CNS Cancer Models

EZH2 as a new therapeutic target in brain tumors: Molecular landscape, therapeutic targeting and future prospects

Medulloblastoma, the most common malignant pediatric brain tumor, arises from the cerebellum and spreads throughout the cerebrospinal fluid to the leptomeninges, covering the brain and spinal cord. Leptomeningeal metastasis, a frequent finding at diagnosis and recurrence, is a significant indicator of poor prognosis. Treatment of affected children includes irradiation of the developing brain and spine, and chemotherapy, which cause debilitating neurological complications. Despite the grave consequences of leptomeningeal metastasis, little is known about the cascade of molecular and cellular events that lead to leptomeningeal metastasis. Atonal Homolog 1 (Atoh1), a proneural transcription factor, is crucial for the initiation and progression of the Sonic Hedgehog (Shh) subgroup of medulloblastoma; Atoh1 expression is also detected in metastatic lesions of this tumor subgroup. To examine the role of Atoh1 in leptomeningeal dissemination, we generated transgenic mouse strains that conditionally express Atoh1 using Cre-loxP technology. These Atoh1 transgenic strains (A1G) were further crossed with the Math1-Cre and Ptch1+/- strains, the latter exhibiting aberrant Shh signaling in the cerebellum. Though ∼25% of Ptch1+/- mice develop non-metastatic medulloblastoma in 6-24 months, all Math1-Cre/A1G/Ptch1+/- mice succumbed to medulloblastoma within 5 months. Histological analysis revealed Pax6+ tumor cells with robust expression of Ki67, while the expression of NeuN was significantly decreased or absent, indicating the Atoh1 transgene promotes MB development in Ptch1+/- mice. More importantly, we observed robust leptomeningeal metastasis in these mice: tumor cells were detected within ventricular regions and leptomeningeal spaces covering the spinal cord in all mice, and more than 50% of animals developed metastasis in brain parenchyma, indicating Atoh1 drives leptomeningeal dissemination of medulloblastoma. Similarly, orthotopically transplanted Shh-driven medullolastoma with Atoh1 overexpression exhibited enhanced migration and invasion. Together, our results demonstrate that Atoh1 plays an important role in medulloblastoma leptomeningeal metastasis and may serve as a therapeutic target in this devastating disease.

Tumor angiogenesis has attracted increasing attention because of its potential as a valuable marker in the differential diagnosis of brain tumors as well as a novel therapeutic target. Prostate-specific membrane antigen (PSMA) is expressed by the neovasculature endothelium of some tumors, with little to no expression by the tumor cells or normal vasculature endothelium. The aim of this study was to investigate the potential of PSMA for the evaluation of the tumor neovasculature of various brain tumors and the possibility of detecting PSMA expression in brain tumors using PET imaging with 89Zr-Df-IAB2M (anti-PSMA minibody). Eighty-three tissue specimens including gliomas, metastatic brain tumors, primary central nervous system lymphomas (PCNSL), or radiation necroses were analyzed by immunohistochemical staining with PSMA antibody. 89Zr-Df-IAB2M PET scans were performed in three patients with recurrent high-grade gliomas or metastatic brain tumor. PSMA was highly expressed in the vascular endothelium of high-grade glioma and metastatic brain tumor, whereas PSMA was poorly expressed in the vascular endothelium of PCNSL and radiation necrosis. PSMA expression in high-grade gliomas and a metastatic brain tumor was clearly visualized by PET imaging with 89Zr-Df-IAB2M. Furthermore, a trend toward a positive correlation between the degree of 89Zr-Df-IAB2M uptake and PSMA expression levels in tumor specimens was observed. PET imaging of PSMA using 89Zr-Df-IAB2M may have potential value in the differential diagnosis of high-grade glioma from PCNSL or radiation necrosis as well as in the prediction of treatment efficacy and assessment of treatment response to bevacizumab therapy for high-grade glioma.

Circular RNAs (circRNAs) are a class of RNA with a stable cyclic structure. They are expressed in various tissues and cells with conserved, specific characteristics. CircRNAs have been found to play critical roles in a wide range of cellular processes by regulating gene expression at the epigenetic, transcriptional, and posttranscriptional levels. There is an accumulation of evidence on newly discovered circRNAs, their molecular interactions, and their roles in the development and progression of human brain tumors, including cell proliferation, cell apoptosis, invasion, and chemoresistance. Here we summarize the current state of knowledge of the circRNAs that have been implicated in brain tumor pathogenesis, particularly in gliomas and medulloblastomas. In providing a comprehensive overview of circRNA studies, we highlight how different circRNAs have oncogenic or tumor-suppressive roles in brain tumors, making them attractive therapeutic targets and biomarkers for personalized therapy and precision diagnostics. This review article discusses circRNAs' functional roles and the prospect of using them as diagnostic biomarkers and therapeutic targets in patients with brain tumors.

BackgroundChildhood cancer is still a leading cause of death around the world. To improve outcomes, there is an urgent need for tailored treatment. The systematic evaluation of existing preclinical data can provide an overview of what is known and identify gaps in the current knowledge. Here, we applied the target actionability review (TAR) methodology to assess the strength and weaknesses of available scientific literature on CDK4/6 as a therapeutic target in paediatric solid and brain tumours by structured critical appraisal. MethodsUsing relevant search terms in PubMed, a list of original publications investigating CDK4/6 in paediatric solid tumour types was identified based on relevancy criteria. Each publication was annotated for the tumour type and categorised into separate proof-of-concept (PoC) data modules. Based on rubrics, quality and experimental outcomes were scored independently by two reviewers. A third reviewer evaluated and adjudicated score discrepancies. Scores for each PoC module were averaged for each tumour type and visualised in a heatmap matrix in the publicly available R2 data portal. Results and conclusionsThis CDK4/6 TAR, generated by analysis of 151 data entries from 71 publications, showed frequent genomic aberrations of CDK4/6 in rhabdomyosarcoma, osteosarcoma, high-grade glioma, medulloblastoma, and neuroblastoma. However, a clear correlation between CDK4/6 aberrations and compound efficacy is not coming forth from the literature. Our analysis indicates that several paediatric indications would need (further) preclinical evaluation to allow for better recommendations, especially regarding the dependence of tumours on CDK4/6, predictive biomarkers, resistance mechanisms, and combination strategies. Nevertheless, our TAR heatmap provides support for the relevance of CDK4/6 inhibition in Ewing sarcoma, medulloblastoma, malignant peripheral nerve sheath tumour and to a lesser extent neuroblastoma, rhabdomyosarcoma, rhabdoid tumour and high-grade glioma. The interactive heatmap is accessible through R2 [r2platform.com/TAR/CDK4_6].

Highlights from Recent Cancer Literature

Chaperone proteins are most notable for the proteo- and cyotoprotective capacities they afford during cellular stress. Under conditions of cellular normalcy, chaperones still play integral roles in the folding of nascent polypeptides into functional entities, in assisting in intracellular/intraorganellar transport, in assembly and maintenance of multi-subunit protein complexes, and in aiding and abetting the degradation of senescent proteins. Tumors frequently have relatively enhanced needs for chaperone number and activity because of the stresses of rapid proliferation, increased metabolism, and overall genetic instability. Thus, it may be possible to take advantage of this reliance that tumor cells have on chaperones by pharmacologic and biologic means. Certain chaperones are abundant in the brain, which implies important roles for them. While it is presumed that the requirements of brain tumors for chaperone proteins are similar to those of any other cell type, tumor or otherwise, very little inquiry has been directed at the possibility of using chaperone proteins as therapeutic targets or even as therapeutic agents against central nervous system malignancies. This review highlights some of the research on the functions of chaperone proteins, on what can be done to modify those functions, and on the physiological responses that tumors and organisms can have to chaperone-targeted or chaperone-based therapies. In particular, this review will also underscore areas of research where brain tumors have been part of the field, although in general those instances are few and far between. This relative dearth of research devoted to chaperone protein targets and therapeutics in brain tumors reveals much untrodden turf to explore for potential treatments of these dreadfully refractive diseases.

Current treatment strategies for children with brain tumors focus on improving outcome for tumor types that have historically been relatively resistant to therapy, and reducing treatment-related sequelae for children with therapy-responsive tumors. Refinements in clinical and molecular stratification for many types of childhood brain tumors have facilitated these efforts to achieve risk-adapted treatment planning. In some instances, molecular characterization approaches have also yielded insights into new therapeutic targets. This chapter reviews advances in stratification approaches for several of the most common types of childhood brain tumors, including high- and low-grade gliomas, medulloblastomas and other primitive neuroectodermal tumors (PNETs), and infant brain tumors, and discusses how new information regarding the biological features critical to tumorigenesis is being translated into novel therapeutic approaches for these challenging tumors.

Twenty-six patients with various brain tumors or carcinomatous meningitis were examined for alkaline phosphatase (ALP) in the cerebrospinal fluid. ALP enzyme levels were compared with the respective levels in control groups of 75 patients with epilepsy, stroke, bacterial and viral meningitis and intervertebral disc prolapse. Extremely high ALP levels in CSF (9516 mu/l, 1425 mu/l, and 871 mu/l) were found in patients with pulmonary carcinomatous meningitis. Among all other patients with brain tumors, ALP levels in CSF were in the normal range. Examination of ALP in serum yielded normal results in all patients. In patients with pulmonary carcinomatous meningitis, the enzyme level in CSF was examined during various stages of radiotherapy and chemotherapy. Decreased ALP enzyme level was found during treatment followed by recurring rising levels a month after the treatment coinciding with clinical relapse. No correlation was found between the level of ALP enzyme and the biochemical and cellular content of the CSF during the various stages of treatment.

For over a century physicians have tried to use what they see under the microscope to predict the behavior of brain tumors and to determine which treatment strategies would best benefit their patients. This approach has been particularly frustrating in pediatric neurooncology. What appears to be the same tumor in an infant may behave quite differently in an older child. That “same tumor” may have a very different prognosis in one anatomical location compared to another. A commonality in most pediatric brain tumor patients remains that what we accomplish as neurosurgeons in our attempts to remove a child’s tumor is presently the most important factor in that child’s prognosis. For most pediatric brain tumors, the difference between a grosstotal resection and a subtotal resection doubles the child’s chances of survival. As such, advances in neuroimaging and image-guided surgery are among the greatest adjuncts to surgery. The application of frameless stereotactic image guidance, functional neuroimaging, intraoperative MR imaging, early postoperative MR imaging, and second-look surgery has allowed the neurosurgeon to be more aggressive. This is evidenced by the fact that the number of children enrolled in national clinical trials with no or minimal residual tumor on their MR imaging has nearly doubled over the last 2 decades. Another major advance has been the routine banking of tumor tissue. This resource, coupled with more readily available molecular profiling techniques, has allowed us to understand that two ependymomas that look the same histologically are not the same tumor in the spinal cord as in the posterior fossa or the supratentorial space.8 The understanding of the molecular events giving rise to these tumors has allowed us to develop animal and in vitro models that are both histologically and molecularly the same as those in the human condition.4 The same holds true for small round blue-cell tumors. The recognition that molecular alterations in the INI-1 gene are associated with atypical teratoid rhabdoid tumors was a seminal occurrence.7 We now recognize that what we once called a medulloblastoma is one of several tumor subtypes.1 The Wnt-positive tumors, recognized by nuclear staining for b-catenin, are more likely to arise in younger children, are more likely to be located within the fourth ventricle, and in our last treatment trial were associated with 100% progression-free survival.2 Efforts are now underway to reduce the toxic side effects of treatment in this subgroup of children. Medulloblastomas associated with Sonic hedgehog (Shh) signaling abnormalities arise from a different cancer stem cell, are more likely to be located in the cerebellar hemisphere, and are more likely to be noted in infants and older children.3 With the development of GDC-0449, a specific Shh inhibitor, we now have targeted therapy for children with those medulloblastoma subtypes. For children with c-myc amplification or with large-cell anaplastic medulloblastomas, the prognosis remains dismal and we must develop novel targeted therapies for those children.5 In low-grade astrocytomas, similar progress has been made. The identification of BRAF abnormalities in pilocytic astrocytomas, the recognition that subependymal giant cell tumors respond quite nicely to mTOR inhibitors, and that antiangiogenesis agents such as bevacizumab offer specific molecular targets for treatment in these tumors, is further evidence that the understanding of the molecular pathways involved in tumor formation is our future. In this paper6 by Dr. Pollack, a pediatric neurosurgeon who has dedicated his life to better understanding childhood brain tumors, a very clear and readable overview of the progress made in the management of a variety of childhood brain tumors has been provided. A number of truths can be gleaned from the article. First, given the molecular studies that are available for these tumors, it behooves us at surgery not only to provide tissue for histology but also to bank fresh tumor tissue for future reference in each case. Second, children and their families should be offered enrollment in prospective clinical 133 134

Medulloblastoma is the most common malignant brain tumor in children, accounting for 20-25% of all pediatric brain tumors. The current standard of care includes both craniospinal and focal radiation therapy which lead to negative long term consequences in the pediatric population such as bone and tissue hypoplasia, decreased neurocognitive functioning, as well as an increased risk for secondary radiation induced cancers. Thus, there is a need for novel approaches to radiation therapy that can effectively target and kill tumor cells while minimizing radiation toxicity in healthy tissue. Here, we investigate a new approach to radiation therapy relying on two classes of therapeutic agents, Sonic Hedgehog (SHH) inhibitors and Poly (ADP-ribose) Polymerase (PARP) inhibitors. The dysregulation and constitutive activation of the SHH signaling pathway accounts for ~30% of all medulloblastomas. In addition to playing a role in tumorigenesis, the SHH pathway is known to play a role in the radiation sensitivity of various cancer types. PARP1 is known to play a key role in DNA damage repair, and it has previously been shown to affect the radiation sensitivity of pediatric brain cancers including high grade glioma, medulloblastoma, and ependymoma. We hypothesize that both inhibiting the SHH pathway at Smoothened (Smo) or Gli1 and inhibiting PARP1 will enhance medulloblastoma tumor cell killing following radiation therapy. We found that in vitro treatment with Sonidegib, GANT61, and Veliparib alone without radiation was sufficient to decrease tumor cell viability and self-renewal. When followed by radiation, pre-treatment with Sonidegib, GANT61, and Veliparib, both alone and in combination, resulted in further decreased tumor cell viability and self-renewal. These data suggest that inhibition of Smo, Gli1, or PARP1 alone or in combination is a promising therapeutic strategy for increasing the radiation sensitivity of pediatric SHH medulloblastoma.

BackgroundPediatric brain tumors (PBT) represent a major public health challenge, accounting for approximately 15–20% of all childhood malignancies. The tumor microenvironment (TME) plays a crucial role in tumor progression and prognosis, yet its specific contributions in PBT remain insufficiently explored.ObjectiveThis study aimed to develop and validate a prognostic model based on TME-specific genes in pediatric brain tumors, providing insights into potential therapeutic targets.MethodsWe analyzed gene expression data from a cohort of 70 pediatric brain tumor samples using the ESTIMATE algorithm to classify tumors into high- and low-risk groups based on stromal and immune scores. To identify TME-specific genes, we performed differential gene expression and weighted gene co-expression network analysis (WGCNA). A prognostic model was constructed using LASSO regression and Cox proportional hazards models, comprising eight key genes: CASP10, EPSTI1, FGL2, ITGAX, etc. The model’s predictive accuracy was validated in independent cohorts through ROC curve analysis.ResultsThe model demonstrated strong prognostic capability, with AUC values exceeding 0.8 for 1-year, 3-year, and 5-year survival predictions. Among the identified genes, CASP10 emerged as significantly associated with tumor progression, suggesting its potential as a therapeutic target. Furthermore, Mendelian randomization analysis provided additional support for a causal relationship between CASP10 expression and brain tumor risk.ConclusionThe TME-specific gene-based prognostic model effectively predicts survival outcomes in pediatric brain tumors, offering promising biomarkers for personalized medicine and potential therapeutic targets. However, further research is required to validate these findings across different tumor subtypes and to explore their clinical applications.

Brain tumors are among the most common and most chemoresistant tumors. Despite treatment with aggressive treatment strategies, the prognosis for patients harboring malignant gliomas remains dismal. The kynurenine pathway (KP) is the principal route of L-tryptophan catabolism leading to the formation of the essential pyridine nucleotide, nicotinamide adenine dinucleotide (NAD(+)), and important neuroactive metabolites, including the neurotoxin, quinolinic acid (QUIN), the neuroprotective agent, picolinic acid (PIC), the T(H)17/Treg balance modulator, 3-hydroxyanthranilic acid (3-HAA), and the immunosuppressive agent, L-kynurenine (KYN). This review provides a new perspective on KP dysregulation in defeating antitumor immune responses, specifically bringing light to the lower segment of the KP, particularly QUIN-induced neurotoxicity and downregulation of the enzyme α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) as a potential mechanism of tumor progression. Given its immunosuppressive effects, 3-HAA produced from the KP may also play a role in suppressing antitumor immunity in human tumors. The enzyme indoleamine 2, 3-dioxygenase (IDO-1) initiates and regulates the first step of the KP in most cells. Mounting evidence directly implicates that the induction and overexpression of IDO-1 in various tumors is a crucial mechanism facilitating tumor immune evasion and persistence. Tryptophan 2, 3-dioxygenase (TDO-2), which initiates the same first step of the KP as IDO-1, has likewise recently been shown to be a mechanism of tumoral immune resistance. Further, it was also recently shown that TDO-2-dependent production of KYN by brain tumors might be a novel mechanism for suppressing antitumor immunity and supporting tumor growth through the activation of the Aryl hydrocarbon receptor (AhR). This newly identified TDO-2-KYN-AhR signaling pathway opens up exciting future research opportunities and may represent a novel therapeutic target in cancer therapy. Our discussion points to a number of KP components, namely TDO-2, IDO-1, and ACMSD, as important therapeutic targets for the treatment of brain cancer. Targeting the KP in brain tumors may represent a viable strategy likely to prevent QUIN-induced neurotoxicity and KYN and 3-HAA-mediated immune suppression.

Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and other ncRNA types, have emerged as key regulators in neurodegenerative diseases and brain tumors. This review aims to provide insights into the role of ncRNAs in these conditions and their potential as diagnostic and therapeutic targets. We systematically reviewed literature from databases such as PubMed, Scopus, and Web of Science, applying specific inclusion and exclusion criteria to ensure comprehensive coverage of recent advancements. Although ncRNAs are involved in a range of molecular pathways, challenges in clinical translation, including specificity, cost, and validation, persist. This review highlights innovative strategies to overcome these barriers and promote the clinical application of ncRNAs. Moreover, we explore the emerging role of extracellular vesicle-enriched ncRNAs as cell-free therapeutic options for neurodegenerative diseases. The findings presented here emphasize the need for robust validation and the development of specific ncRNA-based treatments.

Metastases are the most common brain tumors especially in adults. Although they are generally considered a single disease entity which is universally fatal in patients with advanced cancer, brain metastases are remarkably heterogeneous both clinically and pathologically. As members of the multidisciplinary clinical team for the diagnosis and management of metastatic brain tumors, pathologists must be familiar not only with clinicopathologic features of brain metastases but also with any characteristic and clinically significant molecular findings. We discuss here the epidemiology, general gross and microscopic features of brain metastases with emphasis on how to differentiate them from primary brain tumors using immunohistochemistry (e.g., for identification of the primary site and differential diagnosis), and unique pathologic patterns of brain metastases (namely, dural metastasis, leptomeningeal carcinomatosis, miliary metastasis, ‘‘intravascular carcinomatosis’’, and tumor-to-tumor metastasis) with their clinical and radiological characteristics. We specifically address metastatic breast and non-small cell lung cancers which are the two most commonly encountered in daily practice, with emphasis on the molecular alterations related to therapy and their clinicopathologic significance.