**6.5 miRNA mimics**

In addition to miRNA inhibition as a major miRNA therapeutic approach, miRNA replacement treatment with miRNA mimics should be another miRNA therapeutic approach in disease associated with decreased miRNAs expressions. Synthetic miRNA mimics can assume the regulatory role of natural miRNAs. In diseases such as cancer, some tumor suppression-related miRNAs are downregulated. Therefore, artificial double-stranded miRNA (miRNA mimic) has been introduced to inhibit cancer [48]. Recent studies have reported that miRNA-34 is a master regulator of tumor suppression and a well-defined miRNA tumor suppressor [49]. It acts on several cancer relevant cellular pathways, including the p53 and wnt/βcatenin pathways. Down-regulation of miR-34 expression has been found in many tumor types, including lung, liver, breast, and colon carcinoma, and treatment with miR-34 mimic has been shown to inhibit tumor growth and progression [49, 50]. Consequently, miR-34 mimic, the first miRNA replacement therapy, is headed to the clinic for treatment of cancer [49, 50]. Replacement of oncosuppressor miRNAs with their mimics provides an effective strategy against cancer.
