Predicting antisense oligonucleotide inhibitory efficacy: a computational approach using histograms and thermodynamic indices.

Antisense oligonucleotides (ASOs) are designed to bind to a specific mRNA and selectively suppress its translation. To facilitate selection of optimal ASO targets, we have developed three thermodynamic indices to evaluate putative structural complexes important in ASO action. These indices are: a secondary structure score (Sscore), which estimates the strength of local mRNA secondary structures at the ASO target site; a duplex score (Dscore), which estimates the delta Gformation for the ASO:mRNA target sequence duplex; and a competition score (Cscore), which is the difference between the Dscore and the Sscore. We also present two histograms to graphically display these indices from different regions of the mRNA. The indices are compared to the inhibition reported in five studies of ASO-mediated suppression of gene expression. The Dscore is the most consistent predictor of ASO efficacy in four of the five studies (r2 from 0.44 to 0.99), while the results of the fifth study could not be predicted by any thermodynamic or physical index. Thus the Dscores and their histogram may prove useful in selection of ASO targets.