Alternative to RNAi

Ian A. York iayork at
Thu Mar 20 07:09:19 EST 2003

In article <005601c2eed2$38e3ef00$1e93a8c0 at>,
Peter Cherepanov <peter.cherepanov at> wrote:
>Concerning non-viral delivery of siRNA - I am pretty sure it is possible.
>But why not liposomes? You only need to deliver siRNA to cytoplasm, right?

Liposomes (and other transfection reagents) are the usual way of 
delivering siRNA.  The virus approaches are quite new, and are based on 
delivery of a DNA vector that expresses a hairpin RNA, which can be 
processed into a double-stranded small RNA, i.e. a siRNA.  Of course, you 
can get the same results using a plasmid vector and stable transfection 
(and in fact we have got that--yesterday I screened a bunch of clones and 
found that the system works for at least two genes, which are entirely 
undetectable in the screening assay).  (These are published systems, 
although of course everyone including us tweaks them a little.)  

These systems work very well for cells in culture.  The original concern
was that siRNA was of little use because of the difficulty in delivery to
an intact animal, meaning that therapeutic use will be difficult.  As I
say, that's not really the point--you could equally say that, for example,
knockout mice are useless because the technology isn't useful for therapy.  

The viral approaches, with their relatively high efficiency of 
incorporation, are being tested in intact animals.  There are other 
approaches that also might work in animals.  In general this would present 
exactly the same challenges as gene therapy, and the same general 
approaches are being tried.  One possible advantage of siRNA is that the 
delivery of the short RNA (and of short nucleic acid oligos in general) is 
much more efficient than plasmid transfection; we routinely achieve over 
95% transfection efficiency with siRNA, but are pleased to get 50% with 
plasmids, in culture.  

    Ian York   (iayork at  <>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England

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