Iron participated in breast cancer chemoresistance by reinforcing IL-6 paracrine loop.

Chemotherapeutic efficacy is also regulated by the tumor microenvironment. IL-6 produced by TAMs and downstream IL-6/STAT3 signaling pathway is central regulator in chemotherapeutic response. The M2-like phenotype of TAMs is characterized by elevated iron uptake. Whether iron participates in chemo-resistance need to be elucidated. In the present study, we found that IL-6 participated in breast cancer chemoresistance. Local IL-6 paracrine loop acted as exogenous IL-6 rich niche for chemo-sensitive breast cancer cells, leading to de novo acquired drug resistance. Furthermore, Iron reinforced the IL-6 paracrine loop between TAMs and tumor cells resulting in enhanced chemo-resistance. Targeting iron metabolism could disturb the reciprocal interaction between tumor cells and TAMs, breaking the local IL-6 rich niche and blocking IL-6 signaling pathway, which could be promising strategy to overcome chemo-resistance.