Management of diffuse pontine gliomas in children: recent developments

Combination treatment with histone deacetylase and carbonic anhydrase 9 inhibitors shows therapeutic potential in experimental diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) remains a significant therapeutic challenge due to the lack of effective and safe treatment options. This study explores the potential of combining histone deacetylase (HDAC) and carbonic anhydrase 9 (CA9) inhibitors in treating DIPG. Analysis of RNA sequencing data and tumor tissue from patient samples for the expression of the carbonic anhydrase family and hypoxia signaling pathway activity revealed clinical relevance for targeting CA9 in DIPG. A synergy screen was conducted using CA9 inhibitor SLC-0111 and HDAC inhibitors panobinostat, vorinostat, entinostat, and pyroxamide. The combination of SLC-0111 and pyroxamide demonstrated the highest synergy and was selected for further analysis. Combining SLC-0111 and pyroxamide effectively inhibited DIPG cell proliferation, reduced cell migration and invasion potential, and enhanced histone acetylation, leading to decreased cell population in S Phase. Additionally, the combination therapy induced a greater reduction in intracellular pH than either agent alone. Data from this study suggest that the combination of SLC-0111 and pyroxamide holds promise for treating experimental DIPG, and further investigation of this combination therapy in preclinical models is warranted to evaluate its potential as a viable treatment for DIPG.

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.

Past, present and future of Focused Ultrasound as an adjunct or complement to DIPG/DMG therapy: A consensus of the 2021 FUSF DIPG meeting

Diffuse Intrinsic Pontine Glioma (DIPG), now known as Diffuse Midline Glioma (DMG) is a devastating pediatric brain tumor with limited treatment options and a very poor prognosis. Despite more than 250 clinical trials aimed to treat children diagnosed with DMG, no curative therapies currently exist for this patient population. A major obstacle has been the intact blood brain barrier (BBB) which prevents most therapeutics from crossing into the tumor bed. Focused Ultrasound (FUS) is an emerging, noninvasive medical technology which has been shown in both preclinical and clinical research to disrupt the blood brain barrier safely and temporarily. FUS blood brain barrier opening has been studied in combination with chemotherapies in preclinical DMG models, and this technology is now being investigated in clinical trials for the treatment of pediatric brain tumors. Focused ultrasound has additional mechanisms of action, including sonodynamic therapy and radiation sensitization, that hold promise as future DMG therapies as well. This paper, largely based off the proceedings from a workshop held by the Focused Ultrasound Foundation in October of 2021, summarizes the current state of the field of focused ultrasound for DIPG/DMG, including preclinical, technical, and clinical summaries in addition to recommended next steps for continued advancement of the game changing technology of Focused Ultrasound.

Targeted therapy for pediatric diffuse intrinsic pontine glioma: a single-center experience

Background:

Diffuse intrinsic pontine glioma (DIPG) is a fatal disease with a median overall survival (OS) of less than 12 months after diagnosis. Radiotherapy (RT) still remains the mainstay treatment. Several other therapeutic strategies have been attempted in the last years without a significant effect on OS. Although radiological imaging is the gold standard for DIPG diagnosis, the urgent need to improve the survival has led to the reconsideration of biopsy with the aim to better understand the molecular profile of DIPG and support personalized treatment.

Methods:

In this study, we present a single-center experience in treating DIPG patients at disease progression combining targeted therapies with standard of care. Biopsy was proposed to all patients at diagnosis or disease progression. First-line treatment included RT and nimotuzumab/vinorelbine or temozolomide. Immunohistochemistry-targeted research included study of mTOR/p-mTOR pathway and BRAFv600E. Molecular analyses included polymerase chain reaction, followed by Sanger sequences and/or next-generation sequencing.

Results:

Based on the molecular profile, targeted therapy was administered in 9 out of 25 patients, while the remaining 16 patients were treated with standard of care. Personalized treatment included inhibition of the PI3K/AKT/mTOR pathway (5/9), PI3K/AKT/mTOR pathway and BRAFv600E (1/9), ACVR1 (2/9) and PDGFRA (1/9); no severe side effects were reported during treatment. Response to treatment was evaluated according to Response Assessment in Pediatric Neuro-Oncology criteria, and the overall response rate within the cohort was 66%. Patients treated with targeted therapies were compared with the control cohort of 16 patients. Clinical and pathological characteristics of the two cohorts were homogeneous. Median OS in the personalized treatment and control cohort was 20.26 and 14.18 months, respectively (p = 0.032). In our experience, the treatment associated with the best OS was everolimus.

Conclusion:

Despite the small simple size of our study, our data suggest a prognostic advantage and a safe profile of targeted therapies in DIPG patients, and we strongly advocate to reconsider the role of biopsy for these patients.

Adult diffuse intrinsic pontine glioma: clinical, radiological, pathological, molecular features, and treatments of 96 patients

OBJECTIVE

Unlike its pediatric counterpart, adult diffuse intrinsic pontine glioma (DIPG) remains largely unelucidated. In this study, the authors examined the clinical, radiological, pathological, molecular, and clinical aspects of 96 adult DIPGs.

METHODS

The National Brain Tumor Registry of China (April 2013-December 2019) was used to collect data on radiologically diagnosed adult DIPG patients. Survival analysis was conducted using Kaplan-Meier curves and univariate and multivariate Cox regression. The chi-square test/Wilcoxon rank-sum test and multivariable logistic regression were used to examine the clinical and radiological characteristics of patients with long-term survival (LTS). Interaction analyses between clinical factors were also conducted.

RESULTS

The median age at symptom onset was 33.5 years, and the median duration of symptoms was 4.5 months. The frequencies of H3K27M and IDH1 mutations were 37.2% and 26.5%, respectively. All adult DIPG patients had a median overall survival (OS) of 19.5 months, with 1-, 2-, and 3-year survival rates of 67.0%, 42.8%, and 36.0%, respectively. The median OS of 40 patients who did not undergo treatment was 13.4 months. Patients with H3K27M-mutant tumors had a poorer prognosis than those with IDH-mutant tumors (p < 0.001) and H3K27M(-)/IDH-wild-type tumors (p = 0.002), with a median OS of 11.4 months. The median OSs of patients with H3K27M-mutant tumors who received treatment and those who did not were 13.8 months and 7.5 months, respectively (p = 0.016). Among patients with and without a pathological diagnosis, H3K27M mutation (p < 0.001) and contrast enhancement on MRI (p = 0.003), respectively, imparted a worse prognosis. Treatments were the predictive factor for patients with H3K27M-mutant tumors (p = 0.038), whereas contrast enhancement on MRI was the prognostic factor for the H3K27M(-) group (p = 0.038). In addition, H3K27M mutation and treatment were significant predictors for patients with symptom duration ≤ 4 months (H3K27M, p = 0.020; treatment, p = 0.014) and tumors with no contrast enhancement (H3K27M, p = 0.003; treatment, p = 0.042). Patients with LTS were less likely to have cranial nerve palsy (p = 0.002) and contrast enhancement on MRI at diagnosis (p = 0.022).

CONCLUSIONS

It is recommended that all adult DIPG patients undergo genomic testing for H3K27M and IDH mutations. Despite the low prevalence, additional study is needed to better characterize the efficacy of various treatment modalities in adults with DIPG.

TP53 wild-type/PPM1D mutant diffuse intrinsic pontine gliomas are sensitive to a MDM2 antagonist

Diffuse intrinsic pontine gliomas (DIPGs) are high-grade tumors of the brainstem that often occur in children, with a median overall survival of less than one year. Given the fact that DIPGs are resistant to chemotherapy and are not amenable to surgical resection, it is imperative to develop new therapeutic strategies for this deadly disease. The p53 pathway is dysregulated by TP53 (~ 60%) or PPM1D gain-of-function mutations (~ 30%) in DIPG cases. PPM1D gain-of-function mutations suppress p53 activity and result in DIPG tumorigenesis. While MDM2 is a major negative regulator of p53, the efficacy of MDM2 inhibitor has not been tested in DIPG preclinical models. In this study, we performed a comprehensive validation of MDM2 inhibitor RG7388 in patient-derived DIPG cell lines established from both TP53 wild-type/PPM1D-mutant and TP53 mutant/PPM1D wild-type tumors, as well in TP53 knockout isogenic DIPG cell line models. RG7388 selectively inhibited the proliferation of the TP53 wild-type/PPM1D mutant DIPG cell lines in a dose- and time-dependent manner. The anti-proliferative effects were p53-dependent. RNA-Seq data showed that differential gene expression induced by RG7388 treatment was enriched in the p53 pathways. RG7388 reactivated the p53 pathway and induced apoptosis as well as G1 arrest. In vivo, RG7388 was able to reach the brainstem and exerted therapeutic efficacy in an orthotopic DIPG xenograft model. Hence, this study demonstrates the pre-clinical efficacy potential of RG7388 in the TP53 wild-type/PPM1D mutant DIPG subgroup and may provide critical insight on the design of future clinical trials applying this drug in DIPG patients.

Focused ultrasound mediated blood-brain barrier opening is safe and feasible in a murine pontine glioma model

Drug delivery in diffuse intrinsic pontine glioma is significantly limited by the blood-brain barrier (BBB). Focused ultrasound (FUS), when combined with the administration of microbubbles can effectively open the BBB permitting the entry of drugs across the cerebrovasculature into the brainstem. Given that the utility of FUS in brainstem malignancies remains unknown, the purpose of our study was to determine the safety and feasibility of this technique in a murine pontine glioma model. A syngeneic orthotopic model was developed by stereotactic injection of PDGF-B⁺PTEN^−/−p53^−/− murine glioma cells into the pons of B6 mice. A single-element, spherical-segment 1.5 MHz ultrasound transducer driven by a function generator through a power amplifier was used with concurrent intravenous microbubble injection for tumor sonication. Mice were randomly assigned to control, FUS and double-FUS groups. Pulse and respiratory rates were continuously monitored during treatment. BBB opening was confirmed with gadolinium-enhanced MRI and Evans blue. Kondziela inverted screen testing and sequential weight lifting measured motor function before and after sonication. A subset of animals were treated with etoposide following ultrasound. Mice were either sacrificed for tissue analysis or serially monitored for survival with daily weights. FUS successfully caused BBB opening while preserving normal cardiorespiratory and motor function. Furthermore, the degree of intra-tumoral hemorrhage and inflammation on H&E in control and treated mice was similar. There was also no difference in weight loss and survival between the groups (p > 0.05). Lastly, FUS increased intra-tumoral etoposide concentration by more than fivefold. FUS is a safe and feasible technique for repeated BBB opening and etoposide delivery in a preclinical pontine glioma model.

The current state of immunotherapy for primary and secondary brain tumors: similarities and differences

Treatment and resolution of primary and metastatic brain tumors have long presented a challenge to oncologists. In response to the dismal survival outcomes associated with conventional therapies, various immunotherapy modalities, such as checkpoint inhibitors, vaccine, cellular immunotherapy and viral immunotherapy have been actively explored over the past couple of decades. Although improved patient survival has been more frequently noted in treatment of brain metastases, little progress has been made in improving patient survival in cases of primary brain tumors, specifically glioblastoma, which is the representative primary brain tumor discussed in this review. Herein, we will first overview the findings of recent clinical studies for treatment of primary and metastatic brain tumors with immunotherapeutic interventions. The clinical efficacy of these immunotherapies will be discussed in the context of their ability or inability to overcome inherent characteristics of the tumor as well as restricted antigen presentation and its immunosuppressive microenvironment. Additionally, this review aims to briefly inform clinicians in the field of neuro-oncology on the relevant aspects of the immune system as it pertains to the central nervous system, with special focus on the differing modes of antigen presentation and tumor microenvironment of primary and metastatic brain tumors and the role these differences may play in the efficacy of immunotherapy in eradicating the tumor.

Hypofractionated radiotherapy versus conventional radiotherapy for diffuse intrinsic pontine glioma: A systematic review and meta-analysis

BACKGROUND

The standard treatment for diffuse intrinsic pontine glioma (DIPG) is radiotherapy, although conventional fractionated radiotherapy (CFRT) may not be in the best interest of the patient. Instead, hypofractionated radiotherapy (HFRT) may shorten the treatment period and reduce related costs for this treatment, which is typically palliative in nature.

METHODS

This systematic review and meta-analysis evaluated survival outcomes among patients who received HFRT or CFRT for DIPG. The PubMed, Medline, EMBASE, Cochrane Central Register, and Scopus databases were searched to identify relevant studies. Overall survival was the primary outcome of interest and progression-free survival was the secondary outcome of interest.

RESULTS

The search identified a total of 2376 reports, although only 4 reports were ultimately included in the meta-analysis. The studies included 88 patients who underwent HFRT and 96 patients who underwent CFRT. Relative to CFRT, HFRT provided comparable outcomes in terms of overall survival (hazard ratio [HR]: 1.07, 95% confidence interval [CI]: 0.77-1.47) and progression-free survival (HR: 1.04, 95% CI: 0.75-1.45).

CONCLUSIONS

The results of this meta-analysis suggest that CFRT and HFRT provide similar survival outcomes for patients with DIPG.

Targeting tumor hypoxia and mitochondrial metabolism with anti-parasitic drugs to improve radiation response in high-grade gliomas

High-grade gliomas (HGGs), including glioblastoma and diffuse intrinsic pontine glioma, are amongst the most fatal brain tumors. These tumors are associated with a dismal prognosis with a median survival of less than 15 months. Radiotherapy has been the mainstay of treatment of HGGs for decades; however, pronounced radioresistance is the major obstacle towards the successful radiotherapy treatment. Herein, tumor hypoxia is identified as a significant contributor to the radioresistance of HGGs as oxygenation is critical for the effectiveness of radiotherapy. Hypoxia plays a fundamental role in the aggressive and resistant phenotype of all solid tumors, including HGGs, by upregulating hypoxia-inducible factors (HIFs) which stimulate vital enzymes responsible for cancer survival under hypoxic stress. Since current attempts to target tumor hypoxia focus on reducing oxygen demand of tumor cells by decreasing oxygen consumption rate (OCR), an attractive strategy to achieve this is by inhibiting mitochondrial oxidative phosphorylation, as it could decrease OCR, and increase oxygenation, and could therefore improve the radiation response in HGGs. This approach would also help in eradicating the radioresistant glioma stem cells (GSCs) as these predominantly rely on mitochondrial metabolism for survival. Here, we highlight the potential for repurposing anti-parasitic drugs to abolish tumor hypoxia and induce apoptosis of GSCs. Current literature provides compelling evidence that these drugs (atovaquone, ivermectin, proguanil, mefloquine, and quinacrine) could be effective against cancers by mechanisms including inhibition of mitochondrial metabolism and tumor hypoxia and inducing DNA damage. Therefore, combining these drugs with radiotherapy could potentially enhance the radiosensitivity of HGGs. The reported efficacy of these agents against glioblastomas and their ability to penetrate the blood-brain barrier provides further support towards promising results and clinical translation of these agents for HGGs treatment.

Convection Enhanced Delivery for Diffuse Intrinsic Pontine Glioma: Review of a Single Institution Experience

Diffuse intrinsic pontine gliomas (DIPGs) are a pontine subtype of diffuse midline gliomas (DMGs), primary central nervous system (CNS) tumors of childhood that carry a terrible prognosis. Because of the highly infiltrative growth pattern and the anatomical position, cytoreductive surgery is not an option. An initial response to radiation therapy is invariably followed by recurrence; mortality occurs approximately 11 months after diagnosis. The development of novel therapeutics with great preclinical promise has been hindered by the tightly regulated blood-brain barrier (BBB), which segregates the tumor comportment from the systemic circulation. One possible solution to this obstacle is the use of convection enhanced delivery (CED), a local delivery strategy that bypasses the BBB by direct infusion into the tumor through a small caliber cannula. We have recently shown CED to be safe in children with DIPG (NCT01502917). In this review, we discuss our experience with CED, its advantages, and technical advancements that are occurring in the field. We also highlight hurdles that will likely need to be overcome in demonstrating clinical benefit with this therapeutic strategy.

Predicting outcome in childhood diffuse midline gliomas using magnetic resonance imaging based texture analysis

BACKGROUND

Diffuse midline gliomas (DMG) are aggressive brain tumours, previously known as diffuse intrinsic pontine gliomas (DIPG), with 10% overall survival (OS) at 18 months. Predicting OS will help refine treatment strategy in this patient group. MRI based texture analysis (MRTA) is novel image analysis technique that provides objective information about spatial arrangement of MRI signal intensity (heterogeneity) and has potential to be imaging biomarker.

OBJECTIVES

To investigate MRTA in predicting OS in childhood DMG.

METHODS

Retrospective study of patients diagnosed with DMG, based on radiological features, treated at our institution 2007-2017. MRIs were acquired at diagnosis and 6 weeks after radiotherapy (54Gy in 30 fractions). MRTA was performed using commercial available TexRAD research software on T2W sequence and Apparent Diffusion Coefficient (ADC) maps encapsulating tumour in the largest single axial plane. MRTA comprised filtration-histogram technique using statistical and histogram metrics for quantification of texture. Kaplan-Meier survival analysis determined association of MRI texture parameters with OS.

RESULTS

In all, 32 children 2-14 years (median 7 years) were included. MRTA was undertaken on T2W (n=32) and ADC (n=22). T2W-MRTA parameters were better at prognosticating than ADC-MRTA. Children with homogenous tumour texture, at medium scale on diagnostic T2W MRI, had worse prognosis (Mean of Positive Pixels (MPP): P=0.005, mean: P=0.009, SD: P=0.011, kurtosis: P=0.037, entropy: P=0.042). Best predictor MPP was able to stratify patients into poor and good prognostic groups with median survival of 7.5 months versus 17.5 months, respectively.

CONCLUSIONS

DMG with more homogeneous texture on diagnostic MRI is associated with worse prognosis. Texture parameter MPP is the most predictive marker of OS in childhood DMG.

Diffuse intrinsic pontine gliomas: Diagnostic approach and treatment strategies

Diffuse intrinsic pontine gliomas (DIPG) are high grade gliomas of the brainstem with fatal outcomes. Radiation is known to be partially effective to control the immediate flare but relapse is frequent. There has been ongoing research to study the role of molecular subgroups and identification of specific targets but this is not possible with histopathological diagnosis alone. The authors' objective is to highlight the need for and discuss ongoing molecular research. There is an inherent need for the availability of tumor tissue to be able to conduct research studies. The authors advocate the use of neuronavigation assisted stereotactic technique for tumor biopsy. The technique is feasible with a predefined surgical trajectory. After obtaining tissue diagnosis further work can be performed to isolate and identify histone protein genetic mutations and methylation changes responsible for DIPG molecular subgrouping. Moreover, convection enhanced delivery of therapeutic agents is being developed for better instillation of future drug agents. Despite identification of genetic/epigenetic mutations, growth factors, receptors, and tissue biomarkers, the oncogenesis of DIPG remains elusive. The authors' effort to provide a comprehensive review on DIPG to better understand the disease, need for tissue diagnosis, described surgical technique, and need for pre-clinical and clinical future research is novel.

The intersect of neurosurgery with diffuse intrinsic pontine glioma

An invited article highlighting diffuse intrinsic pontine glioma (DIPG) to celebrate the 75th Anniversary of the Journal of Neurosurgery, a journal known to define surgical nuance and enterprise, is paradoxical since DIPG has long been relegated to surgical abandonment. More recently, however, the neurosurgeon is emerging as a critical stakeholder given our role in tissue sampling, collaborative scientific research, and therapeutic drug delivery. The foundation for this revival lies in an expanding reliance on tissue accession for understanding tumor biology, available funding to fuel research, and strides with interventional drug delivery.

Nimotuzumab-containing regimen for pediatric diffuse intrinsic pontine gliomas: a retrospective multicenter study and review of the literature

PURPOSE

Nimotuzumab is an IgG1 antibody that targets epidermal growth factor receptor (EGFR). Overexpression of EGFR is detected in some pediatric brain tumors including diffuse intrinsic pontine gliomas (DIPG)s.

METHODS

Since May 2010, nimotuzumab, combined with carboplatin or vinorelbine or Temozolomide (TMZ), was administered during progressive disease (PD) after the use of the institutional protocol consisting of radiotherapy (RT) + TMZ and adjuvant TMZ. After May 2012, children with newly diagnosed disease received TMZ during RT, and nimotuzumab and TMZ after RT. Nimotuzumab was given as 150 mg/m²/dose once a week for 12 weeks, and then every other week with TMZ until PD. PD patients were switched to nimotuzumab + vinorelbine combination until death.

RESULTS

Nimotuzumab was used in 24 children with DIPG (seven in the PD group, 17 in the newly diagnosed patient group). In the PD group, median survival time was 12 months (7-42 months); 1-year and 2-year overall survival (OS) rates were 42.9 ± 18% and 14.3 ± 13%, respectively. The median survival in this group, after the initiation of nimotuzumab was 6 months (3-8 months). In the newly diagnosed patient group, median survival time was 11 months (3-35 months) and median progression free survival was 4 months (1-21 months). The 1-year OS in this group was 35.3 ± 11% and 2 year OS was 11.8 ± 7%. Nimotuzumab ± chemotherapy was well tolerated with no major adverse effect.

CONCLUSION

Nimotuzumab-containing regimens are feasible and tolerable; it might be that some patients either with newly diagnosed DIPG or with progressive disease may benefit modestly from nimotuzumab-containing combinations.

Prospective feasibility and safety assessment of surgical biopsy for patients with newly diagnosed diffuse intrinsic pontine glioma

Background

Diagnosis of diffuse intrinsic pontine glioma (DIPG) has relied on imaging studies, since the appearance is pathognomonic, and surgical risk was felt to be high and unlikely to affect therapy. The DIPG Biology and Treatment Study (DIPG-BATS) reported here incorporated a surgical biopsy at presentation and stratified subjects to receive FDA-approved agents chosen on the basis of specific biologic targets.

Methods

Subjects were eligible for the trial if the clinical features and imaging appearance of a newly diagnosed tumor were consistent with a DIPG. Surgical biopsies were performed after enrollment and prior to definitive treatment. All subjects were treated with conventional external beam radiotherapy with bevacizumab, and then stratified to receive bevacizumab with erlotinib or temozolomide, both agents, or neither agent, based on O6-methylguanine-DNA methyltransferase status and epidermal growth factor receptor expression. Whole-genome sequencing and RNA sequencing were performed but not used for treatment assignment.

Results

Fifty-three patients were enrolled at 23 institutions, and 50 underwent biopsy. The median age was 6.4 years, with 24 male and 29 female subjects. Surgical biopsies were performed with a specified technique and no deaths were attributed to the procedure. Two subjects experienced grade 3 toxicities during the procedure (apnea, n = 1; hypertension, n = 1). One subject experienced a neurologic deficit (left hemiparesis) that did not fully recover. Of the 50 tumors biopsied, 46 provided sufficient tissue to perform the study assays (92%, two-stage exact binomial 90% CI: 83%-97%).

Conclusions

Surgical biopsy of DIPGs is technically feasible, associated with acceptable risks, and can provide biologic data that can inform treatment decisions.

Diffuse Intrinsic Pontine Glioma : Clinical Features, Molecular Genetics, and Novel Targeted Therapeutics

Diffuse intrinsic pontine glioma (DIPG) is a deadly paediatric brain cancer. Transient response to radiation, ineffective chemotherapeutic agents and aggressive biology result in rapid progression of symptoms and a dismal prognosis. Increased availability of tumour tissue has enabled the identification of histone gene aberrations, genetic driver mutations and methylation changes, which have resulted in molecular and phenotypic subgrouping. However, many of the underlying mechanisms of DIPG oncogenesis remain unexplained. It is hoped that more representative in vitro and preclinical models–using both xenografted material and genetically engineered mice–will enable the development of novel chemotherapeutic agents and strategies for targeted drug delivery. This review provides a clinical overview of DIPG, the barriers to progress in developing effective treatment, updates on drug development and preclinical models, and an introduction to new technologies aimed at enhancing drug delivery.

Novel and shared neoantigen derived from histone 3 variant H3.3K27M mutation for glioma T cell therapy

The median overall survival for children with diffuse intrinsic pontine glioma (DIPG) is less than one year. The majority of diffuse midline gliomas, including more than 70% of DIPGs, harbor an amino acid substitution from lysine (K) to methionine (M) at position 27 of histone 3 variant 3 (H3.3). From a CD8⁺ T cell clone established by stimulation of HLA-A2⁺ CD8⁺ T cells with synthetic peptide encompassing the H3.3K27M mutation, complementary DNA for T cell receptor (TCR) α- and β-chains were cloned into a retroviral vector. TCR-transduced HLA-A2⁺ T cells efficiently killed HLA-A2⁺H3.3K27M⁺ glioma cells in an antigen- and HLA-specific manner. Adoptive transfer of TCR-transduced T cells significantly suppressed the progression of glioma xenografts in mice. Alanine-scanning assays suggested the absence of known human proteins sharing the key amino acid residues required for recognition by the TCR, suggesting that the TCR could be safely used in patients. These data provide us with a strong basis for developing T cell-based therapy targeting this shared neoepitope.

Patient-derived DIPG cells preserve stem-like characteristics and generate orthotopic tumors

Diffuse intrinsic pontine glioma (DIPG) is a devastating brain tumor, with a median survival of less than one year. Due to enormous difficulties in the acquisition of DIPG specimens and the sophisticated technique required to perform brainstem orthotopic injection, only a handful of DIPG pre-clinical models are available. In this study, we successfully established eight patient-derived DIPG cell lines, mostly derived from treatment-naïve surgery or biopsy specimens. These patient-derived cell lines can be stably passaged in serum-free neural stem cell media and displayed distinct morphologies, growth rates and chromosome abnormalities. In addition, these cells retained genomic hallmarks identical to original human DIPG tumors. Notably, expression of several neural stem cell lineage markers was observed in DIPG cell lines. Moreover, three out of eight cell lines can form orthotopic tumors in mouse brainstem by stereotactic injection and these tumors faithfully represented the characteristics of human DIPG by magnetic resonance imaging (MRI) and histopathological staining. Taken together, we established DIPG pre-clinical models resembling human DIPG and they provided a valuable resource for future biological and therapeutic studies.

Epigenetic Targeted Therapy for Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG) is a rare but uniformly fatal cancer of the brain, with peak incidence in children of 5–7 years of age. In contrast to most types of human cancer, there has been no significant improvement in treatment outcomes for patients with DIPG. Since DIPG occurs in the brainstem, a vital region of the brain, there are no surgical options for providing relief to patients, and chemotherapy as well as radiation therapy provide palliative relief at best. To date, more than 250 clinical trials evaluating radiotherapy along with conventional cytotoxic chemotherapy, as well as newer biologic agents, have failed to improve the dismal outcome when compared with palliative radiation alone. The recent discovery of somatic oncogenic histone gene mutations affecting chromatin regulation in DIPG has dramatically improved our understanding of the disease pathogenesis in DIPG, and these findings have stimulated the development of novel therapeutic approaches targeting epigenetic regulators for disease treatment. This review will discuss about the role of histone modification in chromatin machinery and epigenetic therapeutic strategies for the treatment of DIPG.

Multimodal Magnetic Resonance Imaging of Treatment-Induced Changes to Diffuse Infiltrating Pontine Gliomas in Children and Correlation to Patient Progression-Free Survival

PURPOSE

To use multimodal magnetic resonance imaging (MRI) to quantify treatment-induced changes in the whole volume of diffuse infiltrating pontine gliomas and correlate them with progression-free survival (PFS).

METHODS AND MATERIALS

This prospective study included 22 children aged 3.3 to 14.7 years (median, 5.9 years). Multimodal MRI was performed at 3 distinct time points: before treatment, the first week following radiation therapy (RT), and 2 months after RT. The imaging protocol included morphologic, multi b-value diffusion; arterial spin labeling; and dynamic susceptibility contrast-enhanced perfusion. Morphologic and multimodal data-lesion volume, diffusion coefficients, relative cerebral blood flow, and relative cerebral blood volume (rCBV)-were recorded at the 3 aforementioned time points. The Wilcoxon test was used to compare each individual parameter variation between time points, and its correlation with PFS was assessed by the Spearman test.

RESULTS

Following RT, the tumors' solid component volume decreased by 40% (P<.001). Their median diffusion coefficients decreased by 20% to 40% (P<.001), while median relative cerebral blood flow increased by 60% to 80% (P<.001) and median rCBV increased by 70% (P<.001). PFS was positively correlated with rCBV measured immediately after RT (P=.003), and in patients whose rCBV was above the cutoff value of 2.46, the median PFS was 4.6 months longer (P=.001). These indexes tended to return to baseline 2 months after RT. Lesion volume before or after RT was not correlated with survival.

CONCLUSIONS

Multimodal MRI provides useful information about diffuse infiltrating pontine gliomas' response to treatment; rCBV increases following RT, and higher values are correlated with better PFS. High rCBV values following RT should not be mistaken for progression and could be an indicator of response to therapy.

Malignant brainstem tumors in children, excluding diffuse intrinsic pontine gliomas

OBJECT Malignant tumors of the brainstem, excluding classic diffuse intrinsic pontine gliomas (DIPGs), are a very rare, heterogeneous group of neoplasms that have been infrequently described in the literature. In this paper, the authors present their experiences with treating these unique cancers. METHODS A retrospective chart review was conducted to identify eligible cases over a 15-year period. All tumors involving the pons were, by consensus, felt not to be DIPGs based on their neuroimaging features. Demographic information, pathological specimens, neuroimaging characteristics, surgical and nonsurgical management plans, and survival data were gathered for analysis. RESULTS Between January 2000 and December 2014, 29 patients were identified. The mean age at diagnosis was 8.4 years (range 2 months to 25 years), and 17 (59%) patients were male. The most common presenting signs and symptoms were cranial neuropathies (n = 24; 83%), hemiparesis (n = 12; 41%), and ataxia or gait disturbance (n = 10; 34%). There were 18 glial and 11 embryonal tumors. Of the glial tumors, 5 were radiation-induced and 1 was a malignant transformation of a previously known low-grade tumor. Surgical intervention consisted of biopsy alone in 12 patients and some degree of resection in another 15 patients. Two tumors were diagnosed postmortem. The median overall survival for all patients was 196 days (range 15 to 3999 days). There are currently 5 (17%) patients who are still alive: 1 with an anaplastic astrocytoma and the remaining with embryonal tumors. CONCLUSIONS In general, malignant non-DIPG tumors of the brainstem carry a poor prognosis. However, maximal cytoreductive surgery may be an option for select patients with focal tumors. Long-term survival is possible in patients with nonmetastatic embryonal tumors after multimodal treatment, most importantly maximal resection.

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.

Clinicopathology of diffuse intrinsic pontine glioma and its redefined genomic and epigenomic landscape

Diffuse intrinsic pontine glioma (DIPG) is one of the most lethal pediatric central nervous system (CNS) cancers. Recently, a surge in molecular studies of DIPG has occurred, in large part due to the increased availability of tumor tissue through donation of post-mortem specimens. These new discoveries have established DIPGs as biologically distinct from adult gliomas, harboring unique genomic aberrations. Mutations in histone encoding genes are shown to be associated with >70% of DIPG cases. However, the exact molecular mechanisms of the tumorigenicity of these mutations remain elusive. Understanding the driving mutations and genomic landscape of DIPGs can now guide the development of targeted therapies for this incurable childhood cancer.

Clinicopathological features and treatment outcomes of brain stem gliomas in Saudi population

AIM: To analyze experiences to identify treatment outcomes and prognostic factors in a Saudi population.

METHODS: Medical records of patients with brainstem gliomas treated from July 2001 to December 2012 were reviewed to identify treatment outcomes of surgery, radiation therapy and chemotherapy and associated prognostic factors in a Saudi population.

RESULTS: We analyzed 49 brain stem glioma (BSG) patients from July 2001 to December 2012; 31 of them were males (63.3%) with a median age of 12.6 years (range: 8-64 mo). Twenty-two patients (44.9%) had diffuse intrinsic pontine gliomas (DIPG) and 15 (30.6%) presented with focal/tectal BSG. Histopathology was available in 30 patients (61.2%). Median survival time for the whole cohort was 1.5 years. One and two year OS rates were 51.1% and 41.9% respectively. Two year OS rates for focal/tectal, dorsally exophytic, cervicomedullary and DIPG tumors were 60%, 33.3%, 33.3% and 13.6% respectively (P < 0.0001). Significant prognostic factors related to OS were age at diagnosis (worse for > 18 years) P = 0.01, KPS < 70 P = 0.02, duration of symptoms (< 60 d) P = 0.002, histology (better for favorable) P = 0.002, surgery (maximal resection) P = 0.002, and concurrent chemotherapy with radiation therapy in DIPG (better if given) P = 0.01.

CONCLUSION: BSG, especially the DIPG subgroup, had a dismal prognosis, needing more aggressive neurosurgical, radiation and chemotherapy techniques, while focal and tectal tumors were found to have a better prognosis.