Abstract Ovarian cancer (OC) is the fifth leading cause of cancer-related deaths among women in the U. S. Studies show that cancer patients have elevated stress hormones due to various stressors, which can disrupt cancer progression and immune response in the tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSCs) are immature, immunosuppressive cells that play a key role in the TME and are linked to poor prognoses in cancer patients by disrupting several pathways, including the Notch signaling pathway (NSP). In various cancers, NSP dysregulation contributes to cancer progression. Increasing evidence suggests that chronic stress enhances MDSC infiltration, promoting immunosuppression in the TME. However, the role of the NSP in stress-mediated MDSC infiltration and OC progression remains poorly understood. This study explores how chronic stress influences NSP and MDSC biology in the OC TME and its role in disease progression. We hypothesize that chronic stress increases MDSC infiltration in the OC TME, enhancing NSP activity in OC cells. To test this, we inoculated female C57BL/6 mice with ID8Luc or IG10Luc OC cells and subjected them to daily restraint stress. Mice were sacrificed weekly for tumor and bone marrow collection, followed by immunofluorescence and flow cytometry analyses to characterize MDSCs based on surface markers. We also isolated bone marrow from naïve C57BL/6 mice to differentiate myeloid cell precursors into MDSCs. These cells were then exposed to stress hormones (norepinephrine (NE), epinephrine (EPI), and corticosterone (CC) ) for 72 hours to analyze MDSC populations. Our results showed that chronic restraint stress increased MDSC infiltration and enriched polymorphonuclear-MDSCs (PMN-MDSCs) in the TME and bone marrow of both OC mouse models. Ex vivo experiments indicated increased PMN-MDSC enrichment alongside a depletion of monocytic-MDSCs in groups treated with stress hormones. To further examine how stress hormones impact NSP dysregulation, we treated OC cells (ID8 and IG10) in vitro with NE, EPI, or CC. Our findings revealed that stress hormones significantly upregulated the expression of the Notch Intracellular Domain (NICD) in OC cells. We also observed elevated levels of Notch1, Jagged2, and Hes1 mRNA and protein, which may be mediated by GSK-3β phosphorylation. Additionally, we analyzed NSP member expression in tumors from in vivo experiments. The results indicated higher levels of Notch1, Jagged2, NICD, and HES1 in tumors from mice subjected to restraint stress. In addition, Milliplex analysis of cytocytokine/chemokine profiles from ID8Luc or IG10Luc OC-bearing mice serum samples subjected to chronic restraint stress showed higher levels of IL-1β, IL-6, GM-CSF, G-CSF, MCP-1, RANTES, TNF-α, and low levels of IFN-γ, associated with MDSC biology and function. These data suggest that chronic stress may induce MDSC infiltration and activity, possibly mediated by NSP activation, thereby contributing to an immunosuppressive TME and OC progression. Citation Format: Yadiel A. Rivera-Lopez, Luinet L. Meléndez-Rodríguez, Jaydiel A. Casiano-Martínez, Alanis P. Torres-Rosado, Sofia M. Hernández-Carrasquillo, Raian Imad-Hamad, Melanie Ortiz-León, Luis A. Rivera-Pérez, Orlando I. Torres-Rodríguez, Zuliann S. Galarza-Ruiz, Guillermo N. Armaiz-Pena. Chronic stress drives ovarian cancer progression via myeloid-derived suppressor cells infiltration and notch signaling pathway activation abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Ovarian Cancer Research; 2025 Sep 19-21; Denver, CO. Philadelphia (PA): AACR; Cancer Res 2025;85 (18Suppl): Abstract nr PR011.
Rivera-López et al. (Fri,) studied this question.