Intracellular Delivery of Antisense Peptide Nucleic Acid by Fluorescent Mesoporous Silica Nanoparticles

In order to overcome poor cell permeability of antisense peptide nucleic acid (PNA), a fluorescent mesoporous silica nanoparticle (MSNP) carrier was developed to successfully deliver antisense PNA into cancer cells for effective silence of B-cell lymphoma 2 (Bcl-2) protein expression <i>in vitro</i>. First, fluorescent MSNP functionalized with disulfide bond bridged groups was fabricated and characterized. Antisense and negative control PNAs were synthesized and further conjugated with fluorescent dye cyanine 5. Then, the PNAs were covalently connected with fluorescent MSNP via amidation between amino group of PNAs and carboxylic acid group on the MSNP surface. High intracellular concentration of glutathione serves as a natural reducing agent, which could cleave the disulfide bond to trigger the PNA release <i>in vitro</i>. Confocal laser scanning microscopy studies prove that PNA conjugated MSNP was endocytosed by HeLa cancer cells, and redox-controlled intracellular release of antisense PNA from fluorescent MSNP was successfully achieved. Finally, effective silencing of the Bcl-2 protein expression induced by the delivered antisense PNA into HeLa cells was confirmed by Western blot assay

Selective Binding to mRNA Duplex Regions by Chemically Modified Peptide Nucleic Acids Stimulates Ribosomal Frameshifting

Minus-one programmed ribosomal frameshifting (−1 PRF) allows the precise maintenance of the ratio between viral proteins and is involved in the regulation of the half-lives of cellular mRNAs. Minus-one ribosomal frameshifting is activated by several stimulatory elements such as a heptameric slippery sequence (X XXY YYZ) and an mRNA secondary structure (hairpin or pseudoknot) that is positioned 2–8 nucleotides downstream from the slippery site. Upon −1 RF, the ribosomal reading frame is shifted from the normal zero frame to the −1 frame with the heptameric slippery sequence decoded as XXX YYY Z instead of X XXY YYZ. Our research group has developed chemically modified peptide nucleic acid (PNA) L and Q monomers to recognize G-C and C-G Watson–Crick base pairs, respectively, through major-groove parallel PNA·RNA–RNA triplex formation. L- and Q-incorporated PNAs show selective binding to double-stranded RNAs (dsRNAs) over single-stranded RNAs (ssRNAs). The sequence specificity and structural selectivity of L- and Q-modified PNAs may allow the precise targeting of desired viral and cellular RNA structures, and thus may serve as valuable biological tools for mechanistic studies and potential therapeutics for fighting diseases. Here, for the first time, we demonstrate by cell-free <i>in vitro</i> translation assays using rabbit reticulocyte lysate that the dsRNA-specific chemically modified PNAs targeting model mRNA hairpins stimulate −1 RF (from 2% to 32%). An unmodified control PNA, however, shows nonspecific inhibition of translation. Our results suggest that the modified dsRNA-binding PNAs may be advantageous for targeting structured RNAs