Targeting Myeloma Cell-Derived Runx2 By Mirnas Suppresses Multiple Myeloma Growth And Progression

In Multiple myeloma (MM), abnormal plasma cells accumulate in the bone marrow and spread to new bone sites. However, the mechanisms underlying this spread of MM cells remain unclear. Runx2 is a bone specific transcription factor upregulated in various human tumors, including MM. Our studies have previously demonstrated that Runx2 is a major driver of MM progression in bone. In the present study, our goal was to identify miRNAs targeting Runx2 to reduce tumor growth and dissemination of MM to new bone sites and asses their therapeutic potential. Expression analysis of a panel of miRNA9s regulating Runx2 revealed an inverse relationship between Runx2 expression and two miRNAs: miR-342 and miR-363. miRNA expression analysis using the Gene Expression Omnibus database showed that miR-342 and miR-363 are highly expressed in plasma cells of normal donors (n= 3), while Runx2 is detected at very low levels. In contrast, MM cells of patients with newly diagnosed (n=23) and relapsed MM (n=17) expressed very little miR-342 and miR-363 but showed high levels of Runx2 expression. Reconstituting CAG human MM cells with synthetic miR-342, miR-363 or miR-342+miR-363 in combination reduced the expression of Runx2 and the metastasis-promoting Runx2 target genes RANKL, DKK1 and DMP1. Tumor cell viability and migration were also decreased compared to control in vitro. We then transfected miR-342, miR-363 or miR-342+miR-363 in mouse 5TGM1 MM cells expressing high levels of Runx2 and tested bone-homing and growth in syngenic C57Bl/KaLwRij mice by intravenous injection. Mouse sera were collected at week 2 and 4 after tumor cell injection and the levels of IgG2bκ, a marker of 5TGM1 cells, were measured by ELISA. The results showed significantly decreased IgG2bκ levels in mice bearing miR-342 or miR-363 transfected tumors compared to mice bearing control miR-scramble tumors. Additionally, miR-342+miR-363 co-transfection produced a synergistic effect on reducing tumor growth. Mechanistic studies demonstrated that miR-342 and miR-363 induced Runx2 suppression, results in inhibition of Runx2-downstream signaling pathways Akt/β-catenin/survivin, which are required for MM tumor progression. In conclusion, we have identified two novel miRNAs, miR-342 and miR-363, that negatively regulate Runx2 expression in MM cells. We further demonstrated that enhanced expression of miR-342 or miR-363 in MM cells inhibits MM growth in vivo. Thus, miR-342 and miR-363 are potential novel markers of MM prognosis and can be developed as new therapeutic drugs for MM treatment. Citation Format: Pramod S. Gowda, Mohammad Q. Hassan, Timothy N. Trotter, Yang Yang. Targeting myeloma cell-derived runx2 by miRNAs suppresses multiple myeloma growth and progression [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 2525. doi:10.1158/1538-7445.AM2017-2525