RNA-cleaving DNAzymes Research Articles

A MnO2 nanosheet-mediated photo-controlled DNAzyme for intracellular miRNA cleavage to suppress cell growth.

Certain miRNAs, called oncomiRs, play a causal role in the onset and maintenance of cancer when overexpressed, thus, representing a potential new class of targets for therapeutic intervention. RNA-cleaving DNAzymes, mainly aimed at mRNA, have shown potential as therapeutic agents for various diseases. However, it's rarely reported that a DNAzyme was used for intracellular miRNA cleavage to suppress cell growth. Herein, we have developed a MnO2 nanosheet-mediated photo-controlled DNAzyme (NPD) for intracellular miRNA cleavage to suppress cell growth. MnO2 nanosheets adsorb photocaged DNAzymes, protect them from enzymatic digestion, and efficiently deliver them into cells. In the presence of intracellular glutathione (GSH), MnO2 nanosheets are reduced to Mn2+ ions, which serve as cofactors of the 8-17 DNAzyme for miRNA cleavage. Once the DNAzyme is activated by light, it can cyclically cleave endogenous miR-21 inside cells, which would suppress cancer cell migration and invasion, and finally induce cancer cell apoptosis.

In vitro selection and application of lanthanide-dependent DNAzymes.

Highly sensitive and selective detection of lanthanide ions is a major analytical challenge. In recent years, the use of DNA for this purpose has been pursued. For such highly charged cations, it is difficult to select their aptamers due to strong nonspecific binding. On the other hand, the use of catalytic DNA or DNAzymes has an advantage to overcome this problem, especially DNAzymes with RNA-cleaving activity. In this chapter, a few such DNAzymes are introduced and methods for in vitro selection of lanthanide-dependent RNA-cleaving DNAzymes are described in detail, including the selection protocols, the DNA sequences used, the characterization of selected DNAzymes and their conversion into biosensors. All of the experiments use only fluorophore-labeled DNA, and radioisotope labeling is completely avoided. The resulting DNAzymes can distinguish lanthanides from non-lanthanide metals, tell the difference between light and heavy lanthanides, and can be used together to discriminate individual lanthanides.

Core-Shell Nanosystems for Self-Activated Drug-Gene Combinations against Triple-Negative Breast Cancer.

The combination of gene therapy with chemotherapeutics provides an efficacious strategy for enhanced tumor therapy. RNA-cleaving DNAzyme has been recognized as a promising gene-silencing tool, while its combination with chemotherapeutic drugs has been limited by the lack of an effective codelivery system to allow sufficient intracellular DNAzyme activation, which requires specific metal ions as a cofactor. Here, a self-activatable DNAzyme/drug core-shell codelivery system is fabricated to combat triple-negative breast cancer (TNBC). The hydrophobic chemotherapeutic, rapamycin (RAP), is self-assembled into the pure drug nanocore, and the metal-organic framework (MOF) shell based on coordination between Mn2+ and tannic acid (TA) is coated on the surface to coload an autophagy-inhibiting DNAzyme. The nanosystem efficiently delivers the payloads into tumor cells, and upon endocytosis, the MOF shell is disintegrated to release the therapeutics in response to an acidic endo/lysosome environment and intracellular glutathione (GSH). Notably, the coreleased Mn2+ serves as the cofactor of DNAzyme for effective self-activation, which suppresses the expression of Beclin 1 protein, the key initiator of autophagy, resulting in a significantly strengthened antitumor effect of RAP. Using tumor-bearing mouse models, the nanosystem could passively accumulate into the tumor tissue, impose potent gene-silencing efficacy, and thus sensitize chemotherapy to inhibit tumor growth upon intravenous administration, providing opportunities for combined gene-drug TNBC therapy.

DNAzyme–Metal–Organic Framework Two-Photon Nanoprobe for In situ Monitoring of Apoptosis-Associated Zn2+ in Living Cells and Tissues

Monitoring Zn2+ in living cells is critical for fully elucidating the biological process of apoptosis. However, the quantitative intracellular sensing of Zn2+ using DNAzyme remains challenging because of issues related to penetration of the signal through tissue, targeted cellular uptake and activation, and susceptibility toward enzymatic degradation. In this study, we developed a novel phosphate ion-activated DNAzyme-metal-organic frameworks (MOFs) nanoprobe for two-photon imaging of Zn2+ in living cells and tissues. The design of this nanoprobe involved the loading of a Zn2+-specific, RNA-cleaving DNAzyme onto the MOFs through strong coordination between the phosphonate O atoms of the DNAzyme backbone and Zr atoms in the MOFs. This coordination restrained the extracellular activity of DNAzyme; however, after cell entry, the DNAzyme was released from the MOFs through a competitive binding by the phosphate ions present at a high intracellular concentration. Following their release, the two-photon (TP) fluorophore-labeled substrate strands of DNAzyme were cleaved with the aid of Zn2+, which resulted in a strong fluorescence signal. The incorporation of a TP fluorophore into the nanoprobe facilitated near-infrared excitation, which allowed the highly sensitive and specific imaging of Zn2+ in living cells and tissues at greater depths than possible previously. The TP-DNAzyme-MOFs nanoprobe achieved a low detection limit of 3.53 nM, extraordinary selectivity toward Zn2+, and a tissue signal penetration of 120 μm. More importantly, this nanoprobe was successfully used to monitor cell apoptosis, and this application of the DNAzyme-MOFs probe holds great potential for future use in biological studies and medical diagnostics.

Sharp Switching of DNAzyme Activity through the Formation of a CuII -Mediated Carboxyimidazole Base Pair.

DNAzymes are widely used as functional units for creating DNA-based sensors and devices. Switching of DNAzyme activity by external stimuli is of increasing interest. Herein we report a CuII -responsive DNAzyme rationally designed by incorporating one of the most stabilizing artificial metallo-base pairs, a CuII -mediated carboxyimidazole base pair (ImC -CuII -ImC ), into a known RNA-cleaving DNAzyme. Cleavage of the substrate was suppressed without CuII , but the reaction proceeded efficiently in the presence of CuII ions. This is due to the induction of a catalytically active structure by ImC -CuII -ImC pairing. The on/off ratio was as high as 12-fold, which far exceeds that of the previously reported DNAzyme with a CuII -mediated hydroxypyridone base pair. The DNAzyme activity can be regulated specifically in response to CuII ions during the reaction through the addition, removal, or reduction of CuII . This approach should advance the development of stimuli-responsive DNA systems with a well-defined sharp switching function.

Ultrasensitive magnetic DNAzyme-copper nanoclusters fluorescent biosensor with triple amplification for the visual detection of E. coli O157:H7

A relatively-simple and high-efficient fluorescent magnetic biosensor based on DNAzyme was established for the detection of E. coli O157:H7. In order to solve the problem of weak signal and low sensitivity in the detection of foodborne pathogenic bacteria, we ingeniously designed a fluorescent sensor based on triple signal amplification of magnetic beads, DNAzyme and photoluminescence. In the detection process, the E. coli-specific RNA-cleaving DNAzyme can specifically identify the target protein in crude intracellular mixture (CIM), which caused its conformation changes and induced rolling circle amplification (RCA) to the generation and luminescence of copper nanoclusters (CuNCs). This cascade amplification design can capture weak signals in the sample. The biosensor also indicated a good linear range from 10 CFU mL−1 to 1000 CFU mL−1 and obtained a limit of detection (LOD) of 1.57 CFU mL−1, which showed a relatively high sensitivity compared with other studies. Furthermore, the biosensor displayed high-efficient detection capability in 1.5 h and good reproducibility (relative standard deviations < 2%). It has been proved that this sensor is feasible to the detection of E. coli O157:H7 in drinking water and apple juice. Moreover, we found that the final detection product can effectively wrap the magnetic beads and can be driven by the magnetic field. And this unexpected discovery will provide ideas for the development of biosensing robots.

Metal organic framework coated MnO2 nanosheets delivering doxorubicin and self-activated DNAzyme for chemo-gene combinatorial treatment of cancer.

The RNA-cleaving DNAzyme (DZ) holds promising potential for RNA interference (RNAi) applications and is favored over siRNA owing to its high chemical stability, biocompatibility, predictable activity, and substrate versatility. However, its pharmaceutical applications for disease treatment are limited by the requirement of metal cofactor for activation, as well as the lack of effective co-delivery systems to combine with other therapeutic modalities. Herein, we designed and constructed metal organic framework (MOF) coated MnO2 nanosheets to realize the co-delivery of a survivin inhibiting DZ and doxorubicin (DOX) for chemo-gene combinatorial treatment of cancer. In our design, the DOX was adsorbed on MnO2 planar surface, and the DZ was loaded into the MOF shell layer through the coordination between Mn2+ and tannic acid. The nano-system could stably encapsulate the payloads under physiological condition, but rapidly degraded after endocytose into tumor cells in response to intracellular stimuli, resulting in triggered drugs release. Notably, the coreleased Mn2+ could act as metal cofactor for effective DZ activation. Both in vitro and in vivo studies have demonstrated the enhanced anti-tumor efficacy of the nanosystem, with co-contributions from anti-neoplastic DOX, survivin silencing effect of DZ, and to some extent, ROS generation by Mn2+. This work provides an ingenious strategy to address the key limitation of DZ for RNAi applications and realize the combination of DZ with other therapeutic modalities, in which the DZ can be in-situ activated for target gene silencing.

Selection of a metal ligand modified DNAzyme for detecting Ni2+

Nickel is a highly important metal, and the detection of Ni2+ using biosensors is a long-stand analytical challenge. DNA has been widely used for metal detection, although no DNA-based sensors were reported for Ni2+. DNAzymes are DNA-based catalysts, and they recruit metal ions for catalysis. In this work, in vitro selection of RNA-cleaving DNAzymes was carried out using a library containing a region of 50 random nucleotides in the presence of Ni2+. To increase Ni2+ binding, a glycyl–histidine-functionalized tertiary amine moiety was inserted at the cleavage junction. A representative DNAzyme named Ni03 showed a high cleavage yield with Ni2+ and it was further studied. After truncation, the optimal sequence of Ni03l could bind one Ni2+ or two Co2+ for catalysis, while other metal ions were inactive. Its cleavage rates for 100 μM Ni2+ reached 0.63 h−1 at pH 8.0. A catalytic beacon biosensor was designed by labeling a fluorophore and a quencher on the Ni03l DNAzyme. Fluorescence enhancement was observed in the presence of Ni2+ with a detection limit of 12.9 μM. The sensor was also tested in spiked Lake Ontario water achieving a similar sensitivity. This is another example of using single-site modified DNAzyme for sensing transition metal ions.

Selective and sensitive detection of chronic myeloid leukemia using fluorogenic DNAzyme probes

One of the major challenges facing the early diagnosis of chronic myelogenous leukemia (CML) patients today is enhancing the simplicity, rapidness, sensitivity and specificity of detection assay for easy clinical implementation. RNA-cleaving fluorogenic DNAzymes (RFDs) are single-stranded DNA molecules with catalytic activity and can produce fluorescent signals when combined with specific targets. As K562 cells were the first established human immortalized myelogenous leukemia line, we try to screen several RFDs using the crude extracellular mixture of K562 cells through the SELEX process. We obtained an RFD probe A1-3 that is able to distinguish K562 cells from other tumor cell lines. 10 nM of A1-3 can induce an increase of detectable fluorescence signal. Moreover, the RFD assay system can work well for target detection in complex serum matrix. The optimized RFD assay system with low cost also has a desirable ability to exactly distinguish K562 cells after truncation of 20 bases in the 5’end of A1-3. This study is the first report to investigate the RFD system for detection of K562 cells using cell culture supernatants as the complex target. This RFD assay system could potentially be applied for the diagnosis of CML.

A Multi-component All-DNA Biosensing System Controlled by a DNAzyme.

We report on a programmable all-DNA biosensing system that centers on the use of a 4-way junction (4WJ) to transduce a DNAzyme reaction into an amplified signal output. A target acts as a primary input to activate an RNA-cleaving DNAzyme, which then cleaves an RNA-containing DNA substrate that is designed to be a component of a 4WJ. The formation of the 4WJ controls the release of a DNA output that becomes an input to initiate catalytic hairpin assembly (CHA), which produces a second DNA output that controls assembly of a split G-quadruplex as a fluorescence signal generator. The 4WJ can be configured to produce either a turn-off or turn-on switch to control the degree of CHA, allowing target concentration to be determined in a quantitative manner. We demonstrate this approach by creating a sensor for E. coli that could detect as low as 50 E. coli cells mL-1 within 85 min and offers an amplified bacterial detection method that does not require a protein enzyme.

Electrochemical impedance biosensor array based on DNAzyme-functionalized single-walled carbon nanotubes using Gaussian process regression for Cu(II) and Hg(II) determination.

RNA-cleaving DNAzyme is a very useful biomaterial for metal ions determination. However, parts of DNAzymes can be cleaved by several metal ions, which makes it difficult to distinguish the concentrations of different metal ions. A method was applied to determine the Cu(II) concentration by using electrochemical biosensors combined with amathematical model. An electrochemical biosensor was fabricated using single carbon nanotubes/field-effect transistor (SWNTs/FET) functionalized with a DNAzyme named PSCu10 and its complementary DNA embedded phosphorothioate RNA (CS-DNA). The CS-DNA with amino groups at the 5' end was immobilized on the SWNTs' surface via the peptide bond and then combined with PSCu10 by identifying bases complementary pairing (Cuzyme/SWNTs/FET). The CS-DNA can be cleaved when Cu(II) bonded with the PSCu10 sothat the structural change of Cuzyme improves the electrical conductivity of Cuzyme/SWNTs/FET. But CS-DNA also can be cut-off by the Hg(II)directly, which might interfere with the detection of the Cu(II) concentration using Cuzyme/SWNTs/FET. To solve this problem, Hgzyme/SWNTs/FET was employed to monitor the Hg(II) concentration at the same time, thus servingto determine the Cu(II) content through the Gaussian process regression. The biosensor array can determine the Cu(II) concentration varying from 0.01 to 10,000nM when the Hg(II) concentration was ranging from 5 to 10,000nM, and the limits of detection for Cu(II) and Hg(II) were 6.7pM and 3.43nM, respectively. Graphical abstract A biosensor array (Cuzyme/SWNTs/FET and Hgzyme/SWNTs/FET) was developed, and the detecting data were processed using Gaussian process regression. It allows determination of Cu(II) and Hg(II) concentrations with high accuracy.

Target Self-Enhanced Selectivity in Metal-Specific DNAzymes.

Highly selective recognition of metal ions by rational ligand design is challenging, and simple metal binding by biological ligands is often obscured by nonspecific interactions. In this work, binding-triggered catalysis is used and metal selectivity is greatly increased by increasing the number of metal ions involved, as exemplified in a series of in vitro selected RNA-cleaving DNAzymes. The cleavage junction is modified with a glycyl-histidine-functionalized tertiary amine moiety to provide multiple potential metal coordination sites. DNAzymes that bind 1, 2, and 3 Zn2+ ions, increased their selectivity for Zn2+ over Co2+ ions from approximately 20-, 1000-, to 5000-fold, respectively. This study offers important insights into metal recognition by combining rational ligand design and combinatorial selection, and it provides a set of new DNAzymes with excellent selectivity for Zn2+ ions.

A pH-regulated stimuli-responsive strategy for RNA-cleaving DNAzyme

RNA-cleaving DNAzymes possess important roles in DNAzymes and have been widely used in the biosensors, DNA nanomachines owing to their ion-specific dependence. However, there are still challenges in constructing universal but versatile stimuli-responsive strategies of RNA-cleaving DNAzymes. Herein, a stimuli-responsive strategy for RNA-cleaving DNAzyme is proposed by the artful design of hairpin nanostructure, in which the activities of DNAzyme (Pb2+-dependent DNAzyme as a model) in the hairpin’s loop are pH-regulated by using the triplex stem as the “lock”. Upon introducing the “key”, pH values, the DNAzyme will be activated and fragment the substrate of it in the presence of Pb2+, accompanied by the turn-on of the fluorescence quenched by fluorescence resonance energy transfer (FRET). The regulation ability of pH can be controlled by the length and sequence of the triplex stem, and the wide pH regulation range may be helpful for the application of DNAzymes in biological medicine delivery systems.

DNAzyme-Mediated Genetically Encoded Sensors for Ratiometric Imaging of Metal Ions in Living Cells.

Genetically encoded fluorescent proteins (FPs) have been used for metal ion detection. However, their applications are restricted to a limited number of metal ions owing to the lack of available metal-binding proteins or peptides that can be fused to FPs and the difficulty in transforming the binding of metal ions into a change of fluorescent signal. We report herein the use of Mg2+-specific 10-23 or Zn2+-specific 8-17 RNA-cleaving DNAzymes to regulate the expression of FPs as a new class of ratiometric fluorescent sensors for metal ions. Specifically, we demonstrate the use of DNAzymes to suppress the expression of Clover2, a variant of the green FP (GFP), by cleaving the mRNA of Clover2, while the expression of Ruby2, a mutant of the red FP (RFP), is not affected. The Mg2+ or Zn2+ in HeLa cells can be detected using both confocal imaging and flow cytometry. Since a wide variety of metal-specific DNAzymes can be obtained, this method can likely be applied to imaging many other metal ions, expanding the range of the current genetically encoded fluorescent protein-based sensors.

DNAzyme-Mediated Genetically Encoded Sensors for Ratiometric Imaging of Metal Ions in Living Cells.

Genetically encoded fluorescent proteins (FPs) have been used for metal ion detection. However, their applications are restricted to a limited number of metal ions owing to the lack of available metal-binding proteins or peptides that can be fused to FPs and the difficulty in transforming the binding of metal ions into a change of fluorescent signal. We report herein the use of Mg2+ -specific 10-23 or Zn2+ -specific 8-17 RNA-cleaving DNAzymes to regulate the expression of FPs as a new class of ratiometric fluorescent sensors for metal ions. Specifically, we demonstrate the use of DNAzymes to suppress the expression of Clover2, a variant of the green FP (GFP), by cleaving the mRNA of Clover2, while the expression of Ruby2, a mutant of the red FP (RFP), is not affected. The Mg2+ or Zn2+ in HeLa cells can be detected using both confocal imaging and flow cytometry. Since a wide variety of metal-specific DNAzymes can be obtained, this method can likely be applied to imaging many other metal ions, expanding the range of the current genetically encoded fluorescent protein-based sensors.

Highly Sensitive RNA-Cleaving DNAzyme Sensors from Surface-to-Surface Product Enrichment.

The engineering of easy-to-use biosensors with ultra-low detection sensitivity remains a major challenge. Herein, we report a simple approach for creating such sensors through the use of an RNA-cleaving DNAzyme (RcD) and a strategy designed to concentrate its cleavage product significantly. The assay uses micron-sized beads loaded with a target-responsive RcD and a paper strip containing a microzone covered with a DNA oligonucleotide capable of capturing the cleavage product of the RcD through Watson-Crick hybridization. Placing the beads and the paper strip in a target-containing test sample allows the bead-bound RcD molecules to undergo target-induced RNA cleavage, releasing a DNA fragment that is captured by the paper strip. This strategy, though simple, is very effective in achieving high levels of detection sensitivity, being able to enrich the concentration of the cleavage product by three orders of magnitude. It is also compatible with both fluorescence-based and colorimetric reporting mechanisms. This work provides a simple platform for developing ultrasensitive biosensors that take advantage of the widely available RcDs as molecular recognition elements.

Biosensors Made of Synthetic Functional Nucleic Acids Toward Better Human Health.

The invention of the in vitro selection technique, or SELEX (Systematic Evolution of Ligands by EXponential enrichment), in the early 1990s, identified single-stranded (ss) nucleic acid molecules with catalytic or binding properties from random-sequence nucleic acid libraries.1–3 This technique has given rise to intensive examinations of synthetic functional nucleic acids (aptamers and nucleic acid enzymes) for wide-ranging applications including biosensors, diagnostics and therapeutics.4–9After nearly three decades of research by many groups around the world, many functional nucleic acids have been isolated and characterized. A few well-known examples are provided in Figure 1, including two RNA-cleaving DNAzymes (8-17 and 10-23),10 a peroxidase-mimicking DNAzyme (PS2.M),11 two DNA aptamers that bind human α-thrombin (TBA15 and TBA29),12,13 a DNA aptamer that binds ATP,14 and a modified nucleic acid aptamer that binds human VEGF-165 (Pegaptanib).15 Thousands of papers have been published describing the us...

Replacing Mg2+ by Fe2+ for RNA-Cleaving DNAzymes.

It has been proposed that Mg2+ and Fe2+ are very similar in interacting with ribozymes and some protein-based enzymes, but their activities with DNAzymes have yet to be studied. Here, the activity of Fe2+ as cofactor for a few RNA-cleaving DNAzymes is investigated. 17E is a well-studied DNAzyme that is active in the presence of many different divalent metal ions; it is highly active with Fe2+ with an apparent Kd of 29.7±2.3 μm and a kobs of 1.12±0.11 min-1 in the presence of 1 mm Fe2+ at pH 7.5. Fe2+ has 21-fold higher activity than Mg2+ . Six different DNAzymes are then tested, and only the DNAzymes active with Mg2+ (17E, 8-17, and E5) are active with Fe2+ . Fe2+ has 25 and one- to twofold higher activity than Mg2+ for the 8-17 and E5 DNAzymes, respectively. In pH>7 buffer and in presence of air, 1 mm Fe2+ results in a nonspecific degradation of the DNA strand due to reactive oxygen species (ROS). Cleavage reactions in anoxic environment and antioxidant ascorbate can be used to overcome the effect of oxidation. The findings provide insights for potential DNAzyme catalysis in the early Earth, and they further support the similarity between Mg2+ and Fe2+ in enzyme catalysis.

Orthogonal Activation of RNA-Cleaving DNAzymes in Live Cells by Reactive Oxygen Species.

RNA-cleaving DNAzymes are useful tools for intracellular metal-ion sensing and gene regulation. Incorporating stimuli-responsive modifications into these DNAzymes enables their activities to be spatiotemporally and chemically controlled for more precise applications. Despite the successful development of many caged DNAzymes for light-induced activation, DNAzymes that can be intracellularly activated by chemical inputs of biological importance, such as reactive oxygen species (ROS), are still scarce. ROS like hydrogen peroxide (H2 O2 ) and hypochlorite (HClO) are critical mediators of oxidative stress-related cell signaling and dysregulation including activation of immune system as well as progression of diseases and aging. Herein, we report ROS-activable DNAzymes by introducing phenylboronate and phosphorothioate modifications to the Zn2+ -dependent 8-17 DNAzyme. These ROS-activable DNAzymes were orthogonally activated by H2 O2 and HClO inside live human and mouse cells.

Efficient DNA-Catalyzed Porphyrin Metalation for Fluorescent Ratiometric Pb2+ Detection.

Developing biosensors for Pb2+ is an important analytical topic. DNA-based Pb2+ sensors have been designed mainly based on RNA-cleaving DNAzymes and Pb2+-induced folding of G-quadruplex (G4) DNA. Porphyrin metalation is a key reaction in biology and catalysis. Many enzyme mimics have been developed to catalyze this reaction, and some metalation DNAzymes were reported with a G4 structure. Inspired by the excellent G4 binding properties of certain divalent metal ions, we herein screened a few metals and G-rich DNA sequences. The metalation activity of a DNA named T30695 (sequence: (G3T)4) was significantly accelerated by Pb2+. The reaction of Cu2+ insertion into the mesoporphyrin IX had a kcat of 0.89 min-1 and a Km of 9.8 μM, representing a catalytic efficiency similar to that of human ferrochelatase. The reason for the acceleration was attributed to Pb2+ binding of the G4 DNA and the catalytic activity of the large Pb2+ ion for this reaction. A ratiometric sensor for Pb2+ was developed by inserting Zn2+ with a detection limit of 23.5 nM Pb2+. This work has established a new DNA-based reaction that can be used for Pb2+ detection, and it also provides a highly efficient new DNAzyme for porphyrin metalation, which might be used for signal production for other biosensors.