Superparamagnetic iron oxide nanoparticles (SPIONs) may act as an excellent theragnostic tool if properly coated and stabilized in a biological environment, even more, if they have targeting properties towards a specific cellular target. Humanized Archaeoglobus fulgidus Ferritin (HumAfFt) is an engineered ferritin characterized by the peculiar salt-triggered assembly-disassembly of the hyperthermophile Archaeoglobus fulgidus ferritin and is successfully endowed with the human H homopolymer recognition sequence by the transferrin receptor (TfR1 or CD71), overexpressed in many cancer cells in response to the increased demand of iron. For this reason, HumAfFt was successfully used in this study as a coating material for 10 nm SPIONs, in order to produce a new magnetic nanocarrier able to discriminate cancer cells from normal cells and maintain the potential theragnostic properties of SPIONs. HumAfFt-SPIONs were exhaustively characterized in terms of size, morphology, composition, and cytotoxicity. The preferential uptake capacity of cancer cells toward HumAfFt-SPIONs was demonstrated in vitro on human breast adenocarcinoma (MCF7) versus normal human dermal fibroblast (NHDF) cell lines.

The present study introduces a novel theranostic nanoparticle platform that integrates superparamagnetic iron oxide nanoparticles (SPIONs) with a ferritin-based protein nanocage derived from the archaeobacterium Archaeoglobus fulgidus. By exploiting the unique salt-triggered dissociation and reassociation mechanism of the nanocage, SPIONs were successfully encapsulated within the protein’s central cavity. The construct thus obtained was characterized by transmission electron microscopy and circular dichroism spectroscopy. The ferritin-coated SPIONs exhibited remarkable superparamagnetic behavior and robust magnetic properties. Characterization using electron paramagnetic resonance and thermal magnetization analysis confirmed the stability of the nanoparticles and their suitability for magnetic hyperthermia applications. Furthermore, T₂-weighted magnetic resonance imaging (MRI) demonstrated enhanced contrast, with ferritin-coated SPIONs generating distinct dark-spot imaging, highlighting their efficacy as a contrast agent for advanced biomedical applications.

Ferritin, a physiological iron-storage protein, has emerged as a highly attractive platform for drug delivery owing to its biocompatibility, structural robustness, and intrinsic ability to encapsulate and protect therapeutic cargo within its hollow nanocage. Building upon previous studies that established the baseline characteristics of engineered ferritin mutants in comparison to the wild-type protein, this work specifically investigates and directly compares the thermal stability profiles of two distinct mutated variants. These variants of human H-chain ferritin, obtained through targeted site-directed mutagenesis, feature either four or six tryptophan residues per subunit, strategically positioned toward the inner cavity of the protein shell. These modifications were intended to enhance hydrophobic interactions with guest molecules while preserving the native quaternary architecture. Temperature-dependent changes in surface hydrophobicity and solvent accessibility were probed using the environment-sensitive fluorescent dye ANS, enabling a comparative assessment of the conformational behavior of the two mutants. Overall, this study highlights how targeted modulation of the internal cavity composition of ferritin can tune both its physicochemical properties and stability, providing insights relevant for the rational design of ferritin-based nanoplatforms for biomedical applications.