Targeting the epidermal growth factor receptor in high-grade astrocytomas

Role of long noncoding RNAs in the regulation of alternative splicing in glioblastoma

Glioblastoma multiforme (GBM) is a highly severe primary brain tumor. Despite extensive research, effective treatments remain elusive. Long noncoding RNAs (lncRNAs) play a significant role in both cancer and normal biology. They influence alternative splicing (AS), which is crucial in cancer. Advances in lncRNA-specific microarrays and next-generation sequencing have enhanced understanding of AS. Abnormal AS contributes to cancer invasion, metastasis, apoptosis, therapeutic resistance, and tumor development, including glioma. lncRNA-mediated AS affects several cellular signaling pathways, promoting or suppressing cancer malignancy. This review discusses the lncRNAs regulating AS in glioblastoma and their mechanisms.

Differences in Extracellular Vesicle Protein Cargo Are Dependent on Head and Neck Squamous Cell Carcinoma Cell of Origin and Human Papillomavirus Status

To identify potential extracellular vesicle (EV) biomarkers in head and neck squamous cell carcinoma (HNSCC), we evaluated EV protein cargo and whole cell lysates (WCL) from HPV-positive and -negative HNSCC cell lines, as well as normal oral keratinocytes and HPV16-transformed cells. EVs were isolated from serum-depleted, conditioned cell culture media by polyethylene glycol (PEG) precipitation/ultracentrifugation. EV and WCL preparations were analyzed by LC-MS/MS. Candidate proteins detected at significantly higher levels in EV compared with WCL, or compared with EV from normal oral keratinocytes, were identified and confirmed by Wes Simple Western protein analysis. Our findings suggest that these proteins may be potential HNSCC EV markers as proteins that may be (1) selectively included in EV cargo for export from the cell as a strategy for metastasis, tumor cell survival, or modification of tumor microenvironment, or (2) representative of originating cell composition, which may be developed for diagnostic or prognostic use in clinical liquid biopsy applications. This work demonstrates that our method can be used to reliably detect EV proteins from HNSCC, normal keratinocyte, and transformed cell lines. Furthermore, this work has identified HNSCC EV protein candidates for continued evaluation, specifically tenascin-C, HLA-A, E-cadherin, EGFR, EPHA2, and cytokeratin 19.

Alternative RNA Splicing-The Trojan Horse of Cancer Cells in Chemotherapy

Almost all transcribed human genes undergo alternative RNA splicing, which increases the diversity of the coding and non-coding cellular landscape. The resultant gene products might have distinctly different and, in some cases, even opposite functions. Therefore, the abnormal regulation of alternative splicing plays a crucial role in malignant transformation, development, and progression, a fact supported by the distinct splicing profiles identified in both healthy and tumor cells. Drug resistance, resulting in treatment failure, still remains a major challenge for current cancer therapy. Furthermore, tumor cells often take advantage of aberrant RNA splicing to overcome the toxicity of the administered chemotherapeutic agents. Thus, deciphering the alternative RNA splicing variants in tumor cells would provide opportunities for designing novel therapeutics combating cancer more efficiently. In the present review, we provide a comprehensive outline of the recent findings in alternative splicing in the most common neoplasms, including lung, breast, prostate, head and neck, glioma, colon, and blood malignancies. Molecular mechanisms developed by cancer cells to promote oncogenesis as well as to evade anticancer drug treatment and the subsequent chemotherapy failure are also discussed. Taken together, these findings offer novel opportunities for future studies and the development of targeted therapy for cancer-specific splicing variants.

Asymmetric cell division promotes therapeutic resistance in glioblastoma stem cells

Asymmetric cell division (ACD) enables the maintenance of a stem cell population while simultaneously generating differentiated progeny. Cancer stem cells (CSCs) undergo multiple modes of cell division during tumor expansion and in response to therapy, yet the functional consequences of these division modes remain to be determined. Using a fluorescent reporter for cell surface receptor distribution during mitosis, we found that ACD generated a daughter cell with enhanced therapeutic resistance and increased coenrichment of EGFR and neurotrophin receptor (p75NTR) from a glioblastoma CSC. Stimulation of both receptors antagonized differentiation induction and promoted self-renewal capacity. p75NTR knockdown enhanced the therapeutic efficacy of EGFR inhibition, indicating that coinheritance of p75NTR and EGFR promotes resistance to EGFR inhibition through a redundant mechanism. These data demonstrate that ACD produces progeny with coenriched growth factor receptors, which contributes to the generation of a more therapeutically resistant CSC population.

Association of EGFR c.2073A>T Polymorphism with Decreased Risk of Diffusely Infiltrating Astrocytoma in a Brazilian Case-Control Study

Epidermal growth factor receptor (EGFR) gene overexpression has been implicated in the development of many types of tumors, including glioblastomas, the most frequent diffusely infiltrating astrocytomas. However, little is known about the influence of the polymorphisms of EGFR on EGFR production and/or activity, possibly modulating the susceptibility to astrocytomas. This study aimed to examine the association of two EGFR promoter polymorphisms (c-191C>A and c.-216G>T) and the c.2073A>T polymorphism located in exon 16 with susceptibility to astrocytomas, EGFR gene expression and survival in a case-control study of 193 astrocytoma patients and 200 cancer-free controls. We found that the variant TT genotype of the EGFR c.2073A>T polymorphism was associated with a significantly decreased risk of astrocytoma when compared with the AA genotype [sex- and age-adjusted odds ratio 0.51, 95% confidence interval 0.26–0.98]. No association of the two promoter EGFR polymorphisms (or combinations of these polymorphisms) and risk of astrocytomas, EGFR expression or survival was found. Our findings suggest that modulation of the EGFR c.2073A>T polymorphism could play a role in future therapeutic approaches to astrocytoma.

ALA-PpIX mediated photodynamic therapy of malignant gliomas augmented by hypothermia

Background

Malignant gliomas are highly invasive, difficult to treat, and account for 2% of cancer deaths worldwide. Glioblastoma Multiforme (GBM) comprises the most common and aggressive intracranial tumor. The study hypothesis is to investigate the modification of Photodynamic Therapy (PDT) efficacy by mild hypothermia leads to increased glioma cell kill while protecting normal neuronal structures.

Methods

Photosensitizer accumulation and PDT efficacy in vitro were quantified in various glioma cell lines, primary rat neurons, and astrocytes. In vivo studies were carried out in healthy brain and RG2 glioma of naïve Fischer rats. Hypothermia was induced at 1 hour pre- to 2 hours post-PDT, with ALA-PpIX accumulation and PDT treatments effects on tumor and normal brain PDT quantified using optical spectroscopy, histology, immunohistochemistry, MRI, and survival studies, respectively.

Findings

In vitro studies demonstrated significantly improved post-PDT survival in primary rat neuronal cells. Rat in vivo studies confirmed a neuroprotective effect to hypothermia following PpIX mediated PDT by T₂ mapping at day 10, reflecting edema/inflammation volume reduction. Mild hypothermia increased PpIX fluorescence in tumors five-fold, and the median post-PDT rat survival time (8.5 days normothermia; 14 days hypothermia). Histology and immunohistochemistry show close to complete cellular protection in normal brain structures under hypothermia.

Conclusions

The benefits of hypothermia on both normal neuronal tissue as well as increased PpIX fluorescence and RG2 induced rat survival strongly suggest a role for hypothermia in photonics-based surgical techniques, and that a hypothermic intervention could lead to considerable patient outcome improvements.

Complications from pharmacotherapy

The pharmacotherapy management of cancers of the nervous system has significant overlap with systemic solid cancers that may utilize similar drugs or agents. There is however a unique aspect related to central nervous system (CNS) cancers where therapies directed against a malignant process may have enhanced toxicities or toxicities unique to the CNS. In addition, many agents used to treat CNS malignancies have unique CNS toxicities that may require a specific intervention. This chapter attempts to review conventional and biologic therapies utilized for CNS malignancies and characterize expected and, if known, unique toxicities.

Urokinase receptor and resistance to targeted anticancer agents

The urokinase receptor (uPAR) is a GPI-anchored membrane protein, which regulates protease activity at the cell surface and, in collaboration with a system of co-receptors, triggers cell-signaling and regulates gene expression within the cell. In normal tissues, uPAR gene expression is limited; however, in cancer, uPAR is frequently over-expressed and the gene may be amplified. Hypoxia, which often develops in tumors, further increases uPAR expression by cancer cells. uPAR-initiated cell-signaling promotes cancer cell migration, invasion, metastasis, epithelial-mesenchymal transition, stem cell-like properties, survival, and release from states of dormancy. Newly emerging data suggest that the pro-survival cell-signaling activity of uPAR may allow cancer cells to "escape" from the cytotoxic effects of targeted anticancer drugs. Herein, we review the molecular properties of uPAR that are responsible for its activity in cancer cells and its ability to counteract the activity of anticancer drugs.

Activation of EGFR signaling from pilocytic astrocytomas to glioblastomas

INTRODUCTION

EGFR analyses allow for better correlation between genotype and phenotype in astrocytomas and represent an attractive therapeutic target. Most studies emphasize analyses of EGFR in glioblastomas (GBMs) but do not analyze all grades of astrocytomas (from pilocytic to GBM). The purpose of our study was to evaluate the status of EGFR (expression, deletion, and amplification) and EGFR protein expression in all grades of astrocytomas.

PATIENTS AND METHODS

We analyzed a total of 145 surgical tumor specimens that included: 22 pilocytic astrocytomas, 22 grade II astrocytomas, 17 grade III astrocytomas and 84 GBMs. The specimens were compared to 17 non-neoplastic brain tissues obtained from epilepsy surgery. EGFR expression, EGFR amplification and EGFRvIII analyses were performed by quantitative real-time PCR, and protein expression was evaluated by immunohistochemistry.

RESULTS

EGFR relative overexpression and EGFR amplification were observed, respectively, in 50% and 20% of astrocytomas, while EGFRvIII was only found in GBMs (34.5%, p=0.005). Amongst EGFR-amplified GBM cases, 59% also presented EGFRvIII (p<0.001). Cytoplasmic accumulation of EGFR protein was detected in 75% of astrocytomas, and 21% of the astrocytomas showed nuclear localization (p=0.003).

CONCLUSIONS

EGFR alterations were found in all grades of astrocytomas, from pilocytic to GBMs, while EGFRvIII was exclusively found in GBMs. These findings provide important information on the mechanisms involved in the progression of astrocytomas for determining whether EGFR status can be used for effective and specific therapy.

Role of receptor tyrosine kinases and their ligands in glioblastoma

Glioblastoma multiforme is the most frequent, aggressive and fatal type of brain tumor. Glioblastomas are characterized by their infiltrating nature, high proliferation rate and resistance to chemotherapy and radiation. Recently, oncologic therapy experienced a rapid evolution towards “targeted therapy,” which is the employment of drugs directed against particular targets that play essential roles in proliferation, survival and invasiveness of cancer cells. A number of molecules involved in signal transduction pathways are used as molecular targets for the treatment of various tumors. In fact, inhibitors of these molecules have already entered the clinic or are undergoing clinical trials. Cellular receptors are clear examples of such targets and in the case of glioblastoma multiforme, some of these receptors and their ligands have become relevant. In this review, the importance of glioblastoma multiforme in signaling pathways initiated by extracellular tyrosine kinase receptors such as EGFR, PDGFR and IGF-1R will be discussed. We will describe their ligands, family members, structure, activation mechanism, downstream molecules, as well as the interaction among these pathways. Lastly, we will provide an up-to-date review of the current targeted therapies in cancer, in particular glioblastoma that employ inhibitors of these pathways and their benefits.

Therapeutic targeting of EGFR-activated metabolic pathways in glioblastoma

INTRODUCTION

The highly divergent histological heterogeneities, aggressive invasion and extremely poor response to treatment make glioblastoma (GBM) one of the most lethal and difficult cancers in humans. Among key elements driving its behavior is epidermal growth factor receptor (EGFR), however, neither traditional therapy including neurosurgery, radiation, temozolomide, nor targeted EGFR therapeutics in clinic has generated promising results to date. Strategies are now focusing on blocking the downstream EGFR-activated metabolic pathways and the key phosphorylated kinases.

AREAS COVERED

Here, we review two major EGFR-activated downstream metabolic pathways including the PI3K/AKT/mTOR and RAS/RAF/MAPK pathways and their key phosphorylated kinase alterations in GBMs. This review also discusses potential pharmacological progress from bench work to clinical trials in order to evaluate specific inhibitors as well as therapeutics targeting PI3K and RAS signaling pathways.

EXPERT OPINION

Several factors impede clinical progress in targeting GBM, including the high rates of acquired resistance, heterogeneity within and across the tumors, complexity of signaling pathways and difficulty in traversing the blood-brain barrier (BBB). Substantial insight into genetic and molecular pathways and strategies to better tap the potential of these agents include rational combinatorial regimens and molecular phenotype-based patient enrichment, each of which will undoubtedly generate new therapeutic approaches to combat these devastating disabilities in the near future.

Differential effects of low- and high-dose GW2974, a dual epidermal growth factor receptor and HER2 kinase inhibitor, on glioblastoma multiforme invasion

Aberrant expression of epidermal growth factor receptor (EGFR; ErbB1) and HER2 (ErbB2) tyrosine kinases frequently occurs in glioblastoma multiforme (GBM) patients and is considered to be associated with tumor malignancy and poor patient prognosis. In the present study, a dual EGFR and HER2 inhibitor (GW2974) was evaluated for its effects in GBM in vitro and in vivo. Results showed that low-concentration GW2974 inhibited GBM cell invasion, whereas a high concentration of the same compound counteracted this effect. Similar results were observed in an intracranial GBM xenograft model, in which, although both doses of GW2974 slowed tumor growth, no improvement in survival was observed in mice treated with high-dose GW2974, presumably because of the augmentation of tumor invasion. By protein microarray and Western blot analyses, the p38 mitogen-activated protein kinase (MAPK) pathway was found to be activated in GBM cells under high-concentration GW2974. Additionally, blockage of the p38 MAPK pathway reproduced the inhibitory effect of low-concentration GW2974 on cell invasion. These data suggest that the p38 MAPK pathway might contribute to the differential regulation of cell invasion by GW2974. Taken together, our results indicate that GW2974 exerts different effects in GBM depending on drug dosage. This offers a new perspective on the role of GW2974 in tumor progression, providing a potential strategy for GBM treatment based on precise prescription.

A transformation in the mechanism by which the urokinase receptor signals provides a selection advantage for estrogen receptor-expressing breast cancer cells in the absence of estrogen

Binding of urokinase-type plasminogen activator (uPA) to its receptor, uPAR, in estrogen receptor-α (ERα) expressing breast cancer cells, transiently activates ERK downstream of FAK, Src family kinases, and H-Ras. Herein, we show that when uPAR is over-expressed, in two separate ERα-positive breast cancer cell lines, ERK activation occurs autonomously of uPA and is sustained. Autonomous ERK activation by uPAR requires H-Ras and Rac1. A mutated form of uPAR, which does not bind vitronectin (uPAR-W32A), failed to induce autonomous ERK activation. Expression of human uPAR or mouse uPAR but not uPAR-W32A in MCF-7 cells provided a selection advantage when these cells were deprived of estrogen in cell culture for two weeks. Similarly, MCF-7 cells that express mouse uPAR formed xenografts in SCID mice that survived and increased in volume in the absence of estrogen supplementation, probably reflecting the pro-survival activity of phospho-ERK. Autonomous uPAR signaling to ERK was sensitive to the EGFR tyrosine kinase inhibitors, Erlotinib and Gefitinib. The transition in uPAR signaling from uPA-dependent and transient to autonomous and sustained is reminiscent of the transformation in ErbB2/HER2 signaling observed when this gene is amplified in breast cancer. uPAR over-expression may provide a pathway for escape of breast cancer cells from ERα-targeting therapeutics.

Use of magnetic perfusion-weighted imaging to determine epidermal growth factor receptor variant III expression in glioblastoma

Identification of the epidermal growth factor receptor variant III (EGFRvIII) mutation in glioblastoma has become increasingly relevant in the optimization of therapy. Traditionally, determination of tumor EGFRvIII-expression has relied on tissue-based diagnostics. Here, we assess the accuracy of magnetic resonance perfusion-weighted imaging (MR-PWI) in discriminating the EGFRvIII-expressing glioblastoma subtype. We analyzed RNA from 132 primary human glioblastoma tissue samples by reverse-transcription polymerase chain reaction (RT-PCR) for the EGFRvIII and EGFR wild-type mutations and by quantitative RT-PCR for expression of vascular endothelial growth factor (VEGF). Concurrently, 3 independent observers reviewed preoperative 1.5-Tesla (T)/SE or 3.0-Tesla (T)/GE MR perfusion images to determine the maximum relative tumor blood volume (rTBV) of each of these tumors. EGFRvIII-expressing glioblastomas showed significantly higher rTBV, compared with those tumors lacking EGFRvIII expression. This association was observed in both the 1.5T/SE (P = .000) and 3.0T/GE (P = .001) cohorts. By logistic regression analysis, combining the 2 MR system cohorts, rTBV was a very strong predictor of EGFRvIII mutation (odds ratio [rTBV] = 2.70; P = .000; McFadden's ρ(2) = 0.23). Furthermore, by receiver-operating characteristic curve analysis, rTBV discriminated EGFRvIII with very high accuracy (A(z) = 0.81). In addition, we found that VEGF upregulation was associated, although without reaching statistical significance, with EGFRvIII expression (P = .16) and with increased rTBV (F-ratio = 2.71; P = .102). These trends suggest that VEGF-mediated angiogenesis may be a potential mediator of angiogenesis to increase perfusion in EGFRvIII-expressing glioblastomas, but there are likely several other contributing factors. This study demonstrates the potential to use rTBV, a MR-PWI-derived parameter, as a noninvasive surrogate of the EGFRvIII mutation.

Adult diffuse gliomas produce mRNA transcripts encoding EGFR isoforms lacking a tyrosine kinase domain

The epidermal growth factor receptor (EGFR) gene encodes four alternatively spliced mRNA, variants 1, 2, 3 and 4, respectively, encoding the whole isoform a (EGFR) and truncated isoforms b, c and d, all of which lack the receptor’s intracellular domain. In addition, a mutant EGFRvIII differs from isoform a in a truncated extracellular domain. The expression pattern of these isoforms is unknown in adult diffuse gliomas. Thus, we investigated in 47 cases: i) EGFR protein expression by immunohistochemistry using an extracellular domain-recognizing antibody (Ext-Ab) and an intracellular domain specific one (Int-Ab), ii) mRNA expression of EGFRv1, -v2, -v3, -v4 and -vIII by RT-PCR and iii) EGFR amplification by fluorescent in situ hybridization. The relation of these data with histological criteria and patient outcome was studied. The immunostaining was stronger with the Ext-Ab than with the Int-Ab. EGFRv1, -v2, -v3 and -v4 mRNA expression were highly correlated. They were expressed in all tumors, with highest levels in glioblastomas. EGFRv1 strong levels and the presence of vIII mRNAs were more closely associated with Int-Ab staining. EGFR gene amplification concerned only glioblastomas and was associated with the presence of EGFRvIII and high levels of EGFRv2, -v3 and -v4 transcripts. A pejorative outcome was associated with: histology (glioblastomas), EGFR amplification, strong Int-Ab labeling and high levels of variant mRNAs. Our results indicated that the full-length EGFR and mutant EGFRvIII are not the sole EGFR isoform expressed in diffuse gliomas. This could explain discordant immunohistochemical results reported in the literature and may have therapeutic implications.

Crosstalk between the urokinase-type plasminogen activator receptor and EGF receptor variant III supports survival and growth of glioblastoma cells

A truncated and constitutively active form of the EGF receptor, variant III (EGFRvIII), is a major determinant of tumor growth and progression in glioblastoma multiforme (GBM). Extensive bidirectional crosstalk occurs in the cell-signaling pathways downstream of the EGFR and the urokinase-type plasminogen activator receptor (uPAR); however, crosstalk between EGFRvIII and uPAR has not been examined. Here, we show that uPAR does not regulate ERK activation in EGFRvIII-expressing GBM cells; however, in GBM cells isolated from four separate xenografts in which EGFRvIII expression was down-regulated in vivo, uPAR assumed a major role in sustaining ERK activation. Phosphorylation of Tyr-845 in the EGFR, which is mediated by Src family kinases, depended on uPAR in EGFRvIII-expressing GBM cells. Activation of the mitogenic and prosurvival transcription factor, STAT5b, downstream of EGFRvIII, also required uPAR. The EGFR-selective tyrosine kinase inhibitors, erlotinib and gefitinib, blocked not only EGFRvIII signaling to ERK but also uPAR-dependent STAT5b activation. uPAR gene silencing in EGFRvIII-expressing GBM cells and in cells from tumors that escaped dependency on EGFRvIII decreased cell survival and proliferation. Xenografts of EGFRvIII-expressing cancer cell lines and a human GBM, which was propagated as a xenograft, were robustly immunopositive for uPAR and phospho-Tyr-845 by immunohistochemistry. A human GBM in which the EGFR gene was amplified without truncation was immunonegative for both uPAR and phospho-Tyr-845. These studies identify distinct cell-signaling activities for uPAR in GBM cells that express EGFRvIII and in cells released from dormancy when EGFRvIII is neutralized. uPAR and its crosstalk pathways with EGFRvIII emerge as logical targets for therapeutics development in GBM.

Candidate genes influencing sensitivity and resistance of human glioblastoma to Semustine

OBJECTIVE

The prognosis of glioblastoma (GBM) is poor. The therapeutic outcome of conventional surgical and adjuvant treatments remains unsatisfactory, and therefore individualized adjuvant chemotherapy has aroused more attention. Microarrays have been applied to study mechanism of GBM development and progression but it has difficulty in determining responsible genes from the plethora of genes on microarrays unrelated to outcome. The present study was attempted to use bioinformatics method to investigate candidate genes that may influence chemosensitivity of GBM to Semustine (Me-CCNU).

METHODS

Clinical data of 4 GBM patients in Affymetrix microarray were perfected through long-term follow-up study. Differential expression genes between the long- and short-survival groups were picked out, GO-analysis and pathway-analysis of the differential expression genes were performed. Me-CCNU-related signal transduction networks were constructed. The methods combined three steps before were used to screen core genes that influenced Me-CCNU chemosensitivity in GBM.

RESULTS

In Affymetrix microarray there were altogether 2018 differential expression genes that influenced survival duration of GBM. Of them, 934 genes were up-regulated and 1084 down-regulated. They mainly participated in 94 pathways. Me-CCNU-related signal transduction networks were constructed. The total number of genes in the networks was 466, of which 66 were also found in survival duration-related differential expression genes. Studied key genes through GO-analysis, pathway-analysis and in the Me-CCNU-related signal transduction networks, 25 core genes that influenced chemosensitivity of GBM to Me-CCNU were obtained, including TP53, MAP2K2, EP300, PRKCA, TNF, CCND1, AKT2, RBL1, CDC2, ID2, RAF1, CDKN2C, FGFR1, SP1, CDK6, IGFBP3, MDM4, PDGFD, SOCS2, CCNG2, CDK2, SDC2, STMN1, TCF7L1, TUBB.

CONCLUSION

Bioinformatics may help excavate and analyze large amounts of data in microarrays by means of rigorous experimental planning, scientific statistical analysis and collection of complete data about survival of GBM patients. In the present study, a novel differential gene expression pattern was constructed and advanced study will provide new targets for chemosensitivity of GBM.

Epidermal growth factor receptor targeted therapy of squamous cell carcinoma of the head and neck

BACKGROUND

Cumulative evidence implicates the epidermal growth factor receptor (EGFR) as an important therapeutic target in head and neck squamous cell carcinoma (HNSCC). The basis for the lack of correlation between EGFR expression in the HNSCC tumor and clinical responses to EGFR inhibitors is incompletely understood. Although a variety of mechanisms likely contribute to the effectiveness of EGFR blockade, this review focuses on the biologic implications of known EGFR variations and the role of the immune system in mediating clinical responses to EGFR inhibitors.

METHODS

A Medline review of articles published in the last 10 years (1999-present) on EGFR in HNSCC was performed in combination with preliminary data from our laboratories.

RESULTS

Studies published to date suggest no association between the expression of EGFR on HNSCC tumors and clinical responses to EGFR inhibitors. Several mechanisms have been proposed to mediate clinical response to EGFR inhibitors in HNSCC. Cumulative results from our laboratories support the role of several mechanisms, including cellular immune activation and mutated EGFR variants, in contributing to the discrepancy between level of EGFR expression and clinical response to EGFR inhibitors.

CONCLUSION

The efficacy of EGFR targeted therapies may be mediated, at least in part, by the immune system and the presence of the truncated EGFR variant, EGFRvIII, among other factors. Criteria to identify the subset of patients likely to be responsive to EGFR targeted therapies are needed.

Lonafarnib (SCH66336) improves the activity of temozolomide and radiation for orthotopic malignant gliomas

Malignant gliomas are highly lethal tumors resistant to current therapies. The standard treatment modality for these tumors, surgical resection followed by radiation therapy and concurrent temozolomide, has demonstrated activity, but development of resistance and disease progression is common. Although oncogenic Ras mutations are uncommon in gliomas, Ras has been found to be constitutively activated through the action of upstream signaling pathways, suggesting that farnesyltransferase inhibitors may show activity against these tumors. We now report the in vitro and orthotopic in vivo results of combination therapy using radiation, temozolomide and lonafarnib (SCH66336), an oral farnesyl transferase inhibitor, in a murine model of glioblastoma. We examined the viability, proliferation, farnesylation of H-Ras, and activation of downstream signaling of combination-treated U87 cells in vitro. Lonafarnib alone or in combination with radiation and temozolomide had limited tumor cell cytotoxicity in vitro although it did demonstrate significant inhibition in tumor cell proliferation. In vivo, lonafarnib alone had a modest ability to inhibit orthotopic U87 tumors, radiation and temozolomide demonstrated better inhibition, while significant anti-tumor activity was found with concurrent lonafarnib, radiation, and temozolomide, with the majority of animals demonstrating a decrease in tumor volume. The use of tumor neurospheres derived from freshly resected adult human glioblastoma tissue was relatively resistant to both temozolomide and radiation therapy. Lonafarnib had a significant inhibitory activity against these neurospheres and could potentate the activity of temozolomide and radiation. These data support the continued research of high grade glioma treatment combinations of farnesyl transferase inhibitors, temozolomide, and radiation therapy.

Cancer-associated IDH mutations: biomarker and therapeutic opportunities

The discovery of somatic mutations in the isocitrate dehydrogenase (IDH) enzymes through a genome-wide mutational analysis in glioblastoma represents a milestone event in cancer biology. The nature of the heterozygous, point mutations mapping to arginine residues involved in the substrate binding inspired several research teams to investigate their impact on the biochemical activity of these enzymes. Soon, it became clear that the mutations identified impaired the ability of IDH1 and IDH2 to catalyze the conversion of isocitrate to α-ketoglutarate (αKG), whereas conferring a gain of a novel enzymatic activity leading to the reduction of αKG to the metabolite D2-hydroxyglutarate (D-2HG). Across glioma as well as several hematologic malignancies, mutations in IDH1 and IDH2 have shown prognostic value. Several hypotheses implicating the elevated levels of D-2HG and tumorigenesis, and the therapeutic potential of targeting mutant IDH enzymes will be discussed.

The role of sphingosine kinase-1 in EGFRvIII-regulated growth and survival of glioblastoma cells

We have previously shown that high expression levels of the lipid kinase sphingosine kinase-1 (SphK1) correlate with poor survival of glioblastoma (GBM) patients. In this study we examined the regulation of SphK1 expression by epidermal growth factor receptor (EGFR) signaling in GBM cells. As the EGFR gene is often overexpressed and mutated in GBM, and EGFR has been shown to regulate SphK1 in some cell types, we examined the effect of EGF signaling and the constitutively active EGFRvIII mutant on SphK1 in GBM cells. Treatment of glioma cell lines with EGF led to increased expression and activity of SphK1. Expression of EGFRvIII in glioma cells also activated and induced SphK1. In addition, siRNA to SphK1 partially inhibited EGFRvIII-induced growth and survival of glioma cells as well as ERK MAP kinase activation. To further evaluate the connection between EGFR and SphK1 in GBM we examined primary neurosphere cells isolated from fresh human GBM tissue. The GBM-derived neurosphere cell line GBM9, which forms GBM-like tumors intracranially in nude mice, maintained expression of EGFRvIII in culture and had high levels of SphK1 activity. EGFR inhibitors modestly decreased SphK1 activity and proliferation of GBM9 cells. More extensive blockage of SphK1 activity by a SphK inhibitor, potently blocked cell proliferation and induced apoptotic cell death of GBM9 cells. Thus, SphK1 activity is necessary for survival of GBM-derived neurosphere cells, and EGFRvIII partially utilizes SphK1 to further enhance cell proliferation.

Let-7 microRNA inhibits the proliferation of human glioblastoma cells

MicroRNAs (miRNAs) are small noncoding RNAs comprising 21-23 nucleotides that regulate gene expression by transcriptionally repressing their complementary mRNAs. In particular, let-7 miRNA has been postulated to function as a tumor suppressor in various cancer cells, but not yet in glioblastoma. In this study, we investigated the anti-tumorigenic effect of let-7 miRNA in glioblastoma cells. Human glioblastoma cells (U251 or U87 cells) were transfected with let-7 miRNA and assayed for in-vitro proliferation, migration, and in-vivo tumor formation. Transfection of let-7 miRNA reduced expression of pan-RAS, N-RAS, and K-RAS in the glioblastoma cells. Let-7 miRNA also reduced the in-vitro proliferation and migration of the cells, and reduced the sizes of the tumors produced after transplantation into nude mice. However, let-7 miRNA exerted no effect on the proliferation of normal human astrocytes. These results indicate that let-7 miRNA has an anti-tumorigenic effect on glioblastoma cells, and suggest possible use of let-7 miRNA for treating glioblastoma.

ZD6474, a multitargeted inhibitor for receptor tyrosine kinases, suppresses growth of gliomas expressing an epidermal growth factor receptor mutant, EGFRvIII, in the brain

Epidermal growth factor receptor (EGFR) vIII is a mutated EGFR that is frequently overexpressed in glioblastomas and implicated in response to receptor tyrosine kinase inhibitors. In this study, we investigate the effect of ZD6474 (ZACTIMA, vandetanib), a dual inhibitor for vascular endothelial growth factor receptor 2 and EGFR on growth and angiogenesis of gliomas expressing EGFRvIII. We used two glioma xenograft models, U87MG cells overexpressing EGFRvIII and short-term cultured primary glioma GBM8 cells with EGFRvIII. ZD6474 inhibited tumor growth and angiogenesis and induced cell apoptosis in various brain gliomas. Moreover, significant inhibition of EGFRvIII-expressing U87MG and GBM8 gliomas was observed compared with their controls. Magnetic resonance imaging analysis using the apparent diffusion coefficient and three-dimensional T2*weighed measurements validated ZD6474 inhibition on tumor growth and angiogenesis in EGFRvIII-expressing GBM8 gliomas. Mechanistically, ZD6474 shows better inhibition of cell growth and survival of U87MG/EGFRvIII, GBM6, and GBM8 cells that express EGFRvIII than U87MG or GBM14 cells that have nondetectable EGFRvIII through attenuation of activated phosphorylation of signal transducer and activator of transcription 3, Akt, and Bcl-X(L) expression. Albeit in lesser extent, ZD6474 also displays suppressions of U87MG/EGFR and GBM12 cells that overexpress wild-type EGFR. Additionally, ZD6474 inhibits activation of extracellular signal-regulated kinase 1/2 in both types of cells, and expression of a constitutively active phosphoinositide 3-kinases partially rescued ZD6474 inhibition in U87MG/EGFRvIII cells. Taken together, these data show that ZD6474 significantly inhibited growth and angiogenesis of gliomas expressing EGFRvIII by specifically blocking EGFRvIII-activated signaling mediators, suggesting a potential application of ZD6474 in treatments for glioblastomas that overexpress EGFRvIII. Mol Cancer Ther; 9(4); 929-41. (c)2010 AACR.

Epidermal growth factor receptor in glioblastomas: correlation between gene copy number and protein expression

Epidermal growth factor receptor is a transmembrane receptor involved in oncogenesis, including the development of glioblastoma. We studied the prognostic significance of epidermal growth factor receptor amplification as determined by fluorescence in situ hybridization, quantitative polymerase chain reaction, and protein expression by immunohistochemistry. Ninety-nine patients exhibiting glioblastoma were included. Immunohistochemistry was performed on microarray blocks with clone 25, which recognizes both epidermal growth factor receptor wild type and vIII, and scored using a semiquantitative approach. Quantitative polymerase chain reaction and fluorescence in situ hybridization techniques were performed on frozen section: 29.3% of cases had a high epidermal growth factor receptor immunohistochemistry score (score >/=200); and of these cases, 96.5% had gene amplification by fluorescence in situ hybridization and quantitative polymerase chain reaction. Conversely, of cases with a low immunohistochemistry score, 72.9% had normal karyotype or polysomy 7 by fluorescence in situ hybridization technique; but around 25% had gene amplification by fluorescence in situ hybridization and quantitative polymerase chain reaction. In the case of protein overexpression, quantitative polymerase chain reaction and fluorescence in situ hybridization could be avoided in first intention because their positive predictive value for amplification is 97%. In multivariate analysis, there was a trend toward an association between shorter overall survival time and epidermal growth factor receptor amplification as determined by fluorescence in situ hybridization analysis. However, cases with an immunohistochemistry score less 200 require further testing by fluorescence in situ hybridization or quantitative polymerase chain reaction.

Overexpression of c-erbB2 is a negative prognostic factor in anaplastic astrocytomas

The epidermal growth factor receptor (EGFR) family, consisting of four tyrosine kinase receptors, c-erbB1-4, seems to be influential in gliomagenesis. The aim of this study was to investigate EGFR gene amplification and expression of c-erbB1-4 receptor proteins in human anaplastic astrocytomas. Formalin-fixed and paraffin-embedded sections from 31 cases were investigated by standard immunohistochemical procedures for expression of c-erbB1-4 receptor proteins using commercial antibodies. EGFR gene amplification was studied by fluorescence in situ hybridization using paraffin-embedded tissues. Two monoclonal antibodies, NCL-EGFR-384 and NCL-EGFR, were used for EGFR detection and they displayed positive immunoreactivity in 97% and 71%, respectively. For c-erbB2 detection three monoclonal antibodies, CB11, 3B5, and 5A2, were applied and they displayed positive immunoreactivity in 45%, 100%, and 52%, respectively. Positive immunostaining for c-erbB3 and c-erbB4 was encountered in 97% and 74%, respectively. The EGFR gene was amplified in 9 out of 31 tumors (29%). After adjusting for age, Karnofsky performance status, and extent of surgical resection, Cox multiple regression analysis with overall survival as the dependent variable revealed that c-erbB2 overexpression detected by the monoclonal antibody clone CB11 was a statistically significant poor prognostic factor (P = 0.004). This study shows the convenience and feasibility of immunohistochemistry when determining the expression of receptor proteins in tissue sections of human astrocytomas. The synchronous overexpression of c-erbB1-4 proteins in anaplastic astrocytomas supports their role in the pathogenesis of these tumors. Further, c-erbB2 overexpression seems to predict aggressive behaviour.

Nimotuzumab in pediatric glioma

High-grade gliomas and diffuse brainstem gliomas carry a very poor prognosis despite current therapies, and account together for the largest number of deaths in children with brain tumors. Many of these tumors have been found to overexpress the EGF receptor (EGFR). Nimotuzumab (h-R3) is a humanized monoclonal antibody against the EGFR, and consequently inhibits tyrosine kinase activation. In vitro and in vivo studies have supported the antiproliferative, antiangiogenic, pro-apoptotic and radiosensitizing activities of nimotuzumab. Emerging trials suggest a promising role for nimotuzumab as a therapeutic agent in patients with high-grade gliomas. This review attempts to provide a context for the evolving interest and evidence for nimotuzumab in pediatric glioma.

Robust detection of EGFR copy number changes and EGFR variant III: technical aspects and relevance for glioma diagnostics

Epidermal growth factor receptor (EGFR) is commonly affected in cancer, generally in the form of an increase in DNA copy number and/or as mutation variants [e.g., EGFR variant III (EGFRvIII), an in-frame deletion of exons 2-7]. While detection of EGFR aberrations can be expected to be relevant for glioma patients, such analysis has not yet been implemented in a routine setting, also because feasible and robust assays were lacking. We evaluated multiplex ligation-dependent probe amplification (MLPA) for detection of EGFR amplification and EGFRvIII in DNA of a spectrum of 216 diffuse gliomas. EGFRvIII detection was verified at the protein level by immunohistochemistry and at the RNA level using the conventionally used endpoint RT-PCR as well as a newly developed quantitative RT-PCR. Compared to these techniques, the DNA-based MLPA assay for EGFR/EGFRvIII analysis tested showed 100% sensitivity and specificity. We conclude that MLPA is a robust assay for detection of EGFR/EGFRvIII aberrations. While the exact diagnostic, prognostic and predictive value of such EGFR testing remains to be seen, MLPA has great potential as it can reliably and relatively easily be performed on routinely processed (formalin-fixed, paraffin-embedded) tumor tissue in combination with testing for other relevant glioma markers.

Adenoviral virotherapy for malignant brain tumors

Glioblastoma multiforme is the most common form of primary brain cancer. In the past decade, virotherapy of tumors has gained credence, particularly in glioma management, as these tumors are not completely resectable and tend to micro-metastasize. Adenoviral vectors have an advantage over other viral vectors in that they are relatively non-toxic and do not integrate in the genome. However, the lack of coxsackie and adenovirus receptors on surface of gliomas provides for inefficient transduction of wild-type adenoviral vectors in these tumors. By targeting receptors that are overexpressed in gliomas, modified adenoviral constructs have been shown to efficiently infect glioma cells. In addition, by taking advantage of tumor-specific promoter elements, oncolytic adenoviral vectors offer the promise of selective tumor-specific replication. This dual targeting strategy has enabled specificity in both laboratory and pre-clinical settings. This review examines current trends in adenoviral virotherapy of gliomas, with an emphasis on targeting modalities and future clinical applications.

A comprehensive catalogue of functional genetic variations in the EGFR pathway: protein-protein interaction analysis reveals novel genes and polymorphisms important for cancer research

The EGFR pathway is a critical signaling pathway deregulated in many solid tumors. In addition to the initiation and progression of cancer, the EGFR pathway is also implicated in variable treatment responses and prognoses. Genetic variation in the form of Single Nucleotide Polymorphisms (SNPs) can affect the function/expression of the EGFR pathway genes. Here, we applied a systematic and comprehensive approach utilizing diverse public databases and in silico analysis tools to select putative functional genetic variations from 244 genes involved in the EGFR pathway. Our data comprises 649 SNPs. Three hundred sixty SNPs are predicted to have biological consequences (functional SNPs). These SNPs can be directly used in further studies to test their association with risk, treatment response and prognosis in cancer. To systematically cover the EGFR pathway, we also performed a network-based analysis to further select putative functional SNPs from the genes whose protein products physically interact with the EGFR pathway proteins. We utilized protein-protein interaction information and focused on 14 proteins that have a high degree of connectivity (interacting with > or = 10 proteins) with the EGFR pathway genes identified to have functional SNPs (f-EGFR genes). Two of these proteins (FYN and LCK) had interactions with 17 of the f-EGFR genes, yet both lacked any putative functional SNP. However, our analysis indicated the presence of potentially functional SNPs in 9 other highly interactive proteins. The genes and their SNPs identified in the network-based analysis represent potential candidates for gene-gene and SNP-SNP interaction studies in cancer research.

Repeated molecular testing in gliomas: a retrospective study of 53 cases

The value of repeated molecular testing in patients with multiple resections of gliomas is unclear. The purpose of this study was to assess for evidence of molecular changes for chromosome 1p/19q deletions and epidermal growth factor receptor (EGFR) amplification by fluorescence in situ hybridization in 53 glioma cases in which repeated testing was done. Paired results for 1p evaluation demonstrated a change in the profile from intact to loss in 1 (2%) of 50 cases; 19q evaluation demonstrated a change in profile in 4 (10%) of 41 cases. There was no change in the EGFR expression in any of the cases tested. There was no change in the clinical management based on the repeated molecular tests in patients with discrepant repeated results. Hence, there seems to be no indication for reflex repeated 1p/19q or EGFR testing in gliomas at the time of repeated biopsy or resection.

EGF receptor variant III as a target antigen for tumor immunotherapy

The EGF receptor (EGFR) is the first tyrosine kinase receptor ever cloned and remains at the forefront of targeted therapies against cancer. Currently, there are four US FDA-approved drugs and several more in Phase III studies that target the EGFR. These drugs, while resulting in some dramatic remissions, have not resulted in strong nor consistent improvements in survival. EGFR variant III (EGFRvIII) is the most common variant of the EGFR and is present in many different cancer types but not in normal tissue. It results from the fusion of exon 1 to exon 8 of the EGFR gene, which results in a novel glycine at the junction. This mutant receptor is constitutively active in these tumors and can lead directly to cancer phenotypes due to its oncogenic properties. EGFRvIII is an attractive target antigen for cancer immunotherapy because it is not expressed in normal tissue and because cells producing EGFRvIII have an enhanced capacity for dysregulated growth, survival, invasion and angiogenesis. In this review, we will discuss preclinical and clinical data from studies using EGFRvIII as the target antigen for immunotherapy, with a focus on the potential for greatly improved survival for patients diagnosed with glioblastoma multiforme.