Maximizing the potency of siRNA lipid nanoparticles for hepatic gene silencing in vivo.

Special (lipid) delivery: The role of the ionizable lipid pK(a) in the in vivo delivery of siRNA by lipid nanoparticles has been studied with a large number of head group modifications to the lipids. A tight correlation between the lipid pK(a) value and silencing of the mouse FVII gene (FVII ED(50) ) was found, with an optimal pK(a) range of 6.2-6.5. The most potent cationic lipid from this study has ED(50) levels around 0.005 mg kg(-1) in mice and less than 0.03 mg kg(-1) in non-human primates.

Targeted delivery of RNAi therapeutics with endogenous and exogenous ligand-based mechanisms.

Lipid nanoparticles (LNPs) have proven to be highly efficient carriers of short-interfering RNAs (siRNAs) to hepatocytes in vivo; however, the precise mechanism by which this efficient delivery occurs has yet to be elucidated. We found that apolipoprotein E (apoE), which plays a major role in the clearance and hepatocellular uptake of physiological lipoproteins, also acts as an endogenous targeting ligand for ionizable LNPs (iLNPs), but not cationic LNPs (cLNPs). The role of apoE was investigated using both in vitro studies employing recombinant apoE and in vivo studies in wild-type and apoE(-/-) mice. Receptor dependence was explored in vitro and in vivo using low-density lipoprotein receptor (LDLR(-/-))-deficient mice. As an alternative to endogenous apoE-based targeting, we developed a targeting approach using an exogenous ligand containing a multivalent N-acetylgalactosamine (GalNAc)-cluster, which binds with high affinity to the asialoglycoprotein receptor (ASGPR) expressed on hepatocytes. Both apoE-based endogenous and GalNAc-based exogenous targeting appear to be highly effective strategies for the delivery of iLNPs to liver.

Rational design of cationic lipids for siRNA delivery.

We adopted a rational approach to design cationic lipids for use in formulations to deliver small interfering RNA (siRNA). Starting with the ionizable cationic lipid 1,2-dilinoleyloxy-3-dimethylaminopropane (DLinDMA), a key lipid component of stable nucleic acid lipid particles (SNALP) as a benchmark, we used the proposed in vivo mechanism of action of ionizable cationic lipids to guide the design of DLinDMA-based lipids with superior delivery capacity. The best-performing lipid recovered after screening (DLin-KC2-DMA) was formulated and characterized in SNALP and demonstrated to have in vivo activity at siRNA doses as low as 0.01 mg/kg in rodents and 0.1 mg/kg in nonhuman primates. To our knowledge, this represents a substantial improvement over previous reports of in vivo endogenous hepatic gene silencing.

Poly(lactide-co-glycolide) microspheres as a moldable scaffold for cartilage tissue engineering.

This study demonstrates the use of biodegradable poly(lactide-co-glycolide) (PLG) microspheres as a moldable scaffold for cartilage tissue engineering. Chondrocytes were delivered to a cylindrical mold with or without PLG microspheres and cultured in vitro for up to 8 weeks. Cartilagenous tissue formed using chondrocytes and microspheres maintained thickness, shape, and chondrocyte collagen type II phenotype, as indicated by type II collagen staining. The presence of microspheres further enhanced total tissue mass and the amount of glycosaminoglycan that accumulated. Evaluation of microsphere composition demonstrated effects of polymer molecular weight, end group chemistry, and buffer inclusion on tissue-engineered cartilage growth. Higher molecular weight PLG resulted in a larger mass of cartilage-like tissue formed and a higher content of proteoglycans. Cartilage-like tissue formed using microspheres made from low molecular weight and free carboxylic acid end groups did not display increases in tissue mass, yet a modest increased proteoglycan accumulation was detected. Microspheres comprised of PLG with methyl ester end groups yielded a steady increase in tissue mass, with no real increase in matrix accumulation. The microencapsulation of Mg(OH)(2) had negative effects on tissue mass and matrix accumulation. The data herein reflect the potential utility of a moldable PLG-chondrocyte system for tissue-engineering applications.

A novel injectable approach for cartilage formation in vivo using PLG microspheres.

This study documents the use of biodegradable poly(lactide-co-glycolide) (PLG) microspheres as a novel, injectable scaffold for cartilage tissue engineering. Chondrocytes were delivered via injection to the subcutaneous space of athymic mice in the presence and absence of PLG microspheres. Tissue formation was evaluated up to 8 weeks post-injection. Progressive cartilage formation was observed in samples containing microspheres. The presence of microspheres increased the quantity of tissue formed, the amount of glycosaminoglycan that accumulated, and the uniformity of type II collagen deposition. Microsphere composition influenced the growth of the tissue engineered cartilage. Higher molecular weight PLG resulted in a larger mass of cartilage formed and a higher content of proteoglycans. Microspheres comprised PLG with methyl ester end groups yielded increased tissue mass and matrix accumulation, but did not display homogenous matrix deposition. The microencapsulation of Mg(OH)2 had negative effects on tissue mass and matrix accumulation. Matrix accumulation, cell number, and tissue mass were unchanged by microsphere size, but larger microspheres increased the frequency of central necrosis in implants. The data herein reflect the promising utility of an injectable PLG-chondrocyte system for tissue engineering applications.

Protein spray freeze drying. 2. Effect of formulation variables on particle size and stability.

Spray freeze drying produces protein particles suitable for microencapsulation into polymeric microspheres intended for sustained release. Accessibility of encapsulated protein particles to the microsphere surface increases as the protein particle size is increased. Thus, it is desirable that the encapsulated protein particle size be minimized to limit initial release. We have investigated the effect of formulation on spray freeze-dried bovine serum albumin (BSA) as a model protein. Atomization conditions were fixed such that in the absence of excipient, the particle size of the sonicated powder was submicron, and there was substantial protein degradation (loss of monomer). Addition of low concentrations of surfactants (up to the CMC) or mannitol (up to the point where it tended to crystallize upon dehydration) resulted in partial stabilization without impacting particle size. Trehalose was successful in stabilizing the protein; however, there was a marked increase in particle size at the highest levels tested. Ammonium sulfate provided partial stabilization, but also tended to form crystals and increase particle size. FTIR measurements showed a loss of native secondary structure upon spray freeze drying that was ameliorated by addition of trehalose. Other excipients did not prevent structural perturbations. In general, stabilization of spray freeze-dried BSA was related to lowering of the specific surface area in the powder. A balance must be achieved when spray freeze drying proteins intended for encapsulation in sustained-release systems.