Abstract 2923: Targeting DNA repair mechanisms to overcome CIC::DUX4 undifferentiated sarcomas

Abstract Transcription factor (TF) fusion oncoproteins represent cancer specific alterations that arise from chromosomal rearrangements. Through target gene recognition, TF fusions can disseminate transcriptional responses that collectively work to drive tumorigenesis. Thus, identifying the molecular targets that operate as a disease driving network can potentially uncover key actionable dependencies. We have taken this strategy to dissect the underlying biological mechanism by which CIC::DUX4, a fusion oncoprotein associated with dismal outcomes, drives sarcomagenesis. We and others have defined a CIC::DUX4 fusion mediated network that dysregulates cell-cycle and DNA replication checkpoints. Specifically, CIC::DUX4-mediated CCNE1 upregulation compromises the G1/S transition leading to high DNA replication stress and conferring a dependence on the G2/M checkpoint kinase, WEE1. WEE1 provides a molecular brake to enable effective DNA repair prior to mitotic entry. Importantly, the mechanism by which CIC::DUX4 regulates DNA repair remains unknown. Here we show that the catalytic subunit of DNA polymerase epsilon (POLE) is essential for DNA integrity and cellular division in CIC::DUX4 sarcoma. Mechanistically, POLE loss increases DNA damage and induces p21-mediated cellular senescence to limit CIC:DUX4 tumor growth in vitro and tumor formation in vivo. Collectively, we credential POLE as a CIC::DUX4 target and further characterize a functional network through which CIC::DUX4 operates to drive tumor progression and survival. Citation Format: Zeinab Kosibaty, Cuyler Luck, Ross A. Okimoto. Targeting DNA repair mechanisms to overcome CIC::DUX4 undifferentiated sarcomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2923.