RNA interference as a therapeutic
RNA interference (RNAi) is a highly-conserved
biological gene silencing process in which mediates resistance to both
endogenous and exogenous pathogenic nucleic acids, as a result regulates the
expression of protein coding genes (Chin,
Ang and Chu, 2017). In 1996, first RNAi type of phenomenon was reported by
Napoli and Horgensen from observation of lighted and even white petunias when
injected color producing gene to the flowers (Jorgensen et al., 1996). Fire and
Mello revealed that introduction of double stranded RNA in Caenorhabditis elegans lead to gene silencing. Subsequently, RNAi
related events were described in almost all eukaryotic organisms. Various categories
of small double strand RNA have been found. Generally, RNAi
involves three main steps, production of small RNAs by specialized ribonuclease
III-like enzyme named Dicer, formation of an effector complex (RISC), and
sequence specific binding and silencing gene either by degradation of targeted
mRNA or translational inhibition (Carthew and
Sontheimer, 2009). There are some
exceptions. Recently was found biogenesis of unusual miR-451 could use AGO
enzyme process into mature miRNA instead of using Dicer (Herrera-Carrillo and Berkhout, 2017).
The discovery of RNAi facilitated the study of functional
characterization of genes and proteins interactions in the pathway. What’s
more, with the aid of many new developed tools as bioinformatics and
genome-wide reagents, RNAi has enormous potential to develop therapeutic
effects for the diagnosis and treatment of viral infection, dominant disorders,
neurological disorders and many types of cancers (Ultimo et al., 2017). It has been found certain miRNAs
overexpressed to downregulate tumor suppressors contribute to oncogenesis which
could be used to diagnosis of certain cancers (Chen et al., 2016). Mature miRNAs are 20-25nt small noncoding RNA molecules
which primarily bind to the 3′ untranslated region of mRNAs, resulting in a
downregulation of target proteins through the degradation of target mRNAs when
perfectly bind or through translational inhibition when imperfectly bind (Tye et al., 2014). Different miRNA have
different expression pattern. Some kinds of miRNA expressed in all stages while
others have a more restricted spatial and temporal expression pattern (Nagalakshmi
et al., 2014). miRNA expression level has been demonstrated correlates with
both the type of leukemia and the prognosis of patients from a microarray study
Abolhassani, 2017). Therefore, the expression file of miRNA can be used as
biomarkers in diagnosis, differential diagnosis, prognosis and therapy of
hematologic cancer (Wang,
Chen and Sen, 2015).
RNAi Therapeutics is the branch of science that focus on
control of gene activity at RNA level that target the specific mRNA to increase
or decrease production of proteins involved in a disease to eradicate diseases (Aagaard and Rossi, 2007). The combination of
increasing numbers of identified gene
targets and the efficiency that comes from RNAi drug discovery puts science at
the forefront of the potential pharmaceutical leaders of the next decade. RNAi-based therapy works via delivery of small RNA
duplexes, including micro RNA (miRNAs) mimics, short interfering RNAs (siRNAs),
short hairpin RNAs (shRNAs) and Dicer substrate RNAs (dsiRNAs) in clinical
trials. It is a promising and attractive new class of therapeutic, especially
against undruggable targets for the treatment of cancer and other diseases.
Several RNAi cancer therapeutic clinical trials have been
carried out by targeting a variety of cancers (Bobbin and Rossi, 2016). Oncogenes, mutated tumor
suppressor genes and several other genes involved in tumor progression are good
targets for gene silencing by RNAi-based therapy (Behzad, 2014). RNAi can
simultaneous target multiple genes of various cellular pathways involved in
tumor progression which could be an advantage compared to other methods of
cancer therapy. RNAi cancer therapy might also allow the development of
personal drug for specific patients. APN401is one of the several cancer
vaccines using cbl-b siRNA to treat refractory solid tumors. Cbl-b siRNA was uptake
and loaded with tumor antigens by multiple cell types present in Peripheral
blood-derived monocytes (PBMCs) via ex vivo electroporation treatment. Apeiron
hopes this strategy could be used to enhance the antitumor immune reactivity
and improve T cell activation with the knockdown cbl-b (Bobbin and Rossi, 2016). Gradalis developed a cancer vaccine FANG which use two
downstream bifunctional shRNAs to target furin. As a result, maturated
immunosuppressant protein TGF-B will be decrease in overian cancer patients. GI
neuroendocrine tumors, HCC, an adrenocortical carcinoma was treated using
TKM-PLK1 RNAi therapeutic. Polo-like kinase (PLK) is often overexpressed in
cancer cell, LNPs delivered siRNA knockdown PLK gene will reduce cancer cell
division. Additionally, many cancer cells dependent on MYC for growth. Clinical
trials use RNAi therapeutic targeting the MYC oncogene was studied by Dicerna. There
are lots of other RNAi therapeutic in clinical trials are in development of
cancer as well other kind of diseases (Bobbin
and Rossi, 2016).
Although there are lots of clinical trials
for different diseases have been carried out by lots of different companies,
there is no RNAi based drugs have been put on the market. During the design of
RNAi-based therapeutics, there are lots of challenges and issues. Those are
including off-target effects, efficacy of silencing targets, delivery of siRNAs
to target tissues, generate natural immune response and toxicity to the target
cells (Ozcan et al., 2015). Design of siRNA, selection of strand and
choice of targets as well as the number of targets plan an important role in
the effectiveness of RNAi and off-target effects (Chin, Ang and Chu, 2017). Biodistrubution of RNAi drugs includes both technical
and scientific challenges (Dolly). Delivery of siRNAs to target tissues is
impeded by many barriers
(Ozcan et al., 2015).
During the development of RNAi in cancer therapy, various kinds of nano-based
carriers are used to delivery RNAi molecule and has been shown some advantages
compared to viral vectors, lipids, peptides and other delivery methods (Xin et al., 2017). Dysfunctional TTR protein will cause not
only disable transport vitamin A but also accumulated of amyloid deposits that
attack the heart and nerve system (Rizk and Tuzmen,
2017). Patisiran is a drug that use
lipid nanoparticle enriching small interfering RNAs to target mutated
transthyretin (TTR) gene showed extremely positive results during first and
second trials (Rizk and Tuzmen, 2017). Although
nanoparticles have been shown some efficiencies, immunogenicity and toxicity
caused by this technique limit their applications (Xin et al., 2017).
the development bioinformatics, sequencing technology, and delivery technology,
RNAi as a therapeutic technique can be developed and approved at a faster rate.
It can be applied in wide range of diseases diagnosis and genetic medicines
design. Nowadays, several clinical trials are in Phase III development and
might be approved by FDA within the next few years (Bobbin and Rossi, 2016). In the future, RNAi therapeutics is promising and even
could be used to design personal drugs of specific diseases for different
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