PROGESTERONE (MEDROXIPROGESTERONE)-INDUCED IMMUNOSUPRESSION THREATS IMMUNOSURVEILLANCE TO TUMORS AND PROMOTES LUNG METASTASIS IN A BREAST CANCER MODEL

SALATINO M; DALOTTO-MORENO T; RABINOVICH GA

Congreso; Annual meeting of the Amercian Association for Cancer Research; 2013

Exposure to sexual hormones is one of the strongest risk factors for breast cancer. Increased risk is entwined with a greater number of reproductive cycles and the use of progestin-containing hormone replacement therapy. In addition, the importance of progesterone in dampening immune response was illustrated in several models of infection and pregnancy. Based on the tolerogenic properties of progesterone (Pg) and its promoting role in breast cancer, in this work we investigated whether progesterone may threat immunosurveillance and promote tumor metastasis by fostering an immunosuppressive microenvironment in breast cancer. We first showed that exogenously added Pg: (10-8M) or its synthetic analogue medroxiprogesterone acetate (MPA: 10-8M) were able to induce the expression of the immunosuppressive protein galectin-1 (gal1) in the hormone-dependent human breast cancer cell lines T47D and MCF-7 and in the mouse mammary adenocarcinoma C4HD. This effect was abrogated by pre-treatment with RU486 (10-7M) indicating that the progesterone receptor (PR) was involved. Interestingly, in vitro MPA-treatment of human PBMC or mouse splenocytes controlled the expansion of the regulatory T-cells (Tregs) (CD4+CD25+Foxp3+), a population endowed with suppressive activity and skewed the balance toward a Th2-type cytokine profile. Furthermore, Tregs differentiation from naive T-cell was promoted in the presence of MPA, IL-2 and suboptimal concentrations of TGF-â. In addition, in vivo MPA-treatment (15mg 30-day release depot) of C4HD tumor-bearing mice increased both the expression of gal1 and the frequency of Tregs in tumor-draining lymph nodes and within the tumor microenvironment. While the increment in Tregs frequency was associated with an effect of the hormone on SMAD4 expression on Tregs that potentiates TGF-â signalling, Tregs homing to tumor sites was supported through the induction of tumor-derived CCL22 chemokine. Finally, we used a PR negative breast tumor model (4T1) to evaluate the effect of MPA on the tumor microenvironment and how it affects tumor progression and metastasis. Notably we showed that MPA in vivo promoted lung metastasis by inducing an invasive phenotype in breast cancer cells. In particular, co-culture of Tregs differentiated in vivo in the presence of MPA with 4T1 cells promoted its invasive activity and modulate several genes associated with EMT, as Snail. In summary, these results demonstrate that medroxiprogesterone hierarchically fosters an immunosuppressive tumor microenvironment that promotes metastasis by co-ordinately regulating gal1 expression, stimulating the TGF-â pathway and augmenting the frequency of Treg cells. Our findings provide new insights into the role of progestins in breast cancer as a crucial promoter of evasion of the immune response against tumors.