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Purpose:Dopamine receptor D2 (DRD2) is a G protein–coupled receptor antagonized by ONC201, an anticancer small molecule in clinical trials for high-grade gliomas and other malignancies. DRD5 is a dopamine receptor family member that opposes DRD2 signaling. We investigated the expression of these dopamine receptors in cancer and their influence on tumor cell sensitivity to ONC201.Experimental Design:The Cancer Genome Atlas was used to determine DRD2/DRD5 expression broadly across human cancers. Cell viability assays were performed with ONC201 in >1,000 Genomic of Drug Sensitivity in Cancer and NCI60 cell lines. IHC staining of DRD2/DRD5 was performed on tissue microarrays and archival tumor tissues of glioblastoma patients treated with ONC201. Whole exome sequencing was performed in RKO cells with and without acquired ONC201 resistance. Wild-type and mutant DRD5 constructs were generated for overexpression studies.Results:DRD2 overexpression broadly occurs across tumor types and is associated with a poor prognosis. Whole exome sequencing of cancer cells with acquired resistance to ONC201 revealed a de novo Q366R mutation in the DRD5 gene. Expression of Q366R DRD5 was sufficient to induce tumor cell apoptosis, consistent with a gain-of-function. DRD5 overexpression in glioblastoma cells enhanced DRD2/DRD5 heterodimers and DRD5 expression was inversely correlated with innate tumor cell sensitivity to ONC201. Investigation of archival tumor samples from patients with recurrent glioblastoma treated with ONC201 revealed that low DRD5 expression was associated with relatively superior clinical outcomes.Conclusions:These results implicate DRD5 as a negative regulator of DRD2 signaling and tumor sensitivity to ONC201 DRD2 antagonism.

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Supplementary legends for Figures S1-S5 and Tables S1-S2.

Background Diffuse Midline Glioma (DMG) with the H3K27M mutation is a lethal childhood brain cancer, with patients rarely surviving 2 years from diagnosis. Methods We conducted a multi-site Phase 1 trial of the imipridone ONC201 for children with H3K27M-mutant glioma (NCT03416530). Patients enrolled on Arm D of the trial (n = 24) underwent serial lumbar puncture for cell-free tumor DNA (cf-tDNA) analysis and patients on all arms at the University of Michigan underwent serial plasma collection. We performed digital droplet polymerase chain reaction (ddPCR) analysis of cf-tDNA samples and compared variant allele fraction (VAF) to radiographic change (maximal 2D tumor area on MRI). Results Change in H3.3K27M VAF over time (“VAF delta”) correlated with prolonged PFS in both CSF and plasma samples. Nonrecurrent patients that had a decrease in CSF VAF displayed a longer progression free survival (P = .0042). Decrease in plasma VAF displayed a similar trend (P = .085). VAF “spikes” (increase of at least 25%) preceded tumor progression in 8/16 cases (50%) in plasma and 5/11 cases (45.4%) in CSF. In individual cases, early reduction in H3K27M VAF predicted long-term clinical response (>1 year) to ONC201, and did not increase in cases of later-defined pseudo-progression. Conclusion Our work demonstrates the feasibility and potential utility of serial cf-tDNA in both plasma and CSF of DMG patients to supplement radiographic monitoring. Patterns of change in H3K27M VAF over time demonstrate clinical utility in terms of predicting progression and sustained response and possible differentiation of pseudo-progression and pseudo-response.

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.

Background ONC201, a dopamine receptor D2 (DRD2) antagonist and caseinolytic protease P (ClpP) agonist, has induced durable tumor regressions in adults with recurrent H3 K27M-mutant glioma. We report results from the first phase I pediatric clinical trial of ONC201. Methods This open-label, multi-center clinical trial (NCT03416530) of ONC201 for pediatric H3 K27M-mutant diffuse midline glioma (DMG) or diffuse intrinsic pontine glioma (DIPG) employed a dose-escalation and dose-expansion design. The primary endpoint was the recommended phase II dose (RP2D). A standard 3 + 3 dose escalation design was implemented. The target dose was the previously established adult RP2D (625 mg), scaled by body weight. Twenty-two pediatric patients with DMG/DIPG were treated following radiation; prior lines of systemic therapy in addition to radiation were permitted providing sufficient time had elapsed prior to study treatment. Results The RP2D of orally administered ONC201 in this pediatric population was determined to be the adult RP2D (625 mg), scaled by body weight; no dose-limiting toxicities (DLT) occurred. The most frequent treatment-emergent Grade 1-2 AEs were headache, nausea, vomiting, dizziness and increase in alanine aminotransferase. Pharmacokinetics were determined following the first dose: T1/2, 8.4 h; Tmax, 2.1 h; Cmax, 2.3 µg/mL; AUC0-tlast, 16.4 hµg/mL. Median duration of treatment was 20.6 weeks (range 5.1-129). Five (22.7%) patients, all of whom initiated ONC201 following radiation and prior to recurrence, were alive at 2 years from diagnosis. Conclusions The adult 625 mg weekly RP2D of ONC201 scaled by body weight was well tolerated. Further investigation of ONC201 for DMG/DIPG is warranted.

Purpose: Tumor dopamine-like DRD2 receptor expression is higher in pheochromocytoma-paraganglioma (PC-PG) compared with other cancers. ONC201 is a bitopic DRD2 antagonist with preclinical ONC201 activity in desmoplastic small round cell tumor (DSRCT). Patients and Methods: Patients (N = 30) with neuroendocrine tumors were treated on this investigator-initiated trial (NCT03034200). ONC201 dose and schedule were 625 mg orally weekly in cohorts A (PC-PG) + B (other neuroendocrine tumors) and 625 mg orally on 2 consecutive days each week in cohort C, which included 5 responding patients. The primary endpoint was radiographic response measured using RECIST. Secondary endpoints included progression-free survival, overall survival, and safety. Results: In arm A (n = 10; all PC-PG), 50% (5/10) exhibited a partial response (PR) and 2 additional patients had stable disease (SD) >3 months. Median duration of therapy for arm A patients was 9 months (range: 1.5–33 months) with 5 patients treated >1 year. In arm B (n = 12), there were 1 PR (DSRCT) and 2 SD (DSRCT; neuroblastoma) >3 months. Median duration of therapy in arm A was 18 months (range: 1–33 months) and arm B was 3 months (range: 1.5–33 months). Arm C PC-PG (N = 8) showed 1 PR and 7 SD at 3 months, with median duration of therapy >10 months. There was no decline in Karnofsky performance status at week 12 for 28 of 30 patients and no dose modification due to treatment-related adverse events. Conclusions: Oral ONC201 was well tolerated in patients with metastatic neuroendocrine tumors and associated with clinical benefit, including tumor responses, particularly in some patients with DSRCT and the majority of patients with PC-PG. See related commentary by Owen and Trikalinos, p. 1748

Diffuse midline glioma (DMG) with the H3K27M mutation is a lethal childhood brain cancer, with patients rarely surviving 2 years from diagnosis. We conducted a multi-site Phase 1 trial of the imipridone ONC201 for children with H3K27M-mutant glioma ({"type":"clinical-trial","attrs":{"text":"NCT03416530","term_id":"NCT03416530"}}NCT03416530). Patients enrolled on Arm D of the trial (n=24) underwent serial lumbar puncture (baseline, 2, 6 months) for cell-free tumor DNA (cf-tDNA) analysis at time of MRI. Additionally, patients on all arms of the trial at the University of Michigan underwent serial plasma collection. CSF collection was feasible in this cohort, with no procedural complications. We collected 96 plasma samples and 53 CSF samples from 29 patients, including those with H3F3A (H3.3) (n=13), HIST13HB (H3.1) (n= 4), and unknown H3 status/not biopsied (n=12) [range of 0–8 CSF samples and 0–10 plasma samples]. We performed digital droplet polymerase chain reaction (ddPCR) analysis and/or amplicon-based electronic sequencing (Oxford Nanopore) of cf-tDNA samples and compared variant allele fraction (VAF) to radiographic change (maximal 2D tumor area on MRI). Preliminary analysis of samples demonstrates a correlation between changes in tumor size and H3K27M cf-tDNA VAF, when removing samples with concurrent bevacizumab. In multiple cases, early reduction in CSF cf-tDNA predicts long-term clinical response (>1 year) to ONC201, and does not increase in cases of later-defined pseudo-progression (radiation necrosis). For example, a now 9-year old patient with thalamic H3K27M-mutant DMG underwent treatment with ONC201 after initial radiation and developed increase in tumor size at 4 months post-radiation (124% baseline) of unclear etiology at the time. Meanwhile, her ddPCR declined from baseline 6.76% VAF to

ONC201, a bitopic DRD2 antagonist and allosteric ClpP agonist, has shown encouraging efficacy in H3 K27M-mutant glioma. Given that the thalamus has the highest extra-striatal expression of DRD2, we performed an integrated preclinical and clinical analysis of ONC201 in thalamic H3 K27M-mutant glioma. ONC201 was effective in mouse intra-uterine electroporation (IUE)-generated H3 K27M-mutant gliomas, with an in vitro IC50 of 500 nM and 50% prolongation of median survival in vivo (p=0.02, n=14). We analyzed thalamic H3 K27M-mutant glioma patients treated with ONC201 on active clinical trials as of 5/22/19 enrollment (n=19 recurrent and 10 post-radiation, non-recurrent; 5–70 years old). As of 12/18/2019, PFS6 and OS12 are 26.3% and 36.8%, respectively, in the recurrent group. For non-recurrent patients, with median follow up of 21.9 months (8.6–26.6) from diagnosis, median PFS or OS have not been reached. This surpasses historical OS of 13.5 months. Best response by RANO includes 1 CR, 3 PR, 4 SD, 8 PD for recurrent patients and 2 PR, 4 SD, 1 PD for non-recurrent patients (4 on-trial patients experienced regressions that are yet unconfirmed responses). Median duration of response for recurrent patients is 14.0 months (2.0–33.1). Furthermore, H3 K27M cell-free tumor DNA in plasma and CSF correlated with MRI response. In summary, single agent ONC201 administered at recurrence, or adjuvantly following radiation, demonstrates promising clinical efficacy in thalamic H3 K27M-mutant glioma patients who currently have no effective treatments following radiation. Investigations are ongoing to assess whether micro-environmental DRD2 expression explains the early exceptional responses in thalamic H3 K27M-mutant glioma.

Uterine serous carcinoma (USC) is the most aggressive subtype of endometrial cancer. Patients with advanced stage USC have poor survival rates and new treatment regimens are lacking. 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 USC progression and the mechanism of action have not been thoroughly explored. Using both in vitro and in vivo models, and multiple USC cell lines, the effects of ONC206 on cell proliferation and apoptosis were determined. Reverse phase protein arrays (RPPAs) and Western blot analyses were used to determine the effect of ONC206 on the expression of key proteins in various signaling networks in ONC206 treated USC cells. The results showed that ONC206 suppressed USC cell proliferation and induces apoptosis in a dose-dependent manner. Luciferase labeled USC cell ARK1-bearing mice treated with 100mg/kg ONC206 had significantly lower chemiluminescent signals than those treated with the control buffer. RPPA data showed that ONC206 treated USC cells had markedly lower expression signals in p38MAPK, p-AKT, p-S6, and multiple mitochondrial proteins associated with mitochondrial ATP synthesis including MTCO1, and TFAM than the control cells did. Significantly lower ATP levels and cytochrome c oxidase activities in ONC206 treated USC cells than in control cells were demonstrated by luminescent ATP detection assay kit and the cytochrome c oxidase assay kit. These data suggest that ONC206 suppresses USC progression through inhibiting MAPK/AKT network, which subsequently leads to metabolic reprogramming and increased apoptosis. Moreover, by knocking-out DRD2, USC cells became more resistant to ONC206 treatment. This suggested that the effect of ONC206 is likely mediated through its binding to DRD2. ONC206 also showed a synergistic effect with paclitaxel in vitro. Further studies which demonstrate the optimal dosage and the efficacy of treatment of USC using ONC206 are warranted. Citation Format: Chi Lam Au Yeung, Wen Hu, Li Zhang, Sammy Ferri-Borgogno, Rohinton S. Tarapore, Joshua E. Allen, Karen H. Lu, Samuel C. Mok. Novel imipridone ONC206 inhibits cell proliferation and induces apoptosis in uterine serous cancer through altering MAPK/AKT signaling network and metabolic reprogramming [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5321.

Cure rates for pediatric sarcomas have minimally improved with intensification of genotoxic chemotherapy. We have previously shown that activation of the Integrated Stress Response (ISR), a cellular stress response that can lead to apoptosis, is a novel, effective means of selectively inducing the death of rhabdomyosarcoma (RMS) cells. However, context-specific wiring of homeostatic components such as protein chaperones dictates unique barriers to ISR activation. We hypothesized that just as HSP70 inhibition can preferentially activate the ISR in RMS, but not Ewing sarcoma, alternative small molecules might highlight dependencies unique to other sarcoma subtypes. ONC201 is a selective dopamine receptor (DRD2/3) antagonist that has previously shown antitumor activity through ISR activation in solid tumor models. ONC206 is a more potent analogue of ONC201 that was shown to be effective in Ewing sarcoma cell lines with sub-micromolar IC50. We used these molecules to test the hypothesis that DRD2/3 antagonism can activate the ISR in pediatric sarcomas, identifying a new therapeutic strategy. We measured the growth inhibitory effects of ONC201 and ONC206 across a panel of four rhabdomyosarcoma (RMS) and three Ewing sarcoma (ES) patient-derived cell lines. Across all sarcoma cell lines tested, ONC201 and ONC206 inhibited growth with low micromolar and sub-micromolar IC50 values respectively. ES cell lines were more sensitive than RMS lines, with mean ONC201 IC50 of 7.7 micromolar vs 3.2 micromolar (p = 0.0016). To explore this difference, we measured ISR activation by immunoblot. The ISR initiates with phosphorylation of eIF2α, leading to a halt in protein translation. RMS cells showed a strong increase in phosphorylated eIF2α one hour after treatment with either drug that was sustained through 24 hours, but attenuated by 48 hours of treatment. ES cells, however, did not show increased eIF2α phosphorylation until 48 hours of treatment, at which point levels of phosphorylation were much higher than in RMS cells. Correspondingly, PARP cleavage was relatively modest in RMS cells, but robust in ES cells at 48 hours of treatment. We conclude that two phenotypes of ISR activation – early and attenuated, versus late and sustained – correlate with the therapeutic efficacy of these agents. Our data suggest that regulation of the ISR downstream of DRD2/3 antagonism underlies differential response to two clinically relevant agents. The development of biomarkers of the strength and duration of ISR activity may thus guide the clinical application of ONC201, ONC206, or other ISR-activating therapies in pediatric sarcomas. Ongoing work will test the expression and activity of eIF2α phosphatases and the necessity and sufficiency of terminal ISR effectors in controlling this differential response, as well as the efficacy of these agents in relevant in vivo models of disease. Citation Format: David V. Allegakoen, Rohinton S. Tarapore, Joshua E. Allen, Amit J. Sabnis, Trever G. Bivona. Differential activation of the integrated stress response correlates with anti-tumor activity of imipridones ONC201 and ONC206 in pediatric sarcomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2664.

Background: Radiation is widely administered in many treatment settings for solid tumors. ONC201 is the first small molecule DRD2 antagonist for oncology that is being investigated in advanced cancer clinical trials as a single agent. ONC201 has exhibited preclinical and clinical anti-tumor activity in high grade gliomas and its immunostimulatory activity involving natural killer (NK) cells has been recently reported. Given that ONC201 exhibits broad synergy with anti-cancer drugs, excellent safety, and single activity in tumor types where radiation is used routinely, we evaluated the combination of ONC201 with radiation. Methods: Cell viability was evaluated in human and/or mouse breast, prostate and high grade glioma cell lines in response to ONC201 (1 - 10uM), radiation (2- 10 Gy), or the combination. Incubation times ranged from 24 to 96 hours and the sequence of the two agents in combination was varied. Results: Cell viability assays for ONC201 in combination with radiation in breast or prostate cancer cell lines revealed a cytotoxic response to the combination that was superior to either single agent. Western blot analysis of PC3 cells showed a synergistic induction of CHOP and ATF6 that are components of the integrated stress response. In glioblastoma or diffuse intrinsic pontine glioma (DIPG) cell lines, combination indices computed from cell viability experiments indicated modest synergy (~0.7 CI) for the combination ranging between 1-5 µM ONC201 and 2-10 Gy. In MDA-MB-468 breast cancer cells, Western blot analysis demonstrated a striking induction of PARP cleavage, a marker of caspase-mediated apoptosis, with 2 µM ONC201 in combination with 2 Gy radiation, whereas either single agent produced minimal PARP cleavage. In 4T1 murine triple-negative breast cancer subcutaneous tumors, the combination of oral ONC201 and radiation produced antitumor effects at subtherapeutic doses that required CD4+ T cells and NK cells. Conclusions: ONC201 combined with radiation produced additive or synergistic anti-cancer effects in high grade glioma, breast and prostate cancer in vitro and increased anti-tumor efficacy in an in vivo model of breast cancer that involved immune cells. Citation Format: Rohinton S. Tarapore, Sachin Jhawar, Mark Stein, Andrew Zloza, Sabine Mueller, Jie Zhang, Francesca Amoroso, Ian Mills, Wolfgang Oster, Joshua Allen. Combination of ONC201 with radiation exhibits synergistic efficacy in high grade gliomas and other advanced cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 249.

Cancer of the skin is the most common form of malignancy in humans and is divided into two categories – non-malignant skin cancer and cutaneous melanoma. Non-melanoma skin cancer (basal cell and small cell carcinoma) make up a vast majority of skin cancers. According to data from National Cancer Institute (NCI) in 2012, more than 2 million new cases of non-melanomas will be identified with less than a 1000 deaths. Despite according for only 4% of all cases, melanoma is the deadliest of skin cancers resulting in over 79% of skin cancer deaths [1]. In the United States, melanoma is the fifth most common cancer in men and the sixth most common in women. In 2011, 70,230 new melanoma cases were identified with 8,790 deaths. The median age of diagnosis is between 45-55; although 25% of melanomas occur in individ‐ uals over 40 years.