EGFRvIII Signaling Research Articles

WSP from "Nostoc commune" Vauch. suppresses gastric cancer migration via EGFRVIII signaling.

A number of evidences have proved that "Nostoc commune" Vauch can improve human immunity and prevent diseases, however, the specific mechanism remains unclear. The biological activity of the main protein component of "Nostoc commune" Vauch extracellular matrix- a water-stress protein (WSP) still needs to be elucidated. In our study, we validated the role of WSP in gastric cancer metastasis at the cellular level, the organoid level and in mouse models, and also studied the role of EGFRVIII and downstream signaling molecules after WSP treatment. We found that WSP can significantly inhibit the metastasis of gastric cancer cells. Interestingly, we found that the anti-metastasis ability of WSP on gastric cancer was related to membrane protein receptor EGFRVIII, which was realized by inhibiting the downstream EGFRVIII signaling pathway. In terms of mechanism, WSP can inhibit the downstream EGFRVIII signaling pathway Akt-PI3K and further inhibit the secretion of cancer-related metastasis proteins such as MMP2 and MMP9, thus, significantly affecting the metastasis of gastric cancer cells. Given the anticancer properties of WSP, drug developers and manufacturers can further develop protein drugs for cancer patients using protein engineering techniques based on the properties of WSP.

CSIG-03. EGFR LIGAND SHIFTS THE ROLE OF EGFR FROM ONCOGENE TO TUMOR SUPPRESSOR IN EGFR AMPLIFIED GLIOBLASTOMA

Abstract Glioblastoma (GBM) is a devastating cancer largely because of its highly invasive nature. Although pathways that promote GBM invasion have been identified, no pathway that actively suppresses GBM invasion is known and there is no treatment that specifically blocks GBM invasion. EGFR is a prime oncogene and is frequently amplified and mutated in GBM. However multiple clinical trials of EGFR inhibition in GBM have failed. Here, we demonstrate that EGFR ligands activate a tumor suppressor for the EGFR in EGFR-amplified GBMs. Analysis of TCGA data reveals that GBM patients with EGFR amplification and a low level of EGFR ligands have a worse prognosis compared to those with EGFR amplification and a high level of EGFR ligands. We identify the cytoskeletal BAR domain protein BIN3 as a critical suppressor of invasion upregulated by EGFR ligand in EGFR amplified GBMs. BIN3 inhibits a DOCK-7 Rho GTPase pathway, resulting in small hyper-proliferating noninvasive tumors and a better prognosis, while constitutive EGFR wild type or EGFRvIII signaling promotes invasion via activation of a TAB1-TAK1-NF-κB-EMP1 pathway, resulting in large tumors and worse survival in orthotopic models. Consistent with its role as a negative regulator of invasion, BIN3 is deleted in 10% of GBMs and increased expression of BIN3 confers a better prognosis. Thus, increased EGFR ligand shifts the role of EGFR from oncogene to tumor suppressor in EGFR amplified GBMs by suppressing invasion. We identify tofacitinib, a BBB penetrant drug as an upregulator of BIN3 and show that tofacitinib suppresses invasion and prolongs survival in orthotopic models. Our study identifies a new tumor suppressive function of EGFR in GBM and we propose the use of tofacitinib to directly target invasion in EGFR-amplified and EGFR ligand-poor GBMs.

Abstract 101: JAK-independent STAT5 signaling as a node of therapeutic vulnerability in glioblastoma

Abstract Glioblastoma (GBM), the most common primary brain tumor in adults, comprises all WHO Grade IV gliomas of astrocytic origin. Despite extensive characterization of the molecular and genetic features of GBM, there remains a paucity of viable treatment options, and this disease confers a dismal 5% 5-year survival rate. Genomic amplification of epidermal growth factor receptor (EGFR) occurs in 40-60% of primary GBM. Half of all EGFR-amplified cases of GBM also harbor EGFRvIII, a constitutively active, truncated variant of EGFR. EGFR and EGFRvIII transduce oncogenic signals via cytoplasmic mediators, including the JAK/STAT signal transduction pathway. The oncogenic role of STAT3 has been well-studied in CNS malignancies; STAT3 has been found to induce the expression of target genes involved in the proliferative and invasive phenotypes of GBM. However, little is known about the mechanism and role of STAT5 activation in GBM progression. Microenvironmental cues and EGFRvIII signaling, lost in adherent cell culture, are required for STAT5 activation, making STAT5 difficult to study by conventional cell culture methods. Our recent data from patient-derived xenograft (PDX) cultures demonstrates that activation of STAT5 is important in GBM cell invasion and survival. Further, STAT5 activation is present predominantly at the invasive periphery of the tumor. In this study, we seek to characterize the mechanism and role of STAT5 activation downstream of EGFRvIII in GBM. RNA sequencing of PDX tumors expressing stable shRNA knockdown of STAT3 or STAT5 indicate both redundant and distinct transcriptional changes induced by STAT3 and STAT5 in GBM. We also find that while STAT3 activation is dependent upon JAK1/2, STAT5 activation is JAK-independent downstream of EGFRvIII in GBM. Depletion of JAK1/2 expression by siRNA oligonucleotides and pharmacologic inhibition of JAK1/2 suppressed STAT3 activation but not STAT5. In fact, targeting JAK2 with kinase inhibitor WP1066 suppressed STAT3 activation, but increased activation of STAT5 in GBM cells expressing EGFR/EGFRvIII. Inhibition of Src family kinases (SFK), a family of upstream signaling effectors of the JAK/STAT pathway, attenuates both STAT3 and STAT5 activation. These results suggest that activation of STAT5 may provide a therapeutic escape mechanism to JAK-STAT3 inhibition in GBM, necessitating dual STAT3 and STAT5 inhibition to successfully inhibit the distinct oncogenic signals transmitted by STAT3 and STAT5 to promote GBM cell survival and resistance. Citation Format: Mylan Blomquist, Serdar Tuncali, Christopher Sereduk, Jean Kloss, Joseph Loftus, Nhan Tran. JAK-independent STAT5 signaling as a node of therapeutic vulnerability in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 101.

The miR-183/96/182 cluster is upregulated in glioblastoma carrying EGFR amplification

Glioblastoma (GBM) is one of the most frequent primary brain tumors. Limited therapeutic options and high recurrency rates lead to a dismal prognosis. One frequent, putative driver mutation is the genomic amplification of the oncogenic receptor tyrosine kinase EGFR. Often accompanied by variants like EGFRvIII, heterogenous expression and ligand independent signaling render this tumor subtype even more difficult to treat, as EGFR-directed therapeutics show only weak effects at best. So EGFR-amplified GBM is considered to have an even worse prognosis, and therefore, deeper understanding of molecular mechanisms and detection of potential targets for novel therapeutic strategies is urgently needed. In this study, we looked at the level of microRNAs (miRs), small non-coding RNAs frequently deregulated in cancer, both acting as oncogenes and tumor suppressors. Comparative analysis of GBM with and without EGFR amplification should give insight into the expression profiles of miRs, which are considered both as potential targets for directed therapies or as therapeutic reagents. Comparison of miR profiles of EGFR-amplified and EGFR-normal GBM revealed an upregulation of the miR-183/96/182 cluster, which is associated with oncogenic properties in several tumor entities. One prominent target of this miR cluster is FOXO1, a pro-apoptotic factor. By observing FOXO1 downregulation in EGFR-amplified tumors, we can see a significant correlation of EGFR amplification, miR-183/96/182 cluster upregulation, and repression of FOXO1. Although no significant difference in overall survival is shown, these data may contribute to the molecular understanding of this tumor subtype and offer potential targets for miR-based therapies.

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.

Extracellular Hyaluronic Acid Influences the Efficacy of EGFR Tyrosine Kinase Inhibitors in a Biomaterial Model of Glioblastoma.

3D biomaterial models have potential to explore the influence of the tumor microenvironment on aberrant signaling pathways and compensatory signals using patient-derived cells. Glioblastoma (GBM) tumors are highly heterogeneous, with both cell composition and extracellular matrix biophysical factors seen as key regulators of malignant phenotype and treatment outcomes. Amplification, overexpression, and mutation of the epidermal growth factor receptor (EGFR) tyrosine kinase have been identified in 50% of GBM patients. Here, hyaluronic acid (HA) decorated methacrylamide-functionalized gelatin (GelMA) hydrogels are used to examine the synergies between microenvironmental factors and a model EGFR tyrosine kinase inhibitor (TKI) using patient-derived xenograft cells. The in vitro behavior of 3 patient-derived xenografts that reflect a clinically relevant range of EGFR variants is characterized: GBM10 (EGFR, wild type), GBM12 (EGFR+), and GBM6 (EGFRvIII). GelMA hydrogels support xenograft culture; cells remain viable, active, respond to matrix-immobilized HA, and upregulate genes associated with matrix remodeling and tumor growth. Interestingly, matrix-immobilized HA alters the response of GBM cells to a model tyrosine kinase inhibitor, erlotinib. While constitutively activated EGFRvIII cells are sensitive to TKI in gelatin hydrogels, hyaluronic acid mediated adhesive signaling interacts with EGFRvIII signaling to increase cell metabolic activity, increase soluble hyaluronic acid synthesis, and modify response to erlotinib exposure.

Abstract 5776: Glioblastoma tumor model to analyze the mechanisms of resistance to tyrosine kinase inhibitors

Abstract The extracellular matrix (ECM) is increasingly recognized as having a key role in cancer development. We have developed a biomaterial tumor mimic that recapitulates systematically the main characteristics and heterogeneities of glioblastoma ECM. With the use of these 3D in vitro platforms we seek to understand the key features that make this cancer so challenging to treat. We are using this device in three different ways: (1) to further understand how particularities of brain tumor ECM affect cancer cells and assist in the diagnostic of different glioblastoma (GBM) tumor types, (2) provide new models for drug screening to afford more personalized therapies and (3) study the mechanisms of resistance to current therapies in order to identify more effective combinatorial treatments and new therapeutic targets. Hyaluronic acid (HA), is the main component of the brain ECM and GBM is associated with aberrant HA secretion and overexpression of receptors associated with HA, such as CD44 and EGFR. We cultured GBM patient-derived xenograft (PDX) cells within gelatin based hydrogels that contained variable concentrations of HA. Cell proliferation and gene expression analyses demonstrate that biomimetic hydrogels support xenograft culture and cells upregulate matrix remodeling genes and others related to tumor growth in response to matrix biophysical properties. We also used these platforms to evaluate the mechanisms of cell resistance to tyrosine kinase inhibitors. For this purpose, we first focused on the epidermal growth factor receptor (EGFR), which has been identified as a molecular target and associated with worse clinical outcomes. We characterized the 3D in vitro behavior of 3 PDX that represent these EGFR variants: GBM10 (EGFR, wild type), GBM12 (EGFR+) and GBM6 (EGFRvIII). We studied the relationship between the HA contained in the surrounding matrix and response of GBM cells to a tyrosine kinase inhibitor (TKI), erlotinib. Results indicate that while EGFR+ cells are sensitive to TKI in HA hydrogels, HA seems to collaborate with EGFRvIII signaling to stir cell activity. Immunoblots demonstrate that this enhanced cell activity is related to a significant increase in PDGFR concentration. Blockade of the CD44 receptor, in combination with erlotinib treatment, does not affect phosphorylation rates of PI3K or ERK, however, it leads to a significant decrease of STAT3 phosphorylation. This is translated into a lower tumor cell metabolic activity in HA matrices. Finally, we show that, patient-derived xenograft cells resistant to erlotinib in vivo (GBM10), become sensitive when CD44 is blocked in HA-containing matrices, as demonstrated by a decrease of phosphorylated PI3K. In summary, we highlight the importance of extracellular HA in EGFR inhibition efficiency. We demonstrate that this biomaterial tumor model can be used as a valuable tool in the mechanistic studies of tumor development and prediction of tyrosine kinase inhibitors efficacy. Citation Format: Sara Pedron, Gabrielle L. Wolter, Emily Chen, Jann N. Sarkaria, Brendan A. Harley. Glioblastoma tumor model to analyze the mechanisms of resistance to tyrosine kinase inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5776. doi:10.1158/1538-7445.AM2017-5776

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Inhibition of radiation-induced glioblastoma invasion by genetic and pharmacological targeting of MDA-9/Syntenin

Glioblastoma multiforme (GBM) is an intractable tumor despite therapeutic advances, principally because of its invasive properties. Radiation is a staple in therapeutic regimens, although cells surviving radiation can become more aggressive and invasive. Subtraction hybridization identified melanoma differentiation-associated gene 9 [MDA-9/Syntenin; syndecan-binding protein (SDCBP)] as a differentially regulated gene associated with aggressive cancer phenotypes in melanoma. MDA-9/Syntenin, a highly conserved double-PDZ domain-containing scaffolding protein, is robustly expressed in human-derived GBM cell lines and patient samples, with expression increasing with tumor grade and correlating with shorter survival times and poorer response to radiotherapy. Knockdown of MDA-9/Syntenin sensitizes GBM cells to radiation, reducing postradiation invasion gains. Radiation induces Src and EGFRvIII signaling, which is abrogated through MDA-9/Syntenin down-regulation. A specific inhibitor of MDA-9/Syntenin activity, PDZ1i (113B7), identified through NMR-guided fragment-based drug design, inhibited MDA-9/Syntenin binding to EGFRvIII, which increased following radiation. Both genetic (shmda-9) and pharmacological (PDZ1i) targeting of MDA-9/Syntenin reduced invasion gains in GBM cells following radiation. Although not affecting normal astrocyte survival when combined with radiation, PDZ1i radiosensitized GBM cells. PDZ1i inhibited crucial GBM signaling involving FAK and mutant EGFR, EGFRvIII, and abrogated gains in secreted proteases, MMP-2 and MMP-9, following radiation. In an in vivo glioma model, PDZ1i resulted in smaller, less invasive tumors and enhanced survival. When combined with radiation, survival gains exceeded radiotherapy alone. MDA-9/Syntenin (SDCBP) provides a direct target for therapy of aggressive cancers such as GBM, and defined small-molecule inhibitors such as PDZ1i hold promise to advance targeted brain cancer therapy.

Abstract 700: Regulation of Fn14 expression by EGFRvIII-STAT signaling enhances glioblastoma cell invasion and survival

Abstract Glioblastoma Multiforme (GBM) is the most common malignant brain tumor in adults. Most GBM patients succumb to the disease less than one-year post diagnosis due to the highly invasive nature of the tumor, which prevents complete surgical resection and gives rise to tumor recurrence. The invasive phenotype also confers radio-and chemoresistant properties to the tumor cells; therefore, there is a need to develop new therapeutics that target drivers of GBM invasion. Amplification of EGFR is observed in over 50% of GBM tumors, of which half concurrently overexpress the variant EGFRvIII, and expression of both receptors confers a worse prognosis. EGFR and EGFRvIII cooperate to promote tumor progression and invasion, in part, through activation of the JAK/STAT-signaling pathway. Here we report that GBM cells expressing EGFRvIII show increased expression of a previously established mediator of glioma cell invasion and survival, fibroblast growth factor-inducible 14 (Fn14), at the mRNA and protein level. Treatment with STAT3, STAT5, JAK, or Src inhibitors decreased Fn14 mRNA and protein expression. Finally, knockdown of Fn14 levels in the EGFRvIII-expressing glioma cells decreased both cell survival after temozolomide (TMZ) treatment and cell invasion, which suggests that Fn14, in part, mediates the oncogenic phenotypes conferred by EGFRvIII signaling. Since EGFR inhibitors display limited therapeutic efficacy in GBM patients, we hypothesize that Fn14-targeted therapies could potentially limit invasiveness and chemoresistance in EGFRvIII-dependent GBM tumors. Citation Format: Alison Roos, Zachary Mayo, Heather Sonnemann, Michael Pineda, Gil Lambert, Harshil D. Dhruv, Jeffrey A. Winkles, Michael E. Berens, Nhan L. Tran. Regulation of Fn14 expression by EGFRvIII-STAT signaling enhances glioblastoma cell invasion and survival. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 700.

Old player, new partner: EGFRvIII and cytokine receptor signaling in glioblastoma.

The brain cancer glioblastoma relies on aberrant epidermal growth factor receptor (EGFRvIII) signaling for tumorigenesis. An essential co-receptor and feed-forward circuit maintain signaling in this deadly disease.

CSIG-13INVESTIGATING THE ROLE OF Fn14 IN EGFRvIII-DRIVEN GLIOBLASTOMA

Glioblastoma Multiforme (GBM) is the most common malignant brain tumor in adults. Most GBM patients succumb to the disease less than one-year post diagnosis due to the highly invasive nature of the tumor, which prevents complete surgical resection and gives rise to tumor recurrence. The invasive phenotype also confers radio-and chemoresistant properties to the tumor cells; therefore, there is a need to develop new therapeutics that target drivers of GBM invasion. Amplification of EGFR is observed in over 50% of GBM tumors, of which half concurrently overexpress the variant EGFRvIII, and expression of both receptors confers a worse prognosis. EGFR and EGFRvIII cooperate to promote tumor progression and invasion, in part, through activation of the JAK/STAT-signaling pathway. Here we report that GBM cells expressing EGFRvIII show increased expression of a previously established mediator of glioma cell invasion and survival, fibroblast growth factor-inducible 14 (Fn14), at the mRNA and protein level. Treatment with a STAT3, STAT5, or JAK inhibitor decreased Fn14 mRNA and protein expression. Finally, knockdown of Fn14 levels in the EGFRvIII-expressing glioma cells decreased both cell survival after temozolomide (TMZ) treatment and cell invasion, which suggests that Fn14, in part, mediates the oncogenic phenotypes conferred by EGFRvIII signaling. Since EGFR inhibitors display limited therapeutic efficacy in GBM patients, we hypothesize that Fn14-targeted therapies could potentially limit invasiveness and chemoresistance in these tumor subtypes.

Ligand-Independent EGFR Signaling.

Constitutive activation of the EGFR is common in cancer due to EGFR wild-type (EGFRwt) overexpression or the presence of mutant EGFR. Signaling by constitutively active NSCLC EGFR mutants or the EGFRvIII mutant in glioblastoma has been studied intensively and the downstream signals are known. Normally, the EGFRwt is activated when it is exposed to ligand, resulting in activation of canonical signals such as ERK and Akt. The EGFRwt also becomes tyrosine phosphorylated and constitutively activated without ligand when it is overexpressed, but downstream signals are unclear. Recent studies have identified a noncanonical form of signaling triggered by EGFRwt exclusively in the absence of ligand that does not involve ERK or Akt activation but, instead, results in activation of the transcription factor IRF3. The addition of ligand turns off IRF3-dependent transcription and activates ERK and Akt. Thus, the EGFR triggers distinct and mutually exclusive signaling networks, depending on the presence of ligand. Furthermore, noncanonical EGFRwt signaling may influence response to treatment in cancer. Also, there are reports of both synergistic and antagonistic interactions between ligand-dependent EGFRwt and EGFRvIII signaling. Here, we discuss ligand-independent EGFR signal transduction by oncogenic EGFR mutants and EGFRwt, and review the interplay between EGFRwt and EGFRvIII.

Abstract 4153: Investigating the role of Fn14 in EGFRvIII-driven glioblastoma

Abstract Glioblastoma Multiforme (GBM) is the most common malignant brain tumor in adults. Most GBM patients succumb to the disease less than one-year post diagnosis due to the highly invasive nature of the tumor, which prevents complete surgical resection and gives rise to tumor recurrence. The invasive phenotype also confers radio-and chemoresistant properties to the tumor cells; therefore, there is a need to develop new therapeutics that target drivers of GBM invasion. Amplification of EGFR is observed in over 50% of GBM tumors, of which half concurrently overexpress the variant EGFRvIII, and expression of both receptors confers a worse prognosis. EGFR and EGFRvIII cooperate to promote tumor progression and invasion, in part, through activation of the JAK/STAT-signaling pathway. Here we report that GBM cells expressing EGFRvIII show increased expression of a previously established mediator of glioma cell invasion and survival, fibroblast growth factor-inducible 14 (Fn14), at the mRNA and protein level. Treatment with a STAT3, STAT5, or JAK inhibitor decreased Fn14 mRNA and protein expression. Finally, knockdown of Fn14 levels in the EGFRvIII-expressing glioma cells decreased both cell survival after temozolomide (TMZ) treatment and cell invasion, which suggests that Fn14, in part, mediates the oncogenic phenotypes conferred by EGFRvIII signaling. Since EGFR inhibitors display limited therapeutic efficacy in GBM patients, we hypothesize that Fn14-targeted therapies could potentially limit invasiveness and chemoresistance in these tumor subtypes. Citation Format: Alison Roos, Zachary Mayo, Michael Pineda, Jeffery A. Winkles, Michael E. Berens, Nhan L. Tran. Investigating the role of Fn14 in EGFRvIII-driven glioblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4153. doi:10.1158/1538-7445.AM2015-4153

Abstract LB-022: Aptamer-mediated inhibition of EGFRvIII mutant in glioblastoma cells

Abstract High-grade glioblastoma multiforme (GBM) is the most aggressive and common of gliomas in human populations, accounting for 55% of primary brain tumors. The prognosis of GBM is very poor and most patients die of tumor recurrence. The epidermal growth factor receptor (EGFR) and the platelet-derived growth factor receptor β (PDGFRβ) are hallmarks in GBM since they influence multiple aspects of tumor biology including cell proliferation, migration, invasiveness and resistance to treatment. In approximately half of the tumors with amplified EGFR, the EGFRvIII truncated extracellular mutant is detected. EGFRvIII does not bind ligand, is highly oncogenic and appears to be relatively resistant to treatment with conventional anti-EGFR agents such as ligand blocking monoclonal antibodies or EGFR tyrosine kinase inhibitors (TKIs). Recently, 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 PDGFRβ signaling. We have generated two nuclease resistant 2′F-Py RNA aptamers, CL4 and Gint4.T, as high affinity ligands and inhibitors of human wild-type EGFR (EGFRwt) and PDGFRβ, respectively. Thanks to their unique characteristics (low size, good target affinity, no immunogenicity, high stability) aptamers represent a new class of molecules with a great potential to rival monoclonal antibodies in both therapy and diagnosis. Herein, by different approaches we demonstrate that CL4 aptamer binds to the EGFRvIII mutant even though it lacks amino acids 6-273 in the extracellular domain. As a consequence of binding, the aptamer inhibits EGFRvIII activation by hampering receptor homodimerization and downstream STAT3 pathway, thus confirming the critical role of EGFRvIII dimerization for signaling. Further, we show that targeting EGFRvIII by CL4, as well as by erlotinib and gefitinib, causes upregulation of PDGFRβ as a compensatory response to support cancer cell survival. Importantly, CL4 and EGFRTKIs cooperate with the anti-PDGFRβ aptamer in inhibiting survival and proliferation of EGFRvIII-overexpressing glioblastoma cells. Given the paucity of selective inhibitors for receptor tyrosine kinases, this study could have impact in the fields of targeted molecular cancer therapeutics and may result in progress against GBM. Citation Format: Simona Camorani, Elvira Crescenzi, David Colecchia, Andrea Carpentieri, Angela Amoresano, Mario Chiariello, Laura Cerchia. Aptamer-mediated inhibition of EGFRvIII mutant in glioblastoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-022. doi:10.1158/1538-7445.AM2015-LB-022

Current Therapeutic Advances Targeting EGFR and EGFRvIII in Glioblastoma.

Epidermal growth factor receptor (EGFR) and EGFRvIII analysis is of current interest in glioblastoma – the most common malignant primary CNS tumor, because of new EGFRvIII vaccine trials underway. EGFR activation in glioblastoma promotes cellular proliferation via activation of MAPK and PI3K–Akt pathways, and EGFRvIII is the most common variant, leading to constitutively active EGFR. This review explains EGFR and EGFRvIII signaling in GBM; describes targeted therapy approaches to date including tyrosine kinase inhibitor, antibody-based therapies, vaccines and pre-clinical RNA-based therapies, and discusses the difficulties encountered with these approaches including pathway redundancy and intratumoral heterogeneity.

Temozolomide induces the production of epidermal growth factor to regulate MDR1 expression in glioblastoma cells.

Glioblastoma multiforme (GBM) commonly resists the frontline chemotherapy treatment temozolomide. The multidrug resistance gene (MDR1) and its protein, P-glycoprotein (P-gp), are associated with chemoresistance. This study investigated the mechanisms underlying MDR1-mediated resistance by GBM to temozolomide. P-gp trafficking was studied by flow cytometry and Western blot analysis. MDR1 expression was analyzed by real-time PCR and reporter gene assays. AP-1 interaction with MDR1 was studied by chromatin immunoprecipitation assay. EGF production was analyzed by ELISA, EGFR signaling was determined by Western blot analysis, and in vivo response to erlotinib and/or temozolomide was studied in nude mice. During the early phase of temozolomide treatment, intracellular P-gp was trafficked to the cell membrane, followed by conformational change into active P-gp. At the later phase, gene transcription of MDR1 was induced by temozolomide-mediated production of EGF. EGF activated ERK1/2-JNK-AP-1 cofactors (c-jun and c-fos). An inhibitor of EGFR kinase (erlotinib) given to nude mice with GBM prevented temozolomide-induced resistance. The results identified an essential role for activated EGFR in the resistance of GBM to temozolomide. Temozolomide resistance occurred through a biphasic response; first, by a conformational change in P-gp into the active form and, second, by releasing EGF, which caused autocrine stimulation of GBM cells to induce MDR1. Pharmacologic inhibition of EGFR kinase blunted the ability of GBM cells to resist temozolomide. These findings may explain reports on the common occurrence of mutant EGFR (EGFRvIII) and EGFR expansion in the resistance of GBM cells.

The epidermal growth factor receptor variant III (EGFRvIII): where wild things are altered

The epidermal growth factor receptor (EGFR) is overexpressed in a variety of human epithelial tumors, often as a consequence of gene amplification. Tumors with EGFR gene amplification frequently contain EGFR gene rearrangements, with the most common extracellular domain mutation being EGFRvIII. This mutation leads to a deletion of exons 2-7 of the EGFR gene and renders the mutant receptor incapable of binding any known ligand. Despite this, EGFRvIII displays low-level constitutive signaling that is augmented by reduced internalization and downregulation. Aberrant EGFRvIII signaling has been shown to be important in driving tumor progression and often correlates with poor prognosis. It is clear that EGFRvIII is expressed in a considerable proportion of patients with glioblastoma multiforme (GBM). The presence of EGFRvIII in other tumor types, however, remains controversial. In this review, we critically analyze the evidence for the expression of EGFRvIII in a range of tumor types and discuss recent findings pertinent to its function and biology in GBM.

De-Repression of PDGFRβ Transcription Promotes Acquired Resistance to EGFR Tyrosine Kinase Inhibitors in Glioblastoma Patients

Acquired resistance to tyrosine kinase inhibitors (TKI) represents a major challenge for personalized cancer therapy. Multiple genetic mechanisms of acquired TKI resistance have been identified in several types of human cancer. However, the possibility that cancer cells may also evade treatment by co-opting physiologically regulated receptors has not been addressed. Here, we show the first example of this alternate mechanism in brain tumors by showing that EGF receptor (EGFR)-mutant glioblastomas (GBMs) evade EGFR TKIs by transcriptionally de-repressing platelet-derived growth factor receptor β (PDGFRβ). Mechanistic studies show that EGFRvIII signaling actively suppresses PDGFRβ transcription in an mTORC1- and extracellular signal-regulated kinase-dependent manner. Genetic or pharmacologic inhibition of oncogenic EGFR renders GBMs dependent on the consequently de-repressed PDGFRβ signaling for growth and survival. Importantly, combined inhibition of EGFR and PDGFRβ signaling potently suppresses tumor growth in vivo. These data identify a novel, nongenetic TKI resistance mechanism in brain tumors and provide compelling rationale for combination therapy. These results provide the fi rst clinical and biologic evidence for receptor tyrosinekinase (RTK) "switching" as a mechanism of resistance to EGFR inhibitors in GBM and provide a molecular explanation of how tumors can become "addicted" to a non amplified, nonmutated, physiologically regulated RTK to evade targeted treatment.

Conditional Astroglial Rictor Overexpression Induces Malignant Glioma in Mice

BackgroundHyperactivation of the mTORC2 signaling pathway has been shown to contribute to the oncogenic properties of gliomas. Moreover, overexpression of the mTORC2 regulatory subunit Rictor has been associated with increased proliferation and invasive character of these tumor cells.Methodology/Principal FindingsTo determine whether Rictor overexpression was sufficient to induce glioma formation in mice, we inserted a Cre-lox-regulated human Rictor transgene into the murine ROSA26 locus. This floxed Rictor strain was crossed with mice expressing the Cre recombinase driven from the glial fibrillary acidic protein (GFAP) promoter whose expression is limited to the glial cell compartment. Double transgenic GFAP-Cre/RictorloxP/loxP mice developed multifocal infiltrating glioma containing elevated mTORC2 activity and typically involved the subventricular zone (SVZ) and lateral ventricle. Analysis of Rictor-dependent signaling in these tumors demonstrated that in addition to elevated mTORC2 activity, an mTORC2-independent marker of cortical actin network function, was also elevated. Upon histological examination of the neoplasms, many displayed oligodendroglioma-like phenotypes and expressed markers associated with oligodendroglial lineage tumors. To determine whether upstream oncogenic EGFRvIII signaling would alter tumor phenotypes observed in the GFAP-Cre/RictorloxP/loxP mice, transgenic GFAP-EGFRvIII; GFAP-Cre/RictorloxP/loxP mice were generated. These mice developed mixed astrocytic-oligodendroglial tumors, however glioma formation was accelerated and correlated with increased mTORC2 activity. Additionally, the subventricular zone within the GFAP-Cre/RictorloxP/loxP mouse brain was markedly expanded, and a further proliferation within this compartment of the brain was observed in transgenic GFAP-EGFRvIII; GFAP-Cre/RictorloxP/loxP mice.Conclusion/SignificanceThese data collectively establish Rictor as a novel oncoprotein and support the role of dysregulated Rictor expression in gliomagenesis via mTOR-dependent and mTOR-independent mechanisms. Furthermore, oncogenic EGFRvIII signaling appears to potentiate the in vivo proliferative capacity of GFAP-Cre/RictorloxP/loxP gliomas.