Physicochemical and Biological Characterization of Targeted, Nucleic Acid-Containing Nanoparticles

Abstract

Nucleic acid-based therapeutics have the potential to provide potent and highly specific treatments for a variety of human ailments. However, systemic delivery continues to be a significant hurdle to success. Multifunctional nanoparticles are being investigated as systemic, nonviral delivery systems, and here, we describe the physicochemical and biological characterization of cyclodextrin-containing polycations (CDP) and their nanoparticles formed with nucleic acids including plasmid DNA (pDNA) and small interfering RNA (siRNA). These polycation/nucleic acid complexes can be tuned by formulation conditions to yield particles with sizes ranging from 60 to 150 nm, ζ potentials from 10 to 30 mV, and molecular weights from ∼7 × 10⁷ to 1 × 10⁹ g mol^-1 as determined by light scattering techniques. Inclusion complexes formed between adamantane (AD)-containing molecules and the β-cyclodextrin molecules enable the modular attachment of poly(ethylene glycol) (AD−PEG) conjugates for steric stabilization and targeting ligands (AD−PEG−transferrin) for cell-specific targeting. A 70 nm particle can contain ∼10 000 CDP polymer chains, ∼2000 siRNA molecules, ∼4000 AD−PEG₅₀₀₀ molecules, and ∼100 AD−PEG₅₀₀₀−Tf molecules; this represents a significant payload of siRNA and a large ratio of siRNA to targeting ligand (20:1). The particles protect the nucleic acid payload from nuclease degradation, do not aggregate at physiological salt concentrations, and cause minimal erythrocyte aggregation and complement fixation at the concentrations typically used for in vivo application. Uptake of the nucleic acid-containing particles by HeLa cells is measured by flow cytometry and visualized by confocal microscopy. Competitive uptake experiments show that the transferrin-targeted particles display enhanced affinity for the transferrin receptor through avidity effects (multiligand binding). Functional efficacy of the delivered pDNA and siRNA is demonstrated through luciferase reporter protein expression and knockdown, respectively. The analysis of the CDP delivery vehicle provides insights that can be applied to the design of targeted nucleic acid delivery vehicles in general.