BSCI-05. HOW MICROGLIA, BRAIN RESIDENT MYELOID CELLS, RESPOND TO BREAST CANCER METASTASIS INTO THE BRAIN?

Brain metastasis from different cancers, including lung, breast, melanoma, colorectal or renal cell carcinoma is relatively common and its frequency increases with a prolonged survival of cancer patients. New anti-cancer therapies frequently fail to reduce metastatic burden. While the important role of tumor-associated macrophages as pro-tumorigenic cells facilitating tissue remodeling, invasion and metastasis is well documented, much less is known about the immune microenvironment of brain metastases and potential mechanisms that mediate interactions of cancer cells with brain immune cells - microglia. Triple-negative breast cancer metastases to the brain were discovered in 46% of patients. We evaluated the abundance and morphology of microglia on sections from breast cancer metastases using immunohistochemistry. We found that microglia cells are activated, surround the breast tumor cells and do not infiltrate the solid tumor. Searching for a potential attractant of microglia, we determined osteopontin levels in six human breast cancer cell lines and found upregulation of osteopontin in transformed cells, with the highest level in the triple-negative MDA-MB-231 cells. MDA-MB-231 cells activated primary murine microglia cultures when co-cultured. Invasion of MDA-MB-231 cells in co-cultures with murine immortalized BV2 microglial cells and human SV40 immortalized microglia was increased, as demonstrated using Matrigel Invasion Assay. Using immunofluorescence we detected osteopontin in cancer cells in human breast cancer metastases. Moreover, we found that minocycline, a clinically used antibiotic, reduces the osteopontin production in human breast cancer cells and the most sensitive cells were MDA-MB-231 cells. Our study shows that metastatic cancer cells may employ microglia to facilitate extravasation and colonization of brain parenchyma. We postulate that osteopontin mediates interactions between microglia and metastatic cancer cells and minocycline may interfere with those interactions. Funding: TEAM TECH CORE FACILITY FNP: Development of comprehensive diagnostics and personalized therapy in neuro-oncology