Human cortical glial tumors contain neural stem-like cells expressing astroglial and neuronal markers in vitro

Abuhamad A, Syahir A. Understanding Glioblastoma Biomarkers: Knocking a Mountain with a Hammer

Gliomas are the most frequent and deadly form of human primary brain tumors. Among them, the most common and aggressive type is the high-grade glioblastoma multiforme (GBM), which rapidly grows and renders patients a very poor prognosis. Meanwhile, cancer stem cells (CSCs) have been determined in gliomas and play vital roles in driving tumor growth due to their competency in self-renewal and proliferation. Studies of gliomas have recognized CSCs via specific markers. This review comprehensively examines the current knowledge of the most significant CSCs markers in gliomas in general and in glioblastoma in particular and specifically focuses on their outlook and importance in gliomas CSCs research. We suggest that CSCs should be the superior therapeutic approach by directly targeting the markers. In addition, we highlight the association of these markers with each other in relation to their cascading pathways, and interactions with functional miRNAs, providing the role of the networks axes in glioblastoma signaling pathways.

Non-cell autonomous promotion of astrogenesis at late embryonic stages by constitutive YAP activation

Although astrocytes have gained increased recognition as an important regulator in normal brain function and pathology, the mechanisms underlying their genesis are not well understood. In this study, we show that constitutive YAP activation by in utero introduction of a non-degradable form of the YAP gene (YAP 5SA) causes productive GFAP⁺ cell generation at late embryonic periods, and this activity is nuclear localization- and TEAD transcription factor-dependent. Moreover, we found that the GFAP⁺ cells were not YAP 5SA-expressing cells themselves but cells in the vicinity in vivo. Conditioned medium prepared from YAP 5SA-expressing cells induced GFAP⁺ cell production in vitro, suggesting that a soluble factor(s) was mediating the astrogenic activity of YAP 5SA. Indeed, YAP 5SA expression greatly increased CNTF and BMP4 transcription in neural progenitor cells, and a neutralizing antibody against CNTF reduced the astrogenic effects of YAP 5SA-conditioned medium. Furthermore, the YAP 5SA-expressing cells were identified as FN1⁺ mesenchymal cells which are responsible for the precocious astrogenesis. These results suggest a novel molecular mechanism by which YAP activation can induce astrogenesis in a non-cell autonomous manner.

Targeting Cancer Stem Cells by Genetically Engineered Chimeric Antigen Receptor T Cells

The term cancer stem cell (CSC) starts 25 years ago with the evidence that CSC is a subpopulation of tumor cells that have renewal ability and can differentiate into several distinct linages. Therefore, CSCs play crucial role in the initiation and the maintenance of cancer. Moreover, it has been proposed throughout several studies that CSCs are behind the failure of the conventional chemo-/radiotherapy as well as cancer recurrence due to their ability to resist the therapy and their ability to re-regenerate. Thus, the need for targeted therapy to eliminate CSCs is crucial; for that reason, chimeric antigen receptor (CAR) T cells has currently been in use with high rate of success in leukemia and, to some degree, in patients with solid tumors. This review outlines the most common CSC populations and their common markers, in particular CD133, CD90, EpCAM, CD44, ALDH, and EGFRVIII, the interaction between CSCs and the immune system, CAR T cell genetic engineering and signaling, CAR T cells in targeting CSCs, and the barriers in using CAR T cells as immunotherapy to treat solid cancers.

Organoid Models of Glioblastoma to Study Brain Tumor Stem Cells

Glioblastoma represents an aggressive form of brain cancer characterized by poor prognosis and a 5-year survival rate of only 3–7%. Despite remarkable advances in brain tumor research in the past decades, very little has changed for patients, due in part to the recurrent nature of the disease and to the lack of suitable models to perform genotype-phenotype association studies and personalized drug screening. In vitro culture of cancer cells derived from patient biopsies has been fundamental in understanding tumor biology and for testing the effect of various drugs. These cultures emphasize the role of in vitro cancer stem cells (CSCs), which fuel tumor growth and are thought to be the cause of relapse after treatment. However, it has become clear over the years that a 2D monolayer culture of these CSCs has certain disadvantages, including the lack of heterogeneous cell-cell and cell-environment interactions, which can now be partially overcome by the introduction of 3D organoid cultures. This is a novel and expanding field of research and in this review, I describe the emerging 3D models of glioblastoma. I also discuss their potential to advance our knowledge of tumor biology and CSC heterogeneity, while debating their current limitations.

Preferential Expression of B7-H6 in Glioma Stem-Like Cells Enhances Tumor Cell Proliferation via the c-Myc/RNMT Axis

B7 homologue 6 (B7-H6), a newly identified member of the B7 costimulatory molecule family, is not only a crucial regulator of NK cell-mediated immune responses through binding to NKp30 but also has clinical implications due to its abnormal expression in human cancers. Here, we show that B7-H6 expression is abnormally upregulated in glioma tissue and that B7-H6 is coexpressed with stem cell marker Sox2. Intriguingly, B7-H6 was rarely detected on the surface of glioma cell lines but was abundantly expressed in glioma stem-like cells (GSLCs) that were derived from the glioma cell lines in vitro. Surprisingly, B7-H6 was the only one that was preferentially expressed in the GSLCs among the B7 family members. Functionally, knockdown of B7-H6 in GSLCs by siRNAs led to the inhibition of cell proliferation, with decrease in the expression of the oncogene Myc as well as inactivation of PI3K/Akt and ERK/MAPK signaling pathways. Moreover, we determined that three genes CBL (Casitas B-Lineage Lymphoma Proto-Oncogene), CCNT1 (Cyclin T1), and RNMT (RNA guanine-7 methyltransferase) were coexpressed with B7-H6 and c-myc in glioma tissue samples from the TCGA database and found, however that only RNMT expression was inhibited by the knockdown of B7-H6 expression in the GSLCs, suggesting the involvement of RNMT in the B7-H6/c-myc axis. Extending this to 293T cells, we observed that knocking out of B7-H6 with CRISPR-Cas9 system also suppressed cell proliferation. Thus, our findings suggest B7-H6 as a potential molecule for glioma stem cell targeted immunotherapy.

Role of Connexins 30, 36, and 43 in Brain Tumors, Neurodegenerative Diseases, and Neuroprotection

Gap junction (GJ) channels and their connexins (Cxs) are complex proteins that have essential functions in cell communication processes in the central nervous system (CNS). Neurons, astrocytes, oligodendrocytes, and microglial cells express an extraordinary repertory of Cxs that are important for cell to cell communication and diffusion of metabolites, ions, neurotransmitters, and gliotransmitters. GJs and Cxs not only contribute to the normal function of the CNS but also the pathological progress of several diseases, such as cancer and neurodegenerative diseases. Besides, they have important roles in mediating neuroprotection by internal or external molecules. However, regulation of Cx expression by epigenetic mechanisms has not been fully elucidated. In this review, we provide an overview of the known mechanisms that regulate the expression of the most abundant Cxs in the central nervous system, Cx30, Cx36, and Cx43, and their role in brain cancer, CNS disorders, and neuroprotection. Initially, we focus on describing the Cx gene structure and how this is regulated by epigenetic mechanisms. Then, the posttranslational modifications that mediate the activity and stability of Cxs are reviewed. Finally, the role of GJs and Cxs in glioblastoma, Alzheimer's, Parkinson's, and Huntington's diseases, and neuroprotection are analyzed with the aim of shedding light in the possibility of using Cx regulators as potential therapeutic molecules.

MicroRNA miR-100 Decreases Glioblastoma Growth by Targeting SMARCA5 and ErbB3 in Tumor-Initiating Cells

Glioblastoma multiforme (GBM) is the most aggressive and most frequently diagnosed malignant human glioma. Despite the best available standard of care (surgery, radiation, and chemotherapy), the median survival of GBM patients is less than 2 years. Many recent studies have indicated that microRNAs (miRNAs) are important for promoting or reducing/limiting GBM growth. In particular, we previously showed that GBMs express decreased levels of miR-100 relative to control tissue and that restoring miR-100 expression reduced GBM tumorigenicity by modulating SMRT/NCOR2 (Nuclear Receptor Corepressor 2). Here, we demonstrate that miR-100 overexpression decreases expression of the stem cell markers, nestin and L1CAM, and decreases proliferation of GBM tumor-initiating cells (cancer stem cells). We further show that miR-100-mediated anti-tumorigenic activity limits the activity of SMARCA5 and its downstream target STAT3 (known as mTOR-STAT3-Notch pathway). In addition, we report ErbB3 (Her3) as a putative miR-100 target, including inhibition of its downstream AKT and ERK signaling pathways.

A natural compound obtained from Valeriana jatamansi selectively inhibits glioma stem cells

Glioblastoma is one of the most malignant tumors with very poor prognosis. Glioma stem cells (GSCs) occupy a small proportion in glioma, but they are closely associated with radiotherapy and chemotherapy resistance, promoting tumor angiogenesis, hypoxia response, invasion and recurrence. Therefore, GSCs have become a new target for tumor treatment and are used in drug screening. Rupesin E is a natural compound obtained from Valeriana jatamansi, and its antitumor activity has not been reported. In the present study, the antitumor activity of rupesin E was investigated, and the results demonstrated that it inhibited the proliferation of GSCs (GSC-3#, GSC-12#, GSC-18#) with the IC₅₀ values of 7.13±1.41, 13.51±1.46 and 4.44±0.22 µg/ml, respectively. In addition, immunofluorescence cell staining and flow cytometry techniques demonstrated that rupesin E inhibited GSC proliferation and induced apoptosis. Furthermore, rupesin E inhibited the ability of GSC colony formation, indicating its antitumor activity against GSCs in vitro.

Integrin α6 (CD49f), The Microenvironment and Cancer Stem Cells

Cancer is a highly prevalent and potentially terminal disease that affects millions of individuals worldwide. Here, we review the literature exploring the intricacies of stem cells bearing tumorigenic characteristics and collect evidence demonstrating the importance of integrin α6 (ITGA6, also known as CD49f) in cancer stem cell (CSC) activity. ITGA6 is commonly used to identify CSC populations in various tissues and plays an important role sustaining the self-renewal of CSCs by interconnecting them with the tumorigenic microenvironment.

EGFRvIII: An Oncogene with Ambiguous Role

Epidermal growth factor receptor variant III (EGFRvIII) seems to constitute the perfect therapeutic target for glioblastoma (GB), as it is specifically present on up to 28-30% of GB cells. In case of other tumor types, expression and possible role of this oncogene still remain controversial. In spite of EGFRvIII mechanism of action being crucial for the design of small active anticancer molecules and immunotherapies, i.e., CAR-T technology, it is yet to be precisely defined. EGFRvIII is known to be resistant to degradation, but it is still unclear whether it heterodimerizes with EGF-activated wild-type EGFR (EGFRWT) or homodimerizes (including covalent homodimerization). Constitutive kinase activity of this mutated receptor is relatively low, and some researchers even claim that a nuclear, but not a membrane function, is crucial for its activity. Based on the analyses of recurrent tumors that are often lacking EGFRvIII expression despite its initial presence in corresponding primary foci, this oncogene is suggested to play a marginal role during later stages of carcinogenesis, while even in primary tumors EGFRvIII expression is detected only in a small percentage of tumor cells, undermining the rationality of EGFRvIII-targeting therapies. On the other hand, EGFRvIII-positive cells are resistant to apoptosis, more invasive, and characterized with enhanced proliferation rate. Moreover, expression of this oncogenic receptor was also postulated to be a marker of cancer stem cells. Opinions regarding the role that EGFRvIII plays in tumorigenesis and for tumor aggressiveness are clearly contradictory and, therefore, it is crucial not only to determine its mechanism of action, but also to unambiguously define its role at early and advanced cancer stages.

Novel therapies hijack the blood-brain barrier to eradicate glioblastoma cancer stem cells

Glioblastoma (GBM) is amongst the most aggressive brain tumors with a dismal prognosis. Despite significant advances in the current multimodality therapy including surgery, postoperative radiotherapy (RT) and temozolomide (TMZ)-based concomitant and adjuvant chemotherapy (CT), tumor recurrence is nearly universal with poor patient outcomes. These limitations are in part due to poor drug penetration through the blood-brain barrier (BBB) and resistance to CT and RT by a small population of cancer cells recognized as tumor-initiating cells or cancer stem cells (CSCs). Though CT and RT kill the bulk of the tumor cells, they fail to affect CSCs, resulting in their enrichment and their development into more refractory tumors. Therefore, identifying the mechanisms of resistance and developing therapies that specifically target CSCs can improve response, prevent the development of refractory tumors and increase overall survival of GBM patients. Small molecule inhibitors that can breach the BBB and selectively target CSCs are emerging. In this review, we have summarized the recent advancements in understanding the GBM CSC-specific signaling pathways, the CSC-tumor microenvironment niche that contributes to CT and RT resistance and the use of novel combination therapies of small molecule inhibitors that may be used in conjunction with TMZ-based chemoradiation for effective management of GBM.

Penfluridol as a Candidate of Drug Repurposing for Anticancer Agent

Penfluridol has robust antipsychotic efficacy and is a first-generation diphenylbutylpiperidine. Its effects last for several days after a single oral dose and it can be administered once a week to provide better compliance and symptom control. Recently; strong antitumour effects for penfluridol were discovered in various cancer cell lines; such as breast; pancreatic; glioblastoma; and lung cancer cells via several distinct mechanisms. Therefore; penfluridol has drawn much attention as a potentially novel anti-tumour agent. In addition; the anti-cancer effects of penfluridol have been demonstrated in vivo: results showed slight changes in the volume and weight of organs at doses tested in animals. This paper outlines the potential for penfluridol to be developed as a next-generation anticancer drug.

3D extracellular matrix microenvironment in bioengineered tissue models of primary pediatric and adult brain tumors

Dynamic alterations in the unique brain extracellular matrix (ECM) are involved in malignant brain tumors. Yet studies of brain ECM roles in tumor cell behavior have been difficult due to lack of access to the human brain. We present a tunable 3D bioengineered brain tissue platform by integrating microenvironmental cues of native brain-derived ECMs and live imaging to systematically evaluate patient-derived brain tumor responses. Using pediatric ependymoma and adult glioblastoma as examples, the 3D brain ECM-containing microenvironment with a balance of cell-cell and cell-matrix interactions supports distinctive phenotypes associated with tumor type-specific and ECM-dependent patterns in the tumor cells' transcriptomic and release profiles. Label-free metabolic imaging of the composite model structure identifies metabolically distinct sub-populations within a tumor type and captures extracellular lipid-containing droplets with potential implications in drug response. The versatile bioengineered 3D tumor tissue system sets the stage for mechanistic studies deciphering microenvironmental role in brain tumor progression.

PTEN modulates neurites outgrowth and neuron apoptosis involving the PI3K/Akt/mTOR signaling pathway

The present study aimed to explore the role of the PTEN/Akt/mTOR signaling pathway in the neurite outgrowth and apoptosis of cortical neurons. Cortical neurons were seeded on or adjacent to chondroitin sulfate proteoglycans. The length, number and crossing behavior of the neurites were calculated. Immunohistochemical staining and TUNEL data were analyzed. Neurites treated with PTEN inhibitor exhibited significant enhancements in elongation, initiation and crossing abilities when they encountered chondroitin sulfate proteoglycans in vitro. These effects disappeared when the PTEN/Akt/mTOR signaling pathway was blocked. Neurons exhibited significant enhancements in survival ability following PTEN inhibition. The present study demonstrated that PTEN inhibition can promote axonal elongation and initiation in cerebral cortical neurons, as well as the ability to cross the chondroitin sulfate proteoglycan border. In addition, PTEN inhibition is useful for protecting the neuron from apoptosis. The PTEN/Akt/mTOR signaling pathway is an important signaling pathway.

A Ploidy Increase Promotes Sensitivity of Glioma Stem Cells to Aurora Kinases Inhibition

Glioma stem cells account for glioblastoma relapse and resistance to conventional therapies, and protein kinases, involved in the regulation of the mitotic machinery (i.e., Aurora kinases), have recently emerged as attractive therapeutic targets. In this study, we investigated the effect of Aurora kinases inhibition in five glioma stem cell lines isolated from glioblastoma patients. As expected, cell lines responded to the loss of Aurora kinases with cytokinesis failure and mitotic exit without cell division. Surprisingly, this resulted in a proliferative arrest in only two of the five cell lines. These sensitive cell lines entered a senescent/autophagic state following aberrant mitotic exit, while the non-sensitive cell lines continued to proliferate. This senescence response did not correlate with TP53 mutation status but only occurred in the cell lines with the highest chromosome content. Repeated rounds of Aurora kinases inhibition caused a gradual increase in chromosome content in the resistant cell lines and eventually caused a similar senescence response and proliferative arrest. Our results suggest that a ploidy threshold is the main determinant of Aurora kinases sensitivity in TP53 mutant glioma stem cells. Thus, ploidy could be used as a biomarker for treating glioma patients with Aurora kinases inhibitors.

The Autophagy Status of Cancer Stem Cells in Gliobastoma Multiforme: From Cancer Promotion to Therapeutic Strategies

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor featuring rapid cell proliferation, treatment resistance, and tumor relapse. This is largely due to the coexistence of heterogeneous tumor cell populations with different grades of differentiation, and in particular, to a small subset of tumor cells displaying stem cell-like properties. This is the case of glioma stem cells (GSCs), which possess a powerful self-renewal capacity, low differentiation, along with radio- and chemo-resistance. Molecular pathways that contribute to GBM stemness of GSCs include mTOR, Notch, Hedgehog, and Wnt/β-catenin. Remarkably, among the common biochemical effects that arise from alterations in these pathways, autophagy suppression may be key in promoting GSCs self-renewal, proliferation, and pluripotency maintenance. In fact, besides being a well-known downstream event of mTOR hyper-activation, autophagy downregulation is also bound to the effects of aberrantly activated Notch, Hedgehog, and Wnt/β-catenin pathways in GBM. As a major orchestrator of protein degradation and turnover, autophagy modulates proliferation and differentiation of normal neuronal stem cells (NSCs) as well as NSCs niche maintenance, while its failure may contribute to GSCs expansion and maintenance. Thus, in the present review we discuss the role of autophagy in GSCs metabolism and phenotype in relationship with dysregulations of a variety of NSCs controlling pathways, which may provide novel insights into GBM neurobiology.

The Ig superfamily protein PTGFRN coordinates survival signaling in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most malignant primary brain tumor with a median survival of approximately 14 months. Despite aggressive treatment of surgical resection, chemotherapy and radiation therapy, only 3-5% of GBM patients survive more than 3 years. Contributing to this poor therapeutic response, it is believed that GBM contains both intrinsic and acquired mechanisms of resistance, including resistance to radiation therapy. In order to define novel mediators of radiation resistance, we conducted a functional knockdown screen, and identified the immunoglobulin superfamily protein, PTGFRN. In GBM, PTGFRN is found to be overexpressed and to correlate with poor survival. Reducing PTGFRN expression radiosensitizes GBM cells and potently decreases the rate of cell proliferation and tumor growth. Further, PTGFRN inhibition results in significant reduction of PI3K p110β and phosphorylated AKT, due to instability of p110β. Additionally, PTGFRN inhibition decreases nuclear p110β leading to decreased DNA damage sensing and DNA damage repair. Therefore overexpression of PTGFRN in glioblastoma promotes AKT-driven survival signaling and tumor growth, as well as increased DNA repair signaling. These findings suggest PTGFRN is a potential signaling hub for aggressiveness in GBM.

Challenges to curing primary brain tumours

Despite decades of research, brain tumours remain among the deadliest of all forms of cancer. The ability of these tumours to resist almost all conventional and novel treatments relates, in part, to the unique cell-intrinsic and microenvironmental properties of neural tissues. In an attempt to encourage progress in our understanding and ability to successfully treat patients with brain tumours, Cancer Research UK convened an international panel of clinicians and laboratory-based scientists to identify challenges that must be overcome if we are to cure all patients with a brain tumour. The seven key challenges summarized in this Position Paper are intended to serve as foci for future research and investment.

Glioblastoma Stem Cells and Comparison of Isolation Methods

Background

Glioblastoma (GBM) is the most aggressive and the most common primary brain tumor. Over the last few years, studies have identified many genetical and phenotypical molecular situations for developing new treatment modalities in patients with GBM. Nevertheless, main problem for the GBM is radio-chemotherapy resistance and relapse after the surgery. The identification of glioma stem cells and microenvironmental influences has created a paradigm shift in targets of therapy. Current studies have shown that glioma stem cell is responsible for aggressiveness, recurrence and resistance to therapy of GBM. GBM stem cell isolated from human GBM multiforme fresh tissue samples is important both for curative therapeutic options and personalized targeted therapy. The purpose of this study was to determine the most suitable isolation method of GBM stem cells (GSCs).

Methods

Tumor tissue sample was obtained during the surgical resection of lesion in patients with the diagnosis of GBM. Tumor stem cell isolation from tissue was performed in three different ways: 1) GBM cell isolation with trypsin; 2) GBM cell isolation with brain tumor dissociation Kit (BTD Kit); and 3) GBM cell isolation with tumor dissociation enzyme (TDE).

Results

We showed that GSCs were isolated from tumor specimen using flow cytometry and immunofluorescence staining. Our study showed that isolation with BTD Kit is the most suitable method to isolate GBM tissue-derived glial tumor stem cells.

Conclusions

The development of alternative personalized therapies targeting brain tumor stem cell is urgently needed. It is important to understand the fundamental mechanisms of driving stem cells. If their life cycle mechanisms can be identified, we can control the growth of GBM.

Neural stem cells promote glioblastoma formation in nude mice

PURPOSE

Neural stem cells (NSCs) have been characterized with the ability of self-renewal and neurogenesis, which has inspired lots of studies to clarify the functions of NSCs in neural injury, ischemic stroke, brain inflammation and neurodegenerative diseases. We focused on the relationship of NSCs with glioblastoma, since we have discovered that recurrent glioblastomas were inclined to be derived from subventricular zone (SVZ), where NSCs reside. We want to clarify whether NSCs are involved in glioblastoma relapse.

METHODS

Immunocytochemistry was used to confirm the stemness of NSCs. The Cell Counting Kit-8 was used to measure the proliferation of cells. Migration abilities were examined by wound healing and transwell assays, and tumor formation abilities were confirmed in nude mice.

RESULTS

We found in experiments that NSCs promoted proliferation of a glioblastoma cell line-Ln229, the migration ability of Ln229 cells was motivated by co-cultured with NSCs. Tumor formation of Ln229 cells was also accelerated in nude mice when co-transplanted with NSCs. In immunohistochemistry, we found that the Sox2- and Ki67-positive cells were much higher in co-transplanted groups than that of control groups.

CONCLUSIONS

These results imply the potential role that NSCs play in speeding up tumor formation in the process of glioblastoma relapse, providing the basis for dealing with newly diagnosed glioblastoma patients, which may help postpone the recurrence of glioblastoma as far as possible through preprocessing the tumor-adjacent SVZ tissue.

Pathological and Molecular Features of Glioblastoma and Its Peritumoral Tissue

Glioblastoma (GBM) is one of the most aggressive and lethal human brain tumors. At present, GBMs are divided in primary and secondary on the basis of the mutational status of the isocitrate dehydrogenase (IDH) genes. In addition, IDH1 and IDH2 mutations are considered crucial to better define the prognosis. Although primary and secondary GBMs are histologically indistinguishable, they retain distinct genetic alterations that account for different evolution of the tumor. The high invasiveness, the propensity to disperse throughout the brain parenchyma, and the elevated vascularity make these tumors extremely recidivist, resulting in a short patient median survival even after surgical resection and chemoradiotherapy. Furthermore, GBM is considered an immunologically cold tumor. Several studies highlight a highly immunosuppressive tumor microenvironment that promotes recurrence and poor prognosis. Deeper insight into the tumor immune microenvironment, together with the recent discovery of a conventional lymphatic system in the central nervous system (CNS), led to new immunotherapeutic strategies. In the last two decades, experimental evidence from different groups proved the existence of cancer stem cells (CSCs), also known as tumor-initiating cells, that may play an active role in tumor development and progression. Recent findings also indicated the presence of highly infiltrative CSCs in the peritumoral region of GBM. This region appears to play a key role in tumor growing and recurrence. However, until recently, few studies investigated the biomolecular characteristics of the peritumoral tissue. The aim of this review is to recapitulate the pathological features of GBM and of the peritumoral region associated with progression and recurrence.

The Role of SVZ Stem Cells in Glioblastoma

As most common primary brain cancer, glioblastoma is also the most aggressive and malignant form of cancer in the adult central nervous system. Glioblastomas are genetic and transcriptional heterogeneous tumors, which in spite of intensive research are poorly understood. Over the years conventional therapies failed to affect a cure, resulting in low survival rates of affected patients. To improve the clinical outcome, an important approach is to identify the cells of origin. One potential source for these are neural stem cells (NSCs) located in the subventricular zone, which is one of two niches in the adult nervous system where NSCs with the capacity of self-renewal and proliferation reside. These cells normally give rise to neuronal as well as glial progenitor cells. This review summarizes current findings about links between NSCs and cancer stem cells in glioblastoma and discusses current therapeutic approaches, which arise as a result of identifying the cell of origin in glioblastoma.

Ovarian Cancer Stem Cells with High ROR1 Expression Serve as a New Prophylactic Vaccine for Ovarian Cancer

Tumor vaccines offer a number of advantages for cancer treatment. In the study, the vaccination with cancer stem cells (CSCs) with high expression of the type I receptor tyrosine kinase-like orphan receptor (ROR1) was evaluated in a murine model for the vaccine's immunogenicity and protective efficacy against epithelial ovarian carcinoma (EOC). CD117⁺CD44⁺ CSCs were isolated from human EOC HO8910 cell line using a magnetic-activated cell sorting system; murine ID8 EOC suspension sphere cells, which are collectively known as cancer stem-like cells, were acquired from serum-free suspension sphere-forming culture. Mice were subcutaneously immunized with the repeat cycles of freezing and thawing whole HO8910 CD117⁺CD44⁺ CSCs and ID8 cancer stem-like cells, respectively, followed by a challenge with HO8910 or ID8 cells at one week after final vaccination. The results showed that the CSC vaccination significantly induced immunity against EOC growth and markedly prolonged the survival of EOC-bearing mice in the prophylactic setting compared with non-CSC vaccination. Flow cytometry showed significantly increased immunocyte cytotoxicities and remarkably reduced CSC counts in the CSC-vaccinated mice. Moreover, the protective efficacy against EOC was decreased when the ROR1 expression was downregulated by shRNA in CSC vaccines. The findings from the study suggest that CSC vaccines with high ROR1 expression were highly effective in triggering immunity against EOC in vaccinated mice and may serve as an effective vaccine for EOC immunoprophylaxis.

The Transient Receptor Potential Vanilloid Type-2(TRPV2) Ion Channels in Neurogenesis andGliomagenesis: Cross-Talk between TranscriptionFactors and Signaling Molecules

Recently, the finding of cancer stem cells in brain tumors has increased the possibilities for advancing new therapeutic approaches with the aim to overcome the limits of current available treatments. In addition, a role for ion channels, particularly of TRP channels, in developing neurons as well as in brain cancer development and progression have been demonstrated. Herein, we focus on the latest advancements in understanding the role of TRPV2, a Ca²⁺ permeable channel belonging to the TRPV subfamily in neurogenesis and gliomagenesis. TRPV2 has been found to be expressed in both neural progenitor cells and glioblastoma stem/progenitor-like cells (GSCs). In developing neurons, post-translational modifications of TRPV2 (e.g., phosphorylation by ERK2) are required to stimulate Ca²⁺ signaling and nerve growth factor-mediated neurite outgrowth. TRPV2 overexpression also promotes GSC differentiation and reduces gliomagenesis in vitro and in vivo. In glioblastoma, TRPV2 inhibits survival and proliferation, and induces Fas/CD95-dependent apoptosis. Furthermore, by proteomic analysis, the identification of a TRPV2 interactome-based signature and its relation to glioblastoma progression/recurrence, high or low overall survival and drug resistance strongly suggest an important role of the TRPV2 channel as a potential biomarker in glioblastoma prognosis and therapy.

Role of Notch Signaling Pathway in Glioblastoma Pathogenesis

Notch signaling is an evolutionarily conserved pathway that regulates important biological processes, such as cell proliferation, apoptosis, migration, self-renewal, and differentiation. In mammals, Notch signaling is composed of four receptors (Notch1–4) and five ligands (Dll1-3–4, Jagged1–2) that mainly contribute to the development and maintenance of the central nervous system (CNS). Neural stem cells (NSCs) are the starting point for neurogenesis and other neurological functions, representing an essential aspect for the homeostasis of the CNS. Therefore, genetic and functional alterations to NSCs can lead to the development of brain tumors, including glioblastoma. Glioblastoma remains an incurable disease, and the reason for the failure of current therapies and tumor relapse is the presence of a small subpopulation of tumor cells known as glioma stem cells (GSCs), characterized by their stem cell-like properties and aggressive phenotype. Growing evidence reveals that Notch signaling is highly active in GSCs, where it suppresses differentiation and maintains stem-like properties, contributing to Glioblastoma tumorigenesis and conventional-treatment resistance. In this review, we try to give a comprehensive view of the contribution of Notch signaling to Glioblastoma and its possible implication as a target for new therapeutic approaches.

Isolation of Neural Stem Cells from the embryonic mouse hippocampus for in vitro growth or engraftment into a host tissue

For both stem cell research and treatment of the central nervous system disorders, neural stem/progenitor cells (NSPCs) represent an important breakthrough tool. In the expanded stem cell-based therapy use, NSPCs not only provide a powerful cell source for neural cell replacement but a useful model for developmental biology research. Despite numerous approaches were described for isolation of NSPCs from either fetal or adult brain, the main issue remains in extending cell survival following isolation. Here we provide a simple and affordable protocol for making viable NSPCs from the fetal mouse hippocampi, which are capable of maintaining the high viability in a 2D monolayer cell culture or generating 3D neuro-spheroids of cell aggregates. Further, we describe the detailed method for engraftment of embryonic NSPCs onto a host hippocampal tissue for promoting multilinear cell differentiation and maturation within endogenous environment. Our experimental data demonstrate that embryonic NSPCs isolated using this approach show the high viability (above 88%). Within a host tissue, these cells were capable of differentiating to the main neural subpopulations (principal neurons, oligodendrocytes, astroglia). Finally, NSPC-derived neurons demonstrated matured functional properties (electrophysiological activity), becoming functionally integrated into the host hippocampal circuits within a couple of weeks after engraftment.

Targeting Glioblastoma Stem Cells with 2-Deoxy-D-Glucose (2-DG) Potentiates Radiation-Induced Unfolded Protein Response (UPR)

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, and despite optimized treatment options, median survival remains dismal. Contemporary evidence suggests disease recurrence results from expansion of a robustly radioresistant subset of GBM progenitor cells, termed GBM stem cells (GSCs). In this study, we utilized transmission electron microscopy to uncover ultrastructural effects on patient-derived GSC lines exposed to supratherapeutic radiotherapy levels. Elevated autophagosome formation and increased endoplasmic reticulum (ER) internal diameter, a surrogate for ER stress and activation of unfolded protein response (UPR), was uncovered. These observations were confirmed via protein expression through Western blot. Upon interrogating genomic data from an open-access GBM patient database, overexpression of UPR-related chaperone protein genes was inversely correlated with patient survival. This indicated controlled UPR may play a role in promoting radioresistance. To determine if potentiating UPR further can induce apoptosis, we exposed GSCs to radiation with an ER stress-inducing drug, 2-deoxy-D-glucose (2-DG), and found dose-dependent decreases in viability and increased apoptotic marker expression. Taken together, our results indicate GSC radioresistance is, in part, achieved by overexpression and overactivation of ER stress-related pathways, and this effect can be overcome via potentiation of UPR, leading to loss of GSC viability.

Diffuse Intrinsic Pontine Gliomas Exhibit Cell Biological and Molecular Signatures of Fetal Hindbrain-Derived Neural Progenitor Cells

Diffuse intrinsic pontine glioma (DIPG) is the main cause of brain tumor-related death among children. Until now, there is still a lack of effective therapy with prolonged overall survival for this disease. A typical strategy for preclinical cancer research is to find out the molecular differences between tumor tissue and para-tumor normal tissue, in order to identify potential therapeutic targets. Unfortunately, it is impossible to obtain normal tissue for DIPG because of the vital functions of the pons. Here we report the human fetal hindbrain-derived neural progenitor cells (pontine progenitor cells, PPCs) as normal control cells for DIPG. The PPCs not only harbored similar cell biological and molecular signatures as DIPG glioma stem cells, but also had the potential to be immortalized by the DIPG-specific mutation H3K27M in vitro. These findings provide researchers with a candidate normal control and a potential medicine carrier for preclinical research on DIPG.

Introduction to Brain Tumor Stem Cells

From stem cells, to the cancer stem cell hypothesis and intratumoral heterogeneity, the following introductory chapter on brain tumor stem cells explores the history of normal and cancerous stem cells, and their implication in the current model of brain tumor development. The origins of stem cells date back to the 1960s, when they were first described as cells capable of self-renewal, extensive proliferation, and differentiation. Since then, many advances have been made and adult stem cells are now known to be present in a very wide variety of tissues. Neural stem cells were subsequently discovered 30 years later, which was shortly followed by the discovery of cancer stem cells in leukemia and in brain tumors over the next decade, effectively enabling a new understanding of cancer. Since then, many markers including CD133, brain cancer stem cells have been implicated in a variety of phenomena including intratumoral heterogeneity on the genomic, cellular, and functional levels, tumor initiation, chemotherapy-resistance, radiation-resistance, and are believed to be ultimately responsible for tumor relapse. Understanding this small and rare population of cells could be the key to solving the great enigma that is cancer.

Applications of Human Brain Organoids to Clinical Problems

Brain organoids are an exciting new technology with the potential to significantly change how diseases of the brain are understood and treated. These three-dimensional neural tissues are derived from the self-organization of pluripotent stem cells, and they recapitulate the developmental process of the human brain, including progenitor zones and rudimentary cortical layers. Brain organoids have been valuable in investigating different aspects of developmental neurobiology and comparative biology. Several characteristics of organoids also make them attractive as models of brain disorders. Data generated from human organoids are more generalizable to patients because of the match in species background. Personalized organoids also can be generated from patient-derived induced pluripotent stem cells. Furthermore, the three-dimensionality of brain organoids supports cellular, mechanical, and topographical cues that are lacking in planar systems. In this review, we discuss the translational potential of brain organoids, using the examples of Zika virus, autism-spectrum disorder, and glioblastoma multiforme to consider how they could contribute to disease modeling, personalized medicine, and testing of therapeutics. We then discuss areas of improvement in organoid technology that will enhance the translational potential of brain organoids, as well as the possibility of their use as substrates for repairing cerebral circuitry after injury. Developmental Dynamics 248:53-64, 2019. © 2018 Wiley Periodicals, Inc.

Drosophila melanogaster as a Model System for Human Glioblastomas

Glioblastoma multiforme (GBM) is the most common primary malignant adult brain tumor. Genomic amplifications, activating mutations, and overexpression of receptor tyrosine kinases (RTKs) such as EGFR, and genes in core RTK signaling transduction pathways such as PI3K are common in GBM. However, efforts to target these pathways have been largely unsuccessful in the clinic, and the median survival of GBM patients remains poor at 14-15 months. Therefore, to improve patient outcomes, there must be a concerted effort to elucidate the underlying biology involved in GBM tumorigenesis. Drosophila melanogaster has been a highly effective model for furthering our understanding of GBM tumorigenesis due to a number of experimental advantages it has over traditional mouse models. For example, there exists extensive cellular and genetic homology between humans and Drosophila, and 75% of genes associated with human disease have functional fly orthologs. To take advantage of these traits, we developed a Drosophila GBM model with constitutively active variants of EGFR and PI3K that effectively recapitulated key aspects of GBM disease. Researchers have utilized this model in forward genetic screens and have expanded on its functionality to make a number of important discoveries regarding requirements for key components in GBM tumorigenesis, including genes and pathways involved in extracellular matrix signaling, glycolytic metabolism, invasion/migration, stem cell fate and differentiation, and asymmetric cell division. Drosophila will continue to reveal novel biological pathways and mechanisms involved in gliomagenesis, and this knowledge may contribute to the development of effective treatment strategies to improve patient outcomes.

Concise Reviews: Cancer Stem Cell Targeted Therapies: Toward Clinical Success

Cancer stem cells (CSCs) are a subpopulation of cells within tumors that possess the stem cell characteristics of self-renewal, quiescence, differentiation, and the ability to recapitulate the parental tumor when transplanted into a host. CSCs are correlated with poor clinical outcome due to their contribution to chemotherapy resistance and metastasis. Multiple cell surface and enzymatic markers have been characterized to identify CSCs within a heterogeneous tumor, and here we summarize ongoing preclinical and clinical efforts to therapeutically target these cells and improve patient outcomes. Stem Cells Translational Medicine 2019;8:75-81.

Cell Cycle Dynamics in Glioma Cancer Stem Cells

Cancer stem cells, sometimes referred to as tumor initiating cells, play pivotal roles in tumor initiation, progression, metastasis, resistance to therapy, and relapse. Understanding how these populations of cells expand in response to a host of conditions is critical in determining effective cancer therapeutics. A defining feature of cancer stem cells is the ability to switch between modes of quiescence and symmetric/asymmetric division to protect and conserve the population, this feature is traditionally reserved for normal adult stem cell populations. Understanding how the core cell cycle machinery responds to external cues to drive symmetric/asymmetric division vs. quiescence will reveal fundamental information about how cancer stem cell populations survive and expand. This chapter will describe methods to study the cell cycle dynamics in brain cancer stem cell populations and how they compare to the other populations in a tumor.

shRNA-mediated PPARα knockdown in human glioma stem cells reduces in vitro proliferation and inhibits orthotopic xenograft tumour growth

The overall survival for patients with primary glioblastoma is very poor. Glioblastoma contains a subpopulation of glioma stem cells (GSC) that are responsible for tumour initiation, treatment resistance and recurrence. PPARα is a transcription factor involved in the control of lipid, carbohydrate and amino acid metabolism. We have recently shown that PPARα gene and protein expression is increased in glioblastoma and has independent clinical prognostic significance in multivariate analyses. In this work, we report that PPARα is overexpressed in GSC compared to foetal neural stem cells. To investigate the role of PPARα in GSC, we knocked down its expression using lentiviral transduction with short hairpin RNA (shRNA). Transduced GSC were tagged with luciferase and stereotactically xenografted into the striatum of NOD-SCID mice. Bioluminescent and magnetic resonance imaging showed that knockdown (KD) of PPARα reduced the tumourigenicity of GSC in vivo. PPARα-expressing control GSC xenografts formed invasive histological phenocopies of human glioblastoma, whereas PPARα KD GSC xenografts failed to establish viable intracranial tumours. PPARα KD GSC showed significantly reduced proliferative capacity and clonogenic potential in vitro with an increase in cellular senescence. In addition, PPARα KD resulted in significant downregulation of the stem cell factors c-Myc, nestin and SOX2. This was accompanied by downregulation of the PPARα-target genes and key regulators of fatty acid oxygenation ACOX1 and CPT1A, with no compensatory increase in glycolytic flux. These data establish the aberrant overexpression of PPARα in GSC and demonstrate that this expression functions as an important regulator of tumourigenesis, linking self-renewal and the malignant phenotype in this aggressive cancer stem cell subpopulation. We conclude that targeting GSC PPARα expression may be a therapeutically beneficial strategy with translational potential as an adjuvant treatment. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

The effect of transferrin-targeted, resveratrol-loaded liposomes on neurosphere cultures of glioblastoma: implications for targeting tumour-initiating cells

Glioblastomas (GBMs) are known to harbour subsets of cells known as tumour-initiating cells (TICs), which are responsible for the maintenance, invasiveness and recurrence of GBMs. Conventional chemotherapeutics act on rapidly dividing cells, sparing the TICs and result in tumour relapse. Resveratrol (RES) has shown chemopreventive effects in all the major stages of cancer including initiation, promotion and progression, but poor physicochemical and pharmacokinetic properties limit its use as a free drug. Hence we developed a liposomal formulation of RES (RES-L) to eradicate both the bulk tumour cells and TICs in GBMs. Since both these subpopulations of cells are known to over-express transferrin receptors, we developed transferrin-targeted RES-L (Tf-RES-L) to enhance tumour-specific delivery. We studied the effects of RES on neurospheres (NS) used as an in vitro model to study TICs derived from GBM cell lines. Free RES and RES formulations inhibited the anchorage-independent growth of GBM neurospheres. The NS-derived cells expressed TfRs and the Tf-targeted liposomes showed a significantly higher association with NS versus the non-targeted liposomes. Finally an increased activation of caspases 3/7 was seen when NS were treated with RES formulations. Together, these studies advocate for further investigations with RES-L and the use Tf to target the TIC populations.

In vitro neurosphere formation correlates with poor survival in glioma

Sphere formation is an indicator of tumor aggressiveness independent of the tumor grade; however, its relation to progression-free survival (PFS) is less known. This study was designed to assess the neurosphere forming ability among low grade glioma (LGG) and high-grade glioma (HGG), its stem cell marker expression, and correlation to PFS. Tumor samples of 140 patients, including (LGG; n = 67) and (HGG; n = 73) were analyzed. We used sphere forming assay, immunofluorescence, and immunohistochemistry to characterize the tumors. Our study shows that, irrespective of the pathological sub type, both LGG and HGG formed neurospheres in vitro under conventional sphere forming conditions. However, the number of neurospheres formed from tumor tissues were significantly higher in HGG compared to LGG (P < 0.0001). Different grades of glioma were further characterized for the expression of stem cell marker proteins and lineage markers. When neurospheres were analyzed, CD133 positive cells were identified in addition to CD15 and nestin positive cells in both LGG and HGG. When these neurospheres were subjected to differentiation, cells positive for GFAP and β-tubulin III were observed. Expression of stem cell markers and β-tubulin III were prominent in HGG compared to LGG, whereas GFAP expression was higher in LGG than in HGG. Kaplan-Meier survival analysis demonstrated that neurosphere forming ability was significantly associated with shorter PFS (P < 0.05) in both LGG and HGG. Our results supports earlier studies that neurosphere formation may serve as a definitive indicator of stem cell population within the tumor and thus a better predictor of PFS than the tumor grades alone. © 2018 IUBMB Life, 71(1):244-253, 2019.

Valproic Acid Inhibits Proliferation and Reduces Invasiveness in Glioma Stem Cells Through Wnt/β Catenin Signalling Activation

Glioblastoma is the most common malignant brain tumour in adults. The failure of current therapies can be ascribed to glioma stem cells (GSCs), which can rapidly repopulate the tumour following the initial treatment. The study of histone deacetylase inhibitors, such as valproic acid (VPA), is becoming an attractive field in cancer research. However, the exact mechanisms underlying its anti-cancer effect remain to be elucidated due to its pleiotropic effects on several cell-signalling pathways. Ingenuity Pathway Analysis (IPA) bioinformatics analysis was performed on genome-wide data regarding GSCs methylome to identify the signalling pathways mainly affected by methylation changes induced by VPA. Real time PCR and luciferase reporter assay were used to better investigate VPA effects on Wnt/β-catenin signalling pathway. VPA effect on GSC proliferation was evaluated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) and Trypan blue assays. Finally, VPA impact on GSC motility was demonstrated by Boyden chamber assay and further confirmed evaluating the expression levels or localisation, through western blot or immunofluorescence, of Twist1, Snail1, E-Cadherin and N-Cadherin. The bioinformatics analyses performed on GSCs methylome highlighted that Wnt/β-catenin signalling was affected by the methylation changes induced by VPA, which could influence its activation status. In particular, we pointed out a general activation of this pathway after VPA exposure, which was accompanied by an inhibitory potential on GSCs proliferation. Finally, we also proved VPA's ability to inhibit GSCs invasion through Snail1 and Twist1 downregulation and E-Cadherin relocalisation. VPA treatment may represent a new, interesting therapeutic approach to affect GSC proliferation and motility, but further investigations are certainly needed.

Challenges in the Treatment of Glioblastoma: Multisystem Mechanisms of Therapeutic Resistance

Glioblastoma is one of the most lethal human cancers, with poor survival despite surgery, radiation treatment, and chemotherapy. Advances in the treatment of this type of brain tumor are limited because of several resistance mechanisms. Such mechanisms involve limited drug entry into the central nervous system compartment by the blood-brain barrier and by actions of the normal brain to counteract tumor-targeting medications. In addition, the vast heterogeneity in glioblastoma contributes to significant therapeutic resistance by preventing adequate control of the entire tumor mass by a single drug and by facilitating escape mechanisms from targeted agents. The stem cell-like characteristics of glioblastoma promote resistance to chemotherapy, radiation, and immunotherapy through upregulation of efflux transporters, promotion of glioblastoma stem cell proliferation in neurogenic zones, and immune suppression, respectively. Metabolic cascades in glioblastoma prevent effective treatments through the optimization of glucose use, the use of alternative nutrient precursors for energy production, and the induction of hypoxia to enhance tumor growth. In the era of precision medicine, an assortment of molecular techniques is being developed to target an individual's unique tumor, with the hope that this personalized strategy will bypass therapeutic resistance. Although each resistance mechanism presents an array of challenges to effective treatment of glioblastoma, as the field recognizes and addresses these difficulties, future treatments may have more efficacy and promise for patients with glioblastoma.

Genetic Abnormalities, Clonal Evolution, and Cancer Stem Cells of Brain Tumors

Brain tumors are highly heterogeneous and have been classified by the World Health Organization in various histological and molecular subtypes. Gliomas have been classified as ranging from low-grade astrocytomas and oligodendrogliomas to high-grade astrocytomas or glioblastomas. These tumors are characterized by a peculiar pattern of genetic alterations. Pediatric high-grade gliomas are histologically indistinguishable from adult glioblastomas, but they are considered distinct from adult glioblastomas because they possess a different spectrum of driver mutations (genes encoding histones H3.3 and H3.1). Medulloblastomas, the most frequent pediatric brain tumors, are considered to be of embryonic derivation and are currently subdivided into distinct subgroups depending on histological features and genetic profiling. There is emerging evidence that brain tumors are maintained by a special neural or glial stem cell-like population that self-renews and gives rise to differentiated progeny. In many instances, the prognosis of the majority of brain tumors remains negative and there is hope that the new acquisition of information on the molecular and cellular bases of these tumors will be translated in the development of new, more active treatments.

Levetiracetam enhances the temozolomide effect on glioblastoma stem cell proliferation and apoptosis

Background

Glioblastoma multiforme (GBM) is a highly aggressive brain tumor in which cancer cells with stem cell-like features, called cancer stem cells (CSCs), were identified. Two CSC populations have been previously identified in GBM, one derived from the GBM area called enhanced lesion (GCSCs) and the other one from the brain area adjacent to the tumor margin (PCSCs) that greatly differ in their growth properties and tumor-initiating ability. To date the most effective chemotherapy to treat GBM is represented by alkylating agents such as temozolomide (TMZ), whose activity can be regulated by histone deacetylases (HDACs) inhibitors through the modulation of O6-methylguanine-DNA methyltransferase (MGMT) expression. Levetiracetam (LEV), a relatively new antiepileptic drug, modulates HDAC levels ultimately silencing MGMT, thus increasing TMZ effectiveness. However, an improvement in the therapeutic efficacy of TMZ is needed.

Methods

Cell proliferation was investigated by BrdU cell proliferation assay and by Western Blot analysis of PCNA expression. Apoptosis was evaluated by Western Blot and Immunofluorescence analysis of the cleaved Caspase-3 expression. MGMT and HDAC4 expression was analyzed by Western Blotting and Immunofluorescence. Statistical analysis was performed using the Student's t test and Mann-Whitney test.

Results

Here we evaluated the effect of TMZ on the proliferation rate of the IDH-wildtype GCSCs and PCSCs derived from six patients, in comparison with the effects of other drugs such as etoposide, irinotecan and carboplatin. Our results demonstrated that TMZ was less effective compared to the other agents; hence, we verified the possibility to increase the effect of TMZ by combining it with LEV. Here we show that LEV enhances the effect of TMZ on GCSCs proliferation (being less effective on PCSCs) by decreasing MGMT expression, promoting HDAC4 nuclear translocation and activating apoptotic pathway.

Conclusions

Although further studies are needed to determine the exact mechanism by which LEV makes GBM stem cells more  sensitive to TMZ, these results suggest that the clinical therapeutic efficacy of TMZ in GBM might be enhanced by the combined treatment with LEV.

Chemoresistance of cancer floating cells is independent of their ability to form 3D structures: Implications for anticancer drug screening

Three-dimensional (3D) culture systems such as floating spheroids (FSs) and floating tumorspheres (FTs) are widely used as tumor models of chemoresistance. FTs are considered to be enriched in cancer stem-like cells (CS-LCs). In this study, we used cancer cell lines (lung H460, prostate LnCAP, and breast MCF-7) able to form FSs under anchorage-independent conditions and compared with cell lines (prostate PC3 and breast MDA-MB-231) that cannot form FSs under similar conditions. Independent of their ability to form FTs all cell lines growing under anchorage-independent conditions become highly resistant to obatoclax, colchicine, and hydroxyurea. We used anti-E-cadherin antibody (that blocked the formation of FSs) and demonstrated that floating LnCAP cells showed similar chemoresistance regardless of the formation of spheroids. Our results demonstrate that the development of chemoresistance is not because of the formation of a complex 3D structure and/or enrichment of CS-LCs but is likely the result of cell detachment per se and their ability to survive under anchorage-independent conditions. We propose that FSs and FTs could be useful models to study chemoresistance of cancer cells associated with cell detachment (e.g., circulating tumor cells) but they may not be representative of other types of chemoresistance that arise in vivo in attached cells.

Identification and Quantification of Drug-Resistant Cells in Colorectal Tumor and Distal Margin

Cancer stem cells are cellular subpopulations in tumor, which are highly tumorigenic and drug resistant due to their adaptive molecular mechanism. In the recent years, these cells have attracted researchers' focus because of their unique properties which makes them biologically well evolved than other proliferating tumor cells. We have studied the presence of cancer stem cells in colorectal cancer (CRC) and its surgical margins. We report for the first time the presence of drug-resistant cells in distal resection margins in CRC and showed that a closer distal margin of less than 2 cm could have higher possibility of drug-resistant cells to spread.

Paired related homeobox 1 transactivates dopamine D2 receptor to maintain propagation and tumorigenicity of glioma-initiating cells

Glioblastoma multiforme (GBM) is a highly invasive brain tumor with limited therapeutic means and poor prognosis. Recent studies indicate that glioma-initiating cells/glioma stem cells (GICs/GSCs) may be responsible for tumor initiation, infiltration, and recurrence. GICs could aberrantly employ molecular machinery balancing self-renewal and differentiation of embryonic neural precursors. Here, we find that paired related homeobox 1 (PRRX1), a homeodomain transcription factor that was previously reported to control skeletal development, is expressed in cortical neural progenitors and is required for their self-renewal and proper differentiation. Further, PRRX1 is overrepresented in glioma samples and labels GICs. Glioma cells and GICs depleted with PRRX1 could not propagate in vitro or form tumors in the xenograft mouse model. The GIC self-renewal function regulated by PRRX1 is mediated by dopamine D2 receptor (DRD2). PRRX1 directly binds to the DRD2 promoter and transactivates its expression in GICs. Blockage of the DRD2 signaling hampers GIC self-renewal, whereas its overexpression restores the propagating and tumorigenic potential of PRRX1-depleted GICs. Finally, PRRX1 potentiates GICs via DRD2-mediated extracellular signal-related kinase (ERK) and AKT activation. Thus, our study suggests that therapeutic targeting the PRRX1-DRD2-ERK/AKT axis in GICs is a promising strategy for treating GBMs.

Glioblastoma Stem Cells and Their Microenvironment

Glioblastoma (GBM) is the most common primary malignant astrocytoma associated with a poor patient survival. Apart from arising de novo, GBMs also occur due to progression of slower growing grade III astrocytomas. GBM is characterized by extensive hypoxia, angiogenesis, proliferation and invasion. Standard treatment options such as surgical resection, radiation therapy and chemotherapy have increased median patient survival to 14.6 months in adults but recurrent disease arising from treatment resistant cancer cells often results in patient mortality. These treatment resistant cancer cells have been found to exhibit stem cell like properties. Strategies to identify or target these Glioblastoma Stem Cells (GSC) have proven to be unsuccessful so far. Studies on cancer stem cells (CSC) within GBM and other cancers have highlighted the importance of paracrine signaling networks within their microenvironment on the growth and maintenance of CSCs. The study of GSCs and their communication with various cell populations within their microenvironment is therefore not only important to understand the biology of GBMs but also to predict response to therapies and to identify novel targets which could stymy support to treatment resistant cancer cells and prevent disease recurrence. The purpose of this chapter is to introduce the concept of GSCs and to detail the latest findings indicating the role of various cellular subtypes within their microenvironment on their survival, proliferation and differentiation.

Saccharina japonica Extract Suppresses Stemness of Glioma Stem Cells by Degrading Epidermal Growth Factor Receptor/Epidermal Growth Factor Receptor Variant III

Cancer stem cells, a small subpopulation of cells with stem cell-like characteristics found within most solid tumors, are widely reported to be responsible for the malignancy of aggressive cancer cells, and targeting these cells presents a sound therapeutic strategy for reducing the risk of tumor relapse. In the present study, we examined the effects of an extract of Saccharina japonica (ESJ) on glioblastoma stem cells (GSCs). Saccharina japonica is a member of the Phaeophyceae (brown algae) family, which displays biological activities, including antitumor effects. ESJ inhibited the sphere-forming ability of GSCs in vitro as evidenced by neurosphere formation and limiting dilution assays. Treatment with ESJ partially induced apoptosis, reduced cell invasiveness, and sensitized GSCs to ionizing radiation. In addition, ESJ inhibited the maintenance of stemness in GSCs by suppressing the expression of epidermal growth factor receptor (EGFR)/EGFR variant III (EGFRvIII) and Notch intracellular domain. Intriguingly, the observed ESJ-induced suppression also appeared to induce the proteasomal degradation of EGFR/EGFRvIII. Our results indicate that ESJ could be considered a potent therapeutic adjuvant that targets GSCs.

Migration/Invasion of Malignant Gliomas and Implications for Therapeutic Treatment

Malignant tumors of the central nervous system (CNS) are among cancers with the poorest prognosis, indicated by their association with tumors of high-level morbidity and mortality. Gliomas, the most common primary CNS tumors that arise from neuroglial stem or progenitor cells, have estimated annual incidence of 6.6 per 100,000 individuals in the USA, and 3.5 per 100,000 individuals in Taiwan. Tumor invasion and metastasis are the major contributors to the deaths in cancer patients. Therapeutic goals including cancer stem cells (CSC), phenotypic shifts, EZH2/AXL/TGF-β axis activation, miRNAs and exosomes are relevant to GBM metastasis to develop novel targeted therapeutics for GBM and other brain cancers. Herein, we highlight tumor metastasis in our understanding of gliomas, and illustrate novel exosome therapeutic approaches in glioma, thereby paving the way towards innovative therapies in neuro-oncology.

Combination therapy with micellarized cyclopamine and temozolomide attenuate glioblastoma growth through Gli1 down-regulation

Glioblastoma multiforme (GBM) is the most common and deadly brain cancer, characterized by its aggressive proliferation to adjacent tissue and high recurrence rate. We studied the efficacy and related mechanisms of the combination of cyclopamine (Cyp, a Sonic-hedgehog pathway (Shh) inhibitor) and temozolomide (TMZ, the clinically most used chemotherapeutic agent) in anti-GBM treatment. The micellarized Cyp (MCyp) showed better performance than Cyp solution in inhibiting GBM cells proliferation (3.77-fold against U87 MG cells and 3.28-fold against DBTRG-05MG cells) and clonogenity (1.35-fold against U87 MG cells and 2.17-fold against DBTRG-05MG cells), and preferred behavior of inhibiting cell invasion, colony formation through attenuated Gli1 expression. In addition, combination of MCyp and TMZ exhibited synergistic cytotoxicity, correlating with their ability in inducing apoptosis and eliminating neurospheres formation, and the combination of TMZ was accompanied with the enhanced blockage of Shh pathway. The optimal ratio of MCyp combined to TMZ was 1:20. So we proposed to use TMZ to kill tumor parenchyma and MCyp as the cancer stem cells inhibitor to resist tumor recurrence. These findings demonstrated that combination of TMZ with micellarized Cyp is a promising strategy for exerting different functions of drugs for tumor treatment.

RhoGDIα suppresses self-renewal and tumorigenesis of glioma stem cells

Glioma stem cells (GSCs) are a subset of tumor cells that drive glioma initiation and progression. The molecular mechanisms underlying the maintenance of GSCs are still poorly understood. Here we investigated the role of Rho GDP dissociation inhibitor α (RhoGDIα) in GSCs. RhoGDIα was down-regulated in glioma stem cells. Over-expression of RhoGDIα suppressed the self-renewal and tumorigenesis of GSCs. Further data showed that RhoGDIα inhibited the transcription activity of stem cell marker Oct4. Moreover, inactivation of ROCK1, a downstream effector of RhoGDIα, also decreased the self-renewal and Oct4 transcription activity, and rescued the effects caused by RhoGDIα knockdown. Our results indicate that RhoGDIα is involved in the maintenance of GSCs.