Therapeutically targeting the unique disease landscape of pediatric high-grade gliomas

Pediatric high-grade gliomas (pHGG) are a rare yet devastating malignancy of the central nervous system's glial support cells, affecting children, adolescents, and young adults. Tumors of the central nervous system account for the leading cause of pediatric mortality of which high-grade gliomas present a significantly grim prognosis. While the past few decades have seen many pediatric cancers experiencing significant improvements in overall survival, the prospect of survival for patients diagnosed with pHGGs has conversely remained unchanged. This can be attributed in part to tumor heterogeneity and the existence of the blood-brain barrier. Advances in discovery research have substantiated the existence of unique subgroups of pHGGs displaying alternate responses to different therapeutics and varying degrees of overall survival. This highlights a necessity to approach discovery research and clinical management of the disease in an alternative subtype-dependent manner. This review covers traditional approaches to the therapeutic management of pHGGs, limitations of such methods and emerging alternatives. Novel mutations which predominate the pHGG landscape are highlighted and the therapeutic potential of targeting them in a subtype specific manner discussed. Collectively, this provides an insight into issues in need of transformative progress which arise during the management of pHGGs.

Midline Gliomas: A Retrospective Study from a Cancer Center in the Middle East

Midline gliomas are tumors that occur in midline structures and can be circumscribed or diffuse. Classical midline structures include the thalamus, brainstem, and spinal cord. Other midline structures include the corpus callosum, basal ganglia, ventricles, paraventricular structures, and cerebellum. Diffuse midline glioma (DMG) is a diffuse glioma that occurs in the classical midline structures, characterized by a specific genetic alteration, and associated with grim outcome. This study was conducted at King Hussein Cancer Center and reviewed the medical records of 104 patients with circumscribed and diffuse gliomas involving midline structures that underwent biopsy between 2005 and 2022. We included a final cohort of 104 patients characterized by a median age of 23 years and a male-to-female ratio of 1.59-to-1. Diffuse high-grade glioma (DHGG) was the most common pathological variant (41.4%), followed by DMG (28.9%). GFAP was positive in most cases (71.2%). Common positive mutations/alterations detected by surrogate immunostains included H3 K27me3 (28.9%), p53 (25.0%), and H3 K27M (20.2%). Age group, type of treatment, and immunohistochemistry were significantly associated with both the location of the tumor and tumor variant (all; p < 0.05). DMGs were predominantly found in the thalamus, whereas circumscribed gliomas were most commonly observed in the spinal cord. None of the diffuse gliomas outside the classical location, or circumscribed gliomas harbored the defining DMG mutations. The median overall survival (OS) for the entire cohort was 10.6 months. Only the tumor variant (i.e., circumscribed gliomas) and radiotherapy were independent prognosticators on multivariate analysis.

HER2 chimeric antigen receptor T cell immunotherapy is an effective treatment for diffuse intrinsic pontine glioma

Background

Diffuse intrinsic pontine glioma (DIPG) and other diffuse midline gliomas (DMG) of the thalamus and spinal cord are rare but devastating high-grade glial tumors of childhood with no curative treatment. Despite aggressive treatment attempts the prognosis has remained poor. Chimeric antigen receptor (CAR) T cell therapy has been identified as a promising new approach in the treatment of DMG tumors; however, additional targets are urgently required given known tumor heterogeneity and the prospect of antigen escape of this cancer.

Methods

Using cell surface mass spectrometry, we detected high HER2 cell surface protein across a panel of patient-derived DIPG cells, thereby identifying an existing CAR T cell therapy for use in DIPG. Primary human T cells were transduced to express a second-generation HER2 CAR and interrogated for efficacy against patient-derived DIPG cells.

Results

HER2 CAR T cells demonstrated potent and antigen-specific cytotoxicity and cytokine secretion when co-cultured with patient-derived DIPG cells. Furthermore, HER2 CAR T cells provided a significant regression in intracranial DIPG xenograft tumors.

Conclusions

HER2 CAR T cells are already in clinic development and are well tolerated in pediatric patients. Here we provide strong preclinical evidence for the inclusion of DIPG patients in future pediatric CNS tumor HER2 CAR T cell clinical trials.

Epigenetic programming of pediatric high-grade glioma: Pushing beyond proof of concept to clinical benefit

Pediatric high-grade gliomas (pHGG) are a molecularly diverse group of malignancies, each incredibly aggressive and in dire need of treatment advancements. Genomic analysis has revolutionized our understanding of these tumors, identifying biologically relevant subgroups with differing canonical mutational profiles that vary based on tumor location and age. In particular, the discovery of recurrent histone H3 mutations (H3K27M in diffuse midline glioma, H3G34R/V in hemispheric pediatric high-grade gliomas) as unique "oncohistone" drivers revealed epigenetic dysregulation as a hallmark of pediatric high-grade gliomas oncogenesis. While reversing this signature through epigenetic programming has proven effective in several pre-clinical survival models, early results from pediatric high-grade gliomas clinical trials suggest that epigenetic modifier monotherapy will likely not provide long-term disease control. In this review we summarize the genetic, epigenetic, and cellular heterogeneity of pediatric high-grade gliomas, and highlight potential paths forward for epigenetic programming in this devastating disease.

Imipridones affect tumor bioenergetics and promote cell lineage differentiation in diffuse midline gliomas

BACKGROUND

Pediatric diffuse midline gliomas (DMGs) are incurable childhood cancers. The imipridone ONC201 has shown early clinical efficacy in a subset of DMGs. However, the anticancer mechanisms of ONC201 and its derivative ONC206 have not been fully described in DMGs.

METHODS

DMG models including primary human in vitro (n = 18) and in vivo (murine and zebrafish) models, and patient (n = 20) frozen and FFPE specimens were used. Drug-target engagement was evaluated using in silico ChemPLP and in vitro thermal shift assay. Drug toxicity and neurotoxicity were assessed in zebrafish models. Seahorse XF Cell Mito Stress Test, MitoSOX and TMRM assays, and electron microscopy imaging were used to assess metabolic signatures. Cell lineage differentiation and drug-altered pathways were defined using bulk and single-cell RNA-seq.

RESULTS

ONC201 and ONC206 reduce viability of DMG cells in nM concentrations and extend survival of DMG PDX models (ONC201: 117 days, P = .01; ONC206: 113 days, P = .001). ONC206 is 10X more potent than ONC201 in vitro and combination treatment was the most efficacious at prolonging survival in vivo (125 days, P = .02). Thermal shift assay confirmed that both drugs bind to ClpP, with ONC206 exhibiting a higher binding affinity as assessed by in silico ChemPLP. ClpP activation by both drugs results in impaired tumor cell metabolism, mitochondrial damage, ROS production, activation of integrative stress response (ISR), and apoptosis in vitro and in vivo. Strikingly, imipridone treatment triggered a lineage shift from a proliferative, oligodendrocyte precursor-like state to a mature, astrocyte-like state.

CONCLUSION

Targeting mitochondrial metabolism and ISR activation effectively impairs DMG tumorigenicity. These results supported the initiation of two pediatric clinical trials (NCT05009992, NCT04732065).

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.

Synthetic extracellular matrices and astrocytes provide a supportive microenvironment for the cultivation and investigation of primary pediatric gliomas

Background

Pediatric gliomas comprise a diverse set of brain tumor entities that have substantial long-term ramifications for patient survival and quality of life. However, the study of these tumors is currently limited due to a lack of authentic models. Additionally, many aspects of pediatric brain tumor biology, such as tumor cell invasiveness, have been difficult to study with currently available tools. To address these issues, we developed a synthetic extracellular matrix (sECM)-based culture system to grow and study primary pediatric brain tumor cells.

Methods

We developed a brain-like sECM material as a supportive scaffold for the culture of primary, patient-derived pediatric glioma cells and established patient-derived cell lines. Primary juvenile brainstem-derived murine astrocytes were used as a feeder layer to support the growth of primary human tumor cells.

Results

We found that our culture system facilitated the proliferation of various primary pediatric brain tumors, including low-grade gliomas, and enabled ex vivo testing of investigational therapeutics. Additionally, we found that tuning this sECM material allowed us to assess high-grade pediatric glioma cell invasion and evaluate therapeutic interventions targeting invasive behavior.

Conclusion

Our sECM culture platform provides a multipurpose tool for pediatric brain tumor researchers that enables both a wide breadth of biological assays and the cultivation of diverse tumor types.