LAUSR

The overall patient survival rate drops dramatically when localized prostate cancer (PCa) progresses to bone metastatic prostate cancer (BM-PCa). The treatment for BM-PCa is limited to palliative therapy, and it is currently incurable. Neutrophils are the most prevalent immune cell in the bone, and we have found that PCa enhances their recruitment and infiltration into the prostate tumor-bone microenvironment of patients with BM-PCa. Additionally, we observed that bone marrow neutrophils directly induce apoptosis of PCa cells both in vitro and in vivo and that this is mediated by the inhibition of STAT5, a transcription factor that promotes PCa progression. Moreover, STAT5 has also been found to contribute to the development of resistance to standard care androgen deprivation therapy. Neutrophils specifically target and kill only cells that express STAT5, as stable knockdown of STAT5 in BM-PCa cells makes them resistant to neutrophil-mediated cytotoxicity, while the overexpression of STAT5 in STAT5-negative PCa cells, which are generally resistant to killing by neutrophils, sensitizes them to neutrophil-mediated killing. Furthermore, transcriptomic analyses derived from the STAT5 knockdown and STAT5 overexpressing cells suggest that STAT5 expression in PCa induces pro-inflammatory signaling and that neutrophil-mediated cytotoxicity may be exerted via STAT5-induced IL-1 and/or IL-6. Preliminary data in our laboratory show that STAT5-induced production of IL-1 by PCa cells leads to their death by neutrophils, as knocking out the IL-1 receptor on neutrophils reduces their cytotoxic potential against STAT5-positive PCa cells. Interestingly, in addition to killing BM-PCa cells, we have demonstrated that bone marrow-derived neutrophils are also capable of killing pancreatic cancer cells. Further delineation of the role of neutrophils in STAT5 signaling in BM-PCa growth holds promise for enhancing neutrophil cytotoxicity in the bone which could lead to novel therapeutic options for bone metastatic prostate cancer. Citation Format: Sanjana Rajgopal, Massar Alsamraae, Diane Costanzo-Garvey, Leah Cook. Anti-tumor actions of neutrophils are mediated via STAT5 inhibition. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3647.