DNAzymes, generated through in vitro selection processes, are single-stranded DNA catalysts that can catalyze a wide variety of reactions, such as RNA or DNA cleavage and ligation or DNA phosphorylation. Based on specific cofactor dependence and potent catalytic ability, DNAzymes have been extensively used to develop highly sensitive and specific sensing platforms for metal ions, small molecules, and biomacromolecules. However, in spite of their multiple strong enzymatic turnover properties, few reports have addressed the potential application of RNA-cleaving DNAzymes as therapeutic gene-silencing agents. The main challenges are being met with low efficiency of cellular uptake, instability and the lack of sufficient cofactors for cellular or in vivo study, which have limited the development of DNAzymes for clinical application. In recent years, substantial progress has been made to enhance the delivery efficiency and stability of DNAzymes by developing variety of methods. Smart metal oxide nanomaterials have also been used to meet the requirement of cofactors in situ. This review focuses on the gene silencing application of DNAzymes as well as their physicochemical properties. Methods of increasing the efficacy of DNAzymes in gene therapy are also discussed: delivery systems to enhance the cellular uptake, modifications to enhance the stability and smart systems to generate sufficient cofactors in situ. Finally, some future trends and perspectives in these research areas are outlined.
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