Induced chromosomal instability in triple negative breast cancer cells promotes M2-like polarization of macrophages.

Chromosomal instability (CIN) is a defining feature of triple-negative breast cancer (TNBC) and is increasingly recognized as a driver of tumor evolution and immune escape. However, how CINHIGH tumor cells modulate innate immune cells, particularly macrophages, remains unclear. Here, we used the MPS1 inhibitor reversine to induce acute CIN in the TNBC cell line MDA-MB-231 and examined its impact on human macrophage polarization and function. Reversine-induced CIN stably increased the expression of macrophage-attracting cytokines, including CCL2, CCL5, and IL-6. In direct co-cultures, reversine-treated cancer cells promoted M2-like macrophage polarization, accompanied by a modest increase of M1-like markers, whereas in non-contact transwell co-cultures, soluble paracrine signals from reversine-treated TNBC cells only promoted M2-like polarization. Furthermore, macrophages exposed to reversine-treated TNBC cells showed enhanced uptake of cancer cells, further underscoring their activation by cells with reversine-induced CIN. Finally, we found that macrophage activation coincided with the secretion of factors that promoted cancer cell migration, suggesting that immune-cancer cell interaction promotes metastasis. Together, our findings show that drug-induced CIN in TNBC cells promotes polarization of co-cultured macrophages, promoting an immunosuppressive, pro-migratory niche that may be exploitable for therapies targeting CIN-associated immune modulation.