Diffuse Intrinsic Pontine Glioma (DIPG) is an incurable pediatric brain tumor of the pons and brainstem. Therefore, there is a desperate need for new therapeutics. Genomic profiling of tumors identified a highly prevalent dominant negative somatic mutation at lysine (K)-27 in histone genes HIST1H3B and H3F3A. Clonal evolution modeling suggests these mutations are truncal, and studies have demonstrated their contribution to tumorigenesis. ONC201, a first-in-class DRD2 antagonist and ClpP agonist is an anticancer drug developed by Oncoceutics, which targets the unfolded protein response (UPR) and integrated stress response (ISR) signaling and is actively being investigated in patients with recurrent H3 K27M-mutant gliomas. In adults with recurrent glioma, single agent studies showed benign-safety, no dose-limiting toxicities and a durable objective response when administered orally. In addition, intra-tumoral drug levels exceeded therapeutic thresholds, and induced tumor cell apoptosis. Based on this and response seen in a pediatric patient with DIPG for whom compassionate use of ONC201 was approved, a multi-arm, non-randomized multi-institutional Phase I clinical trial (NCT03416530) is actively accruing patients. However, the strength of UPR and ISR in DIPGs and their effect on DIPG response to ONC201 is not known. Our group employed bulk/single cell transcriptomic and single cell proteomic approaches to demonstrate substantial heterogeneity in UPR and ISR signaling in human DIPG samples. Consistent with this, DIPG cell lines exhibited considerable variability in sensitivity to ONC201. Single cell profiling identified tumor sub-populations with significant proliferative capacity even after ONC201 exposure. Incomplete response promotes recurrence. To target these cells, we performed a synthetic lethality screen with a library of 360 FDA-approved CNS penetrant compounds, which identified HDAC inhibitors and DNA damage-inducing chemotherapy as having synergy with ONC201. Thus, we suggest that tumor heterogeneity impacts sensitivity to ONC201 and that this can be reduced by combination treatments.
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.
Diffuse Intrinsic Pontine Glioma (DIPG) is an incurable pediatric brain tumor. An almost ubiquitous dominant negative mutation at lysine (K)-27 in genes encoding histone genes HIST1H3B and H3F3A found in patient tumors is a driver of DIPG development. ONC201, a small molecule DRD2 antagonist and ClpP agonist developed by Chimerix Inc, targets the unfolded protein response (UPR) and integrated stress response (ISR) signaling. It is under clinical investigation in patients with recurrent H3K27M DMGs. In adults, single agent studies have shown durable objective responses when administered orally. A multi-arm, non-randomized multi-institutional Phase I clinical trial (NCT03416530) for pediatric patients with H3K27M DMGs is open and accruing. Preliminary results suggest that the drug has a favorable safety profile and holds promise for patients with DIPGs and other midline gliomas. However, the mechanism of action of ONC201 against DIPGs warrants further study. Here, we show that ONC201 is cytotoxic to DIPGs in vitro and in vivo. RNA Seq analyses revealed cell context specific deployment of PERK-activated UPR and calcium signaling-associated RON tyrosine kinase-macrophage stimulating protein (MSP) signaling in DIPGs. Single cell proteomic assays revealed substantial heterogeneity in the sensitivity of DIPG cells to ONC201, and identified stem-like sub-populations of H3K27M DIPGs with intrinsic insensitivity to the drug. ONC201 treatment, which induces cellular stress, also sensitized DIPG cells to cytolytic activity by ex-vivo expanded and activated innate immune cells, in vitro. Ongoing in vivo experiments are expected to support a novel investigational study in patients with midline gliomas.
Diffuse Intrinsic Pontine Glioma (DIPG) is an incurable pediatric brain tumor. Current standard of care has shown no improvements in survival. Here, we report our study of ONC201, a first-in-class small molecule developed by Oncoceutics, Inc., against a panel of DIPG cells in vitro and in mouse orthotopic models. ONC201 inhibits signaling through dopamine receptor D2 (DRD2), a G protein-coupled receptor (GPCR). MTT assays revealed a delayed but more robust response to ONC201, as measured by IC50 values, in DIPGs with histone H3.3-K27M expression compared to cells expressing wildtype (WT) or K27M mutant histone H3.1. Interestingly, transcriptomic profiling identified an association of this response delay with an elevation of genes controlling the cellular unfolded protein response, lysosomal and vacuole organization, and a decline in nucleic acid biosynthetic genes. These cells were also more committed to neuronal and oligodendrocytic lineage specification. By contrast, WT-H3 DIPGs that survived ONC201 treatment were stem-like and exhibited altered expression of genes controlling cell proliferation and apoptosis induction, respectively. Single cell proteomics validated the increase in anti-apoptotic proteins in these cells. Intraperitoneal administration of ONC201 for 7-weeks in mice bearing pontine xenografts of histone H3.1-K27M mutant DIPGs, caused a complete blockade of tumor growth relative to untreated controls. However, identical treatment of animals with forebrain tumors resulted only in a partial reduction in tumor burden, suggesting that the tumor microenvironment may be involved in the differential effect. These data indicate that tumor intrinsic and extrinsic factors may contribute to the response of DIPG tumors to ONC201.
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