Phase I trial of imatinib in children with newly diagnosed brainstem and recurrent malignant gliomas: a Pediatric Brain Tumor Consortium report

H3 K27M-altered glioma and diffuse intrinsic pontine glioma: Semi-systematic review of treatment landscape and future directions

H3 K27M-mutant diffuse glioma is a recently identified brain tumor associated with poor prognosis. As of 2016, it is classified by the World Health Organization as a distinct form of grade IV glioma. Despite recognition as an important prognostic and diagnostic feature in diffuse glioma, radiation remains the sole standard of care and no effective systemic therapies are available for H3K27M mutant tumors. This review will detail treatment interventions applied to diffuse midline glioma and diffuse intrinsic pontine glioma (DIPG) prior to the identification of the H3 K27M mutation, the current standard-of-care for H3 K27M-mutant diffuse glioma treatment, and ongoing clinical trials listed on www.clinicaltrials.gov evaluating novel therapeutics in this population. Current clinical trials were identified using clinicaltrials.gov, and studies qualifying for this analysis were active or ongoing interventional trials that evaluated a therapy in at least 1 treatment arm or cohort comprised exclusively of patients with DIPG and H3 K27M-mutant glioma. Forty-one studies met these criteria, including trials evaluating H3 K27M vaccination, chimeric antigen receptor T-cell therapy, and small molecule inhibitors. Ongoing evaluation of novel therapeutics is necessary to identify safe and effective interventions in this underserved patient population.

Advances in Treatment of Diffuse Midline Gliomas

PURPOSE OF REVIEW

Diffuse midline gliomas (DMGs) generally carry a poor prognosis, occur during childhood, and involve midline structures of the central nervous system, including the thalamus, pons, and spinal cord.

RECENT FINDINGS

To date, irradiation has been shown to be the only beneficial treatment for DMG. Various genetic modifications have been shown to play a role in the pathogenesis of this disease. Current treatment strategies span targeting epigenetic dysregulation, cell cycle, specific genetic alterations, and the immune microenvironment. Herein, we review the complex features of this disease as it relates to current and past therapeutic approaches.

Decoding Diffuse Midline Gliomas: A Comprehensive Review of Pathogenesis, Diagnosis and Treatment

Diffuse midline gliomas (DMGs) are a group of aggressive CNS tumors, primarily affecting children and young adults, which have historically been associated with dismal outcomes. As the name implies, they arise in midline structures in the CNS, primarily in the thalamus, brainstem, and spinal cord. In more recent years, significant advances have been made in our understanding of DMGs, including molecular features, with the identification of potential therapeutic targets. We aim to provide an overview of the most recent updates in the field of DMGs, including classification, molecular subtypes, diagnostic techniques, and emerging therapeutic strategies including a review of the ongoing clinical trials, thus providing the treating multidisciplinary team with a comprehensive understanding of the current landscape and potential therapeutic strategies for this devastating group of tumors.

Radiotherapy and radio-sensitization in H3K27M -mutated diffuse midline gliomas

BACKGROUND

H3^K27M mutated diffuse midline gliomas (DMGs) are extremely aggressive and the leading cause of cancer-related deaths in pediatric brain tumors with 5-year survival <1%. Radiotherapy is the only established adjuvant treatment of H3^K27M DMGs; however, the radio-resistance is commonly observed.

METHODS

We summarized current understandings of the molecular responses of H3^K27M DMGs to radiotherapy and provide crucial insights into current advances in radiosensitivity enhancement.

RESULTS

Ionizing radiation (IR) can mainly inhibit tumor cell growth by inducing DNA damage regulated by the cell cycle checkpoints and DNA damage repair (DDR) system. In H3K27M DMGs, the aberrant genetic and epigenetic changes, stemness genotype, and epithelial-mesenchymal transition (EMT) disrupt the cell cycle checkpoints and DDR system by altering the associated regulatory signaling pathways, which leads to the development of radio-resistance.

CONCLUSIONS

The advances in mechanisms of radio-resistance in H3^K27M  DMGs promote the potential targets to enhance the sensitivity to radiotherapy.

New natural compound inhibitors of PDGFRA (platelet-derived growth factor receptor α) based on computational study for high-grade glioma therapy

Background

High-grade glioma (HGG) is a malignant brain tumor that is common and aggressive in children and adults. In the current medical paradigm, surgery and radiotherapy are the standard treatments for HGG patients. Despite this, the overall prognosis is still very bleak. Studies have shown that platelet-derived growth factor receptor α (PDGFRA) is an essential target to treat tumors and inhibiting the activity of PDGFRA can improve the prognosis of HGG. Thus, PDGFRA inhibitors are critical to developing drugs and cancer treatment.

Objective

The purpose of this study was to screen lead compounds and candidate drugs with potential inhibitors against platelet-derived growth factor receptor α (PDGFRA) from the drug library (ZINC database) in order to improve the prognosis of patients with high-grade glioma (HGG).

Materials and methods

In our study, we selected Imatinib as the reference drug. A series of computer-aided technologies, such as Discovery Studio 2019 and Schrodinger, were used to screen and assess potential inhibitors of PDGFRA. The first step was to calculate the LibDock scores and then analyze the pharmacological and toxicological properties. Following this, we docked the small molecules selected in the previous steps with PDGFRA to study their docking mechanism and affinity. In addition, molecular dynamics simulation was used to determine whether the ligand-PDGFRA complex was stable in nature.

Results

Two novel natural compounds 1 and 2 (ZINC000008829785 and ZINC000013377891) from the ZINC database were found binding to PDGFRA with more favorable interaction energy. Also, they were predicted with less Ames mutagenicity, rodent carcinogenicity, non-developmental toxic potential, and tolerant with cytochrome P450 2D6 (CYP2D6). The dynamic simulation analysis demonstrated that ZINC000008829785-PDGFRA and ZINC000013377891-PDGFRA dimer complex had more favorable potential energy compared with Imatinib, and they can exist in natural environments stably.

Conclusion

ZINC000008829785 and ZINC000013377891 might provide a solid foundation for drugs that inhibit PDGFRA in HGG. In addition to being safe drug candidates, these compounds had important implications for improving drugs targeting PDGFRA.

Practical Recommendations for the Manipulation of Kinase Inhibitor Formulations to Age-Appropriate Dosage Forms

Over 75 kinase inhibitors (KIs) have been approved for the treatment of various cancers. KIs are orally administrated but mostly lack pediatric age-appropriate dosage forms or instructions for dose manipulation. This is highly problematic for clinical practice in pediatric oncology, as flexible oral formulations are essential to individually set dosages and to adjust it to a child's swallowability. Most KIs are poorly soluble, categorized in Biopharmaceutics Classification System (BCS) class II or IV, and improperly manipulating the KI formulation can alter pharmacokinetics and jeopardize KI drug safety and efficacy. Therefore, the goals of this review were to provide practical recommendations for manipulating the formulation of the 15 most frequently used KIs in pediatric oncology (i.e., bosutinib, cabozantinib, cobimetinib, crizotinib, dabrafenib, dasatinib, entrectinib, imatinib, larotrectinib, nilotinib, ponatinib, ruxolitinib, selumetinib, sunitinib and trametinib) based on available literature studies and fundamental drug characteristics and to establish a decision tool that supports decisions regarding formulation manipulation of solid oral dosages of KIs that have been or will be licensed (for adult and/or pediatric cancers) but are not included in this review.

DNA repair inhibitors and radiotherapy

Radiotherapy (RT) is one of the main cancer treatments and grows in importance due to improved techniques. DNA damage caused by ionizing radiation creates DNA strand breaks that trigger an intervention of DNA repair pathways involving numerous proteins and enzymes. In recent years, we have identified DNA repair inhibitors as targets for inhibiting cellular repair systems and thus causing cell death. Combining RT with these DNA repair inhibitors appears to be a new approach for cancer treatment, but safety and real efficiency of this combination in practice is unclear. Numerous trials are underway in various diseases and initial results are promising overall, yet remain controversial.

Receptor tyrosine kinase (RTK) targeting in pediatric high-grade glioma and diffuse midline glioma: Pre-clinical models and precision medicine

Pediatric high-grade glioma (pHGG), including both diffuse midline glioma (DMG) and non-midline tumors, continues to be one of the deadliest oncologic diagnoses (both henceforth referred to as “pHGG”). Targeted therapy options aimed at key oncogenic receptor tyrosine kinase (RTK) drivers using small-molecule RTK inhibitors has been extensively studied, but the absence of proper in vivo modeling that recapitulate pHGG biology has historically been a research challenge. Thankfully, there have been many recent advances in animal modeling, including Cre-inducible transgenic models, as well as intra-uterine electroporation (IUE) models, which closely recapitulate the salient features of human pHGG tumors. Over 20% of pHGG have been found in sequencing studies to have alterations in platelet derived growth factor-alpha (PDGFRA), making growth factor modeling and inhibition via targeted tyrosine kinases a rich vein of interest. With commonly found alterations in other growth factors, including FGFR, EGFR, VEGFR as well as RET, MET, and ALK, it is necessary to model those receptors, as well. Here we review the recent advances in murine modeling and precision targeting of the most important RTKs in their clinical context. We additionally provide a review of current work in the field with several small molecule RTK inhibitors used in pre-clinical or clinical settings for treatment of pHGG.

Phase I study using crenolanib to target PDGFR kinase in children and young adults with newly diagnosed DIPG or recurrent high-grade glioma, including DIPG

Background

Platelet-derived growth factor receptor (PDGFR) signaling has been directly implicated in pediatric high-grade gliomagenesis. This study evaluated the safety and tolerability of crenolanib, a potent, selective inhibitor of PDGFR-mediated phosphorylation, in pediatric patients with high-grade glioma (HGG).

Methods

We used a rolling-6 design to study the maximum tolerated dose (MTD) of once-daily crenolanib administered during and after focal radiation therapy in children with newly diagnosed diffuse intrinsic pontine glioma (DIPG) (stratum A) or with recurrent/progressive HGG (stratum B). Pharmacokinetics were studied during the first cycle at the first dose and at steady state (day 28). Alterations in PDGFRA were assessed by Sanger or exome sequencing and interphase fluorescence in situ hybridization or single nucleotide polymorphism arrays.

Results

Fifty evaluable patients were enrolled in the 2 strata, and an MTD of 170 mg/m² was established for both. Dose-limiting toxicities were primarily liver enzyme elevations and hematologic count suppression in both strata. Crenolanib AUC_0-48h and C _MAX did not differ significantly for crushed versus whole-tablet administration. Overall, PDGFRA alterations were observed in 25% and 30% of patients in stratum A and B, respectively. Neither crenolanib therapy duration nor survival outcomes differed significantly by PDGFRA status, and overall survival of stratum A was similar to that of historical controls.

Conclusions

Children tolerate crenolanib well at doses slightly higher than the established MTD in adults, with a toxicity spectrum generally similar to that in adults. Studies evaluating intratumoral PDGFR pathway inhibition in biomarker-enriched patients are needed to evaluate further the clinical utility of crenolanib in this population.

Therapeutic Targets in Diffuse Midline Gliomas-An Emerging Landscape

Simple Summary

Diffuse midline gliomas (DMGs) remain one of the most devastating childhood brain tumour types, for which there is currently no known cure. In this review we provide a summary of the existing knowledge of the molecular mechanisms underlying the pathogenesis of this disease, highlighting current analyses and novel treatment propositions. Together, the accumulation of these data will aid in the understanding and development of more effective therapeutic options for the treatment of DMGs.

Abstract

Diffuse midline gliomas (DMGs) are invariably fatal pediatric brain tumours that are inherently resistant to conventional therapy. In recent years our understanding of the underlying molecular mechanisms of DMG tumorigenicity has resulted in the identification of novel targets and the development of a range of potential therapies, with multiple agents now being progressed to clinical translation to test their therapeutic efficacy. Here, we provide an overview of the current therapies aimed at epigenetic and mutational drivers, cellular pathway aberrations and tumor microenvironment mechanisms in DMGs in order to aid therapy development and facilitate a holistic approach to patient treatment.

The Use of Inhibitors of Tyrosine Kinase in Paediatric Haemato-Oncology-When and Why?

The fundamental pathophysiology of malignancies is dysregulation of the signalling pathways. Protein tyrosine kinases (PTKs) are among the enzymes which, if mutated, play a critical role in carcinogenesis. The best-studied rearrangement, which enhances PTK activity and causes atypical proliferation, is BCR-ABL1. Abnormal expression of PTKs has proven to play a significant role in the development of various malignancies, such as chronic myelogenous leukaemia, brain tumours, neuroblastoma, and gastrointestinal stromal tumours. The use of tyrosine kinase inhibitors (TKIs) is an outstanding example of successful target therapy. TKIs have been effectively applied in the adult oncology setting, but there is a need to establish TKIs’ importance in paediatric patients. Many years of research have allowed a significant improvement in the outcome of childhood cancers. However, there are still groups of patients who have a poor prognosis, where the intensification of chemotherapy could even cause death. TKIs are designed to target specific PTKs, which lead to the limitation of severe adverse effects and increase overall survival. These advances will hopefully allow new therapeutic approaches in paediatric haemato-oncology to emerge. In this review, we present an analysis of the current data on tyrosine kinase inhibitors in childhood cancers.

[Diffuse brainstem tumors in children. Tumor biology and hope for a better outcome. Current state of the problem]

Diffuse brainstem tumor is a fatal disease and the main cause of child mortality from neoplasms of central nervous system. So far, no effective therapy has been found for this disease. The authors discuss the modern aspects of clinical data, biology, diagnosis and treatment of patients with diffuse brainstem tumors.

Diffuse Intrinsic Pontine Glioma (DIPG): Breakthrough and Clinical Perspective

Diffuse intrinsic pontine glioma (DIPG) mainly affects children with a median age of 6-7 years old. It accounts for 10% of all pediatric tumors. Unfortunately, DIPG has a poor prognosis, and the median survival is generally less than 16-24 months independently from the treatment received. Up to now, children with DIPG are treated with focal radiotherapy alone or in combination with antitumor agents. In the last decade, ONC201 known as dopamine receptor antagonist was uncovered, by a high throughput screening of public libraries of compounds, to be endowed with cytotoxic activity against several cancer cell lines. Efforts were made to identify the real ONC201 target, responsible for its antiproliferative effect. The hypothesized targets were the Tumor necrosis factor-Related Apoptosis-Inducing Ligand stimulation (TRAIL), two oncogenic kinases (ERK/AKT system) that target the same tumor-suppressor gene (FOXO3a), dopamine receptors (DRD2 and DRD3 subtypes) and finally the mitochondrial Caseynolitic Protease P (ClpP). ONC201 structure-activity relationship is extensively discussed in this review, together with other two classes of compounds, namely ADEPs and D9, already known for their antibiotic activity but noteworthy to be discussed and studied as potential "leads" for the development of new drugs to be used in the treatment of DIPG. In this review, a detailed and critical description of ONC201, ADEPs, and D9 pro-apoptotic activity is made, with particular attention to the specific interactions established with its targets that also are intimately described. Pubmed published patents and clinical trial reports of the last ten years were used as the bibliographic source.

High expression of PYCARD is an independent predictor of unfavorable prognosis and chemotherapy resistance in glioma

Background

PYD and CARD domain-containing (PYCARD) was upregulated in TMZ-resistant cell lines and glioma tissue and was correlated with poor prognosis, its role in glioma is unclear known. The aim of this study was to elucidate the relationship between PYCARD and glioma based on Gene Expression Omnibus (GEO), The Cancer Genome Atlas (TCGA), and Chinese Glioma Genome Atlas (CGGA) databases.

Methods

Glioma-resistant cells were compared with parental cells based on the GSE53014 and GSE113510 data sets. The relationship between PYCARD, tumor microenvironment, and long noncoding RNAs (lncRNAs) was assessed using logistic regression. Moreover, Kaplan-Meier and Cox regression were used to analyze the relationship between PYCARD expression and survival rate. Gene set enrichment analysis (GSEA) was also used to determine the biological function of PYCARD and lncRNAs. Cell viability and cell migration assays were used to evaluate the ability of cells to migrate and proliferate. Finally, we analyzed the expression patterns of PYCARD genes in a wide range of cancers.

Results

Elevated expression of PYCARD promoted glioma cell proliferation and migration. PYCARD expression was significantly positively associated with gamma delta T cells but negatively correlated with M2 macrophages in glioblastoma multiforme (GBM). Likewise, PYCARD expression was significantly positively associated with monocytes but negatively associated with activated mast cells in low grade glioma (LGG). We also found that 3 PYCARD-related lncRNAs in GBM and 4 PYCARD-related lncRNAs in LGG had a predictive value for glioma patients. The pan-cancer analysis showed that PYCARD expression was higher in most cancer groups.

Conclusions

High expression of PYCARD is an independent predictor of unfavorable prognosis and chemotherapy resistance in glioma.

Radiosensitization in Pediatric High-Grade Glioma: Targets, Resistance and Developments

Pediatric high-grade gliomas (pHGG) are the leading cause of cancer-related death in children. These epigenetically dysregulated tumors often harbor mutations in genes encoding histone 3, which contributes to a stem cell-like, therapy-resistant phenotype. Furthermore, pHGG are characterized by a diffuse growth pattern, which, together with their delicate location, makes complete surgical resection often impossible. Radiation therapy (RT) is part of the standard therapy against pHGG and generally the only modality, apart from surgery, to provide symptom relief and a delay in tumor progression. However, as a single treatment modality, RT still offers no chance for a cure. As with most therapeutic approaches, irradiated cancer cells often acquire resistance mechanisms that permit survival or stimulate regrowth after treatment, thereby limiting the efficacy of RT. Various preclinical studies have investigated radiosensitizers in pHGG models, without leading to an improved clinical outcome for these patients. However, our recently improved molecular understanding of pHGG generates new opportunities to (re-)evaluate radiosensitizers in these malignancies. Furthermore, the use of radio-enhancing agents has several benefits in pHGG compared to other cancers, which will be discussed here. This review provides an overview and a critical evaluation of the radiosensitization strategies that have been studied to date in pHGG, thereby providing a framework for improving radiosensitivity of these rapidly fatal brain tumors.

[The art of war as applied to pediatric gliomas: Know your enemy]

Pediatric brain cancers represent the most frequent solid tumors and the leading cause of cancer-driven mortality in children. Pediatric High Grade Gliomas display a very poor prognosis. Among these, DIPG (Diffuse Intrinsic Pontine Gliomas), localized to the brain stem, cannot benefit from a total exeresis due to this critical location and to their highly infiltrating nature. Radiotherapy remains the standard treatment against these tumors for almost five decades, and attempts to improve the prognosis of patients with chemotherapy or targeted therapies have failed. Thanks to the rise of high throughput sequencing, the knowledge of molecular alterations in pediatric gliomas strongly progressed and allowed to highlight distinct biomolecular entities and to establish more accurate diagnoses. In this review, we summarize this new information and the perspectives that it brings for clinical strategies.

Children with DIPG and high-grade glioma treated with temozolomide, irinotecan, and bevacizumab: the Seattle Children's Hospital experience

INTRODUCTION

Beyond focal radiation, there is no consensus standard therapy for pediatric high-grade glioma (pHGG) and outcomes remain dismal. We describe the largest molecularly-characterized cohort of children with pHGG treated with a 3-drug maintenance regimen of temozolomide, irinotecan, and bevacizumab (TIB) following radiation.

METHODS

We retrospectively reviewed 36 pediatric patients treated with TIB at Seattle Children's Hospital from 2009 to 2018 and analyzed survival using the Kaplan-Meier method. Molecular profiling was performed by targeted DNA sequencing and toxicities, steroid use, and palliative care utilization were evaluated.

RESULTS

Median age at diagnosis was 10.9 years (18 months-18 years). Genetic alterations were detected in 26 genes and aligned with recognized molecular subgroups including H3 K27M-mutant (12), H3F3A G34-mutant (2), IDH-mutant (4), and hypermutator profiles (4). Fifteen patients (42%) completed 12 planned cycles of maintenance. Side effects associated with chemotherapy delays or modifications included thrombocytopenia (28%) and nausea/vomiting (19%), with temozolomide dosing most frequently modified. Median event-free survival (EFS) and overall survival (OS) was 16.2 and 20.1 months, with shorter survival seen in DIPG (9.3 and 13.3 months, respectively). Survival at 1, 2, and 5 years was 80%, 10% and 0% for DIPG and 85%, 38%, and 16% for other pHGG.

CONCLUSION

Our single-center experience demonstrates tolerability of this 3-drug regimen, with prolonged survival in DIPG compared to historical single-agent temozolomide. pHGG survival was comparable to analogous 3-drug regimens and superior to historical agents; however, cure was rare. Children with pHGG remain excellent candidates for the study of novel therapeutics combined with standard therapy.

STAT3 is a key molecule in the oncogenic behavior of diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is one of the most lethal childhood brain tumors. This tumor is unique because it is detected exclusively in the ventral pons of patients aged between 6 and 7 years, which suggests a developmental nature of its formation. Signal transducer and activator of transcription 3 (STAT3) is a critical molecule for the differentiation of neural stem cells into astrocytes during neurodevelopment. Additionally, STAT3 is associated with oncogenesis and the epithelial-mesenchymal transition (EMT) in various types of tumor. In recent years, several studies have demonstrated the oncogenic role of STAT3 in high-grade gliomas. However, the role of STAT3 in DIPG at the cellular level remains unknown. To assess the possible association between gliogenesis and DIPG, the expression levels of various molecules participating in the differentiation of neural stem cells were compared between normal brain control tissues and DIPG tissues using open public data. All of the screened genes exhibited significantly increased expression in DIPG tissues compared with normal tissues. As STAT3 expression was the most increased, the effect of STAT3 inhibition in a DIPG cell line was assessed via STAT3 short hairpin (sh)RNA transfection and treatment with AG490, a STAT3 inhibitor. Changes in viability, apoptosis, EMT and radiation therapy efficiency were also evaluated. Downregulation of STAT3 resulted in decreased cyclin D1 expression and cell viability, migration and invasion. Additionally, treatment with STAT3 shRNA or AG490 suppressed the EMT phenotype. Finally, when radiation was administered in combination with STAT3 inhibition, the therapeutic efficiency, assessed by cell viability and DNA damage repair, was increased. The present results suggest that STAT3 is a potential therapeutic target in DIPG, especially when combined with radiation therapy.

Small molecule tyrosine kinase inhibitors in glioblastoma

Glioblastoma (GBM) is the most common malignant primary brain tumor, with poor survival despite treatment with surgery, radiotherapy, and chemotherapy with temozolomide. Little progress has been made over the last two decades, and there remain unmet medical needs. Approximately 45% of patients with GBM carry EGFR mutations, and 13% of them possess altered PDGFR genes. Moreover, VEGF/VEGFR mutations are also observed in the patient population. Tyrosine kinase inhibitors (TKIs) are emerging cancer therapy drugs that inhibit signal transduction cascades affecting cell proliferation, migration, and angiogenesis. Indications for small molecule TKIs have been successfully expanded to multiple types of cancer; however, none of the TKIs have been approved for patients with GBM. In this review, we summarize clinical trials of small molecule TKIs in patients with GBM and plausible hypotheses for negative clinical study results. We also discuss the potential TKI candidates that presented significant preclinical outcomes in patients with GBM.

Pediatric diffuse intrinsic pontine glioma: where do we stand?

Pediatric diffuse intrinsic pontine glioma (DIPG) represents approximately 20% of all pediatric CNS tumors. However, disease outcomes are dismal with a median survival of less than 1 year and a 2-year overall survival rate of less than 10%. Despite extensive efforts to improve survival outcomes, progress towards clinical improvement has been largely stagnant throughout the last 4 decades. Focal radiotherapy remains the standard of care with no promising single-agent alternatives and no evidence for improvement with the addition of a long list of systemic therapies. A better understanding of the biology of DIPG, though not easy due to obstacles in obtaining pathological material to study, is promising for the development of specific individualized treatment for this fatal disease. Recent studies have found epigenetic mutations to be successful predictors and prognostic factors for developing future management policies. The aim of this review is to give a global overview about the epidemiology, diagnosis, and treatment of DIPG. We further examine the controversial biopsy and autopsy issue that is unique to DIPG and assess the subsequent impact this issue has on the research efforts and clinical management of DIPG.

Invaders Exposed: Understanding and Targeting Tumor Cell Invasion in Diffuse Intrinsic Pontine Glioma

Diffuse Intrinsic Pontine Glioma (DIPG) is a rare, highly aggressive pediatric brain tumor that originates in the pons. DIPG is untreatable and universally fatal, with a median life expectancy of less than a year. Resection is not an option, due to the anatomical location of the tumor, radiotherapy has limited effect and no chemotherapeutic or targeted treatment approach has proven to be successful. This poor prognosis is partly attributed to the tumor's highly infiltrative diffuse and invasive spread. Thus, targeting the invasive behavior of DIPG has the potential to be of therapeutic value. In order to target DIPG invasion successfully, detailed mechanistic knowledge on the underlying drivers is required. Here, we review both DIPG tumor cell's intrinsic molecular processes and extrinsic environmental factors contributing to DIPG invasion. Importantly, DIPG represents a heterogenous disease and through advances in whole-genome sequencing, different subtypes of disease based on underlying driver mutations are now being recognized. Recent evidence also demonstrates intra-tumor heterogeneity in terms of invasiveness and implies that highly infiltrative tumor subclones can enhance the migratory behavior of neighboring cells. This might partially be mediated by “tumor microtubes,” long membranous extensions through which tumor cells connect and communicate, as well as through the secretion of extracellular vesicles. Some of the described processes involved in invasion are already being targeted in clinical trials. However, more research into the mechanisms of DIPG invasion is urgently needed and might result in the development of an effective therapy for children suffering from this devastating disease. We discuss the implications of newly discovered invasive mechanisms for therapeutic targeting and the challenges therapy development face in light of disease in the developing brain.

Imatinib inhibits oxidative stress response in spinal cord injury rats by activating Nrf2/HO-1 signaling pathway

Effect of imatinib on rats with spinal cord injury (SCI) was investigated through the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway. Forty-eight Sprague-Dawley rats were randomly divided into sham operation group (n=12), model group (n=12), imatinib group (n=12) and inhibitor group (n=12). The results of immunohistochemistry showed that in comparison with sham operation group, the other three groups had overtly increased positive expression level of Bax and evidently reduced positive expression level of Bcl-2 (P<0.05). Compared with those in model group and inhibitor group, the positive expression level of Bax was distinctly lower, while that of Bcl-2 was notably increased in imatinib group (P<0.05). According to western blot analysis, the protein expression levels of Nrf2 and HO-1 were obviously higher in the other three groups than those in sham operation group (P<0.05), and they were remarkably higher in imatinib group than those in model group and inhibitor group (P<0.05). The results of qPCR assay revealed that the Nrf2 and HO-1 mRNA expression levels were markedly elevated in the other three groups compared with those in sham operation group (P<0.05). Based on ELISA, the other three groups exhibited notably raised content of IL-6, TNF-α, ROS and SOD compared with sham operation group (P<0.05), and imatinib group displayed remarkably decreased content of IL-6, TNF-α and ROS and markedly elevated SOD content in comparison with model group and inhibitor group (P<0.05). The results of TUNEL assay demonstrated that the rate of apoptosis was significantly raised in the other three groups compared with that in sham operation group (P<0.05), and it declined obviously in imatinib group compared with that in model group and inhibitor group (P<0.05). Imatinib inhibits oxidative stress response in SCI rats by activating the Nrf2/HO-1 signaling pathway, thus repressing apoptosis and inflammation.

DNA repair inhibitors to enhance radiotherapy: Progresses and limitations

Radiotherapy is one of the most common form of treatment in oncology care. Indeed, radiotherapy proved to be very effective in treating a wide range of malignancies. Nevertheless, certain tumours are intrinsically radioresistant or may evolve to become radioresistant. Resistance to radiotherapy is often associated with dysregulated DNA damage response and repair. Recently, a number of strategies have been developed to improve radiotherapy efficacy by targeting the DNA damage response and repair pathways. Ongoing clinical trials showed the potential of some of these approaches in enhancing radiotherapy, but also highlighted the possible limitations. Here, we will describe (i) the main mechanisms involved in double-strand break repair; (ii) available strategies that target these DNA repair processes to improve radiotherapy and (iii) the clinical outcomes and challenges that have emerged so far.

Altering DNA Repair to Improve Radiation Therapy: Specific and Multiple Pathway Targeting

Radiation therapy (RT) is widely used in cancer care strategies. Its effectiveness relies mainly on its ability to cause lethal damage to the DNA of cancer cells. However, some cancers have shown to be particularly radioresistant partly because of efficient and redundant DNA repair capacities. Therefore, RT efficacy might be enhanced by using drugs that can disrupt cancer cells' DNA repair machinery. Here we review the recent advances in the development of novel inhibitors of DNA repair pathways in combination with RT. A large number of these compounds are the subject of preclinical/clinical studies and target key enzymes involved in one or more DNA repair pathways. A totally different strategy consists of mimicking DNA double-strand breaks via small interfering DNA (siDNA) to bait the whole DNA repair machinery, leading to its global inhibition.

Pilocytic Midbrain Astrocytoma Presenting with Fresh Bleed after Twenty-one-years Survival Following First Surgery: A Unique Case of Longest Brainstem Glioma Survival

Brainstem glioma usually carries a poor prognosis and prolonged survival is very infrequent. In a detailed Pubmed, Medline search for prolonged survival, authors could got a longest survival only up to seventeen years, reported by Umehara et al, who was subjected to gamma knife therapy and got symptomatic, MRI brain reveled large tumor growth during pregnancy necessitating emergency surgery and histopathological diagnosis was pilocytic astrocytoma. Authors report an interesting case of midbrain glioma diagnosed 21 years back, who underwent gross resection in the year 1993, histopathology was pilocytic astrocytoma, WHO grade I, and received gamma knife surgery for residual subsequently and he presented with sudden onset left sided hemiplegia on the current admission. The cranial MRI imaging revealed an infarct involving right hemi midbrain, contrast MRI brain revealed no residual glioma. To the best knowledge of authors such prolonged survival is not reported with a case of brainstem glioma survived twenty- one years with non residual tumor on the last imaging study represents first case of its kind in the western literature and probably developed hemiplegia due to bleed, highlighting bleed as delayed complication following gamma knife therapy for cranial tumors.

Identification of prognostic markers in diffuse midline gliomas H3K27M-mutant

Pediatric diffuse midline gliomas are devastating diseases. Among them, diffuse midline gliomas H3K27M-mutant are associated with worse prognosis. However, recent studies have highlighted significant differences in clinical behavior and biological alterations within this specific subgroup. In this context, simple markers are needed to refine the prognosis of diffuse midline gliomas H3K27M-mutant and guide the clinical management of patients. The aims of this study were (i) to describe the molecular, immunohistochemical and, especially, chromosomal features of a cohort of diffuse midline gliomas and (ii) to focus on H3K27M-mutant tumors to identify new prognostic markers. Patients were retrospectively selected from 2001 to 2017. Tumor samples were analyzed by immunohistochemistry (including H3K27me3, EGFR, c-MET and p53), next-generation sequencing and comparative genomic hybridization array. Forty-nine patients were included in the study. The median age at diagnosis was 9 years, and the median overall survival (OS) was 9.4 months. H3F3A or HIST1H3B mutations were identified in 80% of the samples. Within the H3K27M-mutant tumors, PDGFRA amplification, loss of 17p and a complex chromosomal profile were significantly associated with worse survival. Three prognostic markers were identified in diffuse midline gliomas H3K27M-mutant: PDGFRA amplification, loss of 17p and a complex chromosomal profile. These markers are easy to detect in daily practice and should be considered to refine the prognosis of this entity.

Diffuse Intrinsic Pontine Glioma: From Diagnosis to Next-Generation Clinical Trials

PURPOSE OF REVIEW

This review of diffuse intrinsic pontine glioma (DIPG) provides clinical background, a systematic approach to diagnosis and initial care, and synthesizes historical, modern, and future directions for treatment. We present evidence supporting neurosurgical biopsy, early palliative care involvement, limitation of glucocorticoid use, and the leveraging of preclinical DIPG models as a pipeline to next-generation clinical trials.

RECENT FINDINGS

New molecular understanding of pediatric high-grade gliomas has led to the reclassification of DIPG as one member of a family of diffuse gliomas occurring in the midline of the central nervous system that exhibit pathognomonic mutations in genes encoding histone 3 (H3 K27M). DIPG remains a clinically relevant term, though diagnostically the 80% of DIPG cases that exhibit the H3 K27M mutation have been reclassified as diffuse midline glioma, H3 K27M-mutant. Re-irradiation has been shown to be well-tolerated and of potential benefit. Epigenetic targeting of transcriptional dependencies in preclinical models is fueling molecularly targeted clinical trials. Chimeric antigen receptor T cell immunotherapy has also demonstrated efficacy in preclinical models and provides a promising new clinical strategy. DIPG is a universally fatal, epigenetically driven tumor of the pons that is considered part of a broader class of diffuse midline gliomas sharing H3 K27M mutations. Radiation remains the standard of care, single-agent temozolomide is not recommended, and glucocorticoids should be used only sparingly. A rapid evolution of understanding in the chromatin, signaling, and immunological biology of DIPG may soon result in clinical breakthroughs.

Targeted Sequencing of Malignant Supratentorial Pediatric Brain Tumors Demonstrates a High Frequency of Clinically Relevant Mutations

Pediatric brain tumors cause more deaths than any other childhood malignancy, and the identification of potentially actionable genomic alterations in this rare heterogeneous group of tumors may improve treatment and outcome. The genetic landscape of common posterior fossa tumors has been described in the past several years, yet the classification of malignant pediatric supratentorial tumors remains controversial. Next-generation sequencing (NGS) is a promising tool to evaluate multiple genes concurrently. The clinical utility of NGS has not been proven in pediatric brain tumors. We identified patients diagnosed with high-grade supratentorial pediatric brain tumors resected between 2008 and 2012 at our institution. DNA from 12 formalin-fixed paraffin-embedded tumor samples from 9 patients was analyzed, including 3 paired samples from diagnosis and relapse. A panel of 194 cancer-related genes was sequenced using targeted next-generation deep sequencing. Genetic findings were correlated with histology, immunohistochemistry, treatment, and survival. We found one or more pathologic genetic change (mutation, amplification, or deletion) in 8 of 9 (89%) of patients studied. Epidermal Growth Factor Receptor ( EGFR) mutations were found in 3 patients, 2 of which had an exon 20 insertion not previously described in pediatric malignancy. Additional genetic changes were found in EGFR and Platelet-Derived Growth Factor Receptor Alpha ( PDGFRA) at relapse not present in the initial samples. Familial cancer predisposition syndromes were suggested by mutations found in 3 genes in 4 patients, including TP53, MSH2, and CHEK2. Seven of 9 patients in this study died of their disease. In summary, targeted deep sequencing may be used in rare pediatric brain tumors to identify driver mutations for targeted therapy, suggest constitutional and familial testing for cancer predisposition syndromes, and select molecular targets worthy of further study.

CDK4/6 and PDGFRA Signaling as Therapeutic Targets in Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine gliomas (DIPGs) are incurable childhood brain tumors, whereby the standard of care is focal radiation, a treatment that provides temporary relief for most patients. Surprisingly, decades of clinical trials have failed to identify additional therapies that can prolong survival in this disease. In this conference manuscript, we discuss how genetic engineered mouse modeling techniques with the use of a retroviral gene delivery system can help dissect the complex pathophysiology of this disease. With this approach, autochthonous murine DIPG models can be readily induced to (1) help interrogate the function of novel genetic alterations in tumorigenesis, (2) identify candidate cells of origin for this disease, (3) address how region-specific differences in the central nervous system influence the process of gliomagenesis, and (4) evaluate novel therapeutics in an immunocompetent model.

Prediction of Apparent Oral Clearance of Small-Molecule Inhibitors in Pediatric Patients

The purpose of this study was to build regression models for the prediction of apparent oral clearance (CL/F) for small-molecule inhibitors in the pediatric population using data obtained from adults. Two approaches were taken; a simple allometric regression model which considers no interdrug or interindividual variability and an allometric regression model with mixed-effects modeling where some variability parameters are included in the model. Average CL/F values were obtained for 15 drugs at various dosages from 31 literatures (a total of 139 data sets) conducted in adults and for 15 drugs from 26 literatures (62 data sets) conducted in children. Data were randomly separated into the "modeling" or "validation" data set, and the 2 allometric regression models were applied to the modeling data set. The predictive ability of the models was examined by comparing the observed and model-predicted CL/F in children using the validation data set. The percentage root mean square error was 17.2% and 26.3% in the simple allometric regression model and the allometric regression model with mixed-effects modeling, respectively. The predictive ability of the 2 models seems acceptable, suggesting that they could be useful for predicting the CL/F of new small-molecule inhibitors and for determining adequate doses in clinical pharmacotherapy for children.

Pharmacology and pharmacokinetics of imatinib in pediatric patients

INTRODUCTION

The tyrosine kinase inhibitor (TKI) imatinib was rationally designed to target BCR-ABL1 which is constitutively activated in chronic myeloid leukemia (CML). Following the tremendous success in adults, imatinib also became licensed for treatment of CML in minors. The rarity of pediatric CML hampers the conduction of formal trials. Thus, imatinib is still the single TKI approved for CML treatment in childhood. Areas covered: This review attempts to provide an overview of the literature on pharmacology, pharmacokinetic, and pharmacogenetic of imatinib concerning pediatric CML treatment. Articles were identified through a PubMed search and by reviewing abstracts from relevant hematology congresses. Additional information was provided from the authors' libraries and expertise and from our own measurements of imatinib trough plasma levels in children. Pharmacokinetic variables (e.g. alpha 1-acid glycoprotein binding, drug-drug/food-drug interactions via cytochrome P450 3A4/5, cellular uptake mediated via OCT-1-influx variations and P-glycoprotein-mediated drug efflux) still await to be addressed in pediatric patients systematically. Expert commentary: TKI response rates vary among different individuals and pharmacokinetic variables all can influence CML treatment success. Adherence to imatinib intake may be the most prominent factor influencing treatment outcome in teenagers thus pointing towards the potential benefits of regular drug monitoring.

Developing chemotherapy for diffuse pontine intrinsic gliomas (DIPG)

Prognosis of diffuse intrinsic pontine glioma (DIPG) is poor, with a median survival of 10 months after radiation. At present, chemotherapy has failed to show benefits over radiation. Advances in biotechnology have enabled the use of autopsy specimens for genomic analyses and molecular profiling of DIPG, which are quite different from those of supratentorial high grade glioma. Recently, combined treatments of cytotoxic agents with target inhibitors, based on biopsied tissue, are being examined in on-going trials. Spontaneous DIPG mice models have been recently developed that is useful for preclinical studies. Finally, the convection-enhanced delivery could be used to infuse drugs directly into the brainstem parenchyma, to which conventional systemic administration fails to achieve effective concentration. The WHO glioma classification defines a diffuse midline glioma with a H3-K27M-mutation, and we expect increase of tissue confirmation of DIPG, which will give us the biological information helping the development of a targeted therapy.

A comparison of safety and efficacy of cytotoxic versus molecularly targeted drugs in pediatric phase I solid tumor oncology trials

BACKGROUND

Prior reviews of phase I pediatric oncology trials involving primarily cytotoxic agents have reported objective response rates (ORRs) and toxic death rates of 7.9-9.6% and 0.5%, respectively. These data may not reflect safety and efficacy in phase I trials of molecularly targeted (targeted) drugs.

METHODS

A systematic review of pediatric phase I solid tumor trials published in 1990-2013 was performed. The published reports were evaluated for patient characteristics, toxicity information, and response numbers.

RESULTS

A total of 143 phase I pediatric clinical trials enrolling 3,896 children involving 53 targeted and 48 cytotoxic drugs were identified. A meta-analysis demonstrated that the ORR is 2.1-fold higher with cytotoxic drugs (0.066 vs. 0.031 per subject; P = 0.007). By contrast, the pooled estimate of the stable disease rate (SDR) is similar for cytotoxic and targeted drugs (0.2 vs. 0.23 per subject; P = 0.27).  The pooled estimate of the dose-limiting toxicity rate is 1.8-fold larger with cytotoxic drugs (0.24 vs. 0.13 per subject; P = 0.0003). The hematologic grade 3-4 (G3/4) toxicity rate is 3.6-fold larger with cytotoxic drugs (0.43 vs. 0.12 per treatment course; P = 0.0001); however, the nonhematologic G3/4 toxicities and toxic deaths occur at similar rates for cytotoxic and targeted drugs.

CONCLUSIONS

In phase I pediatric solid tumor trials, ORRs were significantly higher for cytotoxic versus targeted agents. SDRs were similar in targeted and cytotoxic drug trials. Patients treated with cytotoxic agents were more likely to experience hematologic G3/4 toxicities than those patients receiving targeted drugs.

Vascular heterogeneity and targeting: the role of YKL-40 in glioblastoma vascularization

Malignant glioblastomas (GBM) are highly malignant brain tumors that have extensive and aberrant tumor vasculature, including multiple types of vessels. This review focuses on recent discoveries that the angiogenic factor YKL-40 (CHI3L1) acts on glioblastoma-stem like cells (GSCs) to drive the formation of two major forms of tumor vascularization: angiogenesis and vasculogenic mimicry (VM). GSCs possess multipotent cells able to transdifferentiate into vascular pericytes or smooth muscle cells (PC/SMCs) that either coordinate with endothelial cells (ECs) to facilitate angiogenesis or assemble in the absence of ECs to form blood-perfused channels via VM. GBMs express high levels of YKL-40 that drives the divergent signaling cascades to mediate the formation of these distinct microvascular circulations. Although a variety of anti-tumor agents that target angiogenesis have demonstrated transient benefits for patients, they often fail to restrict tumor growth, which underscores the need for additional therapeutic tools. We propose that targeting YKL-40 may compliment conventional anti-angiogenic therapies to provide a substantial clinical benefit to patients with GBM and several other types of solid tumors.

Imatinib attenuates cerebrovascular injury and phenotypic transformation after intracerebral hemorrhage in rats

This study explored the hypothesis that intracerebral hemorrhage (ICH) promotes release of diffusible factors that can significantly influence the structure and function of cerebral arteries remote from the site of injury, through action on platelet-derived growth factor (PDGF) receptors. Four groups of adult male Sprague-Dawley rats were studied (n = 8 each): 1) sham; 2) sham + 60 mg/kg ip imatinib; 3) ICH (collagenase method); and 4) ICH + 60 mg/kg ip imatinib given 60 min after injury. At 24 h after injury, sham artery passive diameters (+3 mM EGTA) averaged 244 ± 7 µm (at 60 mmHg). ICH significantly increased passive diameters up to 6.4% and decreased compliance up to 42.5%. For both pressure- and potassium-induced contractions, ICH decreased calcium mobilization up to 26.2% and increased myofilament calcium sensitivity up to 48.4%. ICH reduced confocal colocalization of smooth muscle α-actin (αActin) with nonmuscle myosin heavy chain (MHC) and increased its colocalization with smooth muscle MHC, suggesting that ICH promoted contractile differentiation. ICH also enhanced colocalization of myosin light chain kinase (MLCK) with both αActin and regulatory 20-kDa myosin light chain. All effects of ICH on passive diameter, compliance, contractility, and contractile protein colocalization were significantly reduced or absent in arteries from animals treated with imatinib. These findings support the hypothesis that ICH promotes release into the cerebrospinal fluid of vasoactive factors that can diffuse to and promote activation of cerebrovascular PDGF receptors, thereby altering the structure, contractile protein organization, contractility, and smooth muscle phenotype of cerebral arteries remote from the site of hemorrhage.

Experimental Therapeutic Trial Design for Pediatric Brain Tumors

Pediatric brain tumors are the leading cause of cancer-related death during childhood. Since the first pediatric brain tumor clinical trials, the field has seen improved outcomes in some, but not all tumor types. In the past few decades, a number of promising new therapeutic agents have emerged, yet only a few of these agents have been incorporated into clinical trials for pediatric brain tumors. In this review, the authors discuss the process of and challenges in pediatric clinical trial design; this will allow for highly efficient and effective clinical trials with appropriate endpoints to ensure rapid and safe investigation of novel therapeutics for children with brain tumors.

Brainstem Glioma in Adults

Brainstem gliomas are not nearly as common in adults as they are in children. They are likely the final common consequence not of a single disease process but of several. They can be difficult to diagnose, and are challenging to treat. Clinical studies of this diagnosis are few and generally small. Because of these factors, our understanding of the biology of adult brainstem glioma is incomplete. However, the knowledge base is growing and progress is being made. In this article, we review the current state of knowledge for brainstem glioma in adults and identify key areas for which additional information is required.

Pediatric Brain Tumors: Current Knowledge and Therapeutic Opportunities

Great progress has been made in many areas of pediatric oncology. However, tumors of the central nervous system (CNS) remain a significant challenge. A recent explosion of data has led to an opportunity to understand better the molecular basis of these diseases and is already providing a foundation for the pursuit of rationally chosen therapeutics targeting relevant molecular pathways. The molecular biology of pediatric brain tumors is shifting from a singular focus on basic scientific discovery to a platform upon which insights are being translated into therapies.

Identification of novel biologic targets in the treatment of newly diagnosed diffuse intrinsic pontine glioma

Diffuse intrinsic pontine gliomas (DIPGs) carry an extremely poor prognosis. Standard practice has been to base the diagnosis on classic imaging and clinical characteristics and to treat with focal radiation therapy, usually accompanied with experimental therapy. As a result of the desire to avoid upfront biopsy, little has been learned regarding the molecular features of this disease. Findings from several autopsy series have included loss of p53 and PTEN, and amplification of PDGFR. Based on these and other findings, murine models have been generated and provide a new tool for preclinical testing. DIPG biopsy at diagnosis has increasingly become incorporated into national protocols at several centers, bringing the prospect of a better understanding of DIPG biology in the future. Initial analyses of pretreatment tumors cast valuable new light and establish the importance of p53 inactivation and the RTK-PI3K pathway in this disease.

CNS and spinal tumors

Primary CNS tumors consist of a diverse group of neoplasms originating from various cell types in the CNS. Brain tumors are the most common solid malignancy in children under the age of 15 years and the second leading cause of cancer death after leukemia. The most common brain neoplasms in children differ consistently from those in older age groups. Pediatric brain tumors demonstrate distinct patterns of occurrence and biologic behavior according to sex, age, and race. This chapter highlights the imaging features of the most common tumors that affect the child's CNS (brain and spinal cord).

DIPG in Children - What Can We Learn from the Past?

Brainstem tumors represent 10–15% of pediatric central nervous system tumors and diffuse intrinsic pontine glioma (DIPG) is the most common brainstem tumor of childhood. DIPG is almost uniformly fatal and is the leading cause of brain tumor-related death in children. To date, radiation therapy (RT) is the only form of treatment that offers a transient benefit in DIPG. Chemotherapeutic strategies including multi-agent neoadjuvant chemotherapy, concurrent chemotherapy with RT, and adjuvant chemotherapy have not provided any survival advantage. To overcome the restrictive ability of the intact blood–brain barrier (BBB) in DIPG, several alternative drug delivery strategies have been proposed but have met with minimal success. Targeted therapies either alone or in combination with RT have also not improved survival. Five decades of unsuccessful therapies coupled with recent advances in the genetics and biology of DIPG have taught us several important lessons (1). DIPG is a heterogeneous group of tumors that are biologically distinct from other pediatric and adult high grade gliomas (HGG). Adapting chemotherapy and targeted therapies that are used in pediatric or adult HGG for the treatment of DIPG should be abandoned (2). Biopsy of DIPG is relatively safe and informative and should be considered in the context of multicenter clinical trials (3). DIPG probably represents a whole brain disease so regular neuraxis imaging is important at diagnosis and during therapy (4). BBB permeability is of major concern in DIPG and overcoming this barrier may ensure that drugs reach the tumor (5). Recent development of DIPG tumor models should help us accurately identify and validate therapeutic targets and small molecule inhibitors in the treatment of this deadly tumor.

Molecular Biology in Pediatric High-Grade Glioma: Impact on Prognosis and Treatment

High-grade gliomas are the main cause of death in children with brain tumours. Despite recent advances in cancer therapy, their prognosis remains poor and the treatment is still challenging. To date, surgery followed by radiotherapy and temozolomide is the standard therapy. However, increasing knowledge of glioma biology is starting to impact drug development towards targeted therapies. The identification of agents directed against molecular targets aims at going beyond the traditional therapeutic approach in order to develop a personalized therapy and improve the outcome of pediatric high-grade gliomas. In this paper, we critically review the literature regarding the genetic abnormalities implicated in the pathogenesis of pediatric malignant gliomas and the current development of molecularly targeted therapies. In particular, we analyse the impact of molecular biology on the prognosis and treatment of pediatric high-grade glioma, comparing it to that of adult gliomas.

Diffuse intrinsic pontine glioma: time for therapeutic optimism

Diffuse intrinsic pontine glioma (DIPG) is an aggressive tumor that is universally fatal, and to-date we are at a virtual standstill in improving its grim prognosis. Dearth of tissue due to rarity of biopsy has precluded understanding the elusive biology and frustration continues in reproducing faithful animal models for translational research. Furthermore the intricate anatomy of the pons has forestalled locoregional therapy and drug penetration. Over the last few years, biopsy-driven targeted therapy, development of vitro and xenograft animal models for therapeutic testing, profiling immunotherapeutic strategies and locoregional infusion of drugs in brain stem tumors, now provide a sense of hope in the years ahead. This review aims to discuss current status and advances in the management of these tumors.

NVP-BKM120 potentiates apoptosis in tumor necrosis factor-related apoptosis-inducing ligand-resistant glioma cell lines via upregulation of Noxa and death receptor 5

We previously observed that glioma cells are differentially sensitive to TRAIL-induced toxicity. Based on our observation that TRAIL-resistant glioma cell lines typically exhibited high levels of Akt activation, we hypothesized that inhibition of Akt signaling using the PI3 kinase inhibitor NVP-BKM120 could promote TRAIL-induced apoptosis in gliomas. We assessed this combination in established and primary cultured glioma cells. Combination treatment led to significant cellular death when compared to either drug alone, but had no effect in normal human astrocytes, and demonstrated activation of the caspase cascade. This enhanced apoptosis appears dependent upon the loss of mitochondrial membrane potential and the release of Smac/DIABLO, AIF and cytochrome c into the cytosol. The upregulation of Noxa and sequestration of Mcl-1 by Noxa were important factors for cell death. Knockdown of Noxa abrogated apoptosis and suggested dependency on Noxa in combination-induced apoptosis. BKM120 upregulated cell surface expression of death receptor 5 (DR5), but did not increase levels of the other major TRAIL receptor, death receptor 4 (DR4). This study demonstrates that antagonizing apoptosis-resistance pathways, such as the PI3/Akt pathway, in combination with death receptor activation, may induce cell death in TRAIL-resistant glioma.

The genetic signatures of pediatric high-grade glioma: no longer a one-act play

Advances in understanding pediatric high-grade glioma (pHGG) genetics have revealed key differences between pHGG and adult HGG and have uncovered unique molecular drivers among subgroups within pHGG. The 3 core adult HGG pathways, the receptor tyrosine kinase-Ras-phosphatidylinositide 3-kinase, p53, and retinoblastoma networks, are also disrupted in pHGG, but they exhibit a different spectrum of effectors targeted by mutation. There are also similarities and differences in the genomic landscape of diffuse intrinsic pontine glioma (DIPG) and pediatric nonbrainstem (pNBS)-HGG. In 2012, histone H3 mutations were identified in nearly 80% of DIPGs and ~35% of pNBS-HGG. These were the first reports of histone mutations in human cancer, implicating novel biology in pediatric gliomagenesis. Additionally, DIPG and midline pNBS-HGG vary in the frequency and specific histone H3 amino acid substitution compared with pNBS-HGGs arising in the cerebral hemispheres, demonstrating a molecular difference among pHGG subgroups. The gene expression signatures as well as DNA methylation signatures of these tumors are also distinctive, reflecting a combination of the driving mutations and the developmental context from which they arise. These data collectively highlight unique selective pressures within the developing brainstem and solidify DIPG as a specific molecular and biological entity among pHGGs. Emerging studies continue to identify novel mutations that distinguish subgroups of pHGG. The molecular heterogeneity among pHGGs will undoubtedly have clinical implications moving forward. The discovery of unique oncogenic drivers is a critical first step in providing patients with appropriate, targeted therapies. Despite these insights, our vantage point has been largely limited to an in-depth analysis of protein coding sequences. Given the clear importance of histone mutations in pHGG, it will be interesting to see how aberrant epigenetic regulation contributes to tumorigenesis in the pediatric context. New mechanistic insights may allow for the identification of distinct vulnerabilities in this devastating spectrum of childhood tumors.

Pediatric diffuse intrinsic pontine glioma: can optimism replace pessimism?

Pediatric diffuse intrinsic pontine glioma (DIPG) has a dismal prognosis that has not seen a change in outcome despite multiple clinical trials. Possible reasons for failure to make progress in this aggressive childhood brain tumor include: poor understanding of the underlying molecular biology due to lack of access to tumor material; absence of accurate and relevant DIPG preclinical models for drug development; ill-defined therapeutic targets for novel agents; and inadequate drug delivery to the brainstem. This review will demonstrate that systematic studies to identify solutions for each of these barriers is starting to deliver progress that can turn pessimism to optimism in DIPG.

A preclinical study demonstrating the efficacy of nilotinib in inhibiting the growth of pediatric high-grade glioma

Solid tumors arising from malignant transformation of glial cells are one of the leading causes of central nervous system tumor-related death in children. Recurrence in spite of rigorous surgical and chemoradiation therapies remains a major hurdle in management of these tumors. Here, we investigate the efficacy of the second-generation receptor tyrosine kinase inhibitor nilotinib as a therapeutic option for the management of pediatric gliomas. We have utilized two independent pediatric high-grade glioma cell lines with either high platelet-derived growth factor receptor alpha (PDGFRα) or high PDGFRβ expression in in vitro assays to investigate the specific downstream effects of nilotinib treatment. Using in vitro cell-based assays we show that nilotinib inhibits PDGF-BB-dependent activation of PDGFRα. We further show that nilotinib is able to decrease cell proliferation and anchorage-independent growth via suppression of AKT and ERK1/2 signaling pathways. Our results suggest that nilotinib may be effective for management of a PDGFRα-dependent group of pediatric gliomas.