DNAzymes are the DNA molecules which are catalytically active. This technique is also termed as deoxyribozymes, DNA enzymes, or catalytic DNA. In general, DNAzymes are single stranded oligo-deoxy nucleotides with enzymatic activity.To find out the improved and better means for treatment of the diseases like cancer, the new molecules are constantly being discovered and developed. Deoxyribozyme (DNAzyme) is one of such molecules. 10-23 DNAzyme is specifically characterized molecule and this characterization is based on their RNA endonuclease activity that is the capability to cleave RNA molecules after appropriate binding.

DNAzymes are being used as drugs in the treatment of cancer. It is speculated that by accelerating the movement of DNAzyme technique towards the clinical research, better pharmacodynamics and pharmacokinetics will be possible with the development of smart delivery systems for DNAzymes. DNAzymes have the ability to yield the phenomena such as light induced activation and this may be used for the targeted.

The well-known subtype of DNAzyme i.e. 10-23 DNAzyme has the potential to suppress or inhibit gene expressions through sequence-specific mRNA cleavage. 10-23 DNAzyme cannot replicate endogenously.

The first deoxyribozyme was discovered in 1994 by Professor Ronald R. Breaker5 and Gerald Joyce. Many deoxyribozymes catalyses are DNA phosphorylation, DNA cleavage, DNA deglycosylation, porphyrin metallation, DNA adenylation and thymine dimer photoreversion.

30 years ago, it was first reported that nucleic acids could be used to down-regulate gene expression via a direct and highly specific interaction with the transcript. And nowadays several techniques for the down regulation of gene expression are being used.

DNAzymes are being used in treatment of several diseases like brain disorders, muscle disorders and in the treatment of different cancers. DNAzymes are preferred as a potential therapeutics because of they are very advantageous in clinical as well as in molecular research.

A few of the advantages of DNAzymes are listed below:
• The stability of DNAzymes: This is the biggest advantage of DNAzymes. It is highly stable in both in vitro as well as in vivo. In serum (3'-3'-linked inverted T) DNAzymes are more stable than short interfering RNA.
• Relatively inexpensive and easy synthesis
• Non-toxicity (in pre-clinical studies).
• Consist of phophodiester linkages only.
• Self-sufficient catalysis: DNAzymes perform self-catalysis and don't require any catalytic cellular machinery (such as Dicer/RISC) to degrade target substrate.
• DNAzymes are often more active and have higher sequence specificity.

DNAzymes go through a specific mechanism to degrade the target molecule.

In general, there are three steps of this mechanism:
Step 1:
In the very first step, DNAzyme binds to the corresponding sequence of target mRNA.

Step 2:
In the second step, the catalytic domain of DNAzyme becomes active and directly cleavage of the target mRNA molecule takes place.

Then the DNAzyme-RNA-complex dissociates after the successful cleavage of a target mRNA molecule. Thereafter the RNA cleavage products are further degraded by intracellular enzymes.

The DNAzyme molecule is then freely available for the subsequent binding and cleavage of additional target mRNA molecules.

The consequence of mRNA degradation:
The mRNA degradation results in reduction in functional protein because translation into protein is incapacitated and this leads in an inhibition of all down-stream events. DNAzymes requires no additional endogenous co-molecules for the action. However the enzymatic activity of DNAzymes is Mg2+-dependent. This makes the activity of the DNAzyme independent of the endogenous molecular machinery of the cells. Thus, DNAzymes consists of superior specificity of antisense molecules with an inherent catalytic activity and this makes them an attractive tool for the research and specific interference with disease-causing molecules.

There are several ways to control disease progression by induction and/or inhibition of genes which includes DNA-based biopharmaceuticals. These are the potent therapeutics which includes:
1. Plasmids containing transgenes,
2. Antisense oligonucleotides,
3. Aptamers,
4. Ribozymes,
5. DNAzymes and
6. Short interfering RNAs.

DNAzymes were used in cancer cells as a target for the first time by Wu and colleagues. The activity of DNAzyme against cancer is not limited to destruction of the tumor vasculature. DNAzymes cleave RNA substrates in a sequence-specific manner. DNAzymes may produce drugs that are comparatively good and safer than those which are currently available. DNAzymes have been studied as potential therapeutics to target pathogenic mRNAs.

DNA molecules have been utilized in two ways-
1. As powerful synthetic building blocks to create nanoscale architectures,
2. As versatile programmable templates for assembly of nanomaterials.

The functions of DNA molecules have been extended from the storage of pure genetic information to the catalytic functions like
- Those of protein enzymes (DNAzymes),
- Specific binding functions like antibodies (aptamers).

DNAnanotechnology is a new interdisciplinary field which combines the functional DNA biology with nanotechnology to generate more dynamic and controllable DNA-based nanostructures or DNA-templated nanomaterials that are responsive to chemical stimuli.

Discoveries in the field of Nano-biotechnology are triggering a revolution by providing a profusion of potential and actual applications of several diseases.

Nanoparticles have been extensively used in drug delivery systems. DNA nanotechnology derived devices can be used in many other fields for practical applications, such as sensing, environmental monitoring, drug screening, therapeutics, nanoelectronics, nanophotonics, medical diagnostics, and quantum computing.

Allosteric DNAzymes or aptazymes is a new class of DNAzymes which is made by the combination of the DNAzymes and the aptamers (nucleic-acid-based binding molecules which are obtained by a combinatorial selection method known as systematic evolution of ligands by exponential enrichment (SELEX), in which DNA molecules with the desired binding properties are isolated from a library containing as many as 1015 random sequences). New therapeutic approaches can be developed by using allosteric DNAzymes or aptazymes in future and this novel therapeutic agent may be very useful in the treatment of dreadful diseases.

Thus, the research is being carried out where novel therapeutics and drug delivery systems with increased cell specificity and the reduced adverse effects are being produced.

About Author / Additional Info:
2. DNAzyme technology and cancer therapy: cleave and let die
Crispin R. Dass, Peter F.M. Choong and Levon M. Khachigian