Abstract 2123: Myeloma derived macrophage inhibitory factor regulates BMSC IL6/8 via cMYC

Abstract

Abstract Background Multiple Myeloma (MM) is a plasma cell malignancy dependent on the bone marrow microenvironment. Macrophage inhibitory factor (MIF) acts directly on malignant plasma cells affecting homing and chemotherapy resistance, however the adaptive effect that MM derived MIF has on the tumor microenvironment is not yet defined. Here we investigate the function of MM derived MIF in the MM microenvironment by examining its effects on bone marrow mesenchymal stromal cells (BMSC). Methods Primary MM and BMSC were obtained from patient bone marrow. Proteome Profiler Human XL Cytokine Array was used. Inhibitors including JQ1 were purchased from Merck. In-vivo experiments were performed using 8-10 week old NSG mice. Results First we injected 1 x 106 MM.1S MIF-knock down (KD) cells or MM.1S control-KD cells (containing the pCDH-luciferase-T2A-mCherry construct) into the tail vein of 6-8 week old NSG mice. MIF-KD in MM cells resulted in animals with significantly reduced tumor burden and improved overall survival. To further investigate the role of MIF in regulating the BM microenvironment we stimulated primary human BMSC with biologically appropriate doses of recombinant MIF and then used Human XL Cytokine Array and cytokine specific ELISA to assay the supernatant from these MIF stimulated BMSC. Results show that MIF induces IL-6 and IL-8 protein secretion from primary BMSC. To examine the mechanism of action of these observations we used a panel of inhibitors to screen for potential pathways responsible for MIF induced BMSC derived IL-6 and IL-8 expression. The c-Myc inhibitor JQ1 inhibited MIF induced IL-6 and IL-8 expression. Next, we looked at whether c-Myc regulates BMSC pro-tumoral interleukin production in-vivo. We injected NSG mice via the tail vein with human myeloma cell line U266 and then randomized animals to two groups; treating with either JQ1 (50mg/kg, IP) or alternatively vehicle control for 5 days, after which bloods were taken to assess murine IL-6 levels (IL-8 is deleted from the mouse genome). Results show that murine IL-6 was significantly reduced in the JQ1 treated animals (carrying human MM) compared to vehicle control treated animals. Summary MM derived MIF is pro-tumoral through induction of c-Myc and downstream IL-6 and IL-8 in the BMSC of the tumor micro-environment. Identification of this novel pro-tumoral crosstalk mechanism which exists between MM and the bone marrow stroma provides scientific rationale for the clinical evaluation of new therapeutic targets in MM. Citation Format: Rachel E. Piddock, Christopher R. Marlein, Amina Abdul-Aziz, Martin J. Auger, Kristian M. Bowles, Stuart A. Rushworth. Myeloma derived macrophage inhibitory factor regulates BMSC IL6/8 via cMYC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2123.