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.

Calcium enhances the transfection potency of stabilized plasmid-lipid particles.

Previous work from this laboratory has shown that plasmid DNA can be encapsulated in small (70-nm-diameter) stabilized plasmid-lipid particles (SPLP) that consist of a single plasmid encapsulated within a bilayer lipid vesicle. SPLP preferentially transfect tumor tissue following intravenous administration. Although the levels of transgene expression in vivo are greater for SPLP than can be achieved with naked DNA or complexes, they are lower than may be required for therapeutic benefit. In the present work we examine whether Ca2+ can enhance the transfection potency of SPLP. It is shown that Ca2+ can enhance SPLP transfection potency in bovine hamster kidney cells by 60- to 100-fold when treated in serum containing medium and an additional 60-fold when serum is absent for the initial 10 min of the transfection period. When cells are treated with SPLP in the presence of Ca2+, there is a fivefold increase in intact plasmid in the cell. It is also shown that this Ca2+ effect involves the formation of calcium phosphate precipitates; however, these precipitates are not directly associated with the SPLP plasmid DNA. The ability of calcium phosphate to facilitate delivery of other macromolecules without direct association is also demonstrated by the release of large-molecular-weight dextrans from endosomal/lysosomal compartments in the presence of calcium phosphate. Finally, it is shown that, unlike naked DNA, SPLP transfection potency in the presence of calcium phosphate is not affected by nuclease activity.

Alkylated derivatives of poly(ethylacrylic acid) can be inserted into preformed liposomes and trigger pH-dependent intracellular delivery of liposomal contents.

Poly(ethylacrylic acid) (PEAA) is a pH-sensitive polymer that undergoes a transition from a hydrophilic to a hydrophobic form as the pH is lowered from neutral to acidic values. In this work we show that pH sensitive liposomes capable of intracellular delivery can be constructed by inserting a lipid derivative of PEAA into preformed large unilamellar vesicles (LUV) using a simple one step incubation procedure. The lipid derivatives of PEAA were synthesized by reacting a small proportion (3%) of the carboxylic groups of PEAA with C10 alkylamines to produce C10-PEAA. Incubation of C10-PEAA with preformed LUV resulted in the association of up to 8% by weight of derivatized polymer with the LUV without inducing aggregation. The resulting C10-PEAA-LUV exhibited pH-dependent fusion and leakage of LUV contents on reduction of the external pH below pH 6.0 as demonstrated by lipid mixing and release of calcein encapsulated in the LUV. In addition, C10-PEAA-LUV exhibited pH dependent intracellular delivery properties following uptake into COS-7 cells with appreciable delivery to the cell cytoplasm as evidenced by the appearance of diffuse intracellular calcein fluorescence. It is demonstrated that the cytoplasmic delivery of calcein by C10-PEAA-LUV could be inhibited by agents (bafilomycin or chloroquine) that inhibit acidification of endosomal compartments, indicating that this intracellular delivery resulted from the pH-dependent destabilization of LUV and endosomal membranes by the PEAA component of the C10-PEAA-LUV. It is concluded that C10-PEAA-LUV represents a promising intracellular delivery system for in vitro and in vivo applications.