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This study investigated the biological significance of the inhibition of fatty acid synthase (FAS) in multiple myeloma (MM) using the small molecule inhibitor Cerulenin. Cerulenin triggered growth inhibition in both MM cell lines and MM patient cells, and overcame the survival and growth advantages conferred by interleukin-6, insulin-like growth factor-1, and bone marrow stromal cells. It induced apoptosis in MM cell lines with only modest activation of caspase -8, -9, -3 and PARP; moreover, the pan-caspase inhibitor Z-VAD-FMK did not inhibit Cerulenin-induced apoptosis and cell death. In addition, treatment of MM cells with Cerulenin primarily up-regulated apoptosis-inducing factor/endonuclease G, mediators of caspase-independent apoptosis. Importantly, Cerulenin induced endoplasmic reticulum stress response via up-regulation of the Grp78/IRE1α/JNK pathway. Although the C-Jun-NH2-terminal kinase (JNK) inhibitor SP600215 blocked Cerulenin-induced cytotoxicity, it did not inhibit apoptosis and caspase cleavage. Furthermore, Cerulenin showed synergistic cytotoxic effects with various agents including Bortezomib, Melphalan and Doxorubicin. Our results therefore indicate that inhibition of FAS by Cerulenin primarily triggered caspase-independent apoptosis and JNK-dependent cytotoxicity in MM cells. This report demonstrated that inhibition of FAS has anti-tumour activity against MM cells, suggesting that it represents a novel therapeutic target in MM. [ABSTRACT FROM AUTHOR]

We have shown that the proteasome inhibitor bortezomib (formerly known as P5-341) triggers significant antitumor activity in multiple myeloma (MM) in both preclinical models and patients with relapsed refractory disease. Recent studies have shown that unfolded and misfolded ubiquitinated proteins are degraded not only by proteasomes, but also by aggresomes, dependent on histone deacetylase 6 (HDAC6) activity. We therefore hypothesized that inhibition of both mechanisms of protein catabolism could induce accumulation of ubiquitinated proteins followed by significant cell stress and cytotoxicity in MM cells. To prove this hypothesis, we used bortezomib and tubacin to inhibit the proteasome and HDAC6, respectively. Tubacin specifically triggers acetylation of u-tubulin as a result of HDAC6 inhibition in a dose- and time-dependent fashion. It induces cytotoxicity in MM cells at 72 h with an IC50 of 5-20 pM, which is mediated by caspase-dependent apoptosis; no toxicity is observed in normal peripheral blood mononuclear cells. Tubacin inhibits the interaction of HDAC6 with dynein and induces marked accumulation of ubiquitinated proteins. It synergistically augments bortezomib-induced cytotoxicity by c-Jun NH2-terminal kinase/caspase activation. Importantly, this combination also induces significant cytotoxicity in plasma cells isolated from MM patient bone marrow. Finally, adherence of MM cells to bone marrow stromal cells confers growth and resistance to conventional treatments; in contrast, the combination of tubacin and bortezomib triggers toxicity even in adherent MM cells. Our studies therefore demonstrate that tubacin combined with boil-ezomib mediates significant anti-MM activity, providing the frame- work for clinical evaluation of combined therapy to improve patient outcome in MM. [ABSTRACT FROM AUTHOR]