Abstract
Background & AimThe miR-221/222 cluster is upregulated in malignant plasma cells from multiple myeloma (MM) patients harboring the t(4;14) translocation. We previously reported that silencing of miR-221/222 by an antisense oligonucleotide induces anti-MM activity and upregulates canonical miR-221/222 targets. The in vivo anti-tumor activity occurred when miR-221/222 inhibitors were delivered directly into MM xenografts. The aim of the present study was to evaluate the anti-MM activity of a novel phosphorothioate modified backbone 13-mer locked nucleic acid (LNA)-Inhibitor-miR-221 (LNA-i-miR-221) specifically designed for systemic delivery.Methods In vitro anti-MM activity of LNA-i-miR-221 was evaluated by cell proliferation and BrdU uptake assays. In vivo studies were performed with non-obese diabetic/severe combined immunodeficient (NOD.SCID) mice bearing t(4;14) MM xenografts, which were intraperitoneally or intravenously treated with naked LNA-i-miR-221. RNA extracts from retrieved tumors were analyzed for miR-221 levels and modulation of canonical targets expression. H&E staining and immunohistochemistry were performed on retrieved tumors and mouse vital organs.Results In vitro, LNA-i-miR-221 exerted strong antagonistic activity against miR-221 and induced upregulation of the endogenous target p27Kip1. It had a marked anti-proliferative effect on t(4;14)-translocated MM cells but not on MM cells not carrying the translocation and not overexpressing miR-221. In vivo, systemic treatment with LNA-i-miR-221 triggered significant anti-tumor activity against t(4;14) MM xenografts; it also induced miR-221 downregulation, upregulated p27Kip1 and reduced Ki-67. No behavioral changes or organ-related toxicity were observed in mice as a consequence of treatments.ConclusionsLNA-i-miR-221 is a highly stable, effective agent against t(4;14) MM cells, and is suitable for systemic use. These data provide the rationale for the clinical development of LNA-i-miR-221 for the treatment of MM.
Highlights
MicroRNAs are short non-coding RNAs that are highly deregulated in multiple myeloma (MM) cells [1,2,3]
We previously demonstrated that silencing of miR-221/222 with an antisense oligonucleotide (ASO) inhibits proliferation of t(4;14) MM cells in vitro and significantly slows the tumor growth in xenografted non-obese diabetic/severe combined immunodeficient (NOD.SCID) mice [15]
In vitro Silencing of miR-221 by locked nucleic acid (LNA)-i-miR-221 To evaluate the anti-tumor potential of the novel 13-mer inhibitor, LNA-i-miR-221, we first verified that it effectively knocked down miR-221 function in MM cells cultured in vitro
Summary
MicroRNAs (miRNAs) are short non-coding RNAs that are highly deregulated in multiple myeloma (MM) cells [1,2,3]. 29b [13,14] mimics as well as miR-221/222 [15] and miR-21 [16] inhibitors were found to be promising anti-MM therapeutic agents when delivered in vitro and in vivo. Among these miRNAs, the miR-221/222 cluster is of particular interest for translational approaches in MM. The aim of the present study was to evaluate the anti-MM activity of a novel phosphorothioate modified backbone 13-mer locked nucleic acid (LNA)-Inhibitor-miR-221 (LNA-i-miR221) designed for systemic delivery
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