Abstract 1382: Activation of the cGAS-STING pathway by large oncosomes induces type I IFN inflammation in mesenchymal stem cells that triggers an immunosuppressive phenotype in neutrophils

Abstract Extracellular vesicles (EVs) have been recognized as key players in cancer progression and metastasis, particularly large oncosomes (LO), secreted by invasive cancer cells, represent a distinct class of EVs with unique features. Previous research by the Di Vizio lab revealed LO's ability to alter recipient cell behavior, induce vascular morphogenesis, and carry cancer-specific biomolecules. Our preliminary studies point to a new mechanism of intercellular communication that involves the release of LO-containing DNA from PC cells. Notably, LO from prostate cancer exhibits enhanced potency in reprogramming bone marrow-derived mesenchymal stem cells (BM-MSCs) compared to exosomes (Exo) as observed by RNAseq. When evaluating the response to LO and Exo of BM-MSC, which are emerging as important drivers of bone metastasis, LO induces a robust inflammatory response, including metastasis-relevant chemokines and transcription factors involved in type I IFN response such as IRF7 and RASD2. Further, REACTOME pathway analysis of the differentially expressed genes revealed enrichment of the cGAS-STING pathway in BM-MSCs treated with LO, indicating a potential link between DNA/RNA sensors and the inflammatory response. BM cells isolated from WT and mutant Sting1gt/J mice demonstrated that up-regulation of IRF3 and IFNA1 genes induced by LO is inhibited when STING is absent. Suggesting that nucleic acid sensors engage in the LO-induced immune response in BM cells. Gene ontology analysis (GO) also identified several chemokines involved in neutrophil chemotaxis. In line with the observation from GO, neutrophil chemotaxis was significantly promoted by PC-derived LO-treated BM-MSC. Interestingly, human blood-derived neutrophils exposed to a conditioned medium from EVs-treated BM-MSC significantly increased the percentage of a population of LOX-1high and CD62Llow/− after 6h of culture. This was observed in concert with increased expression of Arginase1 and IL-10, suggesting their differentiation into polymorphonuclear-myeloid-derived suppressor cells (PMN-MDSC). An experimental orthotopic model using the breast cancer bone metastatic 4T1.2 cell line, with increased capacity to shed LO, demonstrated an increase in the presence of PMN-MDSC in the bone marrow of tumor-bearing mice in addition to a complete lack of lymphocyte populations, indicating their immunosuppressive activity that could lead to a pre-metastatic niche formation. This comprehensive study unveils the molecular pathways underlying the immune response to LO in the bone marrow, shedding light on mechanisms that could influence metastatic progression in prostate cancer. The findings underscore the unique role of LO in modulating the BM microenvironment, providing potential targets for therapeutic intervention and biomarkers for early disease detection. Citation Format: Taylon F. Silva, Diana Kitka, Blandine Victor, Chen Qian, Minhyung Kim, Tatyana Vagner, Giorgia Guerra, Catherine Grasso, Sungyong You, Fayyazz Sutterwala, Caroline Jefferies, Paola de Candia, Michael Freeman, Helen Goodridge, Karen Cavassani, Jlenia Guarnerio, Dolores Di Vizio. Activation of the cGAS-STING pathway by large oncosomes induces type I IFN inflammation in mesenchymal stem cells that triggers an immunosuppressive phenotype in neutrophils [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1382.