NEUTROPHIL EXTRACELLULAR TRAPS (NETS) INDUCE A TRANSIENT PRO-TUMOR AND CHEMORESISTANT PHENOTYPE IN MCF7 BREAST CANCER CELLS

INTRODUCTION AND OBJECTIVES: Neutrophil extracellular traps (NETs) are chromatin-protein networks released by activated neutrophils that contribute to tumor progression. Our group showed that NETs induce epithelial-mesenchymal transition (EMT) and promote chemoresistance in breast cancer cells. However, it remains unknown how long these modulations persist after stimulus removal and which NET component drives them. This study characterizes the temporal dynamics of NET-induced EMT, pro-tumor gene expression and apoptotic profile in MCF7 cells, determines whether NET-mediated chemoresistance persists, and assesses HMGB1's contribution. MATERIAL AND METHODS: Neutrophils from healthy donors were PMA-stimulated to produce NETs. MCF7 cells were treated with NETs for 24h; stimuli were then removed and cells followed at 2, 5, 9 and 14 days. Expression of EMT markers (ZEB1, SNAIL), pro-tumor factors (CXCL8, MMP9) and apoptotic regulators (BCL2, BAX) was assessed by qPCR. Chemotherapy response was evaluated with doxorubicin for 48h at 24h, 5 and 14 days after NETs removal, with viability by MTT. HMGB1's role was tested with isolated HMGB1 (50 and 100 ng/mL) for 24h prior to doxorubicin exposure. RESULTS AND CONCLUSION: NETs reduced doxorubicin cytotoxicity in a time-dependent manner: significant at 24h, reduced by day 5 and lost by day 14. Molecular changes followed the same pattern. NETs increased BCL2 and reduced BAX, shifting the apoptotic balance toward survival early on, returning to control values within 9-14 days. ZEB1, SNAIL, CXCL8 and MMP9 rose markedly in the first days and progressively normalized. HMGB1 was not cytotoxic but significantly protected cells against doxorubicin, contributing partly to NET chemoprotection. These results indicate that NETs transiently reprogram MCF7 cells toward a pro-tumor, chemoresistant phenotype that resolves within two weeks, with HMGB1 mediating part of this effect, highlighting NETs and HMGB1 as potential targets in breast cancer.