ncRNA therapy

However, even though these regions do not code for protein, they have other functions and carry necessary regulatory information.They can be classified based on the size of the ncRNA.

[5] Long non-coding RNAs include lincRNAs,[6] intronic ncRNAs,[7] circular and linear ncRNA.

[9] Circular RNA (CircRNA) are a novel class of endogenous noncoding RNAs and are characterized by their covalently closed loop structures.

The miRNAs in most cases interact with the 3’ UTR region of target to induce mRNA degradation and translational repression.

It is now accepted that 28S rRNA catalyzes the critical step in polypeptide synthesis in addition to playing a major structural role.

On the other hand, snoRNAs are involved in mRNA editing, modification of the rRNA and tRNA, and genome imprinting.

Miescher identified the presence of a highly acidic molecule that he isolated from the pus cells and labeled it “nuclein”.

[22] It wasn’t until 1944, when Oswald Avery proposed the DNA as a genetic carrier of information that the Miescher discovery was brought back to light.

However, one of the flaws with central dogma was the postulation that information flow proceeds from DNA to RNA to protein, which hinders the understanding of different regulatory mechanisms.

Detailed understanding of the mechanism behind this post translational silencing pathway was established in 2001 by Thomas Tuschl.

It was discovered that the double stranded RNA gets processed into a shorter 25 nucleotides long fragment which is then modified into a short hairpin like structure by Drosha complex.

H19 is peculiar as it functions as a lncRNA but undergoes modifications similar to that of pre-mRNA processing such as splicing, 3’ polyadenylation and is transcribed by RNA polymerase II.

This lncRNA plays a significant role in mice embryonic development and can be lethal if expressed during prenatal stages.

[31] The drug functions as an antisense oligonucleotide and binds to the complementary sequence of the mRNA that inhibits the replication of human cytomegalovirus.

One such example is Nusinersen (Spinaraza), it functions as an ASO and targets pre-mRNA before splicing that corresponds to Survival of motor neuron 2 gene (SMN 2).

[36] Antisense oligonucleotides (ASOs) are single-stranded DNA molecules with full complementarity to one select target mRNA[37] and may act by blocking protein translation (via steric hindrance), causing mRNA degradation (via RNase H-cleavage) or changing pre-mRNA splicing.

[38] Compared to siRNA and microRNA, ASOs are more versatile in reducing protein expression, they have the ability to also enhance target translation.

In humans, 46,XX females carry an extra X chromosome (155Mb of DNA) compared to 46,XY males.

To overcome this dosage imbalance, one X chromosome is randomly inactivated in human females at around the 2-8 cell stage of embryo development.

This inactivation is very stable across cell divisions due to epigenetic contributions both during the initial silencing and the subsequent maintenance of the inactive X chromosome (Xi).

Such experiments have shown to work in cells in the lab setting although no lncRNA based therapeutics are in clinical trials.

The implications of such work can bring trisomy 21 and other chromosomal disorders in the realm of consideration for future gene therapy research.

[41] One of the major issues that hinders the ncRNA therapy is the stability of the single stranded RNA molecule.

Generally, this is overcome by containing the dsRNA in a lipid nanoparticle and using that as a ligand to bind to a receptor on the surface of the target cell.

[44] In particular, adenovirus vector is considered an efficient delivery system due to its stability within live cells and non-pathogenicity.

This draft guidance was directed towards sponsor-investigators who are developing individualized investigational antisense oligonucleotides (ASO) drug products for severely debilitating or life threatening diseases.

However, life-threatening is defined as the disease or condition has a likelihood of death unless the course of treatment leads to an endpoint of survival.

Drug development is usually targeted for a large number of individuals, in this case that is not possible because of the specificity of the mechanism of action of the ASO combined with the rarity of the treatment-amenable patient population.

Also the sponsor needs to include evidence that establishes the role of the gene variant targeted by the ASO drug.

This includes the step of escalating the dodge from its initial dose based on pharmacodynamic effects and/or trial participants' response to the ASO.