Tumor-associated Macrophages Promote Resistance To BET Inhibitors In Triple Negative Breast Cancer

The treatment for triple-negative breast cancer(TNBC)remains a challenge currently due to the lack of targeted medicines.Recently,BET inhibitors are demonstrated to exhibit a strong anti-tumor activity in TNBC.However,the resistance to BET inhibitor has been reported in the clinical treatment of TNBC.The detailed mechanisms of TNBC resistance to BET inhibitors have not been founded.Tumor-associated macrophages(TAMs)are significantly involved in cancer cells resistance to chemotherapy and target therapy and also associated with poor prognosis in TNBC.However,the role of TAMs in BET inhibitors resistance is still unclear.In this study,CCK-8 and Annexin V-FITC/PI dual-staining assays were used to evaluate cell viability and apoptosis.The levels of protein were detected by Western blot and immunofluorescence And the expressions of m RNA were detected by real-time quantitative polymerase chain reaction(RT-PCR).Dual-luciferase reporter assay was conducted to examine the NF-κB activity.PCR array was used to detect the m RNA levels of NF-κB cytoplasmic sequestering molecule.Xenograft experiments were used to analyze tumor growth in vivo.The IL-6 and IL-10 levels in conditioned media were detected by enzyme linked immunosorbent assay(ELISA).We found that BET inhibitors JQ1 and I-BET151 suppressed cells growth and induced cells apoptosis in TNBC by attenuating NF-κB signaling.And Mechanistic analyses suggested that BET inhibition attenuated NF-κB signaling in TNBC by decreasing IKBKE expression.Moreover,we demonstrated that TNBC-stimulated TAMs activated NF-κB signaling by upregulating IKBKE expression to enhance breast cancer cells resistance to BET inhibition.The IKBKE levels were also found to be higher in clinical TNBC tissues than Non-TNBC tissues.The induction of IKBKE expression by TAMs in TNBC cells was identified to be associated with STAT3 signaling,which was activated by TAM-secreted IL-6 and IL-10.In addition,the combination of inhibitors of BET and STAT3 exerted a synergistic inhibition effects in TAM-or TAM CM-treated TNBC cells in vitro and vivo.Our results suggested that blockade of IKBKE or double inhibition of BET and STAT3 might be a novel strategy in the treatment of TNBC.