DDDR-11. Pharmacological inhibition of or reduced EZH2 levels sensitized diffuse intrinsic pontine gliomas (DIPG) to ONC201, leading to synthetic lethality

Abstract BACKGROUND ONC201 is a first-in-class, blood-brain barrier penetrant imipridone that showed promise against H3K27M gliomas. Mechanistically, H3K27M mutation inhibits EZH2 in the methylating H3K27. In this context, we hypothesized that pharmacologic inhibition of EZH2 should recapitulate the physiologic effects of H3K27M mutation, with the corollary of synthetic lethal interactions between EZH2 inhibition and ONC201. OBJECTIVE Here, we investigated i) EZH2 expression level in H3K27 wild-type diffuse intrinsic pontine gliomas correlated with ONC201 sensitivity and ii) potential synergy between ONC201 and EZH2 inhibition. METHODS pre-clinical laboratory investigation. RESULTS In a panel of H3K27 wild-type diffuse intrinsic pontine glioma cell lines, EZH1/EZH2 expression correlated with ONC201 sensitivity. RNA-seq showed that ONC201 and EHZ2 inhibitor tazemetostat-treated cells exhibited similar transcriptional profiles, sharing top-regulated genes. This finding suggests that ONC201 and EHZ2 inhibition converge on regular nodes within the same linear pathway to disrupt shared cellular functions. Supporting this hypothesis, ONC201 and EZH2i-treatment caused similar changes in the profile of cytokine release. In contrast, there was no overlap in the transcription or cytokine profiles obtained after ONC201 and Panobinostat (an HDAC inhibitor) treatment. Across all H3K27 wild-type diffuse intrinsic pontine glioma cell lines, the combination of ONC201 and the EZH2 inhibitor tazemetostat resulted in synergistic cytotoxic effects. Notably, the H3K27 methylation function of EZH2 was not affected by ONC201 treatment, indicating this function does not define the principal convergence point for the physiologic effects of ONC201 and EZH2 inhibition. CONCLUSION ONC201 and EHZ2 inhibition converge on nodes within the same linear pathway and exhibit synthetic lethal interactions. These findings bear therapeutic implications and provide the foundation for drug combinations with ONC201.