Adaptations of nanoscale viruses and other protein cages for medical applications

Nanosized materials (5-100 nm) with multiple functionalities (cell targeting, drug delivery, and bio-imaging) have emerged over the recent years as promising therapeutic agents. Liposomal carriers, amphiphilic co-polymers, silica-based particles, colloidal systems, and dendrimer clusters are among the many available nanoscale scaffolds that have been explored for medical applications such as gene delivery, bio-imaging, and drug delivery. On the other hand, viruses, ferritin, and other protein cages for ages have self-organized in the nanometer range with biologically relevant functionalities. These bio-inspired systems form monodispersed units that are highly amendable through genetic and chemical modifications. In this review the expansion of these protein-based nanosystems, termed bionanoparticles (BNPs), beyond their native functionalities, and their application as building materials for nanomedicine will be discussed. The recent developments of biology-inspired systems with potential medical applications will be outlined, with particular emphasis on adaptations of protein-based nanostructures for gene delivery, bio-imaging, drug encapsulation, and vaccine development. Notable systems already streamlined for medical applications are recombinant virus-like particles derived from human papillomaviruses as multivalent vaccine carriers to immunize patients against genital infections, and vaccinia viruses to treat patients with established cancers.