Abstract LB076: Unleashing cell-intrinsic inflammation as a strategy to kill AML blasts
Authors: Ellegast Jana M. , Alexe Gabriela , Hamze Amanda , Lin Shan , Uckelmann Hannah J. , Rauch Philipp J. , Pimkin Maxim , Ross Linda , Dharia Neekesh V. , Robichaud Amanda L. , Saur Amy Conway , Khalid Delan , Wunderlich Mark , Benajiba Lina , Nabet Behnam , Gray Nathanael S. , Orkin Stuart H. , Stegmaier Kimberly 
Published: June 2022

Abstract
Leukemic blasts are immune cells gone awry. We thus hypothesized that dysregulation of inflammatory pathways can maintain a leukemic state. In contrast to traditional cancer immunotherapy, we exploited inflammatory signaling within AML blasts as cell-intrinsic, self-directed immunotherapy. Corroborating the hypothesis that AML cells depend on proper regulation of inflammatory networks, we identified an AML subgroup enriched for inflammatory pathways, associated with a monocytic lineage signature. To discover AML selective, immune-modulating vulnerabilities, we integrated data from the Cancer Dependency Map on 789 cancer cell lines with independent genome-wide screens, identifying Interferon regulatory factor 2 binding protein 2 (IRF2BP2). We validated AML cell dependency on IRF2BP2 with orthogonal genetic approaches in vitro and in vivo and studied acute IRF2BP2 degradation. Perturbation of IRF2BP2 resulted in cell death with hallmarks of apoptosis. To decipher how IRF2BP2 relates to inflammatory signaling, we studied IRF2BP2 localization on chromatin. We found genome-wide IRF2BP2 binding in promoter and in enhancer regions. Global gene expression studies following degradation of IRF2BP2 showed an increase in expression of the majority of IRF2BP2 bound genes, supporting a role for IRF2BP2 as a transcriptional repressor. Gene set enrichment analyses identified NF-κB-related immune response signatures as the most significantly altered leading us to hypothesize that IRF2BP2 represses NF-κB-mediated TNFα signaling that, when acutely perturbed, leads to leukemia cell death. Indeed, we confirmed an activation of NF-κB-signaling, an increase in nuclear RELA protein, and gain in RELA chromatin binding following degradation of IRF2BP2. Moreover, a mutant “super-repressor” allele of IκBα rescued the impaired cell growth upon IRF2BP2 perturbation, supporting cell death associated with IRF2BP2 loss being mediated through activation of NF-κB signaling. In addition, we identified IL-1ß as an enhancer of the inflammatory response repressed by IRF2BP2. Using patient-derived xenograft models, we demonstrated a significant reduction in leukemia burden and an increase in median survival in mice that had received patient-derived AML cells with IRF2BP2-targeting CRISPR guides compared to control guides. Importantly, loss of IRF2BP2 in normal bone marrow-derived hCD34+ cells had no effect on colony forming capacity. In summary, we demonstrate that IRF2BP2 represses IL-1ß/TNFα signaling via NF-κB, and IRF2BP2 perturbation results in hyperinflammation leading to AML cell death. These findings elucidate a hitherto unexplored AML dependency, reveal cell-intrinsic inflammatory signaling as a mechanism priming leukemic blasts for cell death, and motivate the exploration of alternative immune-mediated therapies in cancers that have yet to reap the benefits of the immunotherapy revolution.
Citation Format: Jana M. Ellegast, Gabriela Alexe, Amanda Hamze, Shan Lin, Hannah J. Uckelmann, Philipp J. Rauch, Maxim Pimkin, Linda Ross, Neekesh V. Dharia, Amanda L. Robichaud, Amy Conway Saur, Delan Khalid, Mark Wunderlich, Lina Benajiba, Behnam Nabet, Nathanael S. Gray, Stuart H. Orkin, Kimberly Stegmaier. Unleashing cell-intrinsic inflammation as a strategy to kill AML blasts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB076.