Resiquimod-loaded magnetic nanoparticles reprogram macrophages and induce oxidative cytotoxicity against triple-negative breast cancer cells.

The development of alternative cancer therapies remains a critical priority to overcome the significant adverse effects associated with conventional chemotherapy. Accordingly, innovative strategies are required to mitigate chemotherapy-induced toxicity. Among these, reprogramming the immunosuppressive tumor microenvironment into an immunostimulatory state has emerged as a promising approach; however, single-modality approaches often underperform. In this work, we engineered resiquimod (R848)-loaded carboxymethyl dextran-coated magnetic nanoparticles (MD-R848) to repolarize M2 macrophages toward an M1 phenotype and to exert direct cytotoxicity against triple-negative breast cancer cells. Nanoparticle physicochemical properties were characterized by dynamic light scattering, X-ray powder diffraction, Fourier-transform infrared spectroscopy, ultraviolet-visible spectrophotometry, and inductively coupled plasma optical emission spectrometry. MD-R848 increased the expression of the M1 surface marker CD80 and reduced the expression of the M2 marker CD206 in macrophages, as determined by flow cytometry. This phenotypic shift was accompanied by increased secretion of the proinflammatory cytokines TNF-α and IL-6, together with upregulation of TNF and IL6 gene expression, supporting M1-like macrophage polarization. MD-R848 also decreased viability of MDA-MB-231 triple-negative breast cancer cells, likely via oxidative stress, as reactive oxygen species and malondialdehyde, a lipid peroxidation marker, increased by 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) fluorescence and lipid peroxidation assays. The elevated reactive oxygen species and malondialdehyde were attributable to the magnetic nanoparticle core. In a transwell co-culture, macrophage reprogramming combined with direct tumor cytotoxicity synergistically intensified cancer cell death. Thus, MD-R848 represents a dual-function nanoplatform that couples immunomodulation with oxidative cytotoxicity, providing a mechanistic basis for improved therapeutic outcomes in cancer treatment.