Inhibition of phosphatidylinositol 3-kinase signaling negates the growth advantage imparted by a mutant epidermal growth factor receptor on human glioblastoma cells

Epidermal Growth Factor Receptor Variant III Mutation, an Emerging Molecular Marker in Glioblastoma Multiforme Patients: A Single Institution Study on the Indian Population

Background

Glioblastoma is the most frequent and the most aggressive primary malignant brain tumor in adults. Standard treatment includes surgical removal of the tumor followed by concomitant chemotherapy and radiotherapy. Temozolomide, an oral alkylating agent, is currently the most commonly used chemotherapy. However, the median survival of glioblastoma multiforme (GBM) patients remains very low. Epidermal growth factor receptor variant III (EGFRvIII) is a novel marker for GBM patients of Indian origin as very few studies have been done on this molecular marker in our country. This is the first study utilizing this molecular marker among GBM patients in Rajasthan, India. This was a single institutional study that aimed to estimate the proportion of EGFRvIII mutation in GBM patients of Indian origin.

Methodology

This was a non-randomized, ambispective, single institutional observational study done on 35 brain tissue biopsies of histopathologically diagnosed and confirmed cases of GBM based on the World Health Organization 2007 Classification received in the pathology department of Dr. Sampurnanand Medical College, Jodhpur from 2015 to 2020 after applying inclusion and exclusion criteria. Molecular study of the EGFRvIII marker was conducted in all cases of GBM in the same institution on the RNA extracted from selected biopsy samples. Statistical analysis was performed using the SPSS version 22.0 software package (IBM Corp., Armonk, NY USA). The correlation between age and gender with EGFR-positive cases was analyzed, and EGFR positivity compared with previous studies.

Results

The occurrence of the EGFRvIII mutation was found to be 17.4% (6/35 cases). The mean age of presentation of a tumor with this mutation was estimated to be 54.3 years. Males were more commonly found to be affected (66.6%, 4/6 cases).

Conclusions

Thus, the identification of this mutation would segregate patients who may benefit from newer therapeutic approaches. In the future, personalized treatment may be advised for GBM patients depending on the presence of the EGFRvIII mutation.

Xyloketal B suppresses glioblastoma cell proliferation and migration in vitro through inhibiting TRPM7-regulated PI3K/Akt and MEK/ERK signaling pathways

Glioblastoma, the most common and aggressive type of brain tumors, has devastatingly proliferative and invasive characteristics. The need for finding a novel and specific drug target is urgent as the current approaches have limited therapeutic effects in treating glioblastoma. Xyloketal B is a marine compound obtained from mangrove fungus Xylaria sp. (No. 2508) from the South China Sea, and has displayed antioxidant activity and protective effects on endothelial and neuronal oxidative injuries. In this study, we used a glioblastoma U251 cell line to (1) explore the effects of xyloketal B on cell viability, proliferation, and migration; and (2) investigate the underlying molecular mechanisms and signaling pathways. MTT assay, colony formation, wound healing, western blot, and patch clamp techniques were employed. We found that xyloketal B reduced cell viability, proliferation, and migration of U251 cells. In addition, xyloketal B decreased p-Akt and p-ERK1/2 protein expressions. Furthermore, xyloketal B blocked TRPM7 currents in HEK-293 cells overexpressing TRPM7. These effects were confirmed by using a TRPM7 inhibitor, carvacrol, in a parallel experiment. Our findings indicate that TRPM7-regulated PI3K/Akt and MEK/ERK signaling is involved in anti-proliferation and migration effects of xyloketal B on U251 cells, providing in vitro evidence for the marine compound xyloketal B to be a potential drug for treating glioblastoma.

Novel therapies in glioblastoma

Conventional treatment of glioblastoma has advanced only incrementally in the last 30 years and still yields poor outcomes. The current strategy of surgery, radiation, and chemotherapy has increased median survival to approximately 15 months. With the advent of molecular biology and consequent improved understanding of basic tumor biology, targeted therapies have become cornerstones for cancer treatment. Many pathways (RTKs, PI3K/AKT/mTOR, angiogenesis, etc.) have been identified in GBM as playing major roles in tumorigenesis, treatment resistance, or natural history of disease. Despite the growing understanding of the complex networks regulating GBM tumors, many targeted therapies have fallen short of expectations. In this paper, we will discuss novel therapies and the successes and failures that have occurred. One clear message is that monotherapies yield minor results, likely due to functionally redundant pathways. A better understanding of underlying tumor biology may yield insights into optimal targeting strategies which could improve the overall therapeutic ratio of conventional treatments.

Both mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinases (ERK) 1/2 and phosphatidylinositide-3-OH kinase (PI3K)/Akt pathways regulate activation of E-twenty-six (ETS)-like transcription factor 1 (Elk-1) in U138 glioblastoma cells

Epidermal growth factor (EGF) and its receptor (EGFR) have been shown to play a significant role in the pathogenesis of glioblastoma. In our study, the EGFR was stimulated with EGF in human U138 glioblastoma cells. We show that the activated mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinases (ERK) 1/2 pathway phosphorylated the E twenty-six (ETS)-like transcription factor 1 (Elk-1) mainly at serine 383 residue. Mitogen-activated protein kinase kinase (MEK) 1/2 inhibitor, UO126 and ERK inhibitor II, FR180204 blocked the Elk-1 phosphorylation and activation. The phosphatidylinositide-3-OH kinase (PI3K)/Akt pathway was also involved in the Elk-1 activation. Activation of the Elk-1 led to an increased survival and a proliferative response with the EGF stimulation in the U138 glioblastoma cells. Knocking-down the Elk-1 using an RNA interference technique caused a decrease in survival of the unstimulated U138 glioblastoma cells and also decreased the proliferative response to the EGF stimulation. The Elk-1 transcription factor was important for the survival and proliferation of U138 glioblastoma cells upon the stimulation of EGFR with EGF. The MAPK/ERK1/2 and PI3K/Akt pathways regulated this response via activation of the Elk-1 transcription factor. The Elk-1 may be one of the convergence points for pathways located downstream of EGFR in glioblastoma cells. Utilization of the Elk-1 as a therapeutic target may lead to a novel strategy in treatment of glioblastoma.

PI3Kinase signaling in glioblastoma

Glioblastoma (GBM) is the most common primary tumor of the CNS in the adult. It is characterized by exponential growth and diffuse invasiveness. Among many different genetic alterations in GBM, e.g., mutations of PTEN, EGFR, p16/p19 and p53 and their impact on aberrant signaling have been thoroughly characterized. A major barrier to develop a common therapeutic strategy is founded on the fact that each tumor has its individual genetic fingerprint. Nonetheless, the PI3K pathway may represent a common therapeutic target to most GBM due to its central position in the signaling cascade affecting proliferation, apoptosis and migration. The read-out of blocking PI3K alone or in combination with other cancer pathways should mainly focus, besides the cytostatic effect, on cell death induction since sublethal damage may induce selection of more malignant clones. Targeting more than one pathway instead of a single agent approach may be more promising to kill GBM cells.

Adenosine diphosphate-ribosylation factor 6 is required for epidermal growth factor-induced glioblastoma cell proliferation

BACKGROUND

: Epidermal growth factor (EGF) signaling plays a pivotal role in gliomagenesis. The authors previously demonstrated that adenosine diphospate-ribosylation factor 6 (ARF6), a member of the Ras-related small guanosine-5'-triphospate-binding protein family, is required for EFA6A-induced glioma cell migration and invasion. However, the role of ARF6 in EGF signaling is unknown.

METHODS

: The authors analyzed messenger RNA (mRNA) levels of ARF6 and EGF receptor (EGFR) in 16 high-grade glioma samples and in 6 low-grade glioma samples by reverse transcriptase-polymerase chain reaction analysis. To determine whether EGF induces ARF6 expression in human glioblastoma U87 cells through transcriptional regulation and EGFR activation, the levels of ARF6 were assayed in EGF-treated U87 cells that were preincubated with a transcriptional inhibitor (actinomycin D) and an EGFR tyrosine kinase inhibitor (PD153035), respectively. The downstream signaling of EGFR-mediated ARF6 up-regulation also was investigated using specific inhibitors of mitogen-activated protein kinase (MEK), phosphatidylinositol 3' kinase (PI3K), and Janus kinase 2. The involvement of SP1 in the downstream signaling was studied by using an SP1 inhibitor (mithramycin A). Small-interfering RNAs (siRNAs) targeting ARF6 were used to investigate the effects of ARF6 on EGF-mediated glioma cell proliferation.

RESULTS

: The results demonstrated that ARF6 and EGFR mRNA levels were elevated in glioma tissues. Furthermore, EGF stimulated ARF6 expression in U87 cells in a dose-dependent and time-dependant manner. This stimulation was caused by increased transcription of ARF6 and by activation of the MEK/extracellular signal-regulated kinase 1 and 2 (ERK1/2) and PI3K signaling pathways. It is noteworthy that SP1 was essential for EGF-induced ARF6 up-regulation. Finally, EGF-induced glioblastoma cell proliferation depended on ARF6, because the suppression of ARF6 by siRNA or by a dominant-negative mutant significantly inhibited EGF-induced cell proliferation.

CONCLUSIONS

: The results of the current study suggested that EGF-induced ARF6 expression plays a significant role in glioma cell proliferation. Cancer 2009. (c) 2009 American Cancer Society.

Activated EGFR signaling increases proliferation, survival, and migration and blocks neuronal differentiation in post-natal neural stem cells

Recent evidence supports the notion that transformation of undifferentiated neural stem cell (NSC) precursors may contribute to the development of glioblastoma multiforme (GBM). The over-expression and mutation of the epidermal growth factor receptor (EGFR), along with other cellular pathway mutations, plays a significant role in GBM maintenance progression. Though EGFR signaling is important in determining neural cell fate and conferring astrocyte differentiation, there is a limited understanding of its role in NSC and tumor stem cell (TSC) biology. We hypothesized that EGFR expression and mutation in post-natal NSCs may contribute to cellular aggressiveness including enhanced cellular proliferation, survival and migration. Stable subclones of C17.2 murine NSCs were transfected to over-express either the wild-type EGFR (wtEGFR) or its most common mutated variant EGFRvIII. Activated EGFR signaling in these cells induced behaviors characteristic of GBM TSCs, including enhanced proliferation, survival and migration, even in the absence of EGF ligand. wtEGFR activation was also found to block neuronal differentiation and was associated with a dramatic increase in chemotaxis in the presence of EGF. EGFRvIII expression lead to an increase in NSC proliferation and survival, while it simultaneously blocked neuronal differentiation and promoted glial fate. Our findings suggest that activated EGFR signaling enhances the aggressiveness of NSCs. Understanding the regulatory mechanisms of NSCs may lend insight into deregulated mechanisms of GBM TSC invasion, proliferation, survival and resistance to current treatment modalities.

Shear Stress Regulates the Flk-1/Cbl/PI3K/NF-κB Pathway Via Actin and Tyrosine Kinases

Vascular endothelial cells (ECs) are continuously exposed to mechanical stimuli (e.g., shear stress). Our previous study has shown that the shear-induced nuclear factor-κB (NF-κB) activation is mediated by integrins [Bhullar, I. S., Y. S. Li, H. Miao, E. Zandi, M. Kim, et al. J. Biol. Chem. 273:30544-30549, 1998]. The shear-activated integrins can also transactivate Flk-1 (a receptor for vascular endothelial growth factor (VEGF)) [Wang, Y., H. Miao, S. Li, K. D. Chen, Y. S. Li, et al. Am. J. Physiol. Cell Physiol. 283:C1540-C1547, 2002], which subsequently recruits Casitas B-lineage lymphoma (Cbl) to regulate inhibitor of κB protein kinase (IKK) [Wang, Y., J. Chang, Y. C. Li, Y. S. Li, J. Y. Shyy, and S. Chien. Am. J. Physiol. Heart Circ. Physiol. 286:H685-H692, 2004], an upstream molecule of NF-κB. Therefore, shear stress may likely utilize the Flk-1/Cbl pathway in regulating NF-κB. In this paper, we confirmed that the inhibition of Flk-1 by its specific inhibitor SU1498 blocked the shear-induced NF-κB translocation. The inhibition of Cbl (an adaptor protein which binds to Flk-1 upon shear) by using a negative mutant (Cbl(nm)) also blocked the promoter activity of NF-κB, and the inhibition of the Cbl-downstream molecule phosphatidylinositol-3-kinase (PI3K) abolished the NF-κB translocation. Further experiments revealed that the disruption of actin cytoskeleton inhibited the Flk-1 and Cbl interaction and NF-κB translocation. The inhibition of focal adhesion kinase (FAK) and Src family kinases, which are involved in the integrin-mediated focal adhesion complex, also blocked the shear-induced NF-κB translocation. Together with our previous findings that integrins mediate the shear-induced activation of Flk-1 and NF-κB [Bhullar, I. S., Y. S. Li, H. Miao, E. Zandi, M. Kim, et al. J. Biol. Chem. 273:30544-30549, 1998; Wang, Y., H. Miao, S. Li, K. D. Chen, Y. S. Li, et al. Am. J. Physiol. Cell Physiol. 283:C1540-C1547, 2002], the present results suggest that Flk-1, Cbl, and PI3K act upstream to NF-κB in response to shear stress. This Flk-1/Cbl/PI3K/NF-κB signaling pathway may be originated from integrins and transmitted by key tyrosine kinases and actin cytoskeleton. These results shed new lights on the molecular mechanism by which mechanical shear stress activates the NF-κB signaling pathway, which is critical for vascular inflammatory responses and atherosclerosis.

The deletion mutant EGFRvIII significantly contributes to stress resistance typical for the tumour microenvironment

BACKGROUND AND PURPOSE

The epidermal growth factor receptor (EGFR) is overexpressed or mutated in many tumour types. The truncated, constitutively active EGFRvIII variant has not been detected in normal tissues but is found in many malignancies. In the current study, we have investigated the hypothesis that EGFRvIII contributes to a growth and survival advantage under tumour microenvironment-related stress conditions.

MATERIALS AND METHODS

U373MG doxycycline-regulated isogenic cells expressing EGFRwt or EGFRvIII were created and validated using Western blot, FACS and qRT-PCR. In vitro proliferation was evaluated with standard growth assays. Cell survival was assayed using clonogenic survival. Animal experiments were performed using NMRI-nu-xenografted mice.

RESULTS

Inducible isogenic cell lines were created and showed high induction of EGFRwt and EGFRvIII upon doxycycline addition. Overexpression of EGFRvIII but not of EGFRwt in this model resulted in a growth and survival advantage upon different tumour microenvironment-related stress conditions in vitro. Induction of EGFRvIII increased tumour growth in vivo, which was reversible upon loss of expression.

CONCLUSIONS

Under conditions where nutrients are limited and stress is apparent, as in the tumour microenvironment, expression of EGFRvIII leads to a growth and survival advantage. These data indicate a potential selection of EGFRvIII-expressing tumour cells under such stress conditions.

Therapeutic inhibition of the epidermal growth factor receptor in high-grade gliomas: where do we stand?

High-grade gliomas account for the majority of intra-axial brain tumors. Despite abundant therapeutic efforts, clinical outcome is still poor. Thus, new therapeutic approaches are intensely being investigated. Overexpression of the epidermal growth factor receptor (HER1/EGFR) is found in various epithelial tumors and represents one of the most common molecular abnormalities seen in high-grade gliomas. Dysregulated HER1/EGFR is found in 40% to 50% of glioblastoma, the most malignant subtype of glioma. Several agents such as tyrosine kinase (TK) inhibitors, antibodies, radio-immuno conjugates, ligand-toxin conjugates, or RNA-based agents have been developed to target HER1/EGFR or its mutant form, EGFRvIII. To date, most agents are in various stages of clinical development. Clinical data are sparse but most advanced for TK inhibitors. Although data from experimental studies seem promising, proof of a significant clinical benefit is still missing. Among the problems that have to be further addressed is the prediction of the individual patient's response to HER1/EGFR-targeted therapeutics based on molecular determinants. It is quite possible that blocking HER1/EGFR alone will not sufficiently translate into a clinical benefit. Therefore, a multiple target approach concomitantly aimed at different molecular sites might be a favorable concept. This review focuses on current HER1/EGFR-targeted therapeutics and their development for high-grade gliomas.

The EGFRvIII variant in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common brain tumour and has the worst prognosis. Epidermal growth factor receptor (EGFR) gene amplification, mutation and re-arrangement (all of which enhance tumour growth, survival, progression and resistance to therapy) are frequently observed in primary GBM. The most common EGFR variant in GBM, the EGFRvIII, is characterised by a deletion of 267 amino acids in the extracellular domain, leading to a receptor which is unable to bind ligand yet is constitutively active. Together with its impaired internalisation and degradation, the EGFRvIII enhances the tumourigenic potential of GBM by activating and sustaining mitogenic, anti-apoptotic and pro-invasive signalling pathways. This EGFRvIII-mediated enhanced tumourigenicity combined with the lack of EGFRvIII expression in normal tissue makes it an ideal candidate for targeted therapy. This review summarizes the current knowledge about the role of EGFRvIII in GBM and discusses therapeutic agents targeting EGFRvIII that are being evaluated as treatments for GBM.

EGFRvIII expression and PTEN loss synergistically induce chromosomal instability and glial tumors

Glioblastomas often show activation of epidermal growth factor receptor (EGFR) and loss of PTEN (phosphatase and tensin homolog deleted on chromosome 10) tumor suppressor, but it is not known if these two genetic lesions act together to transform cells. To answer this question, we infected PTEN-/- neural precursor cells with a retrovirus encoding EGFRvIII, which is a constitutively activated receptor. EGFRvIII PTEN-/- cells formed highly mitotic tumors with nuclear pleomorphism, necrotic areas, and glioblastoma markers. The transformed cells showed increased cell proliferation, centrosome amplification, colony formation in soft agar, self-renewal, expression of the stem cell marker CD133, and resistance to oxidative stress and ionizing radiation. The RAS/mitogen-activated protein kinase (ERK) and phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathways were activated, and checkpoint kinase 1 (Chk1), the DNA damage regulator, was phosphorylated at S280 by Akt, suppressing Chk1 phosphorylation at S345 in response to ionizing irradiation. The PTEN-/- cells showed low levels of DNA damage in the absence of irradiation, which was increased by EGFRvIII expression. Finally, secondary changes occurred during tumor growth in mice. Cells from these tumors showed decreased tumor latencies and additional chromosomal aberrations. Most of these tumor lines showed translocations of mouse chromosome 15. Intracranial injections of one of these lines led to invasive, glial fibrillary acidic protein-positive, nestin-positive tumors. These results provide a molecular basis for the occurrence of these two genetic lesions in brain tumors and point to a role in induction of genomic instability.

Reciprocal regulation of SOCS 1 and SOCS3 enhances resistance to ionizing radiation in glioblastoma multiforme

PURPOSE

The expression of suppressors of cytokine signaling 1 (SOCS1) and SOCS3 genes is dysregulated in several solid tumors, causing aberrant activation of cell growth and survival signaling pathways. In this study, we analyzed SOCS1 and SOCS3 gene expression in glioblastoma multiforme (GBM) and studied the role of each protein in GBM cell signaling and radiation resistance.

EXPERIMENTAL DESIGN

SOCS1 and SOCS3 gene expression was analyzed in 10 GBM cell lines by reverse transcription-PCR and Western blotting. SOCS3 expression was also studied in 12 primary GBM tissues by immunohistochemistry. The methylation status of the SOCS1 and SOCS3 loci was determined by methylation-specific PCR. Extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MAPK) activation in GBM cell lines overexpressing SOCS1 or lacking SOCS3 was determined by phosphorylated-specific Western blotting. Radiation responses in SOCS1-positive and SOCS3-deficient GBM cell lines and fibroblasts from wild-type and SOCS1 or SOCS3 knockout mice were studied in a clonogenic survival assay.

RESULTS

All GBM cell lines tested lacked SOCS1 expression, whereas GBM cell lines and primary GBM tumor samples constitutively expressed SOCS3. SOCS1 gene repression was linked to hypermethylation of the SOCS1 genetic locus in GBM cells. Reintroduction of SOCS1 or blocking SOCS3 expression sensitized cells to radiation and decreased the levels of activated ERK MAPKs in GBM cells.

CONCLUSIONS

SOCS1 and SOCS3 are aberrantly expressed in GBM cell lines and primary tissues. Altered SOCS gene expression leads to increased cell signaling through the ERK-MAPK pathway and may play a role in disease pathogenesis by enhancing GBM radioresistance.

Pediatric CNS tumors: current treatment and future directions

Pediatric CNS tumors are the most common solid tumor of childhood and are the leading cause of cancer-related death in this age group. Improving prognosis is not the only challenge facing physicians managing these young patients as it is vital to consider the quality of survival. Current management strategies rely on surgery, radiotherapy and conventional cytotoxic chemotherapy, and although ongoing clinical trials continue to refine these treatments, newer approaches are required. This article will discuss current treatment standards for the most common pediatric CNS tumors: astrocytomas (low- and high-grade glioma), ependymoma and primitive neuroectodermal tumors (medulloblastoma), as well as future biological-based novel therapies.

A novel small molecule that selectively inhibits glioblastoma cells expressing EGFRvIII

Background

Mutations of the epidermal growth factor receptor (EGFR) are a possible molecular target for cancer therapy. EGFR is frequently amplified in glioblastomas and 30 to 40% of glioblastomas also express the deletion mutation EGFRvIII. This frequent oncogenic mutation provides an opportunity for identifying new anti-glioblastoma therapies. In this study, we sought small molecule inhibitors specific for cancer cells expressing EGFRvIII, using isogenic parental cells without EGFRvIII as a control.

Results

A screen of the NCI small molecule diversity set identified one compound, NSC-154829, which consistently inhibited growth of different human glioblastoma cells expressing EGFRvIII, but permitted normal growth of matched control cells. NSC-154829 had no previously established medicinal use, but has a purine-like structural component. Further experiments showed this compound increased apoptosis in cells with EGFRvIII, and moderately affected the expression of p21, independent of any changes in p53 levels or in Akt phosphorylation.

Conclusion

These initial results suggest that NSC-154829 or a closely related structure might be further investigated for its potential as an anti-glioblastoma drug, although its precise molecular mechanism is still undefined.

Activation of STAT3, MAPK, and AKT in Malignant Astrocytic Gliomas

Diffuse astrocytic gliomas are the most common human glial tumors with glioblastoma being the most malignant form. Epidermal growth factor receptor (EGFR) gene amplification is one of the most common genetic changes in glioblastoma and can lead to the activation of various downstream signaling molecules, including STAT3, MAPK, and AKT. In this study, we investigated the activation status of these 3 signaling molecules as well as wild-type (EGFRwt) and mutant (EGFRvIII) EGFR in 82 malignant astrocytic gliomas (55 glioblastomas and 27 anaplastic astrocytomas) using immunohistochemistry. The presence of EGFRwt, but not EGFRvIII, immunopositivity correlated significantly with prevalent EGFR gene amplification in glioblastomas. STAT3 and AKT activation correlated significantly with EGFR status, although the correlation for p-STAT3 was attributed exclusively to EGFRvIII. The distribution of these 3 activated molecules varied significantly with tumor grade; although activation of STAT3 was essentially identical between anaplastic astrocytomas and glioblastomas, an increase in the activation of MAPK and AKT appeared to correlate with the progression of anaplastic astrocytoma to glioblastoma. Finally, activated STAT3 and AKT were marginally predictive of improved and worse prognosis, respectively. Taken together, these findings begin to elucidate the interrelationship between these signaling pathways in astrocytic gliomas in vivo.

Use of monoclonal anti-EGFR antibody in the radioimmunotherapy of malignant gliomas in the context of EGFR expression in grade III and IV tumors

We investigated the putative benefits of simultaneous teleradiotherapy and anti-epidermal growth factor receptor (EGFR) 125I monoclonal antibody (MAb) 425 radioimmunotherapy, when applied after neurosurgery in high-grade gliomas, over teleradiotherapy alone. In comparison to previous studies which have reported good results with this type of radioimmunotherapy, we advanced the adjuvant radioimmunotherapy step, that is, gave it during, not after, teleradiotherapy. The randomized prospective study examined two groups: simultaneous postoperative teleradiotherapy and radioimmunotherapy (TRT + RIT; eight patients) versus teleradiotherapy alone (TRT; 10 patients). Patients who after primary operation of grade III (6 cases) or IV glioma (12 cases), showed no or less than 2 mL of remnant tumor on post-operative magnetic resonance (MR) study and were not treated postoperatively by chemotherapy were enrolled and randomized. Anti-EGFR 125IMAb 425 RIT was started during week 4 of radiotherapy, not later than 8 weeks after neurosurgery, and was repeated three times at 1-week intervals. Total activity given was 5026 + 739 MBq/patient. The tolerance of TRT was good. No immediate side effects of concomitant anti-EGRF 125I RIT were observed. Observation showed a median total survival (as evaluated from the primary neurosurgical treatment) of 14 months (range 3.5-28 months). There was no improvement in disease-free or total survival in the group of patients treated by TRT + RIT after neurosurgery. In addition, an immunohistochemical analysis of EGFR expression in gliomas was performed in a group of 100 cases and was distinctly positive in 50% grade IV gliomas and 68% grade III gliomas. We conclude that simultaneous radiotherapy and radioimmunotherapy with anti-EGFR 125I-MAb 425 is not beneficial over radiotherapy alone in adjuvant treatment of high-grade gliomas after neurosurgery. We also recommend individual confirmation of EGFR expression in further anti-EGFR radioimmunotherapy trials.

Phase II study of CCI-779 in patients with recurrent glioblastoma multiforme

PURPOSE

Loss of PTEN, which is common in glioblastoma multiforme (GBM), results in activation of the mammalian target of rapapmycin (mTOR), thereby increasing mRNA translation of a number of key proteins required for cell-cycle progression. CCI-779 is an inhibitor of mTOR. The primary objectives of this study were to determine the efficacy of CCI-779 in patients with recurrent GBM and to further assess the toxicity of the drug.

EXPERIMENTAL DESIGN

CCI-779 was administered weekly at a dose of 250 mg intravenously for patients on enzyme-inducing anti-epileptic drugs (EIAEDs). Patients not on EIAEDs were initially treated at 250 mg; however, the dose was reduced to 170 mg because of intolerable side effects. Treatment was continued until unacceptable toxicity, tumor progression, or patient withdrawal. The primary endpoint was 6-month progression-free survival.

RESULTS

Forty-three patients were enrolled; 29 were not on EIAEDs. The expected toxicity profile of increased lipids, lymphopenia, and stomatitis was seen. There were no grade IV hematological toxicities and no toxic deaths. One patient was progression free at 6 months. Of the patients assessable for response, there were 2 partial responses and 20 with stabilization of disease. The median time to progression was 9 weeks.

CONCLUSIONS

CCI-779 was well tolerated at this dose schedule; however, there was no evidence of efficacy in patients with recurrent GBM. Despite initial disease stabilization in approximately 50% of patients, the durability of response was short. Because of the low toxicity profile, CCI-779 may merit exploration in combination with other modalities.

Peroxisome proliferator-activated receptor-γ inhibits cigarette smoke solution-induced mucin production in human airway epithelial (NCI-H292) cells

The main etiologic factor for chronic bronchitis is cigarette smoke. Exposure to cigarette smoke is reported to induce goblet cell hyperplasia and mucus production. Mucin synthesis in airways has been reported to be regulated by the EGFR system. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a member of the ligand-activated nuclear receptor superfamily. PPAR-γ is implicated in anti-inflammatory responses, but mechanisms underlying these varied roles remain ill-defined. Recently, reports have shown that upregulation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) might be one of the mechanisms through which PPAR-γ agonists exert their anti-inflammatory actions. However, no data are available on the role of PPAR-γ in smoke-induced mucin production. In this study, we investigated the effect of PPAR-γ agonist (rosiglitazone) on smoke-induced mucin production in NCI-H292 cells. Exposure to cigarette smoke causes a significant decrease in PTEN expression and increases dose-dependent EGFR-specific tyrosine phosphorylation, resulting in MUC5AC mucin production in NCI-H292 cells. PPAR-γ agonists or specific inhibitors of phosphoinositide 3-kinase exert inhibition of cigarette smoke-induced mucin production, with the upregulation of PTEN signaling and downregulation of Akt expression. This study demonstrates that PPAR-γ agonist functions as a regulator of epithelial cell inflammation that may result in reduction of mucin-producing cells in airway epithelium.

Epidermal growth factor receptor inhibition for the treatment of glioblastoma multiforme and other malignant brain tumours

Gliomas are the most common primary central nervous system tumours and about 55% are glioblastoma multiforme (GBM). Between 40% and 50% of GBM have dysregulated epidermal growth factor receptor (HER1/EGFR), and almost half of these co-express the mutant receptor subtype EGFRvIII, which may contribute to the aggressive and refractory course of GBM. Limited therapeutic options exist for GBM, and recurrence is common. Standard therapy is surgical resection, where possible, and radiotherapy. Adjuvant chemotherapy provides a modest survival benefit. New therapies are essential, and HER1/EGFR-targeted agents may provide a viable strategy. The HER1/EGFR tyrosine kinase inhibitors erlotinib and gefitinib are in advanced clinical development for glioma, and a number of trials are in progress, or have recently been completed. Preliminary results with gefitinib show no objective responses, but do provide evidence of disease control. In contrast, preliminary data with erlotinib appear more encouraging. Erlotinib inhibits wild-type HER1/EGFR and EGFRvIII, which may underlie its promising clinical activity. Other HER1/EGFR-targeted agents are also being investigated for glioma, including monoclonal antibodies, radio-immuno conjugates, ligand-toxin conjugates, antisense oligonucleotides and ribozymes. Further studies will define their clinical potential and hopefully provide new, effective treatments for GBM and other malignant brain tumours.

HER1/EGFR tyrosine kinase inhibitors for the treatment of glioblastoma multiforme

Glioblastoma multiforme (GBM) is a highly malignant brain tumor with limited therapeutic options, a high recurrence rate and mortality. Standard therapy is maximal surgical resection and radiotherapy (RT). Recent data suggest combining temozolomide with RT is better than RT alone. Adjuvant chemotherapy has a modest impact on survival. For relapsed patients there is no standard therapy, but options include chemotherapeutic agents or new agents in development. One approach to improve outcome is using targeted agents that interfere with cell-surface receptors or intracellular signaling pathways. Between 40% and 50% of GBM tumors show HER1/EGFR dysregulation, and almost half co-express the constitutively active mutant receptor subtype EGFRvIII, which may contribute to the aggressive and refractory course of GBM. Numerous studies show a relationship between aberrant HER1/EGFR biology and tumorigenicity in GBM cells. Two available HER1/EGFR tyrosine kinase inhibitors (TKIs) are gefitinib (Iressa) and erlotinib (Tarceva); both show antitumor and radiosensitization effects in vitro and in animal models of GBM. Clinical trials in patients with GBM and other gliomas are ongoing. Preliminary and published results from trials of gefitinib in recurrent GBM show no increased time to progression or overall survival (OS) compared with historical controls. Studies with erlotinib show greater antitumor activity in patients with GBM than with gefitinib, although the impact of both agents on OS remains unclear. GBM treatment with HER1/EGFR TKIs alone or combined with other targeted therapies and conventional modalities deserve further investigation and refinement, as does our understanding of their mechanisms of action and the role of genetics.

Molecular diagnostic techniques for the clinical evaluation of gliomas

Newly developed molecular techniques have been integrated into the routine assessment of gliomas in some laboratories. These tests serve to complement the subjective nature of morphologic analysis. Such strategies add useful information regarding pathogenicity, patient survival, and potential response to treatment. As we learn more about the molecular characteristics of these tumors, this information will provide the basis for the development of specific, targeted therapies. This review will describe the background, methods, clinical utility, and strengths and weaknesses of several molecular approaches, including fluorescence in situ hybridization (FISH), immunohistochemistry (IHC), loss of heterozygosity (LOH)-testing, and nucleic acid sequencing, that are currently being employed in the diagnosis and evaluation of glial tumors.

The tumor-specific de2-7 epidermal growth factor receptor (EGFR) promotes cells survival and heterodimerizes with the wild-type EGFR

Mutations of the epidermal growth factor receptor (EGFR) gene are found at a relatively high frequency in glioma, with the most common being the de2-7 EGFR (or EGFRvIII). This mutation arises from an in-frame deletion of exons 2-7, which removes 267 amino acids from the extracellular domain of the receptor. Despite being unable to bind ligand, the de2-7 EGFR is constitutively active and imparts a significant in vivo growth advantage to glioma cells. In order to examine the signalling pathways activated by the de2-7 EGFR and its biological effects in an in vitro system, the de2-7 EGFR gene was transfected into the murine IL-3-dependent pro-B-cell line BaF/3. Expression of the de2-7 EGFR enhanced the survival of BaF/3 cells in the absence of IL-3 by reducing apoptosis in a phosphatidylinositol 3-kinase (PI3-K)-dependent manner. Interestingly, while de2-7 EGFR also enhanced proliferation of BaF/3 cells in low levels of IL-3, this effect was independent of PI3-K. Survival and proliferation were further enhanced when BaF/3 cells were cotransfected with the de2-7 and wt EGFR. This was due to heterodimerization between the de2-7 and wt EGFR leading to trans-phosphorylation of the wt EGFR. This observation is directly relevant to glioma where de2-7 and wt EGFR appear to be coexpressed. Thus, expression of de2-7 EGFR in BaF/3 cells provides an in vitro model for evaluating the signalling pathways activated by this receptor.

The antitumor monoclonal antibody 806 recognizes a high-mannose form of the EGF receptor that reaches the cell surface when cells over-express the receptor

Overexpression of the EGFR is commonly caused by EGFR gene amplification and is sometimes associated with expression of a variant EGFR (de2-7 EGFR or EGFRvIII) bearing an internal deletion in its extracellular domain. mAb 806 is a novel EGFR antibody with significant antitumor activity that recognizes both the de2-7 EGFR and a subset of the wild-type (wt) EGFR when overexpressed, but does not bind the EGFR expressed in normal tissues. Recently, we demonstrated that the mAb 806 epitope is restricted to a short cysteine loop of the EGFR (amino acids 287-302) that is only available for antibody binding in a transitional form of the receptor, which occurs as the receptor changes from its inactive tethered conformation to a dimeric untethered form. The truncation associated with the de2-7 EGFR mutation renders this receptor constitutively untethered, leading to increased binding of mAb 806. We now show that mAb 806 preferentially binds the immature high-mannose wt and de2-7 EGFR precursors normally located in the endoplasmic reticulum, indicating that this form of the wt EGFR is also constitutively untethered. Using the unique specificity of mAb 806, we clearly demonstrated the presence of these high-mannose EGFR precursors on the cell surface. Given that the high-mannose forms of the wt EGFR must be untethered they may contribute to the spontaneous EGFR signaling reported in cells overexpressing the receptor. These precursor forms of the EGFR thus represent novel tumor targets and contribute to the exceptional selectivity of mAb 806 for EGFR when overexpressed in cancer cells. As our observations are likely to apply to other receptors overexpressed in cancer, they suggest a strategy for developing antitumor antibodies even when the target receptor is expressed in normal tissue.

Mutant epidermal growth factor receptor displays increased signaling through the phosphatidylinositol-3 kinase/AKT pathway and promotes radioresistance in cells of astrocytic origin

Amplification and mutation of the epidermal growth factor receptor (EGFR) are common features of malignant gliomas. The most frequent mutation seen in these tumors involves deletion of exon 2-7 resulting in a constitutively active form of the receptor (EGFRvIII, or deltaEGFR). Since EGFRvIII is found primarily in gliomas and has not been reported in sarcomas, we compared the effects of this altered receptor in immortalized primary astrocytes and fibroblasts. While EGFRvIII displayed ligand-independent autophosphorylation in both cell types, downstream signaling differed. While EGFRvIII increased the proliferative capacity of both astrocytes and fibroblasts consistent with activation of ERK in these cells, EGFRvIII activated AKT only in the immortalized astrocytes. EGFRvIII expression in astrocytes also led to increased radioresistance in that cell type. Furthermore, specific inhibition of phosphotidylinositol-3 kinase (PI-3K) with LY294002 reverted the radioresistant phenotype in the immortalized astrocytes. Thus, selective activation of PI-3K/AKT in astrocytes expressing EGFRvIII appears to be responsible for the observed increase in radioresistance. EGFRvIII's differential ability to activate the PI-3K downstream signal may explain why this mutant receptor is such a prominent lesion in malignant gliomas but less often seen in other tumor types, even those where EGFR signaling has a prominent role.