High levels of apoptosis induced in human glioma cell lines by combined treatment with antagomiR PNAs and pre-miRNA molecules

Peptide nucleic acids (PNAs) are artificially synthesized RNA or DNA analogues with a N-(2-aminoethyl)glycine unit backbone without the sugar-phosphate. These molecules are very interesting because of their capability of forming Watson-Crick double helices despite a radical structural change with respect to DNA and RNA. They can hybridize efficiently to complementary DNA- and RNA-specific sequences. For this reason, they have been proposed as useful tools for the alteration of gene expression. Forced interactions between PNAs and microRNAs have been recently found to alter biological functions. MicroRNAs are non-coding RNA molecules, around 22 nucleotides long, with a regulatory activity on gene translation or a generation of cleaved target RNA transcripts. Among the possible microRNA targets involved in cancer, the cluster miR-221/222 plays a very important role and is responsible for strong anti-apoptotic effects. On the other hand, miR-124-3p has been demonstrated to be a strong pro-apoptotic molecule. In order to induce apoptosis, the human glioma cell lines U251 and T98G were treated with pre-miR-124-3p together with PNAs targeting miR-221 and miR-222 (R8-PNA-a221 and R8-PNA-a222, bearing a oligoarginine peptide R8 to facilitate cell uptake). The effects of this combined treatment were analyzed looking at (a) the rate of cell growth, (b) caspase 3/7 cascade activation and (c) annexin 5 assay. The results obtained clearly indicate a potentiation of the pro-apoptotic effects using a combined treatment of glioma cell lines with pre-miR-124-3p and PNA-base antagomiR-221 and antagomiR-222. In conclusion, combined treatments with pre-miRNA and antagomiR molecules may be taken into consideration in order to achieve an efficient outcome in miRNA therapeutics of cancer diseases including gliomas.