Chemically modified synthetic microRNA-205 inhibits the growth of melanoma cells in vitro and in vivo.

microRNA (miR)-205 is downregulated and acts as a tumor suppressor in human melanoma cells. Previously, for clinical application, we added aromatic benzene-pyridine (BP-type) analogs to the 3'-overhang region of the RNA-strand and changed the sequences of the passenger strand in the miR-143 duplex. Here, we demonstrated the antitumor effect in vitro and in vivo of miR-205 that was also chemically modified by BP and had altered passenger sequence. In in vitro experiments, transfection with the synthetic miR-205 (miR-205BP/S3) significantly inhibited the growth of human melanoma cells. Exogenous miR-205BP/S3 suppressed the protein expression levels of E2F1 and VEGF, which are validated targets of miR-205-5p, and BCL2, a transcribed molecule of E2F1, as did Pre-miR-205, used as a miR-205 mimic having the wild-type sequence. On the basis of the results of a luciferase activity assay, miR-205BP/S3 directly targeted E2F1, as did Pre-miR-205. However, miR-205BP/S3 was much more resistant to RNase than Pre-miR-205 in fetal bovine serum and to RNase in mice xenografted with human melanoma tissues. In addition, the intratumoral injection of miR-205BP/S3 exhibited a significant antitumor effect compared with the case of control miRNA or Pre-miR-205 in human melanoma cell-xenografted mice. These findings indicate that miR-205BP/S3 is a possible promising therapeutic modality for melanoma.