Functional Polymer Conjugates for Medicinal Nucleic Acid Delivery

Click-Shielded and Targeted Lipopolyplexes

Lipopolyplexes present well-established nucleic acid carriers assembled from sequence-defined cationic lipo-oligomers and DNA or RNA. They can be equipped with additional surface functionality, like shielding and targeting, in a stepwise assembly method using click chemistry. Here, we describe the synthesis of the required compounds, an azide-bearing lipo-oligomer structure and dibenzocyclooctyne (DBCO) click agents as well as the assembly of the compounds with siRNA into a surface-functionalized formulation. Both the lipo-oligomer and the DBCO-equipped shielding and targeting agents are produced by solid-phase synthesis (SPS). This enables for precise variation of all functional units, like variation in the amount of DBCO attachment sites or polyethylene glycol (PEG) length. Special cleavage conditions with only 5% trifluoroacetic acid (TFA) must be applied for the synthesis of the shielding and targeting agents due to acid lability of the DBCO unit. The two-step lipopolyplex assembly technique allows for separate optimization of the core and the shell of the formulation.

Solid-phase supported design of carriers for therapeutic nucleic acid delivery

Nucleic acid molecules are important therapeutic agents in the field of antisense oligonucleotide, RNA interference, and gene therapies. Since nucleic acids are not able to cross cell membranes and enter efficiently into cells on their own, the development of efficient, safe, and precise delivery systems is the crucial challenge for development of nucleic acid therapeutics. For the delivery of nucleic acids to their intracellular site of action, either the cytosol or the nucleus, several extracellular and intracellular barriers have to be overcome. Multifunctional carriers may handle the different special requirements of each barrier. The complexity of such macromolecules however poses a new hurdle in medical translation, which is the chemical production in reproducible and well-defined form. Solid-phase assisted synthesis (SPS) presents a solution for this challenge. The current review provides an overview on the design and SPS of precise sequence-defined synthetic carriers for nucleic acid cargos.

Cationic vesicles based on non-ionic surfactant and synthetic aminolipids mediate delivery of antisense oligonucleotides into mammalian cells

A formulation based on a synthetic aminolipid containing a double-tailed with two saturated alkyl chains along with a non-ionic surfactant polysorbate-80 has been used to form lipoplexes with an antisense oligonucleotide capable of inhibiting the expression of Renilla luciferase mRNA. The resultant lipoplexes were characterized in terms of morphology, Zeta potential, average size, stability and electrophoretic shift assay. The lipoplexes did not show any cytotoxicity in cell culture up to 150 mM concentration. The gene inhibition studies demonstrated that synthetic cationic vesicles based on non-ionic surfactant and the appropriate aminolipid play an important role in enhancing cellular uptake of antisense oligonucleotides obtaining promising results and efficiencies comparable to commercially available cationic lipids in cultured mammalian cells. Based on these results, this amino lipid moiety could be considered as starting point for the synthesis of novel cationic lipids to obtain potential non-viral carriers for antisense and RNA interference therapies.

Comparison of four different particle sizing methods for siRNA polyplex characterization

The ability to reliably determine the size of siRNA polyplexes is the key for the rational design of particles and their formulation, as well as, their safe application in vivo. At the moment, no standard technique for size measurements is available. Each method has different underlying principles and hence may give different results. Here, four different analytical methods were evaluated for their suitability to analyze the characteristics of homogeneous and heterogeneous siRNA polyplexes: dynamic light scattering (DLS), atomic force microscopy (AFM), nanoparticle trafficking analysis (NTA), and fluorescence correlation spectroscopy (FCS). Three different siRNA polyplex compositions generated with different, precise, and hydrophobically modified oligoaminoamides were used in this study. All of the evaluated methods were suitable for analysis of medium sized, homogeneous siRNA polyplexes (~120 nm). Small particles (<40 nm) could not be tracked with NTA, but with the other three methods. Heterogeneous polyplexes were generally difficult to analyze. Only by visualization with AFM, the heterogeneity of those polyplexes was observable. FCS was the only method suitable for measuring polyplex stability in 90% fetal bovine serum. Physico-chemical characteristics of polyplexes are important quality criterions for successful in vivo application and future formulation development. Therefore, a comprehensive analysis by more than one method is of particular importance.