Aptamers and aptamer targeted delivery

Abstract

When aptamers first emerged almost two decades ago, most were RNA species that bound and tagged or inhibited simple target ligands. Very soon after, the 'selectionologists' developing aptamer technology quickly realized more potential for the aptamer. In recent years, advances in aptamer techniques have enabled the use of aptamers as small molecule inhibitors, diagnostic tools and even therapeutics. Aptamers are now being employed in novel applications. We review, herein, some of the recent and exciting applications of aptamers in cell-specific recognition and delivery.

Figure 1

The process of in vitro selection (SELEX). A). In a traditional selection, random sequence pools (squiggly lines) are incubated with a target (pink orbs). Non-binding species are washed away, and the bound species are eluted and amplified to regenerate the pool for the next round. B). In more complex target selections, the pool is first incubated with a non-target (green orbs) in a negative selection step. Non-bound species from the negative step are added to the target, and the selection proceeds as usual. Over many cycles of selection, high-affinity sequences (aptamers) can be isolated.

Figure 2

Aptamer-mediated delivery strategies. A). One strand of siRNA (red) is directly linked to the aptamer (black), and the complement siRNA is annealed via hybridization.^, B). siRNA or other cargoes are biotinylated and loaded onto streptavidin. A biotinylated aptamer mediates delivery of the entire particle. C). Toxins or other drugs are directly conjugated to the aptamer for delivery.^, Finally, D). Aptamers are directly bound to nanoparticles.^,