RNA-based approaches and nanoconstructs. One of the most promising avenues for rational
pharmacology of any kind involves approaches that inhibit or degrade specific gene products,
usually by manipulation of messenger RNAs. Recently, two such approaches have moved to the
forefront for potential therapeutic applications. The first uses modified antisense oligonucleotides
(ASOs) that can be customized to hybridize with and inhibit a specific RNA target, either through
degradation by RNase H or steric hindrance of downstream RNA processing (82, 83). Although
initial results with ASO technology were characterized by poor bioavailability and short half-
life due to degradation, these challenges have been overcome by incorporation of chemically
modified nucleic acid backbones that enhance stability in vivo (83). A recent report using this
approach in the CNS demonstrated widespread brain activity of an ASO infused into cerebrospinal
fluid and prolonged target gene knockdown with a single dose of ASO (84). A second approach
targets specific RNA molecules using three-dimensional spherical nucleic acids (SNAs) (85). These
constructs employ a gold nanoparticle core to serve as a docking site for covalent attachment of
single- or double-stranded nucleic acids in a spherical array, which enhances the stability and cell