Abstract 2765: Combination ONC201 and radiation therapy in the treatment of breast cancer
Authors: Jhawar Sachin R. , Schiff Devora , Wu Hao , Thandoni Aditya , Hassan Suemair , Allen Joshua , Stogniew Martin , Tarapore Rohinton , Oster Wolfgang , Stein Mark , Silk Ann W. , Goyal Sharad , Haffty Bruce G. , Zloza Andrew 
Published: August 2018

Abstract
Purpose: Metastatic breast cancer patients continue to have poor outcomes on current treatments, and thus, novel therapies in combination with standard treatments are needed. Towards this we studied the pre-clinical effects of combining ONC201, a first-in-class imipridone (which works via activation of ER stress, upregulation of TRAIL, and activation of death receptor 5 [DR5]) with radiation therapy (RT). Since the DR5 pathway is also required for RT-induced apoptosis, we hypothesized that addition of ONC201 could increase the effectiveness of RT. Pertinent Experimental Procedures: Human and mouse breast cancer cell lines were used to study in vitro cancer cell death (by AlamarBlue and clonogenic assays). Patient-derived breast cancer tissue and mouse cell lines were used to study in vivo tumor growth kinetics. Cell lines and mice were administered radiation (0-8 Gy) delivered via a Gammacell 40 exactor. ONC201 was given at does 0-10 µM. Mechanisms of tumor cell death were elucidated using western blots of cleaved PARP (cPARP) and caspase 3 (cC3). Immune response mechanisms were elucidated using in vivo cell-specific depletion. Summary of Data: Multiple breast cancer lines (MB231, MB468, and 4T1) exhibited decreased cell viability after combination therapy compared to either single therapy. In particular, ON201 (1 µM) followed by RT (8 Gy) resulted in a decreased MB468 breast cancer cell viability compared to no treatment (36.9%, P&lt;0.0001), RT alone (30.5%, p&lt;0.0001) and ONC201 alone (26.9%, p&lt;0.0001). A clonogenic assay using MB468 revealed a decreased surviving fraction at every RT dose (2-8 Gy). Western blot analysis revealed increasing cPARP and cC3 with increasing ONC201 (2-8 Gy). In vivo studies utilizing 4T1 cells demonstrated that combination RT (6 Gy) and ONC201 (48 mg/kg given 3x weekly) decreases tumor growth and prolongs host survival compared to either treatment alone (P&lt;0.01). Depletion of NK or CD8 T cells (but not CD4 or B cells) abrogated the positive effects of ONC201 + RT. Similar efficacy of ONC201 + RT was achieved in NSG mice surgically transplanted breast cancer patient tumor sections and immune reconstituted with autologous patient immune cells. Conclusions: Treatment with combination ONC201 + RT results in decreased in vitro breast cancer cell viability and increased in vivo cancer control. Future studies are aimed at translating this combination therapy for clinical use towards improving and saving cancer patient lives.
Citation Format: Sachin R. Jhawar, Devora Schiff, Hao Wu, Aditya Thandoni, Suemair Hassan, Joshua Allen, Martin Stogniew, Rohinton Tarapore, Wolfgang Oster, Mark Stein, Ann W. Silk, Sharad Goyal, Bruce G. Haffty, Andrew Zloza. Combination ONC201 and radiation therapy in the treatment of breast 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 2765.