In vitro inhibition of tumor growth by low-dose iron oxide nanoparticles activating macrophages

Macrophages as immunocyte are attracting more and more attention in cancer therapy. Our previous study observed that dimercaptosuccinic acid (DMSA)-coated Fe₃O₄ magnetic nanoparticles triggered comprehensive immune responses of mouse macrophages (RAW264.7 cells) and induced production of many kinds of cytokines. This study investigated the effects of Fe₃O₄ magnetic nanoparticles on RAW264.7 cells proliferation, migration, and inhibition of tumor growth in vitro. Fe₃O₄ magnetic nanoparticles had an average size of about 11 nm with good dispersibility and uniformity. Fe₃O₄ magnetic nanoparticles internalized efficiently into RAW264.7 cells. Through Cell Counting Kit-8 (CCK-8) detection, the proliferation of RAW264.7 cells significantly increased by the low-dose Fe₃O₄ magnetic nanoparticles (50 µg/mL) treatment. The results of wound-healing and Transwell assays both displayed a significant promotion of the RAW264.7 cells migratory capability compared with control group ( P<0.01). It is interesting to find that a large number of proliferated RAW264.7 cells were activated to surround quickly and attack mouse liver cancer cell (Hepa1-6) cells by Fe₃O₄ magnetic nanoparticles. The growth of Hepa1-6 cells was effectively inhibited according to microscope imaging and flow cytometry analysis. The inhibition may be cooperative effects of RAW264.7 cells proliferation, migration, and immune activation. The results suggest potential clinical value of low-dose iron oxide nanomaterials in cancer therapy.