[KrutiPaneria]

There are certain disorders like cancer, parasitic and viral infections, which cause excessive production of specific proteins in day to day life. An alternative treatment for these disorders is known as Antisense Technology. A single stranded RNA that is complementary to messenger RNA (mRNA) is referred to as Antisense RNA. The antisense therapy includes inhibition of translation by using single stranded nucleotide, any DNA or RNA sequences or even synthetic ones. From the practical point of view, most of the antisense therapies work efficiently and produce best results if used with RNA since RNA specifically binds to target mRNA and blocks protein synthesis.

Antisense technology was also referred as Gene Subtraction, but it is proven to be a misnomer as this technology does not remove gene, rather it just involves inactivation of the gene. Naturally occurring mRNA antisense mechanism is the hok/sok system in E.Coli R1 plasmid.

The antisense technology is carried out on the basis of the principle that the cloned gene is ligated into the vector in reverse orientation. Now, as the antisense technology obstructs the mechanism of translation it is stoichiometric in nature, and it can prevent synthesis of the product of the gene that it directs against. The antisense RNA mechanism involves hybridization of the antisense and sense copies of RNA. Now, as the ds-RNA molecule is formed, it rapidly degrades by ribonucleases and the expression is blocked. Another reason could also be the antisense RNA preventing ribosomes to bind to the sense strand. In simpler words, if an oligonucleotide is introduced into the cell, it binds to specific mRNA which forms an RNA dimer in the cytoplasm and halts the translation mechanism; this is because the mRNA no longer has access to ribosome and dimeric RNA is rapidly degraded by ribonuclease which in turn on introduction of oligonucleotide complementary to mRNA leads to blockage of translation by particular gene, turning off the gene.

RNAi (RNA interference) and Antisense RNA technology though has the same effect but their mechanisms are quite different. Firstly, RNAi technology involves degradation of mRNA by small interfering RNAs triggering catalytic gene silencing; whereas in Antisense RNA technology mRNA is degraded by RNase H. Secondly, in comparison to antisense RNA, RNAi are twice larger.

The application of Antisense RNA technology is in many sectors. This technology was used in Flavr Savr, for tomato ripening; ripening in tomato produces enzyme Polygalactourodase (PG) which softens tomatoes and finally rotten them quickly. Two biotechnology companies: Calgene, USA and ICI Seeds, UK introduced a gene in plant which synthesizes a complementary mRNA to PG gene and inhibites the synthesis of PG enzyme delaying over ripening and rotting. Antisense therapy is considered for treating certain genetic disorders and infections. This is also referred to as Gene Therapy. It includes: isolation of specific gene; it’s cloning and inserting it into target tissue cells to make desired protein. It has to be ensured that the gene is expressed correctly and sufficiently without causing harm to patient in context with the immune response. Antisense RNA technology is also used for cancer therapy. This therapy is used for treating brain cancer – malignant glioma and cancer of prostate gland, in malignant glioma IGF-I was over produced and in the prostate cancer IGF-IR was synthesized more. These two were used to block the translation. Research is carried on in regard with Antisense RNA drugs for treatment of CMV, HIV, cancer, etc. Antisense antiviral drug named Formivirsen is developed to treat CMV, which was licensed by FDA in August 1998. In 2010, scientist at NIPGR by using Antisense technology developed tomato which could last longer for more than 30 days by silencing two genes (alpha - man and beta – hex) which causes softening and wrinkling in tomatoes during ripening process.

Despite of achieving some success, Antisense technology has few challenges. Like: delivery into the patients body, then possibility of toxic effects due to it’s regulation on both the normal and mutant alleles. Antisense RNA technology is also used to study certain gene functions.

Looking at the advancements in the Antisense RNA technology, it has potentials for development of pharmacological agents, studying physiological and pathological processes as well as it’s use in effective treatment as gene therapy.