OAB-029: Bone marrow adipocytes induce metabolic reprogramming of multiple myeloma cells

Abstract

<h3>Background</h3> Obesity-induced increases in bone marrow adipocyte (BMAd) numbers and volume are associated with an increased risk of MM. However, the associated molecular mechanisms have remained largely unknown. We hypothesize that BMAd support MM cells through metabolic reprogramming. <h3>Methods</h3> BM aspirates of MGUS, SMM, and NDMM patients were used to obtain mature BMAd or stromal cells (BMSCs). Murine BMSC cell-line OP9, MM cell-line 5TGM1, and human-origin MM cell-lines MM.1S, OPM2 were obtained from ATCC. Cell proliferation was assessed by CyQUANT Assay; lipolysis by Lipolysis Assay (Sigma); lipid uptake by flow cytometry (FCM) of fluorescent fatty acids (FA) BODIPY-C12 and -C16, or LipidTox. In-vivo efficacy of FA treatment was assessed in a MM CB17 SCID mouse plasmacytoma model. <h3>Results</h3> In-vitro co-culture revealed that BMSC-derived adipocytes (Ad) from MGUS/SMM and NDMM donors significantly increased the proliferation of MM.1S MM cells. Similarly, mature murine OP9 Ad cells also increased the proliferation of 5TGM1 murine MM cells. Interestingly, co-cultures showed dramatic decrease in LipidTox-stained lipid-droplet size distribution, suggesting increased lipolysis in Ad, further confirmed by increased glycerol content in conditioned media in the presence of MM cells. Moreover, BMAd from MGUS, SMM, and NDMM patients showed increased expression of genes responsible for lipolysis (NR1H3) and increased FA desaturation (SCD1, FASD2). Although MM cells lacked intracellular lipid storage, OPM2 and 5TGM1 MM cells rapidly took up BODIPY-C12 and -C16 FAs. The FA secreted from Ad were directly taken up by MM cells as shown by transfer of LipidTox-labeled lipids from OP9 Ad to unstained 5TGM1 or OPM2 MM cells as assessed by FCM. The addition of acipomox, a small-molecule inhibitor of lipolysis, decreased LipidTox signal in MM cells compared to untreated OP9 cells. FA are transported into cells through FATP (1-6) or CD36 receptors. Bioinformatics analysis of public Oncomine database showed that FATP1 and FATP4 were highly expressed in 21 human MM cell lines. MM cells from NDMM patients expressed high levels of FATP1 and FATP4. The uptake of BODIPY-C12 and -C16 by 5TGM1 or OPM2 MM cells was significantly reduced in the presence of Lipofermata, a pharmacological small-molecule inhibitor of FATP. Lipidomic analysis of BM aspirates from MM patients showed altered expression of various FA, including arachidonic acid (AA). Low doses of AA (0.125 - 2 µM) increased the proliferation and viability of MM cells whereas high doses (25- 100µM) dramatically decreased it, indicating a bimodal cellular effect of AA. Peritumoral AA treatment in a plasmacytoma model decreased tumor volume significantly. <h3>Conclusion</h3> We show that MM cells induce lipolysis in BMAd and that the released FFA are then taken up by MM cells through FATPs. Inhibition of either BMAd lipolysis or FFA transporter into MM cells could be a potential novel strategy to prevent MM progression.