Jagged1 promotes aromatase inhibitor resistance by modulating tumor-associated macrophage differentiation in breast cancer patients

Endocrine resistance limits the efficacy of anti-estrogen therapies. Notch signaling is involved in modulating tumor-associated macrophage (TAM) differentiation and is upregulated in endocrine-resistant breast cancer cells. Here, we analyzed the role of Jagged1 in the regulation of TAM polarization to investigate whether the Jagged1-Notch pathway promotes the acquisition of aromatase inhibitor (AI) resistance by upregulating TAM infiltration. The Jagged1 expression levels and M2 TAM infiltration density, in 203 tumor samples from ER-positive postmenopausal patients, who received AI treatment, were evaluated by immunohistochemical staining and the results were compared with clincopathological parameters and survival. The Jagged1 protein and mRNA levels were analyzed in MCF-7 and long-term endocrine-depleted (LTED) cell lines. The phenotypes of macrophage after macrophages were co-cultured with either MCF-7 or LTED cells, were evaluated using flow cytometry. Cell migration assay was performed to evaluate the mobility of cancer cells. Notch gama secretase inhibitor (GSI) RO4929097 was employed to investigate whether modulation of Notch signaling affects M2 polarization. In the tumor samples, Jagged1 expression was found to be associated with a large tumor size, high histological grade, lymphatic invasion, and high Ki67 expression. Jagged1 expression was also correlated with reduced disease-free and overall survival and was positively associated with the stromal M2 TAM infiltration density in primary tumor tissues. In AI-resistance patients, M2 TAM infiltration was denser in metastatic lesions than in primary tumors. Higher Jagged1 protein and mRNA levels were also found in LTED cells, which model AI-resistant conditions in patients, compared with MCF-7 cells. Macrophages co-cultured with LTED cells expressed higher levels of M2 marker and IL-10. M2 TAM proportion was reduced when macrophages were pre-treated with GSI before co-culture. The Jagged1-Notch pathway showed elevated expression in AI-resistant breast cancer cells, resulting in macrophage differentiation towards M2 TAMs and there contributing to the acquisition of AI resistance.