Magnetically-Induced Brownian Motion of Iron Oxide Nanocages in Cells and Their Application for Efficient siRNA Delivery

While nanoparticle carriers have been used widely to deliver therapeutic RNAs for gene therapy, overcoming endosomal escape to enhance transfection efficiency remains a major challenge. Most RNA carriers are trapped in endosomes, fused with lysosomes, and degraded before they can be released into the cytoplasm, which is the major reason of low transfection efficiency.<br/>Lipids have been the golden standard for transfection reagents, and it has been reported that lipid nanoparticles could alter intracellular transport along cytoskeleton and avoid lysosomal degradation due to their random Brownian movement. Thus, we developed the concept that efficient endosomal escape of nanoparticle carriers and the improvement of efficiency of therapeutic reagent delivery could be achieved if their Brownian motion and diffusion could be externally optimized to release them to cytoplasm.<br/>Superparamagnetic iron oxide nanoparticles (SPIONs) can undergo two types of magnetic relaxations in alternating magnetic fields (AMFs). At a certain range of frequencies of AMFs along with specific sizes of SPIONs, the phase difference of the oscillating magnetic moment with respect to the field direction of AMF can be dissipated by either Néel relaxation or Brownian relaxation. Here, we investigated whether superparamagnetic cage-shaped iron oxide nanoparticles (IO-nanocages), previously demonstrated to carry payloads inside the cavity for therapeutic molecular delivery, can be controlled to undergo magnetically-induced Brownian motion, dependent on size at the conventional AMF frequency of 335 kHz. The combination of SQUID (superconducting quantum interference device) measurement and computational simulation of the magnetic relaxation time for superparamagnetic IO-nanocages reveals their size-sensitivity to these two relaxation modes.<br/>The motivation for this application is to trigger endosomal escape by externally-driven Brownian motion of nanoparticles and deliver siRNAs to cytoplasm efficiently. Superconducting quantum interference device (SQUID) measurements reveal the size-sensitivity of Brownian relaxation, and magnetically-driven Brownian motion of IO-nanocages improved siRNA delivery efficiency in cells by reducing luciferase expression to 51% while endosomal membranes were observed to be compromised to release IO-nanocages to cytoplasm in the presence of AMF. This magnetic delivery system was also applied to deliver anti-cancer therapeutic siRNAs, silencing mGluR5 expression in human and mouse osteosarcoma cell lines, and the proliferation of both human and mouse osteosarcoma cells decreased significantly to 20% with the silencing efficiency via magnetic delivery of IO-nanocages. This outcome suggests that this magnetic delivery method can be further used in future clinical applications in cancer therapy, and we are also exploring the applications of IO-nanocages to intracellular mechano-responsive applications such as mechanotransduction with magnetic fields.