Combined chemisorption and complexation generates siRNA nanocarriers with biophysics optimized for efficient gene-knockdown and air-blood barrier crossing.

Current nucleic acid (NA) nanotherapeutic approaches face challenges because of shortcomings such as limited control on loading-efficiency, complex formulation procedure involving purification steps, low load of NA cargo per nanoparticle, endosomal-trapping and hampered release inside the cell. When combined, these factors significantly limit the amount of biologically active NA delivered per cell in vitro, delivered dosages in vivo for prolonged biological effect, and the upscalability potential, thereby warranting early consideration in the design and developmental phase. Here we report a versatile nanotherapeutic platform, termed auropolyplexes, for improved and efficient delivery of small interfering RNA (siRNA). Semitelechelic, thiolated linear polyethylenimine (PEI) was chemisorbed onto gold nanoparticles to endow them with positive charge. A simple two-step complexation method offers tunable loading of siRNA at concentrations relevant for in vivo studies and the flexibility for inclusion of multiple functionalities, without any purification steps. SiRNA was electrostatically complexed with these cationic gold nanoparticles and further condensed with polycation or polyethyleneglycol-polycation conjugates. The resulting auropolyplexes ensured complete complexation of siRNA into nanoparticles with high load of approx. 15,500 siRNA molecules/ nanoparticle. After efficient internalization into tumor cell, 80% knockdown of luciferase reporter gene was achieved. Auropolyplexes were applied intratracheally in Balb/c mice for pulmonary delivery and their biodistribution studied spatiotemporally and quantitatively by optical tomography. Auropolyplexes were well tolerated with ~25% of the siRNA dose remaining in lungs after 24h. Importantly, siRNA was released from auropolyplexes in vivo and a fraction also crossed the air-blood barrier, which was then excreted via kidneys, whereas >97% of gold nanoparticles were retained in the lung. Linear-PEI based auropolyplexes offer combination of successful endosomal escape and better biocompatibility profile in vivo. Taken together, combined chemisorption and complexation endows auropolyplexes with crucial biophysical attributes enabling a versatile and upscalable nanogold based platform for siRNA delivery in vitro and in vivo.