Elevated CXorf67 Expression in PFA Ependymomas Suppresses DNA Repair and Sensitizes to PARP Inhibitors

EZHIP's role in diffuse midline glioma: echoes of oncohistones?

The enhancer of zeste inhibitory protein (EZHIP) is typically expressed during germ cell development and has been classified as a cancer-testis antigen (CTA) in various cancers. In 2020, 4% of diffuse midline gliomas (DMGs) were shown to aberrantly express EZHIP, mirroring the DMG hallmark histone H3 K27M (H3K27M) oncohistone mutation. Similar to H3K27M, EZHIP is a negative regulator of polycomb repressive complex 2 (PRC2), leading to global epigenomic remodeling. In this opinion, we explore the similarities and disparities between H3K27M- and EZHIP-DMGs with a focus on their shared functional hallmark of PRC2 inhibition, their genetic and epigenomic landscapes, plausible differences in the cell of origin, and therapeutic avenues. Upcoming research on EZHIP will help better understand its role in gliomagenesis and DMG therapy.

EZH2 inhibition sensitizes MYC-high medulloblastoma cancers to PARP inhibition by regulating NUPR1-mediated DNA repair

MYC-driven medulloblastomas (MB) are highly aggressive pediatric brain tumors with poor outcomes, and effective therapies remain limited despite intensive multimodal treatments. Targeting MYC directly is challenging, but exploiting MYC-mediated synthetic lethality holds promise. In this study, we investigated the combined effects of EZH2 and PARP inhibitors in MYC-high medulloblastoma and demonstrated that EZH2 inhibition significantly increased the sensitivity of MYC-high MB tumor cells to PARP inhibitors. This effect occurs through the upregulation of NUPR1, which promotes error-prone non-homologous end-joining (NHEJ) DNA repair by facilitating the recruitment of the XRCC4-LIG4 complex to DNA damage sites. This amplification of error-prone NHEJ DNA repair leads to genetic instability and eventual cell death in cells treated with the PARP inhibitor. The synergistic effect of EZH2 and PARP inhibitors was further validated in both in vitro and in vivo MB models without observed toxicity. These findings reveal a novel therapeutic strategy for MYC-high MB by co-targeting EZH2 and PARP, suggesting that this combination could potentially overcome the clinical challenges associated with this aggressive tumor subtype and warrants further investigation in clinical trials.

Ependymal Tumors: Overview of the Recent World Health Organization Histopathologic and Genetic Updates with an Imaging Characteristic

The 2021 World Health Organization Classification of Tumors of the Central Nervous System (CNS5), introduced significant changes, impacting tumors ranging from glial to ependymal neoplasms. Ependymal tumors were previously classified and graded based on histopathology, which had limited clinical and prognostic utility. The updated CNS5 classification now divides ependymomas into 10 subgroups based on anatomic location (supratentorial, posterior fossa, and spinal compartment) and genomic markers. Supratentorial tumors are defined by zinc finger translocation associated (ZFTA) (formerly v-rel avian reticuloendotheliosis viral oncogene [RELA]), or yes-associated protein 1 (YAP1) fusion; posterior fossa tumors are classified into groups A (PFA) and B (PFB), spinal ependymomas are defined by MYCN amplification. Subependymomas are present across all these anatomic compartments. The new classification kept an open category of "not elsewhere classified" or "not otherwise specified" if no pathogenic gene fusion is identified or if the molecular diagnosis is not feasible. Although there is significant overlap in the imaging findings of these tumors, a neuroradiologist needs to be familiar with updated CNS5 classification to understand tumor behavior, for example, the higher tendency for tumor recurrence along the dural flap for ZFTA fusion-positive ependymomas. On imaging, supratentorial ZFTA-fused ependymomas are preferentially located in the cerebral cortex, carrying predominant cystic components. YAP1-MAMLD1-fused ependymomas are intra- or periventricular with prominent multinodular solid components and have significantly better prognosis than ZFTA-fused counterparts. PFA ependymomas are aggressive paramedian masses with frequent calcification, seen in young children, originating from the lateral part of the fourth ventricular roof. PFB ependymomas are usually midline, noncalcified solid-cystic masses seen in adolescents and young adults arising from the fourth ventricular floor. PFA has a poorer prognosis, higher recurrence, and higher metastatic rate than PFB. Myxopapillary spinal ependymomas are now considered grade II due to high recurrence rates. Spinal-MYCN ependymomas are aggressive tumors with frequent leptomeningeal spread, relapse, and poor prognosis. Subependymomas are noninvasive, intraventricular, slow-growing benign tumors with an excellent prognosis. Currently, the molecular classification does not enhance the clinicopathologic understanding of subependymoma and myxopapillary categories. However, given the molecular advancements, this will likely change in the future. This review provides an updated molecular classification of ependymoma, discusses the individual imaging characteristics, and briefly outlines the latest targeted molecular therapies.

Protocol for the derivation of primary cancer stem cell lines from human ependymal tumors

Cancer stem cells (CSCs) established from surgical biopsies closely mimic the human context and can be used to investigate disease mechanisms, genetic fitness, and therapeutic evaluation. Here, we present a protocol for the derivation of primary patient-derived CSC lines from ependymal tumors. We describe the necessary steps, from surgical intervention and biopsy to the dissociation of ependymomas to derive cultures. We then detail procedures for cell line propagation and define the characteristics of these primary cancer cell lines. For complete details on the use and execution of this protocol, please refer to Michealraj et al.1.

Targeting the KAT8/YEATS4 Axis Represses Tumor Growth and Increases Cisplatin Sensitivity in Bladder Cancer

Bladder cancer (BC) is one of the most common tumors characterized by a high rate of relapse and a lack of targeted therapy. Here, YEATS domain-containing protein 4 (YEATS4) is an essential gene for BC cell viability using CRISPR-Cas9 library screening is reported, and that HUWE1 is an E3 ligase responsible for YEATS4 ubiquitination and proteasomal degradation by the Protein Stability Regulators Screening Assay. KAT8-mediated acetylation of YEATS4 impaired its interaction with HUWE1 and consequently prevented its ubiquitination and degradation. The protein levels of YEATS4 and KAT8 are positively correlated and high levels of these two proteins are associated with poor overall survival in BC patients. Importantly, suppression of YEATS4 acetylation with the KAT8 inhibitor MG149 decreased YEATS4 acetylation, reduced cell viability, and sensitized BC cells to cisplatin treatment. The findings reveal a critical role of the KAT8/YEATS4 axis in both tumor growth and cisplatin sensitivity in BC cells, potentially generating a novel therapeutic strategy for BC patients.

NRDE2 deficiency impairs homologous recombination repair and sensitizes hepatocellular carcinoma to PARP inhibitors

To identify novel susceptibility genes for hepatocellular carcinoma (HCC), we performed a rare-variant association study in Chinese populations consisting of 2,750 cases and 4,153 controls. We identified four HCC-associated genes, including NRDE2, RANBP17, RTEL1, and STEAP3. Using NRDE2 (index rs199890497 [p.N377I], p = 1.19 × 10-9) as an exemplary candidate, we demonstrated that it promotes homologous recombination (HR) repair and suppresses HCC. Mechanistically, NRDE2 binds to the subunits of casein kinase 2 (CK2) and facilitates the assembly and activity of the CK2 holoenzyme. This NRDE2-mediated enhancement of CK2 activity increases the phosphorylation of MDC1 and then facilitates the HR repair. These functions are eliminated almost completely by the NRDE2-p.N377I variant, which sensitizes the HCC cells to poly(ADP-ribose) polymerase (PARP) inhibitors, especially when combined with chemotherapy. Collectively, our findings highlight the relevance of the rare variants to genetic susceptibility to HCC, which would be helpful for the precise treatment of this malignancy.

A Fully Automated Deep-Learning Model for Predicting the Molecular Subtypes of Posterior Fossa Ependymomas Using T2-Weighted Images

PURPOSE

We aimed to develop and validate a deep learning (DL) model to automatically segment posterior fossa ependymoma (PF-EPN) and predict its molecular subtypes [Group A (PFA) and Group B (PFB)] from preoperative MR images.

EXPERIMENTAL DESIGN

We retrospectively identified 227 PF-EPNs (development and internal test sets) with available preoperative T2-weighted (T2w) MR images and molecular status to develop and test a 3D nnU-Net (referred to as T2-nnU-Net) for tumor segmentation and molecular subtype prediction. The network was externally tested using an external independent set [n = 40; subset-1 (n = 31) and subset-2 (n =9)] and prospectively enrolled cases [prospective validation set (n = 27)]. The Dice similarity coefficient was used to evaluate the segmentation performance. Receiver operating characteristic analysis for molecular subtype prediction was performed.

RESULTS

For tumor segmentation, the T2-nnU-Net achieved a Dice score of 0.94 ± 0.02 in the internal test set. For molecular subtype prediction, the T2-nnU-Net achieved an AUC of 0.93 and accuracy of 0.89 in the internal test set, an AUC of 0.99 and accuracy of 0.93 in the external test set. In the prospective validation set, the model achieved an AUC of 0.93 and an accuracy of 0.89. The predictive performance of T2-nnU-Net was superior or comparable to that of demographic and multiple radiologic features (AUCs ranging from 0.87 to 0.95).

CONCLUSIONS

A fully automated DL model was developed and validated to accurately segment PF-EPNs and predict molecular subtypes using only T2w MR images, which could help in clinical decision-making.

Ependymoma from Benign to Highly Aggressive Diseases: A Review

Ependymomas comprise biologically distinct tumor types with respect to age distribution, (epi)genetics, localization, and prognosis. Multimodal risk-stratification, including histopathological and molecular features, is essential in these biologically defined tumor types. Gross total resection (GTR), achieved with intraoperative monitoring and neuronavigation, and if necessary, second-look surgery, is the most effective treatment. Adjuvant radiation therapy is mandatory in high-risk tumors and in case of residual tumor. There is yet growing evidence that some ependymal tumors may be cured by surgery alone. To date, the role of chemotherapy is unclear and subject of current studies.Even though standard therapy can achieve reasonable survival rates for the majority of ependymoma patients, long-term follow-up still reveals a high probability of relapse in certain biological entities.With increasing knowledge of biologically distinct tumor types, risk-adapted adjuvant therapy gains importance. Beyond initial tumor control, and avoidance of therapy-induced morbidity for low-risk patients, intensified treatment for high-risk patients comprises another challenge. With identification of specific risk features regarding molecular alterations, targeted therapy may represent an option for individualized treatment modalities in the future.

Expression of cancer-testis antigens in the immune microenvironment of non-small cell lung cancer

The antigenic repertoire of tumors is critical for successful anti-cancer immune response and the efficacy of immunotherapy. Cancer-testis antigens (CTAs) are targets of humoral and cellular immune reactions. We aimed to characterize CTA expression in non-small cell lung cancer (NSCLC) in the context of the immune microenvironment. Of 90 CTAs validated by RNA sequencing, eight CTAs (DPEP3, EZHIP, MAGEA4, MAGEB2, MAGEC2, PAGE1, PRAME, and TKTL1) were selected for immunohistochemical profiling in cancer tissues from 328 NSCLC patients. CTA expression was compared with immune cell densities in the tumor environment and with genomic, transcriptomic, and clinical data. Most NSCLC cases (79%) expressed at least one of the analyzed CTAs, and CTA protein expression correlated generally with RNA expression. CTA profiles were associated with immune profiles: high MAGEA4 expression was related to M2 macrophages (CD163) and regulatory T cells (FOXP3), low MAGEA4 was associated with T cells (CD3), and high EZHIP was associated with plasma cell infiltration (adj. P-value < 0.05). None of the CTAs correlated with clinical outcomes. The current study provides a comprehensive evaluation of CTAs and suggests that their association with immune cells may indicate in situ immunogenic effects. The findings support the rationale to harness CTAs as targets for immunotherapy.

The AEG-1-USP10-PARP1 axis confers radioresistance in esophageal squamous cell carcinoma via facilitating homologous recombination-dependent DNA damage repair

Radiotherapy is the standard adjuvant treatment for esophageal squamous cell carcinoma (ESCC), yet radioresistance remains a major obstacle leading to treatment failure and unfavorable prognosis. Previous reports have demonstrated the involvement of astrocyte elevated gene-1 (AEG-1) in tumorigenesis and progression of multiple malignancies. Nevertheless, the precise role of AEG-1 in the radioresistance of ESCC remains elusive. Here, we unveiled a strong correlation between aberrant AEG-1 gene overexpression and malignant progression as well as adverse prognosis in ESCC patients. Moreover, both in vitro and in vivo investigations revealed that AEG-1 significantly alleviated irradiation-induced DNA damage and enhanced radiation resistance in ESCC cells. Mechanistically, AEG-1 recruited the deubiquitinase USP10 to remove the K48-linked polyubiquitin chains at the Lys425 of PARP1, thus preventing its proteasomal degradation. This orchestrated process facilitated homologous recombination-mediated DNA double-strand breaks (DSBs) repair, culminating in mitigated DNA damage and acquired radioresistance in ESCC cells. Notably, PARP1 overexpression reversed the radiosensitizing effect caused by AEG-1 deficiency. Collectively, these findings shed new light on the mechanism of ESCC radioresistance, providing potential therapeutic targets to enhance the efficacy of radiotherapy in ESCC.

In Situ STING-Activating Nanovaccination with TIGIT Blockade for Enhanced Immunotherapy of Anti-PD-1-Resistant Tumors

Immunotherapies comprising programmed cell death protein 1/PD ligand 1 (PD-1/PD-L1) immune checkpoint inhibitors are effective cancer treatments. However, the low response rate and immunoresistance resulting from alternative immune checkpoint upregulation and inefficient immune stimulation by T cells are problematic. The present report describes a biomimetic nanoplatform that simultaneously blocks the alternative T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) checkpoint and activates the stimulator of interferon genes (STING) signaling pathway in situ for enhanced antitumor immunity. The nanoplatform is engineered by fusing a red blood cell membrane with glutathione-responsive liposome-encapsulated cascade-activating chemoagents (β-lapachone and tirapazamine), and anchoring them with a detachable TIGIT block peptide (named as RTLT). In the tumor environment, the peptide is spatiotemporally released to reverse T-cell exhaustion and restore antitumor immunity. The cascade activation of chemotherapeutic agents causes DNA damage and inhibits the repair of double-stranded DNA, which induces robust in situ STING activation for an efficient immune response. The RTLT inhibits anti-PD-1-resistant tumor growth, and prevents tumor metastasis and recurrence in vivo by inducing antigen-specific immune memory. This biomimetic nanoplatform thus provides a promising strategy for in situ cancer vaccination.

Histone H3-wild type diffuse midline gliomas with H3K27me3 loss are a distinct entity with exclusive EGFR or ACVR1 mutation and differential methylation of homeobox genes

Diffuse midline gliomas (DMG) harbouring H3K27M mutation are paediatric tumours with a dismal outcome. Recently, a new subtype of midline gliomas has been described with similar features to DMG, including loss of H3K27 trimethylation, but lacking the canonical H3K27M mutation (H3-WT). Here, we report a cohort of five H3-WT tumours profiled by whole-genome sequencing, RNA sequencing and DNA methylation profiling and combine their analysis with previously published cases. We show that these tumours have recurrent and mutually exclusive mutations in either ACVR1 or EGFR and are characterised by high expression of EZHIP associated to its promoter hypomethylation. Affected patients share a similar poor prognosis as patients with H3K27M DMG. Global molecular analysis of H3-WT and H3K27M DMG reveal distinct transcriptome and methylome profiles including differential methylation of homeobox genes involved in development and cellular differentiation. Patients have distinct clinical features, with a trend demonstrating ACVR1 mutations occurring in H3-WT tumours at an older age. This in-depth exploration of H3-WT tumours further characterises this novel DMG, H3K27-altered sub-group, characterised by a specific immunohistochemistry profile with H3K27me3 loss, wild-type H3K27M and positive EZHIP. It also gives new insights into the possible mechanism and pathway regulation in these tumours, potentially opening new therapeutic avenues for these tumours which have no known effective treatment. This study has been retrospectively registered on clinicaltrial.gov on 8 November 2017 under the registration number NCT03336931 ( https://clinicaltrials.gov/ct2/show/NCT03336931 ).

C9orf72 functions in the nucleus to regulate DNA damage repair

The hexanucleotide GGGGCC repeat expansion in the intronic region of C9orf72 is the most common cause of Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The repeat expansion-generated toxic RNAs and dipeptide repeats (DPRs) including poly-GR, have been extensively studied in neurodegeneration. Moreover, haploinsufficiency has been implicated as a disease mechanism but how C9orf72 deficiency contributes to neurodegeneration remains unclear. Here, we show that C9orf72 deficiency exacerbates poly-GR-induced neurodegeneration by attenuating non-homologous end joining (NHEJ) repair. We demonstrate that C9orf72 localizes to the nucleus and is rapidly recruited to sites of DNA damage. C9orf72 deficiency resulted in impaired NHEJ repair through attenuated DNA-PK complex assembly and DNA damage response (DDR) signaling. In mouse models, we found that C9orf72 deficiency exacerbated poly-GR-induced neuronal loss, glial activation, and neuromuscular deficits. Furthermore, DNA damage accumulated in C9orf72-deficient neurons that expressed poly-GR, resulting in excessive activation of PARP-1. PARP-1 inhibition rescued neuronal death in cultured neurons treated with poly-GR peptides. Together, our results support a pathological mechanism where C9orf72 haploinsufficiency synergizes with poly-GR-induced DNA double-strand breaks to exacerbate the accumulation of DNA damage and PARP-1 overactivation in C9orf72 ALS/FTD patients.

Suppression of GCH1 Sensitizes Ovarian Cancer and Breast Cancer to PARP Inhibitor

Background

Breast and ovarian cancers are common malignancies among women, contributing to a significant disease burden, and are characterized by a high level of genomic instability, owing to the failure of homologous recombination repair (HRR). Pharmacological inhibition of poly(ADP-ribose) polymerase (PARP) could elicit the synthetic lethal effect of tumor cells in patients with homologous recombination deficiency, ultimately achieving a favorable clinical benefit. However, primary and acquired resistance remain the greatest hurdle, limiting the efficacy of PARP inhibitors; thus, strategies conferring or augmenting tumor cell sensitivity to PARP inhibitors are urgently required.

Methods

Our RNA-seq data of niraparib-treated and -untreated tumor cells were analyzed by R language. Gene Set Enrichment Analysis (GSEA) was applied to assess the biological functions of GTP cyclohydrolase 1 (GCH1). Quantitative real-time PCR, Western blotting, and immunofluorescence were applied to confirm the upregulation of GCH1 upon niraparib treatment at transcriptional and translational levels. Immunohistochemistry of patient-derived xenograft (PDX)-derived tissue sections further validated that niraparib increased GCH1 expression. Tumor cell apoptosis was detected by flow cytometry, while the superiority of the combination strategy was confirmed in the PDX model.

Results

The expression of GCH1 was aberrantly enriched in breast and ovarian cancers and increased after niraparib treatment via JAK-STAT signaling. GCH1 was also demonstrated to be associated with the HRR pathway. Subsequently, the enhancement of the tumor-killing effect of PARP inhibitors induced by GCH1 suppression using siRNA and GCH1 inhibitor was validated by flow cytometry in vitro. Finally, using the PDX model, we further demonstrated that GCH1 inhibitors markedly potentiated PARP inhibitors' antitumor efficacy in vivo.

Conclusion

Our results illustrated that PARP inhibitors promote GCH1 expression via the JAK-STAT pathway. We also elucidated the potential relationship between GCH1 and the homologous recombination repair pathway and proposed a combination regimen of GCH1 suppression with PARP inhibitors in breast and ovarian cancers.

Delineation of molecular characteristics in pediatric PFA ependymoma involving rare osseous and pulmonary metastases: A case report and literature review

Ependymoma is the third most common pediatric primary brain tumor, with its most aggressive subtype being posterior fossa group A (PFA). Extraneural metastasis of pediatric PFA ependymoma is rare. Herein, we present a case of a 9-year-old girl with PFA ependymoma characterized by a lack of trimethylation of histone H3 at lysine 27 and elevated chromosome X open reading frame 67 expression. Despite multiple surgeries and radiotherapies, the patient had a rapid recurrence and developed osseous and pulmonary metastases, which may be attributed to the homozygous deletion of cyclin-dependent kinase (CDK) inhibitor 2A/B and CDK12 mutation. Importantly, the CDK12 mutation observed in the patient may be indicative of the need for further work-up to consider chemotherapy rather than administering poly (adenosine diphosphate-ribose) polymerase inhibitors. Taken together, this is the first report of pediatric PFA ependymoma with extraneural metastases, wherein we clarified the diagnostic procedures of this newly identified PFA ependymoma and provided new cues to study the invasiveness of this disease and treatment selection for such patients.

The Role of PARP Inhibitors in Patients with Primary Malignant Central Nervous System Tumors

OPINION STATEMENT

Primary malignant central nervous (CNS) tumors are a devastating group of diseases with urgent need for improved treatment options. Surgery, radiation, and cytotoxic chemotherapy remain the primary standard treatment modalities, with molecularly targeted therapies having proven efficacy in only small subsets of cases. Poly(ADP-ribose) polymerase (PARP) inhibitors, which have had immense success in the treatment of extracranial cancers with homologous recombination deficiency (HRD), are emerging as a potential targeted treatment for various CNS tumors. Although few primary CNS tumors display canonical BRCA gene defects, preclinical evidence suggests that PARP inhibitors may benefit certain CNS tumors with functional HRD or elevated replication stress. In addition, other preclinical studies indicate that PARP inhibitors may synergize with standard therapies used for CNS tumors including radiation and alkylating agents and may prevent or overcome drug resistance. Thus far, initial clinical trials with early-generation PARP inhibitors, typically as monotherapy or in the absence of selective biomarkers, have shown limited efficacy. However, the scientific rationale remains promising, and many clinical trials are ongoing, including investigations of more CNS penetrant or more potent inhibitors and of combination therapy with immune checkpoint inhibitors. Early phase trials are also critically focusing on determining active drug CNS penetration and identifying biomarkers of therapy response. In this review, we will discuss the preclinical evidence supporting use of PARP inhibitors in primary CNS tumors and clinical trial results to date, highlighting ongoing trials and future directions in the field that may yield important findings and potentially impact the treatment of these devastating malignancies in the coming years.

Ependymoma: Evaluation and Management Updates

PURPOSE OF REVIEW

To review state of art and relevant advances in the molecular genetics and management of ependymomas of children and adults.

RECENT FINDINGS

Ependymomas may occur either in the brain or in the spinal cord. Compared with intracranial ependymomas, spinal ependymomas are less frequent and exhibit a better prognosis. The new WHO classification of CNS tumors of 2021 has subdivided ependymomas into different histomolecular subgroups with different outcome. The majority of studies have shown a major impact of extent of resection; thus, a complete resection must be performed, whenever possible, at first surgery or at reoperation. Conformal radiotherapy is recommended for grade 3 or incompletely resected grade II tumors. Proton therapy is increasingly employed especially in children to reduce the risk of neurocognitive and endocrine sequelae. Craniospinal irradiation is reserved for metastatic disease. Chemotherapy is not useful as primary treatment and is commonly employed as salvage treatment for patients failing surgery and radiotherapy. Standard treatments are still the mainstay of treatment: the discovery of new druggable pathways will hopefully increase the therapeutic armamentarium in the near future.

Precise Diabetic Wound Therapy: PLS Nanospheres Eliminate Senescent Cells via DPP4 Targeting and PARP1 Activation

Diabetic ulcers, a difficult problem faced by clinicians, are strongly associated with an increase in cellular senescence. Few empirical studies have focused on exploring a targeted strategy to cure diabetic wounds by eliminating senescent fibroblasts (SFs) and reducing side effects. In this study, poly-l-lysine/sodium alginate (PLS) is modified with talabostat (PT100) and encapsulates a PARP1 plasmid (PARP1@PLS-PT100) for delivery to target the dipeptidyl peptidase 4 (DPP4) receptor and eliminate SFs. PARP1@PLS-PT100 releases encapsulated plasmids, displaying high selectivity for SFs over normal fibroblasts by targeting the DPP4 receptor, decreasing senescence-associated secretory phenotypes (SASPs), and stimulating the secretion of anti-inflammatory factors. Furthermore, the increased apoptosis of SFs and the disappearance of cellular senescence alleviates SASPs, accelerates re-epithelialization and collagen deposition, and significantly induces macrophage M2 polarization, which mediates tissue repair and the inflammatory response. This innovative strategy has revealed the previously undefined role of PARP1@PLS-PT100 in promoting diabetic wound healing, suggesting its therapeutic potential in refractory wound repair.

EZHIP: a new piece of the puzzle towards understanding pediatric posterior fossa ependymoma

Ependymomas (EPN) are tumors of the central nervous system (CNS) that can arise in the supratentorial brain (ST-EPN), hindbrain or posterior fossa (PF-EPN) or anywhere in the spinal cord (SP-EPN), both in children and adults. Molecular profiling studies have identified distinct groups and subtypes in each of these anatomical compartments. In this review, we give an overview on recent findings and new insights what is driving PFA ependymomas, which is the most common group. PFA ependymomas are characterized by a young median age at diagnosis, an overall balanced genome and a bad clinical outcome (56% 10-year overall survival). Sequencing studies revealed no fusion genes or other highly recurrently mutated genes, suggesting that the disease is epigenetically driven. Indeed, recent findings have shown that the characteristic global loss of the repressive histone 3 lysine 27 trimethylation (H3K27me3) mark in PFA ependymoma is caused by aberrant expression of the enhancer of zeste homolog inhibitory protein (EZHIP) or in rare cases by H3K27M mutations, which both inhibit EZH2 thereby preventing the polycomb repressive complex 2 (PRC2) from spreading H3K27me3. We present the current status of the ongoing work on EZHIP and its essential role in the epigenetic disturbance of PFA biology. Comparisons to the oncohistone H3K27M and its role in diffuse midline glioma (DMG) are drawn, highlighting similarities but also differences between the tumor entities and underlying mechanisms. A strong focus is to point out missing information and to present directions of further research that may result in new and improved therapies for PFA ependymoma patients.

Molecular Classification and Therapeutic Targets in Ependymoma

Ependymoma is a biologically diverse tumor wherein molecular classification has superseded traditional histological grading based on its superior ability to characterize behavior, prognosis, and possible targeted therapies. The current, updated molecular classification of ependymoma consists of ten distinct subgroups spread evenly among the spinal, infratentorial, and supratentorial compartments, each with its own distinct clinical and molecular characteristics. In this review, the history, histopathology, standard of care, prognosis, oncogenic drivers, and hypothesized molecular targets for all subgroups of ependymoma are explored. This review emphasizes that despite the varied behavior of the ependymoma subgroups, it remains clear that research must be performed to further elucidate molecular targets for these tumors. Although not all ependymoma subgroups are oncologically aggressive, development of targeted therapies is essential, particularly for cases where surgical resection is not an option without causing significant morbidity. The development of molecular therapies must rely on building upon our current understanding of ependymoma oncogenesis, as well as cultivating transfer of knowledge based on malignancies with similar genomic alterations.

Cell-of-Origin and Genetic, Epigenetic, and Microenvironmental Factors Contribute to the Intra-Tumoral Heterogeneity of Pediatric Intracranial Ependymoma

Intra-tumoral heterogeneity (ITH) is a complex multifaceted phenomenon that posits major challenges for the clinical management of cancer patients. Genetic, epigenetic, and microenvironmental factors are concurrent drivers of diversity among the distinct populations of cancer cells. ITH may also be installed by cancer stem cells (CSCs), that foster unidirectional hierarchy of cellular phenotypes or, alternatively, shift dynamically between distinct cellular states. Ependymoma (EPN), a molecularly heterogeneous group of tumors, shows a specific spatiotemporal distribution that suggests a link between ependymomagenesis and alterations of the biological processes involved in embryonic brain development. In children, EPN most often arises intra-cranially and is associated with an adverse outcome. Emerging evidence shows that EPN displays large intra-patient heterogeneity. In this review, after touching on EPN inter-tumoral heterogeneity, we focus on the sources of ITH in pediatric intra-cranial EPN in the framework of the CSC paradigm. We also examine how single-cell technology has shed new light on the complexity and developmental origins of EPN and the potential impact that this understanding may have on the therapeutic strategies against this deadly pediatric malignancy.

Molecular Stratification of Childhood Ependymomas as a Basis for Personalized Diagnostics and Treatment

Ependymomas are among the most enigmatic tumors of the central nervous system, posing enormous challenges for pathologists and clinicians. Despite the efforts made, the treatment options are still limited to surgical resection and radiation therapy, while none of conventional chemotherapies is beneficial. While being histologically similar, ependymomas show considerable clinical and molecular diversity. Their histopathological evaluation alone is not sufficient for reliable diagnostics, prognosis, and choice of treatment strategy. The importance of integrated diagnosis for ependymomas is underscored in the recommendations of Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy. These updated recommendations were adopted and implemented by WHO experts. This minireview highlights recent advances in comprehensive molecular-genetic characterization of ependymomas. Strong emphasis is made on the use of molecular approaches for verification and specification of histological diagnoses, as well as identification of prognostic markers for ependymomas in children.

G-protein-coupled receptor GPR17 inhibits glioma development by increasing polycomb repressive complex 1-mediated ROS production

Glioma is the most common primary tumor in the central nervous system. However, the development of glioma and effective therapeutic strategies remain elusive. Here, we identify GPR17 as a potential target to treat glioma. Data mining with human LGG and GBM samples reveals that GPR17 is negatively correlated with glioma development. Overexpressing GPR17 inhibits glioma cell proliferation and induces apoptosis by raising ROS levels. GPR17-overexpressing glioma cells are less tumorigenic in the brain than in control cells. Mechanistically, GPR17 inhibits the transcription of RNF2, a key component in the PRC1 complex, through cAMP/PKA/NF-κB signaling, leading to reduced histone H2A monoubiquitination. ChIP-Seq and RNA-Seq analyses reveal KLF9 as a direct target of RNF2. KLF9 mediates the functions of GPR17 and RNF2 in glioma cells. Furthermore, activation of GPR17 by its agonist inhibits glioma formation. Our findings have thus identified GPR17 as a key regulator of glioma development and a potential therapeutic target for gliomas.

The roles of Polycomb repressive complexes in mammalian development and cancer

More than 80 years ago, the first Polycomb-related phenotype was identified in Drosophila melanogaster. Later, a group of diverse genes collectively called Polycomb group (PcG) genes were identified based on common mutant phenotypes. PcG proteins, which are well-conserved in animals, were originally characterized as negative regulators of gene transcription during development and subsequently shown to function in various biological processes; their deregulation is associated with diverse phenotypes in development and in disease, especially cancer. PcG proteins function on chromatin and can form two distinct complexes with different enzymatic activities: Polycomb repressive complex 1 (PRC1) is a histone ubiquitin ligase and PRC2 is a histone methyltransferase. Recent studies have revealed the existence of various mutually exclusive PRC1 and PRC2 variants. In this Review, we discuss new concepts concerning the biochemical and molecular functions of these new PcG complex variants, and how their epigenetic activities are involved in mammalian development and cancer.