Abstract 2550: Anti-MALAT1 synthetic oligonucleotides target the proteasome and exert anti-multiple myeloma activity

Abstract

Abstract Dysregulation of non-coding RNAs features prominently in the biology of multiple myeloma (MM). However, if short non-coding RNAs have been extensively studied in this malignancy, the role of long non-coding RNAs remains to be elucidated. A custom annotation pipeline of microarray data investigating lncRNA expression in plasma cells from 20 MGUS, 33 smoldering MM, 170 MM, 36 plasma cell leukemia patients, and 9 healthy donors, indicates overexpression of the lncRNA MALAT1 during MM progression. On this finding, we sought to investigate the functional significance of MALAT1 expression in MM by the use of 16-mer LNA-gapmeR synthetic oligonucleotides, that trigger specific RNAse H-dependent degradation of MALAT1. Transfected or gymnotic (naked) anti-MALAT1 gapmeRs decreased MM patients (n=3) and cell lines growth (n=7), triggering ER stress and apoptosis, while spared healthy peripheral blood mononuclear cells. Microarray gene profiling indicates that MALAT1 depletion was associated with modulation of various gene sets, and specifically had a negative impact on genes encoding for 20S proteasome β subunits, such as PSMβ2/4/5 and 7, whose overexpression is linked to proteasome impairment in cancer cells. Down-modulation of PSMβs after anti-MALAT1 gapmeRs exposure was confirmed at protein level and was associated to reduced trypsine, chymotrypsine and caspase-like proteasomal activities and to the accumulation of poly-ubiquitylated species. Consistently, anti-MALAT1 gapmeRs enhanced the in vitro anti-MM activity of the proteasome inhibitor bortezomib in bortezomib-sensitive and resistant MM cells. In vivo, i.p. administration of naked anti-MALAT1 gapmeRs (10 and 25 mg/kg) inhibited the growth of bortezomib-resistant MM xenografts, with no evidence of organ toxicity. Mechanistically, anti-MALAT1-induced PSMβs down-modulation could be ascribed to the inhibition of the transcription factors NRF1-2, which act as positive regulators of PSMSβs transcription. On the other hand, siRNA or pharmacologic inhibition of NRF1 by all-trans retinoic acid decreased promoter activity and expression of MALAT1, indicating the occurrence of a feedback loop involving MALAT1 and NRF1. Collectively, our data indicate that MALAT1-targeting represents a promising strategy to dampen aberrant proteasome activity in MM cells, and provide the preclinical rationale to use oligonucleotide therapeutics as anti-MALAT1 gapmeRs for MM treatment. Citation Format: Maria Angelica Stamato, Nicola Amodio, Eugenio Morelli, Giada Juli, Martina Manzoni, Maria Eugenia Gallo Cantafio, Lavinia Biamonte, Elisa Taiana, Annamaria Gullà, Emanuela Altomare, Francesca Scionti, Daniele Caracciolo, Cirino Botta, Maria Cucè, Mariamena Arbitrio, Maria Teresa Di Martino, Marco Rossi, Antonino Neri, Pierosandro Tagliaferri, Pierfrancesco Tassone. Anti-MALAT1 synthetic oligonucleotides target the proteasome and exert anti-multiple myeloma activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2550. doi:10.1158/1538-7445.AM2017-2550