Malignant astrocytic gliomas such as glioblastoma are the most common and lethal intracranial tumors. These cancers exhibit a relentless malignant progression characterized by widespread invasion throughout the brain, resistance to traditional and newer targeted therapeutic approaches, destruction of normal brain tissue, and certain death. The recent confluence of advances in stem cell biology, cell signaling, genome and computational science and genetic model systems have revolutionized our understanding of the mechanisms underlying the genetics, biology and clinical behavior of glioblastoma. This progress is fueling new opportunities for understanding the fundamental basis for development of this devastating disease and also novel therapies that, for the first time, portend meaningful clinical responses.Malignant gliomas are classified and subtyped on the basis of histopathological features and clinical presentation (Fig. 1). The most common and biologically aggressive of these is glioblastoma (GBM), World Health Organization (WHO) grade IV, and is defined by the hallmark features of uncontrolled cellular proliferation, diffuse infiltration, propensity for necrosis, robust angiogenesis, intense resistance to apoptosis, and rampant genomic instability. As reflected in the old moniker "multiforme," GBM presents with significant intratumoral heterogeneity on the cytopathological, transcriptional, and genomic levels. This complexity, combined with a putative cancer stem cell (CSC) subpopulation and an incomplete atlas of (epi)genetic lesions driving GBM pathogenesis, has conspired to make this cancer one of the most difficult to understand and to treat. Despite implementation of intensive therapeutic strategies and supportive care, the median survival of GBM has remained at 12 mo over the past decade.In this review, we summarize current basic and translational challenges and highlight the striking scientific advances that promise to improve the clinical course of this lethal disease. These advances include a more comprehensive view of the altered genes and pathways in glioma and how such alterations drive the hallmark pathobiological features of the disease, the identification of new molecular subtypes in GBM, an improved understanding of the cellular origins of the disease and how CSCs may influence therapeutic responses, refined model systems for use in research and preclinical experimental therapeutics, and novel therapeutic strategies for targeting keystone genetic lesions and their pathways. For reasons of length, we have not discussed the advances in such important areas as tumor immunology, the blood-brain barrier, and tumor imaging. For the first time, there is a strong sentiment that meaningful therapeutic advances will soon flow from this explosion of new molecular and biological knowledge; the remarkable technological advances in

Tumor recurrence is a leading cause of cancer mortality. Therapies for recurrent disease may fail, at least in part, because the genomic alterations driving the growth of recurrences are distinct from those in the initial tumor. To explore this hypothesis, we sequenced the exomes of 23 initial low-grade gliomas and recurrent tumors resected from the same patients. In 43% of cases, at least half of the mutations in the initial tumor were undetected at recurrence, including driver mutations in TP53, ATRX, SMARCA4, and BRAF, suggesting recurrent tumors are often seeded by cells derived from the initial tumor at a very early stage of their evolution. Notably, tumors from 6 of 10 patients treated with the chemotherapeutic drug temozolomide (TMZ) followed an alternative evolutionary path to high-grade glioma. At recurrence, these tumors were hypermutated and harbored driver mutations in the RB and AKT-mTOR pathways that bore the signature of TMZ-induced mutagenesis.

Human solid tumors frequently have pronounced heterogeneity of both neoplastic and normal cells on the histological, genetic, and gene expression levels. While current efforts are focused on understanding heterotypic interactions between tumor cells and surrounding normal cells, much less is known about the interactions between and among heterogeneous tumor cells within a neoplasm. In glioblastoma multiforme (GBM), epidermal growth factor receptor gene (EGFR) amplification and mutation (EGFRvIII/DEGFR) are signature pathogenetic events that are invariably expressed in a heterogeneous manner. Strikingly, despite its greater biological activity than wild-type EGFR (wtEGFR), individual GBM tumors expressing both amplified receptors typically express wtEGFR in far greater abundance than the DEGFR lesion. We hypothesized that the minor DEGFR-expressing subpopulation enhances tumorigenicity of the entire tumor cell population, and thereby maintains heterogeneity of expression of the two receptor forms in different cells. Using mixtures of glioma cells as well as immortalized murine astrocytes, we demonstrate that a paracrine mechanism driven by DEGFR is the primary means for recruiting wtEGFR-expressing cells into accelerated proliferation in vivo. We determined that human glioma tissues, glioma cell lines, glioma stem cells, and immortalized mouse Ink4a/Arf À/À astrocytes that express DEGFR each also express IL-6 and/or leukemia inhibitory factor (LIF) cytokines. These cytokines activate gp130, which in turn activates wtEGFR in neighboring cells, leading to enhanced rates of tumor growth. Ablating IL-6, LIF, or gp130 uncouples this cellular cross-talk, and potently attenuates tumor growth enhancement. These findings support the view that a minor tumor cell population can potently drive accelerated growth of the entire tumor mass, and thereby actively maintain tumor cell heterogeneity within a tumor mass. Such interactions between genetically dissimilar cancer cells could provide novel points of therapeutic intervention.[Keywords: Glioblastoma; EGFR; DEGFR; IL-6; LIF; gp130; tumor heterogeneity] Supplemental material is available at http://www.genesdev.org.

Glioblastoma multiforme (GBM) is the most aggressive brain tumor in adults and remains incurable despite multimodal intensive treatment regimens. EGFRvIII is a truncated extracellular mutant of the EGF receptor (EGFR) commonly found in GBMs that confers enhanced tumorigenic behavior. To gain a molecular understanding of the mechanisms by which EGFRvIII acts, we have performed a large-scale analysis of EGFRvIII-activated phosphotyrosinemediated signaling pathways and thereby have identified and quantified 99 phosphorylation sites on 69 proteins. Distinct signaling responses were observed as a function of titrated EGFRvIII receptor levels with the phosphatidylinositol 3-kinase pathway being dominant over the MAPK and STAT3 pathways at a high level of EGFRvIII expression. Within this data set, the activating phosphorylation site on the c-Met receptor was found to be highly responsive to EGFRvIII levels, indicating cross-activation of the c-Met receptor tyrosine kinase by EGFRvIII. To determine the significance of this finding, we devised a combined treatment regimen that used a c-Met kinase inhibitor and either an EGFR kinase inhibitor or cisplatin. This regimen resulted in enhanced cytotoxicity of EGFRvIII-expressing cells compared with treatment with either compound alone. These results suggest that the clinical use of c-Met kinase inhibitors in combination with either EGFR inhibitors or standard chemotherapeutics might represent a previously undescribed therapeutic approach to overcome the observed chemoresistance in patients with GBMs expressing EGFRvIII. mass spectrometry ͉ mutant EGF receptor ͉ signal transduction ͉ tyrosine phosphorylation G lioblastoma multiforme (GBM) is the most aggressive form of adult human brain tumor, with median survival of Ͻ12 months (1). This dismal prognosis is due in part to the lack of therapeutic agents available to eliminate the diffuse glioma infiltrate that remains in the brain after surgical resection. Molecular profiling of genetic lesions in these tumors holds the promise of stratifying tumors into categories amenable to targeted treatment modalities. One such example is the application of EGF receptor (EGFR)-targeted therapeutic agents to treat GBMs that overexpress EGFR. Of these tumors, about half express the deletion mutant EGFRvIII, a truncated extracellular mutant of EGFR lacking exons 2-7, including the extracellular ligand-binding domain. Although EGFRvIII is incapable of binding the EGF family of ligands, it has been shown to be constitutively tyrosine-phosphorylated at Ϸ10% relative to ligand-stimulated wild-type (WT) EGFR (2). This truncated mutant receptor has been exclusively found in tumors, suggesting selection for EGFRvIII during the process of tumorigenesis. Clinical studies have demonstrated a correlation between EGFRvIII expression and poor prognosis for patients with GBM, indicating that it may be important in driving tumorigenic behavior in GBMs.Although much work has been done over the past decade to elucidate pathways involved in EGFRvIII receptor s...

The prognostic impact of TERT mutations has been controversial in IDH-wild tumors, particularly in glioblastomas (GBM). The controversy may be attributable to presence of potential confounding factors such as MGMT methylation status or patients’ treatment. This study aimed to evaluate the impact of TERT status on patient outcome in association with various factors in a large series of adult diffuse gliomas. We analyzed a total of 951 adult diffuse gliomas from two cohorts (Cohort 1, n = 758; Cohort 2, n = 193) for IDH1/2, 1p/19q, and TERT promoter status. The combined IDH/TERT classification divided Cohort 1 into four molecular groups with distinct outcomes. The overall survival (OS) was the shortest in IDH wild-type/TERT mutated groups, which mostly consisted of GBMs (P < 0.0001). To investigate the association between TERT mutations and MGMT methylation on survival of patients with GBM, samples from a combined cohort of 453 IDH-wild-type GBM cases treated with radiation and temozolomide were analyzed. A multivariate Cox regression model revealed that the interaction between TERT and MGMT was significant for OS (P = 0.0064). Compared with TERT mutant-MGMT unmethylated GBMs, the hazard ratio (HR) for OS incorporating the interaction was the lowest in the TERT mutant-MGMT methylated GBM (HR, 0.266), followed by the TERT wild-type-MGMT methylated (HR, 0.317) and the TERT wild-type-MGMT unmethylated GBMs (HR, 0.542). Thus, patients with TERT mutant-MGMT unmethylated GBM have the poorest prognosis. Our findings suggest that a combination of IDH, TERT, and MGMT refines the classification of grade II-IV diffuse gliomas.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0351-2) contains supplementary material, which is available to authorized users.