RNAi offers fresh approach to drug discovery
radical approach to drug discovery, the emphasis is now placed on
finding the most efficient means to deliver or transfect RNAi into
mammalian target genes,writes Wai Lang Chu.
RNAi has evolved into a powerful technique to silence gene expression in cells. It allows researchers to study molecular effects of modulating expression at the level of individual genes. This degree of precision can now be accomplished without the time-consuming efforts previously dedicated to the construction of single gene knock-outs or dominant negative expressing cell lines.
Industry and academic research work in this sector has been increasing, evident from the number of scientific papers published on RNAi. The increase in the number of research papers published following RNAi discovery from 15 in 1998 to nearly 1000 by 2003.
While RNAi is seen as the next big thing in drug discovery and development, current investigations are focussing on fine-tuning this tool. RNAi depends on key factors such as the target cell line, RNAi concentration, ratio of RNAi to the transfection reagent, cell confluence during transfection, and incubation time.
The flexibility of its applications has made RNAi a valuable tool for researchers interested in gene function characterisation, signalling pathway analysis and target validation. These processes have proved increasingly significant in drug research and development.
Giridhar Rao, industry analyst for Frost and Sullivan said: "Determining the most effective snippet of RNA for each gene of interest usually requires testing more than three to four different RNAi sequences."
"To test and compare any given RNAi sequence, researchers need to monitor and optimize RNAi purity, integrity, uptake, and cell viability."
As with all new processes, RNAi is not without its problems. Off-target effects are likely to occur when the sense strand of the RNAi fails to guide the gene silencing process properly. Moreover, potential cross-hybridization with mismatched sequences reduces the specificity of RNAi. The industry believes that these inconsistencies are a result of badly designed RNAi, a factor of the highest priority.
"The design of an RNAi plays a vital role in determining the success of RNAi experiments," said Rao. "A well-designed RNAi is more effective in gene silencing and has better chances of targeting the messenger RNA and minimizing off-target effects."
In addition, the susceptibility of certain RNAi molecules to rapid degradation by nucleases in serum and other body fluids is a concern for researchers since stability is imperative for success in therapeutic applications.
"The key is to attain optimal stability," said Rao. "Very high stability could cause lodging of residual RNAi in the body and this can lead to increased toxicity."
The question reverberating around the industry is exactly what is RNAi good for? Initial studies indicate select RNAi molecules target and demonstrate effective and sustained reduction of the alpha-synuclein gene expression. Pre-clinical results suggest the development of RNAi therapeutics to treat Parkinson's disease.
RNAi has also been used to attack viruses such as HIV, and hepatitis B and C. The technology shows further potential for treating renal and metabolic disorders, cancers, and even diseases of the central nervous system.
RNAi drugs might be a reality by 2010. The RNAi therapy likely to reach humans first is those targeting macular degeneration, a leading cause of blindness.
An alliance between Merck and Alnylam, a specialist in the development of therapeutics based on RNA interference (RNAi), could fast-track the first drug in this class through to market.
The alliance, formed in June, is focused on using RNAi to treat macular degeneration of the eye, as well as other ocular diseases caused by abnormal growth or leakage of small blood vessels in the eye.
The quest to understand RNAi and its future applications have spun off several specialized conferences on RNAi alone. GeneExpressions Systems, a company providing reagents for RNAi research aims to provide the best knowledge management seminars to RNAi researchers in the world.
Companies have been giving up on some of the more disappointing genomics research and have become aligned to RNAi research. One company, Ribozyme Pharmaceuticals in Boulder, Colorado, even rechristened itself 'Sirna Therapeutics' to reflect its new vision.
Four leading companies in siRNA research for therapeutic applications are Alnylam Pharmaceuticals, Sirna Therapeutics, Acuity Pharmaceuticals and Atugen. Atugen was a spin-off of Sirna (1998) but is now an independent company competing with Sirna in this sector.
Benitec of Australia has joined this list of leading providers with its DNA directed RNAi (ddRNAi) therapeutics. Apart from this, Benitec also offers target validation services. Devgen NV, utilizing its proprietary RNAi technology, develops knockdown C. elegans for target validation. Deltagen Inc., based on mouse gene knockout and standardized phenotypic analysis, has developed DeltaBase, a searchable database for in vivo derived mammalian gene targets and function.
