Catalytic nucleic acids, ribozymes and deoxyribozymes can act as efficient ribonucleases and degrade target RNA molecules by complementary Watson-Crick base pairing and catalytic cleavage of their phosphodiester internucleotide bonds. This ability makes ribozymes and deoxyribozymes potent molecular tools for therapeutic applications. Recent achievements in ribozymes design and technology enable the preparation of ribozymes which can be efficiently expressed in cellular systems, co-localize with the target mRNA and exhibit high intracellular activity. Several examples of preclinical and clinical trials of ribozymes directed toward viral genes (HBV, HCV, HIV-1) and oncogenes are discussed in this review.
The discovery of RNA interference caused a revival of the concept of short nucleic acids application as molecular tools for therapeutic control of gene expression. After almost a decade of intensive research by leading pharmaceutical companies, there is only a limited number of clinical trials of synthetic siRNAs. In this review, we shall summarize the present status of knowledge of RNAi mechanism of action and discuss the potential of the use of siRNA in theraphy. We shall also provide data on recent achievements in current clinical trials based on RNAi techniques.
In diverse eukaryotes, dsRNA triggers the destruction of mRNA sharing the same sequence as the dsRNA in the process called RNAi. The guides for sequence-specific degradation of mRNA are 21 nt short interfering RNAs (siRNAs). Synthetic siRNAs can efficiently mediate RNAi, but a drawback of RNAi is its transient nature as a result of the limited availability and stability of synthetic oligonucleotides. Recently, several groups reported the construction of expression plasmid vectors that mediate the production of siRNAs under control of Pol III promoters. These vectors allow the continued expression of siRNAs in the cells resulting in persistent and specific suppression of target genes. The retroviral siRNA expressing system allows for stable inactivation of the genes in primary cells or living organisms.
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