YM155, a Survivin Suppressant, Induces Cell Death Via Suppression Of c-Myc Expression In Multiple Myeloma Cells

Survivin is a member of the inhibitor of apoptosis protein (IAP) family with its dual roles in mitosis and apoptosis, and emerges as an attractive target for cancer therapy. Recent reports have demonstrated that survivin overexpression is associated with drug resistance and poor outcome in hematological malignancy including multiple myeloma (MM). YM155, a novel molecular targeted agent, suppresses survivin through the inhibition of transcription. However, the effect of this agent on MM cells has not been elucidated. In this study, we investigated the effect of YM155 on proliferation and survival of five human MM cell lines. YM155 inhibited the proliferation of these cells in a dose- and time-dependent manner (IC₅₀ = 10 nM in 3 and 100 nM in 2 cell lines, respectively). Annexin V assay showed that YM155 induced apoptosis in these cells. To better understand these effects of YM155 on MM cells, we evaluated the intracellular signaling and apoptosis-associated protein status. Immunoblot analyses showed that YM155 reduced not only survivin but also myeloid cell leukemia sequence 1 (Mcl-1) and X-linked inhibitor of apoptosis protein (XIAP) expression. We also observed the activation of caspase-3 and poly(ADP-ribose) polymerase in YM155-treated cells, indicating that YM155 induces caspase-dependent apoptosis. YM155 did not affect phosphorylation status of Erk1/2 and STAT3. Interestingly, we found that YM155 suppressed c-Myc and interferon regulatory factor 4 (IRF4) expression, both of which are recognized as an important oncogene in the pathogenesis of MM. In addition, c-Myc and IRF4 protein levels were reduced at 6 and 12 hours after treatment with YM155, respectively. As IRF4 and c-Myc form a positive feedback loop in myeloma cells, this observation indicates that c-Myc inhibition by YM155 treatment might lead to subsequent inhibition of IRF4 expression, and thus raises the possibility of YM155 target for c-Myc rather than IRF4. We next examined the mechanism of downregulation of c-Myc in RPMI8226 cells. Real-time quantitative RT-PCR assay showed that YM155 treatment reduced c-Myc mRNA level. On the other hand, proteasome inhibitor did not prevent the suppression of c-Myc expression by YM155 treatment. These Results suggest that YM155 transcriptionally at least in part represses c-Myc in RPMI8226 cells. In conclusion, YM155 suppresses cell proliferation and survival in MM cells in part via not only inhibiting anti-apoptotic proteins such as survivin, Mcl-1 and XIAP but also repressing c-Myc oncogene. Further study is needed to clarify the molecular mechanism of downregulation of c-Myc induced by YM155. Our Results may provide a platform for clinical trials of YM155 in MM.