Abstract 4990: Dual inhibitor of ACVR1 and MEK 1/2 E6201 and PI3K/mTOR inhibitor paxalisib synergistically inhibit cell growth in DMG

Abstract Diffuse midline glioma (DMG) is an aggressive pediatric glioma with no curative treatment options. Mutation in MAPK pathway is common in many DMG tumors, however, has not been largely explored before. E6201 is a dual inhibitor of ACVR1 and MEK 1/2. It is currently in a phase 1 clinical trial for BRAF/MEK mutant melanoma. E6201 achieves higher levels in brain compared to other MEK inhibitors, suggesting it might be a promising therapeutic option for DMG. Previously, E6201 was effective in DMG cell lines with ACVR1 mutation, such as HSJD007. We have evaluated the effect of E6201 in two MAP kinase pathway activated, novel DMG cell lines, DIPG2JA and JHH-DIPG17. DIPG2JA has a KRAS mutation, leading to upregulation of MAPK pathway, and JHH-DIPG17 has two NF1 alterations predicted to disrupt this tumor suppressor, resulting in activation of MAPK pathway. Treatment of DIPG2JA with E6201 identified an IC50 of 44 nM, which is comparable to an IC50 of 71nM in the ACVR1 mutant DMG HSJD007. E6201 suppressed phospho—ERK and induced apoptosis as measured by cPARP western blot in DMG cells. Evaluation of cell viability by CellTiterBlue viability assay demonstrated that E6201 suppressed DMG growth between 0.05uM to 1uM concentrations. (DIPG2JA p=0.0004, JHH-DIPG17 p<0.0001 by t-test compared to control). Compensatory upregulation of mTOR pathway is often associated with downregulation of MAPK pathway, and we hypothesized that E6201 will synergize with a PI3K/mTOR inhibitor to induce DMG cell death. We selected the brain-penetrant PI3K/mTOR inhibitor paxalisib, because this drug is currently being tested in early phase clinical trials for DMG. Through CellTiterBlue cell viability assay, we showed that E6201 synergizes with paxalisib to inhibit cell growth. The ZIP synergy scores were 13.1 for HSJD007 and 12.7 for DIPG2JA according to the SynergyFinder program, suggesting synergistic interaction between E6201 and paxalisib. In vitro experiments for further evaluation of the combination treatment of E6201 and paxalisib are underway and in vivo studies are pending. From our data, E6201 as a single agent is a promising therapeutic option for DMG. With further evaluation of combination of E6201 and paxalisib, we believe that combination therapy will be an even more effective treatment option for DMG. Citation Format: Hyuk Jean Kwon, Abigail Tindall, Charles Eberhart, Jeffrey Rubens, Eric Raabe. Dual inhibitor of ACVR1 and MEK 1/2 E6201 and PI3K/mTOR inhibitor paxalisib synergistically inhibit cell growth in DMG. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4990.