Cyclooxygenase-2 Inhibition Blocks M2 Macrophage Differentiation and Suppresses Metastasis in Murine Breast Cancer Model

Yi-Rang Na,Seung-Hyeok Seok,Da-In Son,Yi-Na Yoon,Fabrizio Mattei

doi:10.1371/journal.pone.0063451

Abstract

Tumor cells are often associated with abundant macrophages that resemble the alternatively activated M2 subset. Tumor-associated macrophages (TAMs) inhibit anti-tumor immune responses and promote metastasis. Cyclooxygenase-2 (COX-2) inhibition is known to prevent breast cancer metastasis. This study hypothesized that COX-2 inhibition affects TAM characteristics potentially relevant to tumor cell metastasis. We found that the specific COX-2 inhibitor, etodolac, inhibited human M2 macrophage differentiation, as determined by decreased CD14 and CD163 expressions and increased TNFα production. Several key metastasis-related mediators, such as vascular endothelial growth factor-A, vascular endothelial growth factor-C, and matrix metalloproteinase-9, were inhibited in the presence of etodolac as compared to untreated M2 macrophages. Murine bone marrow derived M2 macrophages also showed enhanced surface MHCII IA/IE and CD80, CD86 expressions together with enhanced TNFα expressions with etodolac treatment during differentiation. Using a BALB/c breast cancer model, we found that etodolac significantly reduced lung metastasis, possibly due to macrophages expressing increased IA/IE and TNFα, but decreased M2 macrophage-related genes expressions (Ym1, TGFβ). In conclusion, COX-2 inhibition caused loss of the M2 macrophage characteristics of TAMs and may assist prevention of breast cancer metastasis.

Highlights

Tumor associated macrophages (TAMs) and the factors they release amplify various aspects of cancer, including anti-tumor immune suppression, stimulation of tumor progression, and formation of metastases [1,2,3]
Our finding suggest that COX-2 inhibition may inhibit M2 macrophage differentiation and polarization, suppressing tumor metastasis
After differentiation for 7 days with 20 ng/ml M-CSF in the presence or absence of etodolac, macrophages were examined for surface marker expressions (Fig. 1)

Summary

Introduction

Tumor associated macrophages (TAMs) and the factors they release amplify various aspects of cancer, including anti-tumor immune suppression, stimulation of tumor progression, and formation of metastases [1,2,3]. TAMs exhibit a predominantly M2-like phenotype [13,14]. This preferential polarization is due to the abundance of M2 stimuli as well as the absence of M1-orienting signals in the tumor, such as IFN-c or bacterial components. M2-macrophages differentiate from monocytes in response to specific growth factors released by both malignant and stromal tumor compartments, including CCL2, MCSF, vascular endothelial growth factor (VEGF) and CXCL12 ( known as SDF1) [2,15,16]. Data regarding the molecular mechanisms of macrophage polarization remain sparse

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Conclusion