Immunohistochemical expression of four different stem cell markers in prostate cancer: High expression of NANOG in conjunction with hypoxia-inducible factor-1α expression is involved in prostate epithelial malignancy

Cancer stem cells: a target for overcoming therapeutic resistance and relapse

Cancer stem cells (CSCs) are a small subset of cells in cancers that are thought to initiate tumorous transformation and promote metastasis, recurrence, and resistance to treatment. Growing evidence has revealed the existence of CSCs in various types of cancers and suggested that CSCs differentiate into diverse lineage cells that contribute to tumor progression. We may be able to overcome the limitations of cancer treatment with a comprehensive understanding of the biological features and mechanisms underlying therapeutic resistance in CSCs. This review provides an overview of the properties, biomarkers, and mechanisms of resistance shown by CSCs. Recent findings on metabolic features, especially fatty acid metabolism and ferroptosis in CSCs, are highlighted, along with promising targeting strategies. Targeting CSCs is a potential treatment plan to conquer cancer and prevent resistance and relapse in cancer treatment.

Hypoxia promotes conversion to a stem cell phenotype in prostate cancer cells by activating HIF-1α/Notch1 signaling pathway

PURPOSE

The hypoxic tumor microenvironment and the maintenance of stem cells are relevant to the malignancy of prostate cancer (PCa). However, whether HIF-1α in the hypoxic microenvironment mediates the transformation of prostate cancer to a stem cell phenotype and the mechanism have not been elucidated.

MATERIALS AND METHODS

Prostate cancer stem cells (PCSCs) from PC-3 cell lines were examined for the expression of CD44, CD133, ALDH1, HIF-1α, Notch1, and HES1. We observed the effect of knockdown HIF-1α in vitro and mice models and evaluated the impact of HIF-1α on the Notch1 pathway as well as stem cell dedifferentiation. The effects on sphere formation, cell proliferation, apoptosis, cell cycle, and invasive metastasis were evaluated.

RESULTS

In our study, hypoxia upregulated HIF-1α expression and induced a stem cell phenotype through activation of the Notch1 pathway, leading to enhanced proliferation, invasion, and migration of PCa PC-3 cells. The knockdown of HIF-1α significantly inhibited cell dedifferentiation and the ability to proliferate, invade and metastasize. However, the inhibitory effect of knocking down HIF-1α was reversed by Jagged1, an activator of the Notch1 pathway. These findings were further confirmed in vivo, where hypoxia could enhance the tumorigenicity of xenograft tumors by upregulating the expression of HIF-1α to activate the Notch1 pathway. In addition, the expression of HIF-1α and Notch1 was significantly increased in human PCa tissues, and high expression of HIF-1α correlated with the malignancy of PCa.

CONCLUSION

In a hypoxic environment, HIF-1α promotes PCa cell dedifferentiation to stem-like cell phenotypes by activating the Notch1 pathway and enhancing the proliferation and invasive capacity of PC-3 cells.

Epigenetic regulation of pluripotency inducer genes NANOG and SOX2 in human prostate cancer

The cells of multicellular organisms are genetically homogeneous but heterogenous in structure and function by virtue of differential gene expression. During embryonic development, differential gene expression by modification of chromatin (DNA and histone complex) regulates the developmental proceedings before and after the germ layers are formed. Post-replicative DNA modification, where the fifth carbon atom of the cytosine gets methylated (hereafter, DNA methylation), does not incorporate mutations within the DNA. In the past few years, a boom has been observed in the field of research related to various epigenetic regulation models, which includes DNA methylation, post-translational modification of histone tails, control of chromatin structure by non-coding RNAs, and remodeling of nucleosome. Epigenetic effects like DNA methylation or histone modification play a cardinal role in development but also be able to arise stochastically, as observed during aging, in tumor development and cancer progression. Over the past few decades, researchers allured toward the involvement of pluripotency inducer genes in cancer progression and apparent for prostate cancer (PCa); also, PCa is the most diagnosed tumor worldwide and comes to the second position in causing mortality in men. The anomalous articulation of pluripotency-inducing transcription factor; SRY-related HMG box-containing transcription factor-2 (SOX2), Octamer-binding transcription factor 4 (OCT4) or POU domain, class 5, transcription factor 1 (POU5F1), and NANOG have been reported in different cancers which includes breast cancer, tongue cancer, and lung cancer, etc. Although there is a variety in gene expression signatures demonstrated by cancer cells, the epigenetic mode of regulation at the pluripotency-associated genes in PCa has been recently explored. This chapter focuses on the epigenetic control of NANOG and SOX2 genes in human PCa and the precise role thereof executed by the two transcription factors.

Role of prostate cancer stem-like cells in the development of antiandrogen resistance

Androgen deprivation therapy (ADT) is the standard of care treatment for advance stage prostate cancer. Treatment with ADT develops resistance in multiple ways leading to the development of castration-resistant prostate cancer (CRPC). Present research establishes that prostate cancer stem-like cells (CSCs) play a central role in the development of treatment resistance followed by disease progression. Prostate CSCs are capable of self-renewal, differentiation, and regenerating tumor heterogeneity. The stemness properties in prostate CSCs arise due to various factors such as androgen receptor mutation and variants, epigenetic and genetic modifications leading to alteration in the tumor microenvironment, changes in ATP-binding cassette (ABC) transporters, and adaptations in molecular signaling pathways. ADT reprograms prostate tumor cellular machinery leading to the expression of various stem cell markers such as Aldehyde Dehydrogenase 1 Family Member A1 (ALDH1A1), Prominin 1 (PROM1/CD133), Indian blood group (CD44), SRY-Box Transcription Factor 2 (Sox2), POU Class 5 Homeobox 1(POU5F1/Oct4), Nanog and ABC transporters. These markers indicate enhanced self-renewal and stemness stimulating CRPC evolution, metastatic colonization, and resistance to antiandrogens. In this review, we discuss the role of ADT in prostate CSCs differentiation and acquisition of CRPC, their isolation, identification and characterization, as well as the factors and pathways contributing to CSCs expansion and therapeutic opportunities.

Nanog, as a key cancer stem cell marker in tumor progression

Cancer stem cells (CSCs) are a small population of malignant cells that induce tumor onset and development. CSCs share similar features with normal stem cells in the case of self-renewal and differentiation. They also contribute to chemoresistance and metastasis of cancer cells, leading to therapeutic failure. To identify CSCs, multiple cell surface markers have been characterized, including Nanog, which is found at high levels in different cancers. Recent studies have revealed that Nanog upregulation has a substantial association with the advanced stages and poor prognosis of malignancies, playing a pivotal role through tumorigenesis of multiple human cancers, including leukemia, liver, colorectal, prostate, ovarian, lung, head and neck, brain, pancreatic, gastric and breast cancers. Nanog through different signaling pathways, like JAK/STAT and Wnt/β-catenin pathways, induces stemness, self-renewal, metastasis, invasiveness, and chemoresistance of cancer cells. Some of these signaling pathways are common in various types of cancers, but some have been found in one or two cancers. Therefore, this review aimed to focus on the function of Nanog in multiple cancers based on recent studies surveying the suitable approaches to target Nanog and inhibit CSCs residing in tumors to gain favorable results from cancer treatments.

Eggmanone Effectively Overcomes Prostate Cancer Cell Chemoresistance

Prostate cancer chemoresistance is a major therapeutic problem, and the underlying mechanism is not well understood and effective therapies to overcome this problem are not available. Phosphodiesterase-4 (PDE4), a main intracellular enzyme for cAMP hydrolysis, has been previously shown to involve in the early chemo-sensitive prostate cancer cell proliferation and progression, but its role in the more-advanced chemo-resistant prostate cancer is completely unknown. Here we found that the expression of PDE4 subtype, PDE4D, is highly elevated in the chemo-resistant prostate cancer cells (DU145-TxR and PC3-TxR) in comparison to the chemo-sensitive prostate cancer cells (DU145 and PC3). Inhibition of PDE4D with a potent and selective PDED4 inhibitor, Eggmanone, effectively decreases the invasion and proliferation as well as induces cell death of the chemo-resistant prostate cancer cells (DU145-TxR and PC3-TxR). These results were confirmed by siRNA knockdown of PDE4D. We and colleagues previously reported that Eggmanone can effectively blocked sonic Hedgehog signaling via PDE4D inhibition, and here our study suggests that that Eggmanone downregulated proliferation of the chemo-resistant prostate cancer cells via sonic Hedgehog signaling. In addition, Eggmanone treatment dose-dependently increases docetaxel cytotoxicity to DU145-TxR and PC3-TxR. As cancer stem cells (CSCs) are known to be implicated in cancer chemoresistance, we further examined Eggmanone impacts on CSC-like properties in the chemo-resistant prostate cancer cells. Our study shows that Eggmanone effectively down-regulates the expression of CSCs’ marker genes Nanog and ABC sub-family G member 2 (ABCG2) and attenuates sphere formation in DU145-TxR and PC3-TxR cells. In summary, our work shows that Eggmanone effectively overcomes the chemoresistance of prostate cancer cells presumably through sonic Hedgehog signaling and targeting CSCs, suggesting that Eggmanone may serve as a novel agent for chemo-resistant prostate cancer.

Hypoxia theranostics of a human prostate cancer xenograft and the resulting effects on the tumor microenvironment

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Developed a hypoxia theranostic imaging strategy to eliminate hypoxic cells.

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Hypoxic cell elimination resulted in fewer cancer associated fibroblasts (CAFs)

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Collagen 1 fiber patterns were altered with hypoxic cell elimination.

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cDNA nanoparticles with HRE driven prodrug enzyme expression can target hypoxia.

Hypoxia is frequently observed in human prostate cancer, and is associated with chemoresistance, radioresistance, metastasis, and castrate-resistance. Our purpose in these studies was to perform hypoxia theranostics by combining in vivo hypoxia imaging and hypoxic cancer cell targeting in a human prostate cancer xenograft. This was achieved by engineering PC3 human prostate cancer cells to express luciferase as well as a prodrug enzyme, yeast cytosine deaminase, under control of hypoxic response elements (HREs). Cancer cells display an adaptive response to hypoxia through the activation of several genes mediated by the binding of hypoxia inducible factors (HIFs) to HRE in the promoter region of target gene that results in their increased transcription. HIFs promote key steps in tumorigenesis, including angiogenesis, metabolism, proliferation, metastasis, and differentiation. HRE-driven luciferase expression allowed us to detect hypoxia in vivo to time the administration of the nontoxic prodrug 5-fluorocytosine that was converted by yeast cytosine deaminase, expressed under HRE regulation, to the chemotherapy agent 5-fluorouracil to target hypoxic cells. Conversion of 5-fluorocytosine to 5-fluorouracil was detected in vivo by ¹⁹F magnetic resonance spectroscopy. Morphological and immunohistochemical staining and molecular analyses were performed to characterize tumor microenvironment changes in cancer-associated fibroblasts, cell viability, collagen 1 fiber patterns, and HIF-1α. These studies expand our understanding of the effects of eliminating hypoxic cancer cells on the tumor microenvironment and in reducing stromal cell populations such as cancer-associated fibroblasts.

The oncogenic potential of NANOG: An important cancer induction mediator

Cancer stem cells (CSCs) are a unique population in the tumor, but they only comprise 2%-5% of the tumor bulk. Although CSCs share several features with embryonic stem cells, CSCs can give rise to the tumor cells. CSCs overexpress embryonic transcription factor NANOG, which is downregulated in differentiated tissues. This transcription factor confers CSC's stemness, unlimited self-renewal, metastasis, invasiveness, angiogenesis, and drug-resistance with the assistance of WNT, OCT4, SOX2, Hedgehog, BMI-1, and other complexes. NANOG facilitates CSCs development via multiple pathways, like angiogenesis and lessening E-cadherin expression levels, which paves the road for metastasis. Moreover, NANOG represses apoptosis and leads to drug-resistance. This review aims to highlight the pivotal role of NANOG and the pertained pathways in CSCs. Also, this current study intends to demonstrate that targeting NANOG can dimmish the CSCs, sensitize the tumor to chemotherapy, and eradicate the cancer cells.

Characterization of iPS87, a prostate cancer stem cell-like cell line

Prostate cancer affects hundreds of thousands of men and families throughout the world. Although chemotherapy, radiation, surgery, and androgen deprivation therapy are applied, these therapies do not cure metastatic prostate cancer. Patients treated by androgen deprivation often develop castration resistant prostate cancer which is incurable. Novel approaches of treatment are clearly necessary. We have previously shown that prostate cancer originates as a stem cell disease. A prostate cancer patient sample, #87, obtained from prostatectomy surgery, was collected and frozen as single cell suspension. Cancer stem cell cultures were grown, single cell-cloned, and shown to be tumorigenic in SCID mice. However, outside its natural niche, the cultured prostate cancer stem cells lost their tumor-inducing capability and stem cell marker expression after approximately 8 transfers at a 1:3 split ratio. Tumor-inducing activity could be restored by inducing the cells to pluripotency using the method of Yamanaka. Cultures of human prostate-derived normal epithelial cells acquired from commercial sources were similarly induced to pluripotency and these did not acquire a tumor phenotype in vivo. To characterize the iPS87 cell line, cells were stained with antibodies to various markers of stem cells including: ALDH7A1, LGR5, Oct4, Nanog, Sox2, Androgen Receptor, and Retinoid X Receptor. These markers were found to be expressed by iPS87 cells, and the high tumorigenicity in SCID mice of iPS87 was confirmed by histopathology. This research thus characterizes the iPS87 cell line as a cancer-inducing, stem cell-like cell line, which can be used in the development of novel treatments for prostate cancer.

ZBP-89 negatively regulates self-renewal of liver cancer stem cells via suppression of Notch1 signaling pathway

Liver cancer stem cells (LCSCs) initiate hepatocellular carcinoma (HCC) and contribute to its recurrence and treatment resistance. Studies have suggested ZBP-89 as a candidate tumor suppressor in HCC. We explored the role of ZBP-89 in the regulation of LCSCs. This study was performed in liver tissue samples from 104 HCC patients, 2 cell lines and mouse tumor models. We demonstrated that ZBP-89 was weakly expressed in LCSCs. Patients with high expression of LCSC markers displayed reduced survivals and higher recurrence rates after curative surgical operation. The expression of ZBP-89 was predictive for decreased recurrence. LCSC markers were negatively correlated with ZBP-89 in HCC tissues and in enriched liver tumor spheres. The exogenous expression of ZBP-89 attenuated the tumor-sphere formation and secondary colony formation capabilities of LCSCs in vitro and tumorigenicity in vivo. Furthermore, the negative effect of ZBP-89 on cancer stemness was Notch1-dependent. Localized with Notch1 intracellular domain (NICD1) in the nucleus, ZBP-89 repressed the Notch1 signaling pathway by competitive binding to NICD1 with MAML1. Collectively, ZBP-89 negatively regulates HCC stemness via inhibiting the Notch1 signaling.

Hypoxia induced cancer stem cell enrichment promotes resistance to androgen deprivation therapy in prostate cancer

Androgen deprivation therapy (ADT) is the main treatment to prolong survival in advance stage prostate cancer (PCa) but associated resistance leads to the development of terminal castrate resistant PCa (CRPC). Current research demonstrates that prostate cancer stem cells (PCSC) play a critical role in the development of treatment resistance and subsequent disease progression. Despite uncertainty surrounding the origin of these cells, studies clearly show they are associated with poorer outcomes and that ADT significantly enhances their numbers. Here in we highlight how activation of HIF signalling, in response to hypoxic conditions within the tumour microenvironment, results in the expression of genes associated with stemness and EMT promoting PCSC emergence which ultimately drives tumour relapse to CRPC. Hypoxic conditions are not only enhanced by ADT but the associated decrease in AR activation also promotes PI3K/AKT signalling which actively enhances HIF and its effects on PCSC's. Furthermore, emerging evidence now indicates that HIF-2α, rather than the commonly considered HIF-1α, is the main family member that drives PCSC emergence. Taken together this clearly identifies HIF and associated pathways as key targets for new therapeutic strategies that could potentially prevent or slow PCSC promoted resistance to ADT, thus holding potential to prolong patient survival.

Hypoxia inducible factors in the tumor microenvironment as therapeutic targets of cancer stem cells

Cancer stem cells (CSC) constitute a small area of the tumor mass and are characterized by self-renewal, differentiation and the ability to promote the development of secondary chemo-resistant tumors. Self-renewal of CSCs is regulated through various signaling pathways including Hedgehog, Notch, and Wnt/β-catenin pathways. A few surface markers have been identified, which provide a means of targeting CSCs according to tumor type. Depending on the proximity of CSCs to the tumor hypoxic niche, hypoxia-inducible factors (HIFs) can play a critical role in modulating several CSC-related characteristics. For instance, the upregulation of HIF-1 and HIF-2 at tumor sites, which correlates with the expansion of CSCs and poor cancer prognosis, has been demonstrated. In this review, we will discuss the mechanisms by which hypoxia enhances the development of CSCs in the tumor microenvironment. Targeting HIFs in combination with other common therapeutics is pre-requisite for effective eradication of CSCs.

Elimination of SOX2/OCT4-Associated Prostate Cancer Stem Cells Blocks Tumor Development and Enhances Therapeutic Response

SOX2 and OCT4 are key regulators of embryonic stem cell pluripotency. They are overexpressed in prostate cancers and have been associated with cancer stem cell (CSC) properties. However, reliable tools for detecting and targeting SOX2/OCT4-overexpressing cells are lacking, limiting our understanding of their roles in prostate cancer initiation, progression, and therapeutic resistance. Here, we show that a fluorescent reporter called SORE6 can identify SOX2/OCT4-overexpressing prostate cancer cells. Among tumor cells, the SORE6 reporter identified a small fraction with CSC hallmarks: rapid self-renewal, the capability to form tumors and metastasize, and resistance to chemotherapies. Transcriptome and biochemical analyses identified PI3K/AKT signaling as critical for maintaining the SORE6⁺ population. Moreover, a SORE6-driven herpes simplex virus thymidine kinase (TK) expression construct could selectively ablate SORE6⁺ cells in tumors, blocking tumor initiation and progression, and sensitizing tumors to chemotherapy. This study demonstrates a key role of SOX2/OCT4-associated prostate cancer stem cells in tumor development and therapeutic resistance, and identifies the SORE6 reporter system as a useful tool for characterizing CSCs functions in a native tumor microenvironment.

Characterization of OCT3/4, Nestin, NANOG, CD44 and CD24 as stem cell markers in canine prostate cancer

The cancer cell population is heterogeneous, and cancer stem cells (CSCs) are important for tumor growth and maintenance. The CSC population is associated with different neoplastic characteristics, such as cell migration, resistance to apoptosis, radiation therapy and chemotherapy. To increase the knowledge of CSCs in canine prostate cancer (PC), we characterized CSC markers in canine PC tissues and tumorspheres. We performed immunohistochemistry of OCT3/4, Nestin, NANOG, CD44 and CD24 in 10 normal canine prostatic tissue samples, 10 prostatic hyperplastic (PH) tissue samples and 28 PC tissue samples. Then, we established two canine prostate cancer cell cultures and characterized the CSC profile of tumorspheres grown from these cultures. Normal and PH tissues were positive for Nestin, NANOG, CD44 and CD24 only in the basal cell layer. OCT3/4 was expressed in the luminal cells of normal and PH tissues. There was no significant difference in Nestin expression among the prostatic tissues. However, we found higher expression of NANOG and CD44 in canine PC tissues than that in normal and PH tissues. Tumorspheres from canine prostate cancer cells express OCT3/4, Nestin, NANOG and CD44, indicating that these markers may be potential cancer stem cell markers in canine PC. The results obtained can be useful to better characterize the stem cell population in canine prostatic cancer and to guide future studies in comparative oncology.

AMPK Promotes SPOP-Mediated NANOG Degradation to Regulate Prostate Cancer Cell Stemness

NANOG is an essential transcriptional factor for the maintenance of embryonic stem cells (ESCs) and cancer stem cells (CSCs) in prostate cancer (PCa). However, the regulation mechanism of NANOG protein stability in cancer progression is still elusive. Here, we report that NANOG is degraded by SPOP, a frequently mutated tumor suppressor of PCa. Cancer-associated mutations of SPOP or the mutation of NANOG at S68Y abrogates the SPOP-mediated NANOG degradation, leading to elevated PCa cancer stemness and poor prognosis. In addition, SPOP-mediated NANOG degradation is controlled by the AMPK-BRAF signal axis through the phosphorylation of NANOG at Ser68, which blocked the interaction between SPOP and NANOG. Thus, our study provides a regulation mechanism of PCa stemness controlled by phosphorylation-mediated NANOG stability, which helps to identify novel drug targets and improve therapeutic strategy for PCa.

Hyaluronic Acid-Based Multilayer Films Regulate Hypoxic Multicellular Aggregation of Pancreatic Cancer Cells with Distinct Cancer Stem-Cell-like Properties

In vitro spherical cancer models have been widely used in cancer stem cell (CSC) research, and the ability of CSCs to form multicellular colonies is recognized as a morphological marker. However, although several spherical/colony models share a common three-dimensional (3D) conformation, each model displays its own intrinsic properties. Thus, the CSC phenotypes with distinct multicellular aggregate morphologies must be defined and clarified. Here, a novel 3D model was designed to regulate the type of pancreatic CSC colonies that form using niche mimetic hyaluronic acid (HA)-based multilayer nanofilms and hypoxia. The multicellular aggregate morphology, CSC phenotypes, CSC-related marker expression, cell cycle, invasion, and drug resistance were determined. On the basis of the results of a cell morphology analysis, colonies formed on multilayer nanofilms in response to both normoxia and hypoxia, but round and island-type colonies, were investigated. Immunostaining results revealed a significantly higher expression of stem cell markers, such as OCT4, CXCR4, and CD44v6, in colonies that formed on multilayer nanofilms. These colonies also expressed higher levels of E-cadherin, hypoxia-inducible factor-1α, and vimentin, particularly the round-type colonies that formed on HA-based multilayer nanofilms, [poly(allylamine) (PAH)/HA]₃, indicating that these colonies exhibit hybrid and metastable epithelial/mesenchymal phenotypes. Moreover, the cell cycle and invasion tests revealed that most of the cells in colonies growing on multilayer nanofilms showed a quiescent, slow cycling phenotype but displayed higher invasion after induction. Furthermore, a hypoxic environment strongly influences the drug resistance. This study describes a useful tool to investigate the diverse phenotypes of pancreatic CSC colonies and to study their regulatory factors that may benefit CSC research.

Characterization of Human Fetal Cartilage Progenitor Cells During Long-Term Expansion in a Xeno-Free Medium

BACKGROUND

Stem cell therapy requires a serum-free and/or chemically-defined medium for commercialization, but it is difficult to find one that supports long-term expansion of cells without compromising their stemness, particularly for novel stem cells.

METHODS

In this study, we tested the efficiency of StemPro® MSC SFM Xeno Free (SFM-XF), a serum-free medium, for the long-term expansion of human fetal cartilage-derived progenitor cells (hFCPCs) from three donors in comparison to that of the conventional α-Modified Eagle's Medium (α-MEM) supplemented with 10% fetal bovine serum (FBS).

RESULTS

We found that SFM-XF supported the expansion of hFCPCs for up to 28-30 passages without significant changes in the doubling time, while α-MEM with 10% FBS showed a rapid increase in doubling time at 10-18 passages depending on the donor. Senescence of hFCPCs was not observed until passage 10 in both media but was induced in approximately 15 and 25% of cells at passage 20 in SFM-XF and α-MEM with 10% FBS, respectively. The colony forming ability of hFCPCs in SFX-XF was also comparable to that in α-MEM with 10% FBS. hFCPCs expressed pluripotency genes like Oct-4, Sox-2, Nanog, SCF, and SSEA4 at passage 20 and 31 in SFM-XF; however, this was not observed when cells were cultured in α-MEM with 10% FBS. The ability of hFCPCs to differentiate into three mesodermal lineages decreased gradually in both media but it was less significant in SFM-XF. Finally we found no chromosomal abnormality after long-term culture of hFCPCs until passage 17 by karyotype analysis.

CONCLUSION

These results suggest that SFM-XF supports the long-term expansion of hFCPCs without significant phenotypic and chromosomal changes. This study have also shown that hFCPCs can be mass-produced in vitro, proving their commercial value as a novel source for developing cell therapies.

NANOGP8 is the key regulator of stemness, EMT, Wnt pathway, chemoresistance, and other malignant phenotypes in gastric cancer cells

BACKGROUND

Accumulating evidence demonstrated that NANOG1, the key transcription factor for embryonic stem cells, is associated with human cancers. NANOGP8, one of the pseudogenes in NANOG gene family, contains an intact open reading frame and also said to be expressed in cancer tissues. Therefore, a systematic study is greatly needed to address the following questions: among NANOG1 and NANOGP8, which gene is the main contributor for NANOG expression in cancer cells and which one is the key regulator responsible for stemness, epithelial-mesenchymal transition (EMT), metastasis, chemoresistance and other malignant phenotypes. Here we try to explore these issues with gastric adenocarcinoma cell lines in vitro using variety of molecular and cellular techniques.

METHODS

Special primers were designed to distinguish PCR products from NANOG1 and NANOGP8. Sphere-forming cells were cultured with serum-free and selective medium. A stable cell line was established with infection of lentivirus containing NANOGP8. qPCR was performed to measure NANOGP8 expression and its association with stemness, EMT and CSC markers in adherent cells and sphere-forming cells. Western blot analysis was deployed to confirm results of the transcript analysis. Experiments of cell proliferation, migration, invasion, clonogenic assay, sphere cell growth assays, cell cycle analysis, β-catenin accumulation and translocation in nucleus, and drug resistance were conducted to measure the impact of NANOGP8 on malignant statuses of gastric cancer cells. Immunofluorescence staining was used to analyze cell subpopulations with different markers.

RESULTS

NANOGP8 is mainly responsible for NANOG expression in sphere-forming (stem cell-like) cells derived from gastric cancer cell lines regardless their differentiation status. Ectopic expression of NANOGP8 significantly up-regulates stemness transcription factors, EMT inducers, and cancer stem cell markers (CSC) including Lgr5. NANOGP8 also promotes expression of the signature genes vimentin and N-caderin for mesenchymal cells and down-regulates the signature gene E-caderin for epithelial cells whereby confer the cells with mesenchymal cell phenotype. In NANOGP8 over-expressed adherent and sphere-forming cells, Lgr5+ cells are significantly increased. Ectopic expression of NANOGP8 endows gastric cells with enhanced proliferation, migration, invasion, sphere-forming and clonogenic capacity, and chemoresistance. NANOGP8 expression also enhances β-catenin accumulation in nucleus and strengthens Wnt signal transduction.

CONCLUSION

NANOGP8 is the main regulator of gastric cancer stem cells. It is closely associated with EMT, stemness, and CSC marker as well as Wnt signal pathway. NANOGP8 is correlated with cell proliferation, migration, invasion, clonogenic capacity, β-catenin accumulation in nucleus, and chemoresistance in gastric cancer. NANOGP8 is a promising molecular target for clinical intervention of gastric cancer.

Visualization of early prostatic adenocarcinoma as a stem cell disease

Prostate Cancer represents the second leading cause of cancer death among men in the United States, and the third leading cause of cancer death among men in Europe. We have previously shown that cells possessing Cancer Stem Cell (CSC) characteristics can be grown from human PrCa tissue harvested at the time of prostatectomy. However, the cellular origin of these CSCs was not previously known. In most cases, simple hematoxylin and eosin (H&E) stained sections are sufficient to make a definitive diagnosis of prostatic adenocarcinoma (PrCa) in needle biopsy samples. We utilized six different antibodies specific for stem cell antigens to examine paraffin sections of PrCa taken at the time of needle-biopsy diagnosis. These antisera were specific for CD44, CD133, ALDH7A1, LGR-5, Oct-4 and NANOG. We demonstrate specific staining of tumor cells with all six antisera specific for stem cell antigens. Some of these antibodies also react with cells of hyperplastic glands, but the patterns of reactivity differ from those of malignant glands. These findings demonstrate that at the time of diagnosis, PrCa consists of cells exhibiting properties of CSCs and consistent with the possibility that PrCa is a stem cell disease.

Reactive oxygen species generation and increase in mitochondrial copy number: new insight into the potential mechanism of cytotoxicity induced by aurora kinase inhibitor, AZD1152-HQPA

Aurora-B kinase overexpression plays important roles in the malignant progression of prostate cancer (PCa). AZD1152-HQPA, as an inhibitor of Aurora-B, has recently emerged as a promising agent for cancer treatment. In this study, we aimed to investigate the effects of AZD1152-HQPA on reactive oxygen species (ROS) generation and mitochondrial function in PCa. We used AZD1152-HQPA (Barasertib), a highly potent and selective inhibitor of Aurora-B kinase. The effects of AZD1152-HQPA on cell viability, DNA content, cell morphology, and ROS production were studied in the androgen-independent PC-3 PCa cell line. Moreover, the mitochondrial copy number and the expression of genes involved in cell survival and cancer stem cell maintenance were investigated. We found that AZD1152-HQPA treatment induced defective cell survival, polyploidy, micronuclei formation, cell enlargement, and cell death by significant overexpression of p73, p21 and downregulation of cell cycle-regulatory genes in a drug concentration-dependent manner. Moreover, AZD1152 treatment led to an excessive ROS generation and an increase in the mitochondrial copy number not only in PC-3 but also in several other malignant cells. AZD1152 treatment also led to downregulation of genes involved in the maintenance of cancer stem cells. Our results showed a functional relationship between the aurora kinase inhibition, an increase in mitochondrial copy number, and ROS generation in therapeutic modalities of cancer. This study suggests that the excessive ROS generation may be a novel mechanism of cytotoxicity induced by the aurora kinase inhibitor, AZD1152-HQPA.

Targeting aggressive prostate cancer-associated CD44v6 using phage display selected peptides

There is a crucial need to identify new biomarkers associated with aggressive prostate cancer (PCa) including those associated with cancer stem cells (CSCs). CD44v6, generated by alternative splicing of CD44, has been proposed as a CSC biomarker due to its correlation with aggressive PCa disease. We hypothesized that phage display selected peptides that target CD44v6 may serve as theranostic agents for aggressive PCa. Here, a 15 amino acid peptide ("PFT") was identified by affinity selection against a peptide derived from the v6 region of CD44v6. Synthesized PFT exhibited specific binding to CD44v6 with an equilibrium dissociation constant (Kd) of 743.4 nM. PFT also bound CD44v6 highly expressed on human PCa cell lines. Further, an aggressive form of PCa cells (v6A3) was isolated and tagged by a novel CSC reporter vector. The v6A3 cells had a CSC-like phenotype including enriched CD44v6 expression, enhanced clonogenicity, resistance to chemotherapeutics, and generation of heterogeneous offspring. PFT exhibited preferential binding to v6A3 cells compared to parental cells. Immunohistofluorescence studies with human PCa tissue microarrays (TMA) indicated that PFT was highly accurate in detecting CD44v6-positive aggressive PCa cells, and staining positivity was significantly higher in late stage, metastatic and higher-grade samples. Taken together, this study provides for the first time phage display selected peptides that target CD44v6 overexpressed on PCa cells. Peptide PFT may be explored as an aid in the diagnosis and therapy of advanced PCa disease.

Prostate Cancer Stem Cell Markers Drive Progression, Therapeutic Resistance, and Bone Metastasis

Metastatic or recurrent tumors are the primary cause of cancer-related death. For prostate cancer, patients diagnosed with local disease have a 99% 5-year survival rate; however, this 5-year survival rate drops to 28% in patients with metastatic disease. This dramatic decline in survival has driven interest in discovering new markers able to identify tumors likely to recur and in developing new methods to prevent metastases from occurring. Biomarker discovery for aggressive tumor cells includes attempts to identify cancer stem cells (CSCs). CSCs are defined as tumor cells capable of self-renewal and regenerating the entire tumor heterogeneity. Thus, it is hypothesized that CSCs may drive primary tumor aggressiveness, metastatic colonization, and therapeutic relapse. The ability to identify these cells in the primary tumor or circulation would provide prognostic information capable of driving prostate cancer treatment decisions. Further, the ability to target these CSCs could prevent tumor metastasis and relapse after therapy allowing for prostate cancer to finally be cured. Here, we will review potential CSC markers and highlight evidence that describes how cells expressing each marker may drive prostate cancer progression, metastatic colonization and growth, tumor recurrence, and resistance to treatment.

Epithelial-Mesenchymal Transition in Docetaxel-Resistant Prostate Cancer

Castration-resistant prostate cancer (CRPCa) is an advanced stage of prostate cancer in which a tumour progresses even under androgen deprivation. Treatment alternatives for CRPCa remain very limited and mostly rely on docetaxel-based chemotherapy. Despite being shown to increase patients’ overall survival, docetaxel’s clinical efficacy is impaired by development of chemoresistance. Most patients do not respond to docetaxel treatment and even those initially responsive ultimately develop resistance. Recently, chemoresistance was found to be closely related to epithelial-mesenchymal transition (EMT), a process in which epithelial cells transition into a mesenchymal phenotype. In fact, EMT markers are overexpressed in prostate cancer and are correlated to a higher Gleason score. For this reason, new therapeutic strategies are being studied to inhibit this process in several cancers. However, the clinical usefulness of targeting EMT as a way to overcome docetaxel resistance in CRPCa is still questionable and suffers from some significant limitations. This review briefly summarises the most common mechanisms of EMT-induced chemoresistance and evaluates its use as a new approach to overcome docetaxel resistance in CRPCa.

Distance in cancer gene expression from stem cells predicts patient survival

The degree of histologic cellular differentiation of a cancer has been associated with prognosis but is subjectively assessed. We hypothesized that information about tumor differentiation of individual cancers could be derived objectively from cancer gene expression data, and would allow creation of a cancer phylogenetic framework that would correlate with clinical, histologic and molecular characteristics of the cancers, as well as predict prognosis. Here we utilized mRNA expression data from 4,413 patient samples with 7 diverse cancer histologies to explore the utility of ordering samples by their distance in gene expression from that of stem cells. A differentiation baseline was obtained by including expression data of human embryonic stem cells (hESC) and human mesenchymal stem cells (hMSC) for solid tumors, and of hESC and CD34+ cells for liquid tumors. We found that the correlation distance (the degree of similarity) between the gene expression profile of a tumor sample and that of stem cells orients cancers in a clinically coherent fashion. For all histologies analyzed (including carcinomas, sarcomas, and hematologic malignancies), patients with cancers with gene expression patterns most similar to that of stem cells had poorer overall survival. We also found that the genes in all undifferentiated cancers of diverse histologies that were most differentially expressed were associated with up-regulation of specific oncogenes and down-regulation of specific tumor suppressor genes. Thus, a stem cell-oriented phylogeny of cancers allows for the derivation of a novel cancer gene expression signature found in all undifferentiated forms of diverse cancer histologies, that is competitive in predicting overall survival in cancer patients compared to previously published prediction models, and is coherent in that gene expression was associated with up-regulation of specific oncogenes and down-regulation of specific tumor suppressor genes associated with regulation of the multicellular state.

Immunohistochemical analysis of NANOG expression and epithelial-mesenchymal transition in pulmonary sarcomatoid carcinoma

Pulmonary sarcomatoid carcinomas (PSCs) are defined as a group of poorly differentiated non-small cell lung cancers that demonstrate sarcoma-like differentiation. The mechanism of mesenchymal differentiation in PSC is epithelial-mesenchymal transition (EMT). The expression of homeobox protein NANOG (NANOG), which regulates the pluripotency of embryonic stem cells, is associated with the EMT process. Therefore, the present study aimed to assess the expression level of NANOG and the status of the EMT process in PSC. The data of patients with PSC were retrospectively reviewed and immunohistochemical analyses were performed on patient samples to examine the expression of NANOG and EMT-associated proteins. The comparator group included randomly selected patients with matched clinicopathological characteristics who had pulmonary adenocarcinoma (PA). In the present study, 12 patients with PSC (4 females and 8 males) were enrolled; their median age was 65 years (range, 36-79 years), and the number of patients with stage IB, IIB, IIIA, IIIB and IV disease were 1, 1, 1, 1 and 8, respectively. The immunoreactive score (IRS) for E-cadherin was significantly lower in the PSC group compared with the PA group (P<0.0001), whereas the IRS for vimentin was significantly higher in the PSC group compared with the PA group (P<0.0001). However, the IRS for NANOG was significantly decreased in the PSC group compared with the PA group (P<0.0001), which suggests that NANOG does not serve an essential role in EMT in PSC. In addition, the overall survival of patients with PSC was significantly lower compared with that of patients with PA (median survival time, 7.0 vs. 35.6 months, respectively; P=0.0256). However, no significant difference was observed in the OS of patients who expressed low compared with high levels of NANOG (P=0.4416). In conclusion, it was clearly demonstrated that cytoplasmic NANOG expression was significantly lower in PSC compared with PA, and that the EMT process in PSC was accelerated, compared with that in PA.

The role of NANOG transcriptional factor in the development of malignant phenotype of cancer cells

NANOG is a transcription factor that is involved in the self-renewal of embryonic stem cells (ES) and is a critical factor for the maintenance of the undifferentiated state of pluripotent cells. Extensive data in the literature show that the NANOG gene is aberrantly expressed during the development of malignancy in cancer cells. ES and cancer stem cells (CSCs), a subpopulation of cancer cells within the tumor, are thought to share common phenotypic properties. This review describes the role of NANOG in cancer cell proliferation, epithelial-mesenchymal transition (EMT), apoptosis and metastasis. In addition, this paper illustrates a correlation between NANOG and signal transducer and activator of transcription 3 (STAT3) in the maintenance of cancer stem cell properties and multidrug resistance. Together, the available data demonstrate that NANOG is strictly involved in the process of carcinogenesis and is a potential prognostic marker of malignant tumors.

CRISPR/Cas9-mediated gene knockout of NANOG and NANOGP8 decreases the malignant potential of prostate cancer cells

NANOG expression in prostate cancer is highly correlated with cancer stem cell characteristics and resistance to androgen deprivation. However, it is not clear whether NANOG or its pseudogenes contribute to the malignant potential of cancer. We established NANOG- and NANOGP8-knockout DU145 prostate cancer cell lines using the CRISPR/Cas9 system. Knockouts of NANOG and NANOGP8 significantly attenuated malignant potential, including sphere formation, anchorage-independent growth, migration capability, and drug resistance, compared to parental DU145 cells. NANOG and NANOGP8 knockout did not inhibit in vitro cell proliferation, but in vivo tumorigenic potential decreased significantly. These phenotypes were recovered in NANOG- and NANOGP8-rescued cell lines. These results indicate that NANOG and NANOGP8 proteins are expressed in prostate cancer cell lines, and NANOG and NANOGP8 equally contribute to the high malignant potential of prostate cancer.

Prostate Cancer Stem-like Cells Contribute to the Development of Castration-Resistant Prostate Cancer

Androgen deprivation therapy (ADT) has been the standard care for patients with advanced prostate cancer (PC) since the 1940s. Although ADT shows clear benefits for many patients, castration-resistant prostate cancer (CRPC) inevitably occurs. In fact, with the two recent FDA-approved second-generation anti-androgens abiraterone and enzalutamide, resistance develops rapidly in patients with CRPC, despite their initial effectiveness. The lack of effective therapeutic solutions towards CRPC largely reflects our limited understanding of the underlying mechanisms responsible for CRPC development. While persistent androgen receptor (AR) signaling under castration levels of serum testosterone (<50 ng/mL) contributes to resistance to ADT, it is also clear that CRPC evolves via complex mechanisms. Nevertheless, the physiological impact of individual mechanisms and whether these mechanisms function in a cohesive manner in promoting CRPC are elusive. In spite of these uncertainties, emerging evidence supports a critical role of prostate cancer stem-like cells (PCSLCs) in stimulating CRPC evolution and resistance to abiraterone and enzalutamide. In this review, we will discuss the recent evidence supporting the involvement of PCSLC in CRPC acquisition as well as the pathways and factors contributing to PCSLC expansion in response to ADT.

Diminution of miR-340-5p levels is responsible for increased expression of ABCB5 in melanoma cells under oxygen-deprived conditions

Melanoma is usually highly refractory to chemotherapy. This resistance to treatment is mainly due to high heterogeneity and plasticity of melanoma cells strictly connected to changes in tumor microenvironment. Hypoxia can drastically alter cancer biology. Solid tumor cells under hypoxia gain stem-like features, they are more invasive and drug-resistant than their normoxic counterparts. These effects could be mediated by changes in miRNA expression under hypoxia. MiRNAs are small non-coding RNA molecules that can negatively control gene expression. In the present study using microarray technology we evaluated the expression of miRNAs in melanoma cells derived from nodular melanoma and grown under normoxic and hypoxic conditions. Using R environment for statistical analysis we found that 70 miRNAs were differentially-expressed, and 16 of them were significantly down-regulated in melanoma cells grown in hypoxic conditions compared to cells grown in normoxia. We intended to find transcripts whose expression is increased due to down-regulation of selected miRNAs. Bioinformatics analysis revealed that increased levels of HIF-2α, ABCB5, OCT4, SOX2 and ZEB1 in different melanoma populations under hypoxia could be a result of significant down-regulation of miR-340-5p. Inhibition of miR-340-5p confirmed that this miRNA negatively influences the expression of ABCB5. This is the first study showing the relationship between miR-340-5p and expression of ABCB5, a transmembrane transporter involved in drug resistance considered as a marker of melanoma stem-like cells.

Clinical significance of Gremlin 1 in cervical cancer and its effects on cancer stem cell maintenance

Gremlin 1 is one of the bone morphogenetic protein (BMP) antagonists and is also related to differentiation in combination with BMPs and is associated with various types of diseases. Gremlin 1 is overexpressed in various types of human cancers and has been reported to play a role in cervical cancer oncogenesis. However, there is no report concerning the relationship between Gremlin 1 and cervical cancer stem cells (CSCs). The objective of the present study was to identify the clinical significance of Gremlin 1 in cervical cancer and its effects on CSC-like properties in vitro. Clinical samples were obtained. Gremlin 1 mRNA expression levels in the cervical cancer tissues were measured by RT-qPCR and assessed for correlation with their clinical prognosis [overall survival (OS), progression-free survival (PFS)] and with other prognostic factors. In vitro, cervical cancer, CaSki cells, exposed to Gremlin 1 (1,000 ng/ml) for 24 h were evaluated for expression of undifferentiated-cell markers (Nanog, Oct3/4, Sox2) by RT-qPCR, the population of ALDH-positive cells by flow cytometry and sphere-forming ability on a ultra-low attachment culture dish. Cervical cancer tissues from 104 patients were collected. A high mRNA expression level of Gremlin 1 was an independent poor prognostic factor of PFS but not of OS. A high mRNA expression level of Gremlin 1 was correlated with bulky (>4 cm) tumors. The Nanog mRNA expression level was significantly increased in the CaSki cells exposed to Gremlin 1 (P=0.0008) but not Oct3/4 and Sox2 mRNA expression levels. The population of ALDH-positive cells in the Gremlin 1-exposed cells was 1.41-fold higher compared with the control (P=0.0184). Sphere-forming ability was increased when 1,000 Gremlin 1-exposed cells were seeded (P=0.0379). In cervical cancer, it is suggested that Gremlin 1 may have a role in clinical recurrence and maintaining CSC-like properties.

Reconsideration of the clinical and histopathological significance of angiogenesis in prostate cancer: Usefulness and limitations of microvessel density measurement

Angiogenesis plays important roles in tumor growth and cancer cell dissemination in almost all cancers. In prostate cancer, there is general agreement that increased angiogenesis is an important factor in determining tumor development and prognosis in these patients. Microvessel density is recognized as a useful marker for evaluating the angiogenic status of cancer tissues. Many investigators have reported that microvessel density is significantly associated with pathological features and outcomes in prostate cancer patients; however, some researchers have expressed opposing opinions. As the reason for such discrepancy, previous reports have suggested differences in the methodologies of measuring microvessel density in cancer tissues. In the present review, we focus on the variation in such methods, including the selected area and the method used for (semi)quantification. In particular, we discuss the relationship between malignancy potential, tumor progression, and survival and differences in the antibodies used for detection of endothelial cells in detail. We briefly compare the pathological significance and prognostic roles of microvessel density measured using von Willebrand factor, CD31, CD34, and CD105. Based on these analyses, the advantages and limitations of microvessel density measurements in prostate cancer tissues are clarified. Improved "real" and "specific" markers of cancer-related angiogenesis are necessary for better predictions of prognoses and for discussion of treatment strategies for patients with prostate cancer. However, establishment of a satisfactory cancer-related endothelial marker could take a long time. Therefore, knowledge regarding the pathological significance of microvessel density - based on understanding of the advantages and limitations of microvessel density determination methods - is important.

Epigenetics of cancer stem cells: Pathways and therapeutics

BACKGROUND

Epigenetic alterations including DNA methylation and histone modifications are the key factors in the differentiation of stem cells into different tissue subtypes. The generation of cancer stem cells (CSCs) in the process of carcinogenesis may also involve similar kind of epigenetic reprogramming where, in contrast, it leads to the loss of expression of genes specific to the differentiated state and regaining of stem cell-specific characteristics. The most important predicament with treatment of cancers includes the non-responsive quiescent CSC.

SCOPE OF REVIEW

The distinctive capabilities of the CSCs make cancer treatment even more difficult as this population of cells tends to remain quiescent for longer intervals and then gets reactivated leading to tumor relapse. Therefore, the current review is aimed to focus on recent advances in understanding the relation of epigenetic reprogramming to the generation, self-renewal and proliferation of CSCs.

MAJOR CONCLUSION

CSC-targeted therapeutic approaches would improve the chances of patient survival by reducing the frequency of tumor relapse. Differentiation therapy is an emerging therapeutic approach in which the CSCs are induced to differentiate from their quiescent state to a mature differentiated form, through activation of differentiation-related signalling pathways, miRNA-mediated alteration and epigenetic differentiation therapy. Thus, understanding the origin of CSC and their epigenetic regulation is crucial to develop treatment strategy against not only for the heterogeneous population of cancer cells but also to CSCs.

GENERAL SIGNIFICANCE

Characterizing the epigenetic marks of CSCs and the associated signalling cascades might help in developing therapeutic strategies against chemo-resistant cancers.