In vitro selection of RNA-based irreversible inhibitors of human neutrophil elastase Original Research Article

Introduction: We describe a new approach to drug discovery which joins the technologies of medicinal and combinatorial chemistry, allowing selection of the most active variant of a lead compound from a large (>1012) pool. A small-molecule covalent inhibitor of elastase was coupled to a randomized pool of RNA, and this assembly was iteratively selected for oligonucleotide sequences that promote the covalent reaction of the inhibitor with the human neutrophil elastase (hNE) active site. Results: Incorporation of the covalent inhibitor into the randomized pool increases the second-order rate of inactivation of hNE by ∼-15-fold; sequences selected from this pool show an additional ∼-20-fold increase in activity. The relative rate of cross-reaction with another serine protease, cathepsin G, was reduced >100-fold. Low doses of the inhibitor were found to prevent lung damage inflicted by human neutrophils in an isolated rat lung model of acute respiratory distress syndrome (ARDS). Conclusions: This result supports the hypothesis that neutrophil elastase is a significant effector of inflammatory disease. More generally, our findings demonstrate that blending small molecules into combinatorial libraries is a feasible method of drug discovery.