Abstract PR11: EP300 controls the oncogenic enhancer landscape of high-risk neuroblastoma

Abstract High-risk neuroblastoma (NB) is an aggressive tumor of the peripheral sympathetic nervous system. Patients with NB have poor overall survival despite increases in intensity of anti-NB therapy, and survivors are typically left with long-term treatment-related morbidities. Thus, there is a need to develop novel targeted therapies that kill tumor cells without toxicity to normal tissues. We recently demonstrated that NB relies on a set of genes for survival, termed “dependencies.” One NB dependency that regulates numerous other dependencies is the histone acetyltransferase (HAT) enzyme, EP300. EP300 catalyzes the acetylation of histone H3, lysine-27 (H3K27ac) that defines active enhancer and promoter elements. This mark can also be catalyzed by the paralogous protein CBP; however, CBP is not required for NB survival despite generally being expressed in NB. Thus, selective inhibition of EP300 may result in anti-NB effects with minimal toxicity to normal tissues where CBP compensates. Here, we demonstrate that EP300, but not CBP, controls NB cell survival through regulation of the oncogenic enhancer landscape of NB. Conventional small-molecule inhibition of EP300/CBP or CRISPR-cas9-mediated knockout of EP300, but not CBP, results in neuroblastic differentiation associated with loss of the NB lineage-defining and oncogenic core transcriptional regulatory circuitry. All agents targeting EP300 equivalently target CREBBP due to their extensive protein homology. Thus, to pharmacologically eliminate EP300 and spare CBP, we designed a novel proteolysis-targeting chimera (PROTAC) agent (“JQAD1”). JQAD1 is a cereblon-dependent, selective degrader of EP300 with minimal off-target effects on CBP in NB cell lines, low passage primary cells, and in xenografts in vivo. JQAD1 is exceedingly stable and well tolerated in vivo. JQAD1 treatment results in loss of the transcriptional circuitry driving NB, transcriptional collapse. and irreversible commitment of NB cells to apoptosis in vitro and in vivo. This study defines the mechanism by which EP300 centrally regulates NB cell fate through epigenetic regulation of the transcriptional state and provides the first EP300-selective pharmacologic agent for evaluation in a myriad of other EP300-dependent malignancies. This abstract is also being presented as Poster B11. Citation Format: Adam D. Durbin, Virangika Wimalasena, Mark W. Zimmerman, Li Deyao, Elizabeth S. Frank, Paul Park, Ken Morita, Neekesh V. Dharia, Ken N. Ross, Ernst Schonbrunn, Richard A. Young, Brian J. Abraham, Kimberly Stegmaier, A. Thomas Look, Jun Qi. EP300 controls the oncogenic enhancer landscape of high-risk neuroblastoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr PR11.