Abstract 717: Monocytic and granulocytic MDSCs display distinct molecular properties and coordinate the dynamic switches between EMT-MET in breast cancer model

Abstract

Abstract It is widely accepted that the epithelial-mesenchymal plasticity of malignant cells is required during cancer metastatic cascade. The complex phenotypic changes highly depend on the collaboration of various molecular signaling and extracellular cues originating from wide range of stromal cells in the tumor microenvironment. However, the specific mechanisms of how EMT plasticity spatiotemporally regulates metastasis are poorly defined. Myeloid-derived suppressor cells (MDSCs) have been identified in most cancer patients and animal models due to their immune suppressive functions, but recent studies implicate their direct role in promoting metastasis by activating tumor-angiogenesis. To determine the roles of MDSCs in breast cancer metastasis, we utilized murine breast cancer cells, non-metastatic EMT6 and metastatic 4T1 cells. We showed that the metastatic 4T1 murine breast tumors induced early systemic expansion and mobilization of MDSCs in distant sites as well as in the primary tumor. We investigated the direct functions of MDSCs in tumor progression by isolating monocytic and granulocytic MDSCs from primary tumor, lung and bone marrow of tumor-bearing mice and then they were co-cultured with non-metastatic EMT6 cells. We found that tumor infiltrating m-MDSCs from 4T1 tumor-bearing mice increased the expression of Vimentin, Twist1, TGF-â and IL-6 in EMT6 tumor cells. In contrast, flow cytometry sorted lung infiltrating MDSCs from 4T1 tumor-bearing mice enhanced the EpCAM expression and proliferation in EMT6 cells. Cell invasion assay showed that invasive ability of EMT6 cells were significantly increased when they were co-cultured with m-MDSCs while g-MDSCs slightly decreased the number of invaded cells, compared to control group. We utilized immunofluorescence staining and confirmed the increased expression of Vimentin, CK14 (cytokeratin 14) in EMT6 cells co-cultured with m-MDSCs. In contrast, g-MDSCs induced down-regulation of these markers while they increased cell proliferation as assessed by Ki67 staining. Furthermore, flow cytometry analysis showed the increased CD24+CD29+ population, a marker of murine cancer stem cell (CSC) phenotype, in EMT6 cells when co-cultured with m-MDSCs from 4T1 tumor-bearing mice. Tumor sphere assay confirmed that m-MDSCs enhanced sphere forming ability of tumor cells. Taken together, these data suggest that m-MDSCs derived from metastatic 4T1 tumor-bearing mice are able to confer EMT/CSC phenotype on tumor cells while g-MDSCs are more potent in inducing epithelial phenotype and proliferation in tumor cells. Citation Format: Eunmi Lee, Maria Ouzounova, Raziye Piranlioglu, Abdeljabar El Andaloussi, Mehmet Demirci, Ena Novakovic, Alicia Hudson, Sumeyye Korkaya, Gang Zhou, Hasan Korkaya. Monocytic and granulocytic MDSCs display distinct molecular properties and coordinate the dynamic switches between EMT-MET in breast cancer model. [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 717.