DNA interference (DNAi) is the technology that looks set to break through the barriers, which have previously hampered the development of DNA related therapies. For several years the promise of DNA related therapies has gone largely unfulfilled due to a number of obstacles, including lack of specificity, potency, high manufacturing, as well as the inability to deliver effective doses of DNA based drugs.
The DNA interference technology perform their function by acting at the DNA level, where only one or two copies of the gene exist per cell and the treatment can be targeted more efficiently by DNAi drugs. The action of drugs' developed based on the DNA interference technology is expected to last longer at lower doses and reduce the incidence of toxicity.
DNA related therapies are potentially more cost effective to produce. The DNAi therapies need to target only one to two copies of the disease gene in each cell to reduce their negative effects. In contrast to RNAi, DNAi would focus on "plugging the firehose", instead of laboriously wiping up each droplet of water. A further advantage of DNAi is that it works at the DNA level and can possibly be employed against disease considered untreatable by small molecules. This capability alone goes far to validate DNAi-based drugs as a promising therapeutic avenue.
The DNAi technology enables drug design by reducing lead identification time for drug candidates. In the development of small molecule drug design, DNAi technologies obviate the necessity to screen large chemical libraries to find effective compounds for proteins. Their protein can leverage publicly available information from the human genome project to guide targeted therapy research. The current progress has helped DNAi to overcome previous obstacles to DNA based therapies and enabled DNAi drug candidates to anneal directly to disease genes in preclinical studies. The DNA interference technology is a method adopted to turn off the gene making it silent, i.e., the cells stop making the protein specified by the gene. This technology can be used for the treatment for several diseases which was thought to be incurable. This technology could offer a safe and effective way of turning off a gene and can see its potential in biotechnology and in pharma industry.
GENE SILENCING
It is the interruption or suppression of the expression of a gene at transcription or translational levels. Scientists have been working on strategies to selectively turn off specific genes in diseased tissues for the past thirty years.
● 1980's-Antisense oligodeoxynucleotides (ODNs)
● 1990's - Ribozymes
● 2000's - RNA interference (RNAi)
The antisense and RNAi are referred as gene knockdown technologies. The transcription of the gene is unaffected. However, gene expression, i.e., protein synthesis, is lost because mRNA molecule becomes unstable or inaccessible. Furthermore, RNAi is based on naturally occurring phenomenon known as post-transcriptional gene silencing (PTGS).
The gene silencing can also be done by DNA methylation, which involves a type of chemical modification of DNA that can be inherited without changing the DNA sequence. These can silence the gene resulting in loss of gene function. The DNA- like for example to the number 5 carbon of the cystienes pyramidine ring. In plants, cytosines are methylated both symmetrically (CpG or CpNpG) and asymmetrically (CpNpNp) where N can be any nucleotide. The methylation status of specific cytosines can be determined using a method based on bisulfite sequencing. In some organism like fruit flies there is no DNA methylation. In mammals between 60 and 70 per cent of all CpGs are methylated. The unmethylated CpGs are grouped in clusters called CpG islands that are present in the 5 regulatory regions of several genes. In human, the process of DNA methylation is carried out by three enzymes - DNA methyltransferase, 3a and 3b (DNMT1, DNMT3a, DNMT3Bb). In plants the cytosine can be methylated in the Cpg, CpNpG and CpNpN.