EGFRvIII-mediated transactivation of receptor tyrosine kinases in glioma: mechanism and therapeutic implications

An updated overview of the application of CAR-T cell therapy in neurological diseases

Genetically modified immune cells, especially CAR-T cells, have captured the attention of scientists over the past 10 years. In the fight against cancer, these cells have a special place. Treatment for hematological cancers, autoimmune disorders, and cancers must include CAR-T cell therapy. Determining the therapeutic targets, side effects, and use of CAR-T cells in neurological disorders, including cancer and neurodegenerative diseases, is the goal of this study. Due to advancements in genetic engineering, CAR-T cells have become crucial in treating some neurological disorders. CAR-T cells have demonstrated a positive role in treating neurological cancers like Glioblastoma and Neuroblastoma due to their ability to cross the blood-brain barrier and use diverse targets. However, CAR-T cell therapy for MS diseases is being researched and could be a potential treatment option. This study aimed to access the most recent studies and scientific articles in the field of CAR-T cells in neurological diseases and/or disorders.

Increased EGFRvIII Epitope Accessibility after Tyrosine Kinase Inhibitor Treatment of Glioblastoma Cells Creates More Opportunities for Immunotherapy

The number of glioblastoma (GB) cases is increasing every year, and the currently available therapies remain ineffective. A prospective antigen for GB therapy is EGFRvIII, an EGFR deletion mutant containing a unique epitope that is recognized by the L8A4 antibody used in CAR-T (chimeric antigen receptor T cell) therapy. In this study, we observed that the concomitant use of L8A4 with particular tyrosine kinase inhibitors (TKIs) does not impede the interaction between L8A4 and EGFRvIII; moreover, in this case, the stabilization of formed dimers results in increased epitope display. Unlike in wild-type EGFR, a free cysteine at position 16 (C16) is exposed in the extracellular structure of EGFRvIII monomers, leading to covalent dimer formation in the region of L8A4-EGFRvIII mutual interaction. Following in silico analysis of cysteines possibly involved in covalent homodimerization, we prepared constructs containing cysteine-serine substitutions of EGFRvIII in adjacent regions. We found that the extracellular part of EGFRvIII possesses plasticity in the formation of disulfide bridges within EGFRvIII monomers and dimers due to the engagement of cysteines other than C16. Our results suggest that the EGFRvIII-specific L8A4 antibody recognizes both EGFRvIII monomers and covalent dimers, regardless of the cysteine bridging structure. To summarize, immunotherapy based on the L8A4 antibody, including CAR-T combined with TKIs, can potentially increase the chances of success in anti-GB therapy.

Anoctamins and Calcium Signalling: An Obstacle to EGFR Targeted Therapy in Glioblastoma?

Glioblastoma is the most common form of high-grade glioma in adults and has a poor survival rate with very limited treatment options. There have been no significant advancements in glioblastoma treatment in over 30 years. Epidermal growth factor receptor is upregulated in most glioblastoma tumours and, therefore, has been a drug target in recent targeted therapy clinical trials. However, while many inhibitors and antibodies for epidermal growth factor receptor have demonstrated promising anti-tumour effects in preclinical models, they have failed to improve outcomes for glioblastoma patients in clinical trials. This is likely due to the highly plastic nature of glioblastoma tumours, which results in therapeutic resistance. Ion channels are instrumental in the development of many cancers and may regulate cellular plasticity in glioblastoma. This review will explore the potential involvement of a class of calcium-activated chloride channels called anoctamins in brain cancer. We will also discuss the integrated role of calcium channels and anoctamins in regulating calcium-mediated signalling pathways, such as epidermal growth factor signalling, to promote brain cancer cell growth and migration.

Potassium Ion Channels in Malignant Central Nervous System Cancers

Malignant central nervous system (CNS) cancers are among the most difficult to treat, with low rates of survival and a high likelihood of recurrence. This is primarily due to their location within the CNS, hindering adequate drug delivery and tumour access via surgery. Furthermore, CNS cancer cells are highly plastic, an adaptive property that enables them to bypass targeted treatment strategies and develop drug resistance. Potassium ion channels have long been implicated in the progression of many cancers due to their integral role in several hallmarks of the disease. Here, we will explore this relationship further, with a focus on malignant CNS cancers, including high-grade glioma (HGG). HGG is the most lethal form of primary brain tumour in adults, with the majority of patient mortality attributed to drug-resistant secondary tumours. Hence, targeting proteins that are integral to cellular plasticity could reduce tumour recurrence, improving survival. This review summarises the role of potassium ion channels in malignant CNS cancers, specifically how they contribute to proliferation, invasion, metastasis, angiogenesis, and plasticity. We will also explore how specific modulation of these proteins may provide a novel way to overcome drug resistance and improve patient outcomes.

ErbB4 in the brain: Focus on high grade glioma

The epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases (RTKs) consists of EGFR, ErbB2, ErbB3, and ErbB4. These receptors play key roles in cell proliferation, angiogenesis, cell migration, and in some cases, tumor promotion. ErbB4 is a unique member of the EGFR family, implicated not only in pro-tumorigenic mechanisms, such as cell proliferation and migration, but also in anti-tumorigenic activities, including cell differentiation and apoptosis. ErbB4 is differentially expressed in a wide variety of tissues, and interestingly, as different isoforms that result in vastly different signalling outcomes. Most studies have either ignored the presence of these isoforms or used overexpression models that may mask the true function of ErbB4. ErbB4 is widely expressed throughout the body with significant expression in skeletal tissue, mammary glands, heart, and brain. Knockout models have demonstrated embryonic lethality due to disrupted heart and brain development. Despite high expression in the brain and a critical role in brain development, remarkably little is known about the potential signalling activity of ErbB4 in brain cancer.This review focuses on the unique biology of ErbB4 in the brain, and in particular, highlights brain cancer research findings. We end the review with a focus on high grade gliomas, primarily glioblastoma, a disease that has been shown to involve EGFR and its mutant forms. The role of the different ErbB4 isotypes in high grade gliomas is still unclear and future research will hopefully shed some light on this question.

Research Progress on the Regulation Mechanism of Key Signal Pathways Affecting the Prognosis of Glioma

As is known to all, glioma, a global difficult problem, has a high malignant degree, high recurrence rate and poor prognosis. We analyzed and summarized signal pathway of the Hippo/YAP, PI3K/AKT/mTOR, miRNA, WNT/β-catenin, Notch, Hedgehog, TGF-β, TCS/mTORC1 signal pathway, JAK/STAT signal pathway, MAPK signaling pathway, the relationship between BBB and signal pathways and the mechanism of key enzymes in glioma. It is concluded that Yap1 inhibitor may become an effective target for the treatment of glioma in the near future through efforts of generation after generation. Inhibiting PI3K/Akt/mTOR, Shh, Wnt/β-Catenin, and HIF-1α can reduce the migration ability and drug resistance of tumor cells to improve the prognosis of glioma. The analysis shows that Notch1 and Sox2 have a positive feedback regulation mechanism, and Notch4 predicts the malignant degree of glioma. In this way, notch cannot only be treated for glioma stem cells in clinic, but also be used as an evaluation index to evaluate the prognosis, and provide an exploratory attempt for the direction of glioma treatment. MiRNA plays an important role in diagnosis, and in the treatment of glioma, VPS25, KCNQ1OT1, KB-1460A1.5, and CKAP4 are promising prognostic indicators and a potential therapeutic targets for glioma, meanwhile, Rheb is also a potent activator of Signaling cross-talk etc. It is believed that these studies will help us to have a deeper understanding of glioma, so that we will find new and better treatment schemes to gradually conquer the problem of glioma.

Research Progress on the Regulation Mechanism of Key Signal Pathways Affecting the Prognosis of Glioma

As is known to all, glioma, a global difficult problem, has a high malignant degree, high recurrence rate and poor prognosis. We analyzed and summarized signal pathway of the Hippo/YAP, PI3K/AKT/mTOR, miRNA, WNT/β-catenin, Notch, Hedgehog, TGF-β, TCS/mTORC1 signal pathway, JAK/STAT signal pathway, MAPK signaling pathway, the relationship between BBB and signal pathways and the mechanism of key enzymes in glioma. It is concluded that Yap1 inhibitor may become an effective target for the treatment of glioma in the near future through efforts of generation after generation. Inhibiting PI3K/Akt/mTOR, Shh, Wnt/β-Catenin, and HIF-1α can reduce the migration ability and drug resistance of tumor cells to improve the prognosis of glioma. The analysis shows that Notch1 and Sox2 have a positive feedback regulation mechanism, and Notch4 predicts the malignant degree of glioma. In this way, notch cannot only be treated for glioma stem cells in clinic, but also be used as an evaluation index to evaluate the prognosis, and provide an exploratory attempt for the direction of glioma treatment. MiRNA plays an important role in diagnosis, and in the treatment of glioma, VPS25, KCNQ1OT1, KB-1460A1.5, and CKAP4 are promising prognostic indicators and a potential therapeutic targets for glioma, meanwhile, Rheb is also a potent activator of Signaling cross-talk etc. It is believed that these studies will help us to have a deeper understanding of glioma, so that we will find new and better treatment schemes to gradually conquer the problem of glioma.

A Novel Classification Model for Lower-Grade Glioma Patients Based on Pyroptosis-Related Genes

Recent studies demonstrated that pyroptosis plays a crucial role in shaping the tumor-immune microenvironment. However, the influence of pyroptosis on lower-grade glioma regarding immunotherapy and targeted therapy is still unknown. This study analyzed the variations of 33 pyroptosis-related genes in lower-grade glioma and normal tissues. Our study found considerable genetic and expression alterations in heterogeneity among lower-grade gliomas and normal brain tissues. There are two pyroptosis phenotypes in lower-grade glioma, and they exhibited differences in cell infiltration characteristics and clinical characters. Then, a PyroScore model using the lasso-cox method was constructed to measure the level of pyroptosis in each patient. PyroScore can refine the lower-grade glioma patients with a stratified prognosis and a distinct tumor immune microenvironment. Pyscore may also be an effective factor in predicting potential therapeutic benefits. In silico analysis showed that patients with a lower PyroScore are expected to be more sensitive to targeted therapy and immunotherapy. These findings may enhance our understanding of pyroptosis in lower-grade glioma and might help optimize risk stratification for the survival and personalized management of lower-grade glioma patients.

Advancements, Challenges, and Future Directions in Tackling Glioblastoma Resistance to Small Kinase Inhibitors

Despite clinical intervention, glioblastoma (GBM) remains the deadliest brain tumor in adults. Its incurability is partly related to the establishment of drug resistance, both to standard and novel treatments. In fact, even though small kinase inhibitors have changed the standard clinical practice for several solid cancers, in GBM, they did not fulfill this promise. Drug resistance is thought to arise from the heterogeneity of GBM, which leads the development of several different mechanisms. A better understanding of the evolution and characteristics of drug resistance is of utmost importance to improve the current clinical practice. Therefore, the development of clinically relevant preclinical in vitro models which allow careful dissection of these processes is crucial to gain insights that can be translated to improved therapeutic approaches. In this review, we first discuss the heterogeneity of GBM, which is reflected in the development of several resistance mechanisms. In particular, we address the potential role of drug resistance mechanisms in the failure of small kinase inhibitors in clinical trials. Finally, we discuss strategies to overcome therapy resistance, particularly focusing on the importance of developing in vitro models, and the possible approaches that could be applied to the clinic to manage drug resistance.

Most clinical anti-EGFR antibodies do not neutralize both wtEGFR and EGFRvIII activation in glioma

BACKGROUND

Although epidermal growth factor receptor (EGFR) and its truncated, autoactive mutant EGFR variant (v)III are bona fide drivers of tumorigenesis in some gliomas, therapeutic antibodies developed to neutralize this axis have not improved patient survival in a limited number of trials. Previous studies using cells transduced to exogenously express EGFRvIII may have compromised mechanistic studies of anti-EGFR therapeutics. Therefore, we re-assessed the activity of clinical EGFR antibodies in patient-derived gliomaspheres that endogenously express EGFRvIII.

METHODS

The antitumor efficacy of antibodies was assessed using in vitro proliferation assays and intracranial orthografts. Receptor activation status, antibody engagement, oncogenic signaling, and mechanism of action after antibody treatment were analyzed by immunoprecipitation and western blotting. Tracking of antibody receptor complexes was conducted using immunofluorescence.

RESULTS

The EGFR domain III-targeting antibodies cetuximab, necitumumab, nimotuzumab, and matuzumab did not neutralize EGFRvIII activation. Chimeric monoclonal antibody 806 (ch806) neutralized EGFRvIII, but not wild-type (wt)EGFR activation. Panitumumab was the only antibody that neutralized both EGFRvIII and wtEGFR, leading to reduction of p-S6 signaling and superior in vitro and in vivo antitumor activity. Mechanistically, panitumumab induced recycling of receptor but not degradation as previously described. Panitumumab, via its unique avidity, stably cross-linked EGFRvIII to prevent its activation, while ch806 induced a marked reduction in the active EGFRvIII disulphide-bonded dimer.

CONCLUSIONS

We discovered a previously unknown major resistance mechanism in glioma in that most EGFR domain III-targeting antibodies do not neutralize EGFRvIII. The superior in vitro and in vivo antitumor activity of panitumumab supports further clinical testing of this antibody against EGFRvIII-stratified glioma.

EGFRvIII tumorigenicity requires PDGFRA co-signaling and reveals therapeutic vulnerabilities in glioblastoma

Focal amplification of epidermal growth factor receptor (EGFR) and its ligand-independent, constitutively active EGFRvIII mutant form are prominent oncogenic drivers in glioblastoma (GBM). The EGFRvIII gene rearrangement is considered to be an initiating event in the etiology of GBM, however, the mechanistic details of how EGFRvIII drives cellular transformation and tumor maintenance remain unclear. Here, we report that EGFRvIII demonstrates a reliance on PDGFRA co-stimulatory signaling during the tumorigenic process in a genetically engineered autochthonous GBM model. This dependency exposes liabilities that were leveraged using kinase inhibitors treatments in EGFRvIII-expressing GBM patient-derived xenografts (PDXs), where simultaneous pharmacological inhibition of EGFRvIII and PDGFRA kinase activities is necessary for anti-tumor efficacy. Our work establishes that EGFRvIII-positive tumors have unexplored vulnerabilities to targeted agents concomitant to the EGFR kinase inhibitor repertoire.

Chimeric Antigen Receptor T-Cell Therapy in Glioblastoma: Current and Future

Glioblastoma (GBM) is a highly aggressive glioma with an extremely poor prognosis after conventional treatment. Recent advances in immunotherapy offer hope for these patients with incurable GBM. Our present review aimed to provide an overview of immunotherapy for GBM, especially chimeric antigen receptor T-cell (CAR T) therapy. CAR T-cell immunotherapy, which involves the engineering of T cells to kill tumors by targeting cell surface-specific antigens, has been successful in eliminating B-cell leukemia by targeting CD19. IL-13Rα2, EGFRvIII, and HER2-targeted CAR T cells have shown significant clinical efficacy and safety in phase 1 or 2 clinical trials conducted in patients with GBM; these findings support the need for further studies to examine if this therapy can ultimately benefit this patient group. However, local physical barriers, high tumor heterogeneity, and antigen escape make the use of CAR T therapy, as a treatment for GBM, challenging. The potential directions for improving the efficacy of CAR T in GBM are to combine the existing traditional therapies and the construction of multi-target CAR T cells.

EGFRvIII: An Oncogene with Ambiguous Role

Epidermal growth factor receptor variant III (EGFRvIII) seems to constitute the perfect therapeutic target for glioblastoma (GB), as it is specifically present on up to 28-30% of GB cells. In case of other tumor types, expression and possible role of this oncogene still remain controversial. In spite of EGFRvIII mechanism of action being crucial for the design of small active anticancer molecules and immunotherapies, i.e., CAR-T technology, it is yet to be precisely defined. EGFRvIII is known to be resistant to degradation, but it is still unclear whether it heterodimerizes with EGF-activated wild-type EGFR (EGFRWT) or homodimerizes (including covalent homodimerization). Constitutive kinase activity of this mutated receptor is relatively low, and some researchers even claim that a nuclear, but not a membrane function, is crucial for its activity. Based on the analyses of recurrent tumors that are often lacking EGFRvIII expression despite its initial presence in corresponding primary foci, this oncogene is suggested to play a marginal role during later stages of carcinogenesis, while even in primary tumors EGFRvIII expression is detected only in a small percentage of tumor cells, undermining the rationality of EGFRvIII-targeting therapies. On the other hand, EGFRvIII-positive cells are resistant to apoptosis, more invasive, and characterized with enhanced proliferation rate. Moreover, expression of this oncogenic receptor was also postulated to be a marker of cancer stem cells. Opinions regarding the role that EGFRvIII plays in tumorigenesis and for tumor aggressiveness are clearly contradictory and, therefore, it is crucial not only to determine its mechanism of action, but also to unambiguously define its role at early and advanced cancer stages.

The soluble form of pan-RTK inhibitor and tumor suppressor LRIG1 mediates downregulation of AXL through direct protein-protein interaction in glioblastoma

Background

Targeted approaches for inhibiting epidermal growth factor receptor (EGFR) and other receptor tyrosine kinases (RTKs) in glioblastoma (GBM) have led to therapeutic resistance and little clinical benefit, raising the need for the development of alternative strategies. Endogenous LRIG1 (Leucine-rich Repeats and ImmunoGlobulin-like domains protein 1) is an RTK inhibitory protein required for stem cell maintenance, and we previously demonstrated the soluble ectodomain of LRIG1 (sLRIG1) to potently inhibit GBM growth in vitro and in vivo.

Methods

Here, we generated a recombinant protein of the ectodomain of LRIG1 (sLRIG1) and determined its activity in various cellular GBM models including patient-derived stem-like cells and patient organoids. We used proliferation, adhesion, and invasion assays, and performed gene and protein expression studies. Proximity ligation assay and NanoBiT complementation technology were applied to assess protein-protein interactions.

Results

We show that recombinant sLRIG1 downregulates EGFRvIII but not EGFR, and reduces proliferation in GBM cells, irrespective of their EGFR expression status. We find that sLRIG1 targets and downregulates a wide range of RTKs, including AXL, and alters GBM cell adhesion. Mechanistically, we demonstrate that LRIG1 interferes with AXL but not with EGFR dimerization.

Conclusions

These results identify AXL as a novel sLRIG1 target and show that LRIG1-mediated RTK downregulation depends on direct protein interaction. The pan-RTK inhibitory activity of sLRIG1 warrants further investigation for new GBM treatment approaches.

MET in glioma: signaling pathways and targeted therapies

Gliomas represent the most common type of malignant brain tumor, among which, glioblastoma remains a clinical challenge with limited treatment options and dismal prognosis. It has been shown that the dysregulated receptor tyrosine kinase (RTK, including EGFR, MET, PDGFRα, ect.) signaling pathways have pivotal roles in the progression of gliomas, especially glioblastoma. Increasing evidence suggests that expression levels of the RTK MET and its specific stimulatory factors are significantly increased in glioblastomas compared to those in normal brain tissues, whereas some negative regulators are found to be downregulated. Mutations in MET, as well as the dysregulation of other regulators of cross-talk with MET signaling pathways, have also been identified. MET and its ligand hepatocyte growth factor (HGF) play a critical role in the proliferation, survival, migration, invasion, angiogenesis, stem cell characteristics, and therapeutic resistance and recurrence of glioblastomas. Therefore, combined targeted therapy for this pathway and associated molecules could be a novel and attractive strategy for the treatment of human glioblastoma. In this review, we highlight progress made in the understanding of MET signaling in glioma and advances in therapies targeting HGF/MET molecules for glioma patients in recent years, in addition to studies on the expression and mutation status of MET.

Targeted Molecular Imaging Using Aptamers in Cancer

Imaging is not only seeing, but also believing. For targeted imaging modalities, nucleic acid aptamers have features such as superior recognition of structural epitopes and quick uptake in target cells. This explains the emergence of an evolved new class of aptamers into a wide spectrum of imaging applications over the last decade. Genetically encoded biosensors tagged with fluorescent RNA aptamers have been developed as intracellular imaging tools to understand cellular signaling and physiology in live cells. Cancer-specific aptamers labeled with fluorescence have been used for assessment of clinical tissue specimens. Aptamers conjugated with gold nanoparticles have been employed to develop innovative mass spectrometry tissue imaging. Also, use of chemically conjugated cancer-specific aptamers as probes for non-invasive and high-resolution imaging has been transformative for in vivo imaging in multiple cancers.

Anti-EGFRvIII Chimeric Antigen Receptor-Modified T Cells for Adoptive Cell Therapy of Glioblastoma

Glioblastoma (GBM) is one of the most devastating brain tumors with poor prognosis and high mortality. Although radical surgical treatment with subsequent radiation and chemotherapy can improve the survival, the efficacy of such regimens is insufficient because the GBM cells can spread and destroy normal brain structures. Moreover, these non-specific treatments may damage adjacent healthy brain tissue. It is thus imperative to develop novel therapies to precisely target invasive tumor cells without damaging normal tissues. Immunotherapy is a promising approach due to its capability to suppress the growth of various tumors in preclinical model and clinical trials. Adoptive cell therapy (ACT) using T cells engineered with chimeric antigen receptor (CAR) targeting an ideal molecular marker in GBM, e.g. epidermal growth factor receptor type III (EGFRvIII) has demonstrated a satisfactory efficacy in treating malignant brain tumors. Here we summarize the recent progresses in immunotherapeutic strategy using CAR-modified T cells oriented to EGFRvIII against GBM.

Role of Chimeric Antigen Receptor T Cell Therapy in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common primary malignant cancer of brain, which is extremely aggressive and carries a dreadful prognosis. Current treatment protocol runs around radiotherapy, surgical resection, and temozolomide with median overall survival of around 12-15 months. Due to its heterogeneity and mutational load, immunotherapy with chimeric antigen receptor (CAR) T cell therapy can be a promising treatment option for recurrent glioblastoma. Initial phase 1 studies have shown that this therapy is safe without dose-limiting side effects and it also has a better clinical outcome. Therefore, CAR T cell therapy can be a great future tool in our armamentarium to treat advanced GBM. In this article, we have explained the structure, mechanism of action, and rationale of CAR T cell therapy in GBM; we also discussed various antigenic targets and clinical outcome of initial studies of this novel therapy.

Epidermal growth factor receptor and EGFRvIII in glioblastoma: signaling pathways and targeted therapies

Amplification of epidermal growth factor receptor (EGFR) and its active mutant EGFRvIII occurs frequently in glioblastoma (GBM). While EGFR and EGFRvIII play critical roles in pathogenesis, targeted therapy with EGFR-tyrosine kinase inhibitors (TKIs) or antibodies has only shown limited efficacy in patients. Here we discuss signaling pathways mediated by EGFR/EGFRvIII, current therapeutics, and novel strategies to target EGFR/EGFRvIII-amplified GBM.

Radiotherapy Upregulates Programmed Death Ligand-1 through the Pathways Downstream of Epidermal Growth Factor Receptor in Glioma

Background

In the present study, we aimed to investigate the role of epidermal growth factor receptor (EGFR) pathway in the up-regulation of programmed death ligand-1 (PD-L1) caused by radiotherapy (RT).

Materials and Methods

Tissue microarrays (TMA) consisting of glioma cancer specimens from 64 patients were used to examine the correlation between PD-L1 and EGFR levels. Furthermore, we performed in vitro experiments to assess the role of EGFR pathway in RT-upregulated PD-L1 expression using human glioma cell lines U87 and U251.

Results

Our data demonstrated that the PD-L1 expression was significantly correlated with EGFR expression in glioma specimens (χ² = 5.00, P = 0.025). The expressions of PD-L1 at the protein and mRNA levels were both significantly up-regulated by RT (P < 0.05). The expressions of phosphorylated EGFR and janus kinase 2 (JAK2) were also induced by RT (P < 0.05). Besides, inhibition of EGFR pathway could abrogate the RT-triggered PD-L1 up-regulation (P > 0.05). The combination of RT with EGFR inhibitor exhibited the same effect on antitumor immune response compared with the combination of RT with PD-L1 neutralizing antibody (Ab).

Conclusions

RT could up-regulate the PD-L1 expression through the pathways downstream of EGFR in glioma.

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The PD-L1 expression was significantly correlated with EGFR expression in glioma specimens.

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RT promoted the phosphorylation of EGFR to activate the JAK2 pathway, which resulted in the upregulation of PD-L1.

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Inhibition of EGFR pathway could abrogate the RT-triggered PD-L1 up-regulation.

Glioma is a highly lethal and common central nervous system tumor with poor 5-year survival rate. It is still urgently necessary to develop more effective therapeutic strategies for glioma. We found radiotherapy up-regulated the PD-L1 expression through the pathways downstream of EGFR in glioma. This finding provides new evidence for the combination of RT with PD-1/PD-L1 or EGFR-TKI inhibitor. That may contribute to the development of new therapeutic strategy for glioma.

Cyclic trans-phosphorylation in a homodimer as the predominant mechanism of EGFRvIII action and regulation

Despite intensive research no therapies targeted against the oncogenic EGFRvIII are present in the clinic. One of the reasons is the elusive nature of the molecular structure and activity of the truncated receptor. The recent publications indicate the EGF-bound wild-type EGFR to trans-phosphorylate the EGFRvIII initiating aberrant signaling cascade. The elevated stability of the mutant receptor contributes towards oncogenic potential, preventing termination of signaling by receptor degradation. Here, we show that inhibition of phosphatases leads to a marked increase in phosphorylation of wild-type EGFR and EGFRvIII, indicating that both undergo cyclic rounds of phosphorylation and dephosphorylation on all investigated tyrosine residues, including Tyr1045. Still, we observe elevated stability of the mutant receptor, suggesting phosphorylation as insufficient to cause degradation. Hyperphosphorylation of EGFRvIII was hindered only by EGFR tyrosine kinase inhibitors. Co-immunoprecipitation as well as semi-native Western blotting structural analyses together with functional investigation of EGFRvIII's phosphorylation following depletion of wild-type EGFR by shRNA or EGF-mediated degradation indicated homodimerization as the predominant quaternary structure of the mutant receptor. Dimers were observed only under non-reducing conditions, suggesting that homodimerization is mediated by covalent bonds. Previous reports indicated cysteine at position 16 to mediate covalent homodimerization. Upon its substitution to serine, we have observed impaired formation of dimers and lower phosphorylation levels of the mutated oncogene. Based on the obtained results we propose that EGFRvIII is predominantly regulated dynamically by phosphatases that counteract the process of trans-phosphorylation occurring within the homodimers.

Interleukin-13 receptor alpha 2 cooperates with EGFRvIII signaling to promote glioblastoma multiforme

The interleukin-13 receptor alpha2 (IL-13Rα2) is a cancer-associated receptor overexpressed in human glioblastoma multiforme (GBM). This receptor is undetectable in normal brain which makes it a highly suitable target for diagnostic and therapeutic purposes. However, the pathological role of this receptor in GBM remains to be established. Here we report that IL-13Rα2 alone induces invasiveness of human GBM cells without affecting their proliferation. In contrast, in the presence of the mutant EGFR (EGFRvIII), IL-13Rα2 promotes GBM cell proliferation in vitro and in vivo. Mechanistically, the cytoplasmic domain of IL-13Rα2 specifically binds to EGFRvIII, and this binding upregulates the tyrosine kinase activity of EGFRvIII and activates the RAS/RAF/MEK/ERK and STAT3 pathways. Our findings support the "To Go or To Grow" hypothesis whereby IL-13Rα2 serves as a molecular switch from invasion to proliferation, and suggest that targeting both receptors with STAT3 signaling inhibitor might be a therapeutic approach for the treatment of GBM.

Genomic copy number gains of ErbB family members predict poor clinical outcomes in glioma patients

The aim of this study was to investigate copy number of ErbB family members (including EGFR, HER2, HER3 and HER4) in a cohort of gliomas and benign meningiomas (control subjects), and explore the associations of their copy number with clinicopathological characteristics and clinical outcomes of glioma patients. Using real-time quantitative PCR assay, we demonstrated that copy number of EGFR, HER2, HER3 and HER4 in glioma patients was significantly increased compared to control subjects. Moreover, our data also showed that the risk of cancer-related death was positively associated with copy number gain (CNG) of EGFR, HER3 and HER4, but not HER2. CNG of EGFR and HER2 was positively related to radiotherapy, while CNG of HER3 and HER4 was negatively related to chemotherapy. Importantly, EGFR CNG significantly shortened median survival times of glioma patients regardless of gender, tumor grade and therapeutic regimens. Stratified analysis showed that CNG of HER2-4 almost did not influence the survival of male patients, patients with high-grade tumors and patients receiving chemotherapy, but dramatically shortened median survival times of female patients, those with low-grade tumors and those receiving radiotherapy. Collectively, our data not only demonstrate that the members of ErbB family are frequently amplified in gliomas, but also suggest that these common genetic events may be prognostic factors for poor clinical outcomes in glioma patients.

The power of the few

This Outlook discusses the study in this issue by Zanca et al., in which mutant EGFR expression in a small population of cancer cells in high-grade brain tumors (glioblastoma) can orchestrate the complex behavior of the entire tumor.

Converging evidence from numerous laboratories has revealed that malignant brain cancers are complex ecological systems composed of distinct cellular and acellular elements that collectively dictate glioblastoma biology. Our understanding of the individual contributions of each of these components is vital to the design of effective therapies against these cancers. In this issue of Genes & Development, Zanca and colleagues (pp. 1212–1227) demonstrate that one subpopulation of glioblastoma cells expressing a mutant epidermal growth factor receptor (EGFRvIII) is responsible for the survival of non-EGFRvIII-expressing tumor cells as well as for evading molecularly targeted therapy.

A TNF-JNK-Axl-ERK signaling axis mediates primary resistance to EGFR inhibition in glioblastoma

Aberrant EGFR signaling is widespread in cancer, making the EGFR an important target for therapy. EGFR gene amplification and mutation are common in glioblastoma (GBM), but EGFR inhibition has not been effective in treating this tumor. Here, we propose that primary resistance to EGFR inhibition in glioma cells results from a rapid compensatory response to EGFR inhibition that mediates cell survival. We show that in glioma cells expressing either EGFR wild type or the mutant EGFRvIII, EGFR inhibition triggers a rapid adaptive response driven by increased TNF secretion that leads to activation of a TNF-JNK-Axl-ERK signaling axis. Inhibition of this adaptive axis at multiple nodes renders glioma cells with primary resistance sensitive to EGFR inhibition. Our findings provide a possible explanation for the multiple failures of anti-EGFR therapy in GBM and suggest a new approach to the treatment of EGFR expressing GBM using a combination of EGFR and TNF inhibition.

A novel, somatic, transforming mutation in the extracellular domain of Epidermal Growth Factor Receptor identified in myeloproliferative neoplasm

We describe a novel ERBB1/EGFR somatic mutation (p. C329R; c.985 T > C) identified in a patient with JAK2^V617F Polycythaemia Vera (PV). This substitution affects a conserved cysteine residue in EGFR domain 2 and leads to the formation of a ligand-independent covalent receptor dimer, associated with increased transforming potential. Aberrant signalling from the EGFR^C329R receptor is cell type-dependent and in the TF1.8 erythroid cell line expression of this mutant suppresses EPO-induced differentiation. Clonal analysis shows that the dominant JAK2^V617F-positive clone in this PV patient harbors EGFR^C329R, thus this mutation may contribute to clonal expansion. Somatic mutations affecting other ERBB and related receptor tyrosine kinases are observed in myeloproliferative neoplasms (MPN), and we show elevated EGFR levels in MPN samples, consistent with previous reports. Thus activation of this group of receptors, via multiple mechanisms, may contribute to clonal growth and survival of the JAK2^V617F disease clone in MPN.

Aptamer-conjugated PEGylated quantum dots targeting epidermal growth factor receptor variant III for fluorescence imaging of glioma

The extent of resection is a significant prognostic factor in glioma patients. However, the maximum safe resection level is difficult to determine due to the inherent infiltrative character of tumors. Recently, fluorescence-guided surgery has emerged as a new technique that allows safe resection of glioma. In this study, we constructed a new kind of quantum dot (QD)-labeled aptamer (QD-Apt) nanoprobe by conjugating aptamer 32 (A32) to the QDs surface, which can specially bind to the tumors. A32 is a single-stranded DNA capable of binding to the epidermal growth factor receptor variant III (EGFRvIII) specially distributed on the surface of glioma cells. To detect the expression of EGFRvIII in human brain tissues, 120 specimens, including 110 glioma tissues and 10 normal brain tissues, were examined by immunohistochemistry, and the results showed that the rate of positive expression of EGFRvIII in the glioma tissues was 41.82%, and 0.00% in normal brain tissues. Besides, the physiochemical properties of QD-Apt nanoparticles (NPs) were thoroughly characterized. Biocompatibility of the NPs was evaluated, and the results suggested that the QD-Apt was nontoxic in vivo and vitro. Furthermore, the use of the QD-Apt in labeling glioma cell lines and human brain glioma tissues, and target gliomas in situ was also investigated. We found that not only could QD-Apt specially bind to the U87-EGFRvIII glioma cells but also bind to human glioma tissues in vitro. Fluorescence imaging in vivo with orthotopic glioma model mice bearing U87-EGFRvIII showed that QD-Apt could penetrate the blood-brain barrier and then selectively accumulate in the tumors through binding to EGFRvIII, and consequently, generate a strong fluorescence, which contributed to the margins of gliomas that were visualized clearly, and thus, help the surgeons realize the maximum safe resection of glioma. In addition, QD-Apt can also be applied in preoperative diagnosis and postoperative examination of glioma. Therefore, these achievements facilitate the use of tumor-targeted fluorescence imaging in the diagnosis, surgical resection, and postoperative examination of glioma.

Cyclin-dependent kinase 7 is a therapeutic target in high-grade glioma

High-grade glioma (HGG) is an incurable brain cancer. The transcriptomes of cells within HGG tumors are highly heterogeneous. This renders the tumors unresponsive or able to adapt to therapeutics targeted at single pathways, thereby causing treatment failure. To overcome this, we focused on cyclin-dependent kinase 7 (CDK7), a ubiquitously expressed molecule involved in two major drivers of HGG pathogenesis: cell cycle progression and RNA polymerase-II-based transcription. We tested the activity of THZ1, an irreversible CDK7 inhibitor, on patient-derived primary HGG cell lines and ex vivo HGG patient tissue slices, using proliferation assays, microarray analysis, high-resolution respirometry, cell cycle analysis and in vivo tumor orthografts. The cellular processes affected by CDK7 inhibition were analyzed by reverse transcriptase–quantitative PCR, western blot, flow cytometry and immunofluorescence. THZ1 perturbed the transcriptome and disabled CDK activation, leading to cell cycle arrest at G2 and DNA damage. THZ1 halted transcription of the nuclear-encoded mitochondrial ribosomal genes, reducing mitochondrial translation and oxidative respiration. It also inhibited the expression of receptor tyrosine kinases such as epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor-α (PDGFR-α), reducing signaling flux through the AKT, extracellular-signal-regulated kinase 1/2 (ERK1/2) and signal transducer and activator of transcription 3 (STAT3) downstream pathways. Finally, THZ1 disrupted nucleolar, Cajal body and nuclear speckle formation, resulting in reduced cytosolic translation and malfunction of the spliceosome and thus leading to aberrant mRNA processing. These findings indicate that CDK7 is crucial for gliomagenesis, validate CDK7 as a therapeutic target and provide new insight into the cellular processes that are affected by THZ1 and induce antitumor activity.

Exploiting receptor tyrosine kinase co-activation for cancer therapy

Studies over the past decade have shown that many cancers have evolved receptor tyrosine kinase (RTK) co-activation as a mechanism to drive tumour progression and limit the lethal effects of therapy. This review summarises the general principles of RTK co-activation and discusses approaches to exploit this phenomenon in cancer therapy and drug discovery. Computational strategies to predict kinase co-dependencies by integrating drug screening data and kinase inhibitor selectivity profiles will also be described. We offer a perspective on the implications of RTK co-activation on tumour heterogeneity and cancer evolution and conclude by surveying emerging computational and experimental approaches that will provide insights into RTK co-activation biology and deliver new developments in effective cancer therapies.

Incomplete target neutralization by the anti-cancer antibody rilotumumab

The antibody rilotumumab, which has been tested in multiple Phase 2 and Phase 3 trials, has been reported to neutralize hepatocyte growth factor (HGF), the ligand for the oncogene MET. However, we report that rilotumumab does not prevent HGF from directly binding to MET on conventional and primary patient-derived human gliomasphere lines, a trait driven by the HGF α-chain, which remains free to engage cell-surface glycosaminoglycans and the receptor MET. This binding induces MET phosphorylation, initiates robust AKT and ERK signaling and potentiates biological effects such as cell scattering. This partial antagonism was highly exacerbated in the presence of activated epidermal growth factor receptor, which is common in several cancers. Hence, we confirm that rilotumumab is only a partial antagonist of HGF activity, a finding that has considerable implications for the therapeutic use of rilotumumab.

A focused compound screen highlights the significance of epidermal growth factor receptor signalling in chordoma pathogenesis

Chordoma is a rare primary bone cancer with limited treatment options. Surgical resection followed by radiotherapy has proven effective; however, when, in 30-40% of patients, tumours recur and metastasize, a high level of resistance to chemotherapies leaves these patients with a dearth of treatment options. Recent work published in the Journal of Pathology by Scheipl et al describing a focused compound drug screen highlights the significance of epidermal growth factor receptor (EGFR) signalling in chordoma, and shows potential for EGFR inhibitors as a way forward for developing an effective treatment for chordoma. Importantly, combining EGFR inhibitors with a MET inhibitor induces a synergistic effect on growth inhibition of resistant chordoma cells, highlighting the significance of combined EGFR and MET inhibitors as a potential avenue to defeat chemoresistance in chordoma patients. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Aptamer targeting EGFRvIII mutant hampers its constitutive autophosphorylation and affects migration, invasion and proliferation of glioblastoma cells

Glioblastoma Multiforme (GBM) is the most common and aggressive human brain tumor, associated with very poor survival despite surgery, radiotherapy and chemotherapy.The epidermal growth factor receptor (EGFR) and the platelet-derived growth factor receptor β (PDGFRβ) are hallmarks in GBM with driving roles in tumor progression. In approximately half of the tumors with amplified EGFR, the EGFRvIII truncated extracellular mutant is detected. EGFRvIII does not bind ligands, is highly oncogenic and its expression confers resistance to EGFR tyrosine kinase inhibitors (TKIs). It has been demonstrated that EGFRvIII-dependent cancers may escape targeted therapy by developing dependence on PDGFRβ signaling, thus providing a strong rationale for combination therapy aimed at blocking both EGFRvIII and PDGFRβsignaling.We have recently generated two nuclease resistant RNA aptamers, CL4 and Gint4.T, as high affinity ligands and inhibitors of the human wild-type EGFR (EGFRwt) and PDGFRβ, respectively.Herein, by different approaches, we demonstrate that CL4 aptamer binds to the EGFRvIII mutant even though it lacks most of the extracellular domain. As a consequence of binding, the aptamer inhibits EGFRvIII autophosphorylation and downstream signaling pathways, thus affecting migration, invasion and proliferation of EGFRvIII-expressing GBM cell lines.Further, we show that targeting EGFRvIII by CL4, as well as by EGFR-TKIs, erlotinib and gefitinib, causes upregulation of PDGFRβ. Importantly, CL4 and gefitinib cooperate with the anti-PDGFRβ Gint4.T aptamer in inhibiting cell proliferation.The proposed aptamer-based strategy could have impact on targeted molecular cancer therapies and may result in progresses against GBMs.

EGFR Activation Leads to Cell Death Independent of PI3K/AKT/mTOR in an AD293 Cell Line

The Epidermal Growth Factor Receptor (EGFR) and its mutations contribute in various ways to tumorigenesis and biology of human cancers. They are associated with tumor proliferation, progression, drug resistance and the process of apoptosis. There are also reports that overexpression and activation of wild-type EGFR may lead to cell apoptosis. To study this phenomenon, we overexpressed in an AD293 cell line two most frequently observed forms of the EGFR receptor: wild-type and the constitutively active mutant–EGFR variant III (EGFRvIII). Then, we compared the effect of EGF stimulation on cell viability and downstream EGFR signaling. AD293 cells overexpressing wild-type EGFR, despite a significant proliferation increase in serum supplemented medium, underwent apoptosis after EGF stimulation in serum free conditions. EGFRvIII expressing cells, however, were unaffected by either serum starvation or EGF treatment. The effect of EGF was completely neutralized by tyrosine kinase inhibitors (TKIs), indicating the specificity of this observation. Moreover, apoptosis was not prevented by inhibiting EGFR downstream proteins (PI3K, AKT and mTOR). Here we showed another EGFR function, dependent on environmental factors, which could be employed in therapy and drug design. We also proposed a new tool for EGFR inhibitor analysis.

Progress in the application of molecular biomarkers in gliomas

Gliomas are a common adult central nervous system tumor, and glioblastoma (GBM), which has a poor prognosis, is the most lethal of all gliomas. The overall survival of GBM patients is only 12-14 months after diagnosis. With progress in the precision of personal medication, therapeutic options for various tumors have become gradually dependent on the molecular profiles of patients. GBM is one of the tumors in which treatment response relies largely on the molecular characteristics of the tumor. Therefore, awareness of the genetic background of each patient will help decision-making regarding the best treatment strategy to use. In this review, a novel molecular classification of gliomas based on recent findings of their genetic characteristics is introduced. Representative molecular markers, such as IDH1 mutation, 1p19q co-deletion, MGMT promoter methylation and EGFRvIII amplification, are described. Furthermore, the development of non-coding RNAs and omics studies of GBM are briefly discussed. Finally, a novel concept for non-invasive detection that could facilitate both diagnosis and treatment monitoring is presented. There is no doubt that the use of molecular profiling by biomarkers will indeed improve the overall survival and quality of life of GBM patients.