Abstract 4957: The novel imipridone ONC212 highly synergizes with the BCL-2 inhibitor ABT-199 in AML and activates orphan receptor GPR132
Authors: Nii Takenobu , Ishizawa Jo , Prabhu Varun V. , Ruvolo Vivian , Madhukar Neel , Zhao Ran , Mu Hong , Heese Lauren , Kojima Kensuke , Garnett Mathew , McDermott Ultan , Benes Cyril , Charter Neil , Deacon Sean , Elemento Olivier , Allen Joshua , Oster Wolfgang , Stogniew Martin , Andreeff Michael 
Published: August 2018

Abstract
Imipridones are first-in-class anti-tumor compounds including ONC201, which has shown promising clinical activity. ONC212 was designed as a second-generation imipridone. We first confirmed the ONC212 effects in a collection of 1,088 human cancer cell lines available from the Genomic of Drug Sensitivity in Cancer Project; leukemia was identified as the most sensitive tumor type. In fact, ONC212 exerted prominent apoptogenic effects in acute myeloid leukemia (AML) cell lines and primary AML, but not normal bone marrow (BM) cells. We investigated the effects of ONC212 in vivo in an aggressive systemic AML xenograft model using OCI-AML3 cells. ONC212 markedly inhibited AML expansion and prolonged median survival (controls: 43 d, ONC212: 49 d; p = 0.0003). For in vivo functional assessment of ONC212's anti-tumor effects against leukemia stem and progenitor cells (LSPCs), we treated patient-derived xenograft (PDX) cells with ONC212 (250 nM, 36 hr) ex vivo, and then injected into recipient NSG mice. After one month, the human leukemic CD45+ cells in the peripheral blood, spleen, and BM were significantly decreased in the ONC212 treated group. The median survival was remarkably prolonged (controls: 36 d, ONC212: 82 d; p &lt; 0.0001). These results indicate that ONC212 has anti-LSPC effects to reduce the engraftment potential. We previously demonstrated that the prototype it compound ONC201 induces apoptosis via an atypical integrated stress response (ISR; Ishizawa et al., Sci Signal, 2016). As expected, ONC212 induced the transcription factor ATF4, a key effector of ISR. Because BCL-2 is generally considered to be protective against ISR-mediated apoptosis, we hypothesized that the BCL-2 inhibitor ABT-199 could further sensitize AML cells to ONC212. Indeed, the in vitro combination of ONC212 plus ABT-199 synergistically induced apoptosis in AML cells. Furthermore, the combination showed highly significant synergistic anti-leukemia effects in vivo. The combinatorial treatment prolonged overall median survival (controls: 20 d, each agent: 21 d, the combination 30 d; p &lt; 0.0001). Since the G-protein-coupled receptor (GPCR) dopamine receptor D2 is the putative target of ONC201, we hypothesized that ONC212 also targets GPCRs. The PathHunter β-arrestin screening discovered that ONC212 specifically activated the orphan GPCR GPR132. Consistently, the GPR132 mRNA expression was correlated with ONC212 sensitivity. On the other hand, GPR132 overexpression induced cell death in AML cells, which is consistent with previous reports implicating GPR132 as a tumor suppressor. Furthermore, ONC212 increased GPR132 mRNA expression. These results suggest that GPR132 could be a potential therapeutic target in AML. Taken together, ONC212 has potential as a novel agent for AML therapy. This study provides the first reported opportunity to therapeutically target GPR132 in oncology.
Citation Format: Takenobu Nii, Jo Ishizawa, Varun V. Prabhu, Vivian Ruvolo, Neel Madhukar, Ran Zhao, Hong Mu, Lauren Heese, Kensuke Kojima, Mathew Garnett, Ultan McDermott, Cyril Benes, Neil Charter, Sean Deacon, Olivier Elemento, Joshua Allen, Wolfgang Oster, Martin Stogniew, Michael Andreeff. The novel imipridone ONC212 highly synergizes with the BCL-2 inhibitor ABT-199 in AML and activates orphan receptor GPR132 [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 4957.