Wednesday, May 23, 2007
RNAi-related Phenomena and their Relevance for RNAi Therapeutics
One concern in the development of RNAi Therapeutics for human use would therefore be that small RNAs may engage unwanted small RNA-directed processes. In humans, the microRNA pathway and RNAi-related chromatin silencing are probably the main concerns. The microRNA pathway is actually the main reason for off-targeting in RNAi experiments, and I have outlined potential strategies about how to selectively engage RNAi and not the microRNA pathway in earlier posts. Silencing chromatin through the introduction of small RNAs in human cells, however, is much more controversial. Even if we assume that this pathway does exist, then according to published papers you would probably need more than one small RNA targeting the same gene. Moreover, one would likely have to introduce small RNAs targeted to the promoter region and not the transcribed gene as siRNAs do in RNAi. A possibly related interesting phenomena that was reported recently is RNA activation, or RNAa. In these examples small RNAs targeted to certain promoters actually upregulated gene activity. It is clear, however, that not any small RNA will have this effect, and again siRNAs targeted towards the transcribed genes are not likely to result in promoter activation.
Alone from the fact that there are 4 Argonaute genes and additional related Piwi genes, and new classes of small RNAs being discovered on almost a monthly basis, one can expect the RNAi-related universe to expand ever more. However, largely based on microarray studies, it seems that exogenous small RNAs almost exclusively engage the RNAi machinery and the related microRNA pathway. It is therefore a focus on the microRNA pathway that is most likely to ultimately improve the specificity of RNAi Therapeutics.
Disclaimer: This blog is not intended for distribution to or use by any person or entity who is a citizen or resident of, or located in any locality, state, country or other jurisdiction where such distribution, publication, availability or use would be contrary to law or regulation or which would subject the author or any of his collaborators and contributors to any registration or licensing requirement within such jurisdiction. This blog expresses only my opinions, they may be flawed and are for entertainment purposes only. Opinions expressed are a direct result of information which may or may not be accurate, and I do not assume any responsibility for material errors or to provide updates should circumstances change. Opinions expressed in this blog may have been disseminated before to others. This blog should not be taken as investment, legal or tax advice. The investments referred to herein may not be suitable for you. Investments particularly in the field of RNAi Therapeutics and biotechnology carry a high risk of total loss. You, the reader must make your own investment decisions in consultation with your professional advisors in light of your specific circumstances. I reserve the right to buy, sell, or short any security including those that may or may not be discussed on my blog.