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.

DNAzyme-based probe for circulating microRNA detection in peripheral blood.

BACKGROUND: The recent discovery of microRNAs (miRNAs) and their extracellular presence suggest a potential role of these regulatory molecules in defining the metastatic potential of cancer cells and mediating the cancer-host communication. This study aims to improve the sensitivity of miRNA detection via DNAzyme-based method and enhance the selectivity by using the DNAzyme-based probe to reduce nonspecific amplification. METHODS: The miRNA probes were chemically synthesized with a phosphate at the 5' end and purified by polyacrylamide gel electrophoresis. Exosomal RNA from peripheral blood was isolated. Carboxylated magnetic microsphere beads (MBs) were functionalized with streptavidin (SA) according to a previously reported method with some modification. T capture probe-coated SA-MBs (DNA-MBs) were also prepared. The fluorescent spectra were measured using a spectrofluorophotometer. RESULTS: We designed an incomplete DNAzyme probe with two stems and one bubble structure as a recognition element for the specific detection of miRNA with high sensitivity. The background effects were decreased with increase of the added of DNA-MBs and capturing times. Therefore, 20 minutes was selected as the optimal concentration in the current study. The fluorescence intensity increases as the hybridization time changed and reached a constant level at 40 minutes, and 1 µM is the optimum signal probe concentration for self-assembled DNA concatemers formation. In the presence of miRNA, the fluorescence of the solution increased with increasing miRNA concentration. There is no obvious fluorescence in the presence of 10 mM of other nontarget DNA. CONCLUSION: A simple, rapid method with high performance has been constructed based on identified circulating miRNA signatures using miRNA-induced DNAzyme. This assay is simple, inexpensive, and sensitive, enabling quantitative detection of as low as 10 fM miRNA.

DNAzyme hybridization, cleavage, degradation, and sensing in undiluted human blood serum.

RNA-cleaving DNAzymes provide a unique platform for developing biosensors. However, a majority of the work has been performed in clean buffer solutions, while the activity of some important DNAzymes in biological sample matrices is still under debate. Two RNA-cleaving DNAzymes (17E and 10-23) are the most widely used. In this work, we carefully studied a few key aspects of the 17E DNAzyme in human blood serum, including hybridization, cleavage activity, and degradation kinetics. Since direct fluorescence monitoring is difficult due to the opacity of serum, denaturing and nondenaturing gel electrophoresis were combined for studying the interaction between serum proteins and DNAzymes. The 17E DNAzyme retains its activity in 90% human blood serum with a cleavage rate of 0.04 min(-1), which is similar to that in the PBS buffer (0.06 min(-1)) with a similar ionic strength. The activity in serum can be accelerated to 0.3 min(-1) with an additional 10 mM Ca(2+). As compared to 17E, the 10-23 DNAzyme produces negligible cleavage in serum. Degradation of both the substrate and the DNAzyme strand is very slow in serum, especially at room temperature. Degradation occurs mainly at the fluorophore label (linked to DNA via an amide bond) instead of the DNA phosphodiester bonds. Serum proteins can bind more tightly to the 17E DNAzyme complex than to the single-stranded substrate or enzyme. The 17E DNAzyme hybridizes extremely fast in serum. With this understanding, the detection of DNA using the 17E DNAzyme is demonstrated in serum.

Biodistribution of the GATA-3-specific DNAzyme hgd40 after inhalative exposure in mice, rats and dogs.

The DNAzyme hgd40 was shown to effectively reduce expression of the transcription factor GATA-3 RNA which plays an important role in the regulation of Th2-mediated immune mechanisms such as in allergic bronchial asthma. However, uptake, biodistribution and pharmacokinetics of hgd40 have not been investigated yet. We examined local and systemic distribution of hgd40 in naive mice and mice suffering from experimental asthma. Furthermore, we evaluated the pharmacokinetics as a function of dose following single and repeated administration in rats and dogs. Using intranasal administration of fluorescently labeled hgd40 we demonstrated that the DNAzyme was evenly distributed in inflamed asthmatic mouse lungs within minutes after single dose application. Systemic distribution was investigated in mice using radioactive labeled hgd40. After intratracheal application, highest amounts of hgd40 were detected in the lungs. High amounts were also detected in the bladder indicating urinary excretion as a major elimination pathway. In serum, low systemic hgd40 levels were detected already at 5 min post application (p.a.), subsequently decreasing over time to non-detectable levels at 2h p.a. As revealed by Single Photon Emission Computed Tomography, trace amounts of hgd40 were detectable in lungs up to 7 days p.a. Also in the toxicologically relevant rats and dogs, hgd40 was detectable in blood only shortly after inhalative application. The plasma pharmacokinetic profile was dose and time dependent. Repeated administration did not lead to drug accumulation in plasma of dogs and rats. These pharmacokinetic of hgd40 provide guidance for clinical development, and support an infrequent and convenient dose administration regimen.

Spiegelzymes: sequence specific hydrolysis of L-RNA with mirror image hammerhead ribozymes and DNAzymes.

In this manuscript we describe for the first time mirror image catalytic nucleic acids (Spiegelzymes), which hydrolyze sequence specifically L-ribonucleic acid molecules. The mirror image nucleic acid ribozymes designed are based upon the known hammerhead ribozyme and DNAzyme structures that contain L-ribose or L-deoxyribose instead of the naturally occurring D-ribose or D-deoxyribose, respectively. Both Spiegelzymes show similar hydrolytic activities with the same L-RNA target molecules and they also exhibit extra ordinary stabilities when tested with three different human sera. In this respect they are very similar to Spiegelmers (mirror image aptamers), which we had previously developed and for which it has been shown that they are non-toxic and non-immunogenic. Since we are also able to demonstrate that the hammerhead and DNAzyme Spiegelzymes can also hydrolyze mirror image oligonucleotide sequences, like they occur in Spiegelmers, in vivo, it seems reasonable to assume that Spiegelzymes may in principle be used as an antidote against Spiegelmers. Since the Spiegelzymes contain the same building blocks as the Spiegelmers, it can be expected that they will have similar favorable biological characteristics concerning toxicity and immunogenety. In trying to understand the mechanism of action of the Spiegelzymes described in this study, we have initiated for the first time a model building system with L-nucleic acids. The models for L-hammerhead ribozyme and L-DNAzyme interaction with the same L-RNA target will be presented.