Preclinical Combination of ONC201 with Radiotherapy and Temozolomide in a GBM Mouse Orthotopic Model Results in Reduced Tumor Burden and Prolonged Survival

Abstract Glioblastoma (GBM) is the most common and lethal primary malignancy of the central nervous system. It is estimated that more than 13,000 new cases of GBM will be diagnosed this year in the United States. Despite multidisciplinary treatments such as surgery, chemotherapy, and radiotherapy, the five-year survival rate for GBM patients is only 6.8 percent and has shown no notable improvement in the last three decades. There have only been five drugs and one device ever approved by the FDA for the treatment of GBM since it was first identified in the scientific literature in the 1920’s. Our in vitro studies suggested that first-in-class small-molecule imipridone TIC10/ONC201 can inactivate ERK/AKT, induce the integrated stress response (ISR), upregulate pro-apoptotic TRAIL receptor DR5, deplete cancer stem cells, and induce mitochondrial dysfunction, growth arrest or cell death in GBM cells. Knockdown of ClpP protects GBM cells from ONC201 but not TMZ. ONC201 crosses the blood-brain barrier and has induced durable tumor regressions in adult and pediatric H3K27M-mutant diffuse midline glioma patients. We hypothesized that ONC201 may synergize with radiotherapy and temozolomide in GBM. GBM mouse orthotopic models were established through intracranial injection of luciferase expressing U251 GBM cells with a KOPF model 940 small animal stereotaxic frame and a Stoelting Quintessential Stereotaxic Injector. Tumor formation and growth was confirmed with bioluminescence imaging. Randomized treatment group mice received weekly treatment of ONC201 (100 mg/kg p.o.) and/or radiotherapy (2 Gy local irradiation) and/or TMZ (20 mg/kg i.p.) for four weeks for long term survival and tumor monitoring or one week for short term biomarker studies. We observed that the triple combination of ONC201, radiotherapy and TMZ significantly prolongs survival and reduces tumor burden compared to single treatment and dual combinations. Short term biomarker studies demonstrated that triple combination treatment decreases tumor cell proliferation, induces more apoptosis and inhibits ClpX to unleash mitochondrial ClpP. Our data support further development of the triple combination regimen of ONC201, TMZ and radiation therapy for GBM first-line treatment. Citation Format: Lanlan Zhou, Laura Jinxuan Wu, Jun Zhang, Andrew George, Marina Hahn, Leiqing Zhang, Attila A. Seyhan, Wafik S. El-Deiry. Preclinical combination of ONC201 with radiotherapy and Temozolomide in a GBM mouse orthotopic model results in reduced tumor burden and prolonged survival. [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 5494.