Cancer cell-monocyte co-culture spheroids recapitulate pro-tumorigenic, immunosuppressive, and drug-resistant microenvironments in brain metastatic breast cancer

Monocyte derived macrophages (MDMs) comprise a major cellular fraction of the brain metastatic breast cancer (BMBC) tumor microenvironment (TME), however, their role in BMBC growth and response to therapeutics remains elusive. We developed heterotypic three-dimensional (3D) co-culture spheroid platform of triple negative BMBC cell line MDA-MB-231Br or BMBC patient xenograft derived cell line F2-7 and THP1 monocytes and assessed the impact of monocytes/MDMs on BMBC proliferation, immune modulation, and response to paclitaxel. BMBC cell and monocyte interactions enhanced BMBC cell proliferation and upregulated markers pertaining to M2 macrophage, immune suppression and evasion. Additionally, F2-7 and monocyte co-culture upregulated M1 macrophage and both pro- and anti-inflammatory markers. Co-culture spheroids exhibited higher resistance to paclitaxel as compared to monoculture BMBC spheroids. Our 3D co-culture platform successfully recapitulated to an extent the pro-tumorigenic, immunosuppressive, therapy resistant TME, and tumor immune heterogeneity of BMBC and could contribute towards understanding tumor immune interactions in BMBC.