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The design of modified oligonucleotides that combine in one molecule several therapeutically beneficial properties still poses a major challenge. Recently a new type of modified mesyl phosphoramidate (or µ-) oligonucleotide was described that demonstrates high affinity to RNA, exceptional nuclease resistance, efficient recruitment of RNase H, and potent inhibition of key carcinogenesis processes in vitro. Herein, using a xenograft mouse tumor model, it was demonstrated that microRNA miR-21-targeted µ-oligonucleotides administered in complex with folate-containing liposomes dramatically inhibit primary tumor growth via long-term down-regulation of miR-21 in tumors and increase in biosynthesis of miR-21-regulated tumor suppressor proteins. This antitumoral effect is superior to the effect of the corresponding phosphorothioate. Peritumoral administration of µ-oligonucleotide results in its rapid distribution and efficient accumulation in the tumor. Blood biochemistry and morphometric studies of internal organs revealed no pronounced toxicity of µ-oligonucleotides. This new oligonucleotide class provides a powerful tool for antisense technology.

Original publication




Journal article


Proc Natl Acad Sci U S A

Publication Date





32370 - 32379


DNA modification, antisense oligonucleotide, mesyl oligonucleotide, oncogenic microRNA, phosphorothioate, Amides, Animals, Antineoplastic Agents, Cell Line, Tumor, Gene Expression Regulation, Neoplastic, Male, Melanoma, Mice, SCID, MicroRNAs, Molecular Targeted Therapy, Oligonucleotides, Antisense, Phosphoric Acids, Tissue Distribution, Xenograft Model Antitumor Assays