PDTM-25. STUDY OF ONC201 IN PRE-CLINICAL MODELS OF DIPG

Abstract

Abstract Diffuse Intrinsic Pontine Glioma (DIPG) is an incurable pediatric brain tumor that occur in the pons and brainstem and have a peak onset of age between 6–9 years of age. Radiation is currently used as standard of care. Chemotherapy has shown no improvements in survival. Here, we report our study of ONC201, a first-in-class anticancer small molecule developed by Oncoceutics, Inc., against DIPG cells in vitro and in mouse orthotopic models. ONC201 was discovered in a screen as a p53-independent inducer of the pro-apoptotic cytokine TRAIL. It is known to directly and selectively inhibit dopamine receptor D2 (DRD2), a member of the G protein-coupled receptor (GPCR) family. MTT assays to determine the sensitivity of DIPG cells to ONC201 revealed a slight but not significantly different response to the drug based on their expression of wild type (WT) histone H3 or histone H3K27M mutant protein, with IC50 values in the range of 3-8mM. Decrease in cell growth was associated with a decrease in AKT and ERK phosphorylation and an increase in TRAIL expression. In vivo, intraperitoneal administration of ONC201 to mice bearing pontine DIPG tumors, once every week for 6 weeks, caused a significant reduction in tumor burden relative to untreated controls as measured by bioluminescence assays. However, stoppage of treatment resulted in tumor regrowth within 6 weeks, suggesting the existence of a population that were not eliminated by the current schedule of ONC210. Single cell proteomic analyses-based comparison of untreated and ONC201-treated DIPG cells showed an expected global reduction in pro-survival signals such as phosphorylated AKT and ERK. Molecules with potential to predict susceptibility of cells to ONC201 were also revealed, and are being confirmed by transcriptome analyses. Results of a chemical screen to target ONC201-refractory tumor cells will be discussed.