Targeting glioma stem cells: a novel framework for brain tumors

Parthenolide prodrug LC-1 slows growth of intracranial glioma

LC-1 (also known as DMAPT or dimethylamino-parthenolide), a prodrug of parthenolide, was tested for anti-proliferative activity against glioma. LC-1 was found to have low micromolar cytotoxic activity against three glioma cell lines and was also found to be brain penetrant in healthy mice (2.1-3.0 brain-to-plasma ratio). In a syngeneic GL261 murine glioma model, LC-1 slowed tumor growth kinetics and extended the survival time of tumor-bearing mice in comparison to the vehicle control. Consequently, LC-1 represents a promising lead compound for further development as a glioma therapy.

Fenofibrate in cancer: mechanisms involved in anticancer activity

Objective: To review the mechanisms of anti-cancer activity of fenofibrate (FF) and other Peroxisome Proliferator Activator Receptor α (PPARα) agonists based on evidences reported in the published literature.Methods: We extensively reviewed the literature concerning FF as an off target anti-cancer drug. Controversies regarding conflicting findings were also addressed.Results: The main mechanism involved in anti-cancer activity is anti-angiogenesis through down-regulation of  Vascular Endothelial Growth Factor (VEGF), Vascular Endothelial Growth Factor Receptor (VEGFR) and Hypoxia Inducible factor-1 α (HIF-1α), inhibition of endothelial cell migration, up-regulation of endostatin and thrombospondin-1, but there are many other contributing mechanisms like apoptosis and cell cycle arrest, down-regulation of Nuclear Factor Kappa B (NF-kB) and Protein kinase B (Akt) and decrease of cellular energy by impairing mitochondrial function. Growth impairment is related to down-regulation of Phospho-Inositol 3 Kinase (PI3K)/Akt axis and down-regulation of the p38 map kinase (MAPK) cascade. A possible role should be assigned to FF stimulated over-expression of Tribbles Homolog-3 (TRIB3) which inhibits Akt phosphorylation. Important anti-cancer and anti-metastatic activities are due to down-regulation of MCP-1 (monocyte chemotactic protein-1), decreased Metalloprotease-9 (MMP-9) production, weak down-regulation of adhesion molecules like E selectin, intercellular adhesion molecules (ICAM) and Vascular Endothelial Adhesion Molecules (VCAM), and decreased secretion of chemokines like Interleukin-6 (IL-6), and down-regulation of cyclin D-1. There is no direct link between FF activity in lipid metabolism and anticancer activity, except for the fact that many anticancer actions are dependent from PPARα agonism. FF exhibits also PPARα independent anti-cancer activities.Conclusions: There are strong evidences indicating that FF can disrupt growth-related activities in many different cancers, due to anti-angiogenesis and anti-inflammatory effects. Therefore FF may be useful as a complementary adjunct treatment of cancer, particularly included in anti-angiogenic protocols like those currently increasingly used in glioblastoma. There are sound reasons to initiate well planned phase II clinical trials for FF as a complementary adjunct treatment of cancer.

Cytotoxic effects on tumour cell lines of fatty acids from the marine sponge Scopalina ruetzleri

OBJECTIVES

Marine sponges are among the most promising sources of chemically diversified fatty acids (FAs). In addition, several studies have shown the effect of polyunsaturated FAs on cancer therapy. This research carried out a biological and chemical evaluation of the sponge Scopalina ruetzleri collected on the South Brazilian coastline.

METHODS

Bioassay-guided fractionation of S. ruetzleri was performed in human glioma (U87) and neuroblastoma (SH-SY5Y) cell lines, and the in-vitro effects on free radicals were evaluated.

KEY FINDINGS

The ethyl acetate fraction of S. ruetzleri showed promising cytotoxic effects in cancer cell lines, with IC50  < 20 μg/ml. Fingerprint (1) H Nuclear Magnetic Resonance (NMR) analysis showed that this fraction is mainly constituted of FAs. Through FA methyl ester analysis, it was possible to identify 32 FAs. In addition, some minor unusual FAs for the marine biosphere were identified. The results of conjugated dienes method showed that FAs fraction, at concentrations above 50 μg/ml, has a pro-oxidant effect, indicating that lipid peroxidation may be partially responsible for the mechanism of cytotoxicity on cancer cells.

CONCLUSION

This work also contributes to studies that focus on the application of FAs on cancer therapy as a new adjuvant to radio or chemotherapy, or as a chemotherapeutic agent.

The cancer stem cell hypothesis: a guide to potential molecular targets

Common cancer theories hold that tumor is an uncontrolled somatic cell proliferation caused by the progressive addition of random mutations in critical genes that control cell growth. Nevertheless, various contradictions related to the mutation theory have been reported previously. These events may be elucidated by the persistence of residual tumor cells, called Cancer Stem Cells (CSCs) responsible for tumorigenesis, tumor maintenance, tumor spread, and tumor relapse. Herein, we summarize the current understanding of CSCs, with a focus on the possibility to identify specific markers of CSCs, and discuss the clinical application of targeting CSCs for cancer treatment.

New advances of microRNAs in glioma stem cells, with special emphasis on aberrant methylation of microRNAs

Malignant brain tumors are thought to be originate from a small population of cells that display stem cell properties, including the capacity of self-renewal, multipotent differentiation, initiation of tumor tissues. Cancer stem cells (CSCs) have been identified in gliomas in which they are named as glioma stem cells (GSCs). GSCs, sharing some characteristics with normal neural stem cells (NSCs), contribute to the cellular origin for primary gliomas and the recurrence of malignant gliomas after current conventional therapy. Recently, increasing evidences have showed that miRNAs play a central role in GSCs. In this review we focus on the role of GSCs in gliomas and in the abnomal expression of miRNAs in GSCs. Furthermore, we also discuss epigenetic dysregulation of tumor-suppressor miRNAs by promoter DNA methylation is involved in the regulation of GSCs biology. Recent advances in understanding dysregulated expression of miRNAs and methylation of tumor-suppressor miRNAs in GSCs and their possible use as new therapeutic targets of gliomas.

Targeting the NF-E2-related factor 2 pathway: a novel strategy for glioblastoma (review)

Glioblastoma is the most common and malignant subtype among all brain tumors. Nuclear factor erythroid 2-related factor 2 (Nrf2) is an essential component of cellular defense against a variety of endogenous and exogenous stresses. A marked increase in research over the past few decades focusing on Nrf2 and its role in regulating glioblastoma has revealed the potential value of Nrf2 in the treatment of glioblastoma. In the present review, we discuss a novel framework of Nrf2 in the regulation of glioblastoma and the mechanisms regarding the downregulation of Nrf2 in treating glioblastoma. The candidate mechanisms include direct and indirect means. Direct mechanisms target tumor molecular pathways in order to overcome resistance to chemotherapy and radiotherapy, to inhibit proliferation, to block invasion and migration, to induce apoptosis, to promote differentiation, to enhance autophagy and to target glioblastoma stem cells. Indirect mechanisms target the reaction between glioblastoma cells and the surrounding microenvironment. Overall, the value of the Nrf2 pathway in glioblastoma provides a promising opportunity for new approaches by which to treat glioblastoma.

Expression of neonatal Nav1.5 in human brain astrocytoma and its effect on proliferation, invasion and apoptosis of astrocytoma cells

In the present study, we designed and conducted a series of assays to determine the expression of voltage-gated sodium channel (VGSC) neonatal isoform Nav1.5 (nNav1.5) in human brain astrocytoma and its effect on the proliferation, migration, invasion and apoptosis of astrocytoma U251 cells. The results showed that nNav1.5 mRNA and protein were expressed in both human brain astrocytoma and normal brain tissues, but their expression levels in astrocytoma were significantly higher (P<0.05). In astrocytomas, nNav1.5 mRNA and protein levels were also different (P<0.05) and were correlated with pathological grades. The immunofluorescence confocal microscopy observations demonstrated that nNav1.5 protein was expressed in the nucleus, cytoplasm and membrane of the astrocytoma cells. After transfection, the small interfering RNA (siRNA) targeted to nNav1.5 significantly reduced the expression levels of SCN5A/nNav1.5 mRNA and protein by 57.2% (P<0.05) and 66.6% (P<0.05), respectively. The MTT, wound healing, Matrigel invasion and flow cytometric assays confirmed that following siRNA downregulation of the expression of the SCN5A/nNav1.5 gene, the in vitro proliferation and in vitro invasiveness of the U251 cells were significantly reduced (P<0.05 for both comparisons), and the apoptosis rate was significantly increased (P<0.05). These results revealed that nNav1.5 expression in human brain astrocytoma was upregulated, and its expression was positively correlated with the degree of malignancy. Additionally, reduced nNav1.5 expression significantly suppressed the proliferation and invasiveness of astrocytoma cells, indicating a new target in the molecular diagnosis and therapy of astrocytoma.

MicroRNA-137 is downregulated in glioblastoma and inhibits the stemness of glioma stem cells by targeting RTVP-1

Glioblastomas (GBM), the most common and aggressive malignant astrocytic tumors, contain a small subpopulation of cancer stem cells (GSCs) that are implicated in therapeutic resistance and tumor recurrence. Here, we study the expression and function of miR-137, a putative suppressor miRNA, in GBM and GSCs. We found that the expression of miR-137 was significantly lower in GBM and GSCs compared to normal brains and neural stem cells (NSCs) and that the miR-137 promoter was hypermethylated in the GBM specimens. The expression of miR-137 was increased in differentiated NSCs and GSCs and overexpression of miR-137 promoted the neural differentiation of both cell types. Moreover, pre-miR-137 significantly decreased the self-renewal of GSCs and the stem cell markers Oct4, Nanog, Sox2 and Shh. We identified RTVP-1 as a novel target of miR-137 in GSCs; transfection of the cells with miR-137 decreased the expression of RTVP-1 and the luciferase activity of RTVP-1 3'-UTR reporter plasmid. Furthermore, overexpression of RTVP-1 plasmid lacking its 3'-UTR abrogated the inhibitory effect of miR-137 on the self-renewal of GSCs. Silencing of RTVP-1 decreased the self-renewal of GSCs and the expression of CXCR4 and overexpression of CXCR4 abrogated the inhibitory effect of RTVP-1 silencing on GSC self-renewal. These results demonstrate that miR-137 is downregulated in GBM probably due to promoter hypermethylation. miR-137 inhibits GSC self-renewal and promotes their differentiation by targeting RTVP-1 which downregulates CXCR4. Thus, miR-137 and RTVP-1 are attractive therapeutic targets for the eradication of GSCs and for the treatment of GBM.

Characterization of fenofibrate-mediated anti-proliferative pro-apoptotic effects on high-grade gliomas and anti-invasive effects on glioma stem cells

Glioblastoma is the most common, and at the same time, most aggressive type of high-grade glioma (HGG). The prognosis of glioblastoma patients treated with standard therapy including surgery, temozolomide and radiation therapy remains poor. Peroxisome proliferator-activated receptor-α (PPARα) agonists are in widespread clinical use for the treatment of hyperlipidemia. Recent evidence has suggested a potential role in various cancers including glioblastoma. In this study, we characterized the effects of PPARα agonist, fenofibrate, directly on HGG cells and glioma stem cells (GSC). Fenofibrate exhibited dose-dependent p53-independent anti-proliferative effects on HGG starting at 25 μM and pro-apoptotic effects starting at 50 μM, suggesting that the anti-proliferative actions are present only at 25 μM. PPARα was expressed in all HGG cell lines. Inhibition of PPARα with specific inhibitor GW6471 did not affect either proliferation or apoptosis suggesting that these are PPARα-independent effects. Fenofibrate treatment of HGG cells robustly diminished the expression of key signaling pathways, including NF-κB and cyclin D1. Phosphorylation of Akt was also diminished, with no change in total Akt. Effects on apoptotic signaling molecules, Bax and Bcl-xL, had a trend towards pro-apoptotic effects. With respect to GSC, fenofibrate treatment at 25 μM significantly decreased invasion in association with a decrease in CD133 and Oct4 expression. Overall, results support consideration of fenofibrate as an anti-glioma agent and establish its potential as an adjunct treatment strategy for HGG. Translation to the clinical setting could be rapid given its current use as a clinical agent and its low toxicity profile.

Pivotal role for ROS activation of p38 MAPK in the control of differentiation and tumor-initiating capacity of glioma-initiating cells

Reactive oxygen species (ROS) are involved in various aspects of cancer cell biology, yet their role in cancer stem cells (CSCs) has been poorly understood. In particular, it still remains unclear whether and how ROS control the self-renewal/differentiation process and the tumor-initiating capacity of CSCs. Here we show that ROS-mediated activation of p38 MAPK plays a pivotal role in the control of differentiation and tumor-initiating capacity of glioma-initiating cells (GICs) derived from human glioblastomas. Mechanistically, ROS triggered p38-dependent Bmi1 protein degradation and FoxO3 activation in GICs, which were shown to be responsible for the loss of their self-renewal capacity and differentiation, respectively. Thus, the results suggest that Bmi1 and FoxO3 govern distinct phases of transition from undifferentiated to fully differentiated cells. Furthermore, we also demonstrate in this study that oxidative stress deprives GICs of their tumor-initiating capacity through the activation of the ROS-p38 axis. As such, this is the first study to the best of our knowledge to delineate how ROS control self-renewal/differentiation and the tumor-initiating capacity of stem-like cancer cells. This study also suggests that targeting of the ROS-p38 axis could be a novel approach in the development of therapeutic strategies against gliomas, represented by glioblastoma.

Anti-cancer Therapies in High Grade Gliomas

High grade gliomas represent one of the most aggressive and treatment-resistant types of human cancer, with only 1–2 years median survival rate for patients with grade IV glioma. The treatment of glioblastoma is a considerable therapeutic challenge; combination therapy targeting multiple pathways is becoming a fast growing area of research. This review offers an up-to-date perspective of the literature about current molecular therapy targets in high grade glioma, that include angiogenic signals, tyrosine kinase receptors, nodal signaling proteins and cancer stem cells related approaches. Simultaneous identification of proteomic signatures could provide biomarker panels for diagnostic and personalized treatment of different subsets of glioblastoma. Personalized medicine is starting to gain importance in clinical care, already having recorded a series of successes in several types of cancer; nonetheless, in brain tumors it is still at an early stage.

Nrf2 is required to maintain the self-renewal of glioma stem cells

Background

Glioblastomas are deadly cancers that display a functional cellular hierarchy maintained by self-renewing glioma stem cells (GSCs). Self-renewal is a complex biological process necessary for maintaining the glioma stem cells. Nuclear factor rythroid 2-related factor 2(Nrf2) plays a significant role in protecting cells from endogenous and exogenous stresses. Nrf2 is a key nuclear transcription factor that regulates antioxidant response element (ARE)-containing genes. Previous studies have demonstrated the significant role of Nrf2 in the proliferation of glioblastoma, and in their resistance to radioactive therapies. We examined the effect of knocking down Nrf2 in GSCs.

Methods

Nrf2 expression was down-regulated by shRNA transinfected with lentivirus. Expression levels of Nestin, Nrf2, BMI-1, Sox2 and Cyclin E were assessed by western blotting, quantitative polymerase chain reaction (qPCR) and immunohistochemistry analysis. The capacity for self-renewal in vitro was assessed by genesis of colonies. The capacity for self-renewal in vivo was analyzed by tumor genesis of xenografts in nude mice.

Results

Knockdown of Nrf2 inhibited the proliferation of GSCs, and significantly reduced the expression of BMI-1, Sox2 and CyclinE. Knocking down of Nrf2 changed the cell cycle distribution of GSCs by causing an uncharacteristic increase in the proportion of cells in the G2 phase and a decrease in the proportion of cells in the S phase of the cell cycle.

Conclusions

Nrf2 is required to maintain the self-renewal of GSCs, and its down-regulation can attenuate the self-renewal of GSCs significantly.

The ultrastructural difference between CD133-positive U251 glioma stem cells and normal U251 glioma cells

Glioma stem cells (GSC) have higher tumorigenic potential and stronger chemoresistance and radioresistance than normal glioma cells. The mechanisms behind these phenomena have remained elusive. The authors have isolated CD133-positive U251 GSCs from U251 glioma cells and detected the expression of stem cell markers (CD133 and nestin) of U251 GSCs by immunofluorescence staining. Then the ultrastructures of U251 GSCs and normal U251 glioma cells were observed by transmission electron microscopy and the ultrastructural differences between them were compared. Increased cell nucleus atypia, rougher endoplasmic reticulum, and more microvilli were observed in CD133-positive U251 GSCs than in normal U251 glioma cells. In summary, these ultrastructural differences support the hypothesis that GSCs have stronger tumorigenic ability and resistance to chemotherapy and radiotherapy.

Pathological features of highly invasive glioma stem cells in a mouse xenograft model

Glioma stem cells (GSCs) may be a source of tumor progression and recurrence after multimodal therapy, because of their high invasive potential. The purpose of this study was to compare the invasive and migratory properties of GSCs and non-GSCs and examine the distribution of these cells in a mouse xenograft model. Three GSC lines, G144, Y02, and Y10, cultured from human glioblastoma, were used in the study. Matrigel-invasion assays of infiltration and time-lapse studies of migration were performed for comparison of the GSCs with the corresponding differentiated non-GSC lines. Cells were also transplanted into mouse brain and the different distribution of GSCs and non-GSCs was examined in the tumor xenograft model. All 3 GSC lines had greater invasion and migration ability than the corresponding non-GSCs. In vivo, GSCs infiltrated more widely than non-GSCs and reached the contralateral hemisphere via the corpus callosum in the early stage of tumorigenesis. GSCs also primarily penetrated the subventricular zone (SVZ). GSCs have high invasive potential and tend to be present in the outer tumor bulk and infiltrate the contralateral hemisphere via the corpus callosum, in addition to penetrating the SVZ.

High-throughput chemical screens identify disulfiram as an inhibitor of human glioblastoma stem cells

Glioblastoma Multiforme (GBM) continues to have a poor patient prognosis despite optimal standard of care. Glioma stem cells (GSCs) have been implicated as the presumed cause of tumor recurrence and resistance to therapy. With this in mind, we screened a diverse chemical library of 2,000 compounds to identify therapeutic agents that inhibit GSC proliferation and therefore have the potential to extend patient survival. High-throughput screens (HTS) identified 78 compounds that repeatedly inhibited cellular proliferation, of which 47 are clinically approved for other indications and 31 are experimental drugs. Several compounds (such as digitoxin, deguelin, patulin and phenethyl caffeate) exhibited high cytotoxicity, with half maximal inhibitory concentrations (IC₅₀) in the low nanomolar range. In particular, the FDA approved drug for the treatment of alcoholism, disulfiram (DSF), was significantly potent across multiple patient samples (IC₅₀ of 31.1 nM). The activity of DSF was potentiated by copper (Cu), which markedly increased GSC death. DSF–Cu inhibited the chymotrypsin-like proteasomal activity in cultured GSCs, consistent with inactivation of the ubiquitin-proteasome pathway and the subsequent induction of tumor cell death. Given that DSF is a relatively non-toxic drug that can penetrate the blood-brain barrier, we suggest that DSF should be tested (as either a monotherapy or as an adjuvant) in pre-clinical models of human GBM. Data also support targeting of the ubiquitin-proteasome pathway as a therapeutic approach in the treatment of GBM.

Pediatric glioma stem cells: biologic strategies for oncolytic HSV virotherapy

While glioblastoma multiforme (GBM) is the most common adult malignant brain tumor, GBMs in childhood represent less than 10% of pediatric malignant brain tumors and are phenotypically and molecularly distinct from adult GBMs. Similar to adult patients, outcomes for children with high-grade gliomas (HGGs) remain poor. Furthermore, the significant morbidity and mortality yielded by pediatric GBM is compounded by neurotoxicity for the developing brain caused by current therapies. Poor outcomes have been attributed to a subpopulation of chemotherapy and radiotherapy resistant cells, termed “glioma stem cells” (GSCs), “glioma progenitor cells,” or “glioma-initiating cells,” which have the ability to initiate and maintain the tumor and to repopulate the recurring tumor after conventional therapy. Future innovative therapies for pediatric HGG must be able to eradicate these therapy-resistant GSCs. Oncolytic herpes simplex viruses (oHSV), genetically engineered to be safe for normal cells and to express diverse foreign anti-tumor therapeutic genes, have been demonstrated in preclinical studies to infect and kill GSCs and tumor cells equally while sparing normal brain cells. In this review, we discuss the unique aspects of pediatric GSCs, including markers to identify them, the microenvironment they reside in, signaling pathways that regulate them, mechanisms of cellular resistance, and approaches to target GSCs, with a focus on the promising therapeutic, genetically engineered oHSV.

The future of glioma treatment: stem cells, nanotechnology and personalized medicine

The development of novel therapies, imaging techniques and insights into the processes that drive growth of CNS tumors have allowed growing enthusiasm for the treatment of CNS malignancies. Despite this energized effort to investigate and treat brain cancer, clinical outcomes for most patients continue to be dismal. Recognition of diverse tumor subtypes, behaviors and outcomes has led to an interest in personalized medicine for the treatment of brain tumors. This new paradigm requires evaluation of the tumor phenotype at the time of diagnosis so that therapy can be specifically tailored to each individual patient. Investigating novel therapies involving stem cells, nanotechnology and molecular medicine will allow diversity of therapeutic options for patients with brain cancer. These exciting new therapeutic strategies for brain tumors are reviewed in this article.

Cancer stem cells, microRNAs, and therapeutic strategies including natural products

Embryonic stem cells divide continuously and differentiate into organs through the expression of specific transcription factors at specific time periods. Differentiated adult stem cells on the other hand remain in quiescent state and divide by receiving cues from the environment (extracellular matrix or niche), as in the case of wound healing from tissue injury or inflammation. Similarly, it is believed that cancer stem cells (CSCs), forming a smaller fraction of the tumor bulk, also remain in a quiescent state. These cells are capable of initiating and propagating neoplastic growth upon receiving environmental cues, such as overexpression of growth factors, cytokines, and chemokines. Candidate CSCs express distinct biomarkers that can be utilized for their identification and isolation. This review focuses on the known and candidate cancer stem cell markers identified in various solid tumors and the promising future of disease management and therapy targeted at these markers. The review also provides details on the differential expression of microRNAs (miRNAs), and the miRNA- and natural product-based therapies that could be applied for the treatment of cancer stem cells.

Malignant behaviorial characteristics of CD133(+/-) glioblastoma cells from a Northern Chinese population

Following emergence of the tumor stem cell theory, the increasing number of related studies demonstrates the theory’s growing importance in cancer research and its potential for clinical applications. Few studies have addressed the in vitro or in vivo properties of glioma stem cells from a Han Chinese population. In the present study, surgically obtained glioblastoma tissue was classified into two subtypes, CD133⁺ and CD133⁻. The hierarchy, invasiveness, growth tolerance under low nutrient conditions and colony forming abilities of the tissue samples were analyzed. Additionally, the characteristics of tumor cells transplanted subcutaneously or re-transplanted into nude mice were observed. The results demonstrated that CD133⁺ glioblastoma cells derived from Han Chinese glioma specimens were more prone to primitive cell differentiation and more invasive than CD133⁻ glioblastoma cells, leading to increased tumor malignancy compared with CD133⁻ cells. The tumor formation rates of CD133⁺ and CD133⁻ cells in mice were 26/30 and 2/30, respectively. A comparison of tumor subtypes demonstrated that CD133⁺ glioblastoma cells had a lower incidence of cell apoptosis in the tumor tissue and higher protein expression levels of Oct4, Sox2, PCNA, EGFR, Ang2, MMP2 and MMP9 compared with CD133⁻ cells. Flow cytometry revealed that in the CD133⁺ and CD133⁻ glioblastoma cell-induced tumors, the percentage of CD133⁺ cells was 2.47±0.67 and 0.44±0.14%, respectively. The tumor formation rates following the re-transplantation of CD133⁺ or CD133⁻ tumors into nude mice were 10/10 and 4/10, respectively. These findings suggest that the CD133⁺ glioblastoma cell subpopulation has a stronger malignant cell phenotype than the CD133⁻ subpopulation and that its recurrence rate is increased compared with the primitive tumorigenic rate following in vivo transplantation.

Oxygen levels and the regulation of cell adhesion in the nervous system: a control point for morphogenesis in development, disease and evolution?

In this article, I discuss the hallmarks of hypoxia in vitro and in vivo and review work showing that many types of stem cell proliferate more robustly in lowered oxygen. I then discuss recent studies showing that alterations in the levels and the types of cell and substrate adhesion molecules are a notable response to reduced O(2) levels in both cultured primary neural stem cells and brain tissues in response to hypoxia in vivo. The ability of O(2) levels to regulate adhesion molecule expression is linked to the Wnt signaling pathway, which can control and be controlled by adhesion events. The ability of O(2) levels to influence cell adhesion also has far-reaching implications for development, ischemic trauma and neural regeneration, as well as for cancer and other diseases. Finally I discuss the possibility that the fluctuations in O(2) levels known to have occurred over evolutionary time could, by influencing adhesion systems, have contributed to early symbiotic events in unicellular organisms and to the emergence of multicellularity. It is not my intention to be exhaustive in these domains, which are far from my own field of study. Rather this article is meant to provoke and stimulate thinking about molecular evolution involving O(2) sensing and signaling during eras of geologic and atmospheric change that might inform modern studies on development and disease.

Radiosurgery for high-grade glioma

Background:

For patients with newly diagnosed high-grade gliomas (HGG), the current standard-of-care treatment involves surgical resection, followed by concomitant temozolomide (TMZ) and external beam radiation therapy (XRT), and subsequent TMZ chemotherapy. For patients with recurrent HGG, there is no standard of care. Stereotactic radiosurgery (SRS) is used to deliver focused, relatively large doses of radiation to a small, precisely defined target. Treatment is usually delivered in a single fraction, but may be delivered in up to five fractions. The role of SRS in the management of patients with HGG is not well established.

Methods:

The PubMed database was searched with combinations of relevant MESH headings and limits. Case reports and/or small case series were excluded. Attention was focused on overall median survival as an objective measure, and data were examined separately for newly diagnosed and recurrent HGG.

Results:

With respect to newly diagnosed HGG, there is strong evidence that addition of an SRS boost prior to standard XRT provides no survival benefit. However, recent retrospective evidence suggests a possible survival benefit when SRS is performed after XRT. With respect to recurrent HGG, there is suggestion that SRS may confer a survival benefit but with potentially higher complication rates. Newer studies are investigating the combination of SRS with targeted molecular agents. Controlled prospective clinical trials using advanced imaging techniques are necessary for a complete assessment.

Conclusions:

SRS has the potential to provide a survival benefit for patients with HGG. Further research is clearly warranted to define its role in the management of newly diagnosed and recurrent HGG.

A new prospect in cancer therapy: targeting cancer stem cells to eradicate cancer

According to the cancer stem cell theory, cancers can be initiated by cancer stem cells. This makes cancer stem cells prime targets for therapeutic intervention. Eradicating cancer stem cells by efficient targeting agents may have the potential to cure cancer. In this review, we summarize recent breakthroughs that have improved our understanding of cancer stem cells, and we discuss the therapeutic strategy of targeting cancer stem cells, a promising future direction for cancer stem cell research.