Rohinton Tarapore

Background: Dopamine receptor D2 (DRD2) is a G protein-coupled receptor that is overexpressed in several malignancies and is also expressed in a variety of immune cells including Natural Killer (NK) cells. Interestingly, pharmacological antagonism of DRD2 results in induction of apoptosis in tumor cells and proliferation of immune cells. ONC201 is an anti-cancer, small molecule DRD2 antagonist that is in clinical trials for various cancers that overexpress DRD2 following completion of the first-in-human trial that established its recommended phase II dose of 625mg. Methods: A Phase I trial previously investigated single agent oral ONC201 in adult advanced solid tumor patients on a once every one (Q1W) or three weeks (Q3W) administration schedule. Twenty-eight evaluable patients received ONC201 on a Q3W schedule while 20 evaluable patients received ONC201 on a Q1W schedule. Levels of serum immune cytokines and effector molecules were evaluated throughout treatment using the Legendplex Assay. Peripheral blood mononuclear cells (PBMCs) and tumor biopsies from patients were also probed for immunomodulatory effects following treatment initiation. Results: Early serum immune cytokine induction occurred in the majority of patients on the trial, whereas delayed induction of immune effectors was exclusive to patients who experienced at least stable disease by RECIST criteria. Analysis of PBMCs revealed an increase in the number of circulating NK cells, as well as their expression of granzyme B, which occurs with NK cell activation, up to 3 days after initiating ONC201. Intratumoral infiltration of granzyme B+ NK cells was evident in one patient who underwent an on-treatment biopsy 10 days after beginning ONC201. A statistically significant increase in the induction of immune cytokines and effectors was apparent in patients who received ONC201 once every week versus once every three weeks. PK analyses in patients dosed on a Q1W schedule revealed therapeutic Cmax, AUC, and half-life values that were consistent with that of Q3W dosing and similar between the first (cycle 1) and fourth (cycle 2) dose. Prolonged stable disease for >6 months was observed in several prostate and endometrial cancer patients. Patients who had stable disease for >12 weeks had a significantly higher induction of cytokines and effector molecules compared to patients that progressed rapidly. Conclusions: ONC201 exhibits immunostimulatory activity in advanced cancer patients that is well tolerated and may be associated with clinical benefit. Activation of immune cells by ONC201 is another dimension of its efficacy that should accounted for when considering its clinical evaluation as a single agent or in combination for the treatment of advanced cancers. Citation Format: Rohinton S. Tarapore, Mark N. Stein, Andrew Zloza, Lorna Rodriguez, Jenna Newman, Charles Cheeson, Martin Stogniew, Wolfgang Oster, Joshua E. Allen. Clinical immunostimulatory activity of imipridone ONC201, a selective DRD2 antagonist, in advanced solid tumor patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5568.

Dopamine receptor D2 (DRD2) is a G protein-coupled receptor (GPCR) overexpressed in many cancers and its antagonism causes anti-tumor effects. ONC201, founding member of the imipridone class of small molecules, is a DRD2 antagonist in Phase II advanced cancer clinical trials. We evaluated the binding target and anti-tumor activity of ONC206, an ONC201 analog. An orphan small molecule target prediction algorithm revealed that ONC206, like ONC201, antagonizes DRD2. Experimental GPCR profiling using the PathHunter® β-Arrestin assay, confirmed that ONC206 selectively antagonizes D2-like (DRD2/3) but not D1-like (DRD 1/5) dopamine receptors. In this assay, ONC206 possesses a ~10-fold increased potency for DRD2 compared to ONC201 with a Ki of ~320nM with selectivity that was superior to approved antipsychotics. Shotgun mutagenesis across 350 amino acids of DRD2 identified 7 residues critical for ONC206-mediated antagonism of DRD2-induced calcium flux. Consistent with competitive inhibition, mutated residues were within the orthosteric binding site. While 6 mutated residues were also critical for ONC201 activity, one of the mutated residues was unique to ONC206, suggesting differentiated receptor pharmacology. TCGA analysis and immunohistochemistry of patient-derived tissue microarrays revealed DRD2 was overexpressed in neuroblastoma, sarcoma and pheochromocytoma specimens relative to normal tissues. In vitro profiling of ONC206 in the Genomic of Drug Sensitivity in Cancer collection of cell lines revealed broad nanomolar efficacy across most tumor types (GI50 <78-889nM) and ~5 to 20-fold improved potency relative to ONC201. Bone cancer and neuroblastoma were identified as the most ONC206-responsive solid tumor types that were comparatively less responsive to ONC201. Within bone cancer, Ewing's sarcoma (n=16) was most sensitive to ONC206 with nanomolar sensitivity (GI50 168-303nM) that was superior to ONC201. ONC206 was highly efficacious in neuroblastoma (n=35, GI50 87-589nM) including cell lines derived from metastatic sites and with MYCN amplification associated with poor prognosis. In the PC12 rat pheochromocytoma cell line ONC206 (GI50 200nM) was superior to ONC201. ONC206 time-course experiments revealed anti-cancer effects occurring at 48-72 post-treatment, similar to ONC201. In support of a wide therapeutic window, ONC206 reduced the viability of normal human fibroblasts at relatively high doses (GI50 > 5µM). Efficacy evaluation in the MHH-ES-1 Ewing's sarcoma xenograft model demonstrated that ONC206 (100 mg/kg PO every 10 days) causes significant tumor growth inhibition that was comparable to methotrexate (400 mg/kg, IP) while being better tolerated. Thus, imipridone ONC206 acts as a selective antagonist of DRD2/3 at nanomolar concentrations and may address tumor types where the properties of ONC201 do not permit for complete therapeutic engagement in vivo. Citation Format: Varun Vijay Prabhu, Neel Madhukar, Rohinton Tarapore, Mathew Garnett, Ultan McDermott, Cyril Benes, Neil Charter, Sean Deacon, Alexander VanEngelenburg, Joseph Rucker, Benjamin Doranz, Olivier Elemento, Wolfgang Oster, Martin Stogniew, Joshua Allen. Receptor pharmacology and anti-cancer activity of selective DRD2/3 antagonist imipridone ONC206 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4874.

D2-like dopamine receptors (DRD2/3/4) are G protein-coupled receptors (GPCRs) that are overexpressed in glioblastoma (GBM) and their antagonism induces tumor cell apoptosis. We describe the first selective DRD2/3 antagonist for neuro-oncology using computational, receptor pharmacology, biochemical and clinical studies. Consistent with an in-silico prediction and in contrast to antipsychotics that target several dopamine receptors and other GPCRs, β-arrestin recruitment and cAMP assays determined that ONC201 is a selective DRD2/3 antagonist. Schild analyses and radioligand competition assays revealed competitive and non-competitive DRD2 antagonism with a potency (2-3 µM) that is consistent with anticancer activity and driven by an unusually slow association rate. Proof-of-concept studies show that selective DRD2 inhibition induces superior anti-cancer efficacy relative to pan-targeting of the dopamine receptor family. In accordance with superior selectivity, ONC201 also exhibited a wider therapeutic window compared to antipsychotics. Shotgun mutagenesis across 350 amino acids of DRD2 identified 8 residues that are critical for ONC201-mediated DRD2 antagonism. Consistent with competitive inhibition, several mutated residues were within the orthosteric binding site. However, distal residues were identified that were not involved in DRD2 antagonism by antipsychotics and may explain the selectivity and non-competitive antagonism of ONC201. In vitro and in vivo studies have previously demonstrated single agent ONC201 efficacy in GBM models (Allen et al 2013). Analyses of The Cancer Genome Atlas and tissue microarrays revealed high DRD2 expression relative to other dopamine receptors, correlation with poor prognosis and high DRD2 expression in primary rather than secondary GBM. A linear correlation between DRD2 mRNA and ONC201 GI50 was observed among GBM cell lines in the NCI60 panel. Interestingly expression of DRD5, a D1-like dopamine receptor that counteracts DRD2 signaling, was significantly inversely correlated with ONC201 potency in the NCI60 dataset (P <.05). Furthermore, a de novo missense DRD5 mutation was identified in cancer cells with acquired resistance to ONC201, and overexpression of the mutant construct could recapitulate resistance. ONC201 exhibited biological activity in a phase II recurrent GBM study, including tumor regressions (Arrillaga et al, 2017). Among the 15 available archival patient tumor specimens from the first cohort of this trial, all had DRD2 expression and 8 had low DRD5 expression that was associated with superior progression-free and overall survival, with 4/8 DRD5- and 0/7 DRD5+ patients alive after 15 months (P=0.012). Thus, ONC201 possesses unique receptor pharmacology as the first selective DRD2/3 antagonist for clinical neuro-oncology that has exhibited clinical activity in biomarker-defined recurrent high grade glioma patients. Citation Format: Varun Vijay Prabhu, Neel Madhukar, C. Leah B. Kline, Rohinton Tarapore, Wafik S. El-Deiry, Joseph Rucker, Benjamin Doranz, Faye Doherty, Alexander VanEngelenburg, Jessica Durrant, Cyril Benes, Sean Deacon, Neil Charter, R. Benjamin Free, Wolfgang Oster, David Sibley, Isabel Arrillaga, Olivier Elemento, Joshua E. Allen. Selective targeting of dopamine receptor dysregulation in high grade gliomas with imipridone ONC201 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3857.

Background: BRAFV600E mutations occur in ~10% of colorectal cancer (CRC), are associated with poor survival and have limited responses to BRAF/MEK inhibition with or without EGFR inhibition. There is an unmet need to understand the biology of poor prognostic BRAFMT CRC. Using gene expression data from BRAFMT CRC patient samples, we recently identified that dopamine receptor degradation and unfolded protein response are dominant pathways deregulated in the BRAFMT subgroup with the poorest outcome. The aim of this study was to investigate the role of the dopamine receptor 2 (DRD2) pathway as novel target in BRAFMT CRC cells. Methods: Small molecule DRD2 antagonists ONC-201 and ONC-206 (Oncoceutics Inc) and a panel of isogenic paired and non-isogenic BRAFMT and BRAFWT cells were used. MTT, Flow Cytometry, Western blotting and caspase- 8, 3/7 activity assays were used to measure cell survival/death. DR5 cell localization was performed using flow cytometry. A compound library including small molecules approved by the FDA was used. Results: BRAFMT CRC cells were highly sensitive to the DRD2 antagonists ONC-201 and ONC-206 with IC50 values between 1.9-4.5μM and 0.16 and 0.24μM respectively. Treatment with ONC-201 and ONC-206 resulted in marked increases in expression levels of the endoplasmic reticulum stress proteins ATF4, CHOP and the active (spliced) form of XBP1 (sXBP1) (indicators of activation of the PERK and IRE1α UPR branches), and this was associated with apoptosis induction as indicated by PARP cleavage, caspase-9 cleavage and increased caspase-3/7 activity in the BRAFMT VACO432 cell line but not in the WT VT1 clone. Importantly, no significant effect on proliferation or apoptosis was obtained in the normal colon CCD-18 fibroblast cell line following treatment with ONC-201 or ONC-206. Using a small molecule compound library, we found that the taxanes paclitaxel and docetaxel resulted in strong synergy and apoptosis when combined with ONC-201 or ONC-206, in particular in BRAFMT CRC cells. Mechanistically, we found that the apoptosis induced by combined ONC-201/paclitaxel treatment was dependent on caspase-8 activation and on up-regulation of the death receptor 5 (DR5). Conclusions: Taken together, we have identified a role for DRD2 signalling in the survival of BRAFMT CRC cells. Our data support the development of DRD2 antagonists, in particular in combination with taxanes, for the treatment of BRAFMT CRC tumours. Citation Format: Arman Javadi, Nicholas Forsythe, Alaa Refaat, Jessica-Ann Weir, Hajrah Khawaja, David Waugh, Rohinton Tarapore, Joshua E. Allen, Patrick Johnston, Sandra Van Schaeybroeck. Targeting the dopamine receptor 2 in BRAF mutant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3448.

Background: ONC201, an imipridone that is a selective antagonist of the G protein-coupled receptors dopamine receptor D2 (DRD2) and D3 (DRD3), has exhibited biologic activity and an exceptional safety profile in a phase II study in bevacizumab-naïve recurrent glioblastoma (Arrillaga et a.l, 2017). Single-agent ONC201 efficacy has been observed in preclinical glioblastoma models in addition to robust penetrance of the blood-brain barrier (Allen et al., 2013). DRD2 antagonism induces tumor cell apoptosis via the same signaling pathways affected by ONC201. In addition, DRD2 is expressed on NK and other immune cells and DRD2 antagonism can induce their activation. Methods: Cell viability assays were performed with ONC201 in >1000 Genomic of Drug Sensitivity in Cancer (GDSC) cell lines and NCI60. Immunohistochemistry staining of DRD2/DRD5 was performed in glioblastoma tissue microarrays and archival tumor tissues. Whole exome sequencing was performed in RKO cells with acquired resistance to ONC201. DRD5 wild-type and mutant constructs were generated for overexpression studies. ELISA was used to quantitate serum prolactin and immune effector (perforin) levels. Intratumoral drug concentrations were evaluated by LC-MS assays conducted on glioblastoma tissue resected from patients following the second dose of 625mg ONC201. Results: Evaluation of ONC201 in GDSC cell lines confirmed broad anticancer efficacy with high sensitivity (~1-3 µM) in human brain cancer. The Cancer Genome Atlas (TCGA) revealed that DRD2 is highly expressed in glioblastoma relative to other dopamine receptors and that genetic aberrations are rare. High expression of DRD2 occurred in primary, rather than secondary, glioblastoma and was associated with a poor prognosis. Immunohistochemistry of tissue microarrays revealed DRD2 overexpression in glioblastoma relative to normal brain. A linear correlation between DRD2 mRNA and ONC201 GI50 was observed among glioblastoma cell lines in the NCI60 panel. Interestingly, expression of DRD5, a D1-like dopamine receptor that counteracts DRD2 signaling, was significantly inversely correlated with ONC201 potency in the NCI60 and GDSC datasets (P <.05). Furthermore, a missense DRD5 mutation was identified in cancer cells with acquired resistance to ONC201. Resistance could be recapitulated with overexpression of the mutant or wild-type DRD5 gene. A significant induction of serum prolactin, a surrogate biomarker of target engagement, was detected upon ONC201 administration to recurrent glioblastoma patients. Intratumoral drug concentrations surpassed therapeutic levels, ranging from ~0.6-10µM at 24 hours post-dose. Immune effector levels in the serum correlated with the kinetics of a durable objective response observed in a patient with an H3.3 K27M glioma. Among the 15 available archival tumor tissue specimens, all had expression of DRD2 and 8/17 patients had low expression of DRD5. Patients with PFS>5 month had no detectable expression of DRD5, unlike those with PFS<5 months. In addition, 4/8 DRD2+DRD5- and 0/7 DRD2+DRD5+ patients are still alive with a median follow-up of 47.4 weeks. Conclusion: The dopamine receptor pathway is a novel therapeutic target that is dysregulated in glioblastoma and provides predictive and pharmacodynamic biomarkers of tumor sensitivity to ONC201. Citation Format: Varun Vijay Prabhu, Neel Madhukar, C. Leah B. Kline, Rohinton Tarapore, Wafik El-Deiry, Olivier Elemento, Faye Doherty, Alexander VanEngelenburg, Jessica Durrant, Andrew Zloza, Cyril Benes, Isabel Arrillaga, Wolfgang Oster, Joshua E. Allen. Targeting DRD2 dysregulation in recurrent glioblastoma with imipridone ONC201: predictive and pharmacodynamic clinical biomarker analyses [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A060.

ONC201 is the founding member of the imipridone class of compounds which selectively target G protein-coupled receptors (GPCRs). ONC201, currently in clinical trials, possesses an exceptional safety profile combined with anti-cancer effects that are driven by activation of the integrated stress response and inhibition of Ras signaling. In this study, we identified and characterized the previously unknown binding target of ONC201. Following its phenotypic discovery, a series of experiments indicated that ONC201 does not directly interact with many known cancer drug targets. BANDIT - a machine learning based drug target identification platform - predicted that ONC201 selectively antagonizes the GPCR dopamine receptor D2 (DRD2). DRD2 is overexpressed in many cancers, controls various pro-survival mechanisms including Ras signaling and stress pathways, and its antagonism causes anti-proliferative and pro-apoptotic effects in malignant cells. PathHunter® β-Arrestin and cAMP assays determined that ONC201 selectively antagonizes DRD2 and DRD3. Antipsychotics antagonize multiple dopamine receptor family members that belong to either the D1-like or D2-like subfamilies that cause opposing downstream effects. Consistent with BANDIT, in contrast to antipsychotics, ONC201 did not antagonize other dopamine receptors or other GPCRs with known ligands. Schild analysis and radioligand competition assays revealed a DRD2 affinity of ~3uM, consistent with ONC201 anticancer activity. In accordance with superior selectivity of ONC201 among the GPCR superfamily, ONC201 exhibited a wide therapeutic window in tumor versus normal cell viability assays compared to antipsychotics. In support of the hypothesis that selectively targeting D2-like receptors yields superior anti-cancer efficacy, combined DRD2/DRD1 inhibition with tool compounds was inferior to DRD2 inhibition alone. Further characterization revealed that ONC201 had a very slow association rate for DRD2 relative to antipsychotics, whereas the dissociation rate was similar to atypical antipsychotics that are well tolerated. Shotgun mutagenesis alanine scan mapping across 350 amino acids of DRD2 identified 8 residues critical for ONC201-mediated antagonism of dopamine-induced calcium flux. Several of these residues were not conserved among the dopamine receptor family and the residue with the largest effect is not conserved in any other family member, suggesting the basis of ONC201 specificity. Consistent with competitive inhibition, several residues were within the orthosteric binding site, however, two allosteric residues were also identified. In summary, ONC201 is the first DRD2 antagonist under clinical development for oncology and its differentiated receptor pharmacology explains its unique selectivity, anti-cancer activity, and safety that has been observed in clinical trials. Citation Format: Neel Madhukar, Varun Vijay Prabhu, Lakshmi Anantharaman, Chidananda Sulli, Edgar Davidson, Sean Deacon, Rohinton Tarapore, Joseph Rucker, Neil Charter, Banjamin Doranz, Wolfgang Oster, Olivier Elemento, Joshua Allen. Differentiated receptor pharmacology of imipridone ONC201: The first DRD2 antagonist in clinical development for oncology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5223. doi:10.1158/1538-7445.AM2017-5223

DRD2 is a G protein-coupled receptor (GPCR) that is overexpressed in many cancers, controls an array of pro-survival signaling pathways, and its antagonism causes anti-cancer effects. ONC201, the founding member of the imipridone class of anti-cancer compounds, is a small molecule DRD2 antagonist that is in Phase I/II advanced cancer clinical trials. In this study, we evaluated the binding target and antitumor activity of ONC206, a chemical analogue of ONC201. An orphan small molecule target prediction algorithm revealed that ONC206, like ONC201, antagonizes DRD2. Experimental GPCR profiling using the PathHunter® β-Arrestin assay, determined that ONC206 selectively antagonizes the D2-like (DRD2/3/4), but not the D1-like (DRD 1/5), subfamily of dopamine receptors. ONC206 possesses a ~10-fold increased affinity for DRD2 compared to ONC201 with a Ki of ~320nM with selectivity that was superior to approved antipsychotics. The increased association rate for the ONC206-DRD2 interaction was responsible for the increased affinity, whereas the dissociation rate was similar to ONC201 and atypical antipsychotics that are well tolerated. TCGA analysis and immunohistochemistry of patient-derived tissue microarrays revealed DRD2 was overexpressed in neuroblastoma, sarcoma and pheochromocytoma specimens relative to normal tissues. In vitro efficacy profiling of ONC206 in the Genomic of Drug Sensitivity in Cancer collection of cell lines revealed broad efficacy across most tumor types (GI50 <78-889nM). Bone cancer and neuroblastoma were identified as the most ONC206-responsive solid tumor types that were comparatively less responsive to ONC201. Within bone cancer cell lines, Ewing’s sarcoma (n=16) was the most sensitive to ONC206 with nanomolar sensitivity (GI50 168-303nM) that was superior to ONC201. ONC206 was highly efficacious in neuroblastoma (n=35, GI50 87-589nM) including cell lines derived from metastatic sites and with MYCN amplification associated with poor prognosis. In the PC12 rat pheochromocytoma cell line ONC206 (GI50 200nM) was superior to ONC201. ONC206 time-course experiments revealed anti-cancer effects occurring at 48-72 post-treatment, similar to ONC201. In support of a wide therapeutic window, ONC206 reduced the viability of normal fibroblasts (HFF-1) at relatively high doses (GI50 > 5µM). Efficacy evaluations in MHH-ES-1 athymic nude mice xenografts demonstrated that ONC206 (100 mg/kg PO every 10 days) causes significant tumor growth inhibition that was comparable to methotrexate (400 mg/kg, IP) while being better tolerated. In summary, ONC206 is an imipridone that acts as a selective antagonist of DRD2 at nanomolar concentrations and has broad-spectrum anti-tumor activity. ONC206 may address tumor types where the properties of ONC201 do not permit for complete therapeutic engagement in vivo. Citation Format: Varun Vijay Prabhu, Neel Madhukar, Jessica Wagner, Rohinton Tarapore, Mathew Garnett, Ultan McDermott, Cyril Benes, Neil Charter, Sean Deacon, Alexander VanEngelenburg, Olivier Elemento, Wafik El-Deiry, Martin Stogniew, Wolfgang Oster, Joshua Allen. Potent anti-cancer activity of the imipridone ONC206: A selective dopamine D2-like receptor antagonist [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4147A. doi:10.1158/1538-7445.AM2017-4147A

ONC201, founding member of the imipridone class of compounds, is a highly selective small molecule G protein-coupled receptor (GPCR) antagonist that is in Phase I/II advanced cancer clinical trials. In this study, we evaluated GPCR engagement and antitumor activity of ONC212, an imipridone that is a chemical analogue of ONC201. Experimental GPCR profiling using the PathHunter® β-Arrestin assay, determined that ONC212 is a selective agonist of the orphan GPCR GPR132/G2A. Multidose validation confirmed nanomolar GPR132 agonist activity (EC50 ~400nM). GPR132 is a stress-inducible orphan GPCR that causes G2/M arrest. The tumor suppressive role of GPR132 has been demonstrated most notably in lymphoid leukemia. Gene expression analysis of samples in the Cancer Genome Atlas (TCGA) revealed GPR132 is expressed in a range of tumor types with highest expression in leukemia and lymphoma. The in vitro efficacy of ONC212 was assessed in the Genomic of Drug Sensitivity in Cancer (GDSC) collection of cell lines (>1,000 cell lines). Cell viability assays were performed at 72 hours post-treatment to generate dose responses curves at concentrations from 78nM up to 20μM. ONC212 was broadly efficacious across most solid tumors and hematological malignancies in the low nanomolar range. Ranking the sensitivity of cancer lines to ONC212 by tumor type revealed that leukemia and lymphoma are the most responsive tumor types based on completeness of response (area under the dose-response curve). Interestingly, we also observed that high expression of GPR132 significantly correlated with ONC212 efficacy in GDSC cell lines, suggesting the importance of GPR132 agonist activity for ONC212 efficacy. ONC212 was tested in 62 human leukemia cell lines that included acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myelogenous leukemia (CML) and hairy cell leukemia. ONC212 demonstrated broad spectrum anti-leukemic activity and was equally efficacious across all leukemia subtypes tested. Most cell lines (60/62) were responsive to ONC212 with GI50 ranging from <78nM to 456nM. Within ALL, both B-cell and T-cell ALL were highly sensitive to ONC212. ONC212 reduced cell viability in AML independent of complex karyotypes and p53 mutations that are associated with poor clinical prognoses. ONC212 was also tested in 58 lymphoma cell lines comprised of anaplastic large cell lymphoma, Burkitt's lymphoma, cutaneous T-cell lymphoma (CTCL), diffuse large B-cell lymphoma (DLBCL), Mantle cell lymphoma (MCL), Follicular Lymphoma and Hodgkin’s lymphoma. ONC212 reduced cell viability in most cell lines (56/58) and was equally efficacious regardless of subtypes with GI50 ranging from <78nM to 261nM. Thus, GPR132 agonist ONC212 possesses robust anti-cancer activity in hematological malignancies irrespective of leukemia and lymphoma subtype and provides further validation of the anti-cancer efficacy of the novel imipridone class of small molecules. Citation Format: Varun Vijay Prabhu, Neel Madhukar, Rohinton Tarapore, Mathew Garnett, Ultan McDermott, Cyril Benes, Neil Charter, Sean Deacon, Wolfgang Oster, Michael Andreeff, Olivier Elemento, Martin Stogniew, Joshua Allen. Potent anti-cancer effects of selective GPR132/G2A agonist imipridone ONC212 in leukemia and lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1155. doi:10.1158/1538-7445.AM2017-1155

ONC201, the founding member of the imipridone class of anti-cancer compounds, is a highly selective small molecule GPCR antagonist that is in Phase I/II advanced cancer clinical trials. In this study, we evaluated the anti-cancer effects of ONC212, an ONC201 analogue that possess the same unique core chemical structure shared by imipridones. The in vitro efficacy of ONC212 was assessed in the Genomics of Drug Sensitivity in Cancer collection of cell lines (>1,000 cell lines). Cell viability assays were performed to generate dose responses curves at concentrations from 78nM upto 20uM and at 72 hours post-treatment. ONC212 was broadly efficacious across most solid tumors and hematological malignancies in the low nanomolar range. Ranking the ONC212 sensitivity dataset revealed that leukemia is the most responsive tumor type based on completeness of response (area under the dose-response curve, AUC). ONC212 was tested in 65 leukemia cell lines in this study that is comprised of acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myelogenous leukemia (CML) and hairy cell leukemia. ONC212 demonstrated broad spectrum anti-leukemic activity and was equally efficacious across all leukemia subtypes tested, in terms of AUC. Most cell lines (63/65) were responsive to ONC212 with GI50 ranging from <78nM to 312nM. Within ALL, both B-cell and T-cell ALL were highly sensitive to ONC212. ONC212 reduced cell viability in AML independent of complex karyotypes that are associated with poor clinical prognoses. Thus, ONC212 possesses robust anti-leukemic activity irrespective of subtype and provides further validation of the anti-cancer efficacy of the novel imipridone class of small molecules. Disclosures Prabhu: Oncoceutics: Employment. Tarapore:Oncoceutics: Employment, Equity Ownership. El-Deiry:Oncoceutics: Equity Ownership. Stogniew:Oncoceutics Inc.: Employment, Equity Ownership. Oster:Oncoceutics: Employment, Equity Ownership. Allen:Oncoceutics: Employment, Equity Ownership.

ONC201 is a first-in-class small molecule inducer of the integrated stress response that is currently in phase II clinical trials in select advanced cancers with promising early clinical results. The efficacy of this novel agent has been demonstrated in numerous preclinical advance cancer models in multiple indications with an exceptional safety profile that has translated well to the clinic. To determine the preclinical sensitivity profile of ONC201 in cancer, we performed an in vitro efficacy screen across >1,000 human cancer cell lines that represent a diverse array of tumor types and genetic aberrations. Sensitivity profiling was assessed by cell viability assays using dose responses curves at concentrations up to 20uM and at 72 hours post-treatment. Ranking the sensitivity dataset by tumor type, non-Hodgkin's lymphomas and multiple myeloma were the most sensitive tumor type to ONC201. The mutation-agnostic efficacy that is most pronounced in lymphomas and multiple myeloma is in accordance with the recent findings that ONC201 induces the integrated stress response through a novel target to trigger is downstream late apoptotic effects. B-cell malignancies are particularly susceptible to induction of apoptosis via the integrated stress response, as they have relatively high basal activation of this pathway due to ER stress conferred by immunoglobulin production. Confirmatory studies revealed that multiple myeloma cell lines indeed possess pronounced sensitivity with nanomolar GI50s, unlike most other tumor types, that is particularly encouraging given the systemic concentrations observed in the first-in-man study. Together, these studies suggest specific advanced cancer indications, such as non-Hodgkin's lymphoma and multiple myeloma, as promising lead indications for this novel agent that are being evaluated in phase II clinical trials. Disclosures Allen: Oncoceutics, Inc: Employment, Equity Ownership. Tarapore:Oncoceutics, Inc: Employment, Equity Ownership.

TRAIL is an endogenous protein that initiates apoptosis selectively in cancer without toxic side effects, prompting interest in therapeutic modulation. We previously screened for small molecules that could upregulate the endogenous TRAIL gene to trigger apoptosis and restore anti-tumor immunity within tumor cells in a p53-independent manner. We showed that ONC201 (previously referred to as TIC10) is a dual inactivator of Akt and ERK, leading to nuclear translocation of Foxo3a and TRAIL gene activation (Allen et al., Science Translational Medicine, 2013). We recently found that ONC201 causes an early-stage upregulation of the integrated stress response through ATF4/CHOP/DR5 (Kline et al., Science Signaling, in press) and can inhibit cancer stem cell self-renewal (Prabhu et al., Cancer Research, 2015). ONC201 recently completed its first-in-man phase I clinical trial and several other trials in select advanced cancers are ongoing (NCT02250781, NCT02324621, NCT02420795, NCT02392572, NCT02609230, NCT02525692, NCT02038699). Leveraging the unique pharmacophore of ONC201, we synthesized ONC201 analogues in search for compounds with distinct therapeutic properties. After establishing the importance of the pyrido[3,4-e]pyrimidinone core structure of ONC201 in its anti-tumor activity (Wagner et al., Oncotarget, 2014), we performed detailed structure activity relationship (SAR) studies. We evaluated several ONC201 analogues with differing N-substituents around the core structure. Certain ONC201 analogues exhibit more rapid kinetics of activity and lowered IC50 values in some human cancer cell lines in vitro. Interim results of ONC212 sensitivity profiling in >100 genetically annotated cell lines from the Genomic of Drug Sensitivity in Cancer collection have corroborated this improvement in potency. One analogue, ONC212, has demonstrated compelling efficacy against several tumor types in vivo with no evidence of toxicity at therapeutic doses. Furthermore, in vitro mechanism studies have demonstrated overlap between ONC201- and ONC212-mediated signaling in tumor cells that includes activation of the integrated stress response. With a wide safety margin, distinct pharmacokinetics (PK), and robust potency, ONC212 is being developed as the next drug candidate from the new class of compounds defined by the novel pharmacophore of ONC201 in indications that complement the parent compound's use spectrum. Citation Format: Jessica Wagner, Gary Olson, Nallaganchu Rao Bhaskara, Richard S. Pottorf, Garnett J. Mathew, Cyril H. Benes, Rohinton Tarapore, Martin Stogniew, Lee Schalop, Wolfgang Oster, Josh E. Allen, Wafik S. El-Deiry. Structure-activity relationships and mechanistic analysis of analogues of the clinical-stage anti-cancer small molecule ONC201. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 349.

ONC201 is a first-in-class small molecule inducer of the integrated stress response that is currently in phase II clinical trials in select advanced cancers and exhibits a benign safety profile and promising early clinical results. The efficacy of this novel agent has been demonstrated in a variety of preclinical advanced cancer models in multiple indications with an exceptional safety profile that has translated well to the clinic. To better characterize the differential sensitivity of tumor cells to ONC201 we performed in vitro efficacy assays in the Genomic of Drug Sensitivity in Cancer collection of cell lines (>1,000 cell lines), in addition to profiling in NCI60 panel. Sensitivity profiling was assessed by cell viability assays using dose responses curves at concentrations up to 20uM and at 72 hours post-treatment. Ranking the sensitivity dataset by tumor type revealed that lymphoma, colon, prostate and brain cancers were highly responsive to ONC201. The strongest predictor of sensitivity to ONC201 was tumor type, with lymphoma being the strong predictor. Within lymphomas, diffuse histiocytic lymphoma was the most sensitive subtype. Mutations that are frequent in lymphoma were not associated with ONC201 sensitivity. Recent mechanistic studies have implicated the ER stress response in the early stage mechanism of ONC201 that triggers its downstream antitumor effects. The mutation-agnostic efficacy that is pronounced in lymphomas, prostate, colon, and brain cancers is in accordance with the recent findings that ONC201 induces the integrated stress response through a novel target to trigger is downstream late apoptotic effects. Cancers of the prostate and brain (glioblastoma multiforme) are among some of the solid tumors that are susceptible to induction of apoptosis via the integrated stress response, as they have relatively high basal activation of this pathway due to ER stress. Confirmatory studies revealed that brain cancer cell lines and ex vivo samples indeed possess pronounced sensitivity with nanomolar GI50s, unlike most other tumor types, which is particularly encouraging given the systemic concentrations observed in the first-in-man study. Together, these studies suggest specific advanced cancer indications, such as non-Hodgkin's lymphoma, multiple myeloma, and glioblastoma as promising lead indications for this novel agent that are being evaluated in phase II clinical trials. Citation Format: Rohinton Tarapore, Mathew Garnett, Ultan McDermott, Cyril Benes, Joshua Allen. ONC201 sensitivity profiling indicates pronounced sensitivity in lymphoid, prostate, colon and brain tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1236.

Advanced ovarian cancer (stages III and IV) is the most lethal gynecologic malignancy in the United States. Survival of this cancer has not improved to a major extent over the past decade. High-grade serous ovarian cancer (HGSC), in particular, is notable for its initial sensitivity to chemotherapy using platinum and taxane combination following debulking surgery. However, the vast majority of these cancers (>75-80%) recur within 12-24 months after diagnosis, and patients die of progressively chemotherapy-resistant disease. The identification of prognostic or predictive markers, for ovarian cancer is crucial to the development of therapeutic targets and thus improvement of survival. ONC201 is the first clinical bitopic antagonist of dopamine receptor D2 (DRD2), that is well tolerated and currently being investigated in several clinical trials for oncology. ONC206 is a chemical derivative of ONC201 with the same impridone core structure, which is also a DRD2 antagonist that exhibits distinct receptor pharmacology and nanomolar potency in various preclinical cancer models. However, the effects of ONC206 on HGSC progression and the mechanism of action have not been thoroughly explored. Preliminary data demonstrated that overexpression of DRD2 is associated with poor overall survival rates in patients with advanced stage HGSC. ONC206-treated HGSC cells demonstrated significantly lower growth rates and higher percentage of apoptotic cells than ONC201-treated cells did in vitro. Besides, intraperitoneal injection of ONC206 (100 mg/kg) twice a week into HGSC-bearing immunocompetent mice demonstrated decreased tumor volume in vivo. In addition, by using suspension mass cytometry with a panel of 28 antibodies, fresh tumor tissues from ONC206-treated mice showed markedly increase in intratumoral NK cells and activated CD8+ T cells densities. These data suggest that ONC206 is more potent than ONC201 in suppressing HGSC growth directly. In addition, ONC206 may also suppresses HGSC growth through activating immune cell response in tumor tissues. Further studies that define the molecular mechanism by which DRD2 modulates the tumor suppressive effect of ONC206 on HGSC cells by suppressing HGSC directly or enhancing anti-tumor immune cell activity will be perform to establish ONC206 as a novel therapeutic agent in treatment of HGSC patients. Citation Format: Chi Lam Au Yeung, Wen Hu, Sammy Ferri-Borgogno, Rohinton S. Tarapore, Joshua E. Allen, Karen H. Lu, Samuel C. Mok. Novel imipridone ONC206 suppresses ovarian cancer progression through modulating immune cell response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1440.

e14037 Background: H3 K27M-mutant diffuse midline glioma is an invariably lethal form of brain cancer that disproportionately affects children and young adults and has no effective treatment following front-line radiation. The initial disease definition in the 2016 WHO Classification of Tumors of the Central Nervous System regarded the H3 K27M mutation as pathognomonic, though the definition was updated in 2018 restricting the diagnosis to histologically diffuse gliomas that involve midline CNS structures (cIMPACT-NOW update 2). ONC201 is an investigational anti-cancer small molecule, DRD2 antagonist and ClpP agonist that has induced durable tumor regressions by RANO-HGG criteria in a registration cohort of recurrent diffuse midline glioma, H3 K27M-mutant patients treated with single agent ONC201. Methods: We present 7 patients with H3 K27M-mutant diffuse gliomas were enrolled in ONC201 clinical studies, though excluded from the registration cohort due to involvement of non-midline CNS structures, all within the cerebral hemispheres (3 frontal, 1 temporal, 1 frontotemporal, 1 parietal, and 1 corona radiata). Results: Two of the 7 patients underwent objective responses by RANO-HGG criteria as assessed by investigator, which was associated with clinical benefit that included increased mobility and level of alertness. Conclusions: These results demonstrate that H3 K27M-mutant diffuse gliomas occur outside of midline CNS structures, and suggest that ONC201 has single agent activity in H3 K27M-mutant gliomas irrespective of CNS location.

Background: H3 K27M-mutant diffuse midline glioma is a universally fatal malignancy primarily affecting children and young adults. While radiotherapy (RT) provides transient benefit, no effective systemic therapy is currently available and current standard of care is RT followed by monitoring. Dordaviprone (ONC201), a first-in-class imipridone, is an oral, blood-brain barrier penetrating, selective small molecule antagonist of dopamine receptor D2/3 (DRD2) and agonist of the mitochondrial protease ClpP. An integrated pooled analysis of five open-label trials previously demonstrated efficacy in dordaviprone-treated patients with recurrent disease. This phase 3 trial will be the first randomized, controlled study evaluating dordaviprone in patients with H3 K27M-mutant disease. Methods: ACTION (NCT05580562) is a randomized, double-blind, placebo-controlled, parallel-group, international Phase 3 study of dordaviprone in patients with newly diagnosed H3 K27M-mutant diffuse glioma. Patients who have completed standard frontline radiotherapy will be randomized 1:1:1 to receive placebo, once-weekly dordaviprone, or twice-weekly dordaviprone on two consecutive days. Primary efficacy endpoints are overall survival (OS) and progression-free survival (PFS) in all participants; PFS will be assessed by response assessment in neuro-oncology-high grade glioma by blind independent central review. Other objectives include assessments of safety, additional efficacy endpoints, clinical benefit, quality of life, pharmacokinetics, biomarkers, and healthcare resource utilization. Eligible patients will have histologically confirmed H3 K27M-mutant diffuse glioma, a Karnofsky/Lansky performance status ≥70, and completed first-line radiotherapy. Eligibility will not be restricted based on age; however, patients must be ≥10 kg at time of randomization. Patients with a primary spinal tumor, diffuse intrinsic pontine glioma, leptomeningeal disease, or cerebrospinal fluid dissemination are not eligible. ACTION is currently enrolling in the United States, with additional sites to be open internationally in 2023. Citation Format: Isabel Arrillaga-Romany, Andrew Lassman, Susan L. McGovern, Sabine Mueller, Louis B. Nabors, Martin van den Bent, Michael Vogelbaum, Joshua E. Allen, Allen S. Melemed, Rohinton S. Tarapore, Dewen Yang, Patrick Wen, Timothy Cloughsey. ACTION: A randomized phase 3 study of dordaviprone (ONC201) in patients with newly diagnosed H3 K27M-mutant diffuse glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT060.

5592 Background: mEC is a generally incurable, with limited therapeutic options. ONC201 is the founding member of the new class of compounds called imipridones that are orally active small molecules. ONC201 a specific antagonist of the G protein-coupled receptor DRD2 exerts antitumor activity via a series of established signaling pathways (dual inhibition ERK/AKT, integrated stress response). DRD2 expression is elevated in malignant versus normal endometrial tissue. Furthermore ONC201 has shown anti-cancer activity in preclinical models of EC. Methods: In a Phase I trial that included an expansion cohort, a total of 28 evaluable patients (pts) were treated with ONC201 at doses from 125mg every 3 weeks to 625 weekly. Five of these patients had advanced mEC. Results: The median age for the mEC patients was 60 years (56-72), the median number of prior treatments was 5 (3-6), 3 patients had prior radiation and all patients had prior surgery. One patient received 375mg ONC201 while the other 4 patients received 625mg ONC201, orally every 3 weeks. The median number of doses was 3 (2-14). Two of 5 patients exhibited regressions in individual metastatic lesions, however they did not qualify as overall objective responses by RECIST criteria. One of these two patients experienced stable disease for 42 weeks. There were no reported SAEs and no Grade > 1 AEs attributed to study drug. Conclusions: ONC201 is clinically active and well tolerated with oral administration in refractory mEC patients. Clinical trial information: NCT02250781. [Table: see text]

2059Background: ONC201 is a DRD2 antagonist in Phase II trials for cancers that exhibit dysregulation of the dopamine pathway. We previously reported an objective response in the first recurrent H3 K27M midline glioma patient who received ONC201 and that H3 K27M gliomas exhibit enhanced sensitivity to the compound in vitro. Here, we report the clinical experience with ONC201 to date in adult and pediatric H3 K27M glioma. Methods: As of February 1, 2018, 14 patients with H3 K27M glioma have received single agent ONC201 and had at least one post-treatment MRI. This includes 9 adult patients (8 glioblastoma, 1 diffuse midline glioma) and 5 pediatric patients (3 DIPG, 2 other diffuse midline gliomas). All patients had recurrent disease, except for 2 DIPG patients who had completed radiotherapy. Seven patients were enrolled on a clinical trial and seven were enrolled on compassionate use protocols. ONC201 was orally administered at 625 mg to adult patients and scaled based on body weight for pediatric patients...

ONC201 is the founding member of the imipridone class of anti-cancer small molecules that possess a unique core chemical structure. ONC201 is currently being evaluated in several Phase I/II clinical trials for advanced cancers. In the current study, we evaluated the single agent and combinatorial efficacy of ONC201 in preclinical models of acute leukemia and multiple myeloma (MM). In acute leukemia, we evaluated ONC201 anti-cancer effects in acute myeloid leukemia (AML) (Kasumi-1, HL60) and acute lymphoblastic leukemia (ALL) (Reh, Jurkat and MOLT-4) cell lines. We observed a time- and dose-dependent decrease in cell viability for every cell line in the panel (EC50 1-5 µM). Vincristine-resistant cells HL60/VCR were also sensitive to single agent ONC201 with EC50 values on par with corresponding vincristine-sensitive parental cells. Dose- and time-dependent induction of apoptosis was noted in Western blot analysis of caspase-3 cleavage in AML cell lines treated with 2.5 µM or 5 µM of ONC201 for 48 hr. Western Blot analysis further demonstrated inhibition of Akt and Foxo3a phosphorylation in Kasumi-1 cells, in line with the previously reported late-stage signaling effects of ONC201 in solid tumor cells (Allen et al, 2013). Sub-G1 analysis indicated that ONC201 induces apoptosis in ALL cells and a pan-caspase inhibitor reduced ONC201-mediated apoptosis. Western blot analysis revealed ONC201-mediated apoptosis involves PARP cleavage and caspase-9 activation in ALL cells. Anti-apoptotic Bcl-2 family members Bcl-2 and Bcl-xl were downregulated while the pro-apoptotic Bcl-2 family member Bim is upregulated in response to ONC201 treatment in ALL cells. ONC201 also downregulates the inhibitor of apoptosis (IAP) family proteins cIAP1 and cIAP2 in ALL cells. We observed inhibition of Akt phosphorylation upon ONC201 treatment of ALL cells. Fresh AML patient cells were also found to be sensitive to ONC201 in cell viability and caspase 3/7 activity assays at 5µM. We observed that independent clones of cancer cells with acquired resistance to ONC201 were more sensitive to cytarabine compared to parental ONC201-sensitive cancer cells. In addition, ONC201 demonstrated synergistic reduction in cell viability in combination with cytarabine in AML cell lines. Determination of combination indices (CI) revealed synergy at several concentrations (CI 0.336-0.75 in CMK cells). Also, ONC201 combined additively with midostaurin in CMK cells and vincristine in HL60/VCR cells. Thus, ONC201 is a promising combinatorial partner for AML therapies based on these preclinical sensitization results. In accordance with ONC201-mediated activation of the integrated stress response that B cells are highly sensitive to (Kline et al and Ishizawa et al, 2016), MM was identified as one of the most ONC201-sensitive tumor types in the Genomics of Drug Sensitivity in Cancer collection of cell lines. Three human MM cell lines were used for validation (KMS18, MM.1S and RPMI-8226), which revealed a time- and dose-dependent decrease in cell viability (EC50 1-2.5 µM). Bortezomib-resistant cells MM.1S 33X were sensitive to ONC201 as a single agent with EC50 values comparable to bortezomib-sensitive parental cells. We observed an average of 10-fold induction of ONC201-mediated apoptosis using Sub-G1 analyses in MM cells at 5 µM, 48 hrs post-treatment. Rescue of ONC201-mediated apoptosis was demonstrated using the pan-caspase inhibitor (Z-VAD-FMK). In addition, Western blot analysis in MM cells indicated a dose-dependent decrease in the anti-apoptotic protein XIAP which is a key mediator of apoptosis inhibition and is reported to be highly up-regulated in MM cells. Furthermore, ONC201 demonstrated synergistic reduction in cell viability at various concentrations in combination with either ixazomib or dexamethasone, which are used in the clinical treatment of MM, in RPMI8226 cells (CI 0.228-0.75). Also, ONC201 combined additively with bortezomib in RPMI8226 and MM.1S 33X cells. In summary, these preclinical studies support the ongoing ONC201 single agent trials in acute leukemias and MM. Our findings suggest that ONC201 may be an important therapeutic option for patients with hematological malignancies who have developed resistance to approved therapies. Additionally, our results point to specific standard-of-care therapies that may be combined with ONC201 to exert durable responses without adding to the burden of toxicity. Disclosures Prabhu: Oncoceutics: Employment. Tarapore:Oncoceutics: Employment, Equity Ownership. Oster:Oncoceutics: Employment, Equity Ownership. Allen:Oncoceutics: Employment, Equity Ownership. El-Deiry:Oncoceutics: Equity Ownership.

e14034Background: ONC201 is an antagonist of the G protein-coupled receptor DRD2 that crosses the blood-brain barrier and induces tumor cell apoptosis in preclinical models. The anti-tumor activity of ONC201 is pronounced in cells with low DRD5 expression and is associated with induction of the ATF4/CHOP/DR5-mediated integrated stress response pathway to trigger apoptosis. We previously reported the single agent activity of ONC201 in 17 adult patients with recurrent glioblastoma that demonstrated the safety, systemic pharmacodynamics, and a durable objective response when administered orally once every 3 weeks. Here, we evaluated the intratumoral drug concentrations and pharmacodynamic activity of ONC201 in adult recurrent glioblastoma patients who were treated on a weekly schedule. Methods: Six patients ≥18 years old with first recurrence of glioblastoma who were eligible for salvage surgical resection were enrolled. ONC201 was administered orally as 625 mg once a week. Salvage surgery was performed appr...

Background: ONC201 (also called TIC10) is an orally active, first-in-class small molecule that is in phase II clinical trials for advanced cancers based on its ability to activate apoptosis in tumor cells, but not normal cells, in a p53-independent manner. Recent studies have implicated the integrated stress response as an early stage mechanism of ONC201 that may lead to the previously observed downstream anti-cancer effects. This study was conducted to evaluate the anti-tumor activity of ONC201 on Cutaneous T-Cell Lymphoma (CTCL) cell lines and Sézary cells. Methods: We treated 8 CTCL cell lines (H9, HH, Hut78, Mac2A, MJ, MyLA, Pb2b and SeAx), peripheral blood mononuclear cells (PBMC) from 5 Sézary syndrome (SS) patients and 6 healthy donors with ONC201. MTS viability Assay was used to assess the anti-proliferation effect. Apoptosis was assessed using Annexin V FITC/PI staining and sub-G1 analysis by flow cytometry. Protein expression by western blotting was analyzed in 3 CTCL cell lines (HH, Hut78, MJ) and in PBMCs from 2 SS patients treated for 72 hours with ONC201including Activating Transcription Factor 4 (ATF4), interferon regulatory factor 7 (IRF7/pIRF7), Signal transducer and activator of transcription 3 (STAT3), Janus Kinase 3 (JAK3/pJAK3) and NF-κB family members (p65, RelB, c-Rel and p105). Results: MTS viability assay showed pronounced cell growth inhibition, significantly increasing in a time-dependent manner in H9, HH, Hut78, Mac2A, MJ, MyLa, Pb2b, and SeAx lines after a 96-hour incubation within a very narrow efficacy threshold ranging from 1.25 to 10µM (n = 8, p < 0.05). To determine whether growth inhibition of ONC201 is due to cell-cycle arrest and/or to apoptosis in CTCL cell lines, sub-G1 analysis by flow cytometry was measured in 3 CTCL cell lines (HH, Hut78 and MJ). The percentages of HH, Hut78 and MJ cells with sub-G1 population increased, suggesting that cells are undergoing apoptosis (n = 3, p < 0.05). Induction of apoptosis was further confirmed by Annexin V FITC/PI staining, revealing dose and time dependent apoptosis induction in all 8 cell lines (Figure 1). To confirm cell line results in refractory ex vivo samples, we tested the pro-apoptotic effects of ONC201 on PBMCs from 5 SS patients who had high circulating CD4+CD26- malignant T-cells compared with PBMCs from 6 healthy donors. ONC201 induced significant levels of apoptosis in PBMCs from SS patients, but not in normal PBMCs (Figure 1, p < 0.001). Western blot analysis revealed that ONC201 increased the expression of ATF4, a hallmark of the integrated stress response and a negative regulator of IRF7. ONC201 decreased expression of IRF7/pIRF7 and down-regulated JAK3/pJAK3 and STAT3 expression in CTCL cell lines and PBMCs from SS patients. ONC201 also decreased the protein expression of NF-κB family members ( p65, RelB, c-Rel and p105) that can cause resistance to apoptosis in CTCL cells. Conclusions: ONC201 appears to be active as a single oral agent. It may impact key signaling pathways in CTCL preclinical models by inhibiting proliferation and inducing apoptosis through a mechanism that involves the integrated stress response, leading to inactivation of JAK/STAT signaling and down-regulation of the NFκB pathway. Figure 1. ONC201 induces apoptosis in CTCL cell lines and PBMCs from SS patients Figure 1. ONC201 induces apoptosis in CTCL cell lines and PBMCs from SS patients Disclosures Duvic: Eisai: Research Funding; MiRagen Therapeutics: Consultancy; Cell Medica Ltd: Consultancy; Tetralogics SHAPE: Research Funding; Soligenics: Research Funding; Array Biopharma: Consultancy; Innate Pharma: Research Funding; Allos (spectrum): Research Funding; Rhizen Pharma: Research Funding; Spatz Foundation: Research Funding; Oncoceutics: Research Funding; Huya Bioscience Int'l: Consultancy; Therakos: Research Funding, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Kyowa Hakko Kirin, Co: Membership on an entity's Board of Directors or advisory committees, Research Funding. Off Label Use: Most drugs for ctcl are non approved. This drug is a small molecule and is not approved for any cancer. Tarapore:Oncoceutics, Inc: Employment, Equity Ownership. Allen:Oncoceutics, Inc: Employment, Equity Ownership.

3005 Background: H3 K27M-mutant glioma is associated with a poor prognosis and there is no effective therapy following radiation. We report the clinical experience with single agent ONC201, the first small molecule DRD2 antagonist in oncology, in adults with recurrent H3 K27M-mutant glioma. Methods: Twenty-nine adult patients with recurrent H3 K27M-mutant glioma have been treated with single agent ONC201 as of January 20, 2019: 19 patients on NCT03295396; 8 patients on NCT02525692; 2 patients on compassionate use protocols under the Sponsor’s IND. Median age was 57 years old (range: 17-74), median prior lines of therapy was 2 (range: 1-4) and all patients received prior radiation (median 8.5 months from radiation completion to ONC201 initiation). ONC201 was orally administered at 625 mg weekly, except for one patient dosed once every 3 weeks. Results: As of February 5, 2019, 13 of 29 patients remain on-trial within median follow up of 6.5 months (range: 0.6-33.6), 8 patients are alive but off-trial with median follow up of 2.4 months (range: 0.2-9), and 8 patients have expired. Nine of 29 patients (31%) remain progression-free on ONC201 with a median follow up of 6.5 months (range 0.6-33.6). No dose-limiting toxicities or treatment discontinuations due to toxicity occurred. Three patients have experienced durable partial responses by RANO (4.3-28.5 months). In addition, one patient experienced complete regression that continues for > 14 months of all < 1 cm tumor lesions that are not measurable by RANO. Furthermore, 10 patients had a best response of stable disease by RANO, 12 patients experienced progressive disease, and 3 patients are not yet evaluable. Among the patients with a best response of stable disease by RANO, one patient had > 50% tumor regression in the basal ganglia that did not qualify as a partial response by RANO due to a new lesion on a confirmatory scan. Another patient with stable disease by RANO has had 37% tumor regression so far in the brainstem and remains on-treatment for 6 months. All tumor regressions remain durable to date and some were associated with improvements in disease-associated neurological symptoms. Conclusions: Single agent ONC201 is well tolerated and clinically active in adult recurrent H3 K27M-mutant glioma patients. Clinical trial information: NCT03295396; NCT02525692.

ONC201 is the lead small molecule of the imipridone class of anti-cancer compounds that is currently being evaluated in phase I/II advanced cancer clinical trials. ONC201 is a highly selective antagonist of the G protein-coupled receptor dopamine receptor D2 (DRD2) that has exhibited promising anti-cancer efficacy and an exceptional safety profile. In the current study, we evaluated the influence of the DRD2 pathway on the responsiveness of tumors to ONC201 in preclinical and clinical studies. In vitro and in vivo studies have previously demonstrated robust ONC201 efficacy in glioblastoma (Allen et al 2013) and lymphoma (Ishizawa et al 2016) models. ONC201 Phase I trials have also revealed evidence of clinical benefit in endometrial cancer (Stein et al 2016). In vitro efficacy profiling of ONC201 in the Genomic of Drug Sensitivity in Cancer (GDSC) collection of cell lines confirmed broad-spectrum anti-cancer efficacy with particularly high sensitivity in lymphoma, neuroblastoma, endometrial and brain cancer. DRD2 is overexpressed in many cancers and DRD2 antagonism kills cancer cells via the same signaling pathways that are altered in response to ONC201. Results from the Project Achilles screen indicate that anti-cancer effects of DRD2 knockdown in various tumor types correlated with overall ONC201 efficacy. In particular, we noted that lymphoma cells are highly sensitive to DRD2 knockdown- a tumor type where ONC201 performs well. Gene expression analysis of samples in the Cancer Genome Atlas (TCGA) revealed high DRD2 expression in ONC201-sensitive tumor types, such as lymphoma and glioblastoma, and that high expression of DRD2 in glioma was associated with a poor prognosis. High DRD2 expression was also observed in neuroendocrine prostate cancer relative to other prostate cancer subtypes. In immunohistochemistry analyses of patient-derived tumor tissue microarrays, DRD2 overexpression was particularly noted in endometrial cancer, neuroblastoma and pheochromocytoma relative to normal tissues. The anti-cancer activity of ONC201 in pheochromocytoma and neuroendocrine prostate cancer was confirmed in cell viability assays. In ONC201-treated patients, ELISA was used to quantitate serum prolactin levels, a clinical biomarker of DRD2 antagonism. A 2-fold mean induction of prolactin, was detected in the serum of ONC201-treated patients, in accordance with physiological DRD2 antagonism. Interestingly, expression of DRD5 (a D1-like dopamine receptor), which counteracts DRD2 signaling, was significantly negatively correlated with ONC201 in vitro potency in the NCI60 and GDSC dataset (P <.05). Furthermore, a missense DRD5 mutation was identified in cancer cells with acquired resistance to ONC201. In conclusion, the DRD2 pathway is expressed in ONC201-sensiive tumors and may provide biomarkers of response. Citation Format: Neel Madhukar, Varun Vijay Prabhu, Etienne Dardenne, Faye Doherty, Alexander VanEngelenburg, Rohinton Tarapore, Mathew Garnett, Ultan McDermott, Cyril Benes, Wolfgang Oster, Wafik El-Deiry, Mark Stein, David Rickman, Joshua Allen, Olivier Elemento. The small molecule imipridone ONC201 is active in tumor types with dysregulation of the DRD2 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2792. doi:10.1158/1538-7445.AM2017-2792

2563 Background: High-grade gliomas of the spinal cord are a rare and understudied entity, representing < 5% of all spinal cord tumors. Reported median survival times range from 10-16 months. Up to 53% of tumors harbor the H3 K27M mutation, which is associated with an unfavorable prognosis. Postsurgical treatment often includes radiation ± temozolomide, although the role of chemotherapy has not been conclusively established. At recurrence, there are no effective therapies and most clinical studies exclude patients with spinal cord tumors. We report our clinical experience with ONC201, a small molecule DRD2 antagonist and caseinolytic protease P agonist, in patients with recurrent H3 K27M-mutant diffuse gliomas of the spinal cord (scDG). Methods: Adults and children with recurrent H3 K27M-mutant scDG received ONC201 in two Phase II clinical trials enrolling adult recurrent H3 K27M-mutant glioma patients (NCT02525692; NCT03295396) and in one Phase I clinical trial enrolling pediatric patients (NCT03416530). Adult patients received ONC201 at the RP2D dose of 625 mg weekly and pediatric patients received the RP2D of 625 mg weekly, scaled by body weight. All patients began ONC201 as a single agent until disease progression. Five patients continued ONC201 combined with bevacizumab beyond progression. Results: As of January 15, 2020, 12 evaluable patients (adult n = 8, pediatric n = 4) received ONC201. The median age was 20.9 (range: 7-72) years. The median follow-up time for the single agent ONC201 group was 5.4 (range 1.3-9.7) months while that of the combination group is 7.4 (range 6.2-25.1) months. The median number of ONC201 doses was 10 (range: 5-39) for the ONC201 single agent group and 34 (range: 21-100) for the combination group. Five of 7 patients remain alive in the ONC201 single agent group while 3 of 5 patients remain alive in the combination group. Three patients in the ONC201 single agent group and 2 patients in the combination group continue on treatment. There were no drug-related toxicities requiring dose reduction or discontinuation. Conclusions: Treatment with ONC201 alone or combined with bevacizumab is well tolerated in patients with recurrent H3 K27M-mutant scDG and a subset of patients experiences prolonged survival that exceeds historical outcomes. Clinical trial information: NCT02525692; NCT03295396; NCT03416530 .

10046 Background: ONC201 is the first DRD2 antagonist for clinical oncology. The recommended phase 2 dose (RP2D) of 625mg ONC201 orally once a week has been established in adult patients. ONC201 efficacy has been shown in high-grade glioma preclinical models and radiographic regressions with single agent ONC201 have been reported in adult recurrent H3 K27M-mutant glioma patients. We report results from the first Phase I pediatric clinical trial of ONC201. Methods: This multicenter, open-label, dose-escalation and dose-expansion clinical trial (NCT03416530) determined the RP2D of ONC201 in pediatric H3 K27M-mutant glioma patients as a single agent. ONC201 was orally administered once a week and scaled by body weight. Dose escalation was performed by a 3 + 3 design beginning with one 125mg capsule less than the adult RP2D equivalent. Three patients were treated at the starting dose and 19 were treated at the adult RP2D equivalent. Results: The primary endpoint was achieved by establishing the safety of the adult RP2D scaled by body weight to pediatric patients. Twenty-two patients with a median age of 9 (range 3-18) years old who received at least prior radiation have been treated with ONC201: 15 with diffuse intrinsic pontine glioma (DIPG) (4 recurrent; 11 not recurrent) and 7 with non-DIPG H3 K27M-mutant glioma (all not recurrent). As of February 5, 2019, patients have received a median of 18 ONC201 doses (range 3-41) without instance of dose-limiting toxicity. Pharmacokinetic profiles were comparable to those observed in adults (Cmax ~2.1ug/mL; AUC ~2.3hr*ug/mL) and exposure was similar across body weights. Nine of 22 patients remain on therapy, 13 have discontinued due to progression, and 4 off-study patients are alive with a median follow up of 5.8 months. Five of the 11 (45%) DIPG patients who initiated ONC201 following radiation, but prior to recurrence, remain on therapy (median 7.4 months; range 4.4-9.6): median PFS is 4.4 months from initiation of ONC201 and 9.7 months from diagnosis; 7 of 11 (64%) patients are alive with median follow up of 11.8 months from diagnosis. Conclusions: ONC201 was well tolerated and achieved therapeutic exposure in pediatric H3 K27M-mutant glioma patients at the adult RP2D scaled by body weight. Further investigation of first-line ONC201 to treat H3 K27M-mutant glioma and/or DIPG is ongoing. Clinical trial information: NCT03416530.