M1- and M2-Polarized Macrophages Modified Inflammatory Environment and Affects Malignant Behaviors of Cancer Stem-like Cells (CSCs) Derived from Human Melanoma Cells A375

Tumors contain a sub-population of cells characterized by self-renewal and expanding capacities which were known as cancer stem-like cells (CSCs). Sphere formation in conditioned serum-free medium supplemented with epidermal growth factor and basic fibroblast growth factor is a well-accepted manner for enriching CSCs from several kinds of tumor cells, including melanoma cells A375. The effects of polarized macrophages on malignant behaviors of melanoma cells were well studied, however, little was known about the effects of inflammatory environment modified by polarized macrophages on melanoma CSCs. In this study, tied to figure out these effects, we firstly stimulated the polarization of M1- and M2-state macrophages and confirmed the successful stimulation via detecting hallmarkers. Then the successful enrichment of A375 CSCs was confirmed by performing self-renewal capacity. Via detecting the malignant behaviors, it is observed that inflammatory environment modified by M1-polarized macrophages inhibited proliferation, blocked cell cycle phases at G1/G0, decreased invasive, tumor formatting abilities and induced cisplatin-sensitivity by promoting apoptosis. Contrarily, M2-conditioned medium desensitized A375 CSCs to cisplatin without affecting other malignant behaviors including proliferation, cell cycle, invasion and tumor formation. Meanwhile, M2- conditioned medium protected stemness of CSCs under oxidative stress. How the modified inflammatory microenvironment affects CSCs was performed by adding macrophage-specific cytokines and the results indicate that M1-polarized and M2-polarized macrophages partially affected CSCs via increased secretion of cytokines, including IL-1β, TNF-α and TGF-β. Taken together, we provide evidence that different macrophage polarization affected malignant behaviors of A375 CSCs partially via secretion of cytokines.