Upregulation of Lipid Metabolism Modulators in Myeloma Cells Underlines Their Progression in a Supportive Microenvironment and Linking Metabolic Pathways with Growth Signaling

Abstract 329

Accumulating evidence indicate that cellular metabolism and bi-products also play important roles in signaling associated with tumor cell proliferation, cell cycle, survival and drug resistance. The overall goal of the study was to molecularly characterize MM cells grown in the supportive bone marrow (BM) of clinically relevant SCID-hu or SCID-rab models. MM cells from 22 patients were engrafted in experimental animals. Following establishment of the disease as determined by increased production of circulating human immunoglobulins over a period of 2–4 months, MM cells were isolated from the implanted bones and subjected to global gene expression profile (GEP). Based on stringent criteria (e.g. p<0.05, >2 folds) we identified commonly overexpressed or underexpressed genes in post-engrafted MM cells compared to pre-engrafted cells from the same patients. Among the top upregulated genes we identified several factors associated with lipid metabolism including FABP5 (fatty acid-binding protein 5), SCD (stearoyl CoA desaturase 1), FADS1 (fatty acid desaturase 1) and SLC27A5 (a fatty acid transporter). Clinical GEP data of newly diagnosed patients from Total Therapy program at our institute revealed upregulation of these genes in high risk patients. We further sought to unravel the role of SCD in MM since it has been previously implicated in tumorigenesis and specific inhibitors are being developed for clinical use. SCD (encodes SCD1), is a rate-limiting enzyme responsible for synthesis of monounsaturated fatty acids. We hypothesized that while nutrient unsaturated fatty acids sufficiently satisfy requirement of most normal cells, growing MM cells demand higher content of these lipids for formation of new membrane phospholipids and immediate energy; therefore, inhibiting SCD1 may suppress MM cell survival and proliferation. Small-molecule inhibitor of SCD1 (BioVision) suppressed growth of 5 MM lines dose dependently; 72 hours IC50 ranged between 1μM (p<0.0006) and 2.5 μM (p<0.0001). At 1 μM the SCD1 inhibitor reduced MM cell proliferation by 70±4% (p<0.002) using thymidine incorporation assay and increased number of apoptotic MM cells from 10±1% in control cells to 27±8% in SCD1 inhibitor-treated cells (p<0.03), using annexin V/PI flow cytometry analysis. This inhibitor also disrupted cell cycle progression in MM cell lines as determined by flow cytometry analysis of DNA content. The Akt/mTOR and AMPK pathways, albeit opposing functions, are known central integrators of cellular metabolism and proliferation signaling. SCD1 inhibitor reduced phosphorylated AKT and increased phosphorylated AMPK in MM cells assessed by Western Blot. For in vivo experiments in SCID-rab mice, SCD1 inhibitor was constantly administered (1.25 μg/hour) by osmotic pumps directly connected to the implanted bones that had been engrafted with luciferase-expressing H929 MM cells (6 mice/group). SCD1 inhibitor suppressed MM growth by 60% (p<0.01) assessed by live-animal imaging and measurement of circulating levels of human immunoglobulins in mice sera. These findings suggest that intracellular modulators of lipid metabolism such as SCD1 are induced in MM cells by the supportive BM and mediate signals linking cellular metabolism, survival and proliferation.