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 a 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 a high load of ∼15,500 siRNA
molecules/nanoparticle. After efficient internalization into the tumor
cell, an 80% knockdown of the luciferase reporter gene was achieved.
Auropolyplexes were applied intratracheally in Balb/c mice for pulmonary
delivery, and their biodistribution were studied spatio-temporally
and quantitatively by optical tomography. Auropolyplexes were well
tolerated with ∼25% of the siRNA dose remaining in the lungs
after 24 h. 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 a combination of successful endosomal escape and better biocompatibility
profile
in vivo
. Taken together, combined chemisorption
and complexation endow auropolyplexes with crucial biophysical attributes,
enabling a versatile and upscalable nanogold-based platform for siRNA
delivery
in vitro
and
in vivo
.