Biological activity of weekly ONC201 in adult recurrent glioblastoma patients

BACKGROUND

ONC201 is a dopamine receptor D2 (DRD2) antagonist that penetrates the blood-brain barrier. ONC201 efficacy has been shown in glioblastoma animal models and is inversely correlated with dopamine receptor DRD5 expression. ONC201 is well tolerated in adult recurrent glioblastoma patients with dosing every 3 weeks and has achieved an objective radiographic response in a patient harboring the H3 K27M mutation.

METHODS

In a window-of-opportunity arm, 6 adult subjects initiated ONC201 prior to re-resection of recurrent glioblastoma with intratumoral concentrations as the primary endpoint. An additional 20 adults with recurrent glioblastoma received single agent weekly oral ONC201 at 625 mg, with progression-free survival at 6 months (PFS6) by Response Assessment in Neuro-Oncology (RANO) criteria as the primary endpoint.

RESULTS

The window-of-opportunity arm achieved its primary endpoint with intratumoral ONC201 concentrations at ~24 hours following the second weekly dose ranging from 600 nM to 9.3 µM. Intratumoral pharmacodynamics assessed by activating transcriptional factor 4, death receptor 5, and apoptosis induction relative to archival samples were observed with the strongest intensity and uniformity among patients with low DRD5 tumor expression. The primary endpoint of PFS6 by RANO was not achieved at 5% in this molecularly unselected cohort; however, 1 of 3 patients enrolled with the H3 K27M mutation had a complete regression of enhancing multifocal lesions that remained durable for >1.5 years. No treatment modifications or discontinuations due to toxicity were observed, including in those who underwent re-resection.

CONCLUSIONS

Weekly ONC201 is well tolerated, and meaningful intratumoral concentrations were achieved. ONC201 may be biologically active in a subset of adult patients with recurrent glioblastoma.

HGG-18. CLINICAL EFFICACY OF ONC201 IN THALAMIC H3 K27M-MUTANT GLIOMA

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.

ACTR-34. SINGLE AGENT ONC201 IN PREVIOUSLY-TREATED, PROGRESSIVE ADULT H3 K27M-MUTANT GLIOMA

H3 K27M-mutant gliomas often manifest as midline gliomas, have a dismal prognosis, and have no established or effective treatments at recurrence. ONC201 is the first clinical bitopic DRD2 antagonist/ClpP agonist and is under evaluation in Phase II trials for gliomas and other cancers. We previously reported in vitro studies suggesting dysregulated dopamine receptor expression and enhanced ONC201 sensitivity among H3 K27M-mutant gliomas. Following these observations, adults with midline H3 K27M-mutant glioma patients were enrolled to a dedicated Phase II clinical trial (NCT03295396), a multi-arm Phase II trial (NCT0252569), and expanded access protocols under the Sponsor’s IND. An integrated radiographic analysis with an objective response rate primary endpoint in patients who received ONC201 monotherapy with confirmed H3 K27M-mutant glioma (not primarily in the pons or spinal cord and without leptomeningeal spread) that was progressive and measurable disease by RANO criteria, >90 days from completion of prior radiation, and had KPS >60. As of December 15, 2018, 15 patients have received single agent ONC201 who meet these criteria (n=9 NCT03295396; n=5 NCT0252569; n=1 expanded access). ONC201 was orally administered at 625 mg weekly, except for one patient dosed once every 3 weeks. As midline gliomas can exhibit a mixture of contrast-enhancing and non-contrast-enhancing disease, objective response was assessed by blinded independent central review using RANO-HGG and RANO-LGG criteria for each patient. Best response to date by RANO-HGG criteria is at least 27%: 1 CR, 3 PR, 7 SD, and 4 PD; by RANO-LGG is at least 36%: 1 CR, 1 PR, 3 minor response (MR), 4 SD, 5 PD, 1 unevaluable. By RANO-HGG, median onset of response is 2.6 months (range 1.3–3.4); median duration of response has not been reached with a median follow-up of 7.7 months (range 1.8–29.8). Updated radiographic response, pharmacodynamics, safety, and other clinical outcomes will be reported.

PDCT-12. CLINICAL EFFICACY OF ONC201 IN THALAMIC H3 K27M-MUTANT GLIOMA

ONC201, the first bitopic DRD2 antagonist for clinical oncology, has shown efficacy in H3 K27M-mutant glioma. 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). Elevated DRD2 expression was found in the thalamus of non-malignant brain tissue, leading to the hypothesis that thalamic tumors may be a particularly ONC201-sensitive sub-group. We analyzed thalamic H3 K27M-mutant glioma patients treated with ONC201 as of the 05/22/2019 cutoff date, which included patients who had recurrent disease prior to initiating ONC201 (n=20; 15–73 years old) and post-radiation non-recurrent patients (n=11; 5–19 years old). As of 5/22/2019, 10 of 20 recurrent patients and 9 of 11 non-recurrent patients remain on-treatment. Median PFS has not been reached for either cohort: median follow-up of 2.2 months (range: 0.6–37.9) for recurrent patients and 10.6 months (range: 4.3–20.5) from diagnosis for non-recurrent patients. Best response so far by RANO includes 1 CR, 2 PR, 7 SD, 9 PD, 1 NE for recurrent patients and 1 PR, 7 SD, 3 PD for non-recurrent patients. Additionally, 3 recurrent (-66%, -47%, -34%) and 2 non-recurrent (-40%, -10%) patients experienced regressions but are not yet confirmed PRs. For recurrent patients, median onset of response is 3.5 months (range: 2.2–3.8) and median duration of response has not been reached with a median follow-up of 12.5 months (range: 8.1–32.8). Preliminary analyses demonstrated a strong correlation of cell-free tumor DNA in plasma and CSF with MRI response. In summary, ONC201 demonstrates promising clinical efficacy in thalamic H3 K27M-mutant glioma patients, regardless of age. Micro-environmental DRD2 expression may enhance the overall ONC201 response and extend its therapeutic utility beyond H3 K27M-mutant glioma.

Single agent ONC201 in adult recurrent H3 K27M-mutant glioma

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 in previously-irradiated pediatric H3 K27M-mutant glioma

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.