Abstract 5: Noncanonical NF-kB and notch signaling activity supports ovarian cancer stem-like cells following chemotherapy

Abstract In the United States, ovarian cancer is the most lethal gynecological malignancy and the fifth most lethal cancer for those at risk. Although patients typically respond well to initial chemotherapy treatments, approximately 80% of patients will relapse with chemotherapy-resistant disease. Studies suggest a subpopulation of ovarian cancer cells, termed cancer stem-like cells (CSCs), can resist chemotherapy and repopulate tumors following treatment. The mechanisms enabling these cells to survive chemotherapy and re-establish heterogeneous tumors are unclear but likely involve activation of multiple survival and developmental pathways. Our previous work shows that the noncanonical NF-κB transcription factor, RelB, supports ovarian CSCs, and our preliminary data suggests RelB regulates the expression of Notch pathway genes. Notably, Notch is upregulated in patient-matched tumors following chemotherapy relative to pre-treatment samples. We hypothesize that RelB-mediated upregulation of Notch signaling is required to maintain CSCs and facilitate tumor regrowth after chemotherapy. To test this hypothesis, we first used qRT-PCR and western blot to assess the expression of different Notch receptors and ligands under spheroid-forming 3D culture conditions relative to monolayer 2D conditions. We observed increased expression of most Notch genes in 3D conditions. Interestingly, in sorted CD117+ CSCs, Notch receptor expression (Notch 1 and Notch 3) was maintained, while expression of Notch ligands (DLL1 and DLL3) was reduced, and Jag2 expression was elevated relative to CD117- bulk tumor cells. Additionally, we observed a consistent increase in the Notch target gene CDKN1A in 3D growth conditions relative to 2D. To confirm and further assess Notch activity, we are currently using Notch reporter cells under various conditions, including spheroid culture, treatment with carboplatin and paclitaxel, RelB knockdown, and RelB activation. Our preliminary in vitro data suggests that RelB upregulates Notch signaling in CSCs to enhance stemness and tumor-initiation following chemotherapy treatment. These findings will be validated in an in vivo relapse model to assess the requirement for Notch signaling during relapse. This work highlights a novel collaboration between RelB and Notch activity in CSCs, which may guide the design of more effective therapeutic strategies to reduce relapse and improve survival outcomes for ovarian cancer patients. Citation Format: Gregory J. Jordan, Cecilia Gallo, Mikella Robinson, Omar Lujano-Olazaba, Carrie D. House. Noncanonical NF-kB and notch signaling activity supports ovarian cancer stem-like cells 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 5.