Midline Glioma Research Articles

Glucosylceramide Synthase Inhibitors Induce Ceramide Accumulation and Sensitize H3K27 Mutant Diffuse Midline Glioma to Irradiation.

H3K27M mutant (mut) diffuse midline glioma (DMG) is a lethal cancer with no effective cure. The glycosphingolipids (GSL) metabolism is altered in these tumors and could be exploited to develop new therapies. We tested the effect of the glucosylceramide synthase inhibitors (GSI) miglustat and eliglustat on cell proliferation, alone or in combination with temozolomide or ionizing radiation. Miglustat was included in the therapy protocol of two pediatric patients. The effect of H3.3K27 trimethylation on GSL composition was analyzed in ependymoma. GSI reduced the expression of the ganglioside GD2 in a concentration and time-dependent manner and increased the expression of ceramide, ceramide 1-phosphate, sphingosine, and sphingomyelin but not of sphingosine 1-phosphate. Miglustat significantly increased the efficacy of irradiation. Treatment with miglustat according to dose recommendations for patients with Niemann-Pick disease was well tolerated with manageable toxicities. One patient showed a mixed response. In ependymoma, a high concentration of GD2 was found only in the presence of the loss of H3.3K27 trimethylation. In conclusion, treatment with miglustat and, in general, targeting GSL metabolism may offer a new therapeutic opportunity and can be administered in close proximity to radiation therapy. Alterations in H3K27 could be useful to identify patients with a deregulated GSL metabolism.

Biopsies of Caudal Brainstem Tumors in Pediatric Patients—A Single-Center Retrospective Case Series

The indication for performing biopsies in patients with diffuse lesions in the brain stem is controversial. Possible risks associated with the technical challenging interventions need to be balanced against clarifying the diagnosis and possible therapeutic options. We reviewed the feasibility, risk profile and diagnostic yield of different biopsy techniques in a pediatric cohort. We retrospectively included all patients under 18 years of age that received a biopsy of the caudal brainstem region (pons, medulla oblongata) at our pediatric neurosurgical center from 2009-2022. We identified 27 children. Biopsies were performed using frameless stereotactic (Varioguide) (n=12), robotic assisted (Autoguide) (n=4), endoscopic (n=3) and open biopsy (n=8) technique. Intervention related mortality was not observed. Three patients experienced transient post-surgical neurological deficit. No patient showed intervention related permanent morbidity. Biopsy yielded histopathological diagnosis in all cases. Molecular analysis was feasible in 97% of cases. Most common diagnosis was H3K27M mutated diffuse midline glioma (60%). Low-grade gliomas were identified in 14%. Overall survival was 62.5% after 24 months of follow up. Biopsies of the caudal brainstem in children were feasible and safe in the presented setup. The amount of acquired tumor material allowing integrated diagnosis and was obtained at reasonable risk. The selection of the surgical technique depends on tumor location and growth pattern. We recommend brainstem tumor biopsies in children being performed at specialized centers to better understand the biology and enable possible novel therapeutic options.

An exploratory clinical trial on intra-lumbar injection of B7H3-specific allogeneic universal CAR-T cells in patients with recurrent high-grade gliomas.

2043 Background: No standard-of-care treatment was established for recurrent high-grade gliomas (rHGGs) yet. Intrathecal infusion of autologous chimeric antigen receptor-T (CAR-T) cells has displayed potent anti-tumor activity in one patient (Brown et al. N Engl J Med 2016). We evaluated the safety, efficacy, pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of B7H3-specific allogeneic universal CAR-T (B7H3 UCAR-T) cells in patients with rHGGs. Methods: Eligible patients who had received standard treatment for newly-diagnosed high-grade gliomas but failed were treated with 2.5×107 B7H3 UCAR-T cells via intra-lumbar injection every month. Eligibility criteria included histologic and/or cytologic rHGGs, B7H3-positive antigen expression rate of >50% in tumor tissue and Karnofsky performance status (KPS) ≥ 40. The primary endpoint was treatment-related adverse events (TAEs); secondary endpoints include overall survival (OS) and objective response rate (ORR); exploratory endpoints were PK and PD characteristics of B7H3 UCAR-T cells. Results: In the 7 patients enrolled, 4 (57.1%) were female, 5 (71.4%) glioblastoma (WHO Grade IV) and 2 (28.6%) diffuse midline glioma (WHO Grade IV), and the mean age was 40.4 years. The most common reported TAEs were increased cerebrospinal fluid (CSF) IL-6 (7/7, 100%), headache (7/7, 100%), increased blood IL-6 (6/7, 86%) and fever (6/7, 86%). No adverse events of grade 3 or greater related to B7H3 UCAR-T cells were reported. All the adverse events recovered or relieved after treatment. No typical or severe systemic cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS) or graft versus host disease (GvHD) were observed during the study period. Based on Immunotherapy Response Assessment in Neuro-Oncology (iRANO), 3 of 7 patients had response to therapy (42.9%; 95% CI: 15.8 to 75.0) and 7 of 7 patients were stable disease (100%; 95% CI: 64.6 to 100). As of cutoff date (January 30, 2023), two patients died. The median OS was not reached (95% CI: 12.9 to could not be estimated). The median follow-up for OS was 15.6 months (95% CI: 14.7 to 16.1). OS rate at 12 months was 85.7% (95% CI: 48.7 to 97.4). The CAR DNA copy numbers increased 1 day after each administration and persist at least 1 month in cerebrospinal fluid. IL-6 concentrations in CSF and peripheral blood increased after each administration while the change and concentration values in peripheral blood were much lower than those in CSF. Conclusions: In patients with rHGGs, B7H3 UCAR-T cells was not associated with any toxic effects of grade 3 or higher. B7H3 UCAR-T cells resulted in a significantly longer overall survival and a higher objective response rate than history data. B7H3 UCAR-T cells persist well in patients. Clinical trial information: ChiCTR2100047968 .

A phase 2 study of sirolimus in combination with metronomic chemotherapy (CHOAnome) in children with recurrent and/or refractory solid and CNS tumors.

10024 Background: Multiple low-dose, anti-angiogenic (metronomic) chemotherapy regimens have demonstrated activity in pediatric solid and central nervous system (CNS) tumors. The mTOR pathway is activated in many human cancers and provides an attractive therapeutic target. We previously conducted a phase 1 trial establishing the dose (2 mg/m2), safety and tolerability of sirolimus in combination with metronomic chemotherapy. In the current study, we conducted a prospective, multi-institutional phase 2 trial to determine the objective response rate (ORR) in pediatric patients with recurrent and/or refractory (R/R) solid and CNS tumors treated with this regimen (NCT02574728); herein we report the results of the CNS tumor stratum. Methods: Patients aged 12 months to 30 years with R/R CNS tumors of all world health organization (WHO) grades were eligible. After completion of the trial’s first stage, patients with diffuse intrinsic pontine glioma (DIPG) were excluded due to lack of efficacy. Patients were required to have measurable disease and no known curative therapeutic options. Treatment consisted of continuous sirolimus (2 mg/m2/dose PO daily), celecoxib (100 mg PO BID), and oral etoposide (50 mg/m2/day; max dose: 100 mg) alternating every 21 days with oral cyclophosphamide (2.5 mg/kg/day; max dose: 100 mg) in 42-day cycles. Sirolimus was dose-adjusted to maintain a serum trough concentration of 10-15 ng/ml. Response was determined using a modified Response Assessment in Neuro-Oncology (RANO) criteria. Enrollment proceeded using a Fleming’s two-stage design based on best overall response (BOR), which required two objective disease status determinations. Results: Twenty-two CNS tumor patients were enrolled; 20/22 were evaluable for response. Median age was 11.2 years (range: 5.9 – 18.1); 6 (30%) were female. Diagnoses included DIPG (N = 5), medulloblastoma (N = 3), high-grade (HG) glioma (N = 5), HG/malignant neuroepithelial tumor (N = 3) and one each of diffuse midline glioma, atypical teratoid/rhabdoid tumor (ATRT), choroid plexus carcinoma, and pineoblastoma. Median number of cycles was 2 (range: 1-6). Best response after any cycle was partial response (PR) in 4 [medulloblastoma (N = 3); pineoblastoma (N = 1)], stable disease (SD) in 4, and progressive disease (PD) in 12 for an ORR of 20%; all patients with DIPG had PD at or before their first disease evaluation. BOR was PR in 3 (15%), SD in 2 (10%), PD in 14 (70%), and unknown in 1 (5%). Four patients had SD or response for ≥ 6 months [medulloblastoma (n = 1), pineoblastoma (N = 1), and HG glioma (N = 2)]. Conclusions: The combination of sirolimus with metronomic chemotherapy showed activity in pediatric patients with some R/R CNS tumors, producing objective responses in medulloblastoma and pineoblastoma. Patients with DIPG did not benefit from this regimen and should be offered alternative treatments. Clinical trial information: NCT02574728 .

Investigation of leptomeningeal disease in high grade glioma and characterization of molecular alterations.

2070 Background: Leptomeningeal disease (LMD) is a challenging complication of high grade glioma (HGG) and questions remain regarding risk factors, molecular associations, and optimal treatment. Here we report updated results on a larger cohort from our previously reported multicenter study (Shoaf 2022, Neuro-Oncology). Methods: Patients with molecularly-profiled HGG (Caris Life Sciences; Phoenix, AZ) with LMD at 3 institutions were included. NextGen Sequencing of DNA (592 gene or whole exome) and RNA (whole transcriptome) were tested. Medical records were reviewed for clinicopathologic characteristics and outcome. Kaplan-Meier estimates of survival were performed using Cox’s proportional hazard model. Mann-Whitney U or Chi-square tests were applied for molecular comparison as appropriate and adjusted for multiple comparisons. Results: Seventy-two patients (female: 20, male: 52; median age: 54.5y) were identified, comprising 65 grade 4 tumors (glioblastoma [GBM]: 62; gliosarcoma: 2; H3K27M diffuse midline glioma: 1), 5 grade 3 tumors (astrocytoma: 4; pleomorphic xanthoastrocytoma: 1), and 1 astrocytoma NOS. LMD diagnosed at glioma diagnosis (n=23) vs. recurrence (n=44) was associated with longer post-LMD survival [pLMD-OS: 16.9m vs. 5.5m, p<0.0001] but similar overall survival [mOS: 16.9m vs. 20.9m; p=0.36]. Pathology-diagnosed LMD (n=15) vs. MRI-diagnosed LMD (n=54) was associated with longer post-LMD survival [pLMD-OS: 15.2m vs. 6.2m, p=0.0002] but similar overall survival [mOS: 16.9m vs. 20.9m; p=0.72]. Post-LMD survival [pLMD-OS: 8.7m vs. 6.8m, p=0.33] and overall survival [mOS: 21.1m vs. 20.9m, p=0.20] were similar for supratentorial (n=45) vs. infratentorial/spinal (n=10) locations, and post-LMD survival did not significantly differ for symptomatic (n=40) vs. asymptomatic (n=22) patients [pLMD-OS: 6.6m vs. 10.5m, p=0.13). pTERT mutation (73%), MGMT methylation (38%), EGFR amplification (31%), and PTEN mutation (28%) were the most prevalent molecular alterations in this group. Comparison of grade 4 LMD tumors with an independent GBM cohort (n=5431) suggested a male predominance (73.4% vs. 58.5%, p=0.016) and a trend towards more frequent mutations in RB1 (25% vs. 9.2%, p=0.002) and MDM4 (12.7% vs. 4.3%, p=0.01) and amplification of WIF1 (6.1% vs. 0.3%, p=0.006), CHIC2 (17.0% vs. 5.2%, p=0.002), and LGR5 (5.9% vs. 0.4%, p=0.012). The expression of immune checkpoint-related genes was similar, although a trend towards immunologically “colder” tumors in the LMD cohort was observed. However, these effects were not significant after correcting for multiple comparisons. Conclusions: LMD is more common in male patients and may be associated with various genomic alterations and tumor microenvironment differences. Overall survival does not differ from patients without LMD, but these differences may provide clues to the pathogenesis and treatment resistance of GBM.

Analysis of tumor progression among patients with glioma after COVID-19 infection.

2041 Background: As of January 2023, there have been 6.7 million worldwide deaths attributed to SARS-CoV-2 COVID-19, which has impacted outcomes and medical care for all patients. Relatively little is known about the direct effects mediated by the virus on CNS tumor biology, despite the fact that viral neurotropism is well described, various coronavirus receptors have been observed in glioblastoma (GBM) tissues, and differential monocytic infiltration has been proposed to dysregulate the immune microenvironment. We detected a trend of rapid progression following COVID-19 infection among several patients with primary brain tumor patients and sought to systematically evaluate the pace of progression among infected patients in our institution. Methods: A single-institutional database of COVID-19 patients and an electronic medical record (EMR) search tool were used to identify a total cohort of 67 patients with glioma for retrospective analysis. This included 38 GBMs, 18 IDH-mutant gliomas, 5 ependymomas, 2 pilocytic astrocytomas, 1 diffuse midline glioma, 1 diffuse hemispheric glioma, and 1 ganglioglioma patients, each of whom had a documented COVID-19 infection between June 2020-December 2022. Hyperprogression was defined as tumor increase ≥40% compared to previous scan using RECIST size criteria. Results: Thirty-nine (58%) patients experienced tumor progression following COVID-19 infection at a median of 34 days (range=1-734 days) after testing positive for COVID-19. Twenty-two (56%) had received COVID-19 vaccine before their infection and 5 (13%) had asymptomatic infections. Twenty-two patients had measurably increased tumor area by a median of 63% (range=10-2,900%), 18 of which constituted hyperprogression;16 patients developed multifocal disease, 8 developed new nodular enhancement, 3 developed leptomeningeal disease (LMD), and 2 experienced increased infiltrative disease alone. Ten patients’ presentation with new glioma was preceded by COVID-19 infection by a median of 31 days. GBM patients represented the majority of progression events, among whom 59% progressed within 60 days of documented infection (median 25 days). This subgroup of GBM with rapid progression within 60 days had a mOS from infection of 5.2 months; 89% had TERT promotor mutations and 42% had MGMT promoter methylation. Conclusions: Glioma patients appear to have disease progression at an accelerated pace in the first two months after COVID-19 infection. This suggests that glioma patients should continue observing strict precautions to prevent infection and should be clinically monitored vigilantly after infection, with consideration for short interval imaging during treatment. These preliminary data warrant further investigation exploring changes of immune cell infiltration in the tumor microenvironment and the possible correlation between tumor progression and COVID-19.

OpenPBTA: The Open Pediatric Brain Tumor Atlas

Pediatric brain and spinal cancers are collectively the leading disease-related cause of death in children; thus, we urgently need curative therapeutic strategies for these tumors. To accelerate such discoveries, the Children's Brain Tumor Network (CBTN) and Pacific Pediatric Neuro-Oncology Consortium (PNOC) created a systematic process for tumor biobanking, model generation, and sequencing with immediate access to harmonized data. We leverage these data to establish OpenPBTA, an open collaborative project with over 40 scalable analysis modules that genomically characterize 1,074 pediatric brain tumors. Transcriptomic classification reveals universal TP53 dysregulation in mismatch repair-deficient hypermutant high-grade gliomas and TP53 loss as a significant marker for poor overall survival in ependymomas and H3 K28-mutant diffuse midline gliomas. Already being actively applied to other pediatric cancers and PNOC molecular tumor board decision-making, OpenPBTA is an invaluable resource to the pediatric oncology community.

Promising results for antisense RNA therapy in mouse models of diffuse midline glioma.

Promising results for antisense RNA therapy in mouse models of diffuse midline glioma.

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

H3K27M 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 H3K27M DMGs; however, the radio-resistance is commonly observed. We summarized current understandings of the molecular responses of H3K27M DMGs to radiotherapy and provide crucial insights into current advances in radiosensitivity enhancement. 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. The advances in mechanisms of radio-resistance in H3K27M 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.

A novel CDK4/6 inhibitor combined with irradiation demonstrates potent anti-tumor efficacy in diffuse midline glioma

Diffuse midline glioma, H3 K27-altered (DMG) is a lethal pediatric brainstem tumor. Despite numerous efforts to improve survival benefits, its prognosis remains poor. This study aimed to design and synthesize a novel CDK4/6 inhibitor YF-PRJ8-1011, which exhibited more potent antitumor activity against a panel of patient-derived DMG tumor cells in vitro and in vivo compared with palbociclib. Patient-derived DMG cells were used to assess the antitumor efficacy of YF-PRJ8-1011 in vitro. The liquid chromatography tandem-mass spectrometry method was used to measure the activity of YF-PRJ8-1011 passing through the blood-brain barrier. DMG patient-derived xenograft models were established to detect the antitumor efficacy of YF-PRJ8-1011. The results showed that YF-PRJ8-1011 could inhibit the growth of DMG cells both in vitro and in vivo. YF-PRJ8-1011 could well penetrate the blood-brain barrier. It also significantly inhibited the growth of DMG tumors and prolonged the overall survival of mice compared with vehicle or palbociclib. Most notably, it exerted potent antitumor efficacy in DMG in vitro and in vivo compared with palbociclib. In addition, we also found that YF-PRJ8-1011 combined with radiotherapy also showed more significant inhibition of DMG xenograft tumor growth than radiotherapy alone. Collectively, YF-PRJ8-1011 is a novel, safe, and selective CDK4/6 inhibitor for DMG treatment.

Update on quality assurance in neuropathology: Summary of the round robin trials on TERT promoter mutation, H3-3A mutation, 1p/19q codeletion, and KIAA1549::BRAF fusion testing in Germany in 2020 and 2021.

We previously reported on the first neuropathological round robin trials operated together with Quality in Pathology (QuIP) GmbH in 2018 and 2019 in Germany, i.e., the trials on IDH mutational testing and MGMT promoter methylation analysis [1]. For 2020 and 2021, the spectrum of round robin trials has been expanded to cover the most commonly used assays in neuropathological institutions. In addition to IDH mutation and MGMT promoter methylation testing, there is a long tradition for 1p/19q codeletion testing relevant in the context of the diagnosis of oligodendroglioma. With the 5th edition of the World Health Organization (WHO) classification of the central nervous system tumors, additional molecular markers came into focus: TERT promoter mutation is often assessed as a molecular diagnostic criterion for IDH-wildtype glioblastoma. Moreover, several molecular diagnostic markers have been introduced for pediatric brain tumors. Here, trials on KIAA1549::BRAF fusions (common in pilocytic astrocytomas) and H3-3A mutations (in diffuse midline gliomas, H3-K27-altered and diffuse hemispheric gliomas, H3-G34-mutant) were most desired by the neuropathological community. In this update, we report on these novel round robin trials. In summary, success rates in all four trials ranged from 75 to 96%, arguing for an overall high quality level in the field of molecular neuropathological diagnostics.

CAR T-cells to treat brain tumors.

Tremendous success using CAR T therapy in hematological malignancies has garnered significant interest in developing such treatments for solid tumors, including brain tumors. This success, however, has yet to be mirrored in solid organ neoplasms. CAR T function has shown limited efficacy against brain tumors due to several factors including the immunosuppressive tumor microenvironment, blood-brain barrier, and tumor-antigen heterogeneity. Despite these considerations, CAR T-cell therapy has the potential to be implemented as a treatment modality for brain tumors. Here, we review adult and pediatric brain tumors, including glioblastoma, diffuse midline gliomas, and medulloblastomas that continue to portend a grim prognosis. We describe insights gained from different preclinical models using CAR T therapy against various brain tumors and results gathered from ongoing clinical trials. Furthermore, we outline the challenges limiting CAR T therapy success against brain tumors and summarize advancements made to overcome these obstacles.

Oncohistones and disrupted development in pediatric-type diffuse high-grade glioma.

Recurrent, clonal somatic mutations in histone H3 are molecular hallmarks that distinguish the genetic mechanisms underlying pediatric and adult high-grade glioma (HGG), define biological subgroups of diffuse glioma, and highlight connections between cancer, development, and epigenetics. These oncogenic mutations in histones, now termed "oncohistones", were discovered through genome-wide sequencing of pediatric diffuse high-grade glioma. Up to 80% of diffuse midline glioma (DMG), including diffuse intrinsic pontine glioma (DIPG) and diffuse glioma arising in other midline structures including thalamus or spinal cord, contain histone H3 lysine 27 to methionine (K27M) mutations or, rarely, other alterations that result in a depletion of H3K27me3 similar to that induced by H3 K27M. This subgroup of glioma is now defined as diffuse midline glioma, H3K27-altered. In contrast, histone H3 Gly34Arg/Val (G34R/V) mutations are found in approximately 30% of diffuse glioma arising in the cerebral hemispheres of older adolescents and young adults, now classified as diffuse hemispheric glioma, H3G34-mutant. Here, we review how oncohistones modulate the epigenome and discuss the mutational landscape and invasive properties of histone mutant HGGs of childhood. The distinct mechanisms through which oncohistones and other mutations rewrite the epigenetic landscape provide novel insights into development and tumorigenesis and may present unique vulnerabilities for pHGGs. Lessons learned from these rare incurable brain tumors of childhood may have broader implications for cancer, as additional high- and low-frequency oncohistone mutations have been identified in other tumor types.

Drug Repurposing in Pediatric Brain Tumors: Posterior Fossa Ependymoma and Diffuse Midline Glioma under the Looking Glass.

Tumors of the Central Nervous System (CNS) represent the leading cause of cancer-related deaths in children. Current treatment options are not curative for most malignant histologies, and intense preclinical and clinical research is needed to develop more effective therapeutic interventions against these tumors, most of which meet the FDA definition for orphan diseases. Increased attention is being paid to the repositioning of already-approved drugs for new anticancer indications as a fast-tracking strategy for identifying new and more effective therapies. Two pediatric CNS tumors, posterior fossa ependymoma (EPN-PF) type A and diffuse midline glioma (DMG) H3K27-altered, share loss of H3K27 trimethylation as a common epigenetic hallmark and display early onset and poor prognosis. These features suggest a potentially common druggable vulnerability. Successful treatment of these CNS tumors raises several challenges due to the location of tumors, chemoresistance, drug blood-brain barrier penetration, and the likelihood of adverse side effects. Recently, increasing evidence demonstrates intense interactions between tumor cell subpopulations and supportive tumor microenvironments (TMEs) including nerve, metabolic, and inflammatory TMEs. These findings suggest the use of drugs, and/or multi-drug combinations, that attack both tumor cells and the TME simultaneously. In this work, we present an overview of the existing evidence concerning the most preclinically validated noncancer drugs with antineoplastic activity. These drugs belong to four pharmacotherapeutic classes: antiparasitic, neuroactive, metabolic, and anti-inflammatory. Preclinical evidence and undergoing clinical trials in patients with brain tumors, with special emphasis on pediatric EPN-PF and DMG, are summarized and critically discussed.

Targeting SWI/SNF ATPases in H3.3K27M diffuse intrinsic pontine gliomas

Diffuse midline gliomas (DMGs) including diffuse intrinsic pontine gliomas (DIPGs) bearing lysine-to-methionine mutations in histone H3 at lysine 27 (H3K27M) are lethal childhood brain cancers. These tumors harbor a global reduction in the transcriptional repressive mark H3K27me3 accompanied by an increase in the transcriptional activation mark H3K27ac. We postulated that H3K27M mutations, in addition to altering H3K27 modifications, reprogram the master chromatin remodeling switch/sucrose nonfermentable (SWI/SNF) complex. The SWI/SNF complex can exist in two main forms termed BAF and PBAF that play central roles in neurodevelopment and cancer. Moreover, BAF antagonizes PRC2, the main enzyme catalyzing H3K27me3. We demonstrate that H3K27M gliomas show increased protein levels of the SWI/SNF complex ATPase subunits SMARCA4 and SMARCA2, and the PBAF component PBRM1. Additionally, knockdown of mutant H3K27M lowered SMARCA4 protein levels. The proteolysis targeting chimera (PROTAC) AU-15330 that simultaneously targets SMARCA4, SMARCA2, and PBRM1 for degradation exhibits cytotoxicity in H3.3K27M but not H3 wild-type cells. AU-15330 lowered chromatin accessibility measured by ATAC-Seq at nonpromoter regions and reduced global H3K27ac levels. Integrated analysis of gene expression, proteomics, and chromatin accessibility in AU-15330-treated cells demonstrated reduction in the levels of FOXO1, a key member of the forkhead family of transcription factors. Moreover, genetic or pharmacologic targeting of FOXO1 resulted in cell death in H3K27M cells. Overall, our results suggest that H3K27M up-regulates SMARCA4 levels and combined targeting of SWI/SNF ATPases in H3.3K27M can serve as a potent therapeutic strategy for these deadly childhood brain tumors.

Intratumoral catheter placement in pediatric patients with diffuse midline gliomas.

Diffuse midline brainstem gliomas have a poor prognosis and are generally not amenable to surgical resection. Occasionally, palliative surgical procedures can be performed to improve the quality of life of these patients. We describe three patients with solid-cystic brainstem gliomas in whom an Ommaya reservoir catheter was placed to reduce mass effect. To describe the characteristics, indications for, and operative technique of Ommaya reservoir catheter placement in patients with solid-cystic diffuse midline glioma. A review was conducted of the medical records of pediatric patients with solid-cystic diffuse midline glioma H3 K27-altered, treated with an Ommaya reservoir at Hospital J.P. Garrahan between 2014 and 2021 together with a search of the literature. Three cases of stereotaxic Ommaya placement in solid-cystic diffuse midline gliomas, H3 K27M-altered were identified. After the procedure, clinical improvement and reduction of the size of the tumor cyst size was achieved. No associated complications were seen. At the time of the study, one patient died, and the remaining two patients continued in follow-up at our hospital. We believe that the placement of an intratumoral Ommaya reservoir catheter may be considered a therapeutic option to improve symptoms and quality of life of selected patients with solid-cystic diffuse midline glioma.

Diffuse midline glioma, H3K27-altered, of the conus medullaris presenting as acute urinary retention: illustrative case.

Diffuse midline glioma (DMG), H3K27-altered, is a rare, highly malignant central nervous system neoplasm that arises in midline structures. They are more commonly encountered in children and are rarely encountered in adults, usually in the thalamus or spinal cord. The presence of the H3K27 mutation in the H3F3A gene automatically classifies a tumor as World Health Organization grade IV. These tumors carry a grim prognosis, with an overall median survival of less than 1 year. The authors report the case of a 38-year-old male presenting with acute-onset urinary retention who was found to have an expansile, well-circumscribed mass involving the conus medullaris at the level of T12-L1. A T12-L1 laminectomy and tumor debulking were performed. Pathology revealed glial cells with astrocytic morphology among Rosenthal fibers, microvascular proliferation, and cellular atypia. The H3K27 mutation was confirmed. DMG, H3K27-altered, is a rarely encountered entity that can present in numerous midline structures. If localized to the conus medullaris, it may present as acute-onset urinary retention in a previously asymptomatic patient. Further investigation is needed to characterize its molecular and clinical features in adults to improve the management of those presenting with these tumors.

A case of adult‐onset diffuse midline glioma diagnosed by histone H3K27M immunostaining after death, which required differentiation from brainstem encephalitis and myelitis

AbstractH3K27M‐mutant diffuse midline glioma is a malignant glioma that was newly added to the World Health Organization classification in 2016. In diffuse midline glioma, the H3K27M‐mutant sometimes develops sub‐acutely and requires a differential diagnosis from encephalomyelitis. Here, we report a case of adult‐onset diffuse midline glioma that was diagnosed by immunostaining for histone H3K27M after death. The present case required a differential diagnosis of autoimmune cervical myelitis and brainstem encephalitis.

Abstract CT060: ACTION: A randomized phase 3 study of dordaviprone (ONC201) in patients with newly diagnosed H3 K27M-mutant diffuse glioma

Abstract Background: H3 K27M-mutant diffuse midline glioma is a universally fatal malignancy primarily affecting children and young adults. While radiotherapy (RT) provides transient benefit, no effective systemic therapy is currently available and current standard of care is RT followed by monitoring. Dordaviprone (ONC201), a first-in-class imipridone, is an oral, blood-brain barrier penetrating, selective small molecule antagonist of dopamine receptor D2/3 (DRD2) and agonist of the mitochondrial protease ClpP. An integrated pooled analysis of five open-label trials previously demonstrated efficacy in dordaviprone-treated patients with recurrent disease. This phase 3 trial will be the first randomized, controlled study evaluating dordaviprone in patients with H3 K27M-mutant disease. Methods: ACTION (NCT05580562) is a randomized, double-blind, placebo-controlled, parallel-group, international Phase 3 study of dordaviprone in patients with newly diagnosed H3 K27M-mutant diffuse glioma. Patients who have completed standard frontline radiotherapy will be randomized 1:1:1 to receive placebo, once-weekly dordaviprone, or twice-weekly dordaviprone on two consecutive days. Primary efficacy endpoints are overall survival (OS) and progression-free survival (PFS) in all participants; PFS will be assessed by response assessment in neuro-oncology-high grade glioma by blind independent central review. Other objectives include assessments of safety, additional efficacy endpoints, clinical benefit, quality of life, pharmacokinetics, biomarkers, and healthcare resource utilization. Eligible patients will have histologically confirmed H3 K27M-mutant diffuse glioma, a Karnofsky/Lansky performance status ≥70, and completed first-line radiotherapy. Eligibility will not be restricted based on age; however, patients must be ≥10 kg at time of randomization. Patients with a primary spinal tumor, diffuse intrinsic pontine glioma, leptomeningeal disease, or cerebrospinal fluid dissemination are not eligible. ACTION is currently enrolling in the United States, with additional sites to be open internationally in 2023. Citation Format: Isabel Arrillaga-Romany, Andrew Lassman, Susan L. McGovern, Sabine Mueller, Louis B. Nabors, Martin van den Bent, Michael Vogelbaum, Joshua E. Allen, Allen S. Melemed, Rohinton S. Tarapore, Dewen Yang, Patrick Wen, Timothy Cloughsey. ACTION: A randomized phase 3 study of dordaviprone (ONC201) in patients with newly diagnosed H3 K27M-mutant diffuse glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT060.