Breast cancer spheroids prefer activated macrophages as an accomplice: An in vitro study

Cancer, a heterogeneous disease in nature, often requires help from diverse pro-tumor or tumor-associated- cells, which are recruited and persevered within the stroma. Pro-tumor stromal cells provide the essential support needed for tumor growth, metastasis, and development of drug resistance in due time. Tumor-associated macrophages, one of such cells, are essential to tumor microenvironment and tumor survival. In recent years, TAMs have been identified as potential drug targets and therapeutic agents, which encourages the in-depth characterization of their crosstalk with the tumors. The current study has successfully developed a cost-effective in vitro platform for Chemokine Assisted Recruitment of Macrophages to spheroids mimicking the physiology of TAM recruitment. Firstly, monocytic cell line (U937) were converted into activated naive macrophages (M0) and pro-and anti-inflammatory (M1 and M2) subtypes. Monocytes, M0, M1, and M2 macrophages are characterized extensively. Secondly, the naive and polarized macrophages were subjected to chemokine-dependent recruitment into monotypic and heterotypic breast cancer spheroids. The nature of the recruitment is further investigated by assessing the profile of chemokines and chemokine receptors. Recruited macrophages are also observed to manipulate spheroid behavior in many ways. The recruited macrophages also exhibit an increased level of Siglec-1 (CD169), one of the potential TAM markers. The current platforms potential for application can be extended to understand the recruitment process of other immune/stromal cells to solid tumors. It could be a potential addition to the arrays of in vitro platforms developed to screen the efficiency of cell-based immunotherapeutics in the future.