PNA-based RNA-triggered drug-releasing system.

A three-component sequence-specific RNA-triggered drug-releasing system is described that consists of an 8-mer PNA linked to a coumarin ester (the prodrug component) and a 14-mer PNA linked to histidine (the catalytic component) that are complementary to the C loop of E. coli 5S rRNA (the triggering component). Binding of the catalytic component to the RNA creates a prodrug-metabolizing enzyme that catalyzes a 60,000-fold acceleration in the rate of coumarin release from the prodrug compared to the rate of coumarin release from the ester subunit catalyzed by imidazole alone. RNA-triggered release of hydroxycoumarin is only slightly less efficient than that triggered by a short unfolded DNA sequence corresponding to the PNA binding sites. The lower efficiency results from a decrease in k(cat) and an increase in K(M), presumably due to the bent nature of the RNA. The efficiency of DNA-triggered hydroxycoumarin release was found to depend on the distance between the catalytic and prodrug components.