Mechanisms and strategies for effective delivery of antisense and siRNA oligonucleotides

Abstract

The potential use of antisense and siRNA oligonucleotides as therapeutic agents has elicited a great deal of interest. However, a major issue for oligonucleotide-based therapeutics involves effective intracellular delivery of the active molecules. In this Survey and Summary, we review recent reports on delivery strategies, including conjugates of oligonucleotides with various ligands, as well as use of nanocarrier approaches. These are discussed in the context of intracellular trafficking pathways and issues regarding in vivo biodistribution of molecules and nanoparticles. Molecular-sized chemical conjugates and supramolecular nanocarriers each display advantages and disadvantages in terms of effective and nontoxic delivery. Thus, choice of an optimal delivery modality will likely depend on the therapeutic context.

Figure 1.

Endocytotic pathways. The figure depicts the multiple endocytotic pathways that may be involved in uptake of oligonucleotides. The black arrows represent well-documented trafficking routes within the cell. The names in red indicate well-known protein markers for various endomembrane compartments; in most cases, antibodies to these marker proteins are commercially available.

Figure 2.

Cell penetrating peptides. This describes some of the more commonly used cell penetrating peptides in terms of molecular weight and net charge.

Figure 3.

In vivo barriers. The figure lists key barriers to effective in vivo delivery of oligonucleotides. Rapid excretion is an issue for low molecular weight compounds. Clearance by phagocytes, capillary permeability and slow diffusion in the extracellular matrix apply to larger molecules and nanoparticles. Both small and large delivery agents can be affected by poor cellular uptake and inefficient release from endosomes.