Conclusion
Natural compound emodin suppresses EMT and CSC formation of breast cancer cells by blocking TGF-β1-mediated crosstalk between TAMs and breast cancer cells. Our study provides evidence suggesting that emodin harbors the potential for clinical development as a new effective and safe agent to halt metastatic recurrence of breast cancer.
Methods
Bioinformatical analysis was performed to examine the correlation between macrophage abundance and EMT/CSC markers in human breast tumors. Cell culture and co-culture studies were performed to test if emodin suppresses TGF-β1 or macrophage-induced EMT and CSC formation of breast cancer cells, and if it inhibits breast cancer cell migration and invasion. Using mouse models, we tested if short-term administration of emodin before surgical removal of breast tumors halts breast cancer post-surgery metastatic recurrence in the lungs. The effects of emodin on TGF-β1 signaling pathways in breast cancer cells were examined by western blots and immunofluorescent imaging.
Results
Macrophage abundance positively correlates with EMT and CSC markers in human breast tumors. Emodin suppressed TGF-β1 production in breast cancer cells and macrophages and attenuated TGF-β1 or macrophage-induced EMT and CSC formation of breast cancer cells. Short-term administration of emodin before surgery halted breast cancer post-surgery metastatic recurrence in the lungs by reducing tumor-promoting macrophages and suppressing EMT and CSC formation in the primary tumors. Mechanistic studies revealed that emodin inhibited both canonical and noncanonical TGF-β1 signaling pathways in breast cancer cells and suppressed transcription factors key to EMT and CSC.