Macrophage and Triple-Negative Breast Cancer Cell Phenotype Changes in a 3D Co-Culture Model

Tumor-associated macrophage (TAM) infiltration is a characteristic of triple-negative breast cancer (TNBC) related to drug resistance and poor prognosis. Unraveling intricate cell-cell interactions in the tumor microenvironment (TME) remains challenging, especially when using a standardized 3D culture system. This study used the TNBC cell line, MDA-MB-231, and polarized M1-like or M2-like macrophages derived from THP-1 monocytes to establish 3D co-culture spheroids for mimicking the TME environment. Drug efficacy, epithelial-mesenchymal transition (EMT) in cancer cells, macrophage phenotypes, and RNA sequencing of spheroids were performed. We observed that M2 macrophages increased the viability and proliferation rate of MDA-MB-231 cells in the 3D spheroids, while both M1 and M2 macrophages increased the chemosensitivity of MDA-MB-231 cells to doxorubicin and paclitaxel. Interestingly, instead of maintaining their phenotypes, M1 and M2 macrophages lost some polarization when 3D co-cultured with MDA-MB-231 cells. Compared with 2D cultures, an expected mesenchymal transition was observed in 3D spheroid MDA-MB-231 cells. However, both M1 and M2 macrophages induced a partial epithelial reversion in co-cultured spheroids. Deconvolution of our bulk RNA sequencing results verified the existence of phenotypic transitions between M1 and M2 macrophages when co-cultured with MDA-MB-231 cells in 3D spheroids. In conclusion, our findings suggest that a 3D co-culture system of polarized macrophages and breast cancer cells can serve as an effective platform for studying the dynamic cellular phenotype changes that occur in a heterogeneous environment contributing to chemoresistance. This 3D co-culture system may provide a valuable tool for drug screening to identify targeted therapies for cancer.