Protein-based nanomedicine platforms for drug delivery comprise naturally self-assembled protein subunits of the same protein or a combination of proteins making up a complete system. They are ideal for drug-delivery platforms due to their biocompatibility and biodegradability coupled with low toxicity. A variety of proteins have been used and characterized for drug-delivery systems, including the ferritin/apoferritin protein cage, plant-derived viral capsids, the small Heat shock protein (sHsp) cage, albumin, soy and whey protein, collagen, and gelatin. There are many different types and shapes that have been prepared to deliver drug molecules using protein-based platforms, including various protein cages, microspheres, nanoparticles, hydrogels, films, minirods, and minipellets. The protein cage is the most newly developed biomaterial for drug delivery and therapeutic applications. The uniform size, multifunctionality, and biodegradability push it to the frontier of drug delivery. In this Review, the recent strategic development of drug delivery is discussed with emphasis on polymer-based, especially protein-based, nanomedicine platforms for drug delivery. The advantages and disadvantages are also discussed for each type of protein-based drug-delivery system.

This paper describes the preparation and optimization of the analytical properties of the protein based drug delivery platform apoferritin. In biological systems, the protein cage ferritin is used to store iron and to keep it from building to toxic levels in cells. When the iron atoms are removed from ferritin, apoferritin is formed. In this study, daunomycin, an anthracycline antibiotic drug that has been used for specific types of cancer treatment such as acute myeloid leukemia and acute lymphocytic leukemia, was encapsulated within the protein cage for drug delivery. Daunomycin slows or stops the growth of cancer cells by binding with the cell's DNA. The model for daunomycin-DNA complex binding mechanism is intercalation, where daunomycin binds with approximately every 3 base pairs causing a local unwinding, but a negligible distortion of the helical conformation. The binding affinity for free DNA is higher than that of structured DNA in cells. Upon binding with DNA the fluorescence intensity of daunomycin decreases. We used apoferritin's ability to disassemble and reassemble under pH control to load the therapeutic compound daunomycin. The combination of a modifiable interior and exterior surface and the passable hydrophobic and hydrophilic channels through the cage allows the containment or attachment of both insoluble and soluble drugs for delivery. At experimental pH 5 conditions the interaction between the apoferritin interior cage and daunomycin is weak making it difficult to encapsulate the drug effectively within the protein cage. The incorporation of poly-Laspartic acid (PLAA), a polypeptide and biodegradable material that does not increase the toxicity of the drug delivery system and is negatively charged at pH 5.0, into the drug delivery system resulted in a substantial improvement in the drug encapsulation. The binding properties of free daunomycin with DNA were compared to the newly synthesized apoferritin protein based drug delivery system. Encapsulation of the daunomycin within the apoferritin protein cage had little effect upon the intrinsic binding constant, K i , or the exclusion parameter n as compared to the free daunomycin model. The study resulted in the design and optimization of a unique protein based drug delivery platform using the protein cage apoferritin for potential therapeutic administration of the anti-cancer agent daunomycin.

A novel DNA detection platform based on a hairpin DNA switch, nanoparticles, and enzyme signal amplification for ultrasensitive detection of DNA hybridization has been developed in this work. In this DNA assay, a "stem-loop" DNA probe dually labeled with a thiol at its 5' end and a biotin at its 3' end, respectively, was used. This probe was immobilized on the gold nanoparticles (AuNPs) anchored by a protein, gamma-globulin, on a 96-well microplate. In the absence of target DNA, the immobilized probe with the stem-loop structure shields the biotin from being approached by a bulky horseradish peroxidase linked streptavidin (streptavidin-HRP) conjugate due to the steric hindrance. However, in the presence of target DNA, the hybridization between the hairpin DNA probe and the target DNA causes significant conformational change of the probe, which forces biotin away from the surface of AuNPs. As a result, the biotin becomes accessible by the streptavidin-HRP, and the target hybridization event can be sensitively detected via the HRP catalyzed substrate 3,3',5,5'-tetramethylbenzidine using a spectrophometric method. Some experimental parameters governing the performance of the assay have been optimized. At optimal conditions, this DNA assay can detect DNA at the concentration of femtomolar level by means of a signal amplification strategy based on the combination of enzymes and nanoparticles. This approach also has shown excellent specificity to distinguish single-base mismatches of DNA targets because of the intrinsic high selectivity of the hairpin DNA probe.