The Exosomal Transfer of Acid Sphingomyelinase Contributes to Drug Resistance in Multiple Myeloma

• Published in: Blood 2019-11, Vol.134 (Supplement_1), p.3058-3058
• Main Authors: Oudaert, Inge, Faict, Sylvia, D'Auria, Ludovic, Dehairs, Jonas, Maes, Ken, Vlummens, Philip, Jacobs, Lotte, De Veirman, Kim, De Bruyne, Elke, Fostier, Karel, Vande Broek, Isabelle, Schots, Rik, Vanderkerken, Karin, Swinnen, Johannes V., Menu, Eline
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2019-122857

Introduction Multiple myeloma (MM) is well-known for the development of drug resistance, leading to the need for multiple treatment lines at times of relapse or progression. Even then, most patients ultimately will succumb to this cancer. Therefore, there is a need for new therapeutic strategies to conquer this drug resistance. Lipidomics has recently gained more attention in the search for new cancer therapies. Lipids are mainly found in biological membranes and function as building blocks, but are also important metabolites that can influence energy, structure and signaling cascades. Lipid dysfunction has been correlated to other cancers, like prostate and breast cancer. In this study, we identified changes in lipid content in MM patients and further investigated this altered metabolism in vitro. Methods We performed a lipidomics assay to compare plasma from healthy volunteers to MM patients. For all in vitro experiments, we used four human MM cell lines (JJN3, OPM2, LP1, U266) and primary CD138+ patient samples, isolated by MACS. Differential mRNA expression (SMPD1 = acid sphingomyelinase, ASM) was measured by qRT-PCR and ASM protein levels by western blot. Exosomes were isolated by exoquick, while changes in secretion were measured by nanoparticle tracking analysis. Viability was measured by CellTiter Glo and apoptosis rates for melphalan, bortezomib and ASM inhibitor (amitriptyline) were measured by flow cytometry (annexinV-FITC/7-AAD staining). Drug efficacy of amitriptyline was also confirmed on primary CD138+ samples by CellTiter Glo. Results Lipidomics analysis revealed an increase in ceramides and a decrease in sphingomyelin. Therefore, we believe that the enzyme sphingomyelinase, which converts sphingomyelin into ceramide, is upregulated in MM, which we confirmed on primary CD138+ MM cells for ASM. We also observed an increase in SMPD1 expression by qRT-PCR and ASM levels by western blot after melphalan and bortezomib treatment. Furthermore, we also investigated effects of these drugs on exosome secretion, where we found an increase in the number of exosomes secreted, as well as higher ASM levels in these exosomes. U266-derived exosomes, containing high amounts of ASM, were able to transfer their resistance to ASM-low JJN3 cells as an increase in viability was measured. Inhibition of ASM by amitriptyline, combined with melphalan and bortezomib, increased apoptotic cell death by upregulating cleaved PARP and caspase 3 levels. Combination therapy