Platelet-derived growth factor and its receptor expression in human oligodendrogliomas

Cellular Localization and Distribution of TGF-β1, GDNF and PDGF-BB in the Adult Primate Central Nervous System

The available data on the localization of transforming growth factor beta1 (TGF-β1), glial cell line-derived neurotrophic factor (GDNF), and platelet-derived growth factor-BB (PDGF-BB) in the adult primate and human central nervous system (CNS) are limited and lack comprehensive and systematic information. This study aimed to investigate the cellular localization and distribution of TGF-β1, GDNF, and PDGF-BB in the CNS of adult rhesus macaque (Macaca mulatta). Seven adult rhesus macaques were included in the study. The protein levels of TGF-β1, PDGF-BB, and GDNF in the cerebral cortex, cerebellum, hippocampus, and spinal cord were analyzed by western blotting. The expression and location of TGF-β1, PDGF-BB, and GDNF in the brain and spinal cord was examined by immunohistochemistry and immunofluorescence staining, respectively. The mRNA expression of TGF-β1, PDGF-BB, and GDNF was detected by in situ hybridization. The molecular weight of TGF-β1, PDGF-BB, and GDNF in the homogenate of spinal cord was 25 KDa, 30 KDa, and 34 KDa, respectively. Immunolabeling revealed GDNF was ubiquitously distributed in the cerebral cortex, hippocampal formation, basal nuclei, thalamus, hypothalamus, brainstem, cerebellum, and spinal cord. TGF-β1 was least distributed and found only in the medulla oblongata and spinal cord, and PDGF-BB expression was also limited and present only in the brainstem and spinal cord. Besides, TGF-β1, PDGF-BB, and GDNF were localized in the astrocytes and microglia of spinal cord and hippocampus, and their expression was mainly found in the cytoplasm and primary dendrites. The mRNA of TGF-β1, PDGF-BB, and GDNF was localized to neuronal subpopulations in the spinal cord and cerebellum. These findings suggest that TGF-β1, GDNF and PDGF-BB may be associated with neuronal survival, neural regeneration and functional recovery in the CNS of adult rhesus macaques, providing the potential insights into the development or refinement of therapies based on these factors.

Diverse roles of tumor-stromal PDGFB-to-PDGFRβ signaling in breast cancer growth and metastasis

Over the last couple of decades, it has become increasingly apparent that the tumor microenvironment (TME) mediates every step of cancer progression and solid tumors are only able to metastasize with a permissive TME. This intricate interaction of cancer cells with their surrounding TME, or stroma, is becoming more understood with an ever greater knowledge of tumor-stromal signaling pairs such as platelet-derived growth factors (PDGF) and their cognate receptors. We and others have focused our research efforts on understanding how tumor-derived PDGFB activates platelet-derived growth factor receptor beta (PDGFRβ) signaling specifically in the breast cancer TME. In this chapter, we broadly discuss PDGF and PDGFR expression patterns and signaling in normal physiology and breast cancer. We then detail the expansive roles played by the PDGFB-to-PDGFRβ signaling pathway in modulating breast tumor growth and metastasis with a focus on specific cellular populations within the TME, which are responsive to tumor-derived PDGFB. Given the increasingly appreciated importance of PDGFB-to-PDGFRβ signaling in breast cancer progression, specifically in promoting metastasis, we end by discussing how therapeutic targeting of PDGFB-to-PDGFRβ signaling holds great promise for improving current breast cancer treatment strategies.

MicroRNA-29a inhibits glioblastoma stem cells and tumor growth by regulating the PDGF pathway

BACKGROUND AND PURPOSE

microRNAs are small noncoding RNAs that play important roles in cancer regulation. In this study, we investigated the expression, functional effects and mechanisms of action of microRNA-29a (miR-29a) in glioblastoma (GBM).

METHODS

miR-29a expression levels in GBM cells, stem cells (GSCs) and human tumors as well as normal astrocytes and normal brain were measured by quantitative PCR. miR-29a targets were uncovered by target prediction algorithms, and verified by immunoblotting and 3' UTR reporter assays. The effects of miR-29a on cell proliferation, death, migration and invasion were assessed with cell counting, Annexin V-PE/7AAD flow cytometry, scratch assay and transwell assay, respectively. Orthotopic xenografts were used to determine the effects of miR-29a on tumor growth.

RESULTS

Mir-29a was downregulated in human GBM specimens, GSCs and GBM cell lines. Exogenous expression of miR-29a inhibited GSC and GBM cell growth and induced apoptosis. miR-29a also inhibited GBM cell migration and invasion. PDGFC and PDGFA were uncovered and validated as direct targets of miR-29a in GBM. miR-29a downregulated PDGFC and PDGFA expressions at the transcriptional and translational levels. PDGFC and PDGFA expressions in GBM tumors, GSCs, and GBM established cell lines were higher than in normal brain and human astrocytes. Mir-29a expression inhibited orthotopic GBM xenograft growth.

CONCLUSIONS

miR-29a is a tumor suppressor miRNA in GBM, where it inhibits cancer stem cells and tumor growth by regulating the PDGF pathway.

Phase I-II trial of imatinib mesylate (Gleevec; STI571) in treatment of recurrent oligodendroglioma and mixed oligoastrocytoma. North central cancer treatment group study N0272 (ALLIANCE/NCCTG)

PURPOSE

To evaluate the pharmacokinetics and efficacy of imatinib in patients with recurrent oligodendroglial tumors.

METHODS

Patients with progressive WHO grade II-III recurrent tumors after prior RT and chemotherapy were eligible. A phase I dose-escalation study was conducted for patients on enzyme-inducing anticonvulsants (EIAC). A phase II study for non-EIAC patients utilized a fixed dose of 600 mg/D. Primary efficacy endpoint was 6-month progression-free survival (PFS6). A 2-stage design was utilized, with 90% power to detect PFS6 increase from 25 to 45%.

RESULTS

In the Phase I, maximum tolerated dose was not reached at 1200 mg/D. For phase II patients, overall PFS6 was 33% and median PFS 4.0 months (95% CI 2.1, 5.7). Median overall survival (OS) was longer in imatinib-treated patients compared with controls (16.6 vs. 8.0 months; HR = 0.64, 95% CI 0.41,1.0, p = 0.049), and longer in patients with 1p/19q-codeleted tumors (19.2 vs. 6.2 months, HR = 0.43, 95% CI 0.21,0.89, p = 0.019). Confirmed response rate was 3.9% (PR = 1; REGR = 1), with stable disease observed in 52.9%. At 600 mg/D, mean steady-state imatinib plasma concentration was 2513 ng/ml (95% CI 1831,3195). Grade 3-4 adverse events (hematologic, fatigue, GI, hypophosphatemia, or hemorrhage) occurred in 61%.

CONCLUSIONS

Although adequate plasma levels were achieved, the observed PFS6 of 33% did not reach our pre-defined threshold for success. Although OS was longer in imatinib-treated patients than controls, this finding would require forward validation in a larger cohort. Imatinib might show greater activity in a population enriched for PDGF-dependent pathway activation in tumor tissue.

Determination of genetic aberrations and novel transcripts involved in the pathogenesis of oligodendroglioma using array comparative genomic hybridization and next generation sequencing

The aim of the present study was to determine the genetic aberrations and novel transcripts, particularly the fusion transcripts, involved in the pathogenesis of low-grade and anaplastic oligodendroglioma. In the present study, tissue samples were obtained from patients with oligodendroglioma and additionally from archived tissue samples from the Brain Tumor Tissue Bank of the Brain Tumor Foundation of Canada. Six samples were obtained, three of which were low-grade oligodendroglioma and the other three anaplastic oligodendroglioma. DNA and RNA were extracted from each tissue sample. The resulting genomic DNA was then hybridized using the Agilent CytoSure 4×180K oligonucleotide array. Human reference DNA and samples were labeled using Cy3 cytidine 5′-triphosphate (CTP) and Cy5 CTP, respectively, while human Cot-1 DNA was used to reduce non-specific binding. Microarray-based comparative genomic hybridization data was then analyzed for genetic aberrations using the Agilent Cytosure Interpret software v3.4.2. The total RNA isolated from each sample was mixed with oligo dT magnetic beads to enrich for poly(A) mRNA. cDNAs were then synthesized and subjected to end-repair, poly(A) addition and connected using sequencing adapters using the Illumina TruSeq RNA Sample Preparation kit. The fragments were then purified and selected as templates for polymerase chain reaction amplification. The final library was constructed with fragments between 350–450 base pairs and sequenced using deep transcriptome sequencing on an Illumina HiSeq 2500 sequencer. The array comparative genomic hybridization revealed numerous amplifications and deletions on several chromosomes in all samples. However, the most interesting result was from the next generation sequencing, where one anaplastic oligodendroglioma sample was demonstrated to have five novel fusion genes that may potentially serve a critical role in tumor pathogenesis and progression.

Cell Signaling Pathways in Brain Tumors

Primary brain tumors, particularly glioblastoma, are associated with significant morbidity and are often recalcitrant to standard therapies. In recent years, brain tumors have been the focus of large-scale genomic sequencing efforts, providing unprecedented insight into the genomic aberrations and cellular signaling mechanisms that drive these cancers. Discoveries from these efforts have translated into novel diagnostic algorithms, biomarkers, and therapeutic strategies in Neuro-Oncology. However, the cellular mechanisms that drive brain tumors are heterogeneous and complex: applying this new knowledge to improve patient outcomes remains a challenge. Efforts to characterize and target these molecular vulnerabilities are evolving.

Transcriptional co-activator TAZ sustains proliferation and tumorigenicity of neuroblastoma by targeting CTGF and PDGF-β

Neuroblastoma is a common childhood malignant tumor originated from the neural crest-derived sympathetic nervous system. A crucial event in the pathogenesis of neuroblastoma is to promote proliferation of neuroblasts, which is closely related to poor survival. However, mechanisms for regulation of cell proliferation and tumorigenicity in neuroblastoma are not well understood. Here, we report that overexpression of TAZ in neuroblastoma BE(2)-C cells causes increases in cell proliferation, self renewal and colony formation, which was restored back to its original levels by knockdown of TAZ in TAZ-overexpression cells. Inhibition of endogenous TAZ attenuated cell proliferation, colony formation and tumor development in neuroblastoma SK-N-AS cell, which could be rescued by re-introduction of TAZ into TAZ-knockdown cells. In addition, we found that overexpressing TAZ-mediated induction of CTGF and PDGF-β expression, cell proliferation and colony formation were inhibited by knocking down CTGF and PDGF-β with siRNA in TAZ-overexpressing cell. Overall, our findings suggested that TAZ plays an essential role in regulating cell proliferation and tumorigenesis in neuroblastoma cells. Thus, TAZ seems to be a novel and promising target for the treatment of neuroblastoma.

Glioblastoma: pathology, molecular mechanisms and markers

Recent advances in genomic technology have led to a better understanding of key molecular alterations that underlie glioblastoma (GBM). The current WHO-based classification of GBM is mainly based on histologic features of the tumor, which frequently do not reflect the molecular differences that describe the diversity in the biology of these lesions. The current WHO definition of GBM relies on the presence of high-grade astrocytic neoplasm with the presence of either microvascular proliferation and/or tumor necrosis. High-throughput analyses have identified molecular subtypes and have led to progress in more accurate classification of GBM. These findings, in turn, would result in development of more effective patient stratification, targeted therapeutics, and prediction of patient outcome. While consensus has not been reached on the precise nature and means to sub-classify GBM, it is clear that IDH-mutant GBMs are clearly distinct from GBMs without IDH1/2 mutation with respect to molecular and clinical features, including prognosis. In addition, recent findings in pediatric GBMs regarding mutations in the histone H3F3A gene suggest that these tumors may represent a 3rd major category of GBM, separate from adult primary (IDH1/2 wt), and secondary (IDH1/2 mut) GBMs. In this review, we describe major clinically relevant genetic and epigenetic abnormalities in GBM-such as mutations in IDH1/2, EGFR, PDGFRA, and NF1 genes-altered methylation of MGMT gene promoter, and mutations in hTERT promoter. These markers may be incorporated into a more refined classification system and applied in more accurate clinical decision-making process. In addition, we focus on current understanding of the biologic heterogeneity and classification of GBM and highlight some of the molecular signatures and alterations that characterize GBMs as histologically defined. We raise the question whether IDH-wild type high grade astrocytomas without microvascular proliferation or necrosis might best be classified as GBM, even if they lack the histologic hallmarks as required in the current WHO classification. Alternatively, an astrocytic tumor that fits the current histologic definition of GBM, but which shows an IDH mutation may in fact be better classified as a distinct entity, given that IDH-mutant GBM are quite distinct from a biological and clinical perspective.

In vivo modeling of malignant glioma: the road to effective therapy

Despite an increased emphasis on developing new therapies for malignant gliomas, they remain among the most intractable tumors faced today as they demonstrate a remarkable ability to evade current treatment strategies. Numerous candidate treatments fail at late stages, often after showing promising preclinical results. This disconnect highlights the continued need for improved animal models of glioma, which can be used to both screen potential targets and authentically recapitulate the human condition. This review examines recent developments in the animal modeling of glioma, from more established rat models to intriguing new systems using Drosophila and zebrafish that set the stage for higher throughput studies of potentially useful targets. It also addresses the versatility of mouse modeling using newly developed techniques recreating human protocols and sophisticated genetically engineered approaches that aim to characterize the biology of gliomagenesis. The use of these and future models will elucidate both new targets and effective combination therapies that will impact on disease management.

FoxM1 Drives a Feed-Forward STAT3-Activation Signaling Loop That Promotes the Self-Renewal and Tumorigenicity of Glioblastoma Stem-like Cells

The growth factor PDGF controls the development of glioblastoma (GBM), but its contribution to the function of GBM stem-like cells (GSC) has been little studied. Here, we report that the transcription factor FoxM1 promotes PDGFA-STAT3 signaling to drive GSC self-renewal and tumorigenicity. In GBM, we found a positive correlation between expression of FoxM1 and PDGF-A. In GSC and mouse neural stem cells, FoxM1 bound to the PDGF-A promoter to upregulate PDGF-A expression, acting to maintain the stem-like qualities of GSC in part through this mechanism. Analysis of the human cancer genomic database The Cancer Genome Atlas revealed that GBM expresses higher levels of STAT3, a PDGF-A effector signaling molecule, as compared with normal brain. FoxM1 regulated STAT3 transcription through interactions with the β-catenin/TCF4 complex. FoxM1 deficiency inhibited PDGF-A and STAT3 expression in neural stem cells and GSC, abolishing their stem-like and tumorigenic properties. Further mechanistic investigations defined a FoxM1-PDGFA-STAT3 feed-forward pathway that was sufficient to confer stem-like properties to glioma cells. Collectively, our findings showed how FoxM1 activates expression of PDGF-A and STAT3 in a pathway required to maintain the self-renewal and tumorigenicity of glioma stem-like cells.

The molecular biology of WHO grade II gliomas

The WHO grading scheme for glial neoplasms assigns Grade II to 5 distinct tumors of astrocytic or oligodendroglial lineage: diffuse astrocytoma, oligodendroglioma, oligoastrocytoma, pleomorphic xanthoastrocytoma, and pilomyxoid astrocytoma. Although commonly referred to collectively as among the "low-grade gliomas," these 5 tumors represent molecularly and clinically unique entities. Each is the subject of active basic research aimed at developing a more complete understanding of its molecular biology, and the pace of such research continues to accelerate. Additionally, because managing and predicting the course of these tumors has historically proven challenging, translational research regarding Grade II gliomas continues in the hopes of identifying novel molecular features that can better inform diagnostic, prognostic, and therapeutic strategies. Unfortunately, the basic and translational literature regarding the molecular biology of WHO Grade II gliomas remains nebulous. The authors' goal for this review was to present a comprehensive discussion of current knowledge regarding the molecular characteristics of these 5 WHO Grade II tumors on the chromosomal, genomic, and epigenomic levels. Additionally, they discuss the emerging evidence suggesting molecular differences between adult and pediatric Grade II gliomas. Finally, they present an overview of current strategies for using molecular data to classify low-grade gliomas into clinically relevant categories based on tumor biology.

Platelet-derived growth factor in glioblastoma-driver or biomarker?

The platelet-derived growth factor (PDGF) family of mitogens exerts vital functions during embryonal development, e.g. in the central nervous system, where PDGF drives the proliferation of oligodendrocyte precursors. PDGF and PDGF receptors are co-expressed in human glioblastoma (GBM). Whether an aberrant activation of the PDGF receptor pathway is a driving force in glioma development has remained an open question. In experimental animals, overexpression of PDGF has convincingly been shown to induce tumors, both in wild-type animals (marmoset, rat, mouse) and in mice with targeted deletions of suppressor genes, e.g. Tp53 or Ink4A. Targeting the PDGF receptor in tumor-bearing mice leads to growth inhibition and reversion of the transformed phenotype. Findings of PDGF receptor amplification or mutations in human GBM are strong indicators of a causative role of the PDGF receptor pathway. However, clinical trials using PDGF receptor antagonists have been disappointing. In conclusion, a PDGF receptor profile may be a biomarker for a subgroup of GBM originating from a PDGF receptor-responsive cell. Although compelling experimental and clinical evidence supports the notion that the PDGF receptor pathway is a driver in GBM, formal proof is still missing.

The methylation status of the platelet-derived growth factor-B gene promoter and its regulation of cellular proliferation following folate treatment in human glioma cells

Platelet-derived growth factor-B (PDGF-B) is a growth factor that regulates cell migration, proliferation, and differentiation, and is involved in several physical and pathological processes. The overexpression of PDGF-B in glioma surgical samples revealed its effect on tumorigenesis. In this study, we determined that the expression of PDGF-B in 54 glioma samples varied among different grades and was correlated with the cell proliferation marker, Ki-67. Using pyrosequencing, we quantitatively assessed PDGF-B gene methylation levels and determined that hypomethylation promotes increased expression of PDGF-B in higher grade gliomas. Furthermore, we treated two glioma cell lines with a demethylating agent (5-aza-2'-deoxycitidine, 5-aza-dC) or a remethylating agent (folate) to alter the methylation status of PDGF-B. The epigenetic regulation of the PDGF-B gene not only modulated the expression levels of PDGF-B but also affected the cellular proliferation induced by TGFβ-Smad activity and the PDGF-B peptide itself. Our work showed the importance of the methylation status of the PDGF-B gene promoter, and suggests that the epigenetic regulation of the PDGF-B gene may serve as a potential therapeutic target for the inhibition of glioma proliferation.

Targeting the PDGF signaling pathway in tumor treatment

Platelet-derived growth factor (PDGF) isoforms and PDGF receptors have important functions in the regulation of growth and survival of certain cell types during embryonal development and e.g. tissue repair in the adult. Overactivity of PDGF receptor signaling, by overexpression or mutational events, may drive tumor cell growth. In addition, pericytes of the vasculature and fibroblasts and myofibroblasts of the stroma of solid tumors express PDGF receptors, and PDGF stimulation of such cells promotes tumorigenesis. Inhibition of PDGF receptor signaling has proven to useful for the treatment of patients with certain rare tumors. Whether treatment with PDGF/PDGF receptor antagonists will be beneficial for more common malignancies is the subject for ongoing studies.

The molecular landscape of diffuse glioma and prospects for biomarker development

INTRODUCTION

High-throughput molecular profiling is transforming long-standing conceptions of diffuse gliomas, the most common primary brain tumors. Indeed, comprehensive genomic, transcriptomic and epigenomic analyses have not only provided striking mechanistic insights into the pathogenesis of diffuse gliomas but also greatly enriched the pool of potential biomarkers for prognostic and predictive patient stratification.

AREAS COVERED

This article summarizes significant recent developments in the molecular characterization of diffuse gliomas, focusing on implications for biomarker development and application. In doing so, we will also address relevant high-throughput molecular profiling technologies and both the opportunities and challenges implicit in their widespread incorporation into disease management workflows.

EXPERT OPINION

Although the number of validated biomarkers guiding diffuse glioma management is currently quite small, rapidly progressing molecular annotation continues to provide a steady stream of clinically relevant candidates, many of which show promise for predictive capabilities in the context of specific targeted therapeutics. Such potential now requires rigorous validation in well-designed clinical trials supported by robust molecular profiling assays operative from standard clinical material.

Lrig2-deficient mice are protected against PDGFB-induced glioma

Background

The leucine-rich repeats and immunoglobulin-like domains (LRIG) proteins constitute an integral membrane protein family that has three members: LRIG1, LRIG2, and LRIG3. LRIG1 negatively regulates growth factor signaling, but little is known regarding the functions of LRIG2 and LRIG3. In oligodendroglial brain tumors, high expression of LRIG2 correlates with poor patient survival. Lrig1 and Lrig3 knockout mice are viable, but there have been no reports on Lrig2-deficient mice to date.

Methodology/Principal Findings

Lrig2-deficient mice were generated by the ablation of Lrig2 exon 12 (Lrig2E12). The Lrig2E12-/- mice showed a transiently reduced growth rate and an increased spontaneous mortality rate; 20-25% of these mice died before 130 days of age, with the majority of the deaths occurring before 50 days. Ntv-a transgenic mice with different Lrig2 genotypes were transduced by intracranial injection with platelet-derived growth factor (PDGF) B-encoding replication-competent avian retrovirus (RCAS)-producing DF-1 cells. All injected Lrig2E12+/+ mice developed Lrig2 expressing oligodendroglial brain tumors of lower grade (82%) or glioblastoma-like tumors of higher grade (18%). Lrig2E12-/- mice, in contrast, only developed lower grade tumors (77%) or had no detectable tumors (23%). Lrig2E12-/- mouse embryonic fibroblasts (MEF) showed altered induction-kinetics of immediate-early genes Fos and Egr2 in response to PDGF-BB stimulation. However, Lrig2E12-/- MEFs showed no changes in Pdgfrα or Pdgfrβ levels or in levels of PDGF-BB-induced phosphorylation of Pdgfrα, Pdgfrβ, Akt, or extracellular signal-regulated protein kinases 1 and 2 (ERK1/2). Overexpression of LRIG1, but not of LRIG2, downregulated PDGFRα levels in HEK-293T cells.

Conclusions

The phenotype of Lrig2E12-/- mice showed that Lrig2 was a promoter of PDGFB-induced glioma, and Lrig2 appeared to have important molecular and developmental functions that were distinct from those of Lrig1 and Lrig3.

Prevalence, clinico-pathological value, and co-occurrence of PDGFRA abnormalities in diffuse gliomas

PDGFRA is a critical gene in glioma biology. Similar to EGFR, PDGFRA has been shown to be overexpressed, amplified, mutated, or truncated in gliomas, particularly glioblastomas. In addition, PDGFRA has been recently shown to be rearranged in glioblastoma. However, the frequency, cooccurrence, and clinical value of PDGFRA abnormalities in diffuse gliomas remain unclear. We investigated PDGFRA abnormalities and their clinical impact on 619 primary diffuse gliomas, including 167 grade II, 168 grade III, and 284 grade IV gliomas, with use of BAC-aCGH and validated our findings by quantitative polymerase chain reaction (PCR). We studied PDGFRA expression using reverse-transcription quantitative PCR in 84 gliomas and 12 non-tumor samples. In 138 samples, we also screened PDGFRA point mutations in exons 5, 7, 8, 9, 10, 11, and 23; presence of KDR-PDGFRA fusion gene; and PDGFRA truncation. PDGFRA was amplified and gained in 5.2% and 1.9% of samples, respectively. In addition PDGFRA was point-mutated, rearranged, and truncated in 2.9%, 0%, and 0.7% of cases, respectively. PDGFRA point mutations were observed exclusively in grade IV gliomas and in 12.5% of PDGFRA-amplified tumors. High-level PDGFRA amplification was associated with PDGFRA overexpression, high malignancy grade, and older patient age. Of interest, high-level PDGFRA amplification has an independent negative prognostic value for progression-free survival and overall survival among patients with grade III tumors. PDGFRA is altered through various genetic mechanisms in a subset of high-grade gliomas in patients who might be ideal candidates for PDGFRA inhibitor treatment, and PDGFRA gene amplification could be used as a prognostic biomarker in anaplastic gliomas.

Prognostic significance of sirtuin 2 protein nuclear localization in glioma: an immunohistochemical study

The sirtuin 2 (SIRT2) protein is a member of the sirtuin family and homologous to Sir2 (silent information regulator 2) of Saccharomyces cerevisiae. To assess the pathobiological significance of SIRT2 protein expression and/or subcellular localization in human glioma, we examined SIRT2 protein expression in human gliomas using a polyclonal anti-SIRT2 antibody and immunohistochemistry. In this study, samples from 23 patients with glioblastoma (GB, grade IV), 8 patients with diffuse astrocytoma (DA, grade II) and 5 healthy individuals were examined. We established a SIRT2 labeling index (SIRT2-LI) that represents the percentage of cells with SIRT2 localized to the nucleus. The mean SIRT2-LI was 65.8±18.6 in GB samples, 41.2±22.8 in DA samples, and 28.6±12.3 in normal control samples. The SIRT2-LI of GB samples was significantly higher than that of normal control samples (P<0.01, Mann-Whitney's U-test) and that of DA samples (P<0.05). Moreover, the SIRT2-LI was positively correlated with malignant progression. Specifically, samples from patients with GB were divided into two groups, low SIRT2-LI (<60%) and high SIRT2-LI (≥60%), and the patients with low SIRT2-LI samples survived significantly longer than patients with high SIRT2-LI samples (P<0.05, Kaplan-Meier method and log-rank test). In conclusion, SIRT2-LI was indicative of glioma malignancy, and it may be predictive of GB patient survival.

Emerging insights into the molecular and cellular basis of glioblastoma

Glioblastoma is both the most common and lethal primary malignant brain tumor. Extensive multiplatform genomic characterization has provided a higher-resolution picture of the molecular alterations underlying this disease. These studies provide the emerging view that "glioblastoma" represents several histologically similar yet molecularly heterogeneous diseases, which influences taxonomic classification systems, prognosis, and therapeutic decisions.

Emerging insights into the molecular and cellular basis of glioblastoma

Glioblastoma is both the most common and lethal primary malignant brain tumor. Extensive multiplatform genomic characterization has provided a higher-resolution picture of the molecular alterations underlying this disease. These studies provide the emerging view that "glioblastoma" represents several histologically similar yet molecularly heterogeneous diseases, which influences taxonomic classification systems, prognosis, and therapeutic decisions.

PDGF and PDGF receptors in glioma

The family of platelet-derived growth factors (PDGFs) plays a number of critical roles in normal embryonic development, cellular differentiation, and response to tissue damage. Not surprisingly, as it is a multi-faceted regulatory system, numerous pathological conditions are associated with aberrant activity of the PDGFs and their receptors. As we and others have shown, human gliomas, especially glioblastoma, express all PDGF ligands and both the two cell surface receptors, PDGFR-α and -β. The cellular distribution of these proteins in tumors indicates that glial tumor cells are stimulated via PDGF/PDGFR-α autocrine and paracrine loops, while tumor vessels are stimulated via the PDGFR-β. Here we summarize the initial discoveries on the role of PDGF and PDGF receptors in gliomas and provide a brief overview of what is known in this field.

Phase II study of Gleevec plus hydroxyurea in adults with progressive or recurrent low-grade glioma

BACKGROUND

We evaluated the efficacy of imatinib plus hydroxyurea in patients with progressive/recurrent low-grade glioma.

METHODS

A total of 64 patients with recurrent/progressive low-grade glioma were enrolled in this single-center study that stratified patients into astrocytoma and oligodendroglioma cohorts. All patients received 500 mg of hydroxyurea twice a day. Imatinib was administered at 400 mg per day for patients not on enzyme-inducing antiepileptic drugs (EIAEDs) and at 500 mg twice a day if on EIAEDs. The primary endpoint was progression-free survival at 12 months (PFS-12) and secondary endpoints were safety, median progression-free survival, and radiographic response rate.

RESULTS

Thirty-two patients were enrolled into each cohort. Eleven patients (17%) had before radiotherapy and 24 (38%) had received before chemotherapy. The median PFS and PFS-12 were 11 months and 39%, respectively. Outcome did not differ between the histologic cohorts. No patient achieved a radiographic response. The most common grade 3 or greater adverse events were neutropenia (11%), thrombocytopenia (3%), and diarrhea (3%).

CONCLUSIONS

Imatinib plus hydroxyurea was well tolerated among recurrent/progressive LGG patients but this regimen demonstrated negligible antitumor activity.

Molecular biology of glioma

Glioblastoma (GBM) is the most aggressive form of glioma. Despite ceaseless efforts by researchers and physicians to find new therapeutic strategies, there have been no significant advances in the treatment of GBMs for several decades and most patients with GBM die within one and half years of diagnosis. Undoubtedly, one reason for this is the insufficient understanding of the initiation and progression of GBMs at the molecular level. However, recent information regarding the genetic and epigenetic alterations and the microRNAs that are aberrantly activated or inactivated in GBMs has helped elucidate the formation of GBM in more detail. Here, we describe recent advances in the understanding of the biology of GBMs.

Inhibitors of Glioma Growth that Reveal the Tumour to the Immune System

Treated glioblastoma patients survive from 6 to 14 months. In the first part of this review, we describe glioma origins, cancer stem cells and the genomic alterations that generate dysregulated cell division, with enhanced proliferation and diverse response to radiation and chemotherapy. We review the pathways that mediate tumour cell proliferation, neo-angiogenesis, tumor cell invasion, as well as necrotic and apoptotic cell death. Then, we examine the ability of gliomas to evade and suppress the host immune system, exhibited at the levels of antigen recognition and immune activation, limiting the effective signaling between glioma and host immune cells.The second part of the review presents current therapies and their drawbacks. This is followed by a summary of the work of our laboratory during the past 20 years, on oligosaccharide and glycosphingolipid inhibitors of astroblast and astrocytoma division. Neurostatins, the O-acetylated forms of gangliosides GD1b and GT1b naturally present in mammalian brain, are cytostatic for normal astroblasts, but cytotoxic for rat C6 glioma cells and human astrocytoma grades III and IV, with ID50 values ranging from 200 to 450 nM. The inhibitors do not affect neurons or fibroblasts up to concentrations of 4 μM or higher.At least four different neurostatin-activated, cell-mediated antitumoral processes, lead to tumor destruction: (i) inhibition of tumor neovascularization; (ii) activation of microglia; (iii) activation of natural killer (NK) cells; (iv) activation of cytotoxic lymphocytes (CTL). The enhanced antigenicity of neurostatin-treated glioma cells, could be related to their increased expression of connexin 43. Because neurostatins and their analogues show specific activity and no toxicity for normal cells, a clinical trial would be the logical next step.

Platelet-derived growth factor receptor (PDGFR) expression in primary spinal cord gliomas

Abnormal signaling through the platelet-derived growth factor receptor (PDGFR) has been proposed as a possible mechanism of spinal cord glioma initiation and progression. However, the extent of PDGFR expression in human spinal cord gliomas remains unknown. In this study we perform immunohistochemical analysis of PDGFRα expression in a series of 33 primary intramedullary spinal cord gliomas of different types and grades. PDGFRα was seen to be expressed in a significant subset of these tumors across all major glioma types including ependymoma, oligodendroglioma, pilocytic astrocytoma, astrocytoma, and glioblastoma. These results support the hypothesis that growth factor signaling through the PDGFR may be important for the development of at least a subset of human spinal cord gliomas. Further studies investigating the prognostic significance of PDGFR expression as well as the role of PDGF signaling on the development of intramedullary spinal cord gliomas are warranted.

Modeling Adult Gliomas Using RCAS/t-va Technology

Malignant gliomas remain the most devastating childhood and adult tumors of the central nervous system. Although adult and pediatric gliomas are histologically indistinguishable, they differ in location, behavior, and molecular characteristics. This implies that the molecular pathways and pathophysiology of malignant gliomagenesis in these two populations are distinct. Such differences between adult and pediatric gliomas may predict different therapeutic responses. Therefore, accurate genetically engineered models of adult and pediatric gliomas may help understand the biology of these tumors and evaluate therapeutic agents in preclinical studies. It has been proposed that gliomas arise from the subventricular zone in mice during development. Here, we demonstrate that, in adult mice, gliomas may arise not only when injected in the subventricular zone but also when injected in the cortex and cerebellum. Our work demonstrates a versatile and highly reproducible adult mouse model of glioma, which can be easily incorporated into preclinical studies.

Recruited cells can become transformed and overtake PDGF-induced murine gliomas in vivo during tumor progression

Background

Gliomas are thought to form by clonal expansion from a single cell-of-origin, and progression-associated mutations to occur in its progeny cells. Glioma progression is associated with elevated growth factor signaling and loss of function of tumor suppressors Ink4a, Arf and Pten. Yet, gliomas are cellularly heterogeneous; they recruit and trap normal cells during infiltration.

Methodology/Principal Findings

We performed lineage tracing in a retrovirally mediated, molecularly and histologically accurate mouse model of hPDGFb-driven gliomagenesis. We were able to distinguish cells in the tumor that were derived from the cell-of-origin from those that were not. Phenotypic, tumorigenic and expression analyses were performed on both populations of these cells. Here we show that during progression of hPDGFb-induced murine gliomas, tumor suppressor loss can expand the recruited cell population not derived from the cell-of-origin within glioma microenvironment to dominate regions of the tumor, with essentially no contribution from the progeny of glioma cell-of-origin. Moreover, the recruited cells can give rise to gliomas upon transplantation and passaging, acquire polysomal expression profiles and genetic aberrations typically present in glioma cells rather than normal progenitors, aid progeny cells in glioma initiation upon transplantation, and become independent of PDGFR signaling.

Conclusions/Significance

These results indicate that non-cell-of-origin derived cells within glioma environment in the mouse can be corrupted to become bona fide tumor, and deviate from the generally established view of gliomagenesis.

Molecular subclassification of diffuse gliomas: seeing order in the chaos

Diffuse gliomas such as astrocytomas and oligodendrogliomas are the most common form of intrinsic brain tumor in adults. Even within a single pathologic class, these tumors are both histologically and molecularly diverse, although not randomly so. Recent large-scale genomic analyses have revealed patterns of molecular changes within tumor subclasses that harbor distinct underlying biology, clinical prognosis, and pathogenetic routes. Stereotypical mutations in isocitrate dehydrogenase genes (IDH) have been identified in a significant proportion of high-grade gliomas and the large majority of lower-grade astrocytomas and oligodendrogliomas. While the role of IDH mutation in oncogenesis is unclear, it appears to carry a positive prognosis and is also highly associated with other prognostic markers such as MGMT methylation, loss of 1p and 19q chromosome arms, and a newly recognized CpG island methylator phenotype (G-CIMP). This constellation of positive prognostic molecular features is enriched in the transcriptionally defined Proneural glioma subclass and appears to reflect a route of pathogenesis distinct from that taken by other high-grade diffuse gliomas. Another newly discovered and frequent alteration in glioma, deletion or mutation of the NF1 gene, is strongly correlated with the Mesenchymal transcriptomal signature associated with highly aggressive gliomas. Thus, while the unprecedented level of newly available molecular profiling data may seem at first to needlessly balkanize and complicate glioma subclassification, these analyses are in fact providing a more unified picture of key pathogenetic routes and potential avenues for therapeutic intervention. © 2011 Wiley-Liss, Inc.

Genetic modeling of gliomas in mice: new tools to tackle old problems

The recently published comprehensive profiles of genomic alterations in glioma have led to a refinement in our understanding of the molecular events that underlie this cancer. Using state-of-the-art genomic tools, several laboratories have created and characterized accurate genetically engineered mouse models of glioma based on specific genetic alterations observed in human tumors. These in vivo brain tumor models faithfully recapitulate the histopathology, etiology, and biology of gliomas and provide an exceptional experimental system to discover novel therapeutic targets and test therapeutic agents. This review focuses on mouse models of glioma with a special emphasis on genetically engineered models developed around key genetic glioma signature mutations in the PDGFR, EGFR, and NF1 genes and pathways. The resulting animal models have provided insight into many fundamental and mechanistic facets of tumor initiation, maintenance and resistance to therapeutic intervention and will continue to do so in the future.

Persistent roles of signal transduction of platelet-derived growth factor B in genesis, growth, and anaplastic transformation of gliomas in an in-vivo serial transplantation model

We previously reported that retrovirally transduced platelet-derived growth factor-B (PDGFB) in glial progenitors of the rat cerebral white matter, subventricular zone, or brain stem induced malignant brain tumors closely resembling human glioblastoma (GBM). While human GBMs may progress over the period of several months to a few years, prospective, long-term in-vivo observation of histological changes of the tumor tissues is not feasible in these models, because the animals undergo rapid tumor progression and mortality within approximately 1 month. We thus performed successive, long-term in-vivo transplantation of the PDGFB-induced tumor cells into the rat cerebrum. Primary retroviral transduction of PDGFB in the glial progenitors of the rat basal ganglia induced malignant glioma resembling human GBM or anaplastic oligodendroglioma (AOL) consisting of relatively monomorphous tumor cells expressing markers for the oligodendrocyte lineage. In the course of long-term successive transplantation, tumor cells presented pleomorphism as well as focal GFAP expression. This suggests that secondary chromosomal aberration and dysregulation of gene expression following accelerated cell cycle by PDGFB stimulation would induce morphological and immunophenotypic changes in tumor cells. Furthermore, while the primary tumors contained only a minor fraction of proviral GFP-expressing or hemagglutinin-expressing cells, most tumor cells came to express these proviral genes in the course of serial transplantation suggesting a persistent role of PDGFB-expressing cells in maintenance and growth of the tumors. This model would be useful for investigation of the long-term effects of PDGFB stimulation in glioma tissues on anaplastic evolution.

Novel medical therapeutics in glioblastomas, including targeted molecular therapies, current and future clinical trials

The prognosis for glioblastoma is poor despite optimal therapy with surgery, radiation, and chemotherapy. New therapies that improve survival and quality of life are needed. Research has increased our understanding of the molecular pathways important for gliomagenesis and disease progression. Novel agents have been developed against these targets, including receptor tyrosine kinases, intracellular signaling molecules, epigenetic abnormalities, and tumor vasculature and microenvironment. This article reviews novel therapies for glioblastoma, with an emphasis on targeted agents.

PDGF-B-driven gliomagenesis can occur in the absence of the proteoglycan NG2

BACKGROUND

In the last years, the transmembrane proteoglycan NG2 has gained interest as a therapeutic target for the treatment of diverse tumor types, including gliomas, because increases of its expression correlate with dismal prognosis. NG2 has been shown to function as a co-receptor for PDGF ligands whose aberrant expression is common in gliomas. We have recently generated a glioma model based on the overexpression of PDGF-B in neural progenitors and here we investigated the possible relevance of NG2 during PDGF-driven gliomagenesis.

METHODS

The survival curves of NG2-KO mice overexpressing PDGF-B were compared to controls by using a Log-rank test. The characteristics of tumors induced in NG2-KO were compared to those of tumors induced in wild type mice by immunostaining for different cell lineage markers and by transplantation assays in adult mice.

RESULTS

We showed that the lack of NG2 does not appreciably affect any of the characterized steps of PDGF-driven brain tumorigenesis, such as oligodendrocyte progenitor cells (OPC) induction, the recruitment of bystander OPCs and the progression to full malignancy, which take place as in wild type animals.

CONCLUSIONS

Our analysis, using both NG2-KO mice and a miRNA based silencing approach, clearly demonstrates that NG2 is not required for PDGF-B to efficiently induce and maintain gliomas from neural progenitors. On the basis of the data obtained, we therefore suggest that the role of NG2 as a target molecule for glioma treatment should be carefully reconsidered.

Glial progenitors in the brainstem give rise to malignant gliomas by platelet-derived growth factor stimulation

Glial progenitors in the white matter and the subventricular zone are the major population of cycling cells in the postnatal central nervous system, and thought to be candidates for glioma-initiating cells. However, less is known about the dividing cell populations in the brainstem than those in the cerebrum, leading to the lag of basic understanding of brainstem gliomas. We herein demonstrate much fewer cycling glial progenitors exist in the brainstem than in the cerebrum. We also show that infecting brainstem glial progenitors with PDGFB-green fluorescent protein (GFP)-expressing retrovirus induced tumors that closely resembled human malignant gliomas. Of note, brainstem tumors grew more slowly than cerebral tumors induced by the same retrovirus, and >80% tumor cells in the brainstem consisted of GFP-positive, infected progenitors while GFP-positive cells in the cerebral tumors were <20%. These indicate that cerebral tumors progressed rapidly by recruiting resident progenitors via paracrine mechanism whereas brainstem tumors grew more slowly by clonal expansion of the infected population. The cerebral and brainstem glial progenitors similarly showed reversible dedifferentiation upon PDGF stimulation in vitro and did not show the intrinsic difference in terms of the responsiveness to PDGF. We therefore suggest that slower, monoclonal progression pattern of the brainstem tumors is at least partly due to the environmental factors including the cell density of the glial progenitors. Together, these findings are the first implications regarding the cell-of-origin and the gliomagenesis in the brainstem.

Targeting brain cancer: advances in the molecular pathology of malignant glioma and medulloblastoma

Malignant brain tumours continue to be the cause of a disproportionate level of morbidity and mortality across a wide range of individuals. The most common variants in the adult and paediatric populations - malignant glioma and medulloblastoma, respectively - have been the subject of increasingly intensive research over the past two decades that has led to considerable advances in the understanding of their basic biology and pathogenesis. This Review summarizes these developments in the context of the evolving notion of molecular pathology and discusses the implications that this work has on the design of new treatment regimens.

Defective DNA double-strand break repair underlies enhanced tumorigenesis and chromosomal instability in p27-deficient mice with growth factor-induced oligodendrogliomas

The tumor suppressive activities of the Kip-family of cdk inhibitors often go beyond their role in regulating the cell cycle. Here, we demonstrate that p27 enhances Rad51 accumulation during repair of double-strand DNA breaks. Progression of PDGF-induced oligodendrogliomas was accelerated in mice lacking the cyclin-cdk binding activities of p27^kip1. Cell lines were developed from RCAS-PDGF infection of nestin-tv-a brain progenitor cells in culture. p27 deficiency did not affect cell proliferation in early passage cell lines; however, the absence of p27 affected chromosomal stability. In p27 deficient cells, the activation of Atm and Chk2, and the accumulation of γH2AX was unaffected compared to wild type cells, and the number of phospho-histone H3 staining mitotic cells was decreased, consistent with a robust G2/M checkpoint activation. However, the percentage of Rad51 foci positive cells was decreased, and the kinase activity that targets the C-terminus of BRCA2, regulating BRCA2/Rad51 interactions, was increased in lysates derived from p27 deficient cells. Increased numbers of chromatid breaks in p27 deficient cells that adapted to the checkpoint were also observed. These findings suggest that Rad51-dependent repair of double stranded breaks was hindered in p27 deficient cells, leading to chromosomal instability, a hallmark of cancers with poor prognosis.

Molecular neuropathology of low-grade gliomas and its clinical impact

The term "low-grade glioma" refers to a heterogeneous group of slowly growing glial tumors corresponding histologically to World Health Organization (WHO) grade I or II. This group includes astrocytic, oligodendroglial, oligoastrocytic and ependymal tumor entities, most of which preferentially manifest in children and young adults. Depending on histological type and WHO grade, growth patterns of low-grade gliomas are quite variable, with some tumors diffusely infiltrating the surrounding central nervous system tissue and others showing well demarcated growth. Furthermore, some entities tend to recur and show spontaneous malignant progression while others remain stable for many years. This review provides a condensed overview concerning the molecular genetics of different glioma entities subsumed under the umbrella of low-grade glioma. For a better understanding the cardinal epidemiological, histological and immunohistochemical features of each entity are shortly outlined. Multiple cytogenetic, chromosomal and genetic alterations have been identified in low-grade gliomas to date, with distinct genetic patterns being associated with the individual tumor subtypes. Some of these molecular alterations may serve as a diagnostic adjunct for tumor classification in cases with ambiguous histological features. However, to date only few molecular changes have been associated with clinical outcome, such as the combined losses of chromosome arms 1p and 19q as a favorable prognostic marker in patients with oligodendroglial tumors.

Expression of receptor tyrosine kinases VEGFR-1 (FLT-1), VEGFR-2 (KDR), EGFR-1, PDGFRalpha and c-Met in canine primary brain tumours

Inhibition of tumour growth and angiogenesis by targeting key growth factor receptors is a promising therapeutic strategy for central nervous system tumours. Characterization of these growth factor receptors in canine primary brain tumours has not been done. Using quantitative real-time TaqMan polymerase chain reaction (PCR), we evaluated the expression of messenger RNA (mRNA) for five tyrosine kinase growth factor receptors (vascular endothelial growth factor receptor [VEGFR]-1, VEGFR-2, endothelial growth factor receptor [EGFR]-1, platelet-derived growth factor receptor a [PDGFRa], and c-Met) relative to normal cerebral cortex in 66 spontaneous canine primary brain tumours. Increased expression of VEGFR-1 and VEGFR-2 mRNA was greatest in grade IV astrocytomas (glioblastoma multiforme) and grade III (anaplastic) oligodendrogliomas. EGFR-1 mRNA expression was more consistently increased than the other receptors in all tumour types, while increased PDGFRa mRNA expression was mostly restricted to oligodendrogliomas. The similarities in increased expression of these tyrosine kinase growth factor receptors in these canine tumours, as compared to data from their human counterparts, suggest that common molecular mechanisms may be present.

Spontaneous canine gliomas: overexpression of EGFR, PDGFRalpha and IGFBP2 demonstrated by tissue microarray immunophenotyping

Fifty-seven spontaneous canine gliomas were histologically classified and graded using the latest World Health Organization (WHO 2007) criteria for classification of human gliomas. A total of 19 canine astrocytomas were classified as follows: grade IV (GBM) n = 7; grade III n = 5; and grade II, n = 7. Thirty-eight oligodendrogliomas were classified as either grade III (anaplastic) n = 35 or low grade II n = 3. Tissue microarray (TMA) immunohistochemistry was used to evaluate tumor expression of EGFR, PDGFRa and IGFBP2, three key molecules of known pathophysiological importance in human gliomas. Findings were correlated with tumor classification and grade. Increased EGFR expression was demonstrated in 57% of GBMs, 40% of grade III and 28% of grade II astrocytomas. EGFR expression occurred in only 3% of grade III oligodendrogliomas. Increased expression of PDGFRalpha was demonstrated in 43% of GBMs, 20% of grade III, and 14% of grade II astrocytomas. In the oligodendroglioma series, 94% of grade III tumors overexpressed PDGFRalpha. IGFBP2 expression was detected in 71, 60 and 28% of GBMs, grade III and grade II astrocytomas respectively. IGFBP2 expression occurred in 48% of anaplastic and in 33% of low grade oligodendrogliomas. Expression of EGFR, PDGFRalpha or IGFBP2 was not detected in normal canine CNS control TMA cores. The incidence of overexpression of EGFR, PDGFRalpha and IGFBP2 in these canine gliomas closely parallels that in human tumors of similar type and grade. These findings support a role for the spontaneous canine glioma model in directed pathway-targeting therapeutic studies.

Genetic alterations and signaling pathways in the evolution of gliomas

Gliomas are the most common primary brain tumors. They account for more than 70% of all neoplasms of the central nervous system and vary considerably in morphology, location, genetic alterations, and response to therapy. Most frequent and malignant are glioblastomas. The vast majority (>90%) develops rapidly after a short clinical history and without evidence of a less malignant precursor lesion (primary or de novo glioblastoma). Secondary glioblastomas develop more slowly through progression from low-grade or anaplastic astrocytoma. These glioblastoma subtypes constitute distinct disease entities that affect patients of different age, develop through distinct genetic pathways, show different RNA and protein expression profiles, and may differ in their response to radio- and chemotherapy. Recently, isocitrate dehydrogenase 1 (IDH1) mutations have been identified as a very early and frequent genetic alteration in the pathway to secondary glioblastomas as well as that in oligodendroglial tumors, providing the first evidence that low-grade astrocytomas and oligodendrogliomas may share common cells of origin. In contrast, primary glioblastomas very rarely contain IDH1 mutations, suggesting that primary and secondary glioblastomas may originate from different progenitor cells, despite the fact that they are histologically largely indistinguishable. In this review, we summarize the current status of genetic alterations and signaling pathways operative in the evolution of astrocytic and oligodendroglial tumors.

Deregulated signalling networks in human brain tumours

Despite the variety of modern therapies against human brain cancer, in its most aggressive form of glioblastoma multiforme (GBM) it is a still deadly disease with a median survival of approximately 1 year. Over the past 2 decades, molecular profiling of low- and high-grade malignant brain tumours has led to the identification and molecular characterisation of mechanisms leading to brain cancer development, maintenance and progression. Genetic alterations occurring during gliomagenesis lead to uncontrolled tumour growth stimulated by deregulated signal transduction pathways. The characterisation of hyperactivated signalling pathways has identified many potential molecular targets for therapeutic interference in human gliomas. Overexpressed or mutated and constitutively active kinases are attractive targets for low-molecular-weight inhibitors. Although the first attempts with mono-therapy using a single targeted kinase inhibitor were not satisfactory, recent studies based on the simultaneous targeting of several core hyperactivated pathways show great promise for the development of novel therapeutic approaches. This review focuses on genetic alterations leading to the activation of key deregulated pathways in human gliomas.

Cytoplasmic LRIG2 expression is associated with poor oligodendroglioma patient survival

The three leucine-rich repeats and immunoglobulin-like domains (LRIG) genes encode integral membrane proteins. Of these, LRIG1 negatively regulates growth factor signaling and is implicated as a tumor suppressor in certain malignancies. In astrocytic tumors, the subcellular distribution of LRIG proteins is associated with specific clinicopathological features and patient survival. The role of LRIG proteins in oligodendroglioma has not previously been studied. Here we used immunohistochemistry to analyze the expression of the LRIG proteins in 63 oligodendroglial tumors, and evaluated possible associations between LRIG protein expression and clinicopathological parameters. Notably, cytoplasmic LRIG2 expression was found to be an independent prognostic factor associated with poor oligodendroglioma patient survival. This is the first report of an LRIG protein showing a negative effect on survival, suggesting that LRIG2 might have a function different from that of LRIG1, and possibly contributing to the etiology of oligodendroglioma.

Expression, mutation and copy number analysis of platelet-derived growth factor receptor A (PDGFRA) and its ligand PDGFA in gliomas

BACKGROUND

Malignant gliomas are the most prevalent type of primary brain tumours but the therapeutic armamentarium for these tumours is limited. Platelet-derived growth factor (PDGF) signalling has been shown to be a key regulator of glioma development. Clinical trials evaluating the efficacy of anti-PDGFRA therapies on gliomas are ongoing. In this study, we intended to analyse the expression of PDGFA and its receptor PDGFRA, as well as the underlying genetic (mutations and amplification) mechanisms driving their expression in a large series of human gliomas.

METHODS

PDGFA and PDGFRA expression was evaluated by immunohistochemistry in a series of 160 gliomas of distinct World Health Organization (WHO) malignancy grade. PDGFRA-activating gene mutations (exons 12, 18 and 23) were assessed in a subset of 86 cases by PCR-single-strand conformational polymorphism (PCR-SSCP), followed by direct sequencing. PDGFRA gene amplification analysis was performed in 57 cases by quantitative real-time PCR (QPCR) and further validated in a subset of cases by chromogenic in situ hybridisation (CISH) and microarray-based comparative genomic hybridisation (aCGH).

RESULTS

PDGFA and PDGFRA expression was found in 81.2% (130 out of 160) and 29.6% (48 out of 160) of gliomas, respectively. Its expression was significantly correlated with histological type of the tumours; however, no significant association between the expression of the ligand and its receptor was observed. The absence of PDGFA expression was significantly associated with the age of patients and with poor prognosis. Although PDGFRA gene-activating mutations were not found, PDGFRA gene amplification was observed in 21.1% (12 out of 57) of gliomas. No association was found between the presence of PDGFRA gene amplification and expression, excepting for grade II diffuse astrocytomas.

CONCLUSION

The concurrent expression of PDGFA and PDGFRA in different subtypes of gliomas, reinforce the recognised significance of this signalling pathway in gliomas. PDGFRA gene amplification rather than gene mutation may be the underlying genetic mechanism driving PDGFRA overexpression in a portion of gliomas. Taken together, our results could provide in the future a molecular basis for PDGFRA-targeted therapies in gliomas.

Platelet-derived growth factor expression correlates with tumor grade and proliferative activity in human oligodendrogliomas

BACKGROUND

For the last one and a half decade, it has been found that platelet-derived growth factor (PDGF) promotes glial tumor growth through autocrine and paracrine loops, by expression of PDGFalpha receptor (PDGFRalpha) on glioma cells and PDGFbeta receptor (PDGFRbeta) on proliferating endothelial cells. However, studies on oligodendrogliomas, correlating expression of PDGF and its receptor with tumor grade and proliferative activity, through MIB-1 labeling index (LI) are relatively few as compared to astroglial counterpart.

METHODS

Formalin-fixed paraffin-embedded tissues from 55 cases of oligodendrogliomas (34 World Health Organization [WHO] grade II and 21 WHO grade III tumors) were subjected to immunohistochemistry. MIB-1 LI was calculated, and a semiquantitative scoring system for expression of PDGF and PDGFRalpha was used.

RESULTS

MIB-1 LI and PDGF expression increased with histologic grades of malignancy ("t" test, P < .001 and Mann Whitney test, U = 109, P < .001 respectively). The PDGF expression scores had a positive correlation with MIB-1 LI, irrespective of tumor grade (Pearson's correlation coefficient, r = 0.566; P < .001). However, there was no significant difference of PDGFRalpha expression between 2 grades of tumors.

CONCLUSIONS

The results of this study showed that MIB-1 LI is a rapid and cost-effective modality for predicting tumor grade in oligodendrogliomas. Immunohistochemistry for PDGF was found to be useful in differentiating various grades of oligodendroglioma, and therefore, it may be involved in tumor cell proliferation and malignant transformation. Platelet-derived growth factor receptor alpha, although expressed in oligodendroglial neoplasms, was not found to be useful in predicting tumor grade.

Tumor progression and oncogene addiction in a PDGF-B-induced model of gliomagenesis

Platelet-derived growth factor B (PDGF-B) overexpression induces gliomas of different grades from murine embryonic neural progenitors. For the first time, we formally demonstrated that PDGF-B-induced neoplasms undergo progression from nontumorigenic low-grade tumors toward highly malignant forms. This result, showing that PDGF-B signaling alone is insufficient to confer malignancy to cells, entails the requirement for further molecular lesions in this process. Our results indicate that one of these lesions is represented by the down-regulation of the oncosuppressor Btg2. By in vivo transplantation assays, we further demonstrate that fully progressed tumors are PDGF-B-addicted because their tumor-propagating ability is lost when the PDGF-B transgene is silenced, whereas it is promptly reacquired after its reactivation. We provide evidence that this oncogene addiction is not caused by the need for PDGF-B as a mitogen but, rather, to the fact that PDGF-B is required to overcome cell-cell contact inhibition and to confer in vivo infiltrating potential on tumor cells.

Interactions between PTEN and receptor tyrosine kinase pathways and their implications for glioma therapy

Gliomas are the most common and deadly form of malignant primary brain tumors. Loss of the tumor-suppressor PTEN and activation of the receptor tyrosine kinases (RTKs) EGF receptor, c-Met, PDGF receptor and VEGF receptor are among the most common molecular dysfunctions associated with glioma malignancy. PTEN interacts with RTK-dependent signaling at multiple levels. These include the ability of PTEN to counteract PI3K activation by RTKs, as well as possible effects of PTEN on RTK activation of the MAPK pathway and RTK-dependent gene-expression regulation. Consequently, PTEN expression affects RTK-induced malignancy. Importantly, the PTEN status was recently found to be critical for the outcome of RTK-targeted clinical therapies that have been developed recently. Combining RTK-targeted therapies with therapies aimed at counteracting the effects of PTEN loss, such as mTOR inhibition, might also have therapeutic advantage. This article reviews the known molecular and functional interactions between PTEN and RTK pathways and their implications for glioma therapy.

PDGF-B induces a homogeneous class of oligodendrogliomas from embryonic neural progenitors

We describe the generation of mouse gliomas following the overexpression of PDGF-B in embryonic neural progenitors. Our histopathological, immunohistochemical and genome-wide expression analyses revealed a surprising uniformity among PDGF-B induced tumors, despite they were generated by transducing a highly heterogeneous population of progenitor cells known for their ability to produce all the cell types of the central nervous system. Comparison of our microarray data with published gene expression data sets for many different murine neural cell types revealed a closest correlation between our tumor cells and oligodendrocyte progenitor cells, confirming definitively that PDGF-B-induced gliomas are pure oligodendrogliomas. Importantly, we show that this uniformity is likely due to the ability of PDGF-B overexpression to respecify competent embryonic neural precursors toward the oligodendroglial lineage, providing evidence that the transforming activity of PDGF-B is influenced by the developmental potential of the targeted cells. Interestingly, we found that PDGF-B-induced tumors harbor different proliferating cell populations. However only PDGF-B-overexpressing cells are tumorigenic, indicating that paracrine signaling from the tumor is unable to transform bystander cells.