Characterization and functional analysis of a slow cycling stem cell-like subpopulation in pancreas adenocarcinoma

Cancer stem cell theory: therapeutic implications for nanomedicine

Evidence continues to accumulate showing that tumors contain a minority population of cells responsible for tumor initiation, growth, and recurrence. These are termed "cancer stem cells" (CSCs). Functional assays have identified the self-renewal and tumor-initiation capabilities of CSCs. Moreover, recent studies have revealed that these CSCs is responsible for chemotherapy resistance within a tumor. Several mechanisms of chemoresistance have been proposed, including increased Wnt/β-catenin and Notch signaling, as well as high expression levels of adenosine triphosphate-binding cassette transporters, an active DNA repair capacity, and slow rate of self-renewal. Nanoscale drug-delivery systems, which transport therapeutically active molecules, prolong circulation, and improve biodistribution in the body, may allow more effective and specific therapies to address the challenges posed by CSCs. In particular, some nanovehicles are being exploited for selective drug delivery to CSCs and show promising results. In this review, we highlight the mechanisms of drug resistance and the novel strategies using nanoscale drugs to eliminate CSCs.

Stem cells from trabecular meshwork home to TM tissue in vivo

PURPOSE

To investigate the potential of human trabecular meshwork stem cells (TMSCs) for homing to mouse TM tissue and survival in vivo.

METHODS

Human TMSCs and fibroblasts were labeled with fluorescent membrane dye DiO and injected into normal mouse anterior chamber. Stem cell and TM cell markers were identified by immunofluorescent staining of cryosections or tissue whole mounts. Apoptosis was determined by TUNEL assay. Replicating and inflammatory cells were detected by bromodeoxyuridine (BrdU) incorporation and anti-CD45 staining, respectively. Quantitative RT-PCR detected gene expression of injected cells after isolation by fluorescence activated cell sorting. Intraocular pressure was measured using a TonoLab rebound tonometer.

RESULTS

Expanded cultures of DiO-labeled TMSCs expressed stem cell markers preferentially in DiO positive cells, demonstrating a slow-cycling, label-retaining stem cell phenotype. DiO-labeled TMSCs injected into the anterior chamber of normal mice localized primarily in TM, remaining in the tissue at least 4 months. Within 1 week, TM-associated TMSCs began expressing TM marker protein CHI3L1. Fibroblasts injected in mouse anterior chamber showed distributed localization in corneal endothelium, lens epithelium, and TM and did not express CHI3L1. Little apoptosis was detected in injected TM tissue and intraocular pressure was not elevated during the experiment. Dividing cells or CD45-staining cells were not detected after TMSC-injection.

CONCLUSIONS

Stem cells isolated from human TM and expanded in vitro exhibit the ability to home to the TM and differentiate into TM cells in vivo. Such cells present a potential for development of a novel cell-based therapy for glaucoma.

MYC regulation of CHK1 and CHK2 promotes radioresistance in a stem cell-like population of nasopharyngeal carcinoma cells

Radiotherapy is the most successful nonsurgical treatment for nasopharyngeal carcinoma (NPC). Despite this, the prognosis remains poor. Although NPCs initially respond well to a full course of radiation, recurrence is frequent. The cancer stem cell (CSC) hypothesis provides a framework for explaining the discrepancy between the response of NPC to therapy and the poor survival rate. In this study, a stem cell-like subpopulation (PKH26+) was identified in NPC cell lines using a label-retention technique. PKH26+ cells were enriched for clonogenicity, sphere formation, side-population cells, and resistance to radiotherapy. Using genomic approaches, we show that the proto-oncogene c-MYC (MYC) regulates radiotolerance through transcriptional activation of CHK1 (CHEK1) and CHK2 (CHEK2) checkpoint kinases through direct binding to the CHK1 and CHK2 promoters. Overexpression of c-MYC in the PKH26+ subpopulation leads to increased expression of CHK1 and CHK2 and subsequent activation of the DNA-damage-checkpoint response, resulting in radioresistance. Furthermore, loss of CHK1 and CHK2 expression reverses radioresistance in PKH26+ (c-MYC high expression) cells in vitro and in vivo. This study elucidates the role of the c-MYC-CHK1/CHK2 axis in regulating DNA-damage-checkpoint responses and stem cell characteristics in the PKH26+ subpopulation. Furthermore, these data reveal a potential therapeutic application in reversal of radioresistance through inhibition of the c-MYC-CHK1/CHK2 pathway.

Hedgehog signaling pathway regulates human pancreatic cancer cell proliferation and metastasis

Pancreatic cancer is one of the most aggressive and devastating malignancies. The Hedgehog (Hh) pathway has been reported to play an important role in pancreatic cancer development and progression. The aim of this study was to examine the activation of the Hh pathway in human pancreatic cancer tissue samples and pancreatic cancer cell lines, and the molecular mechanisms involved in the Hh pathway mediated effects on pancreatic cancer cell proliferation and invasion. The expression levels of Hh molecules in human pancreatic cancer tissue samples and pancreatic cancer cell lines were evaluated using RT-PCR. The role of the Hh pathway in cell proliferation and invasion was evaluated using flow cytometry, MTT, colony formation assays and transwell invasion assays, and the expression of cancer stem cell markers and epithelial-mesenchymal transition (EMT) were evaluated using flow cytometry and RT-PCR. Tumorigenicity assays were used to further investigate the role of the Hh pathway in vivo. Hh molecules were highly expressed in human pancreatic cancer tissue samples and pancreatic cancer cell lines. Inhibition of the Hh pathway notably decreased cell proliferation and induced apoptosis through inhibition of the PI3K/AKT pathway and cancer stem cells. Furthermore, inhibition of the Hh signaling pathway significantly inhibited EMT by suppressing the activation of transcription factors Snail and Slug, which are correlated with significantly reduced pancreatic cancer cell invasion, suggesting that the Hh signaling pathway is involved in early metastasis. These results indicate that activation of the Hh pathway is a common event. Inhibition of the Hh pathway may be a potential molecular target of new therapeutic strategies for pancreatic cancer.

Checkpoint kinase 1 inhibitors for potentiating systemic anticancer therapy

The checkpoint kinase 1 (Chk1) is a key component of the DNA damage response, a molecular network deputed to maintain genome integrity. Nevertheless, cancer cells aberrantly exploit these circuits to overcome chemotherapy-induced cytotoxicity. Chk1 inhibitors have been developed as a chemopotentiating strategy and different molecular mechanisms underlying the synergism with chemotherapeutics have been uncovered. The monotherapy with Chk1 inhibitors seems to be endowed with antitumor activity against cancer cells characterized by specific defects in the DNA damage machinery or characterized by elevated levels of oncogene-induced replication stress. In this biological framework Chk1 neutralization represents a synthetic lethality-based therapeutic approach. Moreover, a dual targeting of the DNA damage machinery has been proposed envisioning the association of Chk1 abrogation with poly-ADP ribose polymerase inhibitors. The spectrum of antitumor properties of Chk1 antagonists is completed by the activity against cancer stem cells, the prominent tumorigenic population that is equipped to survive stressful conditions through multiple and interconnected mechanisms. Although the clinical development of the first generation of Chk1 antagonists was hindered by off-target effects and an unfavorable pharmacokinetic profile, a new wave of early clinical trials with more selective compounds are currently being carried out. To this end, the identification of predictive biomarkers and an in-depth characterization of molecular circuits governed by Chk1 are issues that need to be addressed for sharpening the therapeutic potential of Chk1 inhibitors.

Cancer Stem Cells, EMT, and Developmental Pathway Activation in Pancreatic Tumors

Pancreatic cancer is a disease with remarkably poor patient survival rates. The frequent presence of metastases and profound chemoresistance pose a severe problem for the treatment of these tumors. Moreover, cross-talk between the tumor and the local micro-environment contributes to tumorigenicity, metastasis and chemoresistance. Compared to bulk tumor cells, cancer stem cells (CSC) have reduced sensitivity to chemotherapy. CSC are tumor cells with stem-like features that possess the ability to self-renew, but can also give rise to more differentiated progeny. CSC can be identified based on increased in vitro spheroid- or colony formation, enhanced in vivo tumor initiating potential, or expression of cell surface markers. Since CSC are thought to be required for the maintenance of a tumor cell population, these cells could possibly serve as a therapeutic target. There appears to be a causal relationship between CSC and epithelial-to-mesenchymal transition (EMT) in pancreatic tumors. The occurrence of EMT in pancreatic cancer cells is often accompanied by re-activation of developmental pathways, such as the Hedgehog, WNT, NOTCH, and Nodal/Activin pathways. Therapeutics based on CSC markers, EMT, developmental pathways, or tumor micro-environment could potentially be used to target pancreatic CSC. This may lead to a reduction of tumor growth, metastatic events, and chemoresistance in pancreatic cancer.

Cancer stem cells and metastasis

Cancer stem cells (CSCs) represent a subpopulation of tumour cells endowed with self-renewal and multi-lineage differentiation capacity but also with an innate resistance to cytotoxic agents, a feature likely to pose major clinical challenges towards the complete eradication of minimal residual disease in cancer patients. Operationally, CSCs are defined by their tumour-propagating ability when serially transplanted into immune-compromised mice and by their capacity to fully recapitulate the original heterogeneity of cell types observed in the primary lesions they are derived from. CSCs were first identified in haematopoietic malignancies and later in a broad spectrum of solid tumours including those of the breast, colon and brain. Notably, several CSC characteristics are relevant to metastasis, such as motility, invasiveness and, as mentioned above, resistance to DNA damage-induced apoptosis. Here, we have reviewed the current literature on the relation between CSCs and metastasis formation. Preliminary studies on cancer cell lines and patient-derived material suggest a rate-limiting role for stem-like cells in the processes of tumour cell dissemination and metastasis formation. However, additional studies are needed to deliver formal proof of their identity as the cell of origin of recurrences at distant organ sites. Nevertheless, several studies have already provided pre-clinical evidence of the efficacy of novel therapies directed against disseminated CSCs.

Tumor-initiating properties of breast cancer and melanoma cells in vivo are not invariably reflected by spheroid formation in vitro, but can be increased by long-term culturing as adherent monolayers

Cancer stem cells (CSCs) have been studied intensively in recent years due to their potential importance for understanding neoplastic disease and the design of antitumor therapies. A number of properties attributed to CSCs have been used to define the CSC population, the most important of which is the ability to initiate reproducibly the growth of tumors in vivo. Other assays such as spheroid formation, expression of particular markers and label retention are also used for defining CSCs, although the degree to which these assays invariably reflect the ability to form tumors in vivo remains to be carefully evaluated. Given the importance of correctly defining and isolating CSCs if valid conclusions about their characteristics are to be made, we used syngeneic animal models to compare these different assays. In standard spheroid assays, cell aggregation rather than spheroid growth from single cell suspensions ensued, but aggregation was circumvented by the inclusion of methylcellulose in the medium. Label-retaining subpopulations did not reliably exhibit an enhanced ability to form spheroids and were enriched for senescent cells. Spheroid-forming ability was found to correspond to expression of established CSC markers, although not invariably. Furthermore, spheroid-forming ability was not always reflected in tumor-initiating properties in vivo. Long-term culture of primary mammary tumor cells as adherent monolayers increased their tumor-initiating ability in vivo. This increase was attenuated when the cells were subsequently cultivated as spheroids. Together these data indicate that assays that are widely used to define CSC subpopulations do not invariably reflect tumor-initiating properties in vivo.

The role of epithelial-mesenchymal transition in pancreatic cancer

Pancreatic cancer is the fourth leading cause of cancer related death in the US. Despite the advances in medical and surgical treatment, the 5-year survival rate for such cancer is only approximately 5% when considering all stages of disease. The lethal nature of pancreatic cancer stems from its high metastatic potential to the lymphatic system and distant organs. Lack of effective chemotherapies, which is believed to be due to drug-resistance, also contributes to the high mortality of pancreatic cancer. Recent evidence suggests that epithelial-mesenchymal transition of pancreatic cancer cells contributes to the development of drug resistance and an increase in invasiveness. Future strategies that specifically target against epithelial-mesenchymal transition phenotype could potentially reduce tumoral drug resistance and invasiveness and hence prolong the survival of patients with pancreatic cancer.

Targeting colorectal cancer stem cells with inducible caspase-9

Colorectal cancer stem cells (CSCs) drive tumor growth and are suggested to initiate distant metastases. Moreover, colon CSCs are reportedly more resistant to conventional chemotherapy, which is in part due to upregulation of anti-apoptotic Bcl-2 family members. To determine whether we could circumvent this apoptotic blockade, we made use of an inducible active caspase-9 (iCasp9) construct to target CSCs. Dimerization of iCasp9 with AP20187 in HCT116 colorectal cancer cells resulted in massive and rapid induction of apoptosis. In contrast to fluorouracil (5-FU)-induced apoptosis, iCasp9-induced apoptosis was independent of the mitochondrial pathway as evidenced by Bax/Bak double deficient HCT116 cells. Dimerizer treatment of colon CSCs transduced with iCasp9 (CSC-iCasp9) also rapidly induced high levels of apoptosis, while these cells were unresponsive to 5-FU in vitro. More importantly, injection of the dimerizer into mice that developed a colon CSC-iCasp9-induced tumor resulted in a strong decrease in tumor size, an increase in tumor cell apoptosis and a clear loss of CD133⁺ CSCs. Taken together, our data indicate that dimerization of iCasp9 circumvents the apoptosis block in CSCs, which results in effective tumor regression in vivo.

DNA damage repair pathways in cancer stem cells

The discovery of tumor-initiating cells endowed with stem-like features has added a further level of complexity to the pathobiology of neoplastic diseases. In the attempt of dissecting the functional properties of this uncommon cellular subpopulation, investigators are taking full advantage of a body of knowledge about adult stem cells, as the "cancer stem cell model" implies that tissue-resident stem cells are the target of the oncogenic process. It is emerging that a plethora of molecular mechanisms protect cancer stem cells (CSC) against chemotherapy- and radiotherapy-induced death stimuli. The ability of CSCs to survive stressful conditions is correlated, among others, with a multifaceted protection of genome integrity by a prompt activation of the DNA damage sensor and repair machinery. Nevertheless, many molecular-targeted agents directed against DNA repair effectors are in late preclinical or clinical development while the identification of predictive biomarkers of response coupled with the validation of robust assays for assessing biomarkers is paving the way for biology-driven clinical trials.

Targeting pancreatic cancer stem cells for cancer therapy

Pancreatic cancer (PC) is the fourth most frequent cause of cancer death in the United States. Emerging evidence suggests that pancreatic cancer stem cells (CSCs) play a crucial role in the development and progression of PC. Recently, there is increasing evidence showing that chemopreventive agents commonly known as nutraceuticals could target and eliminate CSCs that have been proposed as the root of the tumor progression, which could be partly due to attenuating cell signaling pathways involved in CSCs. Therefore, targeting pancreatic CSCs by nutraceuticals for the prevention of tumor progression and treatment of PC may lead to the development of novel strategy for achieving better treatment outcome of PC patients. In this review article, we will summarize the most recent advances in the pancreatic CSC field, with particular emphasis on nutraceuticals that target CSCs, for fighting this deadly disease.

Aldehyde dehydrogenase 1A1 confers intrinsic and acquired resistance to gemcitabine in human pancreatic adenocarcinoma MIA PaCa-2 cells

Gemcitabine (GEM) is the front-line standard chemotherapy used for the treatment of pancreatic cancer; however, chemoresistance to GEM remains the major obstacle to the successful control of this disease. Both the expression levels and activity of aldehyde dehydrogenase 1A1 (ALDH1A1) are important features of tumor-initiating and/or cancer stem cell properties in multiple types of human cancer. As one of the intrinsic properties of cancer stem cells is drug resistance, in this study, we examined the correlation between the level and activity of endogenous ALDH1A1 and GEM resistance in the MIA PaCa-2 cell line that contains high expression levels and activity of ALDH1A1. We used small interfering RNAs (siRNAs) to deplete ALDH1A1 and investigate its potential role in conferring GEM resistance. The ALDH1A1 knockdown markedly reduced ALDH1A1 expression and activity and inhibited cell proliferation. Moreover, the combination of ALDH1A1-siRNA and GEM significantly decreased cell viability, increased apoptotic cell death and increased the accumulation of cells at the S-phase compared to the controls. Our data also demonstrated that ALDH1A1 expression and activity were significantly higher in the GEM-resistant MIA PaCa-2 cell line (MIA PaCa-2/GR), compared to the parental MIA PaCa-2 cell line (MIA PaCa-2/P). In the MIA PaCa-2/GR cells, the combination of ALDH1A1-siRNA and GEM also showed a significant decrease in cell viability and an increase in apoptotic cell death, emphasizing the importance of ALDH1A1 in both intrinsic and acquired GEM resistance. This potentially powerful combination treatment of ALDH1A1-siRNA and GEM warrants further investigation as an effective therapeutic regimen to overcome the resistance of pancreatic cancer to GEM.

Current strategies for identification of glioma stem cells: adequate or unsatisfactory?

Cancer stem cells (CSCs) were isolated in multiple tumor types, including human glioblastomas, and although the presence of surface markers selectively expressed on CSCs can be used to isolate them, no marker/pattern of markers are sufficiently robust to definitively identify stem cells in tumors. Several markers were evaluated for their prognostic value with promising early results, however none of them was proven to be clinically useful in large-scale studies, leading to outstanding efforts to identify new markers. Given the heterogeneity of human glioblastomas further investigations are necessary to identify both cancer stem cell-specific markers and the molecular mechanisms sustaining the tumorigenic potential of these cells to develop tailored treatments. Markers for glioblastoma stem cells such as CD133, CD15, integrin-α6, L1CAM might be informative to identify these cells but cannot be conclusively linked to a stem cell phenotype. Overlap of expression, functional state and morphology of different subpopulations lead to carefully consider the techniques employed so far to isolate these cells. Due to a dearth of methods and markers reliably identifying the candidate cancer stem cells, the isolation/enrichment of cancer stem cells to be therapeutically targeted remains a major challenge.

Identification and isolation of slow-dividing cells in human glioblastoma using carboxy fluorescein succinimidyl ester (CFSE)

Tumor heterogeneity represents a fundamental feature supporting tumor robustness and presents a central obstacle to the development of therapeutic strategies(1). To overcome the issue of tumor heterogeneity, it is essential to develop assays and tools enabling phenotypic, (epi)genetic and functional identification and characterization of tumor subpopulations that drive specific disease pathologies and represent clinically relevant targets. It is now well established that tumors exhibit distinct sub-fractions of cells with different frequencies of cell division, and that the functional criteria of being slow cycling is positively associated with tumor formation ability in several cancers including those of the brain, breast, skin and pancreas as well as leukemia(2-8). The fluorescent dye carboxyfluorescein succinimidyl ester (CFSE) has been used for tracking the division frequency of cells in vitro and in vivo in blood-borne tumors and solid tumors such as glioblastoma(2,7,8). The cell-permeant non-fluorescent pro-drug of CFSE is converted by intracellular esterases into a fluorescent compound, which is retained within cells by covalently binding to proteins through reaction of its succinimidyl moiety with intracellular amine groups to form stable amide bonds(9). The fluorescent dye is equally distributed between daughter cells upon divisions, leading to the halving of the fluorescence intensity with every cell division. This enables tracking of cell cycle frequency up to eight to ten rounds of division(10). CFSE retention capacity was used with brain tumor cells to identify and isolate a slow cycling subpopulation (top 5% dye-retaining cells) demonstrated to be enriched in cancer stem cell activity(2). This protocol describes the technique of staining cells with CFSE and the isolation of individual populations within a culture of human glioblastoma (GBM)-derived cells possessing differing division rates using flow cytometry(2). The technique has served to identify and isolate a brain tumor slow-cycling population of cells by virtue of their ability to retain the CFSE labeling.

Adamantyl Retinoid-Related Molecules Induce Apoptosis in Pancreatic Cancer Cells by Inhibiting IGF-1R and Wnt/β-Catenin Pathways

Pancreatic carcinoma has a dismal prognosis as it often presents as locally advanced or metastatic. We have found that exposure to adamantyl-substituted retinoid-related (ARR) compounds 3-Cl-AHPC and AHP3 resulted in growth inhibition and apoptosis induction in PANC-1, Capan-2, and MiaPaCa-2 pancreatic cancer cell lines. In addition, AHP3 and 3-Cl-AHPC inhibited growth and induced apoptosis in spheres derived from the CD44⁺/CD24⁺ (CD133⁺/EpCAM⁺) stem-like cell population isolated from the pancreatic cancer cell lines. 3-Cl-AHPC-induced apoptosis was preceded by decreasing expression of IGF-1R, cyclin D1, β-catenin, and activated Notch-1 in the pancreatic cancer cell lines. Decreased IGF-1R expression inhibited PANC-1 proliferation, enhanced 3-Cl-AHPC-mediated apoptosis, and significantly decreased sphere formation. 3-Cl-AHPC inhibited the Wnt/β-catenin pathway as indicated by decreased β-catenin nuclear localization and inhibited Wnt/β-catenin activation of transcription factor TCF/LEF. Knockdown of β-catenin using sh-RNA also induced apoptosis and inhibited growth in pancreatic cancer cells. Thus, 3-Cl-AHPC and AHP3 induce apoptosis in pancreatic cancer cells and cancer stem-like cells and may serve as an important potential therapeutic agent in the treatment of pancreatic cancer.

On the epigenetic origin of cancer stem cells

Epigenetic mechanisms are the key component of the dynamic transcriptional programming that occurs along the process of differentiation from normal stem cells to more specialized cells. In the development of cancer and according to the cancer stem cell model, aberrant epigenetic changes may ensure the property of cancer cells to switch cancer stem cell markers on and off in order to generate a heterogeneous population of cells. The tumour will then be composed of tumourigenic (cancer stem cells) and non-tumourigenic (the side population that constitutes the bulk of the tumour) cells. Characterizing epigenetic landscapes may thus help discriminate aberrant marks (good candidates for tumour detection) from cancer stem cell specific profiles. In this review, we will give some insights about what epigenetics can teach us about the origin of cancer stem cells. We will also discuss how identification of epigenetic reprogramming may help designing new drugs that will specifically target cancer stem cells.

Membranous and cytoplasmic expression of epidermal growth factor receptor in metastatic pancreatic ductal adenocarcinoma

Recent studies indicate the clinical significance of the cellular localization of epidermal growth factor receptor (EGFR) in a variety of cancer types. Internalization of activated EGFR is reported to be closely associated with patient prognosis. This study investigated the clinical significance of the immunohistochemical localization of EGFR in patients with metastatic pancreatic cancers compared to those with surgically resected pancreatic cancers. Using 44 surgically resected primary pancreatic cancers and 40 primary or meta-static tumors from 20 autopsied patients with far advanced pancreatic cancers, the incidence of membranous and cytoplasmic EGFR overexpression was compared between primary tumors and far advanced tumors by immunohistochemistry using the Dako EGFR pharmDx™ kit, a global standard kit for EGFR assay. In the 44 surgically resected cancers, 13 (30%) exhibited membranous overexpression of EGFR, comprising 1 case (2%) with score 3+ and 12 cases (27%) with score 2+ and 10 (23%) exhibited cytoplasmic overexpression of EGFR. In the 40 tumors at a far advanced stage, the percentage of samples exhibiting positivity for membranous and cytoplasmic EGFR overexpression was 48% (19 of 40) comprising 7 (18%) with score 2+ and 12 (30%) with score 3+ and 33% (13 of 40), respectively. The far advanced tumors tended to show membranous and cytoplasmic EGFR overexpression more frequently than the surgically resected tumors, although the difference was not significant. These findings suggest that membranous and cytoplasmic overexpression of EGFR may be indicative of the potential aggressiveness of pancreatic cancers.

Stem-like cells and therapy resistance in squamous cell carcinomas

Cancer stem cells (CSCs) within squamous cell carcinomas (SCCs) are hypothesized to contribute to chemotherapy and radiation resistance and represent potentially useful pharmacologic targets. Hallmarks of the stem cell phenotype that may contribute to therapy resistance of CSCs include quiescence, evasion of apoptosis, resistance to DNA damage, and expression of drug transporter pumps. A variety of CSC populations within SCCs of the head and neck and esophagus have been defined tentatively, based on diverse surface markers and functional assays. Stem-like self-renewal and differentiation capacities of these SCC subpopulations are supported by sphere formation and clonogenicity assays in vitro as well as limiting dilution studies in xenograft models. Early evidence supports a role for SCC CSCs in intrinsic therapy resistance, while detailed mechanisms by which these subpopulations evade treatment remain to be defined. Development of novel SCC therapies will be aided by pursuing such mechanisms as well as refining current definitions for CSCs and clarifying their relevance to hierarchical versus dynamic models of stemness.

Intratumoral heterogeneity as a therapy resistance mechanism: role of melanoma subpopulations

Malignant melanoma is an aggressive form of skin cancer whose incidence continues to increase worldwide. Increased exposure to sun, ultraviolet radiation, and the use of tanning beds can increase the risk of melanoma. Early detection of melanomas is the key to successful treatment mainly through surgical excision of the primary tumor lesion. But in advanced stage melanomas, once the disease has spread beyond the primary site to distant organs, the tumors are difficult to treat and quickly develop resistance to most available forms of therapy. The advent of molecular and cellular techniques has led to a better characterization of tumor cells revealing the presence of heterogeneous melanoma subpopulations. The discovery of gene mutations and alterations of cell-signaling pathways in melanomas has led to the development of new targeted drugs that show dramatic response rates in patients. Single-agent therapies generally target one subpopulation of tumor cells while leaving others unharmed. The surviving subpopulations will have the ability to repopulate the original tumors that can continue to progress. Thus, a rational approach to target multiple subpopulations of tumor cells with a combination of drugs instead of single-agent therapy will be necessary for long-lasting inhibition of melanoma lesions. In this context, the recent development of immune checkpoint reagents provides an additional armor that can be used in combination with targeted drugs to expand the presence of melanoma reactive T cells in circulation to prevent tumor recurrence.

Slow-cycling therapy-resistant cancer cells

Tumor recurrence after chemotherapy is a major cause of patient morbidity and mortality. Recurrences are thought to be secondary to small subsets of cancer cells that are better able to survive traditional forms of chemotherapy and thus drive tumor regrowth. The ability to isolate and better characterize these therapy-resistant cells is critical for the future development of targeted therapies aimed at achieving more robust and long-lasting responses. Using a novel application for the proliferation marker carboxyfluorescein diacetate, succinimidyl ester (CFSE), we have identified a population of slow-cycling, label-retaining tumor cells in both in vitro sphere cultures and in vivo xenograft models. Strikingly, label-retaining cells exhibit a multifold increase in ability to survive traditional forms of chemotherapy and reenter the cell cycle. Further, we demonstrate the innovative application of CFSE to live sort slow-cycling tumor cells and validate their chemoresistance and tumorigenic potential.

Stem cells, quiescence and rectal carcinoma: an unexplored relationship and potential therapeutic target

Stem cells are responsible for maintaining differentiated cell numbers during normal physiology and at times of tissue stress. They have the unique capabilities of proliferation, self-renewal, clonogenicity and multi-potentiality. It is a widely held belief that stem-like cells, known as cancer stem cells (CSCs), maintain tumours. The majority of currently identified intestinal stem cell populations appear to be rapidly cycling. However, quiescent stem cell populations have been suggested to exist in both normal intestinal crypts and tumours. Quiescent CSCs may have particular significance in the modern management of colorectal cancer making their identification and characterisation a priority. In this review, we discuss the current evidence surrounding the identification and microenvironmental control of stem cell populations in intestinal crypts and tumours as well as exploring the evidence supporting the existence of a quiescent stem and CSC population in the gut and other tissues.

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.

Increased CD13 expression reduces reactive oxygen species, promoting survival of liver cancer stem cells via an epithelial-mesenchymal transition-like phenomenon

BACKGROUND

Recently, it has been reported that a small population of cancer stem cells (CSCs) play a role in resistance to chemotherapy and radiation therapy. We reported that CD13(+) liver CSCs survive in hypoxic lesions after chemotherapy, presumably through increased expression of CD13/Aminopeptidase N, which is a scavenger enzyme in the reactive oxygen species (ROS) metabolic pathway. On the other hand, the concept of epithelial-mesenchymal transition (EMT) was indicated by a recent study showing an increased plasticity linked to the cellular "stemness" of CSCs.

METHODS

To study the relationship between CSCs and EMT, we examined biological characteristics of liver cancer cell lines with EMT by exposing transforming growth factor-β (TGF-β).

RESULTS

We showed that a TGF-β-induced EMT-like phenomenon is associated with increased CD13 expression in liver cancer cells. This phenomenon prevents further increases in the ROS level as well as the induction of apoptosis, promoting the survival of CD13(+) CSCs, whereas inhibition of CD13 stimulates apoptosis. Immunohistochemical analysis also indicated that after chemotherapy, CD13 was coexpressed with N-cadherin in surviving cancer cells within fibrous capsules. We have demonstrated that CD13 expression plays a role in supporting the survival of CSCs and that there is an EMT-associated reduction in ROS elevation.

CONCLUSIONS

This novel and consistent linkage between functional CSC markers and the EMT phenomenon suggests a bona fide candidate for targeted therapy for EMT-mediated invasion and metastasis of liver cancer.

Holoclone forming cells from pancreatic cancer cells enrich tumor initiating cells and represent a novel model for study of cancer stem cells

Background

Pancreatic cancer is one of the direct causes of cancer-related death. High level of chemoresistance is one of the major obstacles of clinical treatment. In recent years, cancer stem cells have been widely identified and indicated as the origin of chemoresistance in multi-types of solid tumors. Increasing evidences suggest that cancer stem cells reside in the cells capable of forming holoclones continuously. However, in pancreatic cancer, holoclone-forming cells have not been characterized yet. Therefore, the goal of our present study was to indentify the holoclone-forming pancreatic cancer stem cells and develop an in vitro continuous colony formation system, which will greatly facilitate the study of pancreatic cancer stem cells.

Methodology/Principal Findings

Pancreatic cancer cell line BxPC3 was submitted to monoclonal cultivation to generate colonies. Based on the morphologies, colonies were classified and analyzed for their capacities of secondary colony formation, long-term survival in vitro, tumor formation in vivo, and drug resistance. Flowcytometry and quantitative RT-PCR were performed to detect the expression level of cancer stem cells associated cell surface markers, regulatory genes and microRNAs in distinct types of colonies. Three types of colonies with distinct morphologies were identified and termed as holo-, mero-, and paraclones, in which only holoclones generated descendant colonies of all three types in further passages. Compared to mero- and paraclones, holoclones possessed higher capacities of long-term survival, tumor initiation, and chemoresistance. The preferential expression of cancer stem cells related marker (CXCR4), regulatory genes (BMI1, GLI1, and GLI2) and microRNAs (miR-214, miR-21, miR-221, miR-222 and miR-155) in holoclones were also highlighted.

Conclusions/Significance

Our results indicate that the pancreatic tumor-initiating cells with high level of chemoresistance were enriched in holoclones derived from BxPC3 cell line. Generation of holoclones can serve as a novel model for studying cancer stem cells, and attribute to developing new anti-cancer drugs.

Expression of CD44, CD24 and ESA in pancreatic adenocarcinoma cell lines varies with local microenvironment

BACKGROUND

Emerging evidence suggests that pancreatic adenocarcinoma is hierarchically organized and sustained by pancreatic cancer stem cells. Furthermore, elimination of these cells is possible and therapeutically relevant. This study aimed to investigate the expression patterns of pancreatic cancer stem cell surface markers CD44, CD24 and ESA in pancreatic adenocarcinoma cell lines and explore the influence of their local microenvironment.

METHODS

Flow cytometry was used to analyze the expression patterns of CD44, CD24 and ESA in five pancreatic adenocarcinoma cell lines (PANC-1, PC-2, MIA-Paca-2, AsPC-1 and BxPC-3). In addition, the capacity for sphere-formation in serum-free medium of four cell lines (PANC-1, PC-2, MIA-Paca-2 and BxPC-3) was assessed. Then, the same assays were performed when tumor cell spheres were developed. The role of sonic hedgehog (SHH) in cell spheres from PANC-1 and MIA-Paca-2 were also assessed by RT-PCR.

RESULTS

CD44 and CD24 were detected in PANC-1. Only CD44 expression was detected in PC-2, MIA-Paca-2 and AsPC-1. CD44, CD24 and ESA were all detected in BxPC-3. Tumor cell spheres developed in PANC-1 and MIA-Paca-2 in serum-free medium. This was accompanied by an increase in CD24 expression and a decrease in CD44 expression in PANC-1. Interestingly, the expression of CD44 and CD24 returned to initial levels once the medium was changed back from serum-free to serum-containing medium. No significant change in the expression of CD44 was detected in MIA-Paca-2. Furthermore, the relative quantification of SHH mRNA in PANC-1 cell spheres was significantly higher than that in cells cultured in the serum-containing medium.

CONCLUSION

The expression patterns of the pancreatic cancer stem cell surface markers CD44, CD24 and ESA were diverse in different pancreatic adenocarcinoma cell lines and changed with their local microenvironment.

Molecular biology of pancreatic ductal adenocarcinoma progression: aberrant activation of developmental pathways

Embryonic development marks a period of peak tissue growth and morphogenesis in the mammalian lifecycle. Many of the pathways that underlie cell proliferation and movement are relatively quiescent in adult animals but become reactivated during carcinogenesis. This phenomenon has been particularly well documented in pancreatic cancer, where detailed genetic studies and a robust mouse model have permitted investigators to test the role of various developmental signals in cancer progression. In this chapter, we review current knowledge regarding the signaling pathways that act during pancreatic development and the evidence that the reactivation of developmentally important signals is critical for the pathogenesis of this treatment-refractory malignancy.

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.

Therapeutic targeting of cancer stem cells

Recent breakthroughs in translational oncology are opening new perspectives for the treatment of cancer. The advent of targeted therapies has provided the proof-of-concept to selectively turn-off deregulated oncogenic proteins, while the identification and validation of predictive biomarkers of response has allowed to improve, at least in some cases, their performance. Moreover, a subpopulation of tumor-propagating cells has been identified from many solid and hematological tumors. These cells share functional properties of normal stem cells, and are commonly referred to as cancer stem cells (CSCs). It is emerging that CSCs are defended against broadly used anticancer agents by means of different, partly interconnected, mechanisms. However, CSCs rely on specific pathways involved in self-renewal that can be pharmacologically antagonized by experimental molecular targeted agents, some of which have recently entered early phases of clinical development. Here, we discuss the spectrum of pharmacological strategies under clinical or preclinical development for CSCs targeting.

A novel synthetic smoothened antagonist transiently inhibits pancreatic adenocarcinoma xenografts in a mouse model

BACKGROUND

Hedgehog (Hh) signaling is over-activated in several solid tumors where it plays a central role in cell growth, stroma recruitment and tumor progression. In the Hh signaling pathway, the Smoothened (SMO) receptor comprises a primary drug target with experimental small molecule SMO antagonists currently being evaluated in clinical trials.

PRINCIPAL FINDINGS

Using Shh-Light II (Shh-L2) and alkaline phosphatase (AP) based screening formats on a "focused diversity" library we identified a novel small molecule inhibitor of the Hh pathway, MS-0022 (2-bromo-N-(4-(8-methylimidazo[1,2-a]pyridin-2-yl)phenyl)benzamide). MS-0022 showed effective Hh signaling pathway inhibition at the level of SMO in the low nM range, and Hh pathway inhibition downstream of Suppressor of fused (SUFU) in the low µM range. MS-0022 reduced growth in the tumor cell lines PANC-1, SUIT-2, PC-3 and FEMX in vitro. MS-0022 treatment led to a transient delay of tumor growth that correlated with a reduction of stromal Gli1 levels in SUIT-2 xenografts in vivo.

SIGNIFICANCE

We document the in vitro and in vivo efficacy and bioavailability of a novel small molecule SMO antagonist, MS-0022. Although MS-0022 primarily interferes with Hh signaling at the level of SMO, it also has a downstream inhibitory effect and leads to a stronger reduction of growth in several tumor cell lines when compared to related SMO antagonists.

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.

Evidence for label-retaining tumour-initiating cells in human glioblastoma

Individual tumour cells display diverse functional behaviours in terms of proliferation rate, cell-cell interactions, metastatic potential and sensitivity to therapy. Moreover, sequencing studies have demonstrated surprising levels of genetic diversity between individual patient tumours of the same type. Tumour heterogeneity presents a significant therapeutic challenge as diverse cell types within a tumour can respond differently to therapies, and inter-patient heterogeneity may prevent the development of general treatments for cancer. One strategy that may help overcome tumour heterogeneity is the identification of tumour sub-populations that drive specific disease pathologies for the development of therapies targeting these clinically relevant sub-populations. Here, we have identified a dye-retaining brain tumour population that displays all the hallmarks of a tumour-initiating sub-population. Using a limiting dilution transplantation assay in immunocompromised mice, label-retaining brain tumour cells display elevated tumour-initiation properties relative to the bulk population. Importantly, tumours generated from these label-retaining cells exhibit all the pathological features of the primary disease. Together, these findings confirm dye-retaining brain tumour cells exhibit tumour-initiation ability and are therefore viable targets for the development of therapeutics targeting this sub-population.

Aldehyde dehydrogenase 1B1 (ALDH1B1) is a potential biomarker for human colon cancer

Aldehyde dehydrogenases (ALDHs) belong to a superfamily of NAD(P)+-dependent enzymes, which catalyze the oxidation of endogenous and exogenous aldehydes to their corresponding acids. Increased expression and/or activity of ALDHs, particularly ALDH1A1, have been reported to occur in human cancers. It is proposed that the metabolic function of ALDH1A1 confers the "stemness" properties to normal and cancer stem cells. Nevertheless, the identity of ALDH isozymes that contribute to the enhanced ALDH activity in specific types of human cancers remains to be elucidated. ALDH1B1 is a mitochondrial ALDH that metabolizes a wide range of aldehyde substrates including acetaldehyde and products of lipid peroxidation (LPO). In this study, we immunohistochemically examined the expression profile of ALDH1A1 and ALDH1B1 in human adenocarcinomas of colon (N=40), lung (N=30), breast (N=33) and ovary (N=33) using an NIH tissue array. The immunohistochemical expression of ALDH1A1 or ALDH1B1 in tumor tissues was scored by their intensity (scale=1-3) and extensiveness (% of total cancer cells). Herein we report a 5.6-fold higher expression score for ALDH1B1 in cancerous tissues than that for ALDH1A1. Remarkably, 39 out of 40 colonic cancer specimens were positive for ALDH1B1 with a staining intensity of 2.8±0.5. Our study demonstrates that ALDH1B1 is more profoundly expressed in the adenocarcinomas examined in this study relative to ALDH1A1 and that ALDH1B1 is dramatically upregulated in human colonic adenocarcinoma, making it a potential biomarker for human colon cancer.

Finding cancer stem cells: are aldehyde dehydrogenases fit for purpose?

Despite many years of intensive effort, there is surprisingly little consensus on the most suitable markers with which to locate and isolate stem cells from adult tissues. By comparison, the study of cancer stem cells is still in its infancy; so, unsurprisingly, there is great uncertainty as to the identity of these cells. Stem cell markers can be broadly categorized into molecular determinants of self-renewal, clonogenicity, multipotentiality, adherence to the niche, and longevity. This review assesses the utility of recognizing cancer stem cells by virtue of high expression of aldehyde dehydrogenases (ALDHs), probably significant determinants of cell survival through their ability to detoxify many potentially cytotoxic molecules, and contributing to drug resistance. Antibodies are available against the ALDH enzyme family, but the vast majority of studies have used cell sorting techniques to enrich for cells expressing these enzymes. Live cells expressing high ALDH activity are usually identified by the ALDEFLUOR kit and sorted by fluorescence activated cell sorting (FACS). For many human tumours, but notably breast cancer, cell selection based upon ALDH activity appears to be a useful marker for enriching for cells with tumour-initiating activity (presumed cancer stem cells) in immunodeficient mice, and indeed the frequency of so-called ALDH(bri) cells in many tumours can be an independent prognostic indicator.

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.

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.

A Distinct Slow-Cycling Cancer Stem-like Subpopulation of Pancreatic Adenocarcinoma Cells is maintained in Vivo

Pancreatic adenocarcinoma has the worst prognosis of any major malignancy, with <5% of patients surviving five years. This can be contributed to the often late diagnosis, lack of sufficient treatment and metastatic spread. Heterogeneity within tumors is increasingly becoming a focus in cancer research, as novel therapies are required to target the most aggressive subpopulations of cells that are frequently termed cancer stem cells (CSCs). In the current study, we describe the identification of a slow-cycling cancer stem-like population of cells in vivo in BxPC-3 and Panc03.27 xenografts. A distinct slow-cycling label-retaining population of cells (DiI+/SCC) was found both at the edge of tumors, and in small circumscribed areas within the tumors. DiI+/SCC in these areas display an epithelial-to-mesenchymal transition (EMT) fingerprint, including an upregulation of the mesenchymal markers vimentin and N-cadherin and a loss of the epithelial marker E-cadherin. DiI+/SCC also displayed a critical re-localization of beta-catenin from the membrane to the nucleus. Additionally, the DiI+/SCC population was found to express the developmental signaling molecule sonic hedgehog. This study represents a novel step in defining the biological activities of a tumorigenic subpopulation within the heterogeneous tumor microenvironment in vivo. Understanding the interactions and functions of a CSC population within the context of the tumor microenvironment is critical to design targeted therapeutics.

Targeting aldehyde dehydrogenase cancer stem cells in ovarian cancer

Aldehyde dehydrogenase-1A1 (ALDH1A1) expression characterizes a subpopulation of cells with tumor-initiating or cancer stem cell properties in several malignancies. Our goal was to characterize the phenotype of ALDH1A1-positive ovarian cancer cells and examine the biological effects of ALDH1A1 gene silencing. In our analysis of multiple ovarian cancer cell lines, we found that ALDH1A1 expression and activity was significantly higher in taxane- and platinum-resistant cell lines. In patient samples, 72.9% of ovarian cancers had ALDH1A1 expression in which the percentage of ALDH1A1-positive cells correlated negatively with progression-free survival (6.05 vs. 13.81 months; P < 0.035). Subpopulations of A2780cp20 cells with ALDH1A1 activity were isolated for orthotopic tumor-initiating studies, where tumorigenicity was approximately 50-fold higher with ALDH1A1-positive cells. Interestingly, tumors derived from ALDH1A1-positive cells gave rise to both ALDH1A1-positive and ALDH1A1-negative populations, but ALDH1A1-negative cells could not generate ALDH1A1-positive cells. In an in vivo orthotopic mouse model of ovarian cancer, ALDH1A1 silencing using nanoliposomal siRNA sensitized both taxane- and platinum-resistant cell lines to chemotherapy, significantly reducing tumor growth in mice compared with chemotherapy alone (a 74%-90% reduction; P < 0.015). These data show that the ALDH1A1 subpopulation is associated with chemoresistance and outcome in ovarian cancer patients, and targeting ALDH1A1 sensitizes resistant cells to chemotherapy. ALDH1A1-positive cells have enhanced, but not absolute, tumorigenicity but do have differentiation capacity lacking in ALDH1A1-negative cells. This enzyme may be important for identification and targeting of chemoresistant cell populations in ovarian cancer.

Quiescent, slow-cycling stem cell populations in cancer: a review of the evidence and discussion of significance

Long-lived cancer stem cells (CSCs) with indefinite proliferative potential have been identified in multiple epithelial cancer types. These cells are likely derived from transformed adult stem cells and are thought to share many characteristics with their parental population, including a quiescent slow-cycling phenotype. Various label-retaining techniques have been used to identify normal slow cycling adult stem cell populations and offer a unique methodology to functionally identify and isolate cancer stem cells. The quiescent nature of CSCs represents an inherent mechanism that at least partially explains chemotherapy resistance and recurrence in posttherapy cancer patients. Isolating and understanding the cell cycle regulatory mechanisms of quiescent cancer cells will be a key component to creation of future therapies that better target CSCs and totally eradicate tumors. Here we review the evidence for quiescent CSC populations and explore potential cell cycle regulators that may serve as future targets for elimination of these cells.

AZGP1 is a tumor suppressor in pancreatic cancer inducing mesenchymal-to-epithelial transdifferentiation by inhibiting TGF-β-mediated ERK signaling

Epithelial-to-mesenchymal transdifferentiation (EMT) mediated by transforming growth factor-β (TGF-β) signaling leads to aggressive cancer progression. In this study, we identified zinc-α2-glycoprotein (AZGP1, ZAG) as a tumor suppressor in pancreatic ductal adenocarcinoma whose expression is lost due to histone deacetylation. In vitro, ZAG silencing strikingly increased invasiveness of pancreatic cancer cells accompanied by the induction of a mesenchymal phenotype. Expression analysis of a set of EMT markers showed an increase in the expression of mesenchymal markers (vimentin (VIM) and integrin-α5) and a concomitant reduction in the expression of epithelial markers (cadherin 1 (CDH1), desmoplakin and keratin-19). Blockade of endogenous TGF-β signaling inhibited these morphological changes and the downregulation of CDH1, as elicited by ZAG silencing. In a ZAG-negative cell line, human recombinant ZAG (rZAG) specifically inhibited exogenous TGF-β-mediated tumor cell invasion and VIM expression. Furthermore, rZAG blocked TGF-β-mediated ERK2 phosphorylation. PCR array analysis revealed that ZAG-induced epithelial transdifferentiation was accompanied by a series of concerted cellular events including a shift in the energy metabolism and prosurvival signals. Thus, epigenetically regulated ZAG is a novel tumor suppressor essential for maintaining an epithelial phenotype.

A simple biological imaging system for detecting viable human circulating tumor cells

The presence of circulating tumor cells (CTCs) in the peripheral blood is associated with short survival, making the detection of CTCs clinically useful as a prognostic factor of disease outcome and/or a surrogate marker of treatment response. Recent technical advances in immunocytometric analysis and quantitative real-time PCR have made it possible to detect a few CTCs in the blood; however, there is no sensitive assay to specifically detect viable CTCs. Here, we report what we believe to be a new approach to visually detect live human CTCs among millions of peripheral blood leukocytes, using a telomerase-specific replication-selective adenovirus expressing GFP. First, we constructed a GFP-expressing attenuated adenovirus, in which the telomerase promoter regulates viral replication (OBP-401; TelomeScan). We then used OBP-401 to establish a simple ex vivo method that was able to detect viable human CTCs in the peripheral blood. The detection method involved a 3-step procedure, including the lysis of rbc, the subsequent addition of OBP-401 to the cell pellets, and an automated scan using fluorescence microscopy. OBP-401 infection increased the signal-to-background ratio as a tumor-specific probe, because the fluorescent signal was amplified only in viable, infected human tumor cells, by viral replication. This GFP-expressing virus-based method is remarkably simple and allows precise enumeration of CTCs.

Hijacking HES1: how tumors co-opt the anti-differentiation strategies of quiescent cells

Quiescent and tumor cells share the ability to evade irreversible cell fates. Recent studies have shown that the transcriptional regulator Hairy and Enhancer of Split 1 (HES1) protects quiescent fibroblasts from differentiation or senescence. HES1 is highly expressed in rhabdomyosarcomas, and the inhibition of HES1 restores differentiation in these cells. Pathways that lead to elevated HES1 levels, such as the Notch and Hedgehog pathways, are frequently upregulated in tumors. Compounds that inhibit these pathways induce differentiation and apoptosis in cancer cells and several are in clinical trials. HES1 might repress gene expression in part by recruiting histone deacetylases (HDACs). HDACs inhibit differentiation, whereas histone deacetylase inhibitors (HDACis) induce differentiation or apoptosis in tumors and are also showing promise as therapeutics. Small molecules that directly target HES1 itself were recently identified. Here, we discuss the importance of HES1 function in quiescent and tumor cells. Elucidating the pathways that control quiescence could provide valuable information not only for treating cancer but also other diseases.

Accomplishments in 2008 in the treatment of metastatic pancreatic cancer

Overview of the DiseaseIncidencePrognosisCurrent Treatment StandardsCytotoxic TherapyTargeted TherapySalvage TherapyAccomplishments or Lack of AccomplishmentsTherapySalvage TherapyBiomarkersApplication of the AccomplishmentsFuture DirectionsCurrent Basic ResearchOngoing Clinical StudiesMajor Obstacles to Progress in Drug DevelopmentGemcitabine PlatformChoice of Molecular TargetsPatient Selection.