Bioactive Molecules Delivery through Ferritin Nanoparticles: Sum Up of Current Loading Methods.

Ferritin (Ft) is a protein with a peculiar three-dimensional architecture. It is characterized by a hollow cage structure and is responsible for iron storage and detoxification in almost all living organisms. It has attracted the interest of the scientific community thanks to its appealing features, such as its nano size, thermal and pH stability, ease of functionalization, and low cost for large-scale production. Together with high storage capacity, these properties qualify Ft as a promising nanocarrier for the development of delivery systems for numerous types of biologically active molecules. In this paper, we introduce the basic structural and functional aspects of the protein, and summarize the methods employed to load bioactive molecules within the ferritin nanocage.

Human ferritin nanocarriers for drug-delivery: A molecular view of the disassembly process.

Ferritins are natural proteins which spontaneously self-assemble forming hollow nanocages physiologically deputed to iron storage and homeostasis. Thanks to their high stability and easy production in vitro, ferritins represent an intriguing system for nanobiotechnology. Here we investigated the mechanism of disassembly and reassembly of a human recombinant ferritin constituted by the heavy chain (hHFt) exploiting a new procedure which involves the use of minimal amounts of sodium dodecyl sulfate (SDS) and assessed its effectiveness in comparison with two commonly used protocols based on pH shift at highly acidic and alkaline values. The interest in this ferritin as drug nanocarrier is related to the strong affinity of the human H-chain for the transferrin receptor TfR-1, overexpressed in several tumoral cell lines. Using different techniques, like NMR, TEM and DLS, we demonstrated that the small concentrations of SDS can eliminate the nanocage architecture without detaching the monomers from each other, which instead remain strongly associated. Following this procedure, we encapsulated into the nanocage a small ruthenium complex with a remarkable improvement with respect to previous protocols in terms of yield, structural integrity of the recovered protein and encapsulation efficiency. In our opinion, the extensive network of interchain interactions preserved during the SDS-based disassembly procedure represents the key for a complete and correct hHFt reassembly.

Structural insights and aggregation propensity of a super-stable monellin mutant: A new potential building block for protein-based nanostructured materials.

Protein fibrillation is commonly associated with pathologic amyloidosis. However, under appropriate conditions several proteins form fibrillar structures in vitro that can be used for biotechnological applications. MNEI and its variants, firstly designed as single chain derivatives of the sweet protein monellin, are also useful models for protein fibrillary aggregation studies. In this work, we have drawn attention to a protein dubbed Mut9, already characterized as a "super stable" MNEI variant. Comparative analysis of the respective X-ray structures revealed how the substitutions present in Mut9 eliminate several unfavorable interactions and stabilize the global structure. Molecular dynamic predictions confirmed the presence of a hydrogen-bonds network in Mut9 which increases its stability, especially at neutral pH. Thioflavin-T (ThT) binding assays and Fourier transform infrared (FTIR) spectroscopy indicated that the aggregation process occurs both at acidic and neutral pH, with and without addition of NaCl, even if with a different kinetics. Accordingly, Transmission Electron Microscopy (TEM) showed a fibrillar organization of the aggregates in all the tested conditions, albeit with some differences in the quantity and in the morphology of the fibrils. Our data underline the great potential of Mut9, which combines great stability in solution with the versatile conversion into nanostructured biomaterials.

Release of a novel peptide from ferritin nanocages: A new tool for therapeutic applications.

The development of new drug delivery systems for targeted chemotherapy release in cancer cells represents a very promising tool. In this contest, protein-based nanocages have considerable potential as drug delivery devices. Notably, ferritin has emerged as an excellent candidate due to its unique architecture, surface properties and high biocompatibility. A promising strategy might then involve ferritin cargos for specifical release of AntiMicrobial Peptides endowed with anticancer activity to cancer cells. In this paper, we encapsulated the TRIL analogue of Temporin-L peptide within a ferritin nanocage and evaluated the cargo biological properties. The results demonstrated a reduced haemolytic activity of the peptide and a selective cytotoxicity activity on cancer cells likely mediated by oxidative stress while having no effects on non-tumoral cells. The combination of the properties of ferritin with TRIL, might open up the way to the development of novel peptide delivery systems for future pharmaceutical applications.

A new and efficient procedure to load bioactive molecules within the human heavy-chain ferritin nanocage.

For their easy and high-yield recombinant production, their high stability in a wide range of physico-chemical conditions and their characteristic hollow structure, ferritins (Fts) are considered useful scaffolds to encapsulate bioactive molecules. Notably, for the absence of immunogenicity and the selective interaction with tumor cells, the nanocages constituted by the heavy chain of the human variant of ferritin (hHFt) are optimal candidates for the delivery of anti-cancer drugs. hHFt nanocages can be disassembled and reassembled in vitro to allow the loading of cargo molecules, however the currently available protocols present some relevant drawbacks. Indeed, protein disassembly is achieved by exposure to extreme pH (either acidic or alkaline), followed by incubation at neutral pH to allow reassembly, but the final protein recovery and homogeneity are not satisfactory. Moreover, the exposure to extreme pH may affect the structure of the molecule to be loaded. In this paper, we report an alternative, efficient and reproducible procedure to reversibly disassemble hHFt under mild pH conditions. We demonstrate that a small amount of sodium dodecyl sulfate (SDS) is sufficient to disassemble the nanocage, which quantitatively reassembles upon SDS removal. Electron microscopy and X-ray crystallography show that the reassembled protein is identical to the untreated one. The newly developed procedure was used to encapsulate two small molecules. When compared to the existing disassembly/reassembly procedures, our approach can be applied in a wide range of pH values and temperatures, is compatible with a larger number of cargos and allows a higher protein recovery.

Evaluation of Auranofin Loading within Ferritin Nanocages.

Auranofin (AF), a gold(I) compound that is currently used for the treatment of rheumatoid arthritis and is in clinical trials for its promising anticancer activity, was encapsulated within the human H-chain and the horse spleen ferritin nanocages using the alkaline disassembly/reassembly protocol. The aim of the work was to highlight possible differences in their drug loading capacity and efficacy. The drug-loaded ferritins were characterized via UV-vis absorption spectroscopy and inductively coupled plasma-atomic emission spectroscopy to assess AF encapsulation and to define the exact amount of gold atoms trapped in the Ft cavity. The crystal structures allowed us to define the nature of AF interaction with both ferritins and to identify the gold binding sites. Moreover, the biological characterization let us to obtain preliminary information on the cytotoxic effect of AF when bound to the human H-chain.

X-ray structure of C-phycocyanin from Galdieria phlegrea: Determinants of thermostability and comparison with a C-phycocyanin in the entire phycobilisome.

Galdieria phlegrea is a polyextremophilic red alga belonging to Cyanidiophyceae. Galdieria phlegrea C-phycocyanin (GpPC), an abundant light-harvesting pigment with an important role in energy capture and transfer to photosystems, is the C-phycocyanin (C-PC) with the highest thermal stability described so far. GpPC also presents interesting antioxidant and anticancer activities. The X-ray structure of the protein was here solved. GpPC is a [(αß)3]2 hexamer, with the phycocyanobilin chromophore attached to Cys84α, Cys82ß and Cys153ß. Details of geometry and interaction with solvent of the chromophores are reported. Comparison with the structure of a C-PC in the entire Porphyridium purpureum phycobilisome system reveals that linker polypeptides have a significant effect on the local structure of the chromophores environment. Comparative analyses with the structures of other purified C-PCs, which were carried out including re-refined models of G. sulphuraria C-PC, reveal that GpPC presents a significantly higher number of inter-trimer salt bridges. Notably, the higher number of salt bridges at the (αß)3/(αß)3 interface is not due to an increased number of charged residues in this region, but to subtle conformational variations of their side chains, which are the result of mutations of close polar and non-polar residues.

Pt(II) versus Pt(IV) in Carbene Glycoconjugate Antitumor Agents: Minimal Structural Variations and Great Performance Changes.

Octahedral Pt(IV) complexes (2Pt-R) containing a glycoconjugate carbene ligand were prepared and fully characterized. These complexes are structural analogues to the trigonal bipyramidal Pt(II) species (1Pt-R) recently described. Thus, an unprecedented direct comparison between the biological properties of Pt compounds with different oxidation states and almost indistinguishable structural features was performed. The stability profile of the novel Pt(IV) compounds in reference solvents was determined and compared to that of the analogous Pt(II) complexes. The uptake and antiproliferative activities of 2Pt-R and 1Pt-R were evaluated on the same panel of cell lines. DNA and protein binding properties were assessed using human serum albumin, the model protein hen egg white lysozyme, and double stranded DNA model systems by a variety of experimental techniques, including UV-vis absorption spectroscopy, fluorescence, circular dichroism, and electrospray ionization mass spectrometry. Although the compounds present similar structures, their in-solution stability, cellular uptake, and DNA binding properties are diverse. These differences may represent the basis of their different cytotoxicity and biological activity.