Abstracts i16 NEURO-ONCOLOGY • June 2023 ABSTRACT CITATION ID: NOAD073.062 DIPG-15. CONCURRENT GB-13 (IL13.E13K-PE4E) IMPROVES THE EFFICACY OF RADIATION THERAPY IN DIFFUSE INTRINSIC PONTINE GLIOMA Julian S. Rechberger 1 , Randy S. Schrecengost 2 , Liang Zhang 1 , Jizhi Ge 1 , Leo F. Nonnenbroich 1,3 , Jann N. Sarkaria 1 , David J. Daniels 1 ; 1 Mayo Clinic, Rochester, USA. 2 Targepeutics, Inc., Hershey, USA. 3 Hopp Children's Cancer Center Heidelberg (KiTZ), Heidelberg, Germany Diffuse midline glioma with H3 K27 alterations (DMG) is the most ag- gressive primary malignant brain tumor in the pediatric population. Radi- ation therapy (RT) is the standard-of-care; however, it has not demonstrated a signifcant improvement in overall survival or stalled disease progression, and children usually succumb to disease within 12-15 months of diagnosis. Consequently, fnding effcient treatments for DMG remains one of the most critical unmet needs in modern neuro-oncology. Interleukin 13 receptor sub- unit alpha 2 (IL-13Rα2) is a cell-surface receptor upregulated in ~80% of DMG versus normal brain, posing a potentially promising therapeutic target. Immunotherapies harnessing IL-13Rα2 to selectively delivery cytotoxic pay- loads, such as pseudomonas exotoxin A (PE), to tumor cells have been previ- ously demonstrated to be safe in DMG patients and effcacious in preclinical models of DMG with high IL-13Rα2 expression using convection-enhanced delivery (CED). Furthermore, there is evidence that PE-based therapies can sensitize cells to RT. In this study, we utilized in vitro and in vivo models of DMG to evaluate clinically-relevant combination treatments of RT and the IL-13/PE immunotoxin GB-13 (IL13.E13K-PE4E). GB-13 improved the ef- fectiveness of low-dose RT in multiple DMG cell lines by promoting caspase activation, which boosted apoptotic cell death. Intratumoral administration of GB-13 via chronic CED decreased tumor burden and prolonged survival in both DMG patient-derived orthotopic xenograft and genetically engin- eered mouse models. When GB-13 and RT were administered concurrently, this impact became even more prominent, informing future preclinical and clinical investigation of a potentially effcacious therapeutic approach in a subset of DMG. ABSTRACT CITATION ID: NOAD073.063 DIPG-16. ACUTE VERSUS PROLONGED CONVECTION-ENHANCED DELIVERY OF ALISERTIB INTO H3 K27M-MUTANT MODELS OF DIFFUSE MIDLINE GLIOMA Julian S. Rechberger, Liang Zhang, Jizhi Ge, David J. Daniels; Mayo Clinic, Rochester, USA Convection-enhanced delivery (CED) is a potentially promising strategy to administer therapeutics directly into the brainstem of children harboring H3 K27-altered diffuse midline glioma (DMG). While early-phase clinical trials have demonstrated the safety of this technique, effcacy has yet to be achieved. Here, we describe how different variations of CED may be exploited to extend survival in a DMG murine patient-derived orthotopic xenograft model. Either 1-day (8 µL/hr) or 7-day (1 µL/hr) continuous CED infusions were performed to deliver an equivalent volume of the aurora kinase inhibitor alisertib to the mouse brainstem. Bioluminescence and magnetic resonance images were acquired to monitor tumor progression, validate CED catheter positioning, and analyze infusion-related imaging changes. Both infusion regimens signifcantly prolonged survival versus con- trol (median survival beneft of 6.5 and 8 days, p=0.03 and p=0.01, for 1-day and 7-day CED, respectively). Postmortem examination of brains revealed no signs of tissue necrosis, cavitary lesions, or cellular (infammatory) infl- trate at the site of infusion. However, the tumor parenchyma surrounding the cannula tract was markedly hypocellular in treated animals. Alisertib induced a robust increase in H3 K27 trimethylation along with decreased H3 K27M and Ki-67. Our fndings indicate that CED of alisertib is well tol- erated and effective, in both the acute and prolonged setting, underscoring the potential of this approach in the management of DMG. ABSTRACT CITATION ID: NOAD073.064 DIPG-17. TREATMENT OF DIFFUSE INTRINSIC PONTINE GLIOMA USING ALLELE-SPECIFIC SIRNA TARGETING H3.3 K27M MUTANT HISTONE Simon Wentworth, Ana Rita Batista, Julia Alterman, Anastasia Khvorova, Miguel Sena-Esteves; UMass Chan Medical School, Worcester, USA In recent years CNS tumors have surpassed leukemia and lymphoma as the deadliest forms of pediatric cancer, yet many of these tumors remain resistant to treatment. Understanding of the molecular pathology of a par- ticularly fatal pediatric glioma, diffuse intrinsic pontine glioma (DIPG), has improved dramatically over the past decade. However, this knowledge has not yet yielded new targeted therapeutics or advances in treatment. The ma- jority of DIPG tumors (~70-80%) harbor a K27M mutation in the histone H3.3 gene resulting in signifcant epigenetic changes which drive tumori- genesis. We are utilizing cutting edge siRNA chemistries to develop a thera- peutic specifcally targeting this oncohistone H3.3 K27M. It has been shown by others that ex vivo disruption of the H3.3 K27M mutant signifcantly delays tumor development in orthotopic xenograft models and could be a promising target for treatment of disease. New siRNA chemistries allow broad distribution and silencing throughout the brain with durable silen- cing for months. Utilizing this technology, we have engineered siRNA com- pounds that can discriminate between wild-type (WT) and K27M mutant H3.3 alleles. Our frst-generation compounds achieved >95% silencing of K27M mutant with only 40% silencing of WT H3.3. We have developed second-generation compounds to improve the discrimination between the two alleles. These compounds allow us to selectively knockdown the mu- tant driver of DIPG tumorigenesis and we hypothesize that silencing of this oncohistone will revert the epigenetic landscape of DIPG to a more wild- type form detrimentally impacting tumor growth and progression. Together the in vivo potency of the new siRNA chemistries combined with the preci- sion allele-specifc targeting of mutant K27M oncohistone may be a prom- ising path towards development of an effective and safe therapy for DIPG. ABSTRACT CITATION ID: NOAD073.065 DIPG-18. AI HUNTING FOR NEW DRUGS IN PEDIATRIC GLIOMA Rintaro Hashizume 1,2 , Patrick Newbury 3 , Yukitomo Ishi 2 , Guisheng Zao 4 , Benjamin Glicksberg 5 , Shreya Paithankar 3 , Javad Nazarian 6,7 , Michael Pacold 4 , Jun Watanabe 1,2 , Eita Uchida 1,2 , Theodore Nicolaides 4 , Bin Chen 3 ; 1 University of Alabama Birmingham, Birmingham, USA. 2 Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, USA. 3 Michigan State University, Michigan, USA. 4 New York University Langone Health, New York, USA. 5 Icahn School of Medicine at Mount Sinai, New York, USA. 6 Children's National Medical Center, Washington, USA. 7 University Children's Hospital Zurich, Zurich, Switzerland Diffuse intrinsic pontine glioma (DIPG) is one of the most devastating pediatric gliomas, with nearly all patients succumbing to progressive tumor growth within two years of diagnosis. The identifcation of effective thera- peutics based on the genetic features is of high importance for improving treatment outcomes for DIPG patients. We have developed machine learning algorithms that allow profling thousands of genetic features, which can all contribute towards drug discovery. This study aimed to identify potential therapeutic agents using a computational pipeline to perform an in-silico screen for novel drugs. We then tested the identifed drugs against a panel of patient-derived DIPG cell lines. Using a systematic computational approach with publicly available databases of gene signature in DIPG patients and cancer cell lines treated with a library of clinically available drugs, we iden- tifed drug hits with the ability to reverse a DIPG gene signature to one that matches normal tissue background. The biological and molecular effects of drug treatment was analyzed by cell viability assay and RNA sequence. In vivo DIPG mouse model survival studies were also conducted. As a result, two of three identifed drugs showed potency against the DIPG cell lines. Triptolide and mycophenolate mofetil (MMF) demonstrated signifcant in- hibition of cell viability in DIPG cell lines. Guanosine rescued reduced cell viability induced by MMF. In vivo, MMF treatment signifcantly inhibited tumor growth in orthotopic DIPG xenograft models. In conclusion, we iden- tifed clinically available drugs with the ability to reverse DIPG gene sig- natures and anti-DIPG activity in vitro and in vivo. This novel approach can repurpose drugs and signifcantly decrease the cost and time normally required in drug discovery. ABSTRACT CITATION ID: NOAD073.066 DIPG-19. BAF COMPLEX PERTURBATION AS A NOVEL THERAPEUTIC OPPORTUNITY IN H3K27M PEDIATRIC GLIOMA Eshini Panditharatna 1 , Joana G. Marques 1 , Tingjian Wang 1 , Maria Trissal 1 , Ilon Liu 1 , Li Jiang 1 , Alexander Beck 2 , Andrew Groves 1 , Neekesh Dharia 1 , Samantha Hoffman 1 , Guillaume Kugener 3 , McKenzie Shaw 1 , Olivia Hack 1 , Joshua Dempster 3 , Caleb Lareau 3 , Michael Quezada 4 , Ann-Catherine Stanton 5 , Meghan Wyatt 3 , Zohra Kalani 3 , Amy Goodale 3 , Francisca Vazquez 3 , Federica Piccioni 3 , John Doench 3 , David Root 3 , Jamie Anastas 6 , Kristen Jones 1 , Amy Conway 1 , Sylwia Stopka 7 , Michael Regan 7 , Yu Liang 1 , Hyuk-Soo Seo 1 , Kijun Song 1 , Puspalata Bashyal 1 , Nathan Mathewson 1 , Sirano Dhe-Paganon 1 , Mario L. Suvà 8 , Angel M. Carcaboso 9 , Cinzia Lavarino 9 , Jaume Mora 9 , Quang-De Nguyen 1 , Keith L. Ligon 1 , Yang Shi 6 , Sameer Agnihotri 5 , Nathalie Y. R. Agar 1 , Kimberly Stegmaier 1 , Charles D. Stiles 1 , Michelle Monje 4 , Todd R. Golub 3 , Jun Qi 1 , Mariella G. Filbin 1 ; 1 Dana- Farber Cancer Institute, Boston, USA. 2 Ludwig Maximilian University of Munich, Munich, Germany. 3 Broad Institute, Cambridge, USA. 4 Stanford University School of Medicine, Stanford, USA. 5 Children’s Hospital of Pittsburgh, Pittsburgh, USA. 6 Boston Children’s Hospital, Boston, USA. 7 Brigham and Women’s Hospital, Boston, USA. 8 Massachusetts General Hospital and Harvard Medical School, Boston, USA. 9 Hospital Sant Joan de Déu, Barcelona, Spain Epigenetic dysregulation resulting in stalled development plays a crucial role in pediatric cancer tumorigenesis. Diffuse midline gliomas (DMG) are Downloaded from https://academic.oup.com/neuro-oncology/article/25/Supplement_1/i16/7194429 by guest on 15 June 2023