A rapid assay for drug sensitivity of glioblastoma stem cells

CD57 defines a novel cancer stem cell that drive invasion of diffuse pediatric-type high grade gliomas

BACKGROUND

Diffuse invasion remains a primary cause of treatment failure in pediatric high-grade glioma (pHGG). Identifying cellular driver(s) of pHGG invasion is needed for anti-invasion therapies.

METHODS

Ten highly invasive patient-derived orthotopic xenograft (PDOX) models of pHGG were subjected to isolation of matching pairs of invasive (HGGINV) and tumor core (HGGTC) cells.

RESULTS

pHGGINV cells were intrinsically more invasive than their matching pHGGTC cells. CSC profiling revealed co-positivity of CD133 and CD57 and identified CD57+CD133- cells as the most abundant CSCs in the invasive front. In addition to discovering a new order of self-renewal capacities, i.e., CD57+CD133- > CD57+CD133+ > CD57-CD133+ > CD57-CD133- cells, we showed that CSC hierarchy was impacted by their spatial locations, and the highest self-renewal capacities were found in CD57+CD133- cells in the HGGINV front (HGGINV/CD57+CD133- cells) mediated by NANOG and SHH over-expression. Direct implantation of CD57+ (CD57+/CD133- and CD57+/CD133+) cells into mouse brains reconstituted diffusely invasion, while depleting CD57+ cells (i.e., CD57-CD133+) abrogated pHGG invasion.

CONCLUSION

We revealed significantly increased invasive capacities in HGGINV cells, confirmed CD57 as a novel glioma stem cell marker, identified CD57+CD133- and CD57+CD133+ cells as a new cellular driver of pHGG invasion and suggested a new dual-mode hierarchy of HGG stem cells.

Unlocking the Secrets of Cancer Stem Cells with γ-Secretase Inhibitors: A Novel Anticancer Strategy

The dysregulation of Notch signaling is associated with a wide variety of different human cancers. Notch signaling activation mostly relies on the activity of the γ-secretase enzyme that cleaves the Notch receptors and releases the active intracellular domain. It is well-documented that γ-secretase inhibitors (GSIs) block the Notch activity, mainly by inhibiting the oncogenic activity of this pathway. To date, several GSIs have been introduced clinically for the treatment of various diseases, such as Alzheimer's disease and various cancers, and their impacts on Notch inhibition have been found to be promising. Therefore, GSIs are of great interest for cancer therapy. The objective of this review is to provide a systematic review of in vitro and in vivo studies for investigating the effect of GSIs on various cancer stem cells (CSCs), mainly by modulation of the Notch signaling pathway. Various scholarly electronic databases were searched and relevant studies published in the English language were collected up to February 2020. Herein, we conclude that GSIs can be potential candidates for CSC-targeting therapy. The outcome of our study also indicates that GSIs in combination with anticancer drugs have a greater inhibitory effect on CSCs.

Culture conditions defining glioblastoma cells behavior: what is the impact for novel discoveries?

In cancer research, the use of established cell lines has gradually been replaced by primary cell cultures due to their better representation of in vivo cancer cell behaviors. However, a major challenge with primary culture involves the finding of growth conditions that minimize alterations in the biological state of the cells. To ensure reproducibility and translational potentials for research findings, culture conditions need to be chosen so that the cell population in culture best mimics tumor cells in vivo. Glioblastoma (GBM) is one of the most aggressive and heterogeneous tumor types and the GBM research field would certainly benefit from culture conditions that could maintain the original plethora of phenotype of the cells. Here, we review culture media and supplementation options for GBM cultures, the rationale behind their use, and how much those choices affect drug-screening outcomes. We provide an overview of 120 papers that use primary GBM cultures and discuss the current predominant conditions. We also show important primary research data indicating that “mis-cultured” glioma cells can acquire unnatural drug sensitivity, which would have devastating effects for clinical translations. Finally, we propose the concurrent test of four culture conditions to minimize the loss of cell coverage in culture.

β-elemene inhibits stemness, promotes differentiation and impairs chemoresistance to temozolomide in glioblastoma stem-like cells

Accumulating evidence indicates that glioblastoma stem-like cells (GSCs) are key factors in tumour development, recurrence and chemoresistance. The impairment of stemness and the enhancement of differentiation contributes to the weakening of radiation and chemotherapy resistance of GSCs. We previously found that β-elemene was an effective anti-glioblastoma agent and chemosensitizer. In this study, we examined the distribution of CD133(+) cells in human glioblastoma tissues by immunohistochemistry. Following treatment with β-elemene, the formation of GSC spheres was investigated by manual counting, the proliferation of GSCs was measured with a Cell Counting Kit-8 (CCK-8) assay, and the dispersion of GSC spheres was observed with an inverted microscope. GSC spheres were treated with β-elemene, and the expression levels of CD133, ATP-binding cassette subfamily G member 2 (ABCG2) and glial fibrillary acidic protein (GFAP) were examined by western blotting. After treatment with β-elemene, the volumes and weights of GSC xenografts were measured, and the expression of CD133, ABCG2 and GFAP was evaluated through immunohistochemistry analysis. After treatment with β-elemene and temozolomide (TMZ), GSC viability was examined by the CCK-8 assay, and the volumes and weights of xenografts were measured. We found that CD133(+) cells were assembled in some vascular walls and also sparsely distributed in other parts of glioblastoma tissues. β-elemene decreased the formation of GSC spheres, dispersed GSC spheres and inhibited the proliferation of GSCs in vitro and in vivo. In the GSC spheres and xenografts treated with β-elemene, the expression of CD133 and ABCG2 was significantly downregulated, and the expression of GFAP increased. Furthermore, the sensitivity of GSCs to TMZ was enhanced in vitro and in vivo. These results suggest that β-elemene impaired the stemness of GSC spheres, promoted their differentiation and sensitized GSCs to TMZ. β-elemene will hopefully become a valuable agent to enhance the effects of radiotherapy and chemotherapy.

Glioblastoma cancer stem cells: Biomarker and therapeutic advances

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in humans. It accounts for fifty-two percent of primary brain malignancies in the United States and twenty percent of all primary intracranial tumors. Despite the current standard therapies of maximal safe surgical resection followed by temozolomide and radiotherapy, the median patient survival is still less than 2 years due to inevitable tumor recurrence. Glioblastoma cancer stem cells (GSCs) are a subgroup of tumor cells that are radiation and chemotherapy resistant and likely contribute to rapid tumor recurrence. In order to gain a better understanding of the many GBM-associated mutations, analysis of the GBM cancer genome is on-going; however, innovative strategies to target GSCs and overcome tumor resistance are needed to improve patient survival. Cancer stem cell biology studies reveal basic understandings of GSC resistance patterns and therapeutic responses. Membrane proteomics using phage and yeast display libraries provides a method to identify novel antibodies and surface antigens to better recognize, isolate, and target GSCs. Altogether, basic GBM and GSC genetics and proteomics studies combined with strategies to discover GSC-targeting agents could lead to novel treatments that significantly improve patient survival and quality of life.

Ex vivo cultures of glioblastoma in three-dimensional hydrogel maintain the original tumor growth behavior and are suitable for preclinical drug and radiation sensitivity screening

Identification of new drugs and predicting drug response are major challenges in oncology, especially for brain tumors, because total surgical resection is difficult and radiation therapy or chemotherapy is often ineffective. With the aim of developing a culture system close to in vivo conditions for testing new drugs, we characterized an ex vivo three-dimensional culture system based on a hyaluronic acid-rich hydrogel and compared it with classical two-dimensional culture conditions. U87-MG glioblastoma cells and seven primary cell cultures of human glioblastomas were subjected to radiation therapy and chemotherapy drugs. It appears that 3D hydrogel preserves the original cancer growth behavior and enables assessment of the sensitivity of malignant gliomas to radiation and drugs with regard to inter-tumoral heterogeneity of therapeutic response. It could be used for preclinical assessment of new therapies.

Three paths to better tyrosine kinase inhibition behind the blood-brain barrier in treating chronic myelogenous leukemia and glioblastoma with imatinib

Chronic myelogenous leukemia (CML) can be controlled for years with the tyrosine kinase inhibitor imatinib but because imatinib poorly penetrates the blood-brain barrier (BBB), on occasion, the CML clone will thrive and evolve to an accelerated phase in the resulting imatinib sanctuary within the central nervous system. In this, CML resembles glioblastoma in that imatinib, which otherwise may be effective, cannot get to the tumor. Although a common street drug of abuse, methamphetamine is Food and Drug Administration-approved and marketed as a pharmaceutical drug to treat attention-deficit disorders. It has shown the ability to open the BBB in rodents. We have some clinical hints that it may do so in humans as well. This short note presents three new points potentially leading to better tyrosine kinase inhibition behind the BBB: 1) Pharmaceutical methamphetamine may have a useful role in treating both CML and glioblastoma by allowing higher imatinib concentrations behind the BBB. 2) The old antidepressant and monoamine oxidase inhibitor selegiline, used to treat Parkinson disease, is catabolized to methamphetamine. Selegiline, as a nonscheduled drug,may therefore be an easier way to open the BBB, allowing more effective chemotherapy with tyrosine kinases. 3) Dasatinib is a tyrosine kinase inhibitor with a spectrum of inhibition only partially overlapping that of imatinib and a mechanism of tyrosine kinase inhibition that is different from that of imatinib. The two should be additive. In addition, dasatinib crosses the BBB poorly, and it can therefore be expected to benefit from methamphetamine-assisted entry.

The Role of Cancer Stem Cells (CD133+) in Malignant Gliomas

Malignant gliomas, particularly glioblastoma multiforme (GBM) tumors, are very difficult to treat by conventional approaches. Although most of the tumor mass can be removed by surgical resection, radiotherapy, and chemotherapy, it eventually recurs. There is growing evidence that cancer stem cells (CSCs) play an important role in tumor recurrence. These stem cells are radioresistant and chemoresistant. The most commonly used tumor marker for CSCs is CD133. The amount of CSC component is closely correlated with tumor malignancy grading. Isolating, identifying, and treating CSCs as the target is crucial for treating malignant gliomas. CSC-associated vascular endothelial growth factor (VEGF) promotes tumor angiogenesis, tumor hemorrhage, and tumor infiltration. Micro-RNA (miRNA) plays a role in CSC gene expression, which may regulate oncogenesis or suppression to influence tumor development or progression. The antigenesis of CSCs and normal stem cells may be different. The CSCs may escape the T-cell immune response. Identifying a new specific antigen from CSCs for vaccine treatment is a key point for immunotherapy. On the other hand, augmented treatment with radiosensitizer or chemosensitizer may lead to reduction of CSCs and lead to CSCs being vulnerable to radiotherapy and chemotherapy. The control of signaling pathway and cell differentiation to CSC growth is another new hope for treatment of malignant gliomas. Although the many physiological behavioral differences between CSCs and normal stem cells are unclear, the more we know about these differences the better we will be able to treat CSCs effectively.

Role of Notch and its oncogenic signaling crosstalk in breast cancer

The Notch signaling plays a key role in cell differentiation, survival, and proliferation through diverse mechanisms. Notch signaling is also involved in vasculogenesis and angiogenesis. Moreover, Notch expression is regulated by hypoxia and inflammatory cytokines (IL-1, IL-6 and leptin). Entangled crosstalk between Notch and other developmental signaling (Hedgehog and Wnt), and signaling triggered by growth factors, estrogens and oncogenic kinases, could impact on Notch targeted genes. Thus, alterations of the Notch signaling can lead to a variety of disorders, including human malignancies. Notch signaling is activated by ligand binding, followed by ADAM/tumor necrosis factor-α-converting enzyme (TACE) metalloprotease and γ-secretase cleavages that produce the Notch intracellular domain (NICD). Translocation of NICD into the nucleus induces the transcriptional activation of Notch target genes. The relationships between Notch deregulated signaling, cancer stem cells and the carcinogenesis process reinforced by Notch crosstalk with many oncogenic signaling pathways suggest that Notch signaling may be a critical drug target for breast and other cancers. Since current status of knowledge in this field changes quickly, our insight should be continuously revised. In this review, we will focus on recent advancements in identification of aberrant Notch signaling in breast cancer and the possible underlying mechanisms, including potential role of Notch in breast cancer stem cells, tumor angiogenesis, as well as its crosstalk with other oncogenic signaling pathways in breast cancer. We will also discuss the prognostic value of Notch proteins and therapeutic potential of targeting Notch signaling for cancer treatment.

Dual blocking of mTor and PI3K elicits a prodifferentiation effect on glioblastoma stem-like cells

Glioblastoma, the most intractable cerebral tumor, is highly lethal. Recent studies suggest that cancer stem-like cells (CSLCs) have the capacity to repopulate tumors and mediate radio- and chemoresistance, implying that future therapies may need to turn from the elimination of rapidly dividing, but differentiated, tumor cells to specifically targeting the minority of tumor cells that repopulate the tumor. However, the mechanism by which glioblastoma CSLCs maintain their immature stem-like state or, alternatively, become committed to differentiation is poorly understood. Here, we show that the inactivation of mammalian target of rapamycin (mTor) by the mTor inhibitor rapamycin or knockdown of mTor reduced sphere formation and the expression of neural stem cell (NSC)/progenitor markers in CSLCs of the A172 glioblastoma cell line. Interestingly, combination treatment with rapamycin and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, not only reduced the expression of NSC/progenitor markers more efficiently than single-agent treatment, but also increased the expression of βIII-tubulin, a neuronal differentiation marker. Consistent with these results, a dual PI3K/mTor inhibitor, NVP-BEZ235, elicited a prodifferentiation effect on A172 CSLCs. Moreover, A172 CSLCs, which were induced to undergo differentiation by pretreatment with NVP-BEZ235, exhibited a significant decrease in their tumorigenicity when transplanted either subcutaneously or intracranially. Importantly, similar results were obtained when patient-derived glioblastoma CSLCs were used. These findings suggest that the PI3K/mTor signaling pathway is critical for the maintenance of glioblastoma CSLC properties, and targeting both mTor and PI3K of CSLCs may be an effective therapeutic strategy in glioblastoma.

Clinically relevant doses of chemotherapy agents reversibly block formation of glioblastoma neurospheres

Glioblastoma patients have a poor prognosis, even after surgery, radiotherapy, and chemotherapy with temozolomide or 1,3-bis(2-chloroethy)-1-nitrosourea. We developed an in vitro recovery model using neurosphere cultures to analyze the efficacy of chemotherapy treatments, and tested whether glioblastoma neurosphere-initiating cells are resistant. Concentrations of chemotherapy drugs that inhibit neurosphere formation are similar to clinically relevant doses. Some lines underwent a transient cell cycle arrest and a robust recovery of neurosphere formation. These results indicate that glioblastoma neurospheres can regrow after treatment with chemotherapy drugs. This neurosphere recovery assay will facilitate studies of chemo-resistant subpopulations and methods to enhance glioblastoma therapy.

The cancer stem cell paradigm: a new understanding of tumor development and treatment

IMPORTANCE OF THE FIELD

Cancer is the second leading cause of death in the United States, and therefore remains a central focus of modern medical research. Accumulating evidence supports a 'cancer stem cell' (CSC) model - where cancer growth and/or recurrence is driven by a small subset of tumor cells that exhibit properties similar to stem cells. This model may provide a conceptual framework for developing more effective cancer therapies that target cells propelling cancer growth.

AREAS COVERED IN THIS REVIEW

We review evidence supporting the CSC model and associated implications for understanding cancer biology and developing novel therapeutic strategies. Current controversies and unanswered questions of the CSC model are also discussed.

WHAT THE READER WILL GAIN

This review aims to describe how the CSC model is key to developing novel treatments and discusses associated shortcomings and unanswered questions.

TAKE HOME MESSAGE

A fresh look at cancer biology and treatment is needed for many incurable cancers to improve clinical prognosis for patients. The CSC model posits a hierarchy in cancer where only a subset of cells drive malignancy, and if features of this model are correct, has implications for development of novel and hopefully more successful approaches to cancer therapy.

Potential Role of Thymosin-alpha1 Adjuvant Therapy for Glioblastoma

Glioblastomas are high-grade, malignant CNS neoplasms that are nearly always fatal within 12 months of diagnosis. Immunotherapy using proinflammatory cytokines such as IL-2 or IL-12 may prolong survival with glioblastoma. Thymosin-α1 (Talpha1) is a thymic hormone and immunemodulator that increase IL-2 production and T-cell proliferation. We examined potential therapeutic effects of Talpha1 in experimental in vivo glioblastoma, and characterized Talpha1's anti-tumor effects in vitro. Rar 9L cells (10⁴) were implanted into the right frontal lobe of adult Long Evans rats that were subsequently treated with vehicle, BCNU, Talpha1, or Talpha1+BCNU from postoperative day 6. Talpha1+BCNU significantly lowered tumor burdens, and increased cure rates. In vitro experiments demonstrated that Talpha1 had no direct effect on viability or mitochondrial function, and instead, it increased expression of pro-apoptosis genes, including FasL, FasR and TNFα-R1 (65.89%, 44.08%, and 22.18%, resp.), and increased 9L cell sensitivity to oxidative stress. Moreover, Talpha1 enhanced 9L cell sensitivity to both Granzyme B- and BCNU-mediated killing. The findings suggest that Talpha1 enhances BCNUmediated eradication of glioblastoma in vivo, and that Talpha1 mediates its effects by activating pro-apoptosis mechanisms, rendering neoplastic cells more sensitive to oxidative stress and immune-mediated killing by Granzyme B and chemotherapeutic agents.

z-Leucinyl-leucinyl-norleucinal induces apoptosis of human glioblastoma tumor-initiating cells by proteasome inhibition and mitotic arrest response

Gamma-secretase inhibitors have been proposed as drugs able to kill cancer cells by targeting the NOTCH pathway. Here, we investigated two of such inhibitors, the Benzyloxicarbonyl-Leu-Leu-Nle-CHO (LLNle) and the N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), to assess whether they were effective in killing human glioblastoma tumor-initiating cells (GBM TIC) in vitro. We found that only LLNle was able at the micromolar range to induce the death of GBM TICs by apoptosis. To determine the cellular processes that were activated in GBM TICs by treatment with LLNle, we analyzed the amount of the NOTCH intracellular domain and the gene expression profiles following treatment with LLNle, DAPT, and DMSO (vehicle). We found that LLNIe, beside inhibiting the generation of the NOTCH intracellular domain, also induces proteasome inhibition, proteolytic stress, and mitotic arrest in these cells by repressing genes required for DNA synthesis and mitotic progression and by activating genes acting as mitotic inhibitors. DNA content flow cytometry clearly showed that cells treated with LLNle undergo arrest in the G(2)-M phases of the cell cycle. We also found that DAPT and L-685,458, another selective Notch inhibitor, were unable to kill GBM TICs, whereas lactacystin, a pure proteasome inhibitor, was effective although at a much less extent than LLNle. These data show that LLNle kills GBM TIC cells by inhibiting the proteasome activity. We suggest that LLNle, being able to target two relevant pathways for GBM TIC survival, may have a potential therapeutic value that deserves further investigation in animal models.

A screening platform for glioma growth and invasion using bioluminescence imaging

Object

The study of tumor cell growth and invasion in cancer biology is often limited by the inability to visualize tumor cell behavior in real time in animal models. The authors provide evidence that glioma cells are heterogeneous, with a subset responsible for increased invasiveness. The use of bioluminescence (BL) imaging to investigate dynamic aspects of glioma progression are discussed.

Methods

Glioblastoma multiforme–initiating cells were generated under conditions typically used to sustain neural stem cells. The invasiveness potential was determined using a Matrigel chamber. The presence of an “invasiveness gene signature” that correlated with patient survival outcome was ascertained through microarray gene expression analysis. To measure invasiveness, the authors devised a method focussed on BL imaging and tested it in vitro and in vivo using a zebrafish xenograft model. Bioluminescence imaging signals were verified using known inhibitors of glioma growth: AEE788, N-[(3,5-Difluorophenyl)acetyl]-L-alanyl-2-phenylglycine-1,1-dimethylethyl ester, and compound E.

Results

The authors' data support the idea that glioblastoma multiforme–initiating cells are heterogeneous and possess an invasive subset; BL imaging was used as a readout method to assess this invasive subset. The in vitro data obtained using a known glioma growth inhibitor, AEE788, showed that BL imaging could detect cellular movement and invasion even before overall cell death was detectable on conventional viability assays. Further work using a zebrafish tumor xenograft model supported the efficacy of BL imaging in monitoring changes in tumor load.

Conclusions

The authors used optically transparent zebrafish and high-resolution confocal imaging to track tumor growth in vivo and demonstrate the efficacy of this model for screening antitumor and antiangiogenic compounds. The integration of zebrafish transgenic technology into human cancer biological studies may aid in the development of cancer models targeting specific organs, tissues, or cell types within tumors. Zebrafish could also provide a cost-effective means for the rapid development of therapeutic agents directed at blocking tumor growth and invasion.

Cryopreservation of neurospheres derived from human glioblastoma multiforme

Cancer stem cells have been shown to initiate and sustain tumor growth. In many instances, clinical material is limited, compounded by a lack of methods to preserve such cells at convenient time points. Although brain tumor-initiating cells grown in a spheroid manner have been shown to maintain their integrity through serial transplantation in immune-compromised animals, practically, it is not always possible to have access to animals of suitable ages to continuously maintain these cells. We therefore explored vitrification as a cryopreservation technique for brain tumor-initiating cells. Tumor neurospheres were derived from five patients with glioblastoma multiforme (GBM). Cryopreservation in 90% serum and 10% dimethyl sulfoxide yielded greatest viability and could be explored in future studies. Vitrification yielded cells that maintained self-renewal and multipotentiality properties. Karyotypic analyses confirmed the presence of GBM hallmarks. Upon implantation into NOD/SCID mice, our vitrified cells reformed glioma masses that could be serially transplanted. Transcriptome analysis showed that the vitrified and nonvitrified samples in either the stem-like or differentiated states clustered together, providing evidence that vitrification does not change the genotype of frozen cells. Upon induction of differentiation, the transcriptomes of vitrified cells associated with the original primary tumors, indicating that tumor stem-like cells are a genetically distinct population from the differentiated mass, underscoring the importance of working with the relevant tumor-initiating population. Our results demonstrate that vitrification of brain tumor-initiating cells preserves the biological phenotype and genetic profiles of the cells. This should facilitate the establishment of a repository of tumor-initiating cells for subsequent experimental designs.

A MT1-MMP/NF-kappaB signaling axis as a checkpoint controller of COX-2 expression in CD133+ U87 glioblastoma cells

Background

The CD133(+) stem cell population in recurrent gliomas is associated with clinical features such as therapy resistance, blood-brain barrier disruption and, hence, tumor infiltration. Screening of a large panel of glioma samples increasing histological grade demonstrated frequencies of CD133(+) cells which correlated with high expression of cyclooxygenase (COX)-2 and of membrane type-1 matrix metalloproteinase (MT1-MMP).

Methods

We used qRT-PCR and immunoblotting to examine the molecular interplay between MT1-MMP and COX-2 gene and protein expression in parental, CD133(+), and neurospheres U87 glioma cell cultures.

Results

We found that CD133, COX-2 and MT1-MMP expression were enhanced when glioma cells were cultured in neurosphere conditions. A CD133(+)-enriched U87 glioma cell population, isolated from parental U87 cells with magnetic cell sorting technology, also grew as neurospheres and showed enhanced COX-2 expression. MT1-MMP gene silencing antagonized COX-2 expression in neurospheres, while overexpression of recombinant MT1-MMP directly triggered COX-2 expression in U87 cells independent from MT1-MMP's catalytic function. COX-2 induction by MT1-MMP was also validated in wild-type and in NF-κB p65^-/- mutant mouse embryonic fibroblasts, but was abrogated in NF-κB1 (p50^-/-) mutant cells.

Conclusion

We provide evidence for enhanced COX-2 expression in CD133(+) glioma cells, and direct cell-based evidence of NF-κB-mediated COX-2 regulation by MT1-MMP. The biological significance of such checkpoint control may account for COX-2-dependent mechanisms of inflammatory balance responsible of therapy resistance phenotype of cancer stem cells.

MIR-451 and Imatinib mesylate inhibit tumor growth of Glioblastoma stem cells

We examined the microRNA profiles of Glioblastoma stem (CD133+) and non-stem (CD133-) cell populations and found up-regulation of several miRs in the CD133- cells, including miR-451, miR-486, and miR-425, some of which may be involved in regulation of brain differentiation. Transfection of GBM cells with the above miRs inhibited neurosphere formation and transfection with the mature miR-451 dispersed neurospheres, and inhibited GBM cell growth. Furthermore, transfection of miR-451 combined with Imatinib mesylate treatment had a cooperative effect in dispersal of GBM neurospheres. In addition, we identified a target site for SMAD in the promoter region of miR-451 and showed that SMAD3 and 4 activate such a promoter-luciferase construct. Transfection of SMAD in GBM cells inhibited their growth, suggesting that SMAD may drive GBM stem cells to differentiate to CD133- cells through up-regulation of miR-451 and reduces their tumorigenicity. Identification of additional miRs and target genes that regulate GBM stem cells may provide new potential drugs for therapy.

Tumor environment dictates medulloblastoma cancer stem cell expression and invasive phenotype

The neural precursor surface marker CD133 is thought to be enriched in brain cancer stem cells and in radioresistant DAOY medulloblastoma-derived tumor cells. Given that membrane type-1 matrix metalloproteinase (MT1-MMP) expression is a hallmark of highly invasive, radioresistant, and hypoxic brain tumor cells, we sought to determine whether MT1-MMP and other MMPs could regulate the invasive phenotype of CD133(+) DAOY cells. We found that when DAOY medulloblastoma or U87 glioblastoma cells were implanted in nude mice, only those cells specifically implanted in the brain environment generated CD133(+) brain tumors. Vascular endothelial growth factor and basic fibroblast growth factor gene expression increases in correlation with CD133 expression in those tumors. When DAOY cultures were induced to generate in vitro neurosphere-like cells, gene expression of CD133, MT1-MMP, MMP-9, and MDR-1 was induced and correlated with an increase in neurosphere invasiveness. Specific small interfering RNA gene silencing of either MT1-MMP or MMP-9 reduced the capacity of the DAOY monolayers to generate neurospheres and concomitantly abrogated their invasive capacity. On the other hand, overexpression of MT1-MMP in DAOY triggered neurosphere-like formation which was further amplified when cells were cultured in neurosphere medium. Collectively, we show that both MT1-MMP and MMP-9 contribute to the invasive phenotype during CD133(+) neurosphere-like formation in medulloblastoma cells. Increases in MMP-9 may contribute to the opening of the blood-brain barrier, whereas increased MT1-MMP would promote brain tumor infiltration. Our study suggests that MMP-9 or MT1-MMP targeting may reduce the formation of brain tumor stem cells.

CD133 identifies perivascular niches in grade II-IV astrocytomas

The aim of the present study was to investigate the localization and distribution of the putative brain tumour stem cell marker CD133 in formalin fixed paraffin embedded astrocytomas. A retrospective analysis of 114 grade II, III and IV astrocytomas was undertaken. The immunohistochemical expression of CD133 in paraffin sections was analysed using morphometry. In all grades, CD133 was expressed on tumour and endothelial cells. Tumour cells were found in perivascular niches, as dispersed single cells and in pseudopalisade formations around necrosis. There was no correlation between the mean volume fraction of CD133(+) niches and all CD133(+) tumour cells and tumour grade. However, the volume fraction of CD133(+) blood vessels increased significantly from 0.4% in diffuse astrocytomas to 2.2% in glioblastomas. Neither of them was related to patient survival. Double immunofluorescence stainings showed that the CD133(+) niches both contained CD133(+) cells with and without co-expression of the intermediate filament protein marker nestin, and only few CD133(+)/MIB-1(+) proliferating cells were found. In conclusion, a CD133(+) perivascular stem cell-like entity exists in astrocytomas. CD133(+) tumour vessels may play an important role in a brain tumour stem cell context, while CD133 alone does not appear to be a specific tumour stem cell marker related to patient survival.

New strategy for the analysis of phenotypic marker antigens in brain tumor-derived neurospheres in mice and humans

OBJECT

Brain tumor stem cells (TSCs) hypothetically drive the malignant phenotype of glioblastoma multiforme (GBM), and evidence suggests that a better understanding of these TSCs will have profound implications for treating gliomas. When grown in vitro, putative TSCs grow as a solid sphere, making their subsequent characterization, particularly the cells within the center of the sphere, difficult. Therefore, the purpose of this study was to develop a new method to better understand the proteomic profile of the entire population of cells within a sphere.

METHODS

Tumor specimens from patients with confirmed GBM and glioma models in mice were mechanically and enzymatically dissociated and grown in traditional stem cell medium to generate neurospheres. The neurospheres were then embedded in freezing medium, cryosectioned, and analyzed with immunofluorescence.

RESULTS

By sectioning neurospheres as thinly as 5 mum, the authors overcame many of the problems associated with immunolabeling whole neurospheres, such as antibody penetration into the core of the sphere and intense background fluorescence that obscures the specificity of immunoreactivity. Moreover, the small quantity of material required and the speed with which this cryosectioning and immunolabeling technique can be performed make it an attractive tool for the rapid assessment of TSC character.

CONCLUSIONS

This study is the first to show that cryosectioning of neurospheres derived from glioma models in mice and GBM in humans is a feasible method of better defining the stem cell profile of a glioma.

Partial biological characterization of cancer stem-like cell line (WJ(2)) of human glioblastoma multiforme

To provide suitable models for human GBM cancer stem cells in vitro and in vivo, and investigate their biological characteristics, a new human GBM cancer stem-like cell line, WJ2, was established in this experiment through serial passages from adherent monolayer culture to nonadherent tumor sphere culture in turns; Its partial biological characteristics were studied through cell proliferation and tumor sphere assay; cell cycle distribution, side population, and CD133 phenotype were analyzed with FCM. The expressions of CD133, Nestin, and GFAP of cancer stem-like cells and xenograft tumor cells were detected with RT-PCR and immunohistochemistry. Biological characterization, side population, CD133 phenotype and CD133 Nestin, BCRP-1, Wnt-1 gene expression revealed the stemness of this cancer stem-like cell line. Tumorigenicity heterotransplanted in nude mice; histopathological characteristics of xenograft tumor, and expressions of CD133, Nestin, and GFAP of xenograft tumor cells indicated that xenograft tumors recapitulated the phenotype and biological characterization of human primary GBM. All findings of this experimental study suggested that WJ(2) cancer stem-like cell line could accurately mimic human GBM cancer stem cell in vitro and in vivo; it would be useful in the cellular and molecular studies as well as in testing novel therapies of CSC-based anti-cancer therapies for human GBM.