Publications by authors named "Rintaro Hashizume"

59 Publications

Therapeutic targeting of transcriptional elongation in diffuse intrinsic pontine glioma.

Neuro Oncol 2021 Jan 20. Epub 2021 Jan 20.

Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.

Background: DIPG is associated with transcriptional dysregulation driven by H3K27 mutation. The super elongation complex (SEC) is required for transcriptional elongation through release of RNA polymerase II (Pol II). Inhibition of transcription elongation by SEC disruption can be an effective therapeutic strategy of H3K27M-mutant diffuse intrinsic pontine glioma (DIPG). Here, we tested the effect of pharmacological disruption of the SEC in H3K27M-mutant DIPG to advance understanding of the molecular mechanism and as a new therapeutic strategy for DIPG.

Methods: Short hairpin RNAs (shRNAs) were used to suppress the expression of AF4/FMR2 4 (AFF4), a central SEC component, in H3K27M-mutant DIPG cells. A peptidomimetic lead compound KL-1 was used to disrupt a functional component of SEC. Cell viability assay, colony formation assay, and apoptosis assay were utilized to analyze the effects of KL-1 treatment. RNA- and ChIP-sequencing were used to determine the effects of KL-1 on gene expression and chromatin occupancy. We treated mice bearing human H3K27M-mutant DIPG xenografts with KL-1. Intracranial tumor growth was monitored by bioluminescence image and therapeutic response was evaluated by animal survival.

Results: Depletion of AFF4 significantly reduced the cell growth of H3K27M-mutant DIPG. KL-1 increased genome-wide Pol II occupancy and suppressed transcription involving multiple cellular processes that promote cell proliferation and differentiation of DIPG. KL-1 treatment suppressed DIPG cell growth, increased apoptosis, and prolonged animal survival with human H3K27M-mutant DIPG xenografts.

Conclusions: SEC disruption by KL-1 increased therapeutic benefit in vitro and in vivo, supporting a potential therapeutic activity of KL-1 in H3K27M-mutant DIPG.
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http://dx.doi.org/10.1093/neuonc/noab009DOI Listing
January 2021

Mesenchymal Stem Cells Successfully Deliver Oncolytic Virotherapy to Diffuse Intrinsic Pontine Glioma.

Clin Cancer Res 2021 Mar 3;27(6):1766-1777. Epub 2020 Dec 3.

Department of Neurological Surgery, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.

Purpose: Diffuse intrinsic pontine glioma (DIPG) is among the deadliest of pediatric brain tumors. Radiotherapy is the standard-of-care treatment for DIPG, but offers only transient relief of symptoms for patients with DIPG without providing significant survival benefit. Oncolytic virotherapy is an anticancer treatment that has been investigated for treating various types of brain tumors.

Experimental Design: Here, we have explored the use of mesenchymal stem cells (MSC) for oncolytic virus (OV) delivery and evaluated treatment efficacy using preclinical models of DIPG. The survivin promoter drives the conditional replication of OV used in our studies. The efficiency of OV entry into the cells is mediated by fiber modification with seven lysine residues (CRAd.S.pK7). Patients' samples and cell lines were analyzed for the expression of viral entry proteins and survivin. The ability of MSCs to deliver OV to DIPG was studied in the context of a low dose of irradiation.

Results: Our results show that DIPG cells and tumors exhibit robust expression of cell surface proteins and survivin that enable efficient OV entry and replication in DIPG cells. MSCs loaded with OV disseminate within a tumor and release OV throughout the DIPG brainstem xenografts in mice. Administration of OV-loaded MSCs with radiotherapy to mice bearing brainstem DIPG xenografts results in more prolonged survival relative to that conferred by either therapy alone ( < 0.01).

Conclusions: Our study supports OV, CRAd.S.pK7, encapsulated within MSCs as a therapeutic strategy that merits further investigation and potential translation for DIPG treatment.
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http://dx.doi.org/10.1158/1078-0432.CCR-20-1499DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7956061PMC
March 2021

Senescence Induced by BMI1 Inhibition Is a Therapeutic Vulnerability in H3K27M-Mutant DIPG.

Cell Rep 2020 10;33(3):108286

Department of Pediatrics and Section of Pediatric Hematology/Oncology/BMT, University of Colorado Denver, Anschutz Medical Campus, Aurora, CO, USA; The Morgan Adams Foundation Pediatric Brain Tumor Research Program, Children's Hospital Colorado, Aurora, CO, USA.

Diffuse intrinsic pontine glioma (DIPG) is an incurable brain tumor of childhood characterized by histone mutations at lysine 27, which results in epigenomic dysregulation. There has been a failure to develop effective treatment for this tumor. Using a combined RNAi and chemical screen targeting epigenomic regulators, we identify the polycomb repressive complex 1 (PRC1) component BMI1 as a critical factor for DIPG tumor maintenance in vivo. BMI1 chromatin occupancy is enriched at genes associated with differentiation and tumor suppressors in DIPG cells. Inhibition of BMI1 decreases cell self-renewal and attenuates tumor growth due to induction of senescence. Prolonged BMI1 inhibition induces a senescence-associated secretory phenotype, which promotes tumor recurrence. Clearance of senescent cells using BH3 protein mimetics co-operates with BMI1 inhibition to enhance tumor cell killing in vivo.
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http://dx.doi.org/10.1016/j.celrep.2020.108286DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7574900PMC
October 2020

LSD1 inhibition in pHGG: the key to unleashing immunotherapy?

Neuro Oncol 2020 09;22(9):1237-1238

Northwestern University, Chicago, Illinois.

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http://dx.doi.org/10.1093/neuonc/noaa171DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7523443PMC
September 2020

Convection-Enhanced Delivery of Enhancer of Zeste Homolog-2 (EZH2) Inhibitor for the Treatment of Diffuse Intrinsic Pontine Glioma.

Neurosurgery 2020 Jul 16. Epub 2020 Jul 16.

Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois.

Background: Diffuse intrinsic pontine glioma (DIPG) is a fatal childhood brain tumor and the majority of patients die within 2 yr after initial diagnosis. Factors that contribute to the dismal prognosis of these patients include the infiltrative nature and anatomic location in an eloquent area of the brain, which precludes total surgical resection, and the presence of the blood-brain barrier (BBB), which reduces the distribution of systemically administered agents. Convection-enhanced delivery (CED) is a direct infusion technique to deliver therapeutic agents into a target site in the brain and able to deliver a high concentration drug to the infusion site without systemic toxicities.

Objective: To assess the efficacy of enhancer of zeste homolog-2 (EZH2) inhibitor by CED against human DIPG xenograft models.

Methods: The concentration of EZH2 inhibitor (EPZ-6438) in the brainstem tumor was evaluated by liquid chromatography-mass spectrometry (LC/MS). We treated mice-bearing human DIPG xenografts with EPZ-6438 using systemic (intraperitoneal) or CED administration. Intracranial tumor growth was monitored by bioluminescence image, and the therapeutic response was evaluated by animal survival.

Results: LC/MS analysis showed that the concentration of EPZ-6438 in the brainstem tumor was 3.74% of serum concentration after systemic administration. CED of EPZ-6438 suppressed tumor growth and significantly extended animal survival when compared to systemic administration of EPZ-6438 (P = .0475).

Conclusion: Our results indicate that CED of an EZH2 inhibitor is a promising strategy to bypass the BBB and to increase the efficacy of an EZH2 inhibitor for the treatment of DIPG.
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http://dx.doi.org/10.1093/neuros/nyaa301DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7666886PMC
July 2020

Combined Therapy of AXL and HDAC Inhibition Reverses Mesenchymal Transition in Diffuse Intrinsic Pontine Glioma.

Clin Cancer Res 2020 07 12;26(13):3319-3332. Epub 2020 Mar 12.

Departments of Pediatric Oncology/Hematology, Cancer Center Amsterdam, Amsterdam University Medical Centers, Amsterdam, the Netherlands.

Purpose: Diffuse intrinsic pontine glioma (DIPG) is an incurable type of pediatric brain cancer, which in the majority of cases is driven by mutations in genes encoding histone 3 (H3K27M). We here determined the preclinical therapeutic potential of combined AXL and HDAC inhibition in these tumors to reverse their mesenchymal, therapy-resistant, phenotype.

Experimental Design: We used public databases and patient-derived DIPG cells to identify putative drivers of the mesenchymal transition in these tumors. Patient-derived neurospheres, xenografts, and allografts were used to determine the therapeutic potential of combined AXL/HDAC inhibition for the treatment of DIPG.

Results: We identified AXL as a therapeutic target and regulator of the mesenchymal transition in DIPG. Combined AXL and HDAC inhibition had a synergistic and selective antitumor effect on H3K27M DIPG cells. Treatment of DIPG cells with the AXL inhibitor BGB324 and the HDAC inhibitor panobinostat resulted in a decreased expression of mesenchymal and stem cell genes. Moreover, this combination treatment decreased expression of DNA damage repair genes in DIPG cells, strongly sensitizing them to radiation. Pharmacokinetic studies showed that BGB324, like panobinostat, crosses the blood-brain barrier. Consequently, treatment of patient-derived DIPG xenograft and murine DIPG allograft-bearing mice with BGB324 and panobinostat resulted in a synergistic antitumor effect and prolonged survival.

Conclusions: Combined inhibition of AXL and HDACs in DIPG cells results in a synergistic antitumor effect by reversing their mesenchymal, stem cell-like, therapy-resistant phenotype. As such, this treatment combination may serve as part of a future multimodal therapeutic strategy for DIPG.
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http://dx.doi.org/10.1158/1078-0432.CCR-19-3538DOI Listing
July 2020

MGMT Expression Contributes to Temozolomide Resistance in H3K27M-Mutant Diffuse Midline Gliomas.

Front Oncol 2019 21;9:1568. Epub 2020 Jan 21.

Department of Neurosurgery, Brain Research Institute, Niigata University, Niigata, Japan.

Diffuse midline gliomas (DMGs) show resistance to many chemotherapeutic agents including temozolomide (TMZ). Histone gene mutations in DMGs trigger epigenetic changes including DNA hypomethylation, one of which is a frequent lack of O6-methyl-guanine-DNA methyltransferase () promoter methylation, resulting in increased MGMT expression. We established the NGT16 cell line with K27M and G328E gene mutations from a DMG patient and used this cell line and other DMG cell lines with gene mutation (SF7761, SF8628, JHH-DIPG1) to analyze promoter methylation, MGMT protein expression, and response to TMZ. Three out of 4 DMG cell lines (NGT16, SF8628, and JHH-DIPG1) had unmethylated promoter, increased MGMT expression, and showed resistance to TMZ treatment. SF7761 cells with gene mutation showed promoter methylation, lacked MGMT expression, and sensitivity to TMZ treatment. NGT16 line showed response to ALK2 inhibitor K02288 treatment . We confirmed that MGMT expression contributes to TMZ resistance in DMG cell lines. There is an urgent need to develop new strategies to treat TMZ-resistant DMGs.
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http://dx.doi.org/10.3389/fonc.2019.01568DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6985080PMC
January 2020

Dramatic response of BRAF V600E-mutant epithelioid glioblastoma to combination therapy with BRAF and MEK inhibitor: establishment and xenograft of a cell line to predict clinical efficacy.

Acta Neuropathol Commun 2019 07 25;7(1):119. Epub 2019 Jul 25.

From the Departments of Neurosurgery, Niigata University, 1-757 Asahimachidori, Chuo-ku, Niigata, Japan.

Epithelioid glioblastoma is a rare aggressive variant of glioblastoma (GBM) characterized by a dismal prognosis of about 6 months and frequent leptomeningeal dissemination. A recent study has revealed that 50% of epithelioid GBMs harbor three genetic alterations - BRAF V600E mutation, TERT promoter mutations, and homozygous deletions of CDKN2A/2B. Emerging evidence support the effectiveness of targeted therapies for brain tumors with BRAF V600E mutation. Here we describe a dramatic radiographical response to combined therapy with BRAF and MEK inhibitors in a patient with epithelioid GBM harboring BRAF V600E mutation, characterized by thick spinal dissemination. From relapsed tumor procured at autopsy, we established a cell line retaining the BRAF V600E mutation, TERT promoter mutation and CDKN2A/2B loss. Intracranial implantation of these cells into mice resulted in tumors closely resembling the original, characterized by epithelioid tumor cells and dissemination, and invasion into the perivascular spaces. We then confirmed the efficacy of treatment with BRAF and MEK inhibitor both in vitro and in vivo. Epithelioid GBM with BRAF V600E mutation can be considered a good treatment indication for precision medicine, and this patient-derived cell line should be useful for prediction of the tumor response and clarification of its biological characteristics.
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http://dx.doi.org/10.1186/s40478-019-0774-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6659204PMC
July 2019

Radiosensitization by Histone H3 Demethylase Inhibition in Diffuse Intrinsic Pontine Glioma.

Clin Cancer Res 2019 09 21;25(18):5572-5583. Epub 2019 Jun 21.

Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois.

Purpose: Radiotherapy (RT) has long been and remains the only treatment option for diffuse intrinsic pontine glioma (DIPG). However, all patients show evidence of disease progression within months of completing RT. No further clinical benefit has been achieved using alternative radiation strategies. Here, we tested the hypothesis that histone demethylase inhibition by GSK-J4 enhances radiation-induced DNA damage, making it a potential radiosensitizer in the treatment of DIPG. We evaluated the effects of GSK-J4 on genes associated with DNA double-strand break (DSB) repair in DIPG cells by RNA sequence, ATAC sequence, and quantitative real-time PCR. Radiation-induced DNA DSB repair was analyzed by immunocytochemistry of DSB markers γH2AX and 53BP1, DNA-repair assay, and cell-cycle distribution. Clonogenic survival assay was used to determine the effect of GSK-J4 on radiation response of DIPG cells. response to radiation monotherapy and combination therapy of RT and GSK-J4 was evaluated in patient-derived DIPG xenografts.

Results: GSK-J4 significantly reduced the expression of DNA DSB repair genes and DNA accessibility in DIPG cells. GSK-J4 sustained high levels of γH2AX and 53BP1 in irradiated DIPG cells, thereby inhibiting DNA DSB repair through homologous recombination pathway. GSK-J4 reduced clonogenic survival and enhanced radiation effect in DIPG cells. studies revealed increased survival of animals treated with combination therapy of RT and GSK-J4 compared with either monotherapy.

Conclusions: Together, these results highlight GSK-J4 as a potential radiosensitizer and provide a rationale for developing combination therapy with radiation in the treatment of DIPG.
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http://dx.doi.org/10.1158/1078-0432.CCR-18-3890DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6744979PMC
September 2019

ABC Transporter Inhibition Plus Dexamethasone Enhances the Efficacy of Convection Enhanced Delivery in H3.3K27M Mutant Diffuse Intrinsic Pontine Glioma.

Neurosurgery 2020 05;86(5):742-751

Department of Neurosurgery, Duke University Medical Center, Durham, North Carolina.

Background: An impermeable blood-brain barrier and drug efflux via ATP-binding cassette (ABC) transporters such as p-glycoprotein may contribute to underwhelming efficacy of peripherally delivered agents to treat diffuse intrinsic pontine glioma (DIPG).

Objective: To explore the pharmacological augmentation of convection-enhanced delivery (CED) infusate for DIPG.

Methods: The efficacy of CED dasatinib, a tyrosine kinase inhibitor, in a transgenic H3.3K27M mutant murine model was assessed. mRNA expression of ABCB1 (p-glycoprotein) was analyzed in 14 tumor types in 274 children. In Vitro viability studies of dasatinib, the p-glycoprotein inhibitor, tariquidar, and dexamethasone were performed in 2 H3.3K27M mutant cell lines. Magnetic resonance imaging (MRI) was used to evaluate CED infusate (gadolinium/dasatinib) distribution in animals pretreated with tariquidar and dexamethasone. Histological assessment of apoptosis was performed.

Results: Continuous delivery CED dasatinib improved median overall survival (OS) of animals harboring DIPG in comparison to vehicle (39.5 and 28.5 d, respectively; P = .0139). Mean ABCB1 expression was highest in K27M gliomas. In Vitro, the addition of tariquidar and dexamethasone further enhanced the efficacy of dasatinib (P < .001). In Vivo, MRI demonstrated no difference in infusion dispersion between animals pretreated with dexamethasone plus tariquidar prior to CED dasatinib compared to the CED dasatinib. However, tumor apoptosis was the highest in the pretreatment group (P < .001). Correspondingly, median OS was longer in the pretreatment group (49 d) than the dasatinib alone group (39 d) and no treatment controls (31.5 d, P = .0305).

Conclusion: ABC transporter inhibition plus dexamethasone enhances the efficacy of CED dasatinib, resulting in enhanced tumor cellular apoptosis and improved survival in H3.3K27M mutant DIPG.
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http://dx.doi.org/10.1093/neuros/nyz212DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7443593PMC
May 2020

Identification of Novel RAS Signaling Therapeutic Vulnerabilities in Diffuse Intrinsic Pontine Gliomas.

Cancer Res 2019 08 14;79(16):4026-4041. Epub 2019 Jun 14.

John G. Rangos Sr. Research Center, Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania.

Diffuse intrinsic pontine gliomas (DIPG) are incurable brain tumors with an aggressive onset. Apart from irradiation, there are currently no effective therapies available for patients with DIPG, who have a median survival time of less than one year. Most DIPG cells harbor mutations in genes encoding histone H3 (H3K27M) proteins, resulting in a global reduction of H3K27 trimethylation and activation of oncogenic signaling pathways. Here we show that the H3K27M mutations contribute to RAS pathway signaling, which is augmented by additional RAS activators including PDGFRA. H3K27M mutation led to increased expression of receptor tyrosine kinases (RTK). A RAS pathway functional screen identified ERK5, but not ERK1/2, as a RAS pathway effector important for DIPG growth. Suppression of ERK5 decreased DIPG cell proliferation and induced apoptosis and . In addition, depletion or inhibition of ERK5 significantly increased survival of mice intracranially engrafted with DIPG cells. Mechanistically, ERK5 directly stabilized the proto-oncogene MYC at the protein level. Collectively, our data demonstrate an underappreciated role of H3K27M in RAS activation and reveal novel therapeutic targets for treating DIPG tumors. SIGNIFICANCE: These findings identify the H3K27M mutation as an enhancer of RAS activation in DIPG and ERK5 as a novel, immediately actionable molecular target. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/79/16/4026/F1.large.jpg.
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http://dx.doi.org/10.1158/0008-5472.CAN-18-3521DOI Listing
August 2019

Global Reduction of H3K4me3 Improves Chemotherapeutic Efficacy for Pediatric Ependymomas.

Neoplasia 2019 06 18;21(6):505-515. Epub 2019 Apr 18.

Falk Brain Tumor Center and Division of Pediatric Neurosurgery, Ann & Robert H. Lurie Children's Hospital of Chicago, Northwestern University Feinberg School of Medicine, Chicago, IL, USA; Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, USA; Department of Development Biology, Ann & Robert H. Lurie Children's Hospital of Chicago, Northwestern University Feinberg School of Medicine, Chicago, IL, USA. Electronic address:

Background: Ependymomas (EPNs) are the third most common brain tumor in children. These tumors are resistant to available chemotherapeutic treatments, therefore new effective targeted therapeutics must be identified. Increasing evidence shows epigenetic alterations including histone posttranslational modifications (PTMs), are associated with malignancy, chemotherapeutic resistance and prognosis for pediatric EPNs. In this study we examined histone PTMs in EPNs and identified potential targets to improve chemotherapeutic efficacy.

Methods: Global histone H3 lysine 4 trimethylation (H3K4me3) levels were detected in pediatric EPN tumor samples with immunohistochemistry and immunoblots. Candidate genes conferring therapeutic resistance were profiled in pediatric EPN tumor samples with micro-array. Promoter H3K4me3 was examined for two candidate genes, CCND1 and ERBB2, with chromatin-immunoprecipitation coupled with real-time PCR (ChIP-PCR). These methods and MTS assay were used to verify a relationship between H3K4me3 levels and CCND1 and ERBB2, and to investigate cell viability in response to chemotherapeutic drugs in primary cultured pediatric EPN cells.

Results: H3K4me3 levels positively correlate with WHO grade malignancy in pediatric EPNs and are associated with progression free survival in patients with posterior fossa group A EPNs (PF-EPN-A). Reduction of H3K4me3 by silencing its methyltransferase SETD1A, in primary cultured EPN cells increased cell response to chemotherapy.

Conclusions: Our results support the development of a novel treatment that targets H3K4me3 to increase chemotherapeutic efficacy in pediatric PF-EPN-A tumors.
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http://dx.doi.org/10.1016/j.neo.2019.03.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6477190PMC
June 2019

Potent Antineoplastic Effects of Combined PI3Kα-MNK Inhibition in Medulloblastoma.

Mol Cancer Res 2019 06 6;17(6):1305-1315. Epub 2019 Mar 6.

Robert H. Lurie Comprehensive Cancer Center of Northwestern University, Chicago, Illinois.

Medulloblastoma is a highly malignant pediatric brain tumor associated with poor outcome. Developing treatments that target the cancer stem cell (CSC) population in medulloblastoma are important to prevent tumor relapse and induce long-lasting clinical responses. We utilized medulloblastoma neurospheres that display CSC characteristics and found activation of the PI3K/AKT pathway in sphere-forming cells. Of all class I PI3Ks, only the PI3Kα isoform was required for sphere formation by medulloblastoma cells. Knockdown of p110α, but not p110β or p110δ, significantly disrupted cancer stem cell frequencies as determined by extreme limiting dilution analysis (ELDA), indicating an essential role for the PI3Kα catalytic isoform in medulloblastoma CSCs. Importantly, pharmacologic inhibition of the MAPK-interacting kinase (MNK) enhanced the antineoplastic effects of targeted PI3Kα inhibition in medulloblastoma. This indicates that MNK signaling promotes survival in medulloblastoma, suggesting dual PI3Kα and MNK inhibition may provide a novel approach to target and eliminate medulloblastoma CSCs. We also observed a significant reduction in tumor formation in subcutaneous and intracranial mouse xenograft models, which further suggests that this combinatorial approach may represent an efficient therapeutic strategy for medulloblastoma. IMPLICATIONS: These findings raise the possibility of a unique therapeutic approach for medulloblastoma, involving MNK targeting to sensitize medulloblastoma CSCs to PI3Kα inhibition.
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http://dx.doi.org/10.1158/1541-7786.MCR-18-1193DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548590PMC
June 2019

ACVR1 R206H cooperates with H3.1K27M in promoting diffuse intrinsic pontine glioma pathogenesis.

Nat Commun 2019 03 4;10(1):1023. Epub 2019 Mar 4.

Department of Pediatrics, Northwestern University, Chicago, IL, 60611, USA.

Diffuse intrinsic pontine glioma (DIPG) is an incurable pediatric brain tumor, with approximately 25% of DIPGs harboring activating ACVR1 mutations that commonly co-associate with H3.1K27M mutations. Here we show that in vitro expression of ACVR1 R206H with and without H3.1K27M upregulates mesenchymal markers and activates Stat3 signaling. In vivo expression of ACVR1 R206H or G328V with H3.1K27M and p53 deletion induces glioma-like lesions but is not sufficient for full gliomagenesis. However, in combination with PDGFA signaling, ACVR1 R206H and H3.1K27M significantly decrease survival and increase tumor incidence. Treatment of ACVR1 R206H mutant DIPGs with exogenous Noggin or the ACVR1 inhibitor LDN212854 significantly prolongs survival, with human ACVR1 mutant DIPG cell lines also being sensitive to LDN212854 treatment. Together, our results demonstrate that ACVR1 R206H and H3.1K27M promote tumor initiation, accelerate gliomagenesis, promote a mesenchymal profile partly due to Stat3 activation, and identify LDN212854 as a promising compound to treat DIPG.
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http://dx.doi.org/10.1038/s41467-019-08823-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6399349PMC
March 2019

Molecular and translational advances in meningiomas.

Neuro Oncol 2019 01;21(Suppl 1):i4-i17

Division of Neurosurgery, University Health Network, University of Toronto, Ontario, Canada.

Meningiomas are the most common primary intracranial neoplasm. The current World Health Organization (WHO) classification categorizes meningiomas based on histopathological features, but emerging molecular data demonstrate the importance of genomic and epigenomic factors in the clinical behavior of these tumors. Treatment options for symptomatic meningiomas are limited to surgical resection where possible and adjuvant radiation therapy for tumors with concerning histopathological features or recurrent disease. At present, alternative adjuvant treatment options are not available in part due to limited historical biological analysis and clinical trial investigation on meningiomas. With advances in molecular and genomic techniques in the last decade, we have witnessed a surge of interest in understanding the genomic and epigenomic landscape of meningiomas. The field is now at the stage to adopt this molecular knowledge to refine meningioma classification and introduce molecular algorithms that can guide prediction and therapeutics for this tumor type. Animal models that recapitulate meningiomas faithfully are in critical need to test new therapeutics to facilitate rapid-cycle translation to clinical trials. Here we review the most up-to-date knowledge of molecular alterations that provide insight into meningioma behavior and are ready for application to clinical trial investigation, and highlight the landscape of available preclinical models in meningiomas.
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http://dx.doi.org/10.1093/neuonc/noy178DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6347079PMC
January 2019

Targeting Processive Transcription Elongation via SEC Disruption for MYC-Induced Cancer Therapy.

Cell 2018 10;175(3):766-779.e17

Simpson Querrey Center for Epigenetics, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA; Department of Biochemistry and Molecular Genetics, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA; Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg, School of Medicine, 303 E. Superior Street, Chicago, IL 60611, USA. Electronic address:

The super elongation complex (SEC) is required for robust and productive transcription through release of RNA polymerase II (Pol II) with its P-TEFb module and promoting transcriptional processivity with its ELL2 subunit. Malfunction of SEC contributes to multiple human diseases including cancer. Here, we identify peptidomimetic lead compounds, KL-1 and its structural homolog KL-2, which disrupt the interaction between the SEC scaffolding protein AFF4 and P-TEFb, resulting in impaired release of Pol II from promoter-proximal pause sites and a reduced average rate of processive transcription elongation. SEC is required for induction of heat-shock genes and treating cells with KL-1 and KL-2 attenuates the heat-shock response from Drosophila to human. SEC inhibition downregulates MYC and MYC-dependent transcriptional programs in mammalian cells and delays tumor progression in a mouse xenograft model of MYC-driven cancer, indicating that small-molecule disruptors of SEC could be used for targeted therapy of MYC-induced cancer.
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http://dx.doi.org/10.1016/j.cell.2018.09.027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6422358PMC
October 2018

Measuring Tumor Metabolism in Pediatric Diffuse Intrinsic Pontine Glioma Using Hyperpolarized Carbon-13 MR Metabolic Imaging.

Contrast Media Mol Imaging 2018 30;2018:3215658. Epub 2018 Jul 30.

Department of Radiology, Chonnam National University Medical School, Gwangju, Republic of Korea.

Objective: The purpose of this study was to demonstrate the feasibility of using hyperpolarized carbon-13 (C) metabolic imaging with [1-C]-labeled pyruvate for evaluating real-time metabolism of orthotopic diffuse intrinsic pontine glioma (DIPG) xenografts.

Materials And Methods: 3D C magnetic resonance spectroscopic imaging (MRSI) data were acquired on a 3T scanner from 8 rats that had been implanted with human-derived DIPG cells in the brainstem and 5 healthy controls, following injection of 2.5 mL (100 mM) hyperpolarized [1-C]-pyruvate.

Results: Anatomical images from DIPG-bearing rats characteristically exhibited T-hyperintensity throughout the cerebellum and pons that was not accompanied by contrast enhancement. Evaluation of real-time C spectroscopic data revealed ratios of lactate-to-pyruvate ( < 0.002), lactate-to-total carbon ( < 0.002), and normalized lactate ( < 0.002) that were significantly higher in T lesions harboring tumor relative to corresponding values of healthy normal brain. Elevated levels of lactate in lesions demonstrated a distinct metabolic profile that was associated with infiltrative, viable tumor recapitulating the histopathology of pediatric DIPG.

Conclusions: Results from this study characterized pyruvate and lactate metabolism in orthotopic DIPG xenografts and suggest that hyperpolarized C MRSI may serve as a noninvasive imaging technique for monitoring of biochemical processes in patients with DIPG.
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http://dx.doi.org/10.1155/2018/3215658DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6098895PMC
January 2019

MELK Inhibition in Diffuse Intrinsic Pontine Glioma.

Clin Cancer Res 2018 11 30;24(22):5645-5657. Epub 2018 Jul 30.

Departments of Pediatric Oncology/Hematology, Cancer Center Amsterdam, VU University Medical Center, Amsterdam, the Netherlands.

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive pediatric brain tumor, for which no effective therapeutic options currently exist. We here determined the potential of inhibition of the maternal embryonic leucine zipper kinase (MELK) for the treatment of DIPG. We evaluated the antitumor efficacy of the small-molecule MELK inhibitor OTSSP167 in patient-derived DIPG cultures, and identified the mechanism of action of MELK inhibition in DIPG by RNA sequencing of treated cells. In addition, we determined the blood-brain barrier (BBB) penetration of OTSSP167 and evaluated its translational potential by treating mice bearing patient-derived DIPG xenografts. This study shows that MELK is highly expressed in DIPG cells, both in patient samples and in relevant and models, and that treatment with OTSSP167 strongly decreases proliferation of patient-derived DIPG cultures. Inhibition of MELK in DIPG cells functions through reducing inhibitory phosphorylation of PPARγ, resulting in an increase in nuclear translocation and consequent transcriptional activity. Brain pharmacokinetic analyses show that OTSSP167 is a strong substrate for both MDR1 and BCRP, limiting its BBB penetration. Nonetheless, treatment of Mdr1a/b;Bcrp1 knockout mice carrying patient-derived DIPG xenografts with OTSSP167 decreased tumor growth, induced remissions, and resulted in improved survival. We show a strong preclinical effect of the kinase inhibitor OTSSP167 in the treatment of DIPG and identify the MELK-PPARγ signaling axis as a putative therapeutic target in this disease. .
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http://dx.doi.org/10.1158/1078-0432.CCR-18-0924DOI Listing
November 2018

Resetting the epigenetic balance of Polycomb and COMPASS function at enhancers for cancer therapy.

Nat Med 2018 06 21;24(6):758-769. Epub 2018 May 21.

Simpson Querrey Center for Epigenetics, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.

The lysine methyltransferase KMT2C (also known as MLL3), a subunit of the COMPASS complex, implements monomethylation of Lys4 on histone H3 (H3K4) at gene enhancers. KMT2C (hereafter referred to as MLL3) frequently incurs point mutations across a range of human tumor types, but precisely how these lesions alter MLL3 function and contribute to oncogenesis is unclear. Here we report a cancer mutational hotspot in MLL3 within the region encoding its plant homeodomain (PHD) repeats and demonstrate that this domain mediates association of MLL3 with the histone H2A deubiquitinase and tumor suppressor BAP1. Cancer-associated mutations in the sequence encoding the MLL3 PHD repeats disrupt the interaction between MLL3 and BAP1 and correlate with poor patient survival. Cancer cells that had PHD-associated MLL3 mutations or lacked BAP1 showed reduced recruitment of MLL3 and the H3K27 demethylase KDM6A (also known as UTX) to gene enhancers. As a result, inhibition of the H3K27 methyltransferase activity of the Polycomb repressive complex 2 (PRC2) in tumor cells harboring BAP1 or MLL3 mutations restored normal gene expression patterns and impaired cell proliferation in vivo. This study provides mechanistic insight into the oncogenic effects of PHD-associated mutations in MLL3 and suggests that restoration of a balanced state of Polycomb-COMPASS activity may have therapeutic efficacy in tumors that bear mutations in the genes encoding these epigenetic factors.
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http://dx.doi.org/10.1038/s41591-018-0034-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6055231PMC
June 2018

Inhibition of polo-like kinase 4 (PLK4): a new therapeutic option for rhabdoid tumors and pediatric medulloblastoma.

Oncotarget 2017 Dec 24;8(67):111190-111212. Epub 2017 Nov 24.

Ann and Robert H. Lurie Children's Hospital of Chicago, Division of Pediatric Neurosurgery, Chicago, IL 60611, USA.

Rhabdoid tumors (RT) are highly aggressive and vastly unresponsive embryonal tumors. They are the most common malignant CNS tumors in infants below 6 months of age. Medulloblastomas (MB) are embryonal tumors that arise in the cerebellum and are the most frequent pediatric malignant brain tumors. Despite the advances in recent years, especially for the most favorable molecular subtypes of MB, the prognosis of patients with embryonal tumors remains modest with treatment related toxicity dreadfully high. Therefore, new targeted therapies are needed. The polo-like kinase 4 (PLK4) is a critical regulator of centriole duplication and consequently, mitotic progression. We previously established that PLK4 is overexpressed in RT and MB. We also demonstrated that inhibiting PLK4 with a small molecule inhibitor resulted in impairment of proliferation, survival, migration and invasion of RT cells. Here, we showed in MB the same effects that we previously described for RT. We also demonstrated that PLK4 inhibition induced apoptosis, senescence and polyploidy in RT and MB cells, thereby increasing the susceptibility of cancer cells to DNA-damaging agents. In order to test the hypothesis that PLK4 is a CNS druggable target, we demonstrated efficacy with oral administration to an orthotropic xenograft model. Based on these results, we postulate that targeting PLK4 with small-molecule inhibitors could be a novel strategy for the treatment of RT and MB and that PLK4 inhibitors (PLK4i) might be promising agents to be used solo or in combination with cytotoxic agents.
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http://dx.doi.org/10.18632/oncotarget.22704DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5762315PMC
December 2017

New therapeutic approaches for brainstem tumors: a comparison of delivery routes using nanoliposomal irinotecan in an animal model.

J Neurooncol 2018 Feb 23;136(3):475-484. Epub 2017 Nov 23.

Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, 300 East Superior Street, Tarry 2-709, Chicago, IL, 60611, USA.

Despite the advances in imaging, surgery and radiotherapy, the majority of patients with brainstem gliomas die within 2 years after initial diagnosis. Factors that contribute to the dismal prognosis of these patients include the infiltrative nature and anatomic location in an eloquent area of the brain, which prevents total surgical resection and the presence of the blood-brain barrier (BBB), which reduces the distribution of systemically administered agents. The development of new therapeutic approaches which can circumvent the BBB is a potential path to improve outcomes for these children. Convection-enhanced delivery (CED) and intranasal delivery (IND) are strategies that permit direct drug delivery into the central nervous system and are an alternative to intravenous injection (IV). We treated rats bearing human brainstem tumor xenografts with nanoliposomal irinotecan (CPT-11) using CED, IND, and IV. A single treatment of CED irinotecan had a similar effect on overall survival as multiple treatments by IV route. IND CPT-11 showed significantly increased survival of animals with brainstem tumors, and demonstrated the promise of this non-invasive approach of drug delivery bypassing the BBB when combined with nanoliposomal chemotherapy. Our results indicated that using CED and IND of nanoliposomal therapy increase likelihood of practical therapeutic approach for the treatment of brainstem gliomas.
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http://dx.doi.org/10.1007/s11060-017-2681-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5807192PMC
February 2018

A cytoplasmic COMPASS is necessary for cell survival and triple-negative breast cancer pathogenesis by regulating metabolism.

Genes Dev 2017 10 14;31(20):2056-2066. Epub 2017 Nov 14.

Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA.

Mutations and translocations within the COMPASS (complex of proteins associated with Set1) family of histone lysine methyltransferases are associated with a large number of human diseases, including cancer. Here we report that SET1B/COMPASS, which is essential for cell survival, surprisingly has a cytoplasmic variant. SET1B, but not its SET domain, is critical for maintaining cell viability, indicating a novel catalytic-independent role of SET1B/COMPASS. Loss of SET1B or its unique cytoplasmic-interacting protein, BOD1, leads to up-regulation of expression of numerous genes modulating fatty acid metabolism, including (), , and Our detailed molecular studies identify ADIPOR1 signaling, which is inactivated in both obesity and human cancers, as a key target of SET1B/COMPASS. Collectively, our study reveals a cytoplasmic function for a member of the COMPASS family, which could be harnessed for therapeutic regulation of signaling in human diseases, including cancer.
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http://dx.doi.org/10.1101/gad.306092.117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5733497PMC
October 2017

Epigenetic Targeted Therapy for Diffuse Intrinsic Pontine Glioma.

Neurol Med Chir (Tokyo) 2017 Jul 7;57(7):331-342. Epub 2017 Jun 7.

Department of Neurological Surgery, Northwestern University.

Diffuse intrinsic pontine glioma (DIPG) is a rare but uniformly fatal cancer of the brain, with peak incidence in children of 5-7 years of age. In contrast to most types of human cancer, there has been no significant improvement in treatment outcomes for patients with DIPG. Since DIPG occurs in the brainstem, a vital region of the brain, there are no surgical options for providing relief to patients, and chemotherapy as well as radiation therapy provide palliative relief at best. To date, more than 250 clinical trials evaluating radiotherapy along with conventional cytotoxic chemotherapy, as well as newer biologic agents, have failed to improve the dismal outcome when compared with palliative radiation alone. The recent discovery of somatic oncogenic histone gene mutations affecting chromatin regulation in DIPG has dramatically improved our understanding of the disease pathogenesis in DIPG, and these findings have stimulated the development of novel therapeutic approaches targeting epigenetic regulators for disease treatment. This review will discuss about the role of histone modification in chromatin machinery and epigenetic therapeutic strategies for the treatment of DIPG.
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http://dx.doi.org/10.2176/nmc.ra.2017-0018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5566706PMC
July 2017

Histone H3.3K27M Represses to Accelerate Gliomagenesis in a Murine Model of DIPG.

Mol Cancer Res 2017 09 18;15(9):1243-1254. Epub 2017 May 18.

Division of Hematology-Oncology, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina.

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive pediatric brainstem tumor genetically distinguished from adult GBM by the high prevalence of the K27M mutation in the histone H3 variant H3.3 (). This mutation reprograms the H3K27me3 epigenetic landscape of DIPG by inhibiting the H3K27-specific histone methyltransferase EZH2. This globally reduces H3K27me2/3, critical repressive marks responsible for cell fate decisions, and also causes focal gain of H3K27me3 throughout the epigenome. To date, the tumor-driving effects of H3.3K27M remain largely unknown. Here, it is demonstrated that H3.3K27M cooperates with PDGF-B enhancing gliomagenesis and reducing survival of p53 wild-type (WT) and knockout murine models of DIPG. H3.3K27M expression drives increased proliferation of tumor-derived murine neurospheres, suggesting that cell-cycle deregulation contributes to increased malignancy in mutant tumors. RNA sequencing on tumor tissue from H3.3K27M-expressing mice indicated global upregulation of PRC2 target genes, and a subset of newly repressed genes enriched in regulators of development and cell proliferation. Strikingly, H3.3K27M induced targeted repression of the p16/ink4a () locus, a critical regulator of the G-G to S-phase transition. Increased levels of H3K27me3 were observed at the p16 promoter; however, pharmacologic reduction of methylation at this promoter did not rescue p16 expression. Although DNA methylation is also present at this promoter, it is not K27M dependent. Intriguingly, inhibition of DNA methylation restores p16 levels and is cytotoxic against murine tumor cells. Importantly, these data reveal that H3.3K27M-mediated p16 repression is an important mechanism underlying the proliferation of H3.3K27M tumor cells, as knockout eliminates the survival difference between H3.3K27M and H3.3WT tumor-bearing mice. This study shows that H3.3K27M mutation and PDGF signaling act in concert to accelerate gliomagenesis in a genetic mouse model and identifies repression of p16 tumor suppressor as a target of H3.3K27M, highlighting the G-S cell-cycle transition as a promising therapeutic avenue. .
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http://dx.doi.org/10.1158/1541-7786.MCR-16-0389DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5581686PMC
September 2017

A Sequentially Priming Phosphorylation Cascade Activates the Gliomagenic Transcription Factor Olig2.

Cell Rep 2017 03;18(13):3167-3177

Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA; Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA. Electronic address:

During development of the vertebrate CNS, the basic helix-loop-helix (bHLH) transcription factor Olig2 sustains replication competence of progenitor cells that give rise to neurons and oligodendrocytes. A pathological counterpart of this developmental function is seen in human glioma, wherein Olig2 is required for maintenance of stem-like cells that drive tumor growth. The mitogenic/gliomagenic functions of Olig2 are regulated by phosphorylation of a triple serine motif (S10, S13, and S14) in the amino terminus. Here, we identify a set of three serine/threonine protein kinases (glycogen synthase kinase 3α/β [GSK3α/β], casein kinase 2 [CK2], and cyclin-dependent kinases 1/2 [CDK1/2]) that are, collectively, both necessary and sufficient to phosphorylate the triple serine motif. We show that phosphorylation of the motif itself serves as a template to prime phosphorylation of additional serines and creates a highly charged "acid blob" in the amino terminus of Olig2. Finally, we show that small molecule inhibitors of this forward-feeding phosphorylation cascade have potential as glioma therapeutics.
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http://dx.doi.org/10.1016/j.celrep.2017.03.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5394178PMC
March 2017

Therapeutic Hypothesis Testing With Rodent Brain Tumor Models.

Neurotherapeutics 2017 04;14(2):385-392

Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.

The development and application of rodent models for preclinical testing of novel therapeutics and approaches for treating brain tumors has been a mainstay of neuro-oncology preclinical research for decades, and is likely to remain so into the foreseeable future. These models serve as an important point of entry for analyzing the potential efficacy of experimental therapies that are being considered for clinical trial evaluation. Although rodent brain tumor models have seen substantial change, particularly since the introduction of genetically engineered mouse models, certain principles associated with the use of these models for therapeutic testing are enduring, and form the basis for this review. Here we discuss the most common rodent brain tumor models while directing specific attention to their usefulness in preclinical evaluation of experimental therapies. These models include genetically engineered mice that spontaneously or inducibly develop brain tumors; syngeneic rodent models in which cultured tumor cells are engrafted into the same strain of rodent from which they were derived; and patient-derived xenograft models in which human tumor cells are engrafted in immunocompromised rodents. The emphasis of this review is directed to the latter.
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http://dx.doi.org/10.1007/s13311-017-0523-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5398994PMC
April 2017

Therapeutic targeting of polycomb and BET bromodomain proteins in diffuse intrinsic pontine gliomas.

Nat Med 2017 Apr 27;23(4):493-500. Epub 2017 Feb 27.

Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive pediatric brainstem tumor characterized by rapid and uniform patient demise. A heterozygous point mutation of histone H3 occurs in more than 80% of these tumors and results in a lysine-to-methionine substitution (H3K27M). Expression of this histone mutant is accompanied by a reduction in the levels of polycomb repressive complex 2 (PRC2)-mediated H3K27 trimethylation (H3K27me3), and this is hypothesized to be a driving event of DIPG oncogenesis. Despite a major loss of H3K27me3, PRC2 activity is still detected in DIPG cells positive for H3K27M. To investigate the functional roles of H3K27M and PRC2 in DIPG pathogenesis, we profiled the epigenome of H3K27M-mutant DIPG cells and found that H3K27M associates with increased H3K27 acetylation (H3K27ac). In accordance with previous biochemical data, the majority of the heterotypic H3K27M-K27ac nucleosomes colocalize with bromodomain proteins at the loci of actively transcribed genes, whereas PRC2 is excluded from these regions; this suggests that H3K27M does not sequester PRC2 on chromatin. Residual PRC2 activity is required to maintain DIPG proliferative potential, by repressing neuronal differentiation and function. Finally, to examine the therapeutic potential of blocking the recruitment of bromodomain proteins by heterotypic H3K27M-K27ac nucleosomes in DIPG cells, we performed treatments in vivo with BET bromodomain inhibitors and demonstrate that they efficiently inhibit tumor progression, thus identifying this class of compounds as potential therapeutics in DIPG.
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http://dx.doi.org/10.1038/nm.4296DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5667640PMC
April 2017

Epigenetic modification in chromatin machinery and its deregulation in pediatric brain tumors: Insight into epigenetic therapies.

Epigenetics 2017 05 6;12(5):353-369. Epub 2017 Jan 6.

a Department of Neurological Surgery , Northwestern University Feinberg School of Medicine , Chicago , IL , USA.

Malignancies are characterized by the reprogramming of epigenetic patterns. This reprogramming includes gains or losses in DNA methylation and disruption of normal patterns of covalent histone modifications, which are associated with changes in chromatin remodeling processes. This review will focus on the mechanisms underlying this reprogramming and, specifically, on the role of histone modification in chromatin machinery and the modifications in epigenetic processes occurring in brain cancer, with a specific focus on epigenetic therapies for pediatric brain tumors.
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http://dx.doi.org/10.1080/15592294.2016.1278095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5453195PMC
May 2017

Combined BRAF and MEK blockade for BRAF-mutant gliomas.

J Neurooncol 2017 02 15;131(3):495-505. Epub 2016 Nov 15.

Department of Pediatrics, University of California San Francisco, 1450 3rd Street, San Francisco, CA, 94158, USA.

BRAF is a common finding in glioma (about 10-60% depending on histopathologic subclassification). BRAF monotherapy shows modest preclinical efficacy against BRAF gliomas and also induces adverse secondary skin malignancies. Here, we examine the molecular mechanism of intrinsic resistance to BRAF inhibition in glioma. Furthermore, we investigate BRAF/MEK combination therapy that overcomes intrinsic resistance to BRAF inhibitor and also prevents BRAF inhibitor induced secondary malignancies. Immunoblotting and Human Phospho-Receptor Tyrosine Kinase Array assays were used to interrogate MAPK pathway activation. The cellular effect of BRAF and MEK inhibition was determined by WST-1 viability assay and cell cycle analysis. Flanked and orthotopic GBM mouse models were used to investigate the in vivo efficacy of BRAF/MEK combination therapy and the effect on secondary malignancies. BRAF inhibition leads to recovery of ERK phosphorylation. Combined BRAF and MEK inhibition prevents reactivation of the MAPK signaling, which correlates with decreased cell viability and augmented cell cycle arrest. Similarly, mice bearing BRAF glioma showed reduced tumor growth when treated with a combination of BRAF and MEK inhibitor compared to BRAF inhibition alone. Additional benefit of BRAF/MEK inhibition was reflected by reduced cutaneous squamous-cell carcinoma (cSCC) growth (a surrogate for RAS-driven secondary maligancies). In glioma, recovery of MAPK signaling upon BRAF inhibition accounts for intrinsic resistance to BRAF inhibitor. Combined BRAF and MEK inhibition prevents rebound of MAPK activation, resulting in enhanced antitumor efficacy and also reduces the risk of secondary malignancy development.
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http://dx.doi.org/10.1007/s11060-016-2333-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5560871PMC
February 2017