Mitochondria-Targeted Gene Silencing Facilitated by Mito-CPDs.

Mitochondrial DNA (mtDNA) plays an essential role in maintaining normal cellular activities. Its heteroplasmic mutations are known to cause various genetic diseases. Current genetic engineering strategies, such as those based on RNA interference (RNAi) and antisense technology, are difficult to genetically alter mtDNA, however, due to the inability of highly negatively charged oligonucleotides to translocate across the double-membrane mitochondria. We report herein a universal mitochondria-targeted gene-delivery approach by using cell-penetrating poly(disulfide)s (CPDs). Novel CPD-based mitochondrial transporters, named Mito-CPDs, were synthesized by using triphenylphosphonium (TPP)-fused propagating monomers containing either disulfide or diselenide backbones. Upon spontaneous complex formation with an oligonucleotide (single- or double-stranded), the resulting nanoscale Mito-CPD@Oligo exhibited excellent properties in common biological media. While the intracellular gene-delivery efficiency of these Mito-CPDs was comparable to that of commercial transfection agents, their unique mitochondria-localized properties enabled effective release of the loaded cargo inside these organelles. Subsequent mitochondrial delivery of siRNA and antisense oligonucleotides against suitable mtDNA-encoded proteins showed successful down-regulation of target protein expression, leading to profound effects on mitochondrial functions. Mito-CPDs thus provide a useful tool for future investigations of mitochondrial biology and treatment of mitochondria-related diseases.