Nanoparticle-Virus Chimeras as a Novel Strategy for Nanoparticle Delivery

The systemic delivery of nanoparticles (NPs) has garnered significant attention from researchers due to its clinical promise. Various strategies have been developed thus far, including the utilization of the enhanced permeability and retention (EPR) effect to target tumors or the modification of NPs with antibodies to target specific proteins. However, delivering NPs to the brain through the blood-brain barrier (BBB) remains a challenge. Additionally, the importance of the communication between the central nervous system (CNS) and the peripheral nervous system (PNS) has been increasingly recognized, leading to a high demand for delivery systems that can flexibly change their target between the CNS and PNS. Translation of delivery strategies between species offers another challenge, especially in the context of bridging the divide between fundamental research in rodents and clinical research in larger models such as non-human primates (NHPs). Therefore, there is a pressing need for a novel strategy for systemic delivery of nanomaterials that is both translational and capable of flexibly selecting targets.<br/><br/>For decades the field of gene therapy has applied engineered viruses to deliver therapeutic transgenes to particular organs or cells of interest. Adeno-associated viruses (AAVs) are the most ubiquitous gene-therapy tools, particularly in neuroscience, owing to their advantageous characteristics: AAVs are non-pathogenic, easily reproducible, and have numerous accessible serotypes, each with distinct tropism. State-of-the-art serotypes, such as AAV.CAP-B10 and AAV.MaCPNS2, have demonstrated the ability to deliver genes to the brain or PNS in mice following intravenous (IV) injection, while simultaneously suppressing gene expression in the liver. These serotypes have also shown promise for gene delivery in NHPs.<br/><br/>In this study, we hypothesized that AAVs could be employed to guide magnetic nanoparticles (MNPs) to particular organs through IV injection. This approach allows for easy modification of the target by swapping AAV serotypes, for instance, from the brain to the PNS. Furthermore, the target species can also be altered based on the serotypes of AAVs. This concept, termed viral guidance of MNPs, has the potential to serve as a versatile targeting strategy.<br/><br/>We covalently conjugated MNPs and AAVs (MNP-AAV chimeras) through click chemistry. The structure of these chimeras was controlled by adjusting the reaction conditions. In vitro tests were conducted to investigate the efficiency of AAVs in guiding MNPs using MNP-AAV chimeras formed from several different serotypes. As a result, MNP-AAV chimeras retained the tropism of original AAV serotype used, indicating that the delivery target is serotype-dependent and can be easily modified by changing the AAV serotype used for conjugation.<br/><br/>We also investigated an opposite application of MNP-AAV chimeras, namely, the magnetic guidance of AAVs. Since AAVs were conjugated to MNPs, we could manipulate the chimeras using an external magnetic field to exert a magnetic force on the MNPs. HEK293 cells were incubated with MNP-AAV chimeras in a presence of a magnetic field. Following a 24-hour incubation period, the HEK cells expressed high levels of fluorescent protein, which was encoded by the AAVs in the chimeras, near the center of the magnetic field. This result suggests that magnetic guidance of AAVs is feasible, and that AAVs in chimera form (conjugated to MNPs) are capable of transducing cells. The specificity of gene delivery targeting with AAV was previously determined by a combination of two factors: serotype (capsid) and regulatory elements (promoter, enhancer, Cre-lox system, etc.). Now, our chimeras enable spatial restriction of transduction, which adds another layer of control to gene delivery. To the best of our knowledge, this is the first report of magnetically controlled transduction with AAVs.