Pediatric Low-grade Astrocytoma Research Articles

IL-5 Targeted Therapies for Nervous System Tumors – Progress, Pitfalls, and Prospects

Abstract The molecular genetic understanding of nervous system tumors has expanded rapidly offering insight into potentially targetable oncogenic driver alterations. In monogenic tumor susceptibility syndromes such as tuberous sclerosis, neurofibromatosis type 1, and von Hippel Lindau syndrome targeted drugs have demonstrated efficacy and are now approved in the United States for the treatment of subependymal giant cell astrocytoma, plexiform neurofibroma, and hemangioblastoma, respectively. Some genetic alterations like BRAF V600E mutations or neurotrophic receptor tyrosine kinase (NTRK) fusions, occur across multiple cancers, including certain types of gliomas. Dabrafenib in combination with trametinib is approved for use in gliomas that harbor BRAF V600E mutations and larotrectinib is approved in gliomas that harbor certain NTRK fusions. In pediatric low-grade astrocytoma, one of the most common solid tumors of childhood, BRAF truncation-fusion events may render these tumors susceptible to tovorafenib, a type 2 RAF inhibitor, which is under study in clinical trials. Mutations in the isocitrate dehydrogenase (IDH) gene occur in the majority of low-grade and anaplastic gliomas, create specific metabolic vulnerabilities, and several IDH-mutant targeting strategies are under investigation. Glioblastoma is characterized by intratumoral molecular heterogeneity so strategies that target single genetic alterations may not be as effective as in other types of gliomas although a number of novel targeted strategies have been advanced to clinical trials. Other types of nervous system tumors such as medulloblastoma, meningioma, primary central nervous system diffuse large B-cell lymphoma, and craniopharyngioma harbor targetable genetic alterations and clinical trials are ongoing. Finally, metastatic brain tumors may harbor targetable genetic alterations that may differ from the primary site of cancer highlighting the importance of biopsy and molecular analysis of the brain metastases in order to enroll patients in clinical trials of targeted therapies.

LG-04 * NOTCH SIGNALING ACTIVATION IN PEDIATRIC LOW-GRADE ASTROCYTOMA

Pilocytic astrocytoma (PA) is the most common primary brain tumor in children, and various signaling pathways have been implicated in its biology. The Notch signaling pathway has been found to play a role in development, stem cell biology and the pathogenesis of several cancers but its role in PA has not been investigated. We studied alterations in Notch signaling components in clinical PA tumor tissue, to identify much needed therapeutic targets. In this study, we found Notch pathway members to be overexpressed at the mRNA (NOTCH1, NOTCH2, HEY1, HEY2) and protein (HES1) level in PA at various anatomical sites compared to non-neoplastic brain. The changes were not associated with specific BRAF alterations. Inhibiting the Notch pathway in pediatric low grade astrocytoma-derived cell lines (Res 186 and Res 259) using either RNA interference or a gamma secretase inhibitor resulted in a significant, but variable reduction in cell growth and migration. This study suggests a role for Notch signaling in the context of pediatric low grade astrocytoma tumorigenesis, and that Notch signaling is a viable pathway to target therapeutically.

Growth-factor-driven rescue to receptor tyrosine kinase (RTK) inhibitors through Akt and Erk phosphorylation in pediatric low grade astrocytoma and ependymoma.

Up to now, several clinical studies have been started investigating the relevance of receptor tyrosine kinase (RTK) inhibitors upon progression free survival in various pediatric brain tumors. However, single targeted kinase inhibition failed, possibly due to tumor resistance mechanisms. The present study will extend our previous observations that vascular endothelial growth factor receptor (VEGFR)-2, platelet derived growth factor receptor (PDGFR)β, Src, the epidermal growth factor receptor (ErbB) family, and hepatocyte growth factor receptor (HGFR/cMet) are potentially drugable targets in pediatric low grade astrocytoma and ependymoma with investigations concerning growth-factor-driven rescue. This was investigated in pediatric low grade astrocytoma and ependymoma cell lines treated with receptor tyrosine kinase (RTK) inhibitors e.g. sorafenib, dasatinib, canertinib and crizotinib. Flow cytometry analyses showed high percentage of cells expressing VEGFR-1, fibroblast growth factor receptor (FGFR)-1, ErbB1/EGFR, HGFR and recepteur d’origine nantais (RON) (respectively 52-77%, 34-51%, 63-90%, 83-98%, 65-95%). Their respective inhibitors induced decrease of cell viability, measured with WST-1 cell viability assays. At least this was partially due to increased apoptotic levels measured by Annexin V/Propidium Iodide apoptosis assays. EGF, HGF and FGF, which are normally expressed in brain (tumor) tissue, showed to be effective rescue inducing growth factors resulting in increased cell survival especially during treatment with dasatinib (complete rescue) or sorafenib (partial rescue). Growth-factor-driven rescue was less prominent when canertinib or crizotinib were used. Rescue was underscored by significantly activating downstream Akt and/or Erk phosphorylation and increased tumor cell migration. Combination treatment showed to be able to overcome the growth-factor-driven rescue. In conclusion, our study highlights the extensive importance of environmentally present growth factors in developing tumor escape towards RTK inhibitors in pediatric low grade astrocytoma and ependymoma. It is of great interest to anticipate upon these results for the design of new therapeutic trials with RTK inhibitors in these pediatric brain tumors.

Notch signaling activation in pediatric low-grade astrocytoma.

Pilocytic astrocytoma (PA) is the most common primary brain tumor in children; various signaling pathways have been implicated in its biology. The Notch signaling pathway has been found to play a role in the development, stem cell biology, and pathogenesis of several cancers, but its role in PA has not been investigated. We studied alterations in Notch signaling components in tumor tissue from 18 patients with PA and 4 with other low-grade astrocytomas to identify much needed therapeutic targets. We found that Notch pathway members were overexpressed at the mRNA (NOTCH1, NOTCH2, HEY1, HEY2) and protein (HES1) levels in PAs at various anatomic sites compared with non-neoplastic brain samples. These changes were not associated with specific BRAF alterations. Inhibiting the Notch pathway in the pediatric low-grade astrocytoma cell lines Res186 and Res259 using either RNA interference or a γ-secretase inhibitor resulted in variable, but significant, reduction in cell growth and migration. This study suggests a potential role for Notch signaling in pediatric low-grade astrocytoma tumorigenesis and that Notch signaling may be a viable pathway therapeutic target.

Abstract B4: Growth-factor-driven rescue to receptor tyrosine kinase inhibitors in pediatric low-grade astrocytoma and ependymoma

Abstract Introduction: Brain tumors are still the leading cause of cancer morbidity and mortality among children, despite different therapeutic options including neurosurgery, chemotherapy and radiation. Up to now, several clinical studies have been started investigating the importance of receptor tyrosine kinase (RTK) inhibitors upon progression free survival in various pediatric brain tumors. However, it has been shown that single targeted kinase inhibition failed due to tumor resistance mechanisms. The present study will extend our previous observations that vascular endothelial growth receptor (VEGFR) 2, platelet derived growth factor receptor (PDGFR) β, Src, the epidermal growth factor receptor (ErbB) family, and hepatocyte growth factor receptor (HGFR/cMet) are potential drugable targets in pediatric low grade astrocytoma and ependymoma with investigations concerning growth-factor-driven rescue. Material and methods: Expression of various RTKs in pediatric low grade astrocytoma (Res-186, Res-259, UW-467) and ependymoma (Res-196) cell lines were determined using flow cytometry analyses. Growth-factor-driven rescue during RTK inhibition with agents including sorafenib, dasatinib, canertinib and crizotinib were analyzed on cell viability level measured with WST-1 cell viability assays and on phosphorylation level of the crucial downstream PI3K/Akt and MAPK/Erk survival signaling pathways using western blot analyses. Results: VEGFR-1, fibroblast growth factor receptor (FGFR) 1, ErbB-1, HGFR and recepteur d'origine nantais (RON) were highly expressed (respectively 52-77%, 34-51%, 63-90%, 83-98%, 65-95%) and their respective inhibitors showed induced decrease of tumor cell viability. EGF, HGF and FGF, which are normally environmentally expressed in brain (tumor) tissue, showed to be effective rescue inducing growth factors resulting in increased cell survival especially during treatment with dasatinib (complete rescue) or sorafenib (partial rescue) in both low grade astrocytoma and ependymoma. Growth-factor-driven rescue was less prominent when canertinib or crizotinib were used. Rescue was underscored by activating downstream Akt and/or Erk phosphorylation. Combination treatment showed to be able to overcome the growth-factor-driven resistance. Conclusions: In conclusion, our study highlights the extensive importance of environmentally present growth factors in developing resistance towards RTK inhibitors. It is of great interest to anticipate upon these results for the design of new therapeutic trials with RTK inhibitors in pediatric low grade astrocytoma and ependymoma. Citation Format: Mariska Sie, Wilfred F.A. den Dunnen, Harm Jan Lourens, Tiny G.J. Meeuwsen-de Boer, Frank J.G. Scherpen, Kim R. Kampen, Eelco W. Hoving, Eveline S.J.M. de Bont. Growth-factor-driven rescue to receptor tyrosine kinase inhibitors in pediatric low-grade astrocytoma and ependymoma. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B4.

Abstract 5085: Less tumor engraftment after anti-VEGF therapy in pediatric low grade astrocytoma.

Abstract Introduction. Low grade astrocytomas are the most frequent brain tumors in children. Although children can benefit from treatments including neurosurgery, chemotherapy and radiotherapy, still children die due to tumor progression. Furthermore, morbidity can be serious. So new therapeutic strategies are warranted for these patients. Previously, we showed that angiogenesis is a characteristic of pediatric low grade astrocytoma (Sie et al, NAN 2010). Therefore, vascular endothelial growth factor (VEGF), the most critical angiogenic factor, may be a potential therapeutic target. The present study aimed to analyze the effect of VEGF inhibition in vitro and in vivo in pediatric low grade astrocytoma. Materials and methods. Three different pediatric low grade astrocytoma cell lines were used: Res-186 (WHO grade I astrocytoma), Res-259 and UW-467 (WHO grade II astrocytoma). Effects in vitro of the anti-VEGF monoclonal antibodies, bevacizumab (0 - 50 ug/ml, Avastin®, anti human VEGF) and B20-4.1.1 (0 - 200 ug/ml, anti human and mouse VEGF) were studied using a WST-1 cell viability assay and a cell proliferation assay with BRDU. Res-259 cells were orthotopically implanted in NOD-scid IL2Rgnull mice. After 6 weeks of treatment intraperitoneal twice weekly with bevacizumab (15 mg/kg), B20-4.1.1 (5 mg/kg) or phosphate buffered saline as control group, mice were euthanized and tumor engraftment was studied in brain slides using Aperio's imagescope viewer. Results. In vitro cell growth was not changed as measured by WST-1 and BRDU incorporation. In vivo results showed less tumor engraftment in bevacizumab (n = 10) and B20-4.1.1 (n = 9) treated mice compared with the control group (n = 10) (resp. 70%, 44%, 100%). In the bevacizumab and B20-4.1.1 treated mice tumor mass was lower as compared with controls (resp. P = 0.062, P = 0.001). Conclusion(s). This study showed less tumor engraftment after anti-VEGF therapy in a newly developed pediatric low grade astrocytoma mouse model. In these tumors anti-VEGF seems to work especially on tumor microenvironment. Suggesting that anti-VEGF could have a potential role in the therapeutic strategy for children with low grade astrocytoma, thoughtfulness on possible tumor escape mechanisms that may arise will be crucial. [W.F.A. den Dunnen and E.S.J.M. de Bont shared senior authorship.] Citation Format: Mariska Sie, Arend H. Sikkema, Frank J.G. Scherpen, Arja ter Elst, Kim R. Kampen, Eelco W. Hoving, Wilfred F.a. den Dunnen, Eveline S.j.m. de Bont. Less tumor engraftment after anti-VEGF therapy in pediatric low grade astrocytoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5085. doi:10.1158/1538-7445.AM2013-5085

Abstract 5048: mTORC1/mTORC2 signaling in pediatric low grade glioma and pilocytic astrocytoma.

Abstract Pilocytic astrocytoma is the most frequent low grade glioma in children and young adults. Previous studies support a role for MAPK pathway signaling, and more recently AKT/mTOR, in its biology. mTOR operates as part of two different multiprotein signaling complexes, mTORC1 and mTORC2. In the current study we evaluated mTORC1/mTORC2 pathway activity in pediatric low grade astrocytoma. We used formalin-fixed paraffin embedded human pilocytic astrocytomas for immunohistochemical studies in tissue microarrays. Moderate (2+) to strong (3+) immunostaining was observed for pS6 in 66/114(58%), p4EBP1 in 35/116(30%), pElF4G in 66/113 (58%), and mTOR (total) in 52/114 (46%), supporting mTOR pathway activation in a subset of pediatric astrocytomas. Specifically, there was increased immunoreactivity in pilocytic astrocytomas of the optic nerve proper (pS6 39/54(72%), p4EBP1 22/54 (41%), 4IF4G 41/53 (77%), and mTOR 28/54 (52%)), a difference that was statistically significant for pS6, p4E-BP1 and pEIF4G (p<0.05, Chi Square). Next, we studied total levels of Raptor (mTORC1 component) and Rictor (mTORC2 component). We observed moderate to strong Raptor reactivity in 81/142 (57%) and Rictor in 69/141(49%) pilocytic astrocytomas. By contrast, we observed increased Rictor immunostaining in 90/144 (63%) diffuse gliomas grade II-IV and Raptor in 28/147 (19%), a difference that was statistically significant between the two groups (p<0.001, Chi Square). Next we studied in vitro the effect of mTORC1 blockade in pediatric low grade glioma cell lines Res 186 and Res 259 with a TORC1 inhibitor. Using the MTT assay, Res 186 cell growth was inhibited with 1nM and 10nM drug concentrations, compared with DMSO (p<0.005, t-test), but the effect was less pronounced in Res 259. Additionally, pS6 levels were decreased by Western Blot in Res 186 cells, but not in Res 259, consistent with mTORC1 inhibition of Res 186 cells. The findings suggest that the mTOR pathway is active in a subset of pediatric low grade gliomas, that it varies by clinicopathologic subtype, and that it is primarily mediated by mTORC1 compared with other glioma subtypes. Furthermore, mTOR may represent a therapeutic target in pediatric low grade glioma that merits further investigation. Citation Format: Smit Shah, Marianne Hutt, Matthias A. Karajannis, Eric Raabe, Charles G. Eberhart, Fausto J. Rodriguez. mTORC1/mTORC2 signaling in pediatric low grade glioma and pilocytic astrocytoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5048. doi:10.1158/1538-7445.AM2013-5048

Neurosurgical treatment of low-grade cerebellar astrocytoma in children and adolescents: a single consecutive institutional series of 100 patients

The objective of this study was to delineate the long-term results of surgical treatment of pediatric low-grade cerebellar astrocytoma. One hundred consecutive children and adolescents (0-19 years old) who underwent primary tumor resection for a low-grade cerebellar astrocytoma during the years 1980-2011 were included in this retrospective study on surgical morbidity, mortality rate, academic achievement, and/or work participation. Gross motor function and activities of daily living were scored according to the Barthel Index. Of the 100 patients, 61 children were in the 1st decade, and 39 were 10-19 years old. The male/female ratio was 1.13:1 (53 males, 47 females). No patients were lost to follow-up. There were no deaths in this series and all 100 patients are currently alive. In 29 patients, the follow-up duration was less than 10 years, in 37 it was between 10 and 19 years, and in 34 it was between 20 and 31 years. The Barthel Index was 100 (normal) in 97 patients, 90 in 2 patients, and 40 in the last patient. A total of 113 tumor resections were performed. Two patients underwent further tumor resection due to MRI-confirmed residual tumor demonstrated on the immediate postoperative MR image (obtained the day after the initial procedure). Furthermore, 9 children underwent repeat tumor resection after MRI-confirmed progressive tumor recurrence up to 10 years after the initial operation. Two of these patients also underwent a third resection, without subsequent radiation therapy, and have experienced 8 and 12 years of tumor-free follow-up thereafter, respectively. A total of 15% of the patients required treatment for persistent hydrocephalus. Low-grade cerebellar astrocytoma is a surgical disease, in need of long-term follow-up, but with excellent long-term results. Nine percent of the children in this study underwent repeated surgery due to progressive tumor recurrence, and 15% were treated for persistent hydrocephalus.

Pathological and Molecular Advances in Pediatric Low-Grade Astrocytoma

Pediatric low-grade astrocytomas are the most common brain tumors in children. They can have similar microscopic and clinical features, making accurate diagnosis difficult. For patients whose tumors are in locations that do not permit full resection, or those with an intrinsically aggressive biology, more effective therapies are required. Until recently, little was known about the molecular changes that drive the initiation and growth of pilocytic and other low-grade astrocytomas beyond the association of a minority of cases, primarily in the optic nerve, with neurofibromatosis type 1. Over the past several years, a wide range of studies have implicated the BRAF oncogene and other members of this signaling cascade in the pathobiology of pediatric low-grade astrocytoma. In this review, we attempt to summarize this rapidly developing field and discuss the potential for translating our growing molecular knowledge into improved diagnostic and prognostic biomarkers and new targeted therapies.

Pilomyxoid astrocytoma: diagnosis, prognosis, and management

Pilomyxoid astrocytoma (PMA) is a recently defined pediatric brain tumor; PMAs were previously classified within the pilocytic astrocytoma (PA) category. Nevertheless, PMA has different histological features and has been shown to behave more aggressively than PA. These findings indicate that PMA may be a unique entity that is distinct from PA, or it may be an unusual variant. To increase awareness of PMA within the neurosurgical community, the authors review the diagnostic criteria, prognostic implications, and current management of this recently described pediatric low-grade astrocytoma.

Low-grade astrocytoma: a decade of experience at St. Jude Children's Research Hospital.

To evaluate the impact of primary tumor site, age at diagnosis, extent of resection, and histology on progression-free survival (PFS) in pediatric low-grade astrocytoma. Medical, pathologic, and imaging information were reviewed for 142 children (ages 2 months to 19 years) with low-grade astrocytoma treated between January 1984 and July 1994. Gross total resection (GTR) was attempted for cerebellar and cerebral hemisphere tumors, with biopsy or less aggressive resection used predominantly for tumors in other sites. Surgery was followed by observation in 107 cases, radiation therapy in 31, and chemotherapy in four. The overall survival rate was 90% +/- 3% (SE) at 4 years. PFS was significantly better for patients with cerebellar and cerebral hemisphere tumors (n = 75) than those with tumors in all other sites (P = .0006). Within the former group, there was no significant difference in PFS for patients in whom GTR was achieved versus those with incomplete resections (4-year estimates, 89% and 77%, respectively). Histology (juvenile pilocytic v astrocytoma not otherwise specified [NOS]) was not related to PFS in an analysis that controlled for tumor site and patient age. Patients younger than 5 years at diagnosis had a significantly poorer PFS than older children, regardless of histology (P < .03) or tumor site (P < .002). Treatment for progressive/recurrent disease was effective in a majority of patients, but appeared more successful in patients with hemispheric than thalamic or hypothalamic tumors. The overall survival in this series of pediatric low-grade astrocytomas is excellent. Age at diagnosis and tumor location, but not histology, had a significant impact on PFS. Efforts to improve treatment outcome should focus on young patients (< 5 years) and on those with central midline tumors. The majority of patients with completely resected hemispheric tumors were monitored without further therapy, which supports attempted GTR of cerebral and cerebellar hemisphere low-grade astrocytoma.