Success of nucleic acid based therapies often depends on target-cell specific delivery of genetic materials such as plasmid DNA, antisense oligonucleotides or small interfering RNA. Such extracellular targeting strategies include the incorporation of hydrophilic shielding domains into nucleic acid carriers which protects them from unspecific interactions with non-target tissues (passive targeting), and the inclusion of targeting moieties which allows recognition of targetspecific cellular receptors (active targeting). Furthermore physical targeting methods such as magnetofection, electroporation or by photochemical means have been used to enhance efficiency of nucleic acid transfer. For optimum efficacy, extracellular targeting concepts are combined with programmed bioresponsive carrier chemistry which confers to the formulation stability during extracellular delivery but controlled disassembly and nucleic acid release after reaching the target cell.
Keywords: Bioresponsive systems, gene therapy, ligands, lipoplexes, nucleic acids, polyplexes, siRNA, targeting
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