Interruption of the NF- B pathway by Bay 11-7082 promotes UCN-01–mediated mitochondrial dysfunction and apoptosis in human multiple myeloma cells

Interactions between pharmacologic NFB inhibitors (eg, Bay 11-7082, SN-50) and the checkpoint abrogator UCN-01 have been examined in human multiple myeloma (MM) cells. Exposure of U266 cells to Bay 11-7082 (Bay) in combination with UCN-01 resulted in the abrogation of NFB/DNA binding activity and the synergistic induction of apoptosis. Comparable synergism was observed in other MM cell lines and patient-derived CD138 cells and between an inhibitory peptide of NFB (SN50) and UCN-01. Bay/UCN-01– mediated lethality involved mitochondrial dysfunction, caspase cleavage, and poly adenosine diphosphate-ribose polymerase (PARP) degradation. Although Bay modestly blocked UCN-01–induced extracellular signal-regulated kinase (ERK) phosphorylation, coadministration activated c-Jun N-terminal kinase (JNK) and cdc2/cdk1 and down-regulated Mcl-1, XIAP, and Bcl-xL. Transfection with a constitutively activated mitogen-activated protein kinase kinase (MEK1)/green fluorescent protein (GFP) construct failed to block apoptosis induced by Bay/UCN-01 but significantly attenuated MEK inhibitor (U0126)/UCN-01–induced lethality. Inhibiting JNK activation with SP600125 or DJNKI1 peptide markedly reduced Bay/UCN01–mediated mitochondrial dysfunction and apoptosis and the down-regulation of Mcl-1, XIAP, and Bcl-xL but not of cdc2/cdk1 activation. Stable transfection of cells with dominant-negative caspase-9 dramatically diminished Bay/UCN-01 lethality without altering JNKorcdc2/cdk1activation.Neither interleukin-6 (IL-6)– nor fibronectin-mediated adherence conferred resistance to Bay/UCN-01– induced apoptosis. Together, these findings suggest that a strategy combining UCN-01 with disruption of the I B kinase (IKK)/I B/ NFB pathway warrants attention in MM. (Blood. 2004;103:2761-2770)