Engineering protein cage nanoparticles as tunable multifunctional nanoplatforms

Abstract

Protein cage nanoparticles are biomolecule-based supramolecular biopolymers and attractive candidates for nano-scale cargo delivery vehicles. While the interior surfaces of the protein cages have been used for encapsulation, attachment and synthesis of organic and inorganic materials, their exterior surfaces have been used for multivalent presentations of molecules, including affinity tags, antibodies, fluorophores, carbohydrates, nucleic acids, and peptides, for molecular targeting and hierarchical structure formation. Using these natural properties, we utilized protein cage nanoparticles as virus-mimic antigen-delivery nanoplatforms and evaluated their efficacy in inducing DC-mediated antigen-specific immune responses and subsequent melanoma tumor rejection in vivo. We also implemented them as intravascular magnetic resonance T contrast conjugates via site-selective attachment of Gd(III)-chelating agents and used them for in vivo MR imaging visualizing a mouse’s intravascular system, including the carotid, mammary arteries, and the superficial vessels of the head at an isotropic resolution of 250 μm. Targeted drug and/or probe delivery using nanoparticles can achieve the localized and enhanced treatment of diseases, minimizing side-effects, and target-specific diagnosis of symptoms even at early stage. A wide range of target-specific ligands, including antibodies, peptides, and affibody molecules, have been used. Affibody molecules, however, are genetically engineered antibody mimics that exhibit high specificity and affinity toward their targets and prove the potential for diagnostic applications in biotechnology and therapeutic developments in biomedicine. By applying a recently developed bacterial superglue, SpyTag/SpyCatcher (ST/SC) protein ligation system to affibody molecules and protein cage nanoparticles, multiple displays of two or more targeting ligands on a polyvalent single nanoparticle were achieved.