Chronic inflammation is a hallmark of the breast cancer tumor microenvironment and is also known to be associated with disease progression and therapeutic response. Interleukin-1 (IL-1) signaling has been widely studied in breast cancer biology; however, the long-term effect of sustained IL-1 exposure on hormone receptor-positive breast cancer cells remain poorly understood. In this study, we investigated how chronic IL-1 exposure influences inflammatory response, hormone dependency, and therapeutic sensitivity in ERα+/PR+ breast cancer models, MCF7 and T47D. Chronic IL-1 exposure attenuated response to subsequent acute IL-1 treatment, but the chronically exposed cells remained sensitive to serum deprivation, retained dependence on estrogen or progesterone receptor signaling, and responded robustly to endocrine and chemotherapeutic treatments. Extensive changes in basal gene expression and histone modification revealed that chronic IL-1 exposure alters transcriptional reprogramming and chromatin remodeling. Together, these findings demonstrate that chronic IL-1 signaling drives selective inflammatory response in hormone receptor-positive MCF7 and T47D breast cancer cells. This work underscores the continued therapeutic relevance of hormone receptor-targeted strategies in chronically inflamed tumors and provides insight into how sustained inflammatory stress shapes tumor behavior and gene regulation predicted to promote tumor progression.

Background: Cancer cells live in a dynamic and favorable ecosystem conducive to their growth and survival, known as the tumor microenvironment (TME). The TME is replete with various proinflammatory cell types that mediate crosstalk via the secretion of cytokines and chemokines to facilitate tumor growth and development. One cardinal proinflammatory cytokine that is present in the TME is interleukin-1 (IL-1). IL-1 promotes tumor angiogenesis and cancer cell metastasis; thus IL-1 receptor antagonist (IL-1Ra) is of clinical interest. Our lab previously reported that chronic exposure to exogenous IL-1 can select for cancer cells that evolve insensitivity to IL-1 signaling, thus rendering IL-1-targeting therapies, like IL-1Ra, irrelevant. While immune cells are the primary source of TME IL-1, cancer cells can also produce and secrete IL-1 to engage in autocrine and/or paracrine signaling. In this context, cancer cell exposure to multiple other sources of exogenous IL-1 beyond autocrine production might also amplify extrinsic IL-1 signaling in these cells, but the consequences of sustained amplified IL-1 signaling on the regulation, function, and therapeutic response of these cancer cells need to be explored. Methods: Using the IL-1-secreting 5637 bladder cancer (BlCa) cell line, we generated chronic IL-1 sublines by spiking the growth medium with additional IL-1α or IL-1β chronically for 6 months. Once established, we assessed subline acute IL-1 sensitivity, paracrine signaling and response to IL-1Ra. Results: Following chronic exposure to elevated exogenous IL-1 levels, the 5637 BlCa cell line retains sensitivity to acute IL-1 and IL-1Ra and maintains the ability to induce IL-1-dependent endothelial cell activation, which is reversed with IL-1Ra. These data suggest that for cancer cells that engage in cell autonomous IL-1 signaling, sustained extrinsic IL-1 exposure does not dampen IL-1 or IL-1Ra sensitivity, supporting the context-dependent use of IL-1 antagonists as rational therapeutics in both acute and chronic inflammatory TMEs.