MB Tumor Research Articles

Conditional generation of free radicals by selective activation of alkoxyamines: towards more effective and less toxic targeting of brain tumors.

Brain tumors are an important cause of suffering and death. Glioblastoma are the most frequent primary tumors of the central nervous system in adults. They are associated with a very poor prognosis, since only 10% of GBM patients survive 5 years after diagnosis. Medulloblastoma are the most frequent brain malignancies in childhood; they affect the cerebellum in children under 10 years of age in 75% of cases. The current multimodal treatment comes at the expense of serious and often long-lasting side effects. Herein, we propose the synthesis of a library of novel alkoxyamines as anticancer drug candidates. The most efficient molecule, ALK4, was selected based on its ability to inhibit both survival and migration of GBM and MB cells in 2D cultures and in 3D tumor spheroids. A fluorescent derivative was used to show the early cytosolic accumulation of ALK4 in tumor cells. Spontaneous homolysis of ALK4 led to the release of alkyl radicals, which triggered the generation of reactive oxygen species, fragmentation of the mitochondrial network and ultimately apoptosis. To control its homolytic process, the selected alkoxyamine was bioconjugated to a peptide selectively recognized by matrix metalloproteases. This bioconjugate, named ALK4-MMPp, successfully inhibited survival, proliferation, and invasion of GBM and MB tumor micromasses. We further developed innovative brain and cerebellum organotypic models to monitor treatment response over time. It confirmed that ALK4-MMPp significantly impaired tumor progression, while no significant damage was observed on normal brain tissue. Lastly, we showed that ALK4-MMPp was well-tolerated in vivo by zebrafish embryos. This study provides a new strategy to control the activation of alkoxyamines, and revealed the bioconjugate ALK4-MMPp bioconjugate as a good anticancer drug candidate.

Novel MRI deformation-heterogeneity radiomic features are associated with molecular subgroups and overall survival in pediatric medulloblastoma: Preliminary findings from a multi-institutional study.

Medulloblastoma (MB) is a malignant, heterogenous brain tumor. Advances in molecular profiling have led to identifying four molecular subgroups of MB (WNT, SHH, Group 3, Group 4), each with distinct clinical behaviors. We hypothesize that (1) aggressive MB tumors, growing heterogeneously, induce pronounced local structural deformations in the surrounding parenchyma, and (b) these local deformations as captured on Gadolinium (Gd)-enhanced-T1w MRI are independently associated with molecular subgroups, as well as overall survival in MB patients. In this work, a total of 88 MB studies from 2 institutions were analyzed. Following tumor delineation, Gd-T1w scan for every patient was registered to a normal age-specific T1w-MRI template via deformable registration. Following patient-atlas registration, local structural deformations in the brain parenchyma were obtained for every patient by computing statistics from deformation magnitudes obtained from every 5mm annular region, 0 < d < 60 mm, where d is the distance from the tumor infiltrating edge. Multi-class comparison via ANOVA yielded significant differences between deformation magnitudes obtained for Group 3, Group 4, and SHH molecular subgroups, observed up to 60-mm outside the tumor edge. Additionally, Kaplan-Meier survival analysis showed that the local deformation statistics, combined with the current clinical risk-stratification approaches (molecular subgroup information and Chang's classification), could identify significant differences between high-risk and low-risk survival groups, achieving better performance results than using any of these approaches individually. These preliminary findings suggest there exists significant association of our tumor-induced deformation descriptor with overall survival in MB, and that there could be an added value in using the proposed radiomic descriptor along with the current risk classification approaches, towards more reliable risk assessment in pediatric MB.

TMIC-81. INCREASED LEVEL OF IGFBP2 PROMOTES TUMOR METASTASIS IN SHH MEDULLOBLASTOMA

Abstract Medulloblastoma (MB) is the most common pediatric brain malignancy. MB comprises 5 major subgroups known as WNT, SHH p53wt, SHH p53mut, Group 3 and Group 4. Among the four MB subgroups SHH group is the most dominant molecular subgroup in infants and adults. These tumors are proposed to arise from cerebellar granule neuron precursors (CGNPs), whose developmental expansion requires SHH signaling from the neighboring Purkinje neurons. Previous reports suggest that SHH group features a unique tumor microenvironment compared with other MB groups. To better understand how SHH MB cells interact with Tumor Microenvironment, we performed cytokine array analysis of culture media from SHH group Patient Tumor cells, spontaneous SHH MB mouse tumor cells and SHH MB cell lines. Further, confirmed these results using ELISA, Western blot, and immunofluorescence from human SHH MB cell lines, Smo/A1 mouse tumor primary cells and PZp53Med cell lines. In continuation to the observation of IGFBP2 expression in various cell types in single cell analysis, we analyzed the presence of IGFBP2 in astrocytes using Smo/A1 mouse tumor Immunohistochemistry. Our data showed increased levels of IGFBP2 produced by SHH MB cell lines compared to others. We analyzed the role of IGFBP2 in SHH MB tumor growth and metastasis. IGFBP2 knock-down stable cell lines showed phenotypic changes including reduced cell proliferation, cell migration and EMT. Further western blot analysis of IGFBP2 KD cells showed reduced expression of EMT markers also reduced the activation of STAT3. Our preliminary in vitro data suggest IGFBP2 exerts it metastasis-promoting role in SHH MB by regulating the expression of EMT marker proteins and matrix remodeling proteins. Further functional studies suggest that in SHH MB, IGFBP2 may regulate a STAT3-mediated EMT program to metastasize. These findings provide a strong rationale for further pursuing how IGFBP2 promotes medulloblastoma tumor cell growth and migration in vivo.

MODL-33. AN ANIMAL MODEL OF GLI2-AMPLIFIED MEDULLOBLASTOMA

Abstract Medulloblastoma (MB) is the most common malignant brain tumor affecting children. Among the known subtypes of MB, GLI2-amplified SHH-MB associated with P53 mutations has the worst prognosis, and a 5-year survival rate of less than 30%. Moreover, GLI2-amplified MBs are non-responsive to SMO inhibitors, the only targeted treatment option available for SHH-MB. To address this treatment gap, there is an urgent need to identify novel potential therapeutic targets, an effort that requires better understanding of key cellular and molecular mechanisms underlying GLI2-amplified MB. To that end, we generated a mouse model of GLI2-amplified MB and identified GL12 as the critical driver of tumorigenesis, and granule cell progenitors (GCPs) as the cells of tumor origin. We further found that GLI2 specifically drives embryonic, but not neonatal, Math1+ GCPs to form SHH-MB tumors. An scRNA-seq analysis revealed MAPK pathway activation specifically in embryonic Math1+ GCPs. The MAPK pathway was activated in mouse and human GLI2-driven MB tumors, and a MEK/ERK inhibitor significantly inhibited GLI2-driven MB in vivo. Based on these findings, we hypothesize that GLI2-driven MB originates from a specific population of Math1+ GCPs during a discrete temporal interval in cerebellar development, and that targeting MAPK/MEK/ERK pathway components represents a novel approach to treatment of GLI2-amplified MB.

EPCO-35. THE ZINC FINGER IN THE CEREBELLUM (ZIC1/4) LOCUS IS A CONTEXT DEPENDENT DRIVER GENE IN MEDULLOBLASTOMA

Abstract Medulloblastoma (MB) is a malignant paediatric brain tumor comprised of 4 molecularly and clinically distinct subgroups: WNT, SHH, Group 3 and Group 4. Previous studies have reported recurrent, mutually exclusive epigenetic modifier mutations converging in these subgroups, as well as aberrant H3K27me3 depositions within these tumors. While these observations hint at aberrant epigenetic mechanisms driving MB pathobiology, detailed understanding of MB chromatin landscape remains elusive to date. As such, chromatin landscape of MB was defined by conducting H3K27Ac ChIP-Seq in 102 primary MB tumors and H3K27me3 ChIP-Seq in 63 overlapping tumors. Chromatin landscape of Medulloblastoma was subgroup specific and H3K27me3 modification recurrently repressed ZIC1 in Group 3 and 4 MB, a driver gene that is also recurrently mutated within Group 4 and SHH MB. Validation cohort comprised of 251 MB samples with matching RNA-Seq and WGS data demonstrated that the ZIC1 - ZIC4 locus (ZIC1/4) undergoes recurrent epigenetic repression of single alleles in 25% of Group 3, 50% of Group 4 but rarely in other subgroups. Strikingly, ZIC1 mutations in the Group 4 tumors always occurred in the context of repression of the wildtype allele, revealing a recurrent convergence of genetic and epigenetic mechanisms targeting both copies of ZIC1. Overexpression of ZIC1 and ZIC4 together, or ZIC1 alone to a lesser extent, lead to reduced proliferation of Group 3 MB cells in vitro and in vivo. Intriguingly, while Group 4 ZIC1 mutations exhibited loss of function phenotypes, SHH ZIC1 mutations exhibited gain of function phenotypes. Overexpression of ZIC1 in Granule Progenitor Cells (GPC), which give rise to SHH MB, resulted in increased proliferation of cells in contrast to Group 3 MB cells. Taken together, we demonstrate that multiple epigenetic and genetic mechanisms converge to govern context dependent driver roles for ZIC1 and ZIC4 underlying MB pathobiology.

DDDR-31. THE THERAPEUTIC POTENTIAL OF THE LONG NON-CODING RNA LNC-HLX-2-7 IN GROUP 3 MEDULLOBLASTOMAS IN CHILDREN

Abstract Medulloblastoma (MB) is an aggressive brain tumor that predominantly affects children. Recent high-throughput sequencing studies suggest that the non-coding RNA genome, in particular long non-coding RNAs (lncRNAs), contributes to MB formation and tumor progression. Here we report the identification of a novel lncRNA, lnc-HLX-2-7, as a potential therapeutic target in group 3 MBs. In this study, we report that lnc-HLX-2-7 RNA specifically accumulates in the HLX (host gene of lnc-HLX-2-7) promoter region and activates HLX expression by recruiting multiple factors including enhancer elements. RNA sequencing and chromatin immunoprecipitation revealed that HLX directly binds to the promoters of several tumor-promoting genes, including MYC, and activates their expression. Furthermore, intravenous treatment with antisense oligonucleotides targeting lnc-HLX-2-7 coated with cerium-oxide nanoparticle (CNP-lnc-HLX-2-7) reduced tumor growth (40-50%) in intracranial MB xenograft mouse model (n = 10, p &amp;lt; 0.01, t-test). We found that the combinatorial therapy of CNP-lnc-HLX-2-7 and cisplatin further inhibits tumor growth and significantly prolongs mouse survival compared to CNP-lnc-HLX-2-7 monotherapy (n = 10, p &amp;lt; 0.01, t-test) only. We report here the importance of the lnc-HLX-2-7-HLX-MYC axis in regulating group 3 MB progression and provide a strong rationale for using lnc-HLX-2-7 as a specific and potent therapeutic target for the group 3 MBs in children.

Complement C3a activates astrocytes to promote medulloblastoma progression through TNF-α

BackgroundMedulloblastoma (MB) is the most common malignant brain tumor in children. Approximately one-third of MB patients remain incurable. Understanding the molecular mechanism of MB tumorigenesis is, therefore, critical for developing specific and effective treatment strategies. Our previous work demonstrated that astrocytes constitute the tumor microenvironment (TME) of MB and play an indispensable role in MB progression. However, the underlying mechanisms by which astrocytes are regulated and activated to promote MB remain elusive.MethodsBy taking advantage of Math1-Cre/Ptch1loxp/loxp mice, which spontaneously develop MB, primary MB cells and astrocytes were isolated and then subjected to administration and coculture in vitro. Immunohistochemistry was utilized to determine the presence of C3a in MB sections. MB cell proliferation was evaluated by immunofluorescent staining. GFAP and cytokine expression levels in C3a-stimulated astrocytes were assessed by immunofluorescent staining, western blotting, q-PCR and ELISA. C3a receptor and TNF-α receptor expression was determined by PCR and immunofluorescent staining. p38 MAPK pathway activation was detected by western blotting. Transplanted MB mice were treated with a C3a receptor antagonist or TNF-α receptor antagonist to investigate their role in MB progression in vivo.ResultsWe found that complement C3a, a fragment released from intact complement C3 following complement activation, was enriched in both human and murine MB tumor tissue, and its receptor was highly expressed on tumor-associated astrocytes (TAAs). We demonstrated that C3a activated astrocytes and promoted MB cell proliferation via the p38 MAPK pathway. Moreover, we discovered that C3a upregulated the production of proinflammatory cytokines, such as IL-6 and TNF-α in astrocytes. Application of the conditioned medium of C3a-stimulated astrocytes promoted MB cell proliferation, which was abolished by preincubation with a TNF-α receptor antagonist, indicating a TNF-α-dependent event. Indeed, we further demonstrated that administration of a selective C3a receptor or TNF-α receptor antagonist to mice subcutaneously transplanted with MB suppressed tumor progression in vivo.ConclusionsC3a was released during MB development. C3a triggered astrocyte activation and TNF-α production via the p38 pathway, which promoted MB cell proliferation. Our findings revealed the novel role of C3a-mediated TNF-α production by astrocytes in MB progression. These findings imply that targeting C3a and TNF-α may represent a potential novel therapeutic approach for human MB.

Abstract 6050: JMJD6 regulates super-enhancer mediated transcriptional dependencies in group 3 medulloblastoma

Abstract Medulloblastoma (MB) is a heterogenous cerebellar tumor that comprises four molecular and clinically significant subgroups. MB is the most common brain malignancy in children with a five-year survival of 70%, however, Group 3 MB patients have the poorest survival due to the amplification of MYC and overexpression of key oncogenes that underly the Group 3 phenotype. Recently, epigenetic modifications bearing super-enhancer, H3K27ac, marks have been suggested to contribute to transcriptional dependencies that define Group 3 MB and represents an emerging target for therapeutic intervention. Currently, the mechanism that establishes and maintains these modifications to the DNA architecture remains unclear. In our study, we hypothesize that an epigenetic modifying protein, JMJD6, regulates the promoter-pause release associated with super-enhancer mediated oncogene addiction in Group 3 MB. This hypothesis is based on evidence in the literature showing that JMJD6 regulates the transcriptional pause release at enhancer regions. Moreover, the promoter-pause release has been shown to be critical for super-enhancer mediated transcription. In our preliminary studies, we demonstrate elevated levels of JMJD6 in Group 3 MB and survival analysis indicating JMJD6 as a predictor for poor prognosis in MB patients. Immunoprecipitation revealed that JMJD6 forms complexes with proteins involved in maintaining and regulating the promoter-pause at super-enhancers. Inducible knockdown of JMJD6 decreased MYC expression, cellular proliferation and stemness in vitro while inhibiting tumor formation and promoting survival in mice. Together, these studies identify JMJD6 as a promising therapeutic target for treating aggressive epigenetically driven Groups 3 MB tumors. Citation Format: Matthew Kling, Sutapa Ray, Don W. Coulter, Nagendra Chaturvedi. JMJD6 regulates super-enhancer mediated transcriptional dependencies in group 3 medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6050.

MEDB-39. Oncogenic mechanisms underlying GLI2-amplified medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor in children. There are several subtypes of MB, and among them, the subtype of GLI2-amplified SHH-MB associated with P53 mutations has the worst prognosis and a poor survival rate; the 5-year survival rate is <30%. Moreover, the GLI2-amplified MBs are non-responsive to the only targeted treatment option available for SHH-MB, the SMO inhibitors. This leaves an unmet critical treatment gap, and there is an urgent need to identify novel targets to develop effective therapeutics. However, a deeper understanding of the cellular and molecular mechanisms driving GLI2-amplified MB tumorigenesis is currently lacking. With a focused goal to resolve this particular type of MB tumorigenesis, we recently generated an engineered mouse model of GLI2-driven MB. Using this model, we demonstrated that GLI2 is the critical driver of tumorigenesis and identified granule cell progenitors (GCPs) as the cells of origin. Interestingly, we have also found that GLI2 drives only Math1+ embryonic GCPs but not neonatal GCPs to form SHH-MB. Correspondingly, our scRNA-seq analysis revealed that the MAPK pathway is specifically enriched in embryonic but not neonatal Math1+ GCPs. Moreover, the MAPK pathway is activated in mouse and human GLI2-driven MB tumors, and a MEK/ERK inhibitor significantly delayed the growth of GLI2-driven MB in vivo. Based on these exciting results, we hypothesize that GLI2-driven MB originates from a specific cell population of Math1+ GCPs and in a particular spatiotemporal window during cerebellar development, and targeting MAPK/MEK/ERK pathway may represent a novel effective approach to treating GLI2-amplified MB.

MEDB-90. Iron Imbalance Can Potentiate Cisplatin Response in Pediatric Medulloblastoma by Regulating Ferroptosis

Medulloblastoma (MB), the most common malignant pediatric brain tumor, is a leading cause of childhood mortality. Of the four primary subgroups, patients with group 3 tumors have the poorest prognosis. Loss of chromosome 17p is a high-risk feature associated with poor outcomes in group 3 tumors. We recently elucidated the tumor suppressive properties of a novel miR, miR-1253, on the terminal end of 17p. In further exploring its anti-neoplastic effects, we discovered that miR-1253 can disrupt iron homeostasis, causing oxidative stress and inducing lipid peroxidation. These concurrent events are capable of triggering an iron-mediated form of cell death called ferroptosis. Notably, our in silico interrogation of ferroptosis regulator genes (FRGs) in group 3 tumors revealed high expression of genes associated with iron transport and glutathione metabolism. These included mitochondrial iron transporters and GPX4, a critical regulator of ferroptosis. Restoration of miR-1253 expression in group 3 cell lines resulted in specific downregulation of ABCB7, an iron-sulfur cluster exporter, and GPX4. Consequently, cytosolic and mitochondrial labile iron pools rose, glutathione levels declined, and mitochondrial oxidative stress and lipid peroxidation were induced. These events were recapitulated by ABCB7 knockdown and potentiated cell death. Treating miR-1253-expressing cancer cells with cisplatin, a group 3 MB chemotherapeutic agent with ferroptotic properties, further elevated oxidative stress, depleted glutathione levels, and augmented lipid peroxidation, with added inhibitory effects on cell viability and colony formation. Treatment with a ferroptosis inhibitor (ferrostatin-1) lead to recovery from the cytotoxic effects of this combination therapy. Our studies highlight a novel mechanism for group 3 MB pathogenesis via ferroptosis regulation and provide a proof-of-concept for exploiting group 3 MB tumor vulnerability to iron imbalance as a novel treatment strategy.

Protocols to Manufacture an Oncolytic Measles Virus-Sensitive Immunocompetent Mouse Model of Medulloblastoma.

Oncolytic virotherapy translational research in the current era is heavily focused on the interaction of the immune system and tumor microenvironment with oncolytic viruses. Preclinical xenograft studies using human cells in immunodeficient mouse models does not serve this purpose. As a consequence, developing syngeneic immunocompetent murine cancer models sensitive to infection and growth of specific oncolytic viruses is required. The group 3 subtype of medulloblastoma, among the four molecular subgroups-WNT, SHH, Group 3, and Group 4, has the worst prognosis and the poorest outcome. Sadly, current treatments cause long-term toxicity and morbidity to survivors adversely affecting their quality of life. Alternate effective therapy with less side effects is urgently needed. We have shown that oncolytic measles virus (MV) is effective against localized as well as CSF-disseminated medulloblastoma in immunodeficient mouse models. To study the interaction of immune system with oncolytic measles virotherapy, we have developed a murine group 3 medulloblastoma cell line (CSCG) that is infectible by MV, is killed by MV, allows replication of MV, and is tumorigenic in the brain of syngeneic transgenic immune-competent mice. Intratumoral injection of MV results in significant prolongation of survival in mice bearing CSCG tumors in the brain. This model provides the first suitable platform to examine therapeutic regimens of MV therapy for MB tumors in the presence of intact immune system. Here, we describe our lab protocols to develop this cell line and the mouse model.

CSIG-32. microRNA 211, A POTENTIAL THERAPEUTIC AGENT FOR GROUP 3 MEDULLOBLASTOMA IN CHILDREN

Abstract Medulloblastoma (MB) is a central nervous system (CNS) tumor that predominantly affects children and requires aggressive therapy. Affected individuals often suffer from treatment-related side-effects and treatment-resistant recurrences associated with high morbidity and mortality rates. There are four major molecular MB subgroups: wingless-type (Wnt)-activated, sonic hedgehog (Shh)-activated, group III (G3), and group IV (G4) MBs. While the molecular pathology of Wnt- and Shh-activated MBs is well defined, rather less is known about G3 and G4 MB's genetic basis, so their molecular diagnosis and consequent management have remained challenging. MBs develop through various genetic, epigenetic, and non-coding (nc)RNA-related mechanisms, with the role of ncRNAs, particularly microRNAs, in MB tumor growth is poorly defined. We addressed this knowledge gap with an exemplar of microRNA-211 (miR-211) implicated in G3 MB tumor growth. Compared to other MB subgroups, miR-211 is significantly downregulated in G3 MB cell lines, underscoring its important role as a therapeutic agent and a biomarker. miR-211 overexpression in G3 MB cells significantly reduced cell proliferation, invasion, 3D colony formation, and induced apoptosis. Oxygen consumption rates are higher in engineered cells, and we postulate that miR-211 is involved in G3 MB mitochondrial energy metabolism. miR-211 expressed G3 MB cells injected into mouse cerebella produce smaller tumors than those derived from parental cells. We applied single-cell RNA sequencing and immune histochemical assays to characterize tumors to identify the molecular mechanism of miR-211- driven tumor reduction in G3 MBs, and our preliminary results support that miR-211 is an attractive therapeutic agent to treat this aggressive MB subtype.

Disruption of rack1 suppresses SHH-type medulloblastoma formation in mice.

IntroductionMedulloblastoma (MB) is a malignant pediatric brain tumor that arises in the cerebellar granular neurons. Sonic Hedgehog subtype of MB (SHH‐MB) is one of the major subtypes of MB in the clinic. However, the molecular mechanisms underlying MB tumorigenesis are still not fully understood.AimsOur previous work demonstrated that the receptor for activated C kinase 1 (Rack1) is essential for SHH signaling activation in granule neuron progenitors (GNPs) during cerebellar development. To investigate the potential role of Rack1 in MB development, human MB tissue array and SHH‐MB genetic mouse model were used to study the expression of function of Rack1 in MB pathogenesis.ResultsWe found that the expression of Rack1 was significantly upregulated in the majority of human cerebellar MB tumors. Genetic ablation of Rack1 expression in SHH‐MB tumor mice could significantly inhibit MB proliferation, reduce the tumor size, and prolong the survival of tumor rescue mice. Interestingly, neither apoptosis nor autophagy levels were affected in Rack1‐deletion rescue mice compared to WT mice, but the expression of Gli1 and HDAC2 was significantly decreased suggesting the inactivation of SHH signaling pathway in rescue mice.ConclusionOur results demonstrated that Rack1 may serve as a potential candidate for the diagnostic marker and therapeutic target of MB, including SHH‐MB.

OMIC-04. IDENTIFICATION AND CHARACTERIZATION OF CIRCULATING RNAS (CODING AND NONCODING) AND METABOLITES IN CEREBROSPINAL FLUID IN MEDULLOBLASTOMA PATIENTS

Medulloblastoma (MB) is the most common malignant brain tumor in children, and monitoring patients for treatment response and recurrence can be challenging with available current technologies in neuro-imaging and performing a biopsy to confirm response or recurrence carries risks, whereas cerebrospinal fluid (CSF) can be obtained with a little invasiveness. MB has altered cellular metabolism due to changes in gene expression, therefore, we hypothesized that any changes in MB cells lead to changes in cell-free transcripts and metabolites in CSF. To test this, we applied RNA-sequencing and mass spectrometry to analyze transcripts and metabolites including lipid in CSF from patients with different sub-groups of MB tumors (i.e., WNT, SHH, G3/4, G4, and unknown) and compared them to non-cancerous CSF. Tumor and sub-group specific transcriptomic and metabolic signatures were shown by unsupervised hierarchical clustering facilitating tumor type differentiation. By comparison with previously published tumor tissue RNA-seq data, we were able to identify a group of upregulated molecular signatures in both tumor tissue and CSF. We also identified a group of lipids that differentiate each MB sub-group from normal CSF, and Pathway analysis confirmed alterations in multiple metabolic pathways. Finally, we attempted to integrate RNA-seq data with lipidomics data, and results depict that the combinatorial analysis of CSF RNAs and metabolites can be useful in diagnosing and monitoring patients with MB tumors. (This research was conducted using samples made available by The Children’s Brain Tumor Network.)

EMBR-02. OLIG2 REPRESENTS A PROGNOSTIC MARKER AND THERAPEUTIC TARGET IN MYC-AMPLIFIED MEDULLOBLASTOMA RELAPSE AND METASTASIS

Medulloblastoma (MB) is one of the most common malignant pediatric brain tumors. Among the multiple MB subtypes, MB with MYC amplification confers an extremely poor prognosis with an overall survival rate of less than 30%. Relapse is often mediated by a small population of therapy-resistant tumor cells which expand and ultimately progress to lethal tumors. Moreover, MYC-amplified MB exhibits a high incidence of leptomeningeal metastases. Approximately one-third of patients with MYC-amplified MB present with metastases and nearly all have this complication at relapse. Metastatic MYC-amplified MB is highly fatal. As such, our ability to effectively treat MYC-amplified MB is largely dependent on our capacity to eradicate the therapy resistant tumor cells, particularly the metastatic tumor cells. The development of clinically effective therapies for this disease will be facilitated by the identification of therapy-resistant tumor cell populations and their molecular signatures involved in tumor metastasis and relapse. Using patient-derived xenograft (PDX) mouse models, we recently discovered that a subset of MYC-amplified MB tumors with strong OLIG2 expression (OLIG2-high) is resistant to radiation and prone to metastasize, whereas MYC-amplified MB tumors without OLIG2 expression (OLIG2-low) are sensitive to radiation without dissemination. Irradiation of OLIG2-high tumors led to either a small number of quiescent OLIG2- cancer stem-like cells (CSLCs) remaining in the cerebellar bed or to the dissemination of highly proliferative OLIG2+ tumor cells along the leptomeninges. All mice harboring these radioresistant CSLCs succumbed to relapse. Further studies demonstrated that the quiescent OLIG2- CSLCs did not contribute to tumor recurrence directly, while elimination of OLIG2+ radioresistant CSLCs with a small molecule OLIG2 antagonist significantly prevented metastatic recurrence, delayed tumor growth and prolonged animal survival. Thus, our studies provide new insights into the role of OLIG2 in radiotherapy resistance and metastasis in MYC-amplified MB and propose a novel therapeutic approach to treating metastatic MYC-amplified MB.

BIOL-06. MIR-1253 POTENTIATES CISPLATIN RESPONSE IN PEDIATRIC GROUP 3 MEDULLOBLASTOMA BY REGULATING FERROPTOSIS

Medulloblastoma (MB), the most common malignant pediatric brain tumor and a leading cause of childhood mortality, is stratified into four primary subgroups, i.e. SHH (sonic hedgehog), WNT (wingless), and non-SHH/WNT groups 3 and 4, the latter representing high-risk MB. Haploinsufficiency of 17p13.3, which houses the tumor suppressor gene miR-1253, characterizes high-risk tumors. Despite improvements in targeted therapies, a limited proportion of these patients survive the disease. Capitalizing on the tumor suppressive properties of miRNAs as adjuncts to chemotherapy provides a promising alternative to current therapeutic strategies. In this study, we explored the potentiating effects of miR-1253 on cisplatin cytotoxicity in group 3 MB. First, in silico and in vitro analyses revealed an upregulation of ABCB7, a mitochondrial iron transporter and putative target of miR-1253, in MB cell lines and group 3 MB tumors. Overexpression of miR-1253 resulted in downregulation of ABCB7 and GPX4, a critical ferroptosis regulator, which consequently increased labile mitochondrial iron pool and, in turn, mitochondrial ROS (mtROS). Complementarily, we demonstrated, using CRISPR knockdown of ABCB7, ferroptosis induction with downregulation of GPx4 expression, liberation of free iron, mtROS generation and lipid peroxidation. Cisplatin is reported as an inducer of both apoptosis and ferroptosis-mediated cancer cell death. Therapeutically, the combination of miR-1253 and cisplatin led to an additive effect on cell viability, colony formation, apoptosis, and ROS generation. In turn, treatment with mtROS inhibitor (MnTBAP) and ferroptosis inhibitor (Ferrostatin) lead to partial recovery from the cytotoxic effects of this combination therapy. These studies identify an miR-1253-induced ferroptosis pathway targeting the ABCB7/GPX4/mtROS axis in group 3 MB. They further provide proof-of-concept in using miR-based therapeutics to augment treatment efficacy of current chemotherapeutics in the treatment of high-risk tumors.

OMIC-05. PHOSPHOPROTEOMIC ANALYSIS IDENTIFIES SUBGROUP ENRICHED PATHWAYS AND KINASE SIGNATURES IN MEDULLOBLASTOMA

Medulloblastoma (MB) is classified into four molecular subgroups: wingless (WNT), sonic hedgehog (SHH), Group 3 (G3) and Group 4 (G4), each with different molecular profiles and patient outcomes. Subgroup heterogeneity and low mutational burdens have hindered the identification of actionable therapeutic targets, especially in G3 MB which has a particularly poor prognosis. Therefore, we took a (phospho)-proteomics approach to identify active pathways and potential therapeutic opportunities in twenty orthotopic patient-derived xenograft (PDX) models of MB comprising SHH, G3 and G4 subtypes. Through our enrichment analysis, we identified processes and pathways specifically upregulated in each MB subgroup. We also utilized neural network derived kinase-substrate predictions and kinase activity scores inferred by a heuristic machine learning algorithm to further characterize phosphosignaling activity. We found that MB PDX models recapitulate many features of primary MB tumors including two distinct proteomic subtypes of G3. G3a was enriched for transcription, translation and MYC target genes while G3b was enriched for axon guidance and neurotrophin signaling pathways. Notably, both G3a and G3b contained higher abundance of mitochondrial proteins, suggesting altered tumor metabolism in G3 MB. SHH PDXs displayed increased NFκB and JNK-MAPK signaling. Group 4 MBs most closely resembled differentiated neuronal cells and were enriched for PKC and AMPK signaling as well as DNA repair pathways. In conclusion, we have provided a comprehensive proteomic and phosphoproteomic characterization of commonly studied MB PDX models and revealed new insights into subgroup enriched pathways and kinase activity in MB.

EMBR-30. A NOVEL PLK1 INHIBITOR ONVANSERTIB EFFECTIVELY SENSITIZES GROUP 3 MEDULLOBLASTOMA TO RADIOTHERAPY

Abstract Medulloblastoma (MB) is often accompanied by MYC amplification. PLK1 is an oncogenic kinase that controls cell cycle and proliferation, and it has been preclinically validated as a cancer therapeutic target. Onvansertib (PCM-075) is a novel, orally available PLK1 inhibitor, which shows tumor growth inhibition in many types of cancer. We examined the effect of Onvansertib on MYC-driven medulloblastoma as a monotherapy or in combination with radiation. A Crisper-Cas9 screen was used to discover essential genes for MB tumor growth. Microarray and immunohistochemistry on pediatric patient samples were performed to examine the expression of PLK1. The effect of Onvansertib in vitro was measure by cell viability, colony-forming assays, extreme limiting dilution assay, and RNA-Seq. ALDH activity, cell-cycle distribution, and apoptosis were analyzed by flow cytometry. DNA damage was assessed by immunofluorescence staining. Medulloblastoma xenografts were generated to explore the monotherapy or radio-sensitizing effect. PLK1 is overexpressed in Group 3 MB. The IC50 concentrations of Onvansertib in Group 3 MB cell lines were between 4.9 and 6 nM. Onvansertib reduced colony formation, cell proliferation, stem cell renewal, and induced G2/M arrest in vitro. Moreover, Onvansertib in combination with radiation increased DNA damage and apoptosis compared with radiation alone. The combination of Onvansertib with radiotherapy resulted in marked tumor regression in orthotopic xenografts. These findings suggest that Onvansertib is an effective strategy in combination with radiotherapy in MB.

Expression of Myoglobin in Normal and Cancer Brain Tissues: Correlation With Hypoxia Markers.

BackgroundMyoglobin (MB) is increasingly recognized as a key player in cancer growth and metastasis. Low oxygen tensions, commonly associated with highly aggressive and recurrent cancers, have been shown to regulate its expression in several cancers such as lung, neck, prostate and breast cancer. However, it is not yet known whether it contributes to the growth and spread of brain cancers especially Glioblastoma multiforme (GBM).MethodsHere we investigate the expression of MB, and its correlation with the hypoxia markers carbonic anhydrase IX (CAIX) and lactate dehydrogenase A (LDHA), in human tissue microarrays of multiple organ tumors, brain tumors, and GBM tumors, and their respective cancer-adjacent normal tissues. Correlation between MB protein expression and tumor grade was also assessed.ResultsWe show that MB protein is expressed in a wide variety of cancers, benign tumors, cancer-adjacent normal tissues, hyperplastic tissue samples and normal brain tissue, and low oxygen tensions modulate MB protein expression in different brain cancers, including GBM. Enhanced nuclear LDHA immune-reactivity in GBM was also observed. Finally, we report for the first time a positive correlation between MB expression and brain tumor grade.ConclusionOur data suggest that hypoxia regulate MB expression in different brain cancers (including GBM) and that its expression is associated with a more aggressive phenotype as indicated by the positive correlation with the brain tumor grade. Additionally, a role for nuclear LDHA in promoting aggressive tumor phenotype is also suggested based on enhanced nuclear expression which was observed only in GBM.

Abstract PO-009: Targeting a unique electrochemical vulnerability in a pediatric brain tumor to potentiate proton beam radiotherapy

Abstract Medulloblastoma (MB) is the most common malignant (WHO Grade IV) primary brain cancer in children, adolescents, and young adults. Radiotherapy (RT) is a mainstay of MB treatment, as it is for most childhood and adult cancers. RT dose and frequency needed to achieve efficacy in MB patients severely impacts survival outcomes and is the cause of long-term cognitive deficits. To improve on short-term side effects and long-term complications, scanning beam proton therapy is employed, when available. While this recent technological advance significantly reduces damage to surrounding healthy brain tissue, survivors continue to experience induced radiation damage, including neurocognitive sequelae. To impact survivors’ health-related quality of life and caregivers’ emotional and financial burden, it is critical to identify approaches that reduce RT dose to mitigate side-effects without impacting RT effectiveness. We are investigating targeting a unique MB electrochemical vulnerability as a means to sensitize MB tumor cells to RT. There are four MB molecular subgroups: wingless, sonic-hedgehog, Group 3, and Group 4. Our analysis of 763 MB tumor transcriptomes reveals that all Group 3 MB tumors share an enhanced expression of genes-coding for subunits of the Type-A GABA receptor (GABAAR), a chloride channel. Using patch-clamp electrophysiology, we found that GABAARs conduct Cl− in MB cells and that a brain-penetrant benzodiazepine (BZ) enhances this effect and triggers cytotoxic responses commensurate with mitochondrial depolarization. We find that BZ combined with RT, even at a sub-lethal dose, is highly effective in impairing the viability of MB tumor cells, greater than RT alone. Our BZis capable of penetrating the blood-brain barrier in minutes, is metabolically stable, and showed no toxicity in a primate model. We are investigating its suitability to be used concomitant with proton beam radiotherapy, replacing standard of care vincristine, to reduce radiation-induced brain toxicity experienced by MB patients and survivors while not decreasing RT effectiveness. Citation Format: Daniel Pomeranz Krummel, Laura Kallay, Debanjan Bhattacharya, Vaibhavkumar Gawali, Kamdem T. Donatien, Taukir Ahmed, James M. Cook, Michael Lamba, Susanne Wells, Ralph E. Vatner, Mathieu Sertorio, Dan T. Ionascu, Soma Sengupta. Targeting a unique electrochemical vulnerability in a pediatric brain tumor to potentiate proton beam radiotherapy [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-009.