Inhibition of fatty acid synthase induces anti-tumor effect in multiple myeloma

Abstract

19522 Background: Fatty acid synthase (FAS) is a key metabolic enzyme that catalyzes the terminal steps in the synthesis of long-chain fatty acids. Several reports have shown that FAS is expressed at significantly higher levels in a variety of human cancers, and FAS inhibitors inhibit tumor cell growth and induce apoptosis in various human cancers both in vitro and in vivo. In this study, we investigate the biological significance of inhibition of FAS in multiple myeloma (MM) cells using the small molecule inhibitor Cerulenin. Methods: FAS expression were analyzed by western blotting (WB) and immunohistochemical analysis. Cell growth was assesed by MTT assay or 3H uptake analysis. Apoptosis was evaluated by Flow cytometric analysis using Apo2.7 staining and WB. ER stress response was analyzed by WB. Assesement of combination effects with Cerulenin and other agents was performed by MTT assay and isobologram analysis. Results: FAS protein is more highly expressed in MM than normal cells. Cerulenin triggers growth inhibition in both MM cell lines and MM patient cells, as well as overcomes the survival and growth advantages conferred by IL-6, IGF-1 and bone marrow stromal cells (BMSC). It induces apoptosis in MM cell lines with only modest activation of caspase-8,-9,-3 and PARP. Moreover, the pan-caspase inhibitor Z- VAD-FMK does not significantly inhibit Cerulenin-induced apoptosis and cell death. In addition, treatment of MM cells with Cerulenin primarily up- regulates both AIF and Endo G, mediators of caspase-independent apoptosis. Importantly, Cerulenin also induces ER stress response via up- regulation of Grp78/IRE1α/JNK pathway. Although C-Jun-NH2-terminal kinase (JNK) inhibitor SP600215 blocks Cerulenin- induced cytotoxicity, it does not inhibit apoptosis and caspase cleavage triggered by Cerulenin. Furthermore, Cerulenin triggers synergistic cytotoxicity with Bortezomib, Melphalan and Doxorubicin, which induce apoptosis via activation of caspase. Conclusions: Our results indicate that inhibition of FAS by Cerulenin triggers primarily non-caspase-dependent apoptosis and JNK-dependent cell death in MM. This is the first report to demonstrate that inhibition of FAS has anti-tumor activity against MM cells, suggesting that it represents a novel therapeutic target in MM. No significant financial relationships to disclose.