Abstract
Summary
RNA interference (RNAi) or gene silencing involves the use of double stranded
RNA (dsRNA). Once inside the cell, this material is processed into short 21-23
nucleotide RNAs termed siRNAs that are used in a sequence-specific manner to
recognize and destroy complementary RNA. The report compares RNAi with other
antisense approaches using oligonucleotides, aptamers, ribozymes, peptide
nucleic acid and locked nucleic acid.
Various RNAi technologies are described, along with design and methods of
manufacture of siRNA reagents. These include chemical synthesis by in vitro
transcription and use of plasmid or viral vectors. Other approaches to RNAi
include DNA-directed RNAi (ddRNAi) that is used to produce dsRNA inside the
cell, which is cleaved into siRNA by the action of Dicer, a specific type of
RNAse III. MicroRNAs are derived by processing of short hairpins that can
inhibit the mRNAs. Expressed interfering RNA (eiRNA) is used to express dsRNA
intracellularly from DNA plasmids.
Delivery of therapeutics to the target tissues is an important consideration.
siRNAs can be delivered to cells in culture by electroporation or by
transfection using plasmid or viral vectors. In vivo delivery of siRNAs can be
carried out by injection into tissues or blood vessels or use of synthetic and
viral vectors.
Because of its ability to silence any gene once the sequence is known, RNAi
has been adopted as the research tool to discriminate gene function. After the
genome of an organism is sequenced, RNAi can be designed to target every gene
in the genome and target for specific phenotypes. Several methods of gene
expression analysis are available and there is still need for sensitive
methods of detection of gene expression as a baseline and measurement after
gene silencing. RNAi microarray has been devised and can be tailored to meet
the needs for high throughput screens for identifying appropriate RNAi probes.
RNAi is an important method for analyzing gene function and identifying new
drug targets that uses double-stranded RNA to knock down or silence specific
genes. With the advent of vector-mediated siRNA delivery methods it is now
possible to make transgenic animals that can silence gene expression stably.
These technologies point to the usefulness of RNAi for drug discovery.
RNAi can be rationally designed to block the expression of any target gene,
including genes for which traditional small molecule inhibitors cannot be
found. Areas of therapeutic applications include virus infections, cancer,
genetic disorders and neurological diseases. Side effects can result from
unintended interaction between an siRNA compound and an unrelated host gene.
If RNAi compounds are designed poorly, there is an increased chance for
non-specific interaction with host genes that may cause adverse effects in the
host.
Regulatory, safety and patent issues are discussed. There are no major safety
concerns and regulations are in preliminary stages as the clinical trials are
just starting. Many of the patents are still pending.
The markets for RNAi are difficult to define as no RNAi-based product is
approved yet but several are in clinical trials. The major use of RNAi
reagents is in research but it partially overlaps that of drug discovery and
therapeutic development. Various markets relevant to RNAi are analyzed from
2008 to 2018. Markets are also analyzed according to breakdown of technologies
and use of siRNAs, miRNAs, etc.
Profiles of 155 companies involved in developing RNAi technologies are
presented along with 202 collaborations. They are a mix of companies that
supply reagents and technologies (nearly half of all) and companies that use
the technologies for drug discovery. Out of these, 30 are developing
RNAi-based therapeutics and 25 are involved in microRNAs. The bibliography
contains selected 500 publications that are cited in the report. The text is
supplemented with 32 tables and 10 figures.
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