Each Mission® synthetic and lentiviral microRNA inhibitor is designed for the long-term suppression of any miRNA endogenous to humans or mice, using an algorithm that evaluates all possible sequences for the design predicted to best maintain the Tough Decoy (TuD) structure, which can help with miRNA recognition and binding. TuD RNAs are double-stranded. This, along with a stem-loop, stabilized secondary structure, can resist cellular nuclease degradation and facilitate sustained miRNA inhibition for over one month. In addition, both strands of a TuD RNA contain a miRNA binding site for good sequestration of target miRNAs at low, nanomolar concentrations.