Polymerization of small interfering RNA (siRNA) has been demonstrated as a promising strategy to improve siRNA delivery, which will change the low-charge and rigid properties of single siRNA and enhance its electrostatic interactions with cationic polymers. For such polymerization strategy, a major breakthrough is still needed to fully eliminate chemical processes and further improve the nanocomplex-forming ability of polymerized siRNAs. Herein, the extremely strong interaction between the DNA product of rolling circle amplification (RCA) and linear poly(ether imide) (PEI) has been disclosed; accordingly, a stable nanocomplex is formed just at its charge neutralization point, which benefits from the high molecular weight of the RCA product (>3 000 000 Da). In addition, as the sequence of the RCA product is determined by the cyclic template, the programmable nature of DNA can simplify the optimization process and maximize the hybridization efficiency between RCA and sticky siRNAs, realizing a superior siRNA polymerization efficiency. Depending on these two effects, the RCA DNA is utilized as a cocarrier material to organize siRNA polymerization and substantially reduce the usage amount of PEI, which greatly improves RNAi efficiency of PEI/RCA-siRNA polyplex both in vitro and in vivo, providing evidence that RCA DNA is a promising material to promote the RNAi-based therapeutics.
Keywords: DNA nanotechnology; RNAi; hydrophobic interaction; rolling circle amplification; siRNA delivery.