Chimeric ferritin nanocages-based imaging probes

Summary form only given. Ferritin is a family of proteins found in different forms in most living organisms. Each ferritin is made up of 24 subunits, which self-assemble to form a cage-like nanostructure, with external and internal diameters of 12 and 8 nm, respectively. This unique architecture provides two interfaces-one outside and one inside-for possible functional loading. These interesting features make ferritin a powerful, capacious nanoplatform with potential in a wide spectrum of applications. In the current study, we evaluated ferritin nanocages as candidate nanoplatforms for multifunctional loading. Ferritin nanocages can be either genetically or chemically modified to impart functionalities to their surfaces, and metal cations can be encapsulated in their interiors by association with metal binding sites. Moreover, different types of ferritin nanocages can be disassembled and reassembled to achieve function hybridization. We were able to use combinations of these unique properties to produce a number of multifunctional ferritin nano structures with precise control of their composition. We then studied these nanoparticles, both in vitro and in vivo, to evaluate their potential suitability as multimodality imaging probes. The results demonstrate promise of ferritin nano structures as prospective nanoplatforms for the era of nanomedicine. In a separate study, we harnessed the disassembly/reassembly nature as the driving force to pack an energy pair into a ferritin nanostructure to arrive at activatable probes. The technique of activatable probes allows the signals to be only amplified at diseased areas upon a designated environment change, a feature which can greatly improve the signal-to-background ratio. Specifically, we coupled Cy5.5-tagged peptide and BHQ-3 (BHQ=black hole quencher), a widely utilized quencher of Cy5.5, onto ferritins to create two sets of protein cages. The core peptide sequence, Pro-Leu-Gly-Val-Arg (PLGVR), has proven selectivity for multiple types of MMPs. We then mixed and broke down both types of proteins to subunits at pH 2 and subsequently tuned the pH back to neutral, which restored the protein nanostructure in a hybrid fashion. The conglomeration of both dyes and quenchers on the protein surface induced a quenched state to the overall nanostructure. Subsequently, when the probes were exposed to an MMP-rich environment, such as in a tumor, the PLGVR substrate would be cut off, thus leading to the release of Cy5.5 and the restoration of fluorescence activity. We then confirmed the feasibility of such probes on a xenograft mouse model. Such a platform can be readily applied to prepare other kinds of probes with different protease sensitivities.