Development of hammerhead ribozymes targeting miR-21

The object of the invention are hammerhead ribozymes directed against the sequence of miR-21 and /or miR-21 precursors, having the ability to specifically cleave miR-21 and /or miR- 21 precursors, and wherein they have acatalytic core with a sequence as shown in SEQ ID No 1. The invention also relates to a composition comprising such ribozymes, a therapeutic agent comprising them, a use of such ribozymes and a method of selective cleavage of miR-21 and /or 1 miR-21 precursors employing such ribozymes.