Abstract A002: MALT1 as a regulator of tumor progression in H3K27-altered diffuse midline glioma
Authors: Butterfield Hannah , Azambuja Juliana Hofstatter , Maurer Lisa , Yerneni Saigopalakrishna S. , Cruz Andrea , Halbert Matthew , Gatesman Taylor , Agnihotri Sameer , Lucas Peter C. , McAllister-Lucas Linda M. 
Published: March 2024

Abstract
Purpose: This study evaluates MALT1 as a potential therapeutic target in H3K27-altered diffuse midline glioma (DMG). Background: H3K27-altered DMG is a devastating pediatric brain tumor that affects 200-300 individuals in the US per year. Median survival is 9-11 months, and there are virtually no long-term survivors. Despite decades of clinical trials, radiation therapy remains standard of care, extending survival by 2-3 months. Development of effective therapies for H3K27-altered DMG is a critical unmet need. MALT1 is the effector molecule of the CARMA-BCL10-MALT1 (CBM) signalosome, a cytoplasmic protein complex that drives downstream signaling, including activation of the pro-survival NF-kB transcription factor. MALT1, which possesses distinct scaffolding and protease activities, has been best characterized as an oncogenic driver in multiple lymphomas. More recently, MALT1 has been shown to act in multiple solid tumor types (breast, lung, glioblastoma) to promote cell viability, proliferation, and migration/invasion. Based on these studies, we hypothesize that MALT1 promotes H3K27-altered DMG cancer cell proliferation and survival and that MALT1 inhibition will abrogate DMG tumor progression. Methods/Results: We screened a panel of patient-derived DMG cell lines by Western blot and found that the CBM signalosome components BCL10 and MALT1 are present in all cell lines tested. We next optimized a brain-penetrant lipid nanoparticle (LNP) delivery system to achieve efficient siRNA knockdown in non-adherent DMG cells and utilized this approach to knockdown MALT1 in DIPG07, BT245, and DIPG XIII FL cell lines. Preliminary findings indicate that loss of MALT1 leads to a reduction in DMG cell viability. To complement this RNAi-based approach, we utilized the blood brain barrier (BBB)-penetrant small molecule MALT1 inhibitor “M1i-124.” This compound, discovered in our laboratory, is a protein-protein interaction inhibitor that disrupts the binding of BCL10 and MALT1 and blocks both MALT1 scaffold and protease activities (manuscript in revision). M1i-124 treatment, at nanomolar-range doses, reduces the viability of both DIPG07 and BT245 DMG cell lines. Conclusions: We found that both siRNA-mediated MALT1 knockdown and the small molecule MALT1 inhibitor M1i-124 are toxic to DMG cells. These preliminary findings point to the potential for therapeutic targeting of MALT1 in H3K27-altered DMG. Future Directions: We will next evaluate the mechanism by which MALT1 knockdown or pharmacological inhibition impacts DMG cell survival using RNA-sequencing and proteomics approaches. We will also use H3K27-altered DMG xenograft models to evaluate the impact of MALT1 inhibition on H3K27-altered DMG tumor progression in vivo.
Citation Format: Hannah Butterfield, Juliana Hofstatter Azambuja, Lisa Maurer, Saigopalakrishna S. Yerneni, Andrea Cruz, Matthew Halbert, Taylor Gatesman, Sameer Agnihotri, Peter C. Lucas, Linda M. McAllister-Lucas. MALT1 as a regulator of tumor progression in H3K27-altered diffuse midline glioma [abstract]. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_1):Abstract nr A002.