Glioblastoma multiforme: State of the art and future therapeutics

Glioblastoma: Overview of Disease and Treatment

BACKGROUND

Glioblastoma (GBM) is the most common and aggressive malignant brain tumor in adults. Current treatment options at diagnosis are multimodal and include surgical resection, radiation, and chemotherapy. Significant advances in the understanding of the molecular pathology of GBM and associated cell signaling pathways have opened opportunities for new therapies for recurrent and newly diagnosed disease. Innovative treatments, such as tumor-treating fields (TTFields) and immunotherapy, give hope for enhanced survival.

OBJECTIVES

This article reviews the background, risks, common complications, and treatment options for GBM.

METHODS

A brief review of GBM, treatment options, and a look at new therapies that have been approved for new and recurrent disease are included in this article.

FINDINGS

Despite aggressive resection and combined modality adjuvant treatment, most GBMs recur. Treatments, such as TTFields, drugs to target molecular receptors, and immunotherapy, are promising new options.

Repurposing platinum-based chemotherapies for multi-modal treatment of glioblastoma

Glioblastoma (GBM) is a fatal brain cancer for which new treatment options are sorely needed. Platinum-based drugs have been investigated extensively for GBM treatment but few have shown significant efficacy without major central nervous system (CNS) and systemic toxicities. The relative success of platinum drugs for treatment of non-CNS cancers indicates great therapeutic potential when effectively delivered to the tumor region(s). New insights into the broad anticancer effects of platinum drugs, particularly immunomodulatory effects, and innovative delivery strategies that can maximize these multi-modal effects and minimize toxicities may promote the re-purposing of this chemotherapeutic drug class for GBM treatment.

Dactolisib (NVP-BEZ235) toxicity in murine brain tumour models

Background

Glioblastomas (GBMs) are highly malignant brain tumours with a poor prognosis, and current cytotoxic regimens provide only a limited survival benefit. The PI3K/Akt/mTOR pathway has been an attractive target for therapy due to its high activation in GBMs as well as other cancers. The dual pan-PI3K/mTOR kinase inhibitor dactolisib (NVP-BEZ235) is an anti-neoplastic compound currently under investigation. However, little is known about its efficacy in human GBMs. We aimed at evaluating the efficacy of dactolisib in human glioblastoma cells, as well as in murine models carrying human GBM xenografts.

Methods

To assess the effect of dactolisib in vitro, MTS assay, manual cell count, BrdU incorporation and Annexin V staining experiments were used to observe growth and apoptosis. Furthermore, Akt phosphorylation (S473), a downstream target of PI3K, was explored by western blotting. Animal studies utilizing orthotopic xenograft models of glioblastoma were performed in nude rats and NOD/SCID mice to monitor survival benefit or inhibition of tumor growth.

Results

We found that dactolisib in vitro shows excellent dose dependent anti-growth properties and increase in apoptosis. Moreover, dose dependent inhibition of Akt phosphorylation (S473), a downstream effect of PI3K, was observed by western blotting. However, in two independent animal studies utilizing nude rats and NOD/SCID mice in orthotopic xenograft models of glioblastoma, we observed no survival benefit or inhibition of tumour growth. Severe side effects were observed, such as elevated levels of blood glucose and the liver enzyme alanine transaminase (ALT), in addition to diarrhoea, hair loss (alopecia), skin rash and accumulation of saliva in the oral cavity.

Conclusion

Taken together, our results suggest that despite the anti-neoplastic efficacy of dactolisib in glioma treatment in vitro, its utility in vivo is questionable due to toxicity.

MiR-215, an activator of the CTNNBIP1/β-catenin pathway, is a marker of poor prognosis in human glioma

MicroRNA-215 (miR-215) promotes tumor growth in various human malignancies. However, its role has not yet been determined in human glioma. Here, we found that levels of miR-215 were higher in glioma tissues than in corresponding non-neoplastic brain tissue. High miR-215 expression was correlated with higher World Health Organization (WHO) grades and shorter overall survival. Multivariate and univariate analysis indicated that miR-215 expression was an independent prognostic factor. We also found that TGF-beta1, phosphorylated beta-catenin, alpha-SMA, and fibronectin were increased in glioma tissues. Additionally, CTNNBIP1, a direct target of miR-215, was decreased in glioma compared to adjacent normal tissue. These data indicate that miR-215 activates Wnt/β-catenin signaling by increasing β-catenin phosphorylation, α-SMA expression, and fibronectin expression. It promotes TGF-β1-induced oncogenesis by suppressing CTNNBIP1 in glioma. In summary, miR-215 is overexpressed in human glioma, is involved in TGF-β1-induced oncogenesis, and can be used as a marker of poor prognosis in glioma patients.

Involvement of microRNA-1297, a new regulator of HMGA1, in the regulation of glioma cell growth in vivo and in vitro

MicroRNAs (miRNAs) are a class of versatile gene expression regulators, participating in the regulation of gene expression at the post-transcriptional level in both physiological and pathological conditions. Gliomas are the most common brain malignancy in adults, and deregulation of microRNAs takes part in the gliomagenesis process. Here, we found that the expression of miR-1297 is significantly reduced in both glioma cell lines and clinical glioma tissues. Using the MTT assay, soft agar colony formation assay and xenograft tumor formation assay, we show that miR-1297 is a tumor suppressor microRNA in gliomas. We demonstrate that the high mobility group protein A1 (HMGA1) is the functional target of miR-1297 in glioma cells. HMGA1 significantly promotes the growth of glioma cells both in vitro and in vivo. Together, we unveil a new molecular mechanism in gliomas that may shed new light on understanding this brain malignancy.

SOX7 inhibits tumor progression of glioblastoma and is regulated by miRNA-24

Objective

Sex-determining region Y-box 7 (SOX7) is a putative tumor suppressor in various types of human cancers. In the present study, the expression and function of SOX7 was investigated in human glioblastoma (GBM) cells.

Methods

Real-time PCR and western blot were carried out to reveal the expression of SOX7 in GBM specimens and cultured cell lines. A short interfering RNA (siRNA) targeting SOX7 was synthesized and transfected into U87 cells. 3-(4,5-Dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay was performed to valuate the cell proliferation ability in U87 cells. Bioinformatics analysis further predicted its regulation by microRNA-24 (miR-24). Luciferase reporter assay was performed to prove this regulation.

Results

SOX7 was downregulated in GBM specimens and cell lines. Inhibition of SOX7 in cultured U87 cells resulted in a slower growth rate. Mechanically, SOX7 was a target of miR-24, demonstrated by reporter assay.

Conclusion

SOX7 was a strong tumor suppressor regulated by miR-24 in human GBM cells.

[What's next in glioblastoma treatment: Tumor-targeted or immune-targeted therapies?]

INTRODUCTION

Glioblastoma (GBM) is associated with a poor prognosis. This review will discuss different directions of treatment, mostly regarding immunotherapies and combinatorial approaches.

DEVELOPMENT

Standard treatment for newly diagnosed GBM is maximal and safe surgical resection followed by concurrent radiochemotherapy (RCT) based on temozolomide, allowing 14.6 months median survival. Nowadays, no combination with molecular-targeted therapy had significantly improved prognosis. Phases I and II data are emerging, highlighting the potential efficacy of associations with other therapies. Studies have suggested the potential of targeting tumor stem cells, at less partially responsible for resistance to RCT. There is now some evidence that immunotherapy is also relevant for brain tumors. Treatment strategies have mainly explored vaccines strategies, such as the dendritic cell, heat shock protein or EGFRvIII vaccines. Of the work initiated in melanoma, immune checkpoints inhibitors have exhibited stimulating results. Others trials have demonstrated potential of autologous stimulated lymphocytes. Moreover, strong data indicates that radiation therapy has the potential to promote immunogenicity and create a sort of in situ personalized vaccine.

CONCLUSION

These data provide strong evidence to support the potential of associating combinatorial targeted and/or immunotherapeutic regimens in patients with GBM that may change patient outcome.

Survival in glioblastoma: a review on the impact of treatment modalities

Glioblastoma (GBM) is the most common and lethal tumor of the central nervous system. The natural history of treated GBM remains very poor with 5-year survival rates of 5 %. Survival has not significantly improved over the last decades. Currently, the best that can be offered is a modest 14-month overall median survival in patients undergoing maximum safe resection plus adjuvant chemoradiotherapy. Prognostic factors involved in survival include age, performance status, grade, specific markers (MGMT methylation, mutation of IDH1, IDH2 or TERT, 1p19q codeletion, overexpression of EGFR, etc.) and, likely, the extent of resection. Certain adjuncts to surgery, especially cortical mapping and 5-ALA fluorescence, favor higher rates of gross total resection with apparent positive impact on survival. Recurrent tumors can be offered re-intervention, participation in clinical trials, anti-angiogenic agent or local electric field therapy, without an evident impact on survival. Molecular-targeted therapies, immunotherapy and gene therapy are promising tools currently under research.

Reproducibility of SNV-calling in multiple sequencing runs from single tumors

We examined 55 technical sequencing replicates of Glioblastoma multiforme (GBM) tumors from The Cancer Genome Atlas (TCGA) to ascertain the degree of repeatability in calling single-nucleotide variants (SNVs). We used the same mutation-calling pipeline on all pairs of samples, and we measured the extent of the overlap between two replicates; that is, how many specific point mutations were found in both replicates. We further tested whether additional filtering increased or decreased the size of the overlap. We found that about half of the putative mutations identified in one sequencing run of a given sample were also identified in the second, and that this percentage remained steady throughout orders of magnitude of variation in the total number of mutations identified (from 23 to 10,966). We further found that using filtering after SNV-calling removed the overlap completely. We concluded that there is variation in the frequency of mutations in GBMs, and that while some filtering approaches preferentially removed putative mutations found in only one replicate, others removed a large fraction of putative mutations found in both.

New perspectives in glioblastoma antiangiogenic therapy

Glioblastoma (GB) is highly vascularised tumour, known to exhibit enhanced infiltrative potential. One of the characteristics of glioblastoma is microvascular proliferation surrounding necrotic areas, as a response to a hypoxic environment, which in turn increases the expression of angiogenic factors and their signalling pathways (RAS/RAF/ERK/MAPK pathway, PI3K/Akt signalling pathway and WTN signalling cascade). Currently, a small number of anti-angiogenic drugs, extending glioblastoma patients survival, are available for clinical use. Most medications are ineffective in clinical therapy of glioblastoma due to acquired malignant cells or intrinsic resistance, angiogenic receptors cross-activation and redundant intracellular signalling, or the inability of the drug to cross the blood-brain barrier and to reach its target in vivo. Researchers have also observed that GB tumours are different in many aspects, even when they derive from the same tissue, which is the reason for personalised therapy. An understanding of the molecular mechanisms regulating glioblastoma angiogenesis and invasion may be important in the future development of curative therapeutic approaches for the treatment of this devastating disease.

Nuclear Protein C23 on the Cell Surface Plays an Important Role in Activation of CXCR4 Signaling in Glioblastoma

The chemokine receptor CXCR4 and its ligand stromal cell-derived factor 1 (SDF-1) plays an important role in tumor progression and are associated with angiogenesis. Meanwhile, the implications of C23 in multiple signaling pathways have been also investigated. However, the effects of C23 on CXCR4 pathway in glioblastoma are not fully characterized. In the present study, C23 and CXCR4 of U87 cell line were inhibited by anti-C23 and anti-CXCR4 antibodies, respectively; and then C23 and CXCR4 siRNAs were used to knock down endogenous C23 and CXCR4, respectively. In addition, MTT assay was also introduced. Our data showed that either anti-C23 or anti-CXCR4 antibodies efficaciously repressed the phosphorylation levels of ERK (p < 0.000) and AKT (p < 0.000) compared with SDF-1 alone and control. As expected, either C23 or CXCR4 siRNAs indeed resulted in C23 and CXCR4 knockdown and further suppressed the expression of p-ERK and p-AKT. Most importantly, immunoprecipitation revealed C23 interacted with CXCR4 once U87 was exposed to SDF-1 treatment. In addition, MTT assay identified that C23 or CXCR4 siRNAs could obviously decreased cell proliferation capacity (p = 0.002). In conclusion, our results suggest that C23 plays a crucial role in activation of SDF-1-induced ERK and PI3K/AKT pathways via interacting with CXCR4. Furthermore, C23 could be recommended as an important element in glioblastoma development and a new target for glioblastoma treatment.

The involvement of anterior gradient 2 in the stromal cell-derived factor 1-induced epithelial-mesenchymal transition of glioblastoma

In recent years, it has been widely identified that the stromal cell-derived factor 1 (SDF-1) and anterior gradient 2 (AGR2) were implicated in the development of epithelial-mesenchymal transition (EMT) in a variety of cancers. However, the involvement of SDF-1-AGR2 pathway in the EMT of glioblastoma has not been investigated. In the present study, the in vitro assays were used to investigate the role of AGR2 in cell cycle, migration, and invasion. We found that the expressions of AGR2 and chemokine (C-X-C motif) receptor 4 (CXCR4) were obviously upregulated in glioblastoma cells T98G, A172, U87, and U251 than those in normal human astrocytes (NHA) (all p < 0.01), among which both U87 and U251 cells presented the highest expression (p > 0.05). Western blot revealed that SDF-1 induced the expression of p-AKT, AGR2, and EMT markers (N-cadherin, matrix metalloproteinase-2 (MMP2), and Slug) in a dose-dependent manner in U87 and U251 cells. However, the depletion of AGR2 reversed SDF-1-induced upregulation of EMT markers rather than p-AKT. Furthermore, functional analysis identified that knockdown of AGR2 induced cell cycle arrest in G0/G1 phase and suppressed the migration and invasion of U87 and U251 cells. Taken together, SDF-1-CXCR4 pathway induced the expression of AGR2 to control the progression of EMT likely via AKT pathway in the development of glioblastoma. Our findings lay a promising foundation for the SDF-1-AGR2 axis-targeting therapy in patients with glioblastoma.

Polymeric drug delivery for the treatment of glioblastoma

Glioblastoma (GBM) remains an almost universally fatal diagnosis. The current therapeutic mainstay consists of maximal safe surgical resection followed by radiation therapy (RT) with concomitant temozolomide (TMZ), followed by monthly TMZ (the "Stupp regimen"). Several chemotherapeutic agents have been shown to have modest efficacy in the treatment of high-grade glioma (HGG), but blood-brain barrier impermeability remains a major delivery obstacle. Polymeric drug-delivery systems, developed to allow controlled local release of biologically active substances for a variety of conditions, can achieve high local concentrations of active agents while limiting systemic toxicities. Polymerically delivered carmustine (BCNU) wafers, placed on the surface of the tumor-resection cavity, can potentially provide immediate chemotherapy to residual tumor cells during the standard delay between surgery and chemoradiotherapy. BCNU wafer implantation as monochemotherapy (with RT) in newly diagnosed HGG has been investigated in 2 phase III studies that reported significant increases in median overall survival. A number of studies have investigated the tumoricidal synergies of combination chemotherapy with BCNU wafers in newly diagnosed or recurrent HGG, and a primary research focus has been the integration of BCNU wafers into multimodality therapy with the standard Stupp regimen. Overall, the results of these studies have been encouraging in terms of safety and efficacy. However, the data must be qualified by the nature of the studies conducted. Currently, there are no phase III studies of BCNU wafers with the standard Stupp regimen. We review the rationale, biochemistry, pharmacokinetics, and research history (including toxicity profile) of this modality.

A concurrent ultra-fractionated radiation therapy and temozolomide treatment: A promising therapy for newly diagnosed, inoperable glioblastoma

We report on a phase II clinical trial to determine the effect of a concurrent ultra-fractionated radiotherapy and temozolomide treatment in inoperable glioblastoma patients. A phase II study opened; patients over 18 years of age who were able to give informed consent and had histologically proven, newly diagnosed inoperable diagnosed and supratentorial glioblastoma were eligible. Three doses of 0.75 Gy spaced apart by at least 4 hr were delivered daily, 5 days a week for six consecutive weeks for a total of 67.5 Gy. Chemotherapy was administered during the same period, which consisted of temozolomide given at a dose of 75 mg/m(2) for 7 days a week. After a 4-week break, chemotherapy was resumed for up to six cycles of adjuvant temozolomide treatment, given every 28 days, according to the standard 5-day regimen. Tolerance and toxicity were the primary endpoints; survival and progression-free survival were the secondary endpoints. In total, 40 patients were enrolled in this study, 29 men and 11 women. The median age was 58 years, and the median Karnofsky performance status was 80. The concomitant ultra-fractionated radiotherapy and temozolomide treatment was well tolerated. Complete responses were seen in four patients, and partial responses were reported in seven patients. The median survival from the initial diagnosis was 16 months. Several long-term survivors were noted. Concurrent ultra-fractionated radiation therapy and temozolomide treatment are well accepted by the patients. The results showed encouraging survival rates for these unfavorable patients.

Design and synthesis of 2-oxindole based multi-targeted inhibitors of PDK1/Akt signaling pathway for the treatment of glioblastoma multiforme

Aggressive behavior and diffuse infiltrative growth are the main features of Glioblastoma multiforme (GBM), together with the high degree of resistance and recurrence. Evidence indicate that GBM-derived stem cells (GSCs), endowed with unlimited proliferative potential, play a critical role in tumor development and maintenance. Among the many signaling pathways involved in maintaining GSC stemness, tumorigenic potential, and anti-apoptotic properties, the PDK1/Akt pathway is a challenging target to develop new potential agents able to affect GBM resistance to chemotherapy. In an effort to find new PDK1/Akt inhibitors, we rationally designed and synthesized a small family of 2-oxindole derivatives. Among them, compound 3 inhibited PDK1 kinase and downstream effectors such as CHK1, GS3Kα and GS3Kβ, which contribute to GCS survival. Compound 3 appeared to be a good tool for studying the role of the PDK1/Akt pathway in GCS self-renewal and tumorigenicity, and might represent the starting point for the development of more potent and focused multi-target therapies for GBM.

NDRG1 overexpressing gliomas are characterized by reduced tumor vascularization and resistance to antiangiogenic treatment

Hypoxia-regulated molecules play an important role in vascular resistance to antiangiogenic treatment. N-myc downstream-regulated-gene 1 (NDRG1) is significantly upregulated during hypoxia in glioma. It was the aim of the present study to analyze the role of NDRG1 on glioma angiogenesis and on antiangiogenic treatment. Orthotopically implanted NDRG1 glioma showed reduced tumor growth and vessel density compared to controls. RT-PCR gene array analysis revealed a 30-fold TNFSF15 increase in NDRG1 tumors. Consequently, the supernatant from NDRG1 transfected U87MG glioma cells resulted in reduced HUVEC proliferation, migration and angiogenic response in tube formation assays in vitro. This effect was provoked by increased TNFSF15 promoter activity in NDRG1 cells. Mutations in NF-κB and AP-1 promoter response elements suppressed TNFSF15 promoter activity. Moreover, U87MG glioma NDRG1 knockdown supernatant contained multiple proangiogenic proteins and increased HUVEC spheroid sprouting. Sunitinib treatment of orhotopically implanted mice reduced tumor volume and vessel density in controls; in NDRG1 overexpressing cells no reduction of tumor volume or vessel density was observed. NDRG1 overexpression leads to reduced tumor growth and angiogenesis in experimental glioma via upregulation of TNFSF15. In NDRG1 overexpressing glioma antiangiogenic treatment does not yield a therapeutic response.

Withania somnifera Suppresses Tumor Growth of Intracranial Allograft of Glioma Cells

Gliomas are the most frequent type of primary brain tumor in adults. Their highly proliferative nature, complex cellular composition, and ability to escape therapies have confronted investigators for years, hindering the advancement toward an effective treatment. Agents that are safe and can be administered as dietary supplements have always remained priority to be most feasible for cancer therapy. Withania somnifera (ashwagandha) is an essential ingredient of Ayurvedic preparations and is known to eliminate cancer cells derived from a variety of peripheral tissues. Although our previous studies have addressed the in vitro anti-proliferative and differentiation-inducing properties of ashwagandha on neuronal cell lines, in vivo studies validating the same are lacking. While exploring the mechanism of its action in vitro, we observed that the ashwagandha water extract (ASH-WEX) induced the G2/M phase blockade and caused the activation of multiple pro-apoptotic pathways, leading to suppression of cyclin D1, bcl-xl, and p-Akt, and reduced the expression of polysialylated form of neural cell adhesion molecule (PSA-NCAM) as well as the activity of matrix metalloproteinases. ASH-WEX reduced the intracranial tumor volumes in vivo and suppressed the tumor-promoting proteins p-nuclear factor kappa B (NF-κB), p-Akt, vascular endothelial growth factor (VEGF), heat shock protein 70 (HSP70), PSA-NCAM, and cyclin D1 in the rat model of orthotopic glioma allograft. Reduction in glial fibrillary acidic protein (GFAP) and upregulation of mortalin and neural cell adhesion molecule (NCAM) expression specifically in tumor-bearing tissue further indicated the anti-glioma efficacy of ASH-WEX in vivo. Combining this enhanced understanding of the molecular mechanisms of ASH-WEX in glioma with in vivo model system offers new opportunities to develop therapeutic strategy for safe, specific, and effective formulations for treating brain tumors.

β-elemene enhances both radiosensitivity and chemosensitivity of glioblastoma cells through the inhibition of the ATM signaling pathway

Glioblastoma multiforme (GBM), a tumor associated with poor prognosis, is known to be resistant to radiotherapy and alkylating agents such as temozolomide (TMZ). β-elemene, a monomer found in Chinese traditional herbs extracted from Curcuma wenyujin, is currently being used as an antitumor drug for different types of tumors including GBM. In the present study, we investigated the roles of β-elemene in the radiosensitivity and chemosensitivity of GBM cells. Human GBM cell lines U87-MG, T98G, U251, LN229 and rat C6 cells were treated with β-elemene combined with radiation or TMZ. We used MTT and colony forming assays to evaluate the proliferation and survival of the cells, and the comet assay to observe DNA damage. Expression of proteins was analyzed by immunoblotting. In the present study, we found that β-elemene inhibited the proliferation and survival of different GBM cell lines when combined with radiotherapy or TMZ via inhibition of DNA damage repair. Treatment of GBM cells with β-elemene decreased the phosphorylation of ataxia telangiectasia mutated (ATM), AKT and ERK following radiotherapy or chemotherapy. These results revealed that β-elemene could significantly increase the radiosensitivity and chemosensitivity of GBM. β-elemene may be used as a potential drug in combination with the radiotherapy and chemotherapy of GBM.

Agomelatine or ramelteon as treatment adjuncts in glioblastoma and other M1- or M2-expressing cancers

The impressive but sad list of over forty clinical studies using various cytotoxic chemotherapies published in the last few years has failed to increase median survival of glioblastoma beyond two years after diagnosis. In view of this apparent brick wall, adjunctive non-cytotoxic growth factor blocking drugs are being tried, as in the CUSP9* protocol. A related theme is searching for agonists at growth inhibiting receptors. One such dataset is that of melatonin agonism at M1 or M2 receptors found on glioblastoma cells, being a negative regulator of these cells’ growth. Melatonin itself is an endogenous hormone, but when used as an exogenously administered drug it has many disadvantages. Agomelatine, marketed as an antidepressant, and ramelteon, marketed as a treatment for insomnia, are currently-available melatonin receptor agonists. These melatonin receptor agonists have significant advantages over the natural ligand: longer half-life, better oral absorption, and higher affinity to melatonin receptors. They have an eminently benign side effect profile. As full agonists they should function to inhibit glioblastoma growth, as demonstrated for melatonin. A potentially helpful ancillary attribute of melatonergic agonists in glioblastoma treatment is an increase in interleukin-2 synthesis, expected, at least partially, to reverse some of the immunosuppression associated with glioblastoma.

Decreased affinity for efflux transporters increases brain penetrance and molecular targeting of a PI3K/mTOR inhibitor in a mouse model of glioblastoma

BACKGROUND

Targeting drug delivery to invasive glioma cells is a particularly difficult challenge because these cells lie behind an intact blood-brain barrier (BBB) that can be observed using multimodality imaging. BBB-associated efflux transporters such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) influence drug distribution to these cells and may negatively impact efficacy. To test the hypothesis that efflux transporters influence brain pharmacokinetics/pharmacodynamics of molecularly targeted agents in glioma treatment, we assessed region-specific penetrance and molecular-targeting capacity for a PI3K/mTOR kinase inhibitor that has high substrate affinity for efflux transporters (GDC-0980) and an analog (GNE-317) that was purposely designed to have reduced efflux.

METHODS

Brain tumor penetrance of GDC-0980 and GNE-317 was compared between FVB/n wild-type mice and Mdr1a/b(-/-)Bcrp(-/-) triple-knockout mice lacking P-gp and BCRP. C57B6/J mice bearing intracranial GL261 tumors were treated with GDC-0980, GNE-317, or vehicle to assess the targeted pharmacokinetic/pharmacodynamic effects in a glioblastoma model.

RESULTS

Animals treated with GNE-317 demonstrated 3-fold greater penetrance in tumor core, rim, and normal brain compared with animals dosed with GDC-0980. Increased brain penetrance correlated with decreased staining of activated p-Akt, p-S6, and p-4EBP1 effector proteins downstream of PI3K and mTOR.

CONCLUSIONS

GDC-0980 is subject to active efflux by P-gp and BCRP at the BBB, while brain penetrance of GNE-317 is independent of efflux, which translates into enhanced inhibition of PI3K/mTOR signaling. These data show that BBB efflux by P-gp and BCRP is therefore an important determinant in both brain penetrance and molecular targeting efficacy in the treatment of invasive glioma cells.

Glioblastoma multiforme: Pathogenesis and treatment

Each year, about 5-6 cases out of 100,000 people are diagnosed with primary malignant brain tumors, of which about 80% are malignant gliomas (MGs). Glioblastoma multiforme (GBM) accounts for more than half of MG cases. They are associated with high morbidity and mortality. Despite current multimodality treatment efforts including maximal surgical resection if feasible, followed by a combination of radiotherapy and/or chemotherapy, the median survival is short: only about 15months. A deeper understanding of the pathogenesis of these tumors has presented opportunities for newer therapies to evolve and an expectation of better control of this disease. Lately, efforts have been made to investigate tumor resistance, which results from complex alternate signaling pathways, the existence of glioma stem-cells, the influence of the blood-brain barrier as well as the expression of 0(6)-methylguanine-DNA methyltransferase. In this paper, we review up-to-date information on MGs treatment including current approaches, novel drug-delivering strategies, molecular targeted agents and immunomodulative treatments, and discuss future treatment perspectives.

The role of metabolic therapy in treating glioblastoma multiforme

Glioblastoma multiforme (GBM) is an aggressive and nearly uniformly fatal malignancy of the central nervous system. Despite extensive research and clinical trials over the past 50 years, very little progress has been made to significantly alter its lethal prognosis. The current standard of care (SOC) includes maximal surgical resection, radiation therapy and chemotherapy and temozolomide (TMZ), including the selective use of glucocorticoids for symptom control. These same treatments, however, have the potential to create an environment that may actually facilitate tumor growth and survival. Research investigating the unique metabolic needs of tumor cells has led to the proposal of a new metabolic treatment for various cancers including GBMs that may enhance the effectiveness of the SOC. The goal of metabolic cancer therapy is to restrict GBM cells of glucose, their main energy substrate. By recognizing the underlying energy production requirements of cancer cells, newly proposed metabolic therapy is being used as an adjunct to standard GBM therapies. This review will discuss the calorie restricted ketogenic diet (CR-KD) as a promising potential adjunctive metabolic therapy for patients with GBMs. The effectiveness of the CR-KD is based on the "Warburg Effect" of cancer metabolism and the microenvironment of GBM tumors. We will review recent case reports, clinical studies, review articles, and animal model research using the CR-KD and explain the principles of the Warburg Effect as it relates to CR-KD and GBMs.

Bioresponsive probes for molecular imaging: concepts and in vivo applications

Molecular imaging is a powerful tool to visualize and characterize biological processes at the cellular and molecular level in vivo. In most molecular imaging approaches, probes are used to bind to disease-specific biomarkers highlighting disease target sites. In recent years, a new subset of molecular imaging probes, known as bioresponsive molecular probes, has been developed. These probes generally benefit from signal enhancement at the site of interaction with its target. There are mainly two classes of bioresponsive imaging probes. The first class consists of probes that show direct activation of the imaging label (from "off" to "on" state) and have been applied in optical imaging and magnetic resonance imaging (MRI). The other class consists of probes that show specific retention of the imaging label at the site of target interaction and these probes have found application in all different imaging modalities, including photoacoustic imaging and nuclear imaging. In this review, we present a comprehensive overview of bioresponsive imaging probes in order to discuss the various molecular imaging strategies. The focus of the present article is the rationale behind the design of bioresponsive molecular imaging probes and their potential in vivo application for the detection of endogenous molecular targets in pathologies such as cancer and cardiovascular disease.

miR-29s inhibit the malignant behavior of U87MG glioblastoma cell line by targeting DNMT3A and 3B

miR-29s (including miR-29a-c) have been confirmed to be effective tumor suppressors for a variety of malignant tumors including glioblastoma. Promoter hypermethylation resulting from DNMT3A and 3B overexpression is an important epigenetic mechanism for tumor suppressive gene silencing. Bioinformatics predicts both DNMT3A and 3B are targets of miR-29s, but the anti-glioblastoma effects of miR-29s induced DNMT3A/3B downregulation deserve further investigation. We herein demonstrated that miR-29s effectively blocked DNMT3A and 3B expression by degrading their mRNAs in U87MG glioblastoma cell line. Exogenous miR-29s substantially inhibited the proliferation, migration and invasion of U87MG cells, and promoted their apoptosis. These effects could be perfectly mimicked by a small interfering RNA against DNMT3A and 3B, and partially compromised by DNMT3A/3B expression plasmids co-transfection, suggesting that miR-29s exerted the above tumor suppressive effects at least partly by silencing DNMT3A/3B. These findings provide a rationale for miR-29s based therapeutic strategies against glioblastoma.

Arginine deprivation by arginine deiminase of Streptococcus pyogenes controls primary glioblastoma growth in vitro and in vivo

Arginine auxotrophy constitutes a weak point of several tumors, among them glioblastoma multiforme (GBM). Hence, those tumors are supposed to be sensitive for arginine-depleting substances, such as arginine deiminase (ADI). Here we elucidated the sensitivity of patient-individual GBM cell lines toward Streptococcus pyogenes-derived ADI. To improve therapy, ADI was combined with currently established and pre-clinical cytostatic drugs. Additionally, effectiveness of local ADI therapy was determined in xenopatients. Half of the GBM cell lines tested responded well toward ADI monotherapy. In those cell lines, viability decreased significantly (up to 50%). Responding cell lines were subjected to combination therapy experiments to test if any additive or even synergistic effects may be achieved. Such promising results were obtained in 2/3 cases. In cell lines HROG02, HROG05 and HROG10, ADI and Palomid 529 combinations were most effective yielding more than 70% killing after 2 rounds of treatment. Comparable boosted antitumoral effects were observed after adding chloroquine to ADI (>60% killing). Apoptosis, as well as cell cycle dysregulation were found to play a minor role. In some, but clearly not all cases, (epi-) genetic silencing of arginine synthesis pathway genes (argininosuccinate synthetase 1 and argininosuccinate lyase) explained obtained results. In vivo, ADI as well as the combination of ADI and SAHA efficiently controlled HROG05 xenograft growth, whereas adding Palomid 529 to ADI did not further increase the strong antitumoral effect of ADI. The cumulative in vitro and in vivo results proved ADI as a very promising candidate therapeutic, especially for development of adjuvant GBM combination treatments.

Biomarkers of glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and lethal primary malignancy of the central nervous system. Modern treatments using surgery and/or chemotherapy and/or radiotherapy are improving survival of patients, but prognosis is still very poor, depending inter alia on the patients' individual genomic traits. Most GBMs are primary; however, secondary GBMs have a better prognosis. Aberrant gene expression and copy number alterations make it possible to identify four subtypes: classical, mesenchymal, proneural, and neural. More and more biomarkers continue to be identified in GBM patients. Such biomarkers are related with varying degrees of specificity to one or more of GBM's subtypes and, in many instances, may provide useful information about prognosis. Biomarkers fall into either the imaging or molecular category. Molecular biomarkers are identified by use of such platforms as genomics, proteomics, and metabolomics. In the future, biomarkers, either individually or in some combination, will more reliably identify the pathogenic type of GBM and determine choice of therapy.

SapC-DOPS nanovesicles: a novel targeted agent for the imaging and treatment of glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor. Classified by the World Health Organization (WHO) as grade IV astrocytoma, GBMs are extremely aggressive, almost always recur, and despite our best efforts, remain incurable. This review describes the traditional treatment approaches that led to moderate successes in GBM patients, discusses standard imaging modalities, and presents data supporting the use of SapC-DOPS, a novel proteoliposomal formulation with tumoricidal activity, as a promising diagnostic imaging tool and an innovative anti-cancer agent against GBM.

Mechanisms and clinical significance of histone deacetylase inhibitors: epigenetic glioblastoma therapy

Glioblastoma is the most common and deadliest of malignant primary brain tumors (Grade IV astrocytoma) in adults. Current standard treatments have been improving but patient prognosis still remains unacceptably devastating. Glioblastoma recurrence is linked to epigenetic mechanisms and cellular pathways. Thus, greater knowledge of the cellular, genetic and epigenetic origin of glioblastoma is the key for advancing glioblastoma treatment. One rapidly growing field of treatment, epigenetic modifiers; histone deacetylase inhibitors (HDACis), has now shown much promise for improving patient outcomes through regulation of the acetylation states of histone proteins (a form of epigenetic modulation) and other non-histone protein targets. HDAC inhibitors have been shown, in a pre-clinical setting, to be effective anticancer agents via multiple mechanisms, by up-regulating expression of tumor suppressor genes, inhibiting oncogenes, inhibiting tumor angiogenesis and up-regulating the immune system. There are many HDAC inhibitors that are currently in pre-clinical and clinical stages of investigation for various types of cancers. This review will explain the theory of epigenetic cancer therapy, identify HDAC inhibitors that are being investigated for glioblastoma therapy, explain the mechanisms of therapeutic effects as demonstrated by pre-clinical and clinical studies and describe the current status of development of these drugs as they pertain to glioblastoma therapy.

Combination treatment with doxorubicin and microRNA-21 inhibitor synergistically augments anticancer activity through upregulation of tumor suppressing genes

Doxorubicin (DOX) is a key chemotherapeutic drug for cancer treatment. The antitumor mechanism of DOX is its action as a topoisomerase II poison by preventing DNA replication. Our study shows that DOX can be involved in epigenetic regulation of gene transcription through downregulation of DNA methyltransferase 1 (DNMT1) then reactivation of DNA methylation-silenced tumor suppressor genes in glioblastoma (GBM). Recent evidence demonstrated that microRNA (miR or miRNA) can mediate expression of genes through post-transcriptional regulation and modulate sensitivity to anticancer drugs. As one of the first miRNAs detected in the human genome, miR-21 has been validated to be overexpressed in GBM. Combination treatment of a chemotherapeutic and miRNA showed synergistically increased anticancer activities which has been proven to be an effective strategy for tumor therapy. In our study, co-treatment of DOX and miR-21 inhibitor (miR-21i) resulted in remarkably increased expression of tumor suppressor genes compared with DOX or the miR-21i treatment alone. Moreover, we demonstrate that combining DOX and miR-21i significantly reduced tumor cell proliferation, invasion and migration in vitro. Our study concludes that combining DOX and miR-21i is a new strategy for the therapy of GBM.

Ephs and Ephrins in malignant gliomas

Eph receptor tyrosine kinases and the corresponding ephrin ligands play a pivotal role in the glioma development and progression. Aberrant protein expression levels of the Eph receptors and ephrins are often associated with higher tumor grade and poor prognosis. Their function in tumorigenesis is complex due to the intricate network of possible co-occurring interactions between neighboring tumor cells and tumor microenvironment. Both Ephs and ephrins localize on the surface of tumor cells, tumor vasculature, glioma stem cells, tumor cells infiltrating brain, and immune cells infiltrating tumors. They can both promote and inhibit tumorigenicity depending on the downstream forward and reverse signalling generated. All the above-mentioned features make the Ephs/ephrins system an intriguing candidate for the development of new therapeutic strategies in glioma treatment. This review will give a general overview on the structure and the function of Ephs and ephrins, with a particular emphasis on the state of the knowledge of their role in malignant gliomas.

Secretory prostate apoptosis response (Par)-4 sensitizes multicellular spheroids (MCS) of glioblastoma multiforme cells to tamoxifen-induced cell death

Glioblastoma multiforme (GBM) is the most malignant form of brain tumor and is associated with resistance to conventional therapy and poor patient survival. Prostate apoptosis response (Par)-4, a tumor suppressor, is expressed as both an intracellular and secretory/extracellular protein. Though secretory Par-4 induces apoptosis in cancer cells, its potential in drug-resistant tumors remains to be fully explored. Multicellular spheroids (MCS) of cancer cells often acquire multi-drug resistance and serve as ideal experimental models. We investigated the role of Par-4 in Tamoxifen (TAM)-induced cell death in MCS of human cell lines and primary cultures of GBM tumors. TCGA and REMBRANT data analysis revealed that low levels of Par-4 correlated with low survival period (21.85 ± 19.30 days) in GBM but not in astrocytomas (59.13 ± 47.26 days) and oligodendrogliomas (58.04 ± 59.80 days) suggesting low PAWR expression as a predictive risk factor in GBM. Consistently, MCS of human cell lines and primary cultures displayed low Par-4 expression, high level of chemo-resistance genes and were resistant to TAM-induced cytotoxicity. In monolayer cells, TAM-induced cytotoxicity was associated with enhanced expression of Par-4 and was alleviated by silencing of Par-4 using specific siRNA. TAM effectively induced secretory Par-4 in conditioned medium (CM) of cells cultured as monolayer but not in MCS. Moreover, MCS were rendered sensitive to TAM-induced cell death by exposure to conditioned medium (CM)-containing Par-4 (derived from TAM-treated monolayer cells). Also TAM reduced the expression of Akt and PKCζ in GBM cells cultured as monolayer but not in MCS. Importantly, combination of TAM with inhibitors to PI3K inhibitor (LY294002) or PKCζ resulted in secretion of Par-4 and cell death in MCS. Since membrane GRP78 is overexpressed in most cancer cells but not normal cells, and secretory Par-4 induces apoptosis by binding to membrane GRP78, secretory Par-4 is an attractive candidate for potentially overcoming therapy-resistance not only in malignant glioma but in broad spectrum of cancers.

CXCR4 Signaling Induced Epithelial-Mesenchymal Transition by PI3K/AKT and ERK Pathways in Glioblastoma

Stromal cell-derived factor 1 (SDF-1) and its receptor, CXCR4, play an important role in tumor progression. Epithelial-mesenchymal transition (EMT) process is linked to disease pathophysiology. This study aimed to investigate the roles and underlying mechanisms of SDF-1/CXCR4 axis in EMT process of glioblastoma. In the present study, CXCR4 activation and inhibition in U87 were induced with exogenous SDF-1 and with CXCR4 small interfering RNA (siRNA), respectively. CXCR4 downstream signal molecules AKT, ERK, and EMT biomarkers (vementin, snail, N-cadherin, and E-cadherin) were tested using the Western blot. Our results showed that SDF-1 can induce AKT and ERK phosphorylation in a dose-dependent manner, and endogenous CXCR4 can be blocked thoroughly by CXCR4 siRNA in U87. Notably SDF-1 alone treatment can induce the upregulation of vementin, snail, and N-cadherin of U87; besides, the downregulation of E-cadherin also occurred. On the contrary, CXCR4 siRNA significantly prohibited SDF-1-induced AKT and ERK phosphorylation, at the same time, EMT biomarker changes were not observed. Function analysis revealed that CXCR4 siRNA obviously interfered with U87 cell migration and proliferation, according to wound healing assay. In conclusion, this study suggested that EMT process can be triggered by the SDF-1/CXCR4 axis in glioblastoma, and then involved in the tumor cell invasion and proliferation via activation of PI3K/AKT and ERK pathway. Our study lays a new foundation for the treatment of glioblastoma through antagonizing CXCR4.