Specificity of antisense oligonucleotides in vivo

Antisense oligonucleotides are widely used as inhibitors of gene expression in cultured cells and have been proposed as potential therapeutic agents, but it is not known to what extent they are specific for their intended target RNAs. Statistical considerations indicate that if oligonucleotides can form hybrids with mRNA molecules in vivo by means of short or imperfect regions of complementarity, then the specificity of oligonucleotides as antisense reagents will be greatly compromised. We have used Xenopus oocytes as a model system in which to investigate the potential specificity of antisense oligonucleotides in vivo. We injected perfect and partially matched antisense oligonucleotides into oocytes and measured the resulting degradation of the target RNA in each case. On the basis of the extent to which antisense oligonucleotides can cause cleavage of RNAs at imperfectly matched target sites, we conclude that in this system it is probably not possible to obtain specific cleavage of an intended target RNA without also causing at least the partial destruction of many nontargeted RNAs.