Abstract 2387: Pre-adipocytes promote myeloma homing to and growth in bone by secretion of soluble molecules

Multiple myeloma (MM) is a hematologic malignancy of plasma cells that thrives in and metastasizes throughout the bone marrow microenvironment. This microenvironment is host to a variety of cell types, including osteoblasts, osteoclasts and stromal cells, that become altered both at the primary tumor site and distant bone sites to support the growth and spread of MM cells. We recently reported that under certain conditions, such as when MM cells overexpress heparanase, MM cells redirect osteoblast progenitors from osteoblastogenesis towards adipogenesis. In addition, adipocytes naturally accumulate in aging marrow and adipocytes/adipose tissues have endocrine functions, secreting soluble factors such as adiponectin and leptin. Thus, adipocytes have the potential to be influential on MM cell behavior. Here, we hypothesized that adipocytes play an active role in MM progression through the secretion of soluble molecules that promote MM growth and metastasis to bone. To test this we used a co-culture system in which 3T3-L1 mouse pre-adipocytes or mature adipocytes were separated by a porous membrane from 5TGM1 mouse MM cells, allowing cross-talk by secreted molecules but not direct cell-cell contact. We then tested the motility of these “educated” 5TGM1 MM cells by migration assay. Somewhat surprisingly, we found that it was not mature adipocyte but pre-adipocyte education that enhanced the migration ability of MM cells compared to MM cells cultured alone. In a separate experiment, we injected 5TGM1 MM cells cultured alone, with pre-adipocytes, or with mature adipocytes into syngeneic C57BL/KaLwRij mice via tail vein and monitored progression by bioluminescent imaging. Total tumor burden was evaluated by IgG2bκ (a soluble marker of 5TGM1 MM cells) levels in mouse serum. Compared to MM cells cultured alone, those cultured with pre-adipocytes homed to the bone sooner and grew faster whereas those cultured with mature adipocytes showed no difference in homing or growth. To identify factors that may contribute to this apparent difference, pre-adipocyte or mature adipocyte conditioned media (CM) was analyzed using a cytokines/chemokines array. The results showed that pre-adipocytes secrete significantly larger quantities of molecules HGF, MCP-1 and IL-6 than mature adipocytes. Additional migration assays also confirmed that MM cells migrate more towards pre-adipocyte CM than to fresh media alone or mature adipocyte CM. In conclusion, this study demonstrates that pre-adipocytes, through the secretion of a variety of soluble molecules, promote a more aggressive phenotype in MM cells and contribute to MM growth and bone homing. Citation Format: Timothy N. Trotter, Patrick D. Rowan, Qianying Pan, Yang Yang. Pre-adipocytes promote myeloma homing to and growth in bone by secretion of soluble molecules. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2387. doi:10.1158/1538-7445.AM2015-2387