Drugging the lncRNA MALAT1 via LNA gapmeR ASO inhibits gene expression of proteasome subunits and triggers anti-multiple myeloma activity

The biological role and therapeutic potential of long non-coding RNAs (lncRNAs) in multiple myeloma (MM) are still to be investigated. Here, we studied the functional significance and the druggability of the oncogenic lncRNA MALAT1 in MM. Targeting MALAT1 by novel LNA-gapmeR anti-sense oligonucleotide antagonized MM cell proliferation and triggered apoptosis both in vitro and in vivo in a murine xenograft model of human MM. Of note, antagonism of MALAT1 dowmodulated the two major transcriptional activators of proteasome subunit genes, namely NRF1 and NRF2, and resulted in reduced trypsin, chymotrypsin and caspase-like proteasome activities and in accumulation of polyubiquitinated proteins. NRF1 and NRF2 decrease upon MALAT1-targeting was due to transcriptional activation of their negative regulator KEAP1, and resulted in reduced expression of anti-oxidant genes and increased ROS levels. In turn, NRF1 promoted MALAT1 expression thus establishing a positive feedback loop. Our findings demonstrate a crucial role of MALAT1 in the regulation of the proteasome machinery, and provide proof-of-concept that its targeting is a novel powerful option for the treatment of MM. A proprietary custom annotation pipeline of microarray data on lncRNA expression in different plasma cell (PC) dyscrasias, including 20 MGUS, 33 smoldering MM, 170 MM, 36 PC leukemia patients and 9 healthy donors, revealed high expression of MALAT1 in MM PCs [GSE66293]. On this finding, we investigated the functional significance of MALAT1 by using novel 16-mer LNA gapmeR synthetic ASOs, that trigger selective RNAse-H dependent degradation of MALAT1, in MM.1S and RPMI-8226 human myeloma cell lines.