Supramolecular Self‐Assembly of Histidine‐Capped‐Dialkoxy‐Anthracene: A Visible‐Light‐Triggered Platform for Facile siRNA Delivery

Supramolecular self‐assembly of histidine‐capped‐dialkoxy‐anthracene (HDA) results in the formation of light‐responsive nanostructures. Single‐crystal X‐ray diffraction analysis of HDA shows two types of hydrogen bonding. The first hydrogen bond is established between the imidazole moieties while the second involves the oxygen atom of one amide group and the hydrogen atom of a second amide group. When protonated in acidic aqueous media, HDA successfully complexes siRNA yielding spherical nanostructures. This biocompatible platform controllably delivers siRNA with high efficacy upon visible‐light irradiation leading up to 90 % of gene silencing in live cells.     

PAMAM Dendrimers for siRNA Delivery: Computational and Experimental Insights

Short double‐stranded RNAs, which are known as short interfering RNA (siRNA), can be used to specifically down‐regulate the expression of the targeted gene in a process known as RNA interference (RNAi). However, the success of gene silencing applications based on the use of synthetic siRNA critically depends on efficient intracellular delivery. Polycationic branched macromolecules such as poly(amidoamine) (PAMAM) dendrimers show a strong binding affinity for RNA molecules and, hence, can provide an effective, reproducible, and relatively nontoxic method for transferring siRNAs into animal cells. Notwithstanding these perspectives, relatively few attempts have been made so far along these lines to study in detail the molecular mechanisms underlying the complexation process between PAMAMs and siRNAs. In this work we combine molecular simulation and experimental approaches to study the molecular requirements of the interaction of RNA‐based therapeutics and PAMAM dendrimers of different generations. The dendrimers and their siRNA complexes were structurally characterized, and the free energy of binding between each dendrimer and a model siRNA was quantified by using the well‐known MM/PBSA approach. DOSY NMR experiments confirmed the structural in silico prediction and yielded further information on both the complex structure and stoichiometry at low N/P ratio values. siRNA/PAMAM complex formation was monitored at different N/P ratios using gel retardation assays, and a simple model was proposed, which related the amount of siRNA complexed to the entropy variation upon complex formation obtained from the computer simulations.     

Reductive Degradation Behavior of Bioreducible Poly(disulfide amine) for Enhancing SiRNA Efficiency

Bioreducible cationic polymer poly(CBA‐DAH) containing repeated disulfide linkages on the polymer backbone was synthesized through Michael‐type polyadditions of CBA to DAH monomers. Poly(CBA‐DAH) could spontaneously form nanoscale polyelectrolyte complexes through electrostatic interactions with siRNA in an aqueous phase. These nanoparticles were rapidly degraded under the reductive cytoplasmic environment with subsequently releasing the siRNA cargo into the cytoplasm where RNAi takes place, as a result of the breakdown of disulfide bonds in the polymers. The reductive degradation behavior of the poly(CBA‐DAH)/siRNA polyplexes is more likely to increase RNAi activity with enhancing the cytoplasmic localization of siRNA molecules. Poly(CBA‐DAH) may have great potential as a gene carrier especially for therapeutic applications of siRNAs owing to the reductive degradation characteristics.

     

Stepwise synthesis of RNA conjugates carrying peptide sequences for RNA interference studies

Oligoribonucleotide conjugates carrying nuclear localization peptide sequences at the 3′-end were prepared stepwise on a single support. The siRNA duplex carrying the nuclear localization peptide sequence at the 3′-end of the passenger strand has similar inhibitory properties as those of unmodified or cholesterol-modified RNA duplexes.     

Lipid‐Like Nanoparticles for Small Interfering RNA Delivery to Endothelial Cells

Here, nanoparticles composed of lipid‐like materials (lipidoids) to facilitate non‐viral delivery of small interfering RNA (siRNA) to endothelial cells (ECs) are developed. Nanoparticles composed of siRNA and lipidoids with small size (～200 nm) and positive charge (～34 mV) are formed by self‐assembly of lipidoids and siRNA. Ten lipidoids are synthesized and screened for their ability to facilitate the delivery of siRNA into ECs. Particles composed of leading lipidoids show significantly better delivery to ECs than a leading commercially available transfection reagent, Lipofectamine 2000. As a model of potential therapeutic application, nanoparticles composed of the top performing lipidoid, NA114, are studied for their ability to deliver siRNA targeting anti‐angiogenic factor (SHP‐1) to human ECs. Silencing of SHP‐1 expression significantly enhances EC proliferation and decreases EC apoptosis under a simulated ischemic condition.     

Dextran Microgels for Time‐Controlled Delivery of siRNA

To apply siRNA as a therapeutic agent, appropriate attention should be paid to the optimization of the siRNA gene silencing effect, both in terms of magnitude and duration. Intracellular time‐controlled siRNA delivery could aid in tailoring the kinetics of siRNA gene knockdown. However, materials with easily tunable siRNA release properties have not been subjected to thorough investigation thus far. This report describes cationic biodegradable dextran microgels which can be loaded with siRNA posterior to gel formation. Even though the siRNAs are incorporated in the hydrogel network based on electrostatic interaction, still a time‐controlled release can be achieved by varying the initial network density of the microgels. To demonstrate the biological functionality of the siRNA loaded gels, we studied their cellular internalization and enhanced green fluorescent protein (EGFP) gene silencing potential in HUH7 human hepatoma cells.     

Advanced design of t and pH dual‐responsive PDEAEMA–PVCL core–shell nanogels for siRNA delivery

The synthesis, characterization, and potential application as gene delivery systems of biodegradable dual‐responsive core–shell nanogels based on poly(2‐diethylaminoethyl) methacrylate (PDEAEMA) and poly(N‐vinylcaprolactam) (PVCL) are reported. These core–shell nanogels, having a PDEAEMA‐based core and a PVCL‐based shell, were synthesized by batch seeded emulsion polymerization. An indepth study of their swelling behavior was carried out, which presented a dual‐dependent thermo‐ and pH sensitivity. Core–shell nanogels synthesized formed complexes spontaneously through electrostatic interactions when mixing with small interfering RNA (siRNA) molecules. Moreover, the core–shell nanogel/siRNA complexes showed higher polyanion exchange resistance compared to that of the PDEAEMA‐based nanogel/siRNA complexes, indicating that the PVCL‐based shell enhanced the stability of the complexes. In vitro siRNA release profiles showed that siRNA release was controlled by the pH of the medium as well as by the crosslinking density of the PVCL‐based shell. These results indicate that dual‐responsive core–shell nanogels synthesized could be potentially useful as gene delivery systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3203–3217