Abstract
Macrophages are the primary cells responsible for nanoparticle processing and mediating host immunological biological outcomes. Their cellular response to nanoparticles is a vital constituent in the safety assessment of new designs for clinical application. An approach for the treatment of solid tumors was developed, based on magnetic hyperthermia, consisting of iron oxide multicore encapsulated nanoparticles named Sarah nanoparticles (SaNPs), and alternating magnetic field irradiation. SaNPs are intravenously injected, accumulate in the liver, spleen and in tumor tissue, where they are passively targeted to malignant cells via the Enhanced Permeability and Retention (EPR) effect and undergo selective heating. SaNP-induced responses after cellular uptake were investigated in murine RAW264.7 macrophages using a wide imaging approach. When activated, macrophages form different phenotypic populations with unique immune functions, however the mechanism/s by which these activated macrophages respond to nanoparticles is unclear. Unraveling these responses is important for the understanding of nanoparticle uptake, potential degradation, and clearance to address both toxicity and regulatory concerns, which was the aim of this study. The results demonstrated that SaNPs undergo internalization, localize within the lysosomal compartment while keeping their integrity, without intracellular toxic degradation, and are cleared with time. The production of tumor necrosis factor alpha (TNF-α) and reactive oxygen species (ROS), superoxide dismutase (SOD) activation, and cytokine secretion in macrophage conditioned medium (CM) were also evaluated. SaNPs effects were both time- and dose- dependent. High SaNP concentrations resulted in reduced RAW264.7 cell viability which correlated with SOD activation and was associated with ROS generation. Lower SaNP concentrations stimulated the time-dependent production of TNF-α. The expression of additional cytokines was also induced, potentially affecting cancer cell growth by CM from SaNP-activated macrophages supporting a potential antitumor effect. These results will help understand the fate of nanoparticles in vivo.