Abstract 6226: Sapanisertib interferes with the NRF2-mediated stress response to synergize with Obatoclax and extend AT/RT survival
Authors: Ashlyn Parkhurst, Sabrina Wang, Harpreet Kaur, Antje Arnold, Charles Eberhart, Eric Raabe, Jeffrey Rubens
Journal: Cancer Research (2020)

Abstract Atypical teratoid rhabdoid tumors (AT/RT) are the most common malignant brain tumors of infancy, highly resistant to all therapies, and responsible for one of the greatest numbers of life years lost due to cancer. We have previously demonstrated that Sapanisertib combines synergistically with cisplatin to extend survival in AT/RT. To understand the mechanisms underlying this synergy and to identify further novel combination therapies to improve AT/RT survival, we performed RNASeq on AT/RT cell models 4 hours after Sapanisertib treatment. Pathway analysis revealed that Sapanisertib disrupts the NRF2-mediated stress response and apoptotic signaling pathway leading to a pro-death phenotype. Activating mutations in the NRF2 coding gene, NFE2L2, have been identified as a possible biomarker predicting Sapanisertib efficacy in lung cancer clinical trials. Short hairpin knockdown of NRF2 led to decreased expression of the anti-apoptotic proteins MCL-1, BCL-2, and BCL-xL suggesting that interfering with NRF2 may drive this pro-death phenotype in AT/RT. Obatoclax is a synthetic small molecule inhibitor of the BCL-2 family of proteins that was well tolerated in phase II clinical trials and readily crosses the blood brain barrier. Obatoclax treatment of NRF2 knockdown AT/RT cell models slows cell growth, induces high rates of apoptosis, and leads to increased oxidative stress compared to short hairpin scramble controls (cell viability assay, t-test p&amp;lt;0.05; ANNEXIN V cell sorting assay t-test p&amp;lt;0.05, MUSE oxidative stress assay t-test p&amp;lt;0.05). We treated AT/RT cell models with Sapanisertib and showed that treatment decreases expression of NRF2 and MCL-1 (western blot). Sapanisertib combines synergistically with Obatoclax to increase oxidative stress, slow cell growth, and increase apoptosis (MUSE oxidative stress assay ANOVA p&amp;lt;0.05; cell viability assay, ANOVA p&amp;lt;0.05; ANNEXIN V cell sorting assay ANOVA p&amp;lt;0.05, Compusyn model of synergy, CI&amp;lt;1.0). We next developed orthotopic mouse models of AT/RT using our luciferase-labeled CHLA06 and BT37 AT/RT cell models. We administered Sapinisertib and Obatoclax using mouse equivalent dosing to human clinical trials (Sapinisertib 6mg/kg oral weekly, Obatoclax 10mg/kg oral twice a week). Combination treatment was well tolerated and more than doubled median survival. Our data supports a new clinical trial combining Sapinisertib with Obatoclax to extend survival in AT/RT. Citation Format: Ashlyn Parkhurst, Sabrina Wang, Harpreet Kaur, Antje Arnold, Charles Eberhart, Eric Raabe, Jeffrey Rubens. Sapanisertib interferes with the NRF2-mediated stress response to synergize with Obatoclax and extend AT/RT survival [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 6226.