Exosome derived from breast cancer cells suppresses tumor growth

Tumor-associated macrophages (TAM) play an important role in tumor microenvironment. Particularly, M2 macrophages contribute to tumor progression, depending on the expression of NF-kappaB. Tumor-derived exosomes can modulate tumor microenvironment by transferring miRNAs to immune cells. Epigallocatechin gallate (EGCG) has well known anti-tumor effects; however, no data are available on the influence of EGCG on communication with cancer cells and TAM.

Researchers at the Seoul National University College of Medicine , Korea found that EGCG suppressed tumor growth in murine breast cancer model, which was associated with decreased TAM and M2 macrophage infiltration. Expression of chemokine for monocytes (CSF-1 and CCL-2) were low in tumor cells from EGCG-treated mice, and cytokines of TAM was skewed from M2- into M1-like phenotype by EGCG as evidenced by decreased IL-6 and TGF-beta and increased TNF-alpha. Ex vivo incubation of isolated tumor cells with EGCG inhibited the CSF-1 and CCL-2 expression. Ex vivo incubation of TAM with exosomes from EGCG-treated 4T1 cells led to IKKalpha suppression and concomitant I-kappaB accumulation; increase of IL-6 and TGF-beta; and, decrease of TNF-alpha. EGCG up-regulated miR-16 in 4T1 cells and in the exosomes. Treatment of tumor cells or TAM with exosomes derived from EGCG-treated and miR-16-knock-downed 4T1 cells restored the above effects on chemokines, cytokines, and NF-kappaB pathway elicited by EGCG-treated exosomes.

This data demonstrate that EGCG up-regulates miR-16 in tumor cells, which can be transferred to TAM via exosomes and inhibits TAM infiltration and M2 polarization. We suggest a novel mechanism by which EGCG exerts anti-tumor activity via regulation of TAM in tumor microenvironment.

• Jang JY, Lee JK, Jeon YK, Kim CW. (2013) Exosome derived from epigallocatechin gallate treated breast cancer cells suppresses tumor growth by inhibiting tumor-associated macrophage infiltration and M2 polarization. BMC Cancer 13(1), 421. [Epub ahead of print]. [article]