Locked Nucleic Acid Oligonucleotides Facilitate RNA•LNA-RNA Triple-Helix Formation and Reduce MALAT1 Levels

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and multiple endocrine neoplasia-beta (MEN beta) are two long noncoding RNAs upregulated in multiple cancers, marking these RNAs as therapeutic targets. While traditional small-molecule and antisense-based approaches are effective, we report a locked nucleic acid (LNA)-based approach that targets the MALAT1 and MEN beta triple helices, structures comprised of a U-rich internal stem-loop and an A-rich tract. Two LNA oligonucleotides resembling the A-rich tract (i.e., A9GCA4) were examined: an LNA (L15) and a phosphorothioate LNA (PS-L15). L15 binds tighter than PS-L15 to the MALAT1 and MEN beta stem loops, although both L15 and PS-L15 enable RNA center dot LNA-RNA triple-helix formation. Based on UV thermal denaturation assays, both LNAs selectively stabilize the Hoogsteen interface by 5-13 degrees C more than the Watson-Crick interface. Furthermore, we show that L15 and PS-L15 displace the A-rich tract from the MALAT1 and MEN beta stem loop and methyltransferase-like protein 16 (METTL16) from the METTL16-MALAT1 triple-helix complex. Human colorectal carcinoma (HCT116) cells transfected with LNAs have 2-fold less MALAT1 and MEN beta. This LNA-based approach represents a potential therapeutic strategy for the dual targeting of MALAT1 and MEN beta.