Tumor-associated macrophages secrete CC-chemokine ligand 2 and induce tamoxifen resistance by activating PI3K/Akt/mTOR in breast cancer

Li, Dongbo; Ji, Hongfei; Niu, Xingjian; Yin, Lei; Wang, Yiran; Gu, Yucui; Wang, Jinlu; Zhou, Xiaoping; Zhang, Han; Zhang, Qingyuan

To determine the clinical relevance of CCL2 and endocrine resistance in the in vitro findings, we selected 100 patients with invasive ER-positive breast cancer who received regular endocrine therapy at the Tumor Hospital of Harbin Medical University from 2004 to 2014 F I G U R E 4 High concentration of CC-chemokine ligand 2 (CCL2) recruits monocytes and macrophages to facilitate an endocrine-resistant microenvironment in breast cancer. A, Representative photos of THP-1 cells recruited by the conditioned medium (CM) of MΦ, TAM from a tamoxifen-sensitive tumor microenvironment (TME) (MS), TAM from tamoxifen-resistant TME (MR), and MR + Bindarit after the chemotaxis assay. Quantitative results show that the chemotaxis ability of TAM to recruit THP-1 cells was enhanced, and TAM in the endocrine-resistant environment had stronger chemotaxis ability. Bindarit reverses the enhanced chemotaxis ability of CM (MR). B, Representative images of immunohistochemical staining for CCL2 and CD163 and HE staining in serial sections from human breast cancer samples. The related correlation analyses showed r = .548. *P < .05, **P < .01 F I G U R E 5 CC-chemokine ligand 2 (CCL2) expression in the stroma correlated with poor recurrence-free survival of patients with hormone receptor-positive breast cancer. A, Different patterns of CCL2 immunohistochemical staining in the stroma of breast cancer cells. B, Kaplan-Meier recurrence-free survival curves of patients with hormone receptorpositive breast cancer with low (n = 71) and high (n = 29) CCL2 expression in the stroma (P = .029). C, Proposed model for TAM-secreted CCL2 activating the PI3K/Akt/mTOR pathway to promote a malignant cycle of endocrine resistance and recruitment of monocytes (Table S3) Results showed that PFS of the CCL2 high-expression group was significantly shorter than that of the CCL2 low-expression group (P < .05). The prognostic value of each clinicopathological feature was assessed using Cox hazard regression analysis. CCL2 expression was found to be an independent risk factor for disease-free survival (DFS) (HR = 2.323, P = .015) ( Table 1) . Taken together, these results indicate a crucial role of CCL2 in promoting endocrine resistance in breast cancer. We also found that TAM promote endocrine resistance by secreting CCL2, which activates the PI3K/Akt/mTOR signaling pathway. Therefore, CCL2 plays an important role in this malignant feedback loop. In addition, CCL2 promotes the aggregation of monocytes and macrophages in the TME. 48 The transition from monocytes to TAM further promotes the formation of the endocrine-resistant microenvironment. Analysis of tissue samples from patients with hormone receptor-positive breast cancer confirmed a correlation between high expression of CCL2 in the paraneoplastic stroma and infiltration of CD163+ macrophages. Moreover, patients with high CCL2 expression in the stroma had a shorter PFS after endocrine therapy. This is consistent with the findings of our previous study that patients with high CD163+ macrophage infiltration tend to develop endocrine resistance. 22 The finding that CCL2 promotes the formation of the TME and the malignant cycle of cells in the TME may partly explain why patients with endocrine resistance in the past are more likely to be resistant to new endocrine therapy.