Editor's choice: Contemporary murine models in preclinical astrocytoma drug development

Despite 6 decades of research, only 3 drugs have been approved for astrocytomas, the most common malignant primary brain tumors. However, clinical drug development is accelerating with the transition from empirical, cytotoxic therapy to precision, targeted medicine. Preclinical animal model studies are critical for prioritizing drug candidates for clinical development and, ultimately, for their regulatory approval. For decades, only murine models with established tumor cell lines were available for such studies. However, these poorly represent the genomic and biological properties of human astrocytomas, and their preclinical use fails to accurately predict efficacy in clinical trials. Newer models developed over the last 2 decades, including patient-derived xenografts, genetically engineered mice, and genetically engineered cells purified from human brains, more faithfully phenocopy the genomics and biology of human astrocytomas. Harnessing the unique benefits of these models will be required to identify drug targets, define combination therapies that circumvent inherent and acquired resistance mechanisms, and develop molecular biomarkers predictive of drug response and resistance. With increasing recognition of the molecular heterogeneity of astrocytomas, employing multiple, contemporary models in preclinical drug studies promises to increase the efficiency of drug development for specific, molecularly defined subsets of tumors.     

Glioblastoma microvesicles promote endothelial cell proliferation through Akt/beta-catenin pathway

Glioblastoma tumor cells release microvesicles, which contain mRNA, miRNA and angiogenic proteins. These tumor-derived microvesicles transfer genetic information and proteins to normal cells. Previous reports demonstrated that the increased microvesicles in cerebrospinal fluid (CSF) of patients with glioblastoma up-regulate procoagulant activity. The concentration of microvesicles was closely related to thromboembolism incidence and clinical therapeutic effects of glioblastoma patients. However, it is still not clear how CSF microvesicles and what factors affect glioblastoma development. In this study, we collected the plasma and CSF from glioblastoma patients and healthy volunteers. Microvesicles acquired from serum or CSF were added to cultured endothelial cells. And the effects of these microvesicles on endothelial cells were examined. Our results showed that microvesicles from CSF of patients, but not from circulating blood, promoted endothelial cells migration and proliferation in vitro. In addition, the degree of endothelial cell proliferation triggered by microvesicles from CSF was reduced when treated with siRNA targeting Akt/beta-catenin, suggesting that the Akt/beta-catenin pathway is involved in the microvesicle-initiated endothelial cell proliferation. In conclusion, glioblastoma mainly affects microvesicles within CSF without showing significant impact on microvesicles in circulating blood. Microvesicles from the CSF of glioblastoma patients may initiate endothelial cell growth and thus promote cell invasion. This effect may be directly exerted by activated Akt/beta-catenin pathway.     

Antiangiogenic blockage: a new treatment for glioblastoma

Background: Angiogenesis is common in cancer and reflects the requirement for a vascular network to support continued uncontrolled growth. Two strategies of antiangiogenic therapy have emerged; one targeting VEGF (growth-factor-ligand-based antagonists) and the second targeting VEGF receptor (receptor-based antagonists, small-molecule tyrosine kinase inhibitors). Methods: The literature as reviewed by Reardon et al. regarding treatment of recurrent high-grade gliomas (HGG) with antiangiogenic therapy (predominantly ligand-based and administered in conjunction with cytotoxic chemotherapy) reports response rates of 30 – 60% and 6-month progression-free survival of 25 – 50%. Problems include new antiangiogenic-class side effects and control of administration and timing in relation to surgery. Results/conclusions: Ligand-based antiangiogenic therapy is a compelling targeted therapy for HGG and will continue to emerge as an important antiglioma therapy. Further studies are required to define the population of patients in whom this therapy is of benefit, identify the optimal dose and schedule, characterize the value of co-administered (cytotoxic and targeted) therapies and establish validated response measures.     

Factor analysis for survival time prediction with informative censoring and diverse covariates

Fulfilling the promise of precision medicine requires accurately and precisely classifying disease states. For cancer, this includes prediction of survival time from a surfeit of covariates. Such data presents an opportunity for improved prediction, but also a challenge due to high dimensionality. Furthermore, disease populations can be heterogeneous. Integrative modeling is sensible, as the underlying hypothesis is that joint analysis of multiple covariates provides greater explanatory power than separate analyses. We propose an integrative latent variable model that combines factor analysis for various data types and an exponential proportional hazards (EPH) model for continuous survival time with informative censoring. The factor and EPH models are connected through low-dimensional latent variables that can be interpreted and visualized to identify subpopulations. We use this model to predict survival time. We demonstrate this model's utility in simulation and on four Cancer Genome Atlas datasets: diffuse lower-grade glioma, glioblastoma multiforme, lung adenocarcinoma, and lung squamous cell carcinoma. These datasets have small sample sizes, high-dimensional diverse covariates, and high censorship rates. We compare the predictions from our model to three alternative models. Our model outperforms in simulation and is competitive on real datasets. Furthermore, the low-dimensional visualization for diffuse lower-grade glioma displays known subpopulations.     

Nobiletin,a Polymethoxylated Flavone,Inhibits Glioma Cell Growth and Migration via Arresting Cell Cycle and Suppressing MAPK and Akt Pathways

Nobiletin, a bioactive polymethoxylated flavone (5,6,7,8,3^',4^'‐hexamethoxyflavone), is abundant in citrus fruit peel. Although nobiletin exhibits antitumor activity against various cancer cells, the effect of nobiletin on glioma cells remains unclear. The aim of this study was to determine the effects of nobiletin on the human U87 and Hs683 glioma cell lines. Treating glioma cells with nobiletin (20–100 µm ) reduced cell viability and arrested the cell cycle in the G0/G1 phase, as detected using a 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay and propidium iodide (PI) staining, respectively; however, nobiletin did not induce cell apoptosis according to PI‐annexin V double staining. Data from western blotting showed that nobiletin significantly attenuated the expression of cyclin D1, cyclin‐dependent kinase 2, cyclin‐dependent kinase 4, and E2 promoter‐binding factor 1 (E2F1) and the phosphorylation of Akt/protein kinase B and mitogen‐activated protein kinases, including p38, extracellular signal‐regulated kinase, and c‐Jun N‐terminal kinase. Our data also showed that nobiletin inhibited glioma cell migration, as detected by both functional wound healing and transwell migration assays. Altogether, the present results suggest that nobiletin inhibits mitogen‐activated protein kinase and Akt/protein kinase B pathways and downregulates positive regulators of the cell cycle, leading to subsequent suppression of glioma cell proliferation and migration. Our findings evidence that nobiletin may have potential for treating glioblastoma multiforme. Copyright © 2015 John Wiley & Sons, Ltd.     

Current and Investigational Drug Strategies for Glioblastoma

Medical treatments for glioblastoma face several challenges. Lipophilic alkylators remain the mainstay of treatment, emphasising the primacy of good blood–brain barrier penetration. Temozolomide has emerged as a major contributor to improved patient survival. The roles of procarbazine and vincristine in the procarbazine, lomustine and vincristine (PCV) schedule have attracted scrutiny and several lines of evidence now support the use of lomustine as effective single-agent therapy. Bevacizumab has had a convoluted development history, but clearly now has no major role in first-line treatment, and may even be detrimental to quality of life in this setting. In later disease, clinically meaningful benefits are achievable in some patients, but more impressively the combination of bevacizumab and lomustine shows early promise. Over the last decade, investigational strategies in glioblastoma have largely subscribed to the targeted kinase inhibitor paradigm and have mostly failed. Low prevalence dominant driver lesions such as the FGFR-TACC fusion may represent a niche role for this agent class. Immunological, metabolic and radiosensitising approaches are being pursued and offer more generalised efficacy. Finally, trial design is a crucial consideration. Progress in clinical glioblastoma research would be greatly facilitated by improved methodologies incorporating: (i) routine pharmacokinetic and pharmacodynamic assessments by preoperative dosing; and (ii) multi-stage, multi-arm protocols incorporating new therapy approaches and high-resolution biology in order to guide necessary improvements in science.     

Static magnetic fields modulate X-ray-induced DNA damage in human glioblastoma primary cells

Although static magnetic fields (SMFs) are used extensively in the occupational and medical fields, few comprehensive studies have investigated their possible genotoxic effect and the findings are controversial. With the advent of magnetic resonance imaging-guided radiation therapy, the potential effects of SMFs on ionizing radiation (IR) have become increasingly important. In this study we focused on the genotoxic effect of 80 mT SMFs, both alone and in combination with (i.e. preceding or following) X-ray (XR) irradiation, on primary glioblastoma cells in culture. The cells were exposed to: (i) SMFs alone; (ii) XRs alone; (iii) XR, with SMFs applied during recovery; (iv) SMFs both before and after XR irradiation. XR-induced DNA damage was analyzed by Single Cell Gel Electrophoresis assay (comet assay) using statistical tools designed to assess the tail DNA (TD) and tail length (TL) as indicators of DNA fragmentation. Mitochondrial membrane potential, known to be affected by IR, was assessed using the JC-1 mitochondrial probe. Our results showed that exposure of cells to 5 Gy of XR irradiation alone led to extensive DNA damage, which was significantly reduced by post-irradiation exposure to SMFs. The XR-induced loss of mitochondrial membrane potential was to a large extent averted by exposure to SMFs. These data suggest that SMFs modulate DNA damage and/or damage repair, possibly through a mechanism that affects mitochondria.     

Preoperative Cell-Mediated Immune Status of Patients with Malignant Glial Tumors

The leukocyte adherence inhibition assay (LAI) was used to measure cell-mediated immunity in 26 patients with malignant glial neoplasms and in 41 control subjects. A significant inhibition of leukocyte adherence was observed in 21 out of 26 (80%) patients with malignant astrocytic gliomas in the presence of a 3M KC1 extract of glioma tissue compared to that of normal brain extract. Among the control group, no significant difference in the percentage of nonadherent leukocytes (NAL) was noted in the presence of either antigen. To study the specificity of the reaction, 3M KC1 extracts of meningioma, pituitary tumor, carcinoma of breast, carcinomas of lung, melanoma, brain, and heart tissues were employed as nonspecific antigens. Such studies revealed significantly lower values of NAL.

These data indicate that patients with malignant glial neoplasms manifest a cellular-immune response to glioma-associated antigens that can be measured by the tube LAI assay and that LAI assay may render additional useful information in the diagnostic and prognostic evaluation of malignant glial neoplasms.     

IDH1 mutation may not be prognostically favorable in glioblastoma when controlled for tumor location: A case-control study

Isocitrate dehydrogenase 1 (IDH1) mutation is a known prognostic factor in glioblastoma multiforme (GBM). It has been well documented that patients with IDH1 mutant (IDH1-mu) GBM have a better outcome compared to patients with IDH1 wild-type (IDH1-WT) GBM. IDH1-mu tumors have been shown to be more commonly located in the frontal lobe, and less likely to be in multiple lobes. It is unclear whether differential location is part of the prognostically favorable profile of these tumors. We performed a case-control study, matching IDH1-mu GBMs to IDH1-WT GBMs that are controlled for age, sex and tumor location. There were 21 IDH1-mu tumors and 21 matched IDH1-WT tumors. Age, sex and tumor location were matched between the two groups. After controlling for the factors described, the IDH1-mu tumors were more likely to be secondary GBM (61.9% secondary vs. 14.3%, p = 0.004). There was an insignificant trend towards smaller tumor volume in the IDH1-mu group (28.13 ± 6.56 vs. 41.8 ± 7.33 cm³, p = 0.173). Extent of surgical resection was similar in both groups (mean 84.49% vs. 89.89%, p = 0.419). There was no survival advantage for IDH1-mu tumors when controlled for location: 25.2 months overall survival for IDH1-mu patients and 23.6 for IDH1-WT patients, p = 0.794. IDH1 mutation may provide part of its prognostic significance by differential localization of tumor, both making IDH1-mu tumors more amenable to gross total resection and placing these tumors in less eloquent areas, thereby lowering neurological morbidity.