With a plethora of advances in nanotechnology and biotechnology, the development of natural particle-based drug delivery vectors is a rapidly emerging field; these vectors are highly optimized for specific functions in vivo, have features typically required of drug delivery vectors, and even possess more efficient drug delivery mechanisms compared to synthetic vectors, such as selective targeting and extended circulation time. Virus-like particles (VLPs) are virus-derived nanoparticles composed of one or more different protein subunits in a highly precise manner with the ability to self-assemble, mimicking the structure and size of viral particles, but unable to infect host cells due to the lack of authentic viral genetic material. The production of viral structural proteins can be performed in a variety of expression systems, and the expressed proteins can spontaneously assemble into internal hollow nanoparticles. As an attractive technology platform for therapeutic agents and antigen epitope delivery, VLPs have made significant contributions to the development of nanomedicine. Due to the fact that viruses are powerful natural vectors for the delivery of genetic material to host cells, VLPs are able to replicate these viral delivery processes and particularly suitable for drug delivery applications. Effective drug delivery depends on several key factors, including specific targeting, effective cellular uptake, in vivo release kinetics, and systemic clearance, to which VLPs are well suited to meet. Moreover, VLPs have many desirable drug delivery characteristics, such as ideal particle size for cellular phagocytosis, nontoxic biodegradability, and the ability to be functionalized at three different interfaces (external, internal, and intersubunit of the protein particle) through genetic engineering, chemical modification, biomineralization, and introduction of non-natural amino acids.In this Account, we systematically highlight our efforts in the rational design of VLPs and their applications in nanomedicine. First, we present the biophysical characteristics of the most widely studied hepatitis B core protein (HBc) VLPs and discuss their structural features with their advantages as a nanodelivery platform. Second, we highlight the design strategies and progress of VLPs for targeted drug delivery. By simulating the ligand receptor-specific interactions of viruses with their host cells, we have constructed a series of bioengineered VLPs that can target focal cells by displaying targeting ligands on the surface, from a disease perspective such as tumors, organ fibrosis, and brain diseases. The therapeutic agents can be effectively loaded through the process of particle self-assembly/reassembly and intermolecular interactions. These VLPs can target delivery cargoes to target cells or tissues to achieve precision therapy. Third, because viruses are powerful immune stimulators, VLPs are particularly suitable for antigen delivery purposes. By presenting tumor antigens at high density in the main immunogenic region of VLPs, we have developed VLPs for immunotherapy of tumors. In addition, VLPs loaded with adjuvants can effectively modulate the tumor immune microenvironment; in combination with chemotherapy or immunomodulatory drugs, the VLPs can effectively enhance tumor immunotherapy. Finally, we summarize the current status, basic understanding, future directions, and challenges for functionalization strategies of VLPs and their biomedical applications.
