interesting comments on RNAi vs. 'antisense' from Sequitur (thank to tuck for the link).
dddmag.com
...RNAi was believed to be a hundred or even a thousand times more active than antisense technology, says Woolf. But Sequitur has not found that to be the case using published siRNA constructs. "We found the activity to be comparable to our antisense oligos," says Woolf. "However, we found the reduction in toxicity to be dramatic because there are no modifications, no phosphorothioate modifications in particular, in the RNAi compounds." This is especially important because toxic effects can confound phenotypic readouts. Sequitur's blocking oligos lack phosphorothioate and are nontoxic, but they are more difficult to work with than RNAi, says Woolf. "So RNAi has essentially taken over," he says.
The persistence of RNAi
Another advantage of RNAi, says Woolf, is that the effect persists for quite a long time depending on the nature of the cells being studied. Whereas antisense technology generally works for 1 to 3 days, gene expression can remain suppressed for 3 to 7 days following RNAi treatment. "That's another advantage in terms of toxicity," says Woolf, "because you don't have to retransfect."
Interestingly, inhibition of gene expression seems to endure even after the transfected siRNA has disappeared from the cells, which happens in 24 hours according to preliminary evidence gathered at Sequitur. "This suggests that RNAi may indeed be more potent than antisense," says Woolf.
Potency is an especially important consideration for therapeutic applications of RNAi, which Sequitur is also currently focusing on. The margin between toxicity and specific effect might be enhanced through stabilization of the native dsRNA. "We do have some stabilized RNAi constructs that seem to be working even better," says Woolf.
Delivered in vivo , RNAi has therapeutic potential in addition to serving as a tool for target validation. Like antisense oligonucleotides, stabilized RNAi should eventually get into the cell, says Woolf. Rather than delivering free RNAi, it can be encapsulated in lipid-based intracellular delivery systems. It is also possible to deliver a vector expressing the RNAi. With an in vitro system, RNAi is simply transfected via cationic lipids into cultured cells that constitute a disease model... |
