Ferritin-based nanoprobes: promising materials for tumor imaging
High sensitivity and specificity imaging of tumors is critical for early tumor detection, effective treatment and prognosis. However, this is challenging owing to the nature of tumors emerging from normal tissues, along with aging and their high degree of complexity. Recent rapid development of functional nanomaterials offers new opportunities for tumor imaging with enhanced capacities for tumor targeting and high sensitivity [1]. In addition to the beneficial properties for tumor imaging, these chemically engineered nanomaterials usually introduced new concerns, such as potential nanotoxicity, lack of biocompatibility and difficulty for integrated functionality [2,3].
One efficient solution to these issues is to make use of the knowledge gained from nanotoxicity studies and to synthesize safer biomedical nanoparticles by design. To this end, the chemical modification of the nanosurface of medical nanoparticles is often applied. In contrast with this common chemical modification strategy, natural protein assemblies, such as ferritins, have been used for the synthesis of hybrid nanomaterials. These protein complexes are archetypical self-assembled nanostructures with superior properties, such as rich biological functions, biocompatibility, feasibility for biofunctionalization and low or no toxicity [4,5]. Therefore, these protein assemblies, functionalized with various additional biological activities, are ideal for various biomedical applications, including tumor imaging. Ferritins are composed of 12 or 24 subunits folded into a stable protein complex 12–13 nm in diameter and naturally occur in both intracellular and secreted forms, mainly for iron ion storage and reuse for metabolic needs [4]. As natural occurring nanomaterials, these proteins offer three interfaces, namely internal, external and interfacial interfaces for genetic and chemical modifications. Such engineered functional ferritins have been used for tumor fluorescence imaging, PET, MRI and tumor microenvironment responsive imaging [5].
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