Abstract 1700: Excessive ROS in ovarian cancer cells impairs anti-tumor capacities of immune cells through exosomal miR-155/PD-L1 pathway

Abstract

Abstract Background and Objective: Genetic and metabolic alterations in cancer cells promote the sustained oxidative stress as reflected by excessive production of reactive oxygen species (ROS). We and other groups have identified that the ROS-sensitive microRNAs regulate the cancer cell response to ROS. However, it has yet to be determined how these miRNAs convey the ROS signal to downstream effectors and thus produce biological consequences. Accumulative evidence indicates that tumor-derived exosomes are emerging mediators of tumorigenesis. In this study, we aimed to investigate how ROS convey the oncogenic signals through cellular interactions via exosomes within the tumor microenvironment. Methods and Results: Through NanoString nCounter miRNA analysis, we identified miR-155-5p as the most abundant miRNAs enriched in the exosomes derived from epithelial ovarian cancer (EOC) cells treated with a ROS scavenger N-acetylcysteine (NAC). Mechanistically, tumor exosomal miR-155-5p was transferred to tumor-associated macrophages (TAM), directly targeting PD-L1 to inhibit the infiltration of TAM into tumor microenvironment. The role of tumor-derived exosomal miR-155-5p was determined by co-culture experiments and gain or loss of function studies in vitro, and confirmed in xenograft mouse models in nude mice and immunocompetent mice. In addition, we established a 3D-3-culture system to entail the co-culture of NAC-treated EOC cell spheroids, TAM and T cells. We found that CD8+ T-cell ratio was increased and production of IFN-γ, IL-2, and TNF-α was promoted. What's more, the immunocompetent EOC mouse model was established and treated with NAC-modified mouse ovarian cancer cell-released exosomes. The results showed that NAC-modified tumor growth was significantly reduced compared to control group. Further analysis showed that miR-155-5p increased in TAM, while PD-L1 expression levels decreased in macrophages from tumors and spleens. Moreover, the T cell function was also augmented as evaluated by the expression of Ki-67 and Granzyme B on CD8+ T cells. Conclusion: In conclusion, our study reveals a novel mechanism underlying PD-L1 expression in EOC. Ovarian cancer cells with excessive ROS levels release exosomes that mediate the interaction between cancer cells and immune cells; it is this interplay that produces an immunosuppressive tumor microenvironment by upregulation of PD-L1 in macrophages, and eventually contributes to the progress of EOC through the ROS/miR-155-5p/PD-L1 pathway. Citation Format: Xiang Li, Gao-chan Wang, Jun He. Excessive ROS in ovarian cancer cells impairs anti-tumor capacities of immune cells through exosomal miR-155/PD-L1 pathway [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1700.