Abstract 1573: The progesterone analogue, Norgestrel, impairs tumor immunity and promotes metastatic breast cancer progression

Abstract

Abstract The immune system is responsible for recognition and elimination of cancer cells. Tumors, however, can elicit different evasive mechanisms that contribute to immune escape Thus, understanding the immunosuppressive pathways that hamper tumor immunity is critical for the identification of novel therapeutic targets. Progestin-containing hormonal supplementation (as hormone replacement therapy or contraceptive) has been associated with an increase in the risk of breast cancer incidence and recurrence. Moreover, progesterone, as a natural hormone, generally impairs cellular immune responses responsible of preventingfetal rejection during pregnancy. We postulated that progestins and in particular the widely used contraceptive Norgestrel may impair tumor immunity and foster immunosuppressive tumor microenvironments. We injected Balb/c mice with the triple-negative 4T1breast tumor,, and treated them with a Norgestrel releasing depot for 30 days. Norgestrel-treated mice displayed a higher frequency of suppressive regulatory T cells (Tregs) in draining lymph nodes and tumors which displayed a CD4+CD25+Foxp3+CD44+ phenotype. Accordingly, norgestrel-treated mice showed greater number of exhausted PD1+ Tim-3+ CD8 T cells in the tumor microenvironment. Furthermore, in vitro exposure to Norgestrel also promoted differentiation and expansion of Tregs which activated the mTOR pathway assessed by phosphorylation of S6 ribonucleoprotein. These effects could not be prevented by the progesterone nuclear receptor antagonist, Zk 230211, suggesting that Norgestrel acts preferentially through membrane progesterone receptors. Although no significant difference regarding tumor growth could be observed, Norgestrel-treated mice showed greater number of lung metastasis. Mechanistically, Norgestrel-driven Treg cells showed increased expression of RANKL, a protein involved in breast cancer development and progression. Our results identify a novel progestin-mediated tumor-promoting mechanism and indicate caution onthe use of Norgestrel-supplementation therapies. Our findings suggest that Norgestrel may impair tumor immunity, thereby promoting metastatic dissemination of breast cancer cells. Citation Format: Tomas Dalotto Moreno, Gabriel Adrian Rabinovich, Mariana Salatino. The progesterone analogue, Norgestrel, impairs tumor immunity and promotes metastatic breast cancer progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1573.