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.
154 companies involved in developing RNAi technologies are presented along
with 199 collaborations. They're a mix of companies that supply reagents and
technologies (nearly half) and companies that use the technologies for drug
discovery. From these, 30 are developing RNAi-based therapeutics and 23 involved
in microRNAs. Bibliography contains selected 500 publications that are in the
report. The text is supplemented with 32 tables and 10 figures.
- Technologies for suppressing gene function
- RNAi Technologies
- Methods of delivery in RNAi
- RNAi in Research
- RNAi in drug discovery
- Therapeutic applications of RNAi
- Safety, regulatory and patent issues
- Markets for RNAi Technologies
- Companies involved in RNAi Technologies