Biocompatibility and Antitumor Effects of Magnetically Targeted L‑Cysteine-Functionalized Superparamagnetic Iron...

Superparamagnetic iron oxide nanoparticles (SPIONs-Fe₃O₄) functionalized with l-cysteine (SPIONs-l-Cys) were evaluated as a biocompatible, magnetically responsive nanosystem in an Ehrlich solid tumor model. The formulation was obtained by chemical coprecipitation, and its complementary physicochemical characterization is provided in the Supporting Information and supported by our previous report on the same l-cysteine-functionalized magnetite system, including X-ray diffraction, FTIR, hydrodynamic size, polydispersity index, ζ-potential, surface thiol quantification by DTNB, magnetic measurements, and complementary in vitro data. The supplementary characterization supports the preservation of the magnetite crystalline structure after functionalization and confirms the presence of free thiol groups in an aqueous dispersion. In vitro cytotoxicity assays using human mononuclear cells and Ehrlich tumor cells indicated low toxicity under selected experimental conditions and biologically relevant redox-associated activities. In vivo evaluation demonstrated preserved hematological and biochemical parameters, the absence of overt systemic toxicity, and reduced tumor burden in groups treated with SPIONs-l-Cys under magnetic targeting conditions. These findings support the biological compatibility of SPIONs-l-Cys and indicate antitumor-associated effects under localized magnetic field conditions, while not establishing intratumoral accumulation, drug delivery, or a definitive mechanism of action.