Virotherapy against malignant glioma stem cells

The Role of Mesenchymal Reprogramming in Malignant Clonal Evolution and Intra-Tumoral Heterogeneity in Glioblastoma

Glioblastoma (GBM) is the most common yet uniformly fatal adult brain cancer. Intra-tumoral molecular and cellular heterogeneities are major contributory factors to therapeutic refractoriness and futility in GBM. Molecular heterogeneity is represented through molecular subtype clusters whereby the proneural (PN) subtype is associated with significantly increased long-term survival compared to the highly resistant mesenchymal (MES) subtype. Furthermore, it is universally recognized that a small subset of GBM cells known as GBM stem cells (GSCs) serve as reservoirs for tumor recurrence and progression. The clonal evolution of GSC molecular subtypes in response to therapy drives intra-tumoral heterogeneity and remains a critical determinant of GBM outcomes. In particular, the intra-tumoral MES reprogramming of GSCs using current GBM therapies has emerged as a leading hypothesis for therapeutic refractoriness. Preventing the intra-tumoral divergent evolution of GBM toward the MES subtype via new treatments would dramatically improve long-term survival for GBM patients and have a significant impact on GBM outcomes. In this review, we examine the challenges of the role of MES reprogramming in the malignant clonal evolution of glioblastoma and provide future perspectives for addressing the unmet therapeutic need to overcome resistance in GBM.

Eltanexor Effectively Reduces Viability of Glioblastoma and Glioblastoma Stem-Like Cells at Nano-Molar Concentrations and Sensitizes to Radiotherapy and Temozolomide

Current standard adjuvant therapy of glioblastoma multiforme (GBM) using temozolomide (TMZ) frequently fails due to therapy resistance. Thus, novel therapeutic approaches are highly demanded. We tested the therapeutic efficacy of the second-generation XPO1 inhibitor Eltanexor using assays for cell viability and apoptosis in GBM cell lines and GBM stem-like cells. For most GBM-derived cells, IC₅₀ concentrations for Eltanexor were below 100 nM. In correlation with reduced cell viability, apoptosis rates were significantly increased. GBM stem-like cells presented a combinatorial effect of Eltanexor with TMZ on cell viability. Furthermore, pretreatment of GBM cell lines with Eltanexor significantly enhanced radiosensitivity in vitro. To explore the mechanism of apoptosis induction by Eltanexor, TP53-dependent genes were analyzed at the mRNA and protein level. Eltanexor caused induction of TP53-related genes, TP53i3, PUMA, CDKN1A, and PML on both mRNA and protein level. Immunofluorescence of GBM cell lines treated with Eltanexor revealed a strong accumulation of CDKN1A, and, to a lesser extent, of p53 and Tp53i3 in cell nuclei as a plausible mechanism for Eltanexor-induced apoptosis. From these data, we conclude that monotherapy with Eltanexor effectively induces apoptosis in GBM cells and can be combined with current adjuvant therapies to provide a more effective therapy of GBM.

Inhibition of Carbonic Anhydrase 2 Overcomes Temozolomide Resistance in Glioblastoma Cells

About 95% of Glioblastoma (GBM) patients experience tumor relapse as a consequence of resistance to the first-line standard chemotherapy using temozolomide (TMZ). Recent studies reported consistently elevated expression levels of carbonic anhydrase CA2 in recurrent glioblastoma and temozolomide-resistant glioblastoma stem-like cells (GSCs). Here we show that CA2 is preferentially expressed in GSCs and upregulated by TMZ treatment. When expressed in GBM cell lines, CA2 exerts significant metabolic changes reflected by enhanced oxygen consumption and increased extracellular acidification causing higher rates of cell invasion. Notably, GBM cells expressing CA2 respond to combined treatment with TMZ and brinzolamide (BRZ), a non-toxic and potent CA2 inhibitor. Interestingly, brinzolamide was more effective than the pan-CA inhibitor Acetazolamide (ACZ) to sensitize naïve GSCs and TMZ-resistant GSCs to TMZ induced cell death. Mechanistically, we demonstrated that the combined treatment of GBM stem cells with TMZ and BRZ caused autophagy of GBM cell lines and GSCs, reflected by enhanced LC3 cleavage (LC3-II) and p62 reduction. Our findings illustrate the potential of CA2 as a chemo-sensitizing drug target in recurrent GBM and propose a combined treatment of TMZ with CA2 inhibitor to tackle GBM chemoresistance and recurrence.

LncRNA MIR155HG Promotes Temozolomide Resistance by Activating the Wnt/β-Catenin Pathway Via Binding to PTBP1 in Glioma

Temozolomide (TMZ) is widely used for glioma therapy in the clinic. Currently, the development of TMZ resistance has largely led to poor prognosis. However, very little is understood about the role of MIR155HG, as a long noncoding RNA, in TMZ resistance. In our study, MIR155HG level was markedly higher in glioma patients than in normal controls and that poor survival was positively correlated with MIR155HG expression. It was apparent that TMZ sensitivity was promoted by downregulation of MIR155HG, and this could be reversed by MIR155HG overexpression in vivo and in vitro. Furthermore, polypyrimidine tract binding protein 1 (PTBP1) was proven to bind with MIR155HG and to regulate MIR155HG-related TMZ resistance. Mechanistic investigation showed that the expression levels of both MIR155HG and PTBP1 influenced the expression of relevant proteins in the Wnt/β-catenin pathway. Collectively, the study demonstrated that the knockdown of MIR155HG increased glioma sensitivity to TMZ by inhibiting Wnt/β-catenin pathway activation via potently downregulating PTBP1.

Comparative Transcriptomic Analysis of Temozolomide Resistant Primary GBM Stem-Like Cells and Recurrent GBM Identifies Up-Regulation of the Carbonic Anhydrase CA2 Gene as Resistance Factor

About 95% of patients with Glioblastoma (GBM) show tumor relapse, leaving them with limited therapeutic options as recurrent tumors are most often resistant to the first line chemotherapy standard Temozolomide (TMZ). To identify molecular pathways involved in TMZ resistance, primary GBM Stem-like Cells (GSCs) were isolated, characterized, and selected for TMZ resistance in vitro. Subsequently, RNA sequencing analysis was performed and revealed a total of 49 differentially expressed genes (|log2-fold change| > 0.5 and adjusted p-value < 0.1) in TMZ resistant stem-like cells compared to their matched DMSO control cells. Among up-regulated genes, we identified carbonic anhydrase 2 (CA2) as a candidate gene correlated with glioma malignancy and patient survival. Notably, we describe consistent up-regulation of CA2 not only in TMZ resistant GSCs on mRNA and protein level, but also in patient-matched clinical samples of first manifest and recurrent tumors. Co-treatment with the carbonic anhydrase inhibitor Acetazolamid (ACZ) sensitized cells to TMZ induced cell death. Cumulatively, our findings illustrate the potential of CA2 as a chemosensitizing target in recurrent GBM and provide a rationale for a therapy associated inhibition of CA2 to overcome TMZ induced chemoresistance.

Glioblastoma cancer stem cell biology: Potential theranostic targets

Glioblastoma multiforme (GBM) is among the most incurable cancers. GBMs survival rate has not markedly improved, despite new radical surgery protocols, the introduction of new anticancer drugs, new treatment protocols, and advances in radiation techniques. The low efficacy of therapy, and short interval between remission and recurrence, could be attributed to the resistance of a small fraction of tumorigenic cells to treatment. The existence and importance of cancer stem cells (CSCs) is perceived by some as controversial. Experimental evidences suggest that the presence of therapy-resistant glioblastoma stem cells (GSCs) could explain tumor recurrence and metastasis. Some scientists, including most of the authors of this review, believe that GSCs are the driving force behind GBM relapses, whereas others however, question the existence of GSCs. Evidence has accumulated indicating that non-tumorigenic cancer cells with high heterogeneity, could undergo reprogramming and become GSCs. Hence, targeting GSCs as the "root cells" initiating malignancy has been proposed to eradicate this devastating disease. Most standard treatments fail to completely eradicate GSCs, which can then cause the recurrence of the disease. To effectively target GSCs, a comprehensive understanding of the biology of GSCs as well as the mechanisms by which these cells survive during treatment and develop into new tumor, is urgently needed. Herein, we provide an overview of the molecular features of GSCs, and elaborate how to facilitate their detection and efficient targeting for therapeutic interventions. We also discuss GBM classifications based on the molecular stem cell subtypes with a focus on potential therapeutic approaches.

Astrocytes, the rising stars of the glioblastoma microenvironment

Glioblastoma (GBM) is an aggressive primary tumor, causing thousands of deaths worldwide every year. The mean survival of patients with GBM remains below 20 months despite current available therapies. GBM cells' interactions with their stromal counterparts are crucial for tumor development. Astrocytes are glial cells that comprise ~50% of all brain cells and are therefore likely to establish direct contact with GBM cells. As other tumor cell types can hijack fibroblasts or immune cells to facilitate tumor growth, GBM cells can actually activate astrocytes, namely, the tumor associated astrocytes (TAAs), to promote GBM invasion in the healthy tissue. TAAs have thus been shown to be involved in GBM cells growth and limited response to radiation or chemotherapy (i.e., Temozolomide). Nevertheless, even though the interest in the cancer research community is increasing, the role of TAAs during GBM development is still overlooked. Yet, obtaining an in-depth understanding of the mechanisms by which TAAs influence GBM progression might lead to the development of new therapeutic strategies. This article therefore reports the different levels of GBM progression at which TAAs have been recently described to be involved in, including tumor cells' proliferation/invasion and resistance to therapies, especially through the activity of extracellular vesicles.

Survivin a radiogenetic promoter for glioblastoma viral gene therapy independently from CArG motifs

Background

Radiogenetic therapy is a novel approach in the treatment of cancer, which employs genetic modification to alter the sensitivity of tumor cells to the effect of applied radiation.

Aim

To select a potent radiation inducible promoter in the context of brain tumors and to investigate if CArG radio responsive motifs or other elements in the promoter nucleotide sequences can correlate to its response to radiation.

Methods

To select initial candidates for promoter inducible elements, the levels of mRNA expression of six different promoters were assessed using Quantitative RTPCR in D54 MG cells before and after radiation exposure. Recombinant Ad/reporter genes driven by five different promoters; CMV, VEGF, FLT-1, DR5 and survivin were constructed. Glioma cell lines were infected with different multiplicity of infection of the (promoter) Ad or CMV Ad. Cells were then exposed to a range of radiation (0–12 Gy) at single fraction. Fluorescent microscopy, Luc assay and X-gal staining was used to detect the level of expression of related genes. Different glioma cell lines and normal astrocytes were infected with Ad survivin and exposed to radiation. The promoters were analyzed for presence of CArG radio-responsive motifs and CCAAT box consensus using NCBI blast bioinformatics software.

Results

Radiotherapy increases the expression of gene expression by 1.25–2.5 fold in different promoters other than survivin after 2 h of radiation. RNA analysis was done and has shown an increase in copy number of tenfold for survivin. Most importantly cells treated with RT and Ad Luc driven by survivin promoter showed a fivefold increase in expression after 2 Gy of radiation in comparison to non-irradiated cells. Presence or absence of CArG motifs did not correlate with promoter response to radiation. Survivin with the best response to radiation had the lowest number of CCAAT box.

Conclusion

Survivin is a selective potent radiation inducible promoter for glioblastoma viral gene therapy and this response to radiation could be independent of CArG motifs.

Hepatocyte nuclear factor 1 beta induces transformation and epithelial-to-mesenchymal transition

Gene amplification can be a cause of cancer, and driver oncogenes have been often identified in amplified regions. However, comprehensive analysis of other genes coamplified with an oncogene is rarely performed. We focused on the 17q12-21 amplicon, which contains ERBB2. We established a screening system for oncogenic activity with the NMuMG epithelial cell line. We identified a homeobox gene, HNF1B, as a novel cooperative transforming gene. HNF1B induced cancerous phenotypes, which were enhanced by the coexpression of ERBB2, and induced epithelial-to-mesenchymal transition and invasive phenotypes. These results suggest that HNF1B is a novel oncogene that can work cooperatively with ERBB2.

Glioma Stem Cells but Not Bulk Glioma Cells Upregulate IL-6 Secretion in Microglia/Brain Macrophages via Toll-like Receptor 4 Signaling

Peripheral macrophages and resident microglia constitute the dominant glioma-infiltrating cells. The tumor induces an immunosuppressive and tumor-supportive phenotype in these glioma-associated microglia/brain macrophages (GAMs). A subpopulation of glioma cells acts as glioma stem cells (GSCs). We explored the interaction between GSCs and GAMs. Using CD133 as a marker of stemness, we enriched for or deprived the mouse glioma cell line GL261 of GSCs by fluorescence-activated cell sorting (FACS). Over the same period of time, 100 CD133(+ )GSCs had the capacity to form a tumor of comparable size to the ones formed by 10,000 CD133(-) GL261 cells. In IL-6(-/-) mice, only tumors formed by CD133(+ )cells were smaller compared with wild type. After stimulation of primary cultured microglia with medium from CD133-enriched GL261 glioma cells, we observed an selective upregulation in microglial IL-6 secretion dependent on Toll-like receptor (TLR) 4. Our results show that GSCs, but not the bulk glioma cells, initiate microglial IL-6 secretion via TLR4 signaling and that IL-6 regulates glioma growth by supporting GSCs. Using human glioma tissue, we could confirm the finding that GAMs are the major source of IL-6 in the tumor context.

Isorhapontigenin suppresses growth of patient-derived glioblastoma spheres through regulating miR-145/SOX2/cyclin D1 axis

BACKGROUND

Glioblastoma (GBM) is the most common malignant brain tumor, and glioma stem cells (GSCs) are considered a major source of treatment resistance for glioblastoma. Identifying new compounds that inhibit the growth of GSCs and understanding their underlying molecular mechanisms are therefore important for developing novel therapy for GBM.

METHODS

We investigated the potential inhibitory effect of isorhapontigenin (ISO), an anticancer compound identified in our recent investigations, on anchorage-independent growth of patient-derived glioblastoma spheres (PDGS) and its mechanism of action.

RESULTS

ISO treatment resulted in significant anchorage-independent growth inhibition, accompanied with cell cycle G0-G1 arrest and cyclin D1 protein downregulation in PDGS. Further studies established that cyclin D1 was downregulated by ISO at transcription levels in a SOX2-dependent manner. In addition, ISO attenuated SOX2 expression by specific induction of miR-145, which in turn suppressed 3'UTR activity of SOX2 mRNA without affecting its mRNA stability. Moreover, ectopic expression of exogenous SOX2 rendered D456 cells resistant to induction of cell cycle G0-G1 arrest and anchorage-independent growth inhibition upon ISO treatment, whereas inhibition of miR-145 resulted in D456 cells resistant to ISO inhibition of SOX2 and cyclin D1 expression. In addition, overexpression of miR-145 mimicked ISO treatment in D456 cells.

CONCLUSIONS

ISO induces miR-145 expression, which binds to the SOX2 mRNA 3'UTR region and inhibits SOX2 protein translation. Inhibition of SOX2 leads to cyclin D1 downregulation and PDGS anchorage-independent growth inhibition. The elucidation of the miR-145/SOX2/cyclin D1 axis in PDGS provides a significant insight into understanding the anti-GBM effect of ISO compound.

Repurposing some older drugs that cross the blood-brain barrier and have potential anticancer activity to provide new treatment options for glioblastoma

Glioblastoma is a brain neoplasm with limited 5-year survival rates. Developments of new treatment regimens that improve patient survival in patients with glioblastoma are needed. It is likely that a number of existing drugs used in other conditions have potential anticancer effects that offer significant survival benefit to glioblastoma patients. Identification of such drugs could provide a novel treatment paradigm.

MT1-MMP silencing by an shRNA-armed glioma-targeted conditionally replicative adenovirus (CRAd) improves its anti-glioma efficacy in vitro and in vivo

MMP14 (MT1-MMP) is a cell membrane-associated proteinase of the extracellular matrix, whose biological roles vary from angiogenesis to cell proliferation and survival. We recently found a direct correlation between MMP14 expression levels in brain tumors of glioma patients and the disease progression. By using gene silencing as an experimental approach we found that MMP14 knockdown decreases production of pro-angiogenic factors such as VEGF and IL8 and thereby suppresses angiogenesis in glioma tumors. Although the clinical relevance of MMP14 down-regulation and its possible implications for glioma therapy in humans remain unclear, we observed a significant improvement in animal survival upon down-regulation of MMP14 in murine intracranial glioma xenografts infected with MMP14 shRNA-expressing CRAd. We further found that down-regulation of MMP14 in gliomas by combinational treatment with CRAd-S-5/3 and Marimastat, a chemical inhibitor of metalloproteinases, augments suppression of pro-angiogenic factors, caused by the replication-competent adenovirus. We also demonstrated that delivery of MMP14-targeting shRNA by a fiber-modified adenoviral vector to the glioma cells effectively suppresses their proliferation in vitro and in vivo. Thus our data indicate that inhibition of MMP14 expression in tumors in combination with glioma virotherapy could be effectively utilized to suppress angiogenesis and neovascularization of glioma tumors by decreasing production of pro-angiogenic factors.

Dendritic Cell-Based Vaccines that Utilize Myeloid Rather than Plasmacytoid Cells Offer a Superior Survival Advantage in Malignant Glioma

Dendritic cells (DCs) are professional APCs that are traditionally divided into two distinct subsets, myeloid DC (mDCs) and plasmacytoid DC (pDCs). pDCs are known for their ability to secrete large amounts of IFN-α. Apart from IFN-α production, pDCs can also process Ag and induce T cell immunity or tolerance. In several solid tumors, pDCs have been shown to play a critical role in promoting tumor immunosuppression. We investigated the role of pDCs in the process of glioma progression in the syngeneic murine model of glioma. We show that glioma-infiltrating pDCs are the major APC in glioma and are deficient in IFN-α secretion (p < 0.05). pDC depletion leads to increased survival of the mice bearing intracranial tumor by decreasing the number of regulatory T cells (Tregs) and by decreasing the suppressive capabilities of Tregs. We subsequently compared the ability of mDCs and pDCs to generate effective antiglioma immunity in a GL261-OVA mouse model of glioma. Our data suggest that mature pDCs and mDCs isolated from naive mice can be effectively activated and loaded with SIINFEKL Ag in vitro. Upon intradermal injection in the hindleg, a fraction of both types of DCs migrate to the brain and lymph nodes. Compared to mice vaccinated with pDC or control mice, mice vaccinated with mDCs generate a robust Th1 type immune response, characterized by high frequency of CD4(+)T-bet(+) T cells and CD8(+)SIINFEKEL(+) T cells. This robust antitumor T cell response results in tumor eradication and long-term survival in 60% of the animals (p < 0.001).

Enhanced antitumor efficacy of an oncolytic herpes simplex virus expressing an endostatin-angiostatin fusion gene in human glioblastoma stem cell xenografts

Viruses have demonstrated strong potential for the therapeutic targeting of glioblastoma stem cells (GSCs). In this study, the use of a herpes simplex virus carrying endostatin–angiostatin (VAE) as a novel therapeutic targeting strategy for glioblastoma-derived cancer stem cells was investigated. We isolated six stable GSC-enriched cultures from 36 human glioblastoma specimens and selected one of the stable GSCs lines for establishing GSC-carrying orthotopic nude mouse models. The following results were obtained: (a) VAE rapidly proliferated in GSCs and expressed endo–angio in vitro and in vivo 48 h and 10 d after infection, respectively; (b) compared with the control gliomas treated with rHSV or Endostar, the subcutaneous gliomas derived from the GSCs showed a significant reduction in microvessel density after VAE treatment; (c) compared with the control, a significant improvement was observed in the length of the survival of mice with intracranial and subcutaneous gliomas treated with VAE; (d) MRI analysis showed that the tumor volumes of the intracranial gliomas generated by GSCs remarkably decreased after 10 d of VAE treatment compared with the controls. In conclusion, VAE demonstrated oncolytic therapeutic efficacy in animal models of human GSCs and expressed an endostatin–angiostatin fusion gene, which enhanced antitumor efficacy most likely by restricting tumor microvasculature development.

Targeting cancer stem cells for treatment of glioblastoma multiforme

Cancer stem cells (CSCs) in glioblastoma multiforme (GBM) are radioresistant and chemoresistant, which eventually results in tumor recurrence. Targeting CSCs for treatment is the most crucial issue. There are five methods for targeting the CSCs of GBM. One is to develop a new chemotherapeutic agent specific to CSCs. A second is to use a radiosensitizer to enhance the radiotherapy effect on CSCs. A third is to use immune cells to attack the CSCs. In a fourth method, an agent is used to promote CSCs to differentiate into normal cells. Finally, ongoing gene therapy may be helpful. New therapeutic agents for targeting a signal pathway, such as epidermal growth factor (EGF) and vascular epidermal growth factor (VEGF) or protein kinase inhibitors, have been used for GBM but for CSCs the effects still require further evaluation. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as cyclooxygenase-2 (Cox-2) inhibitors have proven to be effective for increasing radiation sensitivity of CSCs in culture. Autologous dendritic cells (DCs) are one of the promising immunotherapeutic agents in clinical trials and may provide another innovative method for eradication of CSCs. Bone-morphogenetic protein 4 (BMP4) is an agent used to induce CSCs to differentiate into normal glial cells. Research on gene therapy by viral vector is also being carried out in clinical trials. Targeting CSCs by eliminating the GBM tumor may provide an innovative way to reduce tumor recurrence by providing a synergistic effect with conventional treatment. The combination of conventional surgery, chemotherapy, and radiotherapy with stem cell-orientated therapy may provide a new promising treatment for reducing GBM recurrence and improving the survival rate.

Enhanced MGMT expression contributes to temozolomide resistance in glioma stem-like cells

O⁶-methylguanine DNA methyltransferase (MGMT) can remove DNA alkylation adducts, thereby repairing damaged DNA and contributing to the drug resistance of gliomas to alkylating agents. In addition, glioma stem-like cells (GSCs) have been demonstrated to be involved in the recurrence and treatment resistance of gliomas. In this study, we aimed to investigate MGMT expression and regulatory mechanisms in GSCs and the association of MGMT with temozolomide (TMZ) sensitivity. GSCs were enriched from one MGMT-positive cell line (SF-767) and 7 MGMT-negative cell lines (U251, SKMG-4, SKMG-1, SF295, U87, MGR1, and MGR2) through serum-free clone culture. GSCs from the U251G, SKMG-4G, SF295G, and SKMG-1G cell lines became MGMT-positive, but those from the U87G, MGR1G, and MGR2G cell lines remained MGMT-negative. However, all the GSCs and their parental glioma cell lines were positive for nuclear factor-κB (NF-κB). In addition, GSCs were more resistant to TMZ than their parental glioma cell lines (P < 0.05). However, there was no significant difference in the 50% inhibition concentration (IC₅₀) of TMZ between MGMT-positive and MGMT-negative GSCs (P > 0.05). When we treated the MGMT-positive GSCs with TMZ plus MG-132 (an NF-κB inhibitor), the antitumor activity was significantly enhanced compared to that of GSCs treated with TMZ alone (P < 0.05). Furthermore, we found that MGMT expression decreased through the down-regulation of NF-κB expression by MG-132. Our results show that MG-132 may inhibit NF-κB expression and further decrease MGMT expression, resulting in a synergistic effect on MGMT-positive GSCs. These results indicate that enhanced MGMT expression contributes to TMZ resistance in MGMT-positive GSCs.

Antiglioma oncolytic virotherapy: unattainable goal or a success story in the making?

Initial observations from as early as the mid-1800s suggested that patients suffering from hematological malignancies would transiently go into remission upon naturally contracting viral infections laid the foundation for the oncolytic virotherapy research field. Since then, research focusing on anticancer oncolytic virotherapy has rapidly evolved. Today, oncolytic viral vectors have been engineered to stimulate and manipulate the host immune system, selectively targeting tumor tissues while sparing non-neoplastic cells. Glioblastoma multiforme, the most common adult primary brain tumor, has a disasterous history. It is one of the most deadly cancers known to humankind. Over the last century our understanding of this disease has grown exponentially. However, the median survival of patients suffering from this disease has only been extended by a few months. Even with the best, most aggressive modern therapeutic approaches available, malignant gliomas are still virtually 100% fatal. Motivated by the desperate need to find effective treatment strategies, more investments have been applied to oncolytic virotherapy preclinical and clinical studies. In this review we will discuss the antiglioma oncolytic virotherapy research field. We will survey its history and the principles laid down to serve as basis for preclinical works. We will also debate the variety of viral vectors used, their clinical applications, the lessons learned from clinical trials and possible future directions.

Velogenic newcastle disease virus as an oncolytic virotherapeutics: in vitro characterization

Cancer is one of the killer diseases in humans and needs alternate curative measures despite recent improvement in modern treatment modalities. Oncolytic virotherapy seems to be a promising nonconventional way to treat cancers. Newcastle disease virus (NDV), a poultry virus, is nonpathogenic to human and domestic animals and has a long history of being used in oncotherapy research in several preclinical studies. The ability of NDV to successfully infect and destroy cancer cells is dependent on the strain and the pathotype of the virus. Adaptation of viruses to heterologous hosts without losing its replicative and oncolytic potential is prerequisite for use as cancer virotherapeutics. In the present study, velogenic NDV was adapted for replication in HeLa cells, and its cytotoxic potential was evaluated by observing morphological, biochemical, and nuclear landmarks of apoptosis. Our results indicated that the NDV-induced apoptosis in HeLa cells was dependent on upregulation of TNF-related apoptosis-inducing ligand (TRAIL) and caspases activation. Different determinants of apoptosis evaluated in the present study indicated that this strain could be a promising candidate for cancer therapy in future.

Contribution of microRNAs to radio- and chemoresistance of brain tumors and their therapeutic potential

Glioblastomas, particularly high grade brain tumors such as glioblastoma multiforme, are characterized by increased anaplasy, malignancy, proliferation, and invasion. These tumors exhibit high resistance to radiation therapy and treatment with anti-cancer drugs. The radio- and chemoresistance of gliomas is attributed to cancer stem cells (CSCs) that are considered as major contributors for maintenance and propagation of tumor cell mass, cancer malignancy and invasiveness, and tumor cell survival after courses of radiotherapy and medical interventions. MicroRNAs (miRNAs), key post-transcriptional gene regulators, have altered expression profiles in gliomas. Some of miRNAs whose expression is markedly up-regulated in brain tumors are likely to have a pro-oncogenic role through supporting growth, proliferation, migration, and survival of cancer stem and non-stem cells. In contrast, a population of miRNA possessing anti-tumor effects is suppressed in gliomas. In this review, we will consider miRNAs and their influence on radio- and chemoresistance of gliomas. These miRNAs harbor a great therapeutic significance as potent agents in future targeted anti-cancer therapy to sensitize glioma tumor cells and CSCs to cytotoxic effects of radiation exposure and treatment with anti-cancer drugs.

Neural stem cell-based cell carriers enhance therapeutic efficacy of an oncolytic adenovirus in an orthotopic mouse model of human glioblastoma

The potential utility of oncolytic adenoviruses as anticancer agents is significantly hampered by the inability of the currently available viral vectors to effectively target micrometastatic tumor burden. Neural stem cells (NSCs) have the ability to function as cell carriers for targeted delivery of an oncolytic adenovirus because of their inherent tumor-tropic migratory ability. We have previously reported that in vivo delivery of CRAd-S-pk7, a glioma-restricted oncolytic adenovirus, can enhance the survival of animals with experimental glioma. In this study, we show that intratumoral delivery of NSCs loaded with the CRAD-S-pk7 in an orthotopic xenograft model of human glioma is able to not only inhibit tumor growth but more importantly to increase median survival by ~50% versus animals treated with CRAd-S-pk7 alone (P = 0.0007). We also report that oncolytic virus infection upregulates different chemoattractant receptors and significantly enhances migratory capacity of NSCs both in vitro and in vivo. Our data further suggest that NSC-based carriers have the potential to improve the clinical efficacy of antiglioma virotherapy by not only protecting therapeutic virus from the host immune system, but also amplifying the therapeutic payload selectively at tumor sites.

Glioma stem cells targeted by oncolytic virus carrying endostatin-angiostatin fusion gene and the expression of its exogenous gene in vitro

The development of the cancer stem cell (CSCs) niche theory has provided a new target for the treatment of gliomas. Gene therapy using oncolytic viral vectors has shown great potential for the therapeutic targeting of CSCs. To explore whether a viral vector carrying an exogenous Endo-Angio fusion gene (VAE) can infect and kill glioma stem cells (GSCs), as well as inhibit their vascular niche in vitro, we have collected surgical specimens of human high-grade glioma (world health organization, WHO Classes III-VI) from which we isolated and cultured GSCs under conditions originally designed for the selective expansion of neural stem cells. Our results demonstrate the following: (1) Four lines of GSCs (isolated from 20 surgical specimens) could grow in suspension, were multipotent, had the ability to self-renew and expressed the neural stem cell markers, CD133 and nestin. (2) VAE could infect GSCs and significantly inhibit their viability. (3) The Endo-Angio fusion gene was expressed in GSCs 48 h after VAE infection and could inhibit the proliferation of human brain microvascular endothelial cells (HBMEC). (4) Residual viable cells lose the ability of self-renewal and adherent differentiation. In conclusion, VAE can significantly inhibit the activity of GSCs in vitro and the expression of exogenous Endo-Angio fusion gene can inhibit HBMEC proliferation. VAE can be used as a novel virus-gene therapy strategy for glioma.

Frontiers in targeting glioma stem cells

Patients with glioblastoma multiforme (GBM - WHO grade IV) seldom recover. This is due to the infiltrative nature of these tumours and the presence of cellular populations with ability to escape therapies and drive tumour recurrence and progression. In some cases, these resistant cells exhibit stem properties [glioma stem cells (GSC)]. This article aims at discussing relevant issues on GSC resistance to current therapies and outlines possible and promising avenues in regard to novel therapeutic strategies, such as pharmacological, immunological and viral interventions.

Gene therapy and virotherapy: novel therapeutic approaches for brain tumors

Glioblastoma multiforme (GBM) is a deadly primary brain tumor in adults, with a median survival of ~12-18 months post-diagnosis. Despite recent advances in conventional therapeutic approaches, only modest improvements in median survival have been achieved; GBM usually recurs within 12 months post-resection, with poor prognosis. Thus, novel therapeutic strategies to target and kill GBM cells are desperately needed. Our group and others are pursuing virotherapy and gene therapy strategies for the treatment of GBM. In this review, we will discuss various virotherapy and gene therapy approaches for GBM currently under pre-clinical and clinical evaluation including direct or conditional cytotoxic, and/or immunostimulatory approaches. We also discuss cutting-edge technologies for drug/gene delivery and targeting brain tumors, including the use of stem cells as delivery platforms, the use of targeted immunotoxins, and the therapeutic potential of using GBM microvesicles to deliver therapeutic siRNAs or virotherapies. Finally, various animal models available to test novel GBM therapies are discussed.

Primary brain tumors, neural stem cell, and brain tumor cancer cells: where is the link?

The discovery of brain tumor-derived cells (BTSC) with the properties of stem cells has led to the formulation of the hypothesis that neural stem cells could be the cell of origin of primary brain tumors (PBT). In this review we present the most common molecular changes in PBT, define the criteria of identification of BTSC and discuss the similarities between the characteristics of these cells and those of the endogenous population of neural stem cells (NPCs) residing in germinal areas of the adult brain. Finally, we propose possible mechanisms of cancer initiation and progression and suggest a model of tumor initiation that includes intrinsic changes of resident NSC and potential changes in the microenvironment defining the niche where the NSC reside.