In this work, we develop and evaluate polycationic nanoparticles for the delivery of small interfering RNA (siRNA). Delivery remains a major challenge for translating siRNA to the clinic, and overcoming the delivery challenge requires effective siRNA delivery vehicles that meet the demands of the specific delivery strategy. Cross-linked polycationic nanoparticle formulations were synthesized using ARGET ATRP or UV-initiated polymerization. The one-step, one-pot, surfactant-stabilized monomer-in-water synthesis technique may provide a simpler and faster alternative to complicated, multistep techniques and an alternative to methods that rely on toxic organic solvents. The polymer nanoparticles were synthesized using the cationic monomer 2-(diethylamino)ethyl methacrylate, the hydrophobic monomer tert-butyl methacrylate to tune pH responsiveness, the hydrophilic monomer poly(ethylene glycol) methyl ether methacrylate to improve biocompatibility, and cross-linking agent tetraethylene glycol dimethacrylate to enhance colloidal stability. Four formulations were evaluated for their suitability as siRNA delivery vehicles in vitro with the human embryonic kidney cell line HEK293T or the murine macrophage cell line RAW264.7. The polycationic nanoparticles demonstrated efficient and rapid loading of the anionic siRNA following complexation. Confocal microscopy as well as flow cytometry analysis of cells treated with polycationic nanoparticles loaded with fluorescently labeled siRNA demonstrated that the polycationic nanoparticles promoted cellular uptake of fluorescently labeled siRNA. Knockdown experiments using polycationic nanoparticles to deliver siRNA demonstrated evidence of knockdown, thus demonstrating potential as an alternative route to creating polycationic nanoparticles.

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This work investigates the interactions of a polycationic nanocarrier with siRNA and with cells in order to better understand the capabilities and limitations of the carrier. The polycationic nanocarriers are cross-linked copolymer nanoparticles synthesized in a single-step reaction using ARGET ATRP (activators regenerated by electron transfer atom transfer radical polymerization). The polycationic nanocarriers efficiently bind siRNA for polymer/siRNA mass ratios less than 1. A method to prepare fluorescently labeled polycationic nanocarriers is presented. The fluorescently labeled polycationic nanocarriers are used to investigate cellular internalization with RAW264.7 murine macrophage cells. Flow cytometry demonstrates that the uptake increased with nanoparticle concentration and incubation time. Confocal microscopy confirmed internalization of fluorescently labeled nanoparticles. The investigation of siRNA-induced knockdown demonstrates that higher concentrations of nanoparticles and siRNA are associated with increased knockdown. For the conditions tested in the knockdown experiments, the ARGET ATRP polycationic nanocarriers outperformed a commercially available Lipofectamine control.

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