Activity of core-modified 10-23 DNAzymes against HCV

DNAzymes: Expanding the Potential of Nucleic Acid Therapeutics

Nucleic acids drugs have been proven in the clinic as a powerful modality to treat inherited and acquired diseases. However, key challenges including drug stability, renal clearance, cellular uptake, and movement across biological barriers (foremost the blood-brain barrier) limit the translation and clinical efficacy of nucleic acid-based therapies, both systemically and in the central nervous system. In this study we provide an overview of an emerging class of nucleic acid therapeutic, called DNAzymes. In particular, we review the use of chemical modifications and carrier molecules for the stabilization and/or delivery of DNAzymes in cell and animal models. Although this review focuses on DNAzymes, the strategies described are broadly applicable to most nucleic acid technologies. This review should serve as a general guide for selecting chemical modifications to improve the therapeutic performance of DNAzymes.

Specific DNAzymes cleave the 300-618 nt of 5'UTR to inhibit DHAV-1 translation and replication

DNAzymes effectively inhibit the expression of viral genes. Duck hepatitis A virus type-1 (DHAV-1) genomic RNA carries an internal ribosome entry site (IRES). The IRES initiates the translation of DHAV-1 via a mechanism that differs from that of cap-dependent translation. Therefore, it is an attractive target for the treatment of DHAV-1. In this study, we designed 6 DNAzymes (Dzs) specifically targeting 300-618 nt sequence in the DHAV-1 5'untranslated region (UTR; a predicted IRES-like element). In the presence of divalent metal ions, three designed DNAzymes (DZ369, DZ454, and DZ514) efficiently cleaved the 300-618 nt sequence of the DHAV-1 5'UTR RNA. The activity of the Dzs was particularly dependent on Mg²⁺ ions. Subsequently, the translation inhibitory activity of these Dzs was determined by western blotting experiments. The Dzs effectively inhibited the translation mediated by the 300-618 nt of DHAV-1 5'UTR in duck embryo fibroblasts (DEFs). Importantly, DZ454 showed the strongest inhibitory effect, and its inhibition was time and dose dependent. However, none of the Dzs showed significant inhibition of cap-dependent translation. These results suggest that these Dzs show specificity for target RNA. Moreover, DZ454 inhibited the replication of DHAV-1. In conclusion, the designed DNAzymes can be used as inhibitors of DHAV-1 RNA translation and replication, providing new insights useful for the development of anti-DHAV-1 drugs.

A combination of the modified catalytic core and conjugation of 3'-inverted deoxythymidine for a more efficient and nuclease-resistant 10-23 DNAzyme

10-23 DNAzyme is a catalytic DNA molecule capable of cleaving complementary RNA. Its high cleavage efficiency is being pursued by chemical modifications, for realizing its genetic therapeutics potential. The most efficient and nuclease-resistant DNAzyme was obtained in this study combined two modifications - 7-aminopropyl-8-aza-7-deaza-2'-deoxyadenosine (residue 1) at A9 and 3'-inverted deoxythymidine residue (ⁱT) at 3'-end. Moreover, this combinatorial modification could be a universal approach for designing efficient and enzyme-resistant 10-23 DNAzyme against other RNA targets, and the catalytic core-modification could be further combined with other recognition arm modifications for practical applications as genetic therapeutics and biosensor tools.

Metal-Based Nanomaterials: Work as Drugs and Carriers against Viral Infections

Virus infection is one of the threats to the health of organisms, and finding suitable antiviral agents is one of the main tasks of current researchers. Metal ions participate in multiple key reaction stages of organisms and maintain the important homeostasis of organisms. The application of synthetic metal-based nanomaterials as an antiviral therapy is a promising new research direction. Based on the application of synthetic metal-based nanomaterials in antiviral therapy, we summarize the research progress of metal-based nanomaterials in recent years. This review analyzes the three inhibition pathways of metal nanomaterials as antiviral therapeutic materials against viral infections, including direct inactivation, inhibition of virus adsorption and entry, and intracellular virus suppression; it further classifies and summarizes them according to their inhibition mechanisms. In addition, the use of metal nanomaterials as antiviral drug carriers and vaccine adjuvants is summarized. The analysis clarifies the antiviral mechanism of metal nanomaterials and broadens the application in the field of antiviral therapy.

Modified Nucleic Acids: Expanding the Capabilities of Functional Oligonucleotides

In the last three decades, oligonucleotides have been extensively investigated as probes, molecular ligands and even catalysts within therapeutic and diagnostic applications. The narrow chemical repertoire of natural nucleic acids, however, imposes restrictions on the functional scope of oligonucleotides. Initial efforts to overcome this deficiency in chemical diversity included conservative modifications to the sugar-phosphate backbone or the pendant base groups and resulted in enhanced in vivo performance. More importantly, later work involving other modifications led to the realization of new functional characteristics beyond initial intended therapeutic and diagnostic prospects. These results have inspired the exploration of increasingly exotic chemistries highly divergent from the canonical nucleic acid chemical structure that possess unnatural physiochemical properties. In this review, the authors highlight recent developments in modified oligonucleotides and the thrust towards designing novel nucleic acid-based ligands and catalysts with specifically engineered functions inaccessible to natural oligonucleotides.

Stabilization of Telomeric I-Motif Structures by (2'S)-2'-Deoxy-2'-C-Methylcytidine Residues

G-quadruplexes and i-motifs are tetraplex structures present in telomeres and the promoter regions of oncogenes. The possibility of producing nanodevices with pH-sensitive functions has triggered interest in modified oligonucleotides with improved structural properties. We synthesized C-rich oligonucleotides carrying conformationally restricted (2'S)-2'-deoxy-2'-C-methyl-cytidine units. The effect of this modified nucleoside on the stability of intramolecular i-motifs from the vertebrate telomere was investigated by UV, CD, and NMR spectroscopy. The replacement of selected positions of the C-core with C-modified residues induced the formation of stable intercalated tetraplexes at near-neutral pH. This study demonstrates the possibility of enhancing the stability of the i-motif by chemical modification.

Synthesis, crystallization and preliminary crystallographic analysis of a 52-nucleotide DNA/2'-OMe-RNA oligomer mimicking 10-23 DNAzyme in the complex with a substrate

A 52-nucleotide DNA/2'-OMe-RNA oligomer mimicking 10-23 DNAzyme in the complex with its substrate was synthesized, purified and crystallized by the hanging-drop method using 0.8 M sodium potassium tartrate as a precipitant. A data set to 1.21 Å resolution was collected from a monocrystal at 100 K using synchrotron radiation on a beamline BL14.1 at BESSY. The crystal belonged to the P2₁ group with unit-cell a = 49.42, b = 24.69, c = 50.23, β = 118.48.

Blue-white screening as a new readout for deoxyribozyme activity in bacterial cells

Demonstration of 10–23 deoxyribozyme activity in viable E. coli using blue-white screening as the readout system.

Thirty-five years of research into ribozymes and nucleic acid catalysis: where do we stand today?

Since the discovery of the first catalytic RNA in 1981, the field of ribozyme research has developed from the discovery of catalytic RNA motifs in nature and the elucidation of their structures and catalytic mechanisms, into a field of engineering and design towards application in diagnostics, molecular biology and medicine. Owing to the development of powerful protocols for selection of nucleic acid catalysts with a desired functionality from random libraries, the spectrum of nucleic acid supported reactions has greatly enlarged, and importantly, ribozymes have been accompanied by DNAzymes. Current areas of research are the engineering of allosteric ribozymes for artificial regulation of gene expression, the design of ribozymes and DNAzymes for medicinal and environmental diagnostics, and the demonstration of RNA world relevant ribozyme activities. In addition, new catalytic motifs or novel genomic locations of known motifs continue to be discovered in all branches of life by the help of high-throughput bioinformatic approaches. Understanding the biological role of the catalytic RNA motifs widely distributed in diverse genetic contexts belongs to the big challenges of future RNA research.

Modified Nucleoside Triphosphates for In-vitro Selection Techniques

The development of SELEX (Selective Enhancement of Ligands by Exponential Enrichment) provides a powerful tool for the search of functional oligonucleotides with the ability to bind ligands with high affinity and selectivity (aptamers) and for the discovery of nucleic acid sequences with diverse enzymatic activities (ribozymes and DNAzymes). This technique has been extensively applied to the selection of natural DNA or RNA molecules but, in order to improve chemical and structural diversity as well as for particular applications where further chemical or biological stability is necessary, the extension of this strategy to modified oligonucleotides is desirable. Taking into account these needs, this review intends to collect the research carried out during the past years, focusing mainly on the use of modified nucleotides in SELEX and the development of mutant enzymes for broadening nucleoside triphosphates acceptance. In addition, comments regarding the synthesis of modified nucleoside triphosphate will be briefly discussed.

Probing the effect of minor groove interactions on the catalytic efficiency of DNAzymes 8-17 and 10-23

DNAzymes (Dz) 8-17 and 10-23 are two widely studied and well-characterized RNA-cleaving DNA catalysts. In an effort to further improve the understanding of the fragile interactions and dynamics of the enzymatic mechanism, this study examines the catalytic efficiency of minimally modified DNAzymes. Five single mutants of Dz8-17 and Dz10-23 were prepared by replacing the adenine residues in the corresponding catalytic cores with 3-deazaadenine units. Kinetic assays were used to assess the effect on the catalytic activity and thereby identify the importance of hydrogen bonding that arises from the N3 atoms. The results suggest that modifications at A15 and A15.0 of Dz8-17 have a significant influence and show a reduction in catalytic activity. Modification at each location in Dz10-23 results in a decrease of the observed rate constants, with A12 appearing to be the most affected with a reduction of ∼80% of kobs and ∼25% of the maximal cleavage rate compared to the wild-type DNAzyme. On the other hand, modification of A12 in Dz8-17 showed an ∼130% increase in kobs, thus unraveling a new potential site for the introduction of chemical modifications. A pH-profile analysis showed that the chemical cleavage step is rate-determining, regardless of the presence and/or location of the mutation. These findings point towards the importance of the N3-nitrogens of certain adenine nucleotides located within the catalytic cores of the DNAzymes for efficient catalytic activity and further suggest that they might directly partake in maintaining the appropriate tertiary structure. Therefore, it appears that minor groove interactions constitute an important feature of DNAzymes as well as ribozymes.

DNA Catalysis: The Chemical Repertoire of DNAzymes

Deoxyribozymes or DNAzymes are single-stranded catalytic DNA molecules that are obtained by combinatorial in vitro selection methods. Initially conceived to function as gene silencing agents, the scope of DNAzymes has rapidly expanded into diverse fields, including biosensing, diagnostics, logic gate operations, and the development of novel synthetic and biological tools. In this review, an overview of all the different chemical reactions catalyzed by DNAzymes is given with an emphasis on RNA cleavage and the use of non-nucleosidic substrates. The use of modified nucleoside triphosphates (dN*TPs) to expand the chemical space to be explored in selection experiments and ultimately to generate DNAzymes with an expanded chemical repertoire is also highlighted.