TMIC-48. THREE DIMENSIONAL CANCER CELL-MONOCYTE CO-CULTURE SPHEROIDS RECAPITULATE IMMUNOSUPPRESSIVE AND PRO-TUMORIGENIC MICROENVIRONMENTS IN BRAIN METASTATIC BREAST CANCER

Abstract Brain metastasis occurs in 15 % of breast cancer patients and is one of the major causes of breast cancer related morbidity. Brain metastatic breast cancer (BMBC) microenvironment is a heterogeneous niche of cellular and acellular components of which the innate immune cells, microglia, and macrophages, comprise the major fraction. However, the role of these innate immune cells in the tumor microenvironment (TME) in mediating cancer progression and response to therapy is not well understood. To address this need, herein, we developed three dimensional (3D) co-culture spheroids using brain metastatic triple negative breast cancer (TNBC) cell line MDA-MB-231Br or patient derived brain metastatic TNBC cell line F2-7 with THP1 monocytes. Under co-culture conditions MDA-MB-231Br co-culture spheroids assumed highly protrusive morphology with enhanced mesenchymal and proliferative characteristics. Additionally, phenotypic determination of cocultured macrophages revealed elevated levels of markers associated with alternatively activated macrophages i.e. CD163, CD206, and c-Myc. Furthermore, we found that under coculture conditions immunosuppressive and evasive markers PD1, PDL1, CD47 and CD24 were significantly upregulated. Similarly, F2-7 and monocyte cocultures also led to an immunosuppressive environment with elevated levels of M2 type markers and associated anti-inflammatory cytokines. We further found that the presence of M2 type macrophages in the microenvironment of BMBC spheroids led to acquired resistance against Paclitaxel, a clinically relevant chemotherapeutic drug against BMBC. In sum, in our coculture conditions, brain metastatic TNBC cells polarized monocytes into immunosuppressive and pro-tumorigenic tumor associated macrophages leading to a pro-tumoral microenvironment. Thus, 3D co-culture spheroids of BMBC cells and monocytes can serve as robust platform for studying cancer cell and innate immune cell interactions occurring in the BMBC environment.