Abstract 635: Response to novel imipridone combination therapies targeting H3K27M mutant diffuse midline glioma (DMG)

Abstract

Abstract ONC201, a first-in-class, small molecule, imipridone therapy, is known to induce apoptosis via upregulation of TNF-related apoptosis inducing ligand (TRAIL) and its proapoptotic death receptor (DR5), independent of p53. Current trials have been exploring ONC201 as a monotherapy or in conjunction with radiotherapy, in treatment of patients with newly diagnosed and refractory diffuse intrinsic pontine gliomas (DIPG), a disease which remains incurable at present. We sought to identify synergy between ONC201 or second generation impridones (ONC206 and ONC212), and other chemotherapeutics with known promising pre-clinical activity against DMGs. Seven patient derived H3K27M mutant DIPG cell lines (SU-DIPG-IV, SU-DIPG-13, SU-DIPG-25, SUDIPG-27, SU-DIPG-29, SU-DIPG-36, SF8628) were grown in culture and exposed to ONC201, ONC206, or ONC212 either as monotherapy or in combination with other FDA approved chemotherapeutics (histone de-acetylase inhibitors [HDACi], marizomib, etoposide, and temozolomide). Dose dependent response to imipridone therapy was noted in all cell lines, with mean half maximal inhibitory concentration (IC50) of 1.46 µM in ONC201, 0.11 µM in ONC206, and 0.03 µM in ONC212. Synergy was identified via combination studies, with combination indices of <1 indicating some degree of synergy, and <0.5 indicating very strong synergy. We identified strong synergy between ONC201 and HDAC inhibitors: Panobinostat (CI 0.01) and Romidepsin (CI 0.08), with lesser synergy detected with Entinostat (CI 0.59). Romidepsin similarly showed robust synergy with ONC206 (CI 0.1), as did proteasome inhibitor Marizomib (CI 0.1). Combination of ONC212 and Panobinostat demonstrated induction of apoptosis as measured by the induction of poly (ADP-ribose) polymerase (PARP) cleavage. Our results suggest an increased sensitivity of H3K27M DIPG cell lines to second generation imipridones as compared to ONC201. Additionally, we have shown promising synergism between imipridones with Panobinostat or Romidepsin, which should be considered for clinical translation. Citation Format: Robyn Borsuk, Lanlan Zhou, Yiqun Zhang, Varun V. Prabhu, Joshua E. Allen, Nikos Tapinos, Rishi Lulla, Wafik S. El-Deiry. Response to novel imipridone combination therapies targeting H3K27M mutant diffuse midline glioma (DMG) [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 635.