Citations

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults, with few effective treatments. EGFR alterations, including expression of the truncated variant EGFRvIII, are among the most frequent genomic changes in these tumors. EGFRvIII is known to preferentially signal through STAT5 for oncogenic activation in GBM, yet targeting EGFRvIII has yielded limited clinical success to date. In this study, we employed patient-derived xenograft (PDX) models expressing EGFRvIII to determine the key points of therapeutic vulnerability within the EGFRvIII-STAT5 signaling axis in GBM. Our findings reveal that exogenous expression of paralogs STAT5A and STAT5B augments cell proliferation and that inhibition of STAT5 phosphorylation in vivo improves overall survival in combination with temozolomide (TMZ). STAT5 phosphorylation is independent of JAK1 and JAK2 signaling, instead requiring Src family kinase (SFK) activity. Saracatinib, an SFK inhibitor, attenuates phosphorylation of STAT5 and preferentially sensitizes EGFRvIII+ GBM cells to undergo apoptotic cell death relative to wild-type EGFR. Constitutively active STAT5A or STAT5B mitigates saracatinib sensitivity in EGFRvIII+ cells. In vivo, saracatinib treatment decreased survival in mice bearing EGFR WT tumors compared to the control, yet in EGFRvIII+ tumors, treatment with saracatinib in combination with TMZ preferentially improves 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 Stat-signaling pathway. Here we report that EGFRvIII activates Stat5 and GBM invasion, in part, by inducing the expression of a previously established mediator of glioma cell invasion and survival, fibroblast growth factor-inducible 14 (Fn14). EGFRvIII-mediated induction of Fn14 expression is dependent upon Stat5 and requires activation of Src, whereas EGFR regulation of Fn14 is dependent upon MEK/ERK-Stat3 activation. Notably, treatment of EGFRvIII expressing GBM cells with the FDA approved Stat5 inhibitor pimozide blocked Stat5 phosphorylation, Fn14 expression, and cell migration. Since EGFR inhibitors display limited therapeutic efficacy in GBM patients, we hypothesize that the EGFRvIII-Stat5-Fn14 signaling pathway represents a node of vulnerability in the invasive GB cell population and that targeting critical effectors in this pathway will limit GBM tumor dispersion, mitigate therapeutic resistance, and increase survival. Citation Format: Alison Roos, Harshil D. Dhruv, Sen Peng, Landon J. Inge, Serdar Tuncali, Michael Pineda, Nghia Millard, Jeffrey A. Winkles, Joseph C. Loftus, Nhan L. Tran. EGFRvIII-Stat5 signaling enhances glioblastoma cell invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3462.

Abstract Glioblastoma multiforme (GBM) is the most common brain malignancies in adults. Most GBM patients succumb to the disease less than 1 year after 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 radioresistant and chemoresistant properties to the tumor cells; therefore, there is a critical 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 Stat signaling pathway. Here, it is reported that EGFRvIII activates Stat5 and GBM invasion by inducing the expression of a previously established mediator of glioma cell invasion and survival: fibroblast growth factor-inducible 14 (Fn14). EGFRvIII-mediated induction of Fn14 expression is Stat5 dependent and requires activation of Src, whereas EGFR regulation of Fn14 is dependent upon Src–MEK/ERK–Stat3 activation. Notably, treatment of EGFRvIII-expressing GBM cells with the FDA-approved Stat5 inhibitor pimozide blocked Stat5 phosphorylation, Fn14 expression, and cell migration and survival. Because EGFR inhibitors display limited therapeutic efficacy in GBM patients, the EGFRvIII–Stat5–Fn14 signaling pathway represents a node of vulnerability in the invasive GBM cell populations. Implications: Targeting critical effectors in the EGFRvIII–Stat5–Fn14 pathway may limit GBM tumor dispersion, mitigate therapeutic resistance, and increase survival. Mol Cancer Res; 16(7); 1185–95. ©2018 AACR.

Abstract Glioblastoma is the most frequent primary brain tumor in adults and a highly lethal malignancy with a median survival of about 15 months. The aggressive invasion of the surrounding normal brain makes complete surgical resection impossible, increases the resistance to radiation and chemotherapy, and assures tumor recurrence. Thus, there is an urgent need to develop innovative therapeutics to target the invasive tumor cells for improved treatment outcomes of this disease. Expression of TROY (TNFRSF19), a member of the tumor necrosis factor (TNF) receptor family, increases with increasing glial tumor grade and inversely correlates with patient survival. Increased expression of TROY stimulates glioblastoma cell invasion in vitro and in vivo and increases resistance to temozolomide and radiation therapy. Conversely, silencing TROY expression inhibits glioblastoma cell invasion, increases temozolomide sensitivity, and prolongs survival in an intracranial xenograft model. Here, a novel complex is identified between TROY and EGFR, which is mediated predominantly by the cysteine-rich CRD3 domain of TROY. Glioblastoma tumors with elevated TROY expression have a statistically positive correlation with increased EGFR expression. TROY expression significantly increases the capacity of EGF to stimulate glioblastoma cell invasion, whereas depletion of TROY expression blocks EGF stimulation of glioblastoma cell invasion. Mechanistically, TROY expression modulates EGFR signaling by facilitating EGFR activation and delaying EGFR receptor internalization. Moreover, the association of EGFR with TROY increases TROY-induced NF-κB activation. These findings substantiate a critical role for the TROY–EGFR complex in regulation of glioblastoma cell invasion. Implications: The TROY–EGFR signaling complex emerges as a potential therapeutic target to inhibit glioblastoma cell invasion. Mol Cancer Res; 16(2); 322–32. ©2017 AACR.

Abstract Glioblastoma Multiforme (GBM) is the most common tumor of the CNS with a median survival of approximately 15 months. The highly aggressive invasion of malignant cells into the surrounding normal brain tissue renders complete surgical resection impossible, increases therapeutic resistance, and virtually assures tumor recurrence. We have previously demonstrated that TROY (TNFRSF19) has an important role in GBM invasion and resistance. TROY expression is correlated with glial tumor grade and inversely correlated with patient survival. Increased TROY expression stimulated cell migration/invasion in vitro and in vivo and confers resistance to both ionizing radiation- and temozolomide-induced apoptosis via activation of Akt and NF-κB. These data indicate that TROY stimulated migration/invasion is associated with signaling pathways that also increase survival and therapeutic resistance, however, the mechanistic basis of this signaling remains unclear. To investigate the mechanism by which TROY induces GBM cell invasion, we performed immunoprecipitation of the TROY receptor coupled with MALDI-TOF and MS/MS analysis and identified PDZ-RhoGEF as a binding partner for TROY. We validated the interaction of TROY with PDZ-RhoGEF by immunoprecipitation and western blotting, and demonstrated that PDZ-RhoGEF can exchange for both RhoA and RhoC in glioma cells and is implicated in GBM cell invasion, proliferation, and survival. In order to assess the specific role of PDZ-RhoGEF in TROY signaling, we examined the effects of PDZ-RhoGEF on TROY-mediated activation of NF-κB. While overexpression of TROY alone strongly stimulated NF-κB transcriptional activity in serum-free conditions, increased expression of PDZ-RhoGEF alone had no effect on NF-κB activity. Co-transfection of PDZ-RhoGEF with TROY synergistically promoted NF-κB activation. Mutation of the TRAF binding domain (TBD) in the cytoplasmic domain of TROY abolished its capacity to activate NF-κB, even in the presence of PDZ-RhoGEF, suggesting that the TBD is important for TROY induced NF-κB activation. Furthermore, knockdown of PDZ-RhoGEF by shRNA attenuated NF-κB activation in TROY expressing cells, blocked TROY mediated invasion of primary GBM xenograft cells and increased sensitivity to temozolomide. Collectively, these data indicate that PDZ-RhoGEF plays an important role in TROY signaling and provides insights into a potential node of vulnerability to limit GBM cell invasion and decrease therapeutic resistance. Citation Format: Zonghui Ding, Alison Roos, Jean Kloss, Harshil Dhruv, Marc Symons, Nhan L. Tran, Joseph C. Loftus. PDZ-RhoGEF functions as a critical signaling effector for TROY [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 1878. doi:10.1158/1538-7445.AM2017-1878

Abstract Glioblastoma (GB) is the highest grade and most common form of primary adult brain tumors. Despite surgical removal followed by concomitant radiation and chemotherapy with the alkylating agent temozolomide, GB tumors develop treatment resistance and ultimately recur. Impaired response to treatment occurs rapidly, conferring a median survival of just fifteen months. Thus, it is necessary to identify the genetic and signaling mechanisms that promote tumor resistance to develop targeted therapies to combat this refractory disease. Previous observations indicated that SGEF (ARHGEF26), a RhoG-specific guanine nucleotide exchange factor (GEF), is overexpressed in GB tumors and plays a role in promoting TWEAK-Fn14–mediated glioma invasion. Here, further investigation revealed an important role for SGEF in glioma cell survival. SGEF expression is upregulated by TWEAK-Fn14 signaling via NF-κB activity while shRNA-mediated reduction of SGEF expression sensitizes glioma cells to temozolomide-induced apoptosis and suppresses colony formation following temozolomide treatment. Nuclear SGEF is activated following temozolomide exposure and complexes with the DNA damage repair (DDR) protein BRCA1. Moreover, BRCA1 phosphorylation in response to temozolomide treatment is hindered by SGEF knockdown. The role of SGEF in promoting chemotherapeutic resistance highlights a heretofore unappreciated driver, and suggests its candidacy for development of novel targeted therapeutics for temozolomide-refractory, invasive GB cells. Implication: SGEF, as a dual process modulator of cell survival and invasion, represents a novel target for treatment refractory glioblastoma. Mol Cancer Res; 14(3); 302–12. ©2016 AACR.

Abstract Glioblastoma (GBM) is the most common primary tumor of the CNS and carries a dismal prognosis. The aggressive invasion of GBM cells into the surrounding normal brain makes complete resection impossible, significantly increases resistance to the standard therapy regimen, and virtually assures tumor recurrence. Median survival for newly diagnosed GBM is 14.6 months and declines to 8 months for patients with recurrent GBM. New therapeutic strategies that target the molecular drivers of invasion are required for improved clinical outcome. We have demonstrated that TROY (TNFRSF19), a member of the TNFR super-family, plays an important role in GBM invasion and resistance. TROY expression increases with glial tumor grade and inversely correlates with patient survival. TROY stimulates GBM cell invasion and increases resistance to temozolomide (TMZ) and radiation treatment. Conversely, knockdown of TROY expression inhibits GBM cell invasion, increases sensitivity to temozolomide, and prolongs survival in an intracranial xenograft model. Propentofylline (PPF), an atypical synthetic methylxanthine compound, has been extensively studied in Phase II and Phase III clinical trials for Alzheimer's disease and vascular dementia where it has demonstrated blood-brain permeability and minimal adverse side effects. In this study, we demonstrated that PPF decreases TROY protein expression in glioma cells, and subsequently suppress activation downstream signaling effectors including AKT, NF-κB, and Rac1. PPF treatment of glioma cells also suppressed glioma cell migration and invasion, demonstrated by transwell migration assay and reduced membrane ruffling. Finally, PPF treatment increased vulnerability of glioma cells to Temozolomide (TMZ) and radiation. In summary, this study demonstrates that PPF provides a pharmacologic approach to target TROY to inhibit glioma cell invasion and reduce therapeutic resistance to TMZ and radiation. Citation Format: Harshil D. Dhruv, Serdar Tuncali, Alison Roos, Patrick Tomboc, Nathan Jameson, Ashley Chavez, Joseph Loftus, Michael E. Berens, Nhan L. Tran. Propentofylline inhibits TROY/TNFRSF19 signaling to enhance therapeutic efficacy in invasive 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 5366. doi:10.1158/1538-7445.AM2015-5366

Abstract Glioblastoma (GBM) is a highly lethal CNS malignancy in adults with a median survival of about 15 months. Effective therapeutic control of GBM is thwarted by the invasive nature of the tumor, which prevents complete surgical removal and results in tumor recurrence. Thus, there is a dire need to develop innovative approaches to target the invasive tumor cells for improved treatment of this disease. Expression of TROY, a member of the TNFR family, increases with glial tumor grade and inversely correlates with patient survival. Increased expression of TROY stimulates glioblastoma cell invasion and increases resistance to temozolomide (TMZ) and radiation treatment. We have demonstrated that TROY forms a novel complex with EGFR and modulates EGFR survival signaling. IHC analysis of GBM specimens showed that tumors with elevated TROY expression had a statistically positive correlation with increased EGFR expression. TROY expression enhanced EGFR phosphorylation, stabilized EGFR surface expression in the presence of ligand, and significantly increased EGF-stimulated GBM cell invasion. Consistent with invasion, co-expression of TROY with EGFR increased cell survival to TMZ. Moreover, we have shown that in cells treated with EGF, the TROY and ErbB4 receptor are recruited to the EGFR complex. Although the role of ErbB4 in GBM is not well defined, inhibition of ErbB4 expression suppressed tumor growth and invasion in multiple tumor subtypes, decreased EGFR surface retention, and limited EGF-induced cell migration. These data suggest that the TROY-EGFR-ErbB4 complex may represent an unappreciated therapeutic target to inhibit glioma invasion and decrease therapeutic resistance. Citation Format: Alison Roos, Zachary Mayo, Jean Kloss, Serdar Tuncali, Harshil Dhruv, Michael E. Berens, Joseph C. Loftus, Nhan L. Tran. TROY-EGFR signaling complex mediates glioblastoma cells invasion and survival. [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 506. doi:10.1158/1538-7445.AM2015-506