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that can be further used for the degradation of target sequences, as previously explained. This can be
accomplished via the introduction of short hairpin RNAs, which are usually expressed using either RNA
polymerase II or III enzymes, the same as pri-microRNAs, producing a structure that is similar to pre-
microRNA, followed by processing using Dicer and the formation of the mature siRNAs that will exert their
biological effect . One limitation of using siRNA for RNA interference is that after siRNA is delivered to
[110]
target cells, the effect of knocking down a specific gene gradually decreases as the oligonucleotides are
decreased in concentration by either cellular division or being broken down by nucleases. However, when
delivered on a plasmid vector, shRNA sequences can provide prolonged RNAi over a longer period of time
because double-stranded DNA is more resistant to cellular degradation, in addition to their stable
positioning in the nucleus as episomes, providing a continuous source of the therapeutic RNAi sequence.
Another benefit of using short hairpin RNAs in therapeutics is the ability to selectively lower gene target
expression only in cells relevant to the disease by controlling the expression of the shRNA vectors with
[109]
promoters that can only express the relative genes in specific target cells .

Long non-coding RNAs
There are two approaches to lncRNA therapeutics research: the first is to use synthetic oligonucleotides that
resemble lncRNA in their structure and their binding properties as well, acting as decoys and interfering
[121]
with their function, while the second is to target lncRNAs directly . Despite the greater functional ability
of lncRNAs, their aberrant roles in pathophysiological processes, and their specific tissue and cellular
expression, there has not been, to our knowledge, any role for the introduction of lncRNA-based
therapeutics in any preclinical or clinical studies. However, targeting lncRNAs has been the case for some
RNA-based studies.

RNA interference using siRNAs, according to a study by Modarresi et al., reported that the inhibition of the
lncRNA known as BDNF-AS, a lncRNA antisense transcript that controls BDNF mRNA and protein
expression, caused the chromatin status of the BDNF gene to be altered, increased BDNF protein levels, and
promoted neuronal differentiation and proliferation both in vitro and in vivo . Recent clinical trials are
[122]
also looking into the role of antisense oligonucleotides in suppressing the lncRNA UBE3A-ATS, which
regulates the expression of Ubiquitin ligase E3A in Angelman syndrome . These are just two of many
[123]
studies that have targeted lncRNAs for therapeutic treatment, and we are only scratching the surface of our
understanding and knowledge of the potential benefits of lncRNA-based therapeutics.

RNA THERAPEUTICS: LAB TO MARKET
The translation of the therapeutic potential of RNAs from preclinical studies into actual RNA therapeutics is
a multifaceted process that involves numerous challenges and considerations. Here, we provide a few
examples of RNA therapeutics and delve into their potential applications and impacts.

Fomivirsen
Fomivirsen is a synthetic antisense oligonucleotide that gained prominence as an innovative therapeutic
agent in the field of ophthalmology. It is formed of a 21-mer phosphorothioate oligonucleotide sequence
designed to target the immediate-early 2 gene of Cytomegalovirus. Administered through intraocular
injections, this groundbreaking antiviral medication demonstrated significant efficacy in slowing the
progression of Cytomegalovirus retinitis, particularly in individuals with compromised immune systems,
such as those with HIV/AIDS. Fomivirsen's unique mechanism of action paved the way for a new era in
nucleic acid-based therapies, showcasing the potential of antisense technology in treating challenging viral
infections .
[124]