Inflammatory macrophage derived TNF alpha induces downregulation of estrogen receptor alpha in breast cancer cells by inactivation of Foxo3A.

Breast cancers are divided into different subtypes based on receptor expression status: estrogen receptor (ER), progesterone receptor (PR) and Her2. The luminal A subtype (ER+PR+Her2-) is most often associated with a good prognosis while the triple-negative (TN) cancers (ER-PR-Her2-) have a poor prognosis. ER+ cancer cells depend on estrogen for their growth and can be treated with drugs to block its effects. While most human breast cancers express ER alpha, some tumors are hormone independent despite the presence of ER and others become ER negative over time. Myeloid cells are known to affect tumor development, and infiltration of tumor-associated macrophages is associated with a worse prognosis. Theoretically, however, macrophages can be both beneficial and bad for the patient. Proinflammatory M1 macrophages (CD68+ CD163-) can eliminate cancer cells and promote antitumor immune responses while anti-inflammatory M2 macrophages (CD163+CD68+) or anti-inflammatory myeloid cells (CD68-CD163+) can promote tumor progression by inhibiting proinflammatory immune responses and induce wound-healing processes. This includes angiogenesis and matrix degradation, both of which promote metastatic spread and possibly even EMT. Macrophages have also been proposed to downregulate ER in breast cancer cells through an unknown mechanism. Due to the recent reports suggesting that macrophages can induce EMT and downregulate ER, we evaluated the effect of human primary macrophages on ER expression in breast cancer cells. Immunohistochemistry analyses of breast cancer tumor xenografts, established with co-transplantation of primary human myeloid cells together with ER+ breast cancer cells in NSG mice, showed association of monocytes with downregulation of ER-receptor expression. Using primary human monocyte-derived macrophage cultures In vitro, we show that the different subtypes of macrophages have unique cytokine secretion profiles with M1 macrophages secreting significantly higher levels of TNF alpha compared to M2 macrophages. ER alpha positive MCF-7 and ER alpha negative MDA-MB-231 breast cancer cells were cultured in macrophage condition media, and both Western blot and qPCR analysis showed downregulation of ER was caused by M1 macrophage-derived TNF alpha that inhibits FoxO3A transcription of ER alpha. We propose that proinflammatory macrophages (M1), despite being tumoricidal, may have direct effects on endocrine resistance in breast cancer patients. Our findings suggest that different macrophage subtypes have various and unique impacts on breast cancer progression, and that proinflammatory macrophages, despite being tumoricidal, may have unwanted and direct effects on endocrine resistance mechanisms in breast cancer patients. Citation Format: Frida Bjork Gunnarsdottir, Catharina Hagerling, Caroline Bergenfelz, Camilla M. Rydberg, Meliha Mehmeti, Roni Allaoui, Sofie Mohlin, Sven Pahlman, Daniel Bexell, Karin Leandersson. Inflammatory macrophage derived TNF alpha induces downregulation of estrogen receptor alpha in breast cancer cells by inactivation of Foxo3A [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A39.