An amino acid-based amphoteric liposomal delivery system for systemic administration of siRNA.

We demonstrate a systematic and rational approach to create a library of natural and modified, dialkylated amino acids based upon arginine for development of an efficient small interfering RNA (siRNA) delivery system. These amino acids, designated DiLA2 compounds, in conjunction with other components, demonstrate unique properties for assembly into monodisperse, 100-nm small liposomal particles containing siRNA. We show that DiLA2-based liposomes undergo a pH-dependent phase transition to an inverted hexagonal phase facilitating efficient siRNA release from endosomes to the cytosol. Using an arginine-based DiLA2, cationic liposomes were prepared that provide high in vivo siRNA delivery efficiency and are well-tolerated in both cell and animal models. DiLA2-based liposomes demonstrate a linear dose-response with an ED50 of 0.1 mg/kg against liver-specific target genes in BALB/c mice.

Bio-mimetic surface engineering of plasmid-loaded nanoparticles for active intracellular trafficking by actin comet-tail motility.

Intracellular transport after endosomal escape presents one of the major barriers for efficient non-viral gene delivery because plasmid DNA and synthetic nanoparticulate carriers suffer from significantly restricted diffusion in the cytoplasm. We postulate that forces generated by actin polymerization, a mechanism used by several bacterial pathogens such as Listeria monocytogenes, can be harnessed to propel nanoparticles within the cytoplasm and thereby overcome diffusional limitations associated with gene transport in the cell cytoplasm. In this work, we synthesized and characterized plasmid DNA-containing nanoparticles modified with ActA protein, the single protein in L. monocytogenes responsible for activating actin polymerization and initiating actin comet-tail propulsion. The motility of the ActA-modified nanoparticles was assessed in Xenopus laevis cytoplasmic extract supplemented with fluorescently labeled actin. Nanoparticle motility was monitored using multi-color, time-lapse fluorescence microscopy for the formation of actin comet tails attached to the fluorescently labeled vehicle. We observed particle motility with velocities approximately 0.06 microm/s with anionic-charged plasmid carriers formed from either poly(lactic-co-glycolic acid) (PLGA) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes, but interestingly not with cationic particles assembled by encapsulation of plasmid with either polyethylenimine (PEI) or 1,2-dioleoyl-3-trimethylammonium-propane/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOTAP/DOPE) lipids. Control particles coated with albumin instead of ActA also showed no motility. Taken together, we have demonstrated the feasibility of translating the comet-tail propulsion mechanism to synthetic drug carriers as a potential approach to overcome intracellular transport barriers, and also have identified appropriate gene delivery systems that can be employed for this mechanism.

Spatio-temporal modeling of nanoparticle delivery to multicellular tumor spheroids.

The inefficiency of nanoparticle penetration in tissues limits the therapeutic efficacy of such formulations for cancer applications. Recent work has indicated that modulation of tissue architecture with enzymes such as collagenase significantly increases macromolecule delivery. In this study we developed a mathematical model of nanoparticle penetration into multicellular spheroids that accounts for radially dependent changes in tumor architecture, as represented by the volume fraction of tissue accessible to nanoparticle diffusion. Parameters such as nanoparticle binding, internalization rate constants, and accessible volume fraction were determined experimentally. Unknown parameters of nanoparticle binding sites per cell in the spheroid and pore shape factor were determined by fitting to experimental data. The model was correlated with experimental studies of the penetration of 40 nm nanoparticles in SiHa multicellular spheroids with and without collagenase treatment and was able to accurately predict concentration profiles of nanoparticles within spheroids. The model was also used to investigate the effects of nanoparticle size. This model contributes toward the understanding of the role of tumor architecture on nanoparticle delivery efficiency.

Increased nanoparticle penetration in collagenase-treated multicellular spheroids.

The extracellular matrix of solid tumors presents a transport barrier that restricts nanoparticle penetration, thereby limiting the efficacy of nano-sized delivery vehicles for cancer imaging and therapy. In this study, the effect of nanoparticle size and collagenase treatment on penetration of carboxylated polystyrene nanoparticles was systematically assessed in a multicellular spheroid model. Penetration of the nanoparticles into the spheroid core was limited to particles smaller than 100 nm. Collagenase treatment of spheroids resulted in significantly increased penetration of nanoparticles up to 100 nm with only a minor increase in particle penetration observed for particles larger than 100 nm. Collagenase was immobilized onto the surface of nanoparticles for site-specific degradation of ECM proteins. Collagenase-coated, 100 nm nanoparticles demonstrated a 4-fold increase in the number of particles delivered to the spheroid core compared with control nanoparticles. Thus, nanoparticle delivery to solid tumors may be substantially improved by the incorporation of ECM-modulating enzymes in the delivery formulation.

Gold nanoparticles as a versatile platform for optimizing physicochemical parameters for targeted drug delivery.

The development of targeted vehicles for systemic drug delivery relies on optimizing both the cell-targeting ligand and the physicochemical characteristics of the nanoparticle carrier. A versatile platform based on modification of gold nanoparticles with thiolated polymers is presented in which design parameters can be varied independently and systematically. Nanoparticle formulations of varying particle size, surface charge, surface hydrophilicity, and galactose ligand density were prepared by conjugation of PEG-thiol and galactose-PEG-thiol to gold colloids. This platform was applied to screen for nanoparticle formulations that demonstrate hepatocyte-targeted delivery in vivo. Nanoparticle size and the presence of galactose ligands were found to significantly impact the targeting efficiency. Thus, this platform can be readily applied to determine design parameters for targeted drug delivery systems.Modified gold nanoparticles are a suitable model for nanoparticle-based gene carriers.