeutic targeting of CSC may improve clinical outcome of HNSCC which has two distinct etiologies: infection of epithelial stem cells by high-risk types of the human papillomavirus, or long-term tobacco and alcohol abuse. Recent knowledge on the role of CSC in HNSCC is reviewed and where necessary parallels to CSC of other origin are drawn to give a more comprehensive picture.

Challenges of drug resistance in the management of pancreatic cancer

The current treatment of choice for metastatic pancreatic cancer involves single-agent gemcitabine or a combination of gemcitabine with capecitabine or erlotinib (a tyrosine kinase inhibitor). Only 25&#x2013;30% of patients respond to this treatment and patients who do respond initially ultimately exhibit disease progression. Median survival for pancreatic cancer patients has reached a plateau due to inherent and acquired resistance to these agents. Key molecular factors implicated in this resistance include: deficiencies in drug uptake, alteration of drug targets, activation of DNA repair pathways, resistance to apoptosis and the contribution of the tumor microenvironment. Moreover, for newer agents including tyrosine kinase inhibitors, overexpression of signaling proteins, mutations in kinase domains, activation of alternative pathways, mutations of genes downstream of the target and/or amplification of the target represent key challenges for treatment efficacy. Here we will review the contribution of known mechanisms and markers of resistance to key pancreatic cancer drug treatments.

Discovery of a linear peptide for improving tumor targeting of gene products and treatment of distal tumors by IL-12 gene therapy

Like many effective therapeutics, interleukin-12 (IL-12) therapy often causes side effects. Tumor targeted delivery may improve the efficacy and decrease the toxicity of systemic IL-12 treatments. In this study, a novel targeting approach was investigated. A secreted alkaline phosphatase (SEAP) reporter gene-based screening process was used to identify a mini-peptide which can be produced in vivo to target gene products to tumors. The coding region for the best peptide was inserted into an IL-12 gene to determine the antitumor efficacy. Affinity chromatography, mass spectrometry analysis, and binding studies were used to identify a receptor for this peptide. We discovered that the linear peptide VNTANST increased the tumor accumulation of the reporter gene products in five independent tumor models including one human xenogeneic model. The product from VNTANST-IL-12 fusion gene therapy increased accumulation of IL-12 in the tumor environment, and in three tumor models, VNTANST-IL-12 gene therapy inhibited distal tumor growth. In a spontaneous lung metastasis model, inhibition of metastatic tumor growth was improved compared to wild-type IL-12 gene therapy, and in a squamous cell carcinoma model, toxic liver lesions were reduced. The receptor for VNTANST was identified as vimentin. These results show the promise of using VNTANST to improve IL-12 treatments.

Pancreatic cancer cells resistant to chemoradiotherapy rich in "stem-cell-like" tumor cells

BACKGROUND

Tumor resistance to chemoradiation therapy is partly attributed to the presence of apoptosis-resistant cancer stem cells (CSCs). Chemoradiation therapy can enrich CSCs by killing apoptosis-susceptible cancer cells.

AIM

Our preliminary study showed chemoradiation-resistant pancreatic cancer cells to have some CSC characteristics, and to undergo epithelial-mesenchymal transition (EMT); we aimed to verify that study's implication that chemoradiation-resistant subpopulations are enriched with "stem-cell-like" tumor cells, which may be linked to EMT.

METHODS

Four pancreatic cancer cell lines were cultured in gemcitabine with synchronous radiotherapy to obtain resistant subpopulations. Morphological changes were observed under microscope; migration and invasiveness were assessed by Transwell tests. Protein expression was determined by immunoblotting. Pancreatic CSC markers were studied using fluorescence-activated cell sorting analyses. Colony-formation tests, tumor sphere formation assays, and tumor xenografts in BALB/C nude mice were used to evaluate "stemness" in resistant cells.

RESULTS

Resistant cells expressed more antiapoptotic protein Bcl-2, apoptosis-inhibitory protein survivin, and stem cell markers Oct4, ABCG2, CD24, and CD133, were more tumorigenic in vitro and in vivo, and showed phenotypic and molecular changes consistent with EMT, including upregulation of vimentin and downregulation of E-cadherin. They were also more invasive and migratory.

CONCLUSIONS

We found chemoradiation-resistant pancreatic cancer cells to be similar to CSCs and to undergo EMT, suggesting that chemoradiation resistance-induced EMT is linked to CSC generation.

Markedly increased Oct4 and Nanog expression correlates with cisplatin resistance in oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) is the sixth most prevalent cancer worldwide. Cancer stem cells (CSC) model theoretically contribute to tumor growth, metastasis, and chemo-radioresistance. Cisplatin is a widely used chemotherapeutic agent for OSCC treatment. The aim of this study was to compare stemness genes expression in chemo-sensitive and chemo-resistant specimens and further explore the potential markers that may lead to induce chemo-resistance in OSCC.

METHODS

The study method is the treatment of OC2 cells with cisplatin select cisplatin-resistant OC2 cells. Self-renewal ability was evaluated by cultivating parental and cisplatin-resistant OC2 cells within sphere-forming assay after serial passages. Differential expression profile of stemness markers between parental and cisplatin-resistant OC2 cells was elucidated. The parental and cisplatin-resistant OC2 cells were assessed for migration/invasion/clonogenicity tumorigenic properties in vitro. Expression of stemness markers in chemo-sensitive and chemo-resistant patients with OSCC was performed by immunohistochemistry staining in vivo.

RESULTS

Sphere-forming/self-renewal capability was increased in cisplatin-resistant OC2 cells. Cisplatin-resistant OC2 cells highly expressed the stemness markers (Nanog, Oct4, Bmi1, CD117, CD133, and ABCG2). Furthermore, cisplatin-resistant OC2 cells increased migration/invasion/clonogenicity ability. Notably, up-regulation of Oct4 and Nanog expression was significantly observed in cisplatin-resistant patients with OSCC (**P < 0.01).

CONCLUSIONS

These data indicate that cancer stem-like properties were expanded during the acquisition of cisplatin resistance in OSCC. Clinically, oral cancer stemness markers (Oct4 and Nanog) overexpression may promote the OSCC's recurrence to resist cisplatin.

The sensors and regulators of cell-matrix surveillance in anoikis resistance of tumors

Normal cells continuously monitor the nature of their respective cellular microenvironment. They are equipped with an inherent molecular defense to detect changes that can precipitate and trigger an oncogenic cascade in the internal and external environment of cells. The process called anoikis unleashes many a characteristic molecular change in the cells which eventually program to cell death in response to cell detachment and inappropriate cellular attachment, both of which can otherwise potentiate the ability of cells to preferentially pursue a malignant course due to the release of molecular discipline which conforms them to a benign structural and functional spectrum. The initiation and propagation of signaling that serves as a switch to cell survival or cell death mediated by surveillance of cell microenvironment is comprised of many heterogeneous sets of molecules interacting mainly at the interface of cell-extracellular matrix. Transforming cells continuously reprogram their signaling characteristics in sensing and modulating the stimuli from cell surface molecules like integrins, cadherins and immunoglobulin family of cell adhesion molecules at adhesion complexes, which enables them to resist anoikis and metastasize to different organs. Actin cytoskeleton binds BIM and Bcl2 modifying factor (BMF), which are regulated by the adhesion status and consequent conformation of cytoskeleton in the cells. This review aims at an integrated synopsis of fundamental mechanisms of the critical interactions of cell surface molecules to facilitate a focused analysis of the differential regulation of signaling processes at cell-ECM junctions that collectively rein the anoikis resistance, which in turn impacts metastatic aggressiveness and drug resistance of tumors originating from respective organs.

The ZEB1/miR-200 feedback loop controls Notch signalling in cancer cells

Notch signalling is important for development and tissue homeostasis and activated in many human cancers. Nevertheless, mutations in Notch pathway components are rare in solid tumours. ZEB1 is an activator of an epithelial-mesenchymal transition (EMT) and has crucial roles in tumour progression towards metastasis. ZEB1 and miR-200 family members repress expression of each other in a reciprocal feedback loop. Since miR-200 members target stem cell factors, ZEB1 indirectly induces stemness maintenance and associated drug resistance. Here, we link ZEB1 and its cancer promoting properties to Notch activation. We show that miR-200 members target Notch pathway components, such as Jagged1 (Jag1) and the mastermind-like coactivators Maml2 and Maml3, thereby mediating enhanced Notch activation by ZEB1. We further detected a coordinated upregulation of Jag1 and ZEB1, associated with reduced miR-200 expression in two aggressive types of human cancer, pancreatic adenocarcinoma and basal type of breast cancer. These findings explain increased Notch signalling in some types of cancers, where mutations in Notch pathway genes are rare. Moreover, they indicate an additional way how ZEB1 exerts its tumour progressing functions.

Molecular targeted approaches for treatment of pancreatic cancer

Human pancreatic cancer remains a highly malignant disease with almost similar incidence and mortality despite extensive research. Many targeted therapies are under development. However, clinical investigation showed that single targeted therapies and most combined therapies were not able to improve the prognosis of this disease, even though some of these therapies had excellent anti-tumor effects in pre-clinical models. Cross-talk between cell proliferation signaling pathways may be an important phenomenon in pancreatic cancer, which may result in cancer cell survival even though some pathways are blocked by targeted therapy. Pancreatic cancer may possess different characteristics and targets in different stages of pathogenesis, maintenance and metastasis. Sensitivity to therapy may also vary for cancer cells at different stages. The unique pancreatic cancer structure with abundant stroma creates a tumor microenvironment with hypoxia and low blood perfusion rate, which prevents drug delivery to cancer cells. In this review, the most commonly investigated targeted therapies in pancreatic cancer treatment are discussed. However, how to combine these targeted therapies and/or combine them with chemotherapy to improve the survival rate of pancreatic cancer is still a challenge. Genomic and proteomic studies using pancreatic cancer samples obtained from either biopsy or surgery are recommended to individualize tumor characters and to perform drug sensitivity study in order to design a tailored therapy with minimal side effects. These studies may help to further investigate tumor pathogenesis, maintenance and metastasis to create cellular expression profiles at different stages. Integration of the information obtained needs to be performed from multiple levels and dimensions in order to develop a successful targeted therapy.

Pancreatic cancer: understanding and overcoming chemoresistance

Pancreatic cancer is a highly aggressive malignancy. This feature is believed to be partly attributable to the chemotherapy-resistant characteristics of specific subgroups of pancreatic cancer cells, namely those with an epithelial-mesenchymal transition (EMT) phenotype and cancer stem cells. Accumulating evidence suggests that several new and emerging concepts might be important in the drug-resistant phenotype of these cell types. An understanding of the molecular mechanisms underlying drug resistance in patients with pancreatic cancer might help researchers to devise novel strategies to overcome such resistance. In particular, microRNAs (miRNAs) seem to be critical regulators of drug resistance in pancreatic cancer cells. Selective and targeted elimination of cells with an EMT phenotype and cancer stem cells could be achieved by regulating the expression of specific miRNAs.

Contribution of epithelial-mesenchymal transition to pancreatic cancer progression

Pancreatic adenocarcinoma (PDAC) is one of the most lethal human malignancies, with median survival of less than one year and overall five-year survival of less than 5%. There is increasing evidence demonstrating that epithelial-mesenchymal transition (EMT) contributes to pancreatic cancer metastasis and to treatment resistance. In this review, we will examine the data demonstrating the role and regulation of EMT in pancreatic cancer progression, focusing particularly on the transcription factors and microRNAs involved in EMT. We will examine how EMT is involved in the generation and maintenance of stem cells, and the role of EMT in modulating resistance of PDAC cells to drug therapies. We will also identify putative EMT-targeting agents that may help to reduce the morbidity and mortality associated with pancreatic cancer.

Epithelial-mesenchymal transition in pancreatic carcinoma

Pancreatic carcinoma is the fourth-leading cause of cancer death and is characterized by early invasion and metastasis. The developmental program of epithelial-mesenchymal transition (EMT) is of potential importance for this rapid tumor progression. During EMT, tumor cells lose their epithelial characteristics and gain properties of mesenchymal cells, such as enhanced motility and invasive features. This review will discuss recent findings pertinent to EMT in pancreatic carcinoma. Evidence for and molecular characteristics of EMT in pancreatic carcinoma will be outlined, as well as the connection of EMT to related topics, e.g., cancer stem cells and drug resistance.

EMT- and microRNA-related signaling pathways in tumors

Epithelial-mesenchymal transition (EMT) refers to the process by which cells transit from epithelial phenotype to mesenchymal phenotype. EMT is critical for tumor invasion and metastasis, however, the underlying mechanism is little known so far. It has been known that complex signaling pathways are involved in this process. MicroRNAs also play an important role in tumors via many EMT-related signaling pathways. Numerous studies have established that there is a link between EMT-related signaling pathways and microRNAs in tumors. This review focuses on the action mechanism of various EMT-related signaling pathways and their relationship with microRNAs in tumors.

Targeting Notch signaling pathway to overcome drug resistance for cancer therapy

Chemotherapy is an important therapeutic strategy for cancer treatment and remains the mainstay for the management of human malignancies; however, chemotherapy fails to eliminate all tumor cells because of intrinsic or acquired drug resistance, which is the most common cause of tumor recurrence. Recently, emerging evidences suggest that Notch signaling pathway is one of the most important signaling pathways in drug-resistant tumor cells. Moreover, down-regulation of Notch pathway could induce drug sensitivity, leading to increased inhibition of cancer cell growth, invasion, and metastasis. This article will provide a brief overview of the published evidences in support of the roles of Notch in drug resistance and will further summarize how targeting Notch by "natural agents" could become a novel and safer approach for the improvement of tumor treatment by overcoming drug resistance.

CXCL12-CXCR4 signalling axis confers gemcitabine resistance to pancreatic cancer cells: a novel target for therapy

BACKGROUND

Pancreatic cancer cells are highly resistant to drug therapy; however, underlying causes remain largely unknown. We hypothesised that the activation of CXCL12-CXCR4 signalling confers drug resistance to pancreatic cancer cells by potentiating survival. CXCR4 is overexpressed in precancerous/malignant pancreatic lesions and cancer stem cells, and implicated in its pathogenesis.

METHODS

Effect of CXCR4 activation by CXCL12 on restricting the gemcitabine-induced cytotoxicity and stimulating the survival signalling was examined in pancreatic cancer cells by MTT, DNA laddering, caspase activity, immunoblot, and promoter-reporter assays. Subsequently, we examined the effect of CXCR4 antagonist, AMD3100, in abrogating the rescue effect of activated CXCL12-CXCR4 signalling.

RESULTS

The pancreatic cancer cells treated with gemcitabine exhibited reduced cytotoxicity in the presence of CXCL12 as compared with the cells treated with drug alone. CXCL12 induced the activation of FAK, ERK, and Akt signalling pathways, enhanced transcriptional activities of β-catenin and NF-κB, and expression of survival proteins. AMD3100 arrested the CXCL12-induced pancreatic cancer cell growth and drug resistance.

CONCLUSION

Our findings demonstrate, for the first time, a role of CXCL12-CXCR4 signalling axis in conferring drug resistance to pancreatic cancer cells and suggest that it could serve as a novel therapeutic target for pancreatic cancer therapy, alone and in combination with the cytotoxic drug.

Molecular signature of epithelial-mesenchymal transition (EMT) in human prostate cancer bone metastasis

Prostate cancer (PCa) has a predilection to metastasize to bone. Before metastasis can occur there is transition of the sessile epithelial cancer cells to become motile and invasive mesenchymal phenotypes by an important albeit transient process called Epithelial-to-Mesenchymal Transition (EMT). The cascade of molecular events triggered by this process is clinically relevant as they are associated with cancer stem-like cells (CSC), decreased senescence and eventual drug resistance phenotype. We interrogated some EMT markers that have been implicated in primary and bone metastasis of PCa using archived patient samples. Using an immunohistochemical approach, E-cadherin, Vimentin, ZEB1, Notch-1, PDGF-D and NF-κB were analyzed. Cases were microscopically scored using intensity (0, +1, +2, +3) and percentage of positive cells. Data was statistically analyzed using Fisher's Exact Test. Aberrant expression of EMT markers E-cadherin, Vimentin, PDGF-D, NF-κB, Notch-1 and ZEB1 was observed in PCa (primary tumor specimen) and bone metastasis tissues. The aberrant expression pattern varied according to the location within the tumor with higher expression was observed more at the invasive tumor front (ITF) vs. the center of the tumor. Notch-1 was significantly over-expressed in bone metastasis compared to primary PCa (p=0.057). The expression levels, intensity and % of positive cells of the remaining markers were not statistically significant in PCa vs. bone metastasis. In conclusion, protein expression analysis revealed the existence of EMT phenotype in the PCa and bone metastasis. Variation in the aberrant expression patterns at the invasive tumor front indicates the role of EMT markers in tumor invasion. Our results suggest that Notch-1 could play a role in PCa bone metastasis. Studies in larger patient cohorts are warranted before these EMT molecular markers can be translated to the clinical use.

Tissue transglutaminase promotes drug resistance and invasion by inducing mesenchymal transition in mammary epithelial cells

Recent observations that aberrant expression of tissue transglutaminase (TG2) promotes growth, survival, and metastasis of multiple tumor types is of great significance and could yield novel therapeutic targets for improved patient outcomes. To accomplish this, a clear understanding of how TG2 contributes to these phenotypes is essential. Using mammary epithelial cell lines (MCF10A, MCF12A, MCF7 and MCF7/RT) as a model system, we determined the impact of TG2 expression on cell growth, cell survival, invasion, and differentiation. Our results show that TG2 expression promotes drug resistance and invasive functions by inducing epithelial-mesenchymal transition (EMT). Thus, TG2 expression supported anchorage-independent growth of mammary epithelial cells in soft-agar, disrupted the apical-basal polarity, and resulted in disorganized acini structures when grown in 3D-culture. At molecular level, TG2 expression resulted in loss of E-cadherin and increased the expression of various transcriptional repressors (Snail1, Zeb1, Zeb2 and Twist1). Tumor growth factor-beta (TGF-β) failed to induce EMT in cells lacking TG2 expression, suggesting that TG2 is a downstream effector of TGF-β-induced EMT. Moreover, TG2 expression induced stem cell-like phenotype in mammary epithelial cells as revealed by enrichment of CD44(+)/CD24(-/low) cell populations. Overall, our studies show that aberrant expression of TG2 is sufficient for inducing EMT in epithelial cells and establish a strong link between TG2 expression and progression of metastatic breast disease.