Engineering the Binding Kinetics of Synthetic Polymer Nanoparticles for siRNA Delivery

Area of Science:

• Biomaterials Science
• Nanotechnology
• Molecular Biology

Background:

• Nanoparticle (NP) affinity for target biomacromolecules is governed by association (k_on) and dissociation (k_off) rate constants.
• Controlling these kinetics is crucial for on-demand capture and release, particularly for small interfering RNA (siRNA) delivery systems.
• The binding kinetics of siRNA to NPs significantly impacts gene knockdown efficacy.

Purpose of the Study:

• To demonstrate that the association and dissociation rate constants (k_on, k_off) of siRNA to NPs can be individually engineered.
• To investigate the influence of NP chemical structure and composition on siRNA binding kinetics.
• To correlate engineered binding kinetics with the efficacy of siRNA delivery and gene knockdown.

Main Methods:

• Utilized N-Isopropylacrylamide-based NPs functionalized with hydrophobic and amine monomers.
• Systematically varied the amount of amine groups on the NPs to modulate k_off.
• Assessed the binding kinetics (k_on, k_off) of siRNA to the engineered NPs.
• Evaluated gene knockdown efficiency of NP/siRNA complexes packaged in lipid nanoparticles at different pH values.

Main Results:

• Increasing amine group concentration on NPs decreased the dissociation rate constant (k_off) without affecting the association rate constant (k_on).
• NPs exhibiting low k_off at pH 5.5 and high k_off at pH 7.4 demonstrated superior knockdown efficiency when siRNA complexes were encapsulated in lipid nanoparticles.
• This pH-dependent binding affinity facilitates strong binding in the endosome and release in the cytoplasm.

Conclusions:

• The chemical engineering of NPs allows for precise control over siRNA binding and release kinetics.
• Optimized binding kinetics, characterized by pH-responsive affinity, are critical for effective siRNA delivery.
• These findings support the principle that strong NP-siRNA affinity in the endosome and weak affinity in the cytoplasm enhance gene silencing efficacy.