Biological and Therapeutic Potential of Mir-155, 585 and Let-7f in Myeloma in Vitro and In Vivo.

Abstract 833 A growing body of evidence suggests that the genome of a many organisms, particularly mammals is controlled not only by transcription factors but also by post-transcriptional programs that are modulated by the family of small RNA molecules including microRNAs (miRs). miRs can block mRNA translation and affect mRNA stability. We have evaluated profiles of 384 human miRs in CD138+ cells from 79 patients with multiple myeloma (MM), 11 MM cell lines and 9 healthy donors (HD) using qRT-PCR based microRNA array. This analysis has identified a MM specific miRNA signature that significantly correlates with OS (p=0.05) and EFS (p=0.017) of patients. Based on this signature one group of patients clustered with HD suggesting indolent disease while other with cell lines indicating aggressive disease. We identified significant modulation of expression of 61 microRNAs in MM cells compared to normal plasma cells. Specific miRs with established oncogenic and tumor suppressor functions such as miR-155, miR-585 and Let7-f were significantly dysregulated in MM (p<0.001). Modulation of miRs-155, -585 and Let7 were observed most frequently in the group of patients with poor OS and EFS suggesting their crucial role in MM. However biological role of these miRs have not yet been defined. To further evaluate biological function of these most recurrent miRs in MM, we evaluated role of miR-155, let-7f and mir-585 in MM cell lines by gain- and loss- of function experiments. We used locked nucleic acid (LNA) anti-miR probes for loss of function and pre-miR-155 for gain of function studies using them alone or in combination. Although manipulation of all 3 miRs induced 20-25% change in MM cell proliferation and/or induction of apoptosis, combination of anti-miR-let7f with pre-miR-155, and anti-miR-585 in combination with miR-155 had dramatic effects on MM cell proliferation and over 60% cells undergoing apoptosis. To evaluate the targets of these miRs, we have determined effects of these anti-miRs and pre-miR on global gene and miR expression profile in MM alone and in combinations. This analysis identified modulation of cluster of miRs as well as genes critical for cell growth and survival. Next, we have tested efficacy of these miRs in vivo in murine Xenograft model to evaluate their therapeutic potential. Tumor-bearing mice were treated intraperitoneal for four consecutively days with the LNA anti-miR-585 and Let-7 and pre-miR-155 probes and respective controls alone and in combination. We observed that the single LNA anti-miR-585 and let 7 and pre miR-155 treatment reduced tumor size by 36%, 31% and 155% in animal 7 days after treatment. However, significant tumor size reductions were achieved when animals were treated with combinations; anti-miR-Let 7f plus pre-miR-155 (58 %); LNA anti-miR-Let 7f plus LNA anti-miR-585 (56 %); LNA-anti-miR-585 plus pre-miR-155 (74 %).We did not observe any significant systemic toxicity in the animals. In conclusion our results suggest significant biological role for miR-585, let 7f and miR-155 in myeloma, both in vitro and in vivo; it highlights for the first time a concerted activity of combination of miRs and holds a great promise for developing novel therapeutic approach for myeloma. Disclosures: No relevant conflicts of interest to declare.