Abstract 2694: ID1-4 proteins' contribution to cancer stem-like cell maintenance and ovarian cancer recurrence following chemotherapy

Abstract Although most patients initially respond to chemotherapy, ovarian cancer (OC) remains the most lethal gynecological cancer, primarily because over 80% of advanced cases relapse within 24 months. Current research suggests that cancer recurrence can be attributed to a small subpopulation of cancer stem-like cells (CSCs) that possess the ability to resist chemotherapy, self-renew, and asymmetrically divide. ID1-4 proteins, also known as inhibitors of differentiation or inhibitors of DNA binding proteins, regulate cell fate and differentiation in normal stem and progenitor cells. In gliomas, ID1-4 proteins have been identified as master transcriptional regulators of CSC identity, signaling to downstream pathways important for self-renewal, tumor initiation, and survival, but their role in OC CSCs and recurrence is unclear. We have previously found that ID1-3 gene expression increases following chemotherapy treatment in OC clinical samples and cell lines, and the elevated gene expression of ID1 and ID3 is associated with worse clinical outcomes. In subcutaneous xenograft mouse models, we have found that ID2 and ID4 protein expression significantly increases acutely following carboplatin treatment as compared to vehicle group, but this effect is lost over time. In OVCAR5, OVCAR8, and OV90 OC cell lines, we see a 10-40 fold increase in ID gene expression following two cycles of chemotherapy treatment. We hypothesize that ID proteins are required for OC CSC survival, self-renewal, and tumor recurrence following chemotherapy. Using a pan-ID inhibitor, AGX51, we have significantly knocked down ID expression in chemotherapy-naïve (OVCAR5, OV90) and chemotherapy-resistant (OVCAR4, OVCAR8) OC cell lines. Our data suggest pan-ID inhibition in OC cell lines reduces chemotherapy resistance, and reduces chemotherapy-dependent increases in CSC surface marker expression by flow cytometry, stemness and EMT genes by qRT-PCR, and downstream targets, including IL-6. Future studies will use siRNA silencing to further investigate the role of specific ID proteins in chemotherapy resistance, asymmetric division, spheroid formation, CSC maintenance by gene expression and flow cytometry, and signaling to downstream targets. These studies highlight a novel target important in CSC maintenance in response to chemotherapy that contributes to tumor progression and relapse. Understanding these mechanisms will allow us to develop novel therapeutic approaches to overcome chemotherapy-induced relapse, and better clinical outcomes. Citation Format: Megan Anne Keene, Mikella Robinson, Darren Lighter, Carrie House. ID1-4 proteins' contribution to cancer stem-like cell maintenance and ovarian cancer recurrence following chemotherapy [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 2694.