Signal Transduction in Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG): A review of current and emerging treatment strategies

Diffuse intrinsic pontine glioma (DIPG) is a childhood malignancy of the brainstem with a dismal prognosis. Despite recent advances in its understanding at the molecular level, the prognosis of DIPG has remained unchanged. This article aims to review the current understanding of the genetic pathophysiology of DIPG and to highlight promising therapeutic targets. Various DIPG treatment strategies have been investigated in pre-clinical studies, several of which have shown promise and have been subsequently translated into ongoing clinical trials. Ultimately, a multifaceted therapeutic approach that targets cell-intrinsic alterations, the micro-environment, and augments the immune system will likely be necessary to eradicate DIPG.

A review of current therapeutics targeting the mitochondrial protease ClpP in diffuse midline glioma, H3 K27-altered

Diffuse midline gliomas (DMGs) are devastating pediatric brain tumors recognized as the leading cause of cancer-related death in children. DMGs are high-grade gliomas (HGGs) diagnosed along the brain's midline. Euchromatin is the hallmark feature of DMG, caused by global hypomethylation of H3K27 either through point mutations in histone H3 genes (H3K27M), or by overexpression of the enhancer of zeste homolog inhibitory protein. In a clinical trial for adults with progressive HGGs, a 22-year-old patient with a thalamic DMG, H3 K27-altered, showed a remarkable clinical and radiological response to dordaviprone (ONC201). This response in an H3 K27-altered HGG patient, coupled with the lack of response of patients harboring wildtype-H3 tumors, has increased the clinical interest in dordaviprone for the treatment of DMG. Additional reports of clinical benefit have emerged, but research defining mechanisms of action (MOA) fall behind dordaviprone's clinical use, with biomarkers of response unresolved. Here, we summarize dordaviprone's safety, interrogate its preclinical MOA identifying the mitochondrial protease "ClpP" as a biomarker of response, and discuss other ClpP agonists, expanding the arsenal of potential weapons in the fight against DMG. Finally, we discuss combination strategies including ClpP agonists, and their immunomodulatory effects suggestive of a role for the tumor microenvironment in DMG patient response.

H3K27M mutant glioma: Disease definition and biological underpinnings

High-grade glioma (HGG) is the most common cause of cancer death in children and the most common primary central nervous system tumor in adults. While pediatric HGG was once thought to be biologically similar to the adult form of disease, research has shown these malignancies to be significantly molecularly distinct, necessitating distinct approaches to their clinical management. However, emerging data have shown shared molecular events in pediatric and adult HGG including the histone H3K27M mutation. This somatic missense mutation occurs in genes encoding one of two isoforms of the Histone H3 protein, H3F3A (H3.3), or HIST1H3B (H3.1), and is detected in up to 80% of pediatric diffuse midline gliomas and in up to 60% of adult diffuse gliomas. Importantly, the H3K27M mutation is associated with poorer overall survival and response to therapy compared to patients with H3 wild-type tumors. Here, we review the clinical features and biological underpinnings of pediatric and adult H3K27M mutant glioma, offering a groundwork for understanding current research and clinical approaches for the care of patients suffering with this challenging disease.

Distinct MRI characteristics of spinal cord diffuse midline glioma, H3 K27-altered in comparison to spinal cord glioma without H3 K27-alteration and demyelination disorder

BACKGROUND

An applicable magnetic resonance imaging (MRI) biomarker for diffuse midline glioma (DMG), H3 K27-altered of the spinal cord is important for non-invasive diagnosis.

PURPOSE

To evaluate the efficacy of conventional MRI (cMRI) in distinguishing between DMGs, H3 K27-altered, gliomas without H3 K27-alteration, and demyelinating lesions in the spinal cord.

MATERIAL AND METHODS

Between January 2017 and February 2023, patients with pathology-confirmed spinal cord gliomas (including ependymomas) with definite H3 K27 status and demyelinating diseases diagnosed by recognized criteria were recruited as the training set for this retrospective study. Morphologic parameter assessment was performed by two neuroradiologists on T1-weighted, T2-weighted, and contrast-enhanced T1-weighted imaging. Variables with high inter- and intra-observer agreement were included in univariable correlation analysis and multivariable logistic regression. The performance of the final model was verified by internal and external testing sets.

RESULTS

The training cohort included 21 patients with DMGs (13 men; mean age = 34.57 ± 13.489 years), 21 with wild-type gliomas (10 men; mean age = 46.76 ± 17.017 years), and 20 with demyelinating diseases (5 men; mean age = 49.50 ± 18.872 years). A significant difference was observed in MRI features, including cyst(s), hemorrhage, pial thickening with enhancement, and the maximum anteroposterior diameter of the spinal cord. The prediction model, integrating age, age2, and morphological characteristics, demonstrated good performance in the internal and external testing cohort (accuracy: 0.810 and 0.800, specificity: 0.810 and 0.720, sensitivity: 0.872 and 0.849, respectively).

CONCLUSION

Based on cMRI, we developed a model with good performance for differentiating among DMGs, H3 K27-altered, wild-type glioma, and demyelinating lesions in the spinal cord.

PI3K/mTOR is a therapeutically targetable genetic dependency in diffuse intrinsic pontine glioma

Diffuse midline glioma (DMG), including tumors diagnosed in the brainstem (diffuse intrinsic pontine glioma; DIPG), are uniformly fatal brain tumors that lack effective treatment. Analysis of CRISPR/Cas9 loss-of-function gene deletion screens identified PIK3CA and MTOR as targetable molecular dependencies across patient derived models of DIPG, highlighting the therapeutic potential of the blood-brain barrier-penetrant PI3K/Akt/mTOR inhibitor, paxalisib. At the human-equivalent maximum tolerated dose, mice treated with paxalisib experienced systemic glucose feedback and increased insulin levels commensurate with patients using PI3K inhibitors. To exploit genetic dependence and overcome resistance while maintaining compliance and therapeutic benefit, we combined paxalisib with the antihyperglycemic drug metformin. Metformin restored glucose homeostasis and decreased phosphorylation of the insulin receptor in vivo, a common mechanism of PI3K-inhibitor resistance, extending survival of orthotopic models. DIPG models treated with paxalisib increased calcium-activated PKC signaling. The brain penetrant PKC inhibitor enzastaurin, in combination with paxalisib, synergistically extended the survival of multiple orthotopic patient-derived and immunocompetent syngeneic allograft models; benefits potentiated in combination with metformin and standard-of-care radiotherapy. Therapeutic adaptation was assessed using spatial transcriptomics and ATAC-Seq, identifying changes in myelination and tumor immune microenvironment crosstalk. Collectively, this study has identified what we believe to be a clinically relevant DIPG therapeutic combinational strategy.

Translational considerations for immunotherapy clinical trials in pediatric neuro-oncology

While immunotherapy for pediatric cancer has made great strides in recent decades, including the FDA approval of agents such as dinutuximab and tisgenlecleucel, these successes have rarely impacted children with pediatric central nervous system (CNS) tumors. As our understanding of the biological underpinnings of these tumors evolves, new immunotherapeutics are undergoing rapid clinical translation specifically designed for children with CNS tumors. Most recently, there have been notable clinical successes with oncolytic viruses, vaccines, adoptive cellular therapy, and immune checkpoint inhibition. In this article, the immunotherapy working group of the Pacific Pediatric Neuro-Oncology Consortium (PNOC) reviews the current and future state of immunotherapeutic CNS clinical trials with a focus on clinical trial development. Based on recent therapeutic trials, we discuss unique immunotherapy clinical trial challenges, including toxicity considerations, disease assessment, and correlative studies. Combinatorial strategies and future directions will be addressed. Through internationally collaborative efforts and consortia, we aim to direct this promising field of immuno-oncology to the next frontier of successful application against pediatric CNS 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.

ONC201 in combination with paxalisib for the treatment of H3K27-altered diffuse midline glioma

Diffuse midline gliomas (DMG), including diffuse intrinsic pontine gliomas (DIPGs), are the most lethal of childhood cancers. Palliative radiotherapy is the only established treatment, with median patient survival of 9-11 months. ONC201 is a DRD2 antagonist and ClpP agonist that has shown preclinical and emerging clinical efficacy in DMG. However, further work is needed to identify the mechanisms of response of DIPGs to ONC201 treatment and to determine whether recurring genomic features influence response. Using a systems-biological approach, we showed that ONC201 elicits potent agonism of the mitochondrial protease ClpP to drive proteolysis of electron transport chain and tricarboxylic acid cycle proteins. DIPGs harboring PIK3CA-mutations showed increased sensitivity to ONC201, while those harboring TP53-mutations were more resistant. Metabolic adaptation and reduced sensitivity to ONC201 was promoted by redox-activated PI3K/Akt signaling, which could be counteracted using the brain penetrant PI3K/Akt inhibitor, paxalisib. Together, these discoveries coupled with the powerful anti-DIPG/DMG pharmacokinetic and pharmacodynamic properties of ONC201 and paxalisib have provided the rationale for the ongoing DIPG/DMG phase II combination clinical trial NCT05009992.

Phospho-heavy-labeled-spiketide FAIMS stepped-CV DDA (pHASED) provides real-time phosphoproteomics data to aid in cancer drug selection

Global high-throughput phosphoproteomic profiling is increasingly being applied to cancer specimens to identify the oncogenic signaling cascades responsible for promoting disease initiation and disease progression; pathways that are often invisible to genomics analysis. Hence, phosphoproteomic profiling has enormous potential to inform and improve individualized anti-cancer treatment strategies. However, to achieve the adequate phosphoproteomic depth and coverage necessary to identify the activated, and hence, targetable kinases responsible for driving oncogenic signaling pathways, affinity phosphopeptide enrichment techniques are required and often coupled with offline high-pressure liquid chromatographic (HPLC) separation prior to nanoflow liquid chromatography-tandem mass spectrometry (nLC-MS/MS). These complex and time-consuming procedures, limit the utility of phosphoproteomics for the analysis of individual cancer patient specimens in real-time, and restrict phosphoproteomics to specialized laboratories often outside of the clinical setting. To address these limitations, here we have optimized a new protocol, phospho-heavy-labeled-spiketide FAIMS Stepped-CV DDA (pHASED), that employs online phosphoproteome deconvolution using high-field asymmetric waveform ion mobility spectrometry (FAIMS) and internal phosphopeptide standards to provide accurate label-free quantitation (LFQ) data in real-time. Compared with traditional single-shot LFQ phosphoproteomics workflows, pHASED provided increased phosphoproteomic depth and coverage (phosphopeptides = 4617 pHASED, 2789 LFQ), whilst eliminating the variability associated with offline prefractionation. pHASED was optimized using tyrosine kinase inhibitor (sorafenib) resistant isogenic FLT3-mutant acute myeloid leukemia (AML) cell line models. Bioinformatic analysis identified differential activation of the serine/threonine protein kinase ataxia-telangiectasia mutated (ATM) pathway, responsible for sensing and repairing DNA damage in sorafenib-resistant AML cell line models, thereby uncovering a potential therapeutic opportunity. Herein, we have optimized a rapid, reproducible, and flexible protocol for the characterization of complex cancer phosphoproteomes in real-time, a step towards the implementation of phosphoproteomics in the clinic to aid in the selection of anti-cancer therapies for patients.

B-cell Lymphoma 6 (BCL6): From Master Regulator of Humoral Immunity to Oncogenic Driver in Pediatric Cancers

B-cell lymphoma 6 (BCL6) is a protooncogene in adult and pediatric cancers, first identified in diffuse large B-cell lymphoma (DLBCL) where it acts as a repressor of the tumor suppressor TP53, conferring survival, protection, and maintenance of lymphoma cells. BCL6 expression in normal B cells is fundamental in the regulation of humoral immunity, via initiation and maintenance of the germinal centers (GC). Its role in B cells during the production of high affinity immunoglobins (that recognize and bind specific antigens) is believed to underpin its function as an oncogene. BCL6 is known to drive the self-renewal capacity of leukemia-initiating cells (LIC), with high BCL6 expression in acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and glioblastoma (GBM) associated with disease progression and treatment resistance. The mechanisms underpinning BCL6-driven therapy resistance are yet to be uncovered; however, high activity is considered to confer poor prognosis in the clinical setting. BCL6's key binding partner, BCL6 corepressor (BCOR), is frequently mutated in pediatric cancers and appears to act in concert with BCL6. Using publicly available data, here we show that BCL6 is ubiquitously overexpressed in pediatric brain tumors, inversely to BCOR, highlighting the potential for targeting BCL6 in these often lethal and untreatable cancers. In this review, we summarize what is known of BCL6 (role, effect, mechanisms) in pediatric cancers, highlighting the two sides of BCL6 function, humoral immunity, and tumorigenesis, as well as to review BCL6 inhibitors and highlight areas of opportunity to improve the outcomes of patients with pediatric cancer.

The Intricate Epigenetic and Transcriptional Alterations in Pediatric High-Grade Gliomas: Targeting the Crosstalk as the Oncogenic Achilles’ Heel

Pediatric high-grade gliomas (pHGGs) are a deadly and heterogenous subgroup of gliomas for which the development of innovative treatments is urgent. Advances in high-throughput molecular techniques have shed light on key epigenetic components of these diseases, such as K27M and G34R/V mutations on histone 3. However, modification of DNA compaction is not sufficient by itself to drive those tumors. Here, we review molecular specificities of pHGGs subcategories in the context of epigenomic rewiring caused by H3 mutations and the subsequent oncogenic interplay with transcriptional signaling pathways co-opted from developmental programs that ultimately leads to gliomagenesis. Understanding how transcriptional and epigenetic alterations synergize in each cellular context in these tumors could allow the identification of new Achilles’ heels, thereby highlighting new levers to improve their therapeutic management.

Diffuse Intrinsic Pontine Glioma: Molecular Landscape, Evolving Treatment Strategies and Emerging Clinical Trials

Diffuse intrinsic pontine glioma (DIPG) is a type of intrinsic brainstem glial tumor that occurs primarily in the pediatric population. DIPG is initially diagnosed based on clinical symptoms and the characteristic location on imaging. Histologically, these tumors are characterized by a heterogenous population of cells with multiple genetic mutations and high infiltrative capacity. The most common mutation seen in this group is a lysine to methionine point mutation seen at position 27 (K27M) within histone 3 (H3). Tumors with the H3 K27M mutation, are considered grade 4 and are now categorized within the H3 K27-altered diffuse midline glioma category by World Health Organization classification. Due to its critical location and aggressive nature, DIPG is resistant to the most eradicative treatment and is universally fatal; however, modern advances in the surgical techniques resulting in safe biopsy of the lesion have significantly improved our understanding of this disease at the molecular level. Genomic analysis has shown several mutations that play a role in the pathophysiology of the disease and can be targeted therapeutically. In this review, we will elaborate on DIPG from general aspects and the evolving molecular landscape. We will also review innovative therapeutic options that have been trialed along with new promising treatments on the horizon.

The intrinsic and microenvironmental features of diffuse midline glioma; implications for the development of effective immunotherapeutic treatment strategies

Diffuse midline glioma (DMG), including those of the brainstem (diffuse intrinsic pontine glioma), are pediatric tumors of the central nervous system (CNS). Recognized as the most lethal of all childhood cancers, palliative radiotherapy remains the only proven treatment option, however, even for those that respond, survival is only temporarily extended. DMG harbor an immunologically “cold” tumor microenvironment (TME) with few infiltrating immune cells. The mechanisms underpinning the cold TME are not well understood. Low expression levels of immune checkpoint proteins, including PD-1, PD-L1, and CTLA-4, are recurring features of DMG and likely contribute to the lack of response to immune checkpoint inhibitors (ICIs). The unique epigenetic signatures (including stem cell-like methylation patterns), a low tumor mutational burden, and recurring somatic mutations (H3K27M, TP53, ACVR1, MYC, and PIK3CA), possibly play a role in the reduced efficacy of traditional immunotherapies. Therefore, to circumvent the lack of efficacy thus far seen for the use of ICIs, adoptive cell transfer (including chimeric antigen receptor T cells) and the use of oncolytic viruses, are currently being evaluated for the treatment of DMG. It remains an absolute imperative that we improve our understanding of DMG’s intrinsic and TME features if patients are to realize the potential benefits offered by these sophisticated treatments. Herein, we summarize the limitations of immunotherapeutic approaches, highlight the emerging safety and clinical efficacy shown for sophisticated cell-based therapies, as well as the evolving knowledge underpinning the DMG-immune axis, to guide the development of immunotherapies that we hope will improve outcomes.

Production and Stabilization of Specific Upregulated Long Noncoding RNA HOXD-AS2 in Glioblastomas Are Mediated by TFE3 and miR-661, Respectively

Differential expression of long noncoding RNAs (lncRNA) plays a key role in the development of gliomas. Because gliomas are the most common primary central nervous system tumor and glioblastomas have poor prognosis, it is urgent to develop new diagnostic methods. We have previously reported that lncRNA HOXD-AS2, which is specifically up-regulated in gliomas, can activate cell cycle and promote the development of gliomas. It is expected to be a new marker for molecular diagnosis of gliomas, but little is known about HOXD-AS2. Here, we demonstrate that TFE3 and miR-661 maintain the high expression level of HOXD-AS2 by regulating its production and degradation. We found that TFE3 acted as a transcription factor binding to the HOXD-AS2 promoter region and raised H3K27ac to activate HOXD-AS2. As the cytoplasmic-located lncRNA, HOXD-AS2 could be degraded by miR-661. This process was inhibited in gliomas due to the low expression of miR-661. Our study explains why HOXD-AS2 was specifically up-regulated in gliomas, helps to understand the molecular characteristics of gliomas, and provids insights for the search for specific markers in gliomas.

Diffusion and perfusion imaging biomarkers of H3 K27M mutation status in diffuse midline gliomas

PURPOSE

H3K27M-mutant diffuse midline gliomas (M-DMGs) exhibit a clinically aggressive course. We studied diffusion-weighted imaging (DWI) and perfusion (PWI) MRI features of DMG with the hypothesis that DWI-PWI metrics can serve as biomarkers for the prediction of the H3K27M mutation status in DMGs.

METHODS

A retrospective review of the institutional database (imaging and histopathology) of patients with DMG (July 2016 to July 2020) was performed. Tumoral apparent diffusion coefficient (ADC) and peritumoral ADC (PT ADC) values and their normalized values (nADC and nPT ADC) were computed. Perfusion data were analyzed with manual arterial input function (AIF) and leakage correction (LC) Boxerman-Weiskoff models. Normalized maximum relative CBV (rCBV) was evaluated. Intergroup analysis of the imaging variables was done between M-DMGs and wild-type (WT-DMGs) groups.

RESULTS

Ninety-four cases (M-DMGs-n = 48 (51%) and WT-DMGs-n = 46(49%)) were included. Significantly lower PT ADC (mutant-1.1 ± 0.33, WT-1.23 ± 0.34; P = 0.033) and nPT ADC (mutant-1.64 ± 0.48, WT-1.83 ± 0.54; P = 0.040) were noted in the M-DMGs. The rCBV (mutant-25.17 ± 27.76, WT-13.73 ± 14.83; P = 0.018) and nrCBV (mutant-3.44 ± 2.16, WT-2.39 ± 1.25; P = 0.049) were significantly higher in the M-DMGs group. Among thalamic DMGs, the min ADC, PT ADC, and nADC and nPT ADC were lower in M-DMGs while nrCBV (corrected and uncorrected) was significantly higher. Receiver operator characteristic curve analysis demonstrated that PT ADC (cut-off-1.245), nPT ADC (cut-off-1.853), and nrCBV (cut-off-1.83) were significant independent predictors of H3K27M mutational status in DMGs.

CONCLUSION

DWI and PWI features hold value in preoperative prediction of H3K27M-mutation status in DMGs.

Deploying Kinase Inhibitors to Study Pediatric Gliomas

Pediatric midline gliomas are a uniformly fatal disease for which there is no cure. The location of these tumors makes surgical resection impossible, and so novel therapies are urgently needed to improve outcomes. The biology of these tumors is increasingly understood, with the histone H3K27M mutation playing a critical role in the pathogenesis of these tumors. Efforts to inhibit the growth of these tumors have also focused on inhibiting the Aurora kinase and Janus-associated kinase (JAK)/signal transducer and activator of transcription (STAT) pathway in order to disrupt tumor proliferation. A number of small molecule inhibitors of these kinases have shown promise in early studies. Screening and preclinical assessment of such inhibitors requires a functional assay to assess the degree of kinase inhibition. We detail here a luciferase-based reporter assay for STAT3 transcriptional activity that we have employed frequently in order to assess the efficacy of kinase inhibitors in pediatric gliomas. The assay we describe is specific to STAT3, but the overall methodology is generalizable to other downstream targets of the kinase of interest.

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.

Pharmaco-proteogenomic profiling of pediatric diffuse midline glioma to inform future treatment strategies

Diffuse midline glioma (DMG) is a deadly pediatric and adolescent central nervous system (CNS) tumor localized along the midline structures of the brain atop the spinal cord. With a median overall survival (OS) of just 9–11-months, DMG is characterized by global hypomethylation of histone H3 at lysine 27 (H3K27me3), driven by recurring somatic mutations in H3 genes including, HIST1H3B/C (H3.1K27M) or H3F3A (H3.3K27M), or through overexpression of EZHIP in patients harboring wildtype H3. The recent World Health Organization’s 5th Classification of CNS Tumors now designates DMG as, ‘H3 K27-altered’, suggesting that global H3K27me3 hypomethylation is a ubiquitous feature of DMG and drives devastating transcriptional programs for which there are no treatments. H3-alterations co-segregate with various other somatic driver mutations, highlighting the high-level of intertumoral heterogeneity of DMG. Furthermore, DMG is also characterized by very high-level intratumoral diversity with tumors harboring multiple subclones within each primary tumor. Each subclone contains their own combinations of driver and passenger lesions that continually evolve, making precision-based medicine challenging to successful execute. Whilst the intertumoral heterogeneity of DMG has been extensively investigated, this is yet to translate to an increase in patient survival. Conversely, our understanding of the non-genomic factors that drive the rapid growth and fatal nature of DMG, including endogenous and exogenous microenvironmental influences, neurological cues, and the posttranscriptional and posttranslational architecture of DMG remains enigmatic or at best, immature. However, these factors are likely to play a significant role in the complex biological sequelae that drives the disease. Here we summarize the heterogeneity of DMG and emphasize how analysis of the posttranslational architecture may improve treatment paradigms. We describe factors that contribute to treatment response and disease progression, as well as highlight the potential for pharmaco-proteogenomics (i.e., the integration of genomics, proteomics and pharmacology) in the management of this uniformly fatal cancer.

Emerging Epigenetic Therapies for Brain Tumors

Malignant brain tumors are among the most intractable cancers, including malignancies such as glioblastoma, diffuse midline glioma, medulloblastoma, and ependymoma. Unfortunately, treatment options for these brain tumors have been inadequate and complex, leading to poor prognoses and creating a need for new treatment modalities. Aberrant epigenetics define these types of tumors, with underlying changes in DNA methylation, histone modifications, chromatin structure and noncoding RNAs. Epigenetic-targeted therapies are an alternative that have the potential to reverse the epigenetic deregulation underpinning brain malignancies. Various drugs targeting epigenetic regulators have shown promise in preclinical and clinical testing. In this review, we highlight some of the recent emerging epigenetic targeted therapies for brain tumors being evaluated in the discovery phase and in clinical trials.

Reactive Oxygen Species in Acute Lymphoblastic Leukaemia: Reducing Radicals to Refine Responses

Acute lymphoblastic leukaemia (ALL) is the most common cancer diagnosed in children and adolescents. Approximately 70% of patients survive >5-years following diagnosis, however, for those that fail upfront therapies, survival is poor. Reactive oxygen species (ROS) are elevated in a range of cancers and are emerging as significant contributors to the leukaemogenesis of ALL. ROS modulate the function of signalling proteins through oxidation of cysteine residues, as well as promote genomic instability by damaging DNA, to promote chemotherapy resistance. Current therapeutic approaches exploit the pro-oxidant intracellular environment of malignant B and T lymphoblasts to cause irreversible DNA damage and cell death, however these strategies impact normal haematopoiesis and lead to long lasting side-effects. Therapies suppressing ROS production, especially those targeting ROS producing enzymes such as the NADPH oxidases (NOXs), are emerging alternatives to treat cancers and may be exploited to improve the ALL treatment. Here, we discuss the roles that ROS play in normal haematopoiesis and in ALL. We explore the molecular mechanisms underpinning overproduction of ROS in ALL, and their roles in disease progression and drug resistance. Finally, we examine strategies to target ROS production, with a specific focus on the NOX enzymes, to improve the treatment of ALL.

Prediction of H3K27M mutation status of diffuse midline gliomas using MRI features

BACKGROUND AND PURPOSE

Presurgical prediction of H3K27M mutation in diffuse midline gliomas (DMGs) on MRI is desirable. The purpose of this study is to elaborate conventional MRI (cMRI) features of H3K27M-mutant DMGs and identify features that could discriminate them from wild-type (WT) DMGs.

METHODS

CMRI features of 123 patients with DMG were evaluated conforming to the institutional research protocols. Multimodality MRI was performed on 1.5 or 3.0 Tesla MR Scanners with imaging protocol, including T1-weighted (w), T2w, fluid-attenuated inversion recovery, diffusion-weighted, susceptibility-weighted, and postcontrast T1w sequences. Pertinent cMRI features were annotated along the lines of Visually AcceSAble Rembrandt Images features, and Intra Tumoral Susceptibility Signal score (ITSS) was evaluated. R software was used for statistical analysis.

RESULTS

Sixty-one DMGs were H3K27M-mutant (mutant DMGs). The patients in the H3K27M-mutant DMG group were younger compared to the WT-DMG group (mean age 24.13 ± 13.13 years vs. 35.79±18.74 years) (p = 0.016). The two groups differed on five cMRI features--(1) enhancement quality (p = 0.032), (2) thickness of enhancing margin (p = 0.05), (3) proportion of edema (p = 0.002), (4) definition of noncontrast-enhancing tumor (NCET) margin (p = 0.001), and (5) cortical invasion (p = 0.037). The mutant DMGs showed greater enhancement and greater thickness of enhancing margin, while the WT DMGs exhibited significantly larger edema proportion with poorly defined NCET margins and cortical invasion. ITSS was not significantly different among the groups.

CONCLUSION

CMRI features like enhancement quality, the thickness of the enhancing margin, proportion of edema, definition of NCET margin, and cortical invasion can discriminate between the H3K27M-mutant and WT DMGs.

Dual targeting of the epigenome via FACT complex and histone deacetylase is a potent treatment strategy for DIPG

Diffuse intrinsic pontine glioma (DIPG) is an aggressive and incurable childhood brain tumor for which new treatments are needed. CBL0137 is an anti-cancer compound developed from quinacrine that targets facilitates chromatin transcription (FACT), a chromatin remodeling complex involved in transcription, replication, and DNA repair. We show that CBL0137 displays profound cytotoxic activity against a panel of patient-derived DIPG cultures by restoring tumor suppressor TP53 and Rb activity. Moreover, in an orthotopic model of DIPG, treatment with CBL0137 significantly extends animal survival. The FACT subunit SPT16 is found to directly interact with H3.3K27M, and treatment with CBL0137 restores both histone H3 acetylation and trimethylation. Combined treatment of CBL0137 with the histone deacetylase inhibitor panobinostat leads to inhibition of the Rb/E2F1 pathway and induction of apoptosis. The combination of CBL0137 and panobinostat significantly prolongs the survival of mice bearing DIPG orthografts, suggesting a potential treatment strategy for DIPG.

Clinical and Genetic Features of Brainstem Glioma in Adults: A Report of 50 Cases in a Single Center

Background and Purpose

Brainstem gliomas (BSGs) in adults are rare brain tumors with dismal outcomes. The aim of this study was to determine the clinical and genetic features in a series of BSGs and their association with the prognosis.

Methods

Fifty patients who underwent a stereotactic biopsy between January 2016 and April 2018 at a single institution were collected. Data on clinicopathological characteristics were analyzed and factors associated with patient survival were identified using a Cox regression model.

Results

The median age at diagnosis was 55.5 years, and 62% of the patients were male. Glioblastoma (44%) accounted for the largest proportion of BSGs, and oligodendroglioma (2 of 50) was rarely encountered. The IDH mutation (6 of 44) occurred infrequently in astrocytomas, and IDH-mutant tumors harbored both ATRX loss and MGMT promoter methylation at a relatively low level. Wild-type IDH astrocytomas were identified as having high rates of 1p/19q codeletion (5 of 38) and loss of heterozygosity 1p (8 of 38) or 19q (8 of 38) only. In diffuse midline glioma H3K27M mutant, MGMT promoter methylation occurred in three of four cases. Patients were offered radiotherapy and/or concurrent/adjuvant temozolomide chemotherapy, and their median survival time was 13 months. Multivariate analysis revealed that a low tumor grade, absence of tumor enhancement, duration of symptoms ≥3 months, Karnofsky performance status ≥70, and ATRX loss conferred a survival advantage.

Conclusions

Adult BSGs showed different molecular genetic characteristics, but also resembled supratentorial gliomas in their clinical features associated with oncological outcomes.

Preclinical and clinical evaluation of German-sourced ONC201 for the treatment of H3K27M-mutant diffuse intrinsic pontine glioma

Background

Diffuse intrinsic pontine glioma (DIPG) is a fatal childhood brainstem tumor for which radiation is the only treatment. Case studies report a clinical response to ONC201 for patients with H3K27M-mutant gliomas. Oncoceutics (ONC201) is only available in the United States and Japan; however, in Germany, DIPG patients can be prescribed and dispensed a locally produced compound—ONC201 German-sourced ONC201 (GsONC201). Pediatric oncologists face the dilemma of supporting the administration of GsONC201 as conjecture surrounds its authenticity. Therefore, we compared GsONC201 to original ONC201 manufactured by Oncoceutics Inc.

Methods

Authenticity of GsONC201 was determined by high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy. Biological activity was shown via assessment of on-target effects, in vitro growth, proliferation, and apoptosis analysis. Patient-derived xenograft mouse models were used to assess plasma and brain tissue pharmacokinetics, pharmacodynamics, and overall survival (OS). The clinical experience of 28 H3K27M+ mutant DIPG patients who received GsONC201 (2017–2020) was analyzed.

Results

GsONC201 harbored the authentic structure, however, was formulated as a free base rather than the dihydrochloride salt used in clinical trials. GsONC201 in vitro and in vivo efficacy and drug bioavailability studies showed no difference compared to Oncoceutics ONC201. Patients treated with GsONC201 (n = 28) showed a median OS of 18 months (P = .0007). GsONC201 patients who underwent reirradiation showed a median OS of 22 months compared to 12 months for GsONC201 patients who did not (P = .012).

Conclusions

This study confirms the biological activity of GsONC201 and documents the OS of patients who received the drug; however, GsONC201 was never used as a monotherapy.

Radio-Resistance and DNA Repair in Pediatric Diffuse Midline Gliomas

Malignant gliomas (MG) are among the most prevalent and lethal primary intrinsic brain tumors. Although radiotherapy (RT) is the most effective nonsurgical therapy, recurrence is universal. Dysregulated DNA damage response pathway (DDR) signaling, rampant genomic instability, and radio-resistance are among the hallmarks of MGs, with current therapies only offering palliation. A subgroup of pediatric high-grade gliomas (pHGG) is characterized by H3K27M mutation, which drives global loss of di- and trimethylation of histone H3K27. Here, we review the most recent literature and discuss the key studies dissecting the molecular biology of H3K27M-mutated gliomas in children. We speculate that the aberrant activation and/or deactivation of some of the key components of DDR may be synthetically lethal to H3K27M mutation and thus can open novel avenues for effective therapeutic interventions for patients suffering from this deadly disease.

Ancient Evolutionary Origin of Intrinsically Disordered Cancer Risk Regions

Cancer is a heterogeneous genetic disease that alters the proper functioning of proteins involved in key regulatory processes such as cell cycle, DNA repair, survival, or apoptosis. Mutations often accumulate in hot-spots regions, highlighting critical functional modules within these proteins that need to be altered, amplified, or abolished for tumor formation. Recent evidence suggests that these mutational hotspots can correspond not only to globular domains, but also to intrinsically disordered regions (IDRs), which play a significant role in a subset of cancer types. IDRs have distinct functional properties that originate from their inherent flexibility. Generally, they correspond to more recent evolutionary inventions and show larger sequence variations across species. In this work, we analyzed the evolutionary origin of disordered regions that are specifically targeted in cancer. Surprisingly, the majority of these disordered cancer risk regions showed remarkable conservation with ancient evolutionary origin, stemming from the earliest multicellular animals or even beyond. Nevertheless, we encountered several examples where the mutated region emerged at a later stage compared with the origin of the gene family. We also showed the cancer risk regions become quickly fixated after their emergence, but evolution continues to tinker with their genes with novel regulatory elements introduced even at the level of humans. Our concise analysis provides a much clearer picture of the emergence of key regulatory elements in proteins and highlights the importance of taking into account the modular organisation of proteins for the analyses of evolutionary origin.

Can Hemp Help? Low-THC Cannabis and Non-THC Cannabinoids for the Treatment of Cancer

Cannabis has been used to relieve the symptoms of disease for thousands of years. However, social and political biases have limited effective interrogation of the potential benefits of cannabis and polarised public opinion. Further, the medicinal and clinical utility of cannabis is limited by the psychotropic side effects of ∆⁹-tetrahydrocannabinol (∆⁹-THC). Evidence is emerging for the therapeutic benefits of cannabis in the treatment of neurological and neurodegenerative diseases, with potential efficacy as an analgesic and antiemetic for the management of cancer-related pain and treatment-related nausea and vomiting, respectively. An increasing number of preclinical studies have established that ∆⁹-THC can inhibit the growth and proliferation of cancerous cells through the modulation of cannabinoid receptors (CB1R and CB2R), but clinical confirmation remains lacking. In parallel, the anti-cancer properties of non-THC cannabinoids, such as cannabidiol (CBD), are linked to the modulation of non-CB1R/CB2R G-protein-coupled receptors, neurotransmitter receptors, and ligand-regulated transcription factors, which together modulate oncogenic signalling and redox homeostasis. Additional evidence has also demonstrated the anti-inflammatory properties of cannabinoids, and this may prove relevant in the context of peritumoural oedema and the tumour immune microenvironment. This review aims to document the emerging mechanisms of anti-cancer actions of non-THC cannabinoids.

Hypoxia Inducible Factors' Signaling in Pediatric High-Grade Gliomas: Role, Modelization and Innovative Targeted Approaches

The brain tumor microenvironment has recently become a major challenge in all pediatric cancers, but especially in brain tumors like high-grade gliomas. Hypoxia is one of the extrinsic tumor features that interacts with tumor cells, but also with the blood-brain barrier and all normal brain cells. It is the result of a dramatic proliferation and expansion of tumor cells that deprive the tissues of oxygen inflow. However, cancer cells, especially tumor stem cells, can endure extreme hypoxic conditions by rescheduling various genes' expression involved in cell proliferation, metabolism and angiogenesis and thus, promote tumor expansion, therapeutic resistance and metabolic adaptation. This cellular adaptation implies Hypoxia-Inducible Factors (HIF), namely HIF-1α and HIF-2α. In pediatric high-grade gliomas (pHGGs), several questions remained open on hypoxia-specific role in normal brain during gliomagenesis and pHGG progression, as well how to model it in preclinical studies and how it might be counteracted with targeted therapies. Therefore, this review aims to gather various data about this key extrinsic tumor factor in pHGGs.

Identification of new therapeutic targets and natural compounds against diffuse intrinsic pontine glioma (DIPG)

Diffuse Intrinsic Pontine Glioma (DIPG) is a highly aggressive pediatric brainstem tumor which accounts for about 10-20% of childhood brain tumors. The survival rate for DIPG remains very poor, with a median survival of less than 1 year. The dismal prognosis associated with DIPG has been exacerbated by the failure of a large number of clinical trials to meaningfully improve survival compared with radiotherapy, the current standard of care for DIPG. In the current study, we screened a natural product library and for the first time identified 6 natural compounds displaying inhibitory effects on DIPG proliferation and anchorage-independent growth through inducing tumor cell apoptosis and cell cycle arrest. Subsequent RNA-Sequencing and functional validation revealed the molecular mechanisms of these compounds with anti-DIPG activities, and identified new cellular factors such as Fibronectin 1 (FN1) and Eukaryotic translation initiation factor 3 subunit C-like (EIF3CL), required for DIPG survival as potential therapeutic targets. Our study provides promising directions to fight against this deadly pediatric cancer.