title: The proteasome inhibitor bortezomib promotes mitochondrial injury and apoptosis induced by the small molecule Bcl-2 inhibitor HA14-1 in multiple myeloma cells.
abstract: Interactions between the small molecule Bcl-2 inhibitor HA14-1 and proteasome inhibitors, including bortezomib (Velcade; formerly known as PS-341) and MG-132, have been examined in human multiple myeloma cells. Sequential (but not simultaneous) exposure of MM.1S cells to bortezomib or MG-132 (10 h) followed by HA14-1 (8 h) resulted in a marked increase in mitochondrial injury (loss of DeltaPsim, cytochrome c, Smac/DIABLO, and apoptosis-inducing factor release), activation of procaspases-3, -8, and -9, and Bid, induction of apoptosis, and loss of clonogenicity. Similar interactions were observed in U266 and MM.1R dexamethasone-resistant myeloma cells. These events were associated with Bcl-2 cleavage, Bax, Bak, and Bad accumulation, mitochondrial translocation of Bax, abrogation of Mcl-1, Bcl-xL, and XIAP upregulation, and a marked induction of JNK and p53. Bortezomib/HA14-1 treatment triggered an increase in reactive oxygen species (ROS), which, along with apoptosis, was blocked by the free radical scavenger N-acetyl-L-cysteine (L-NAC). L-NAC also opposed bortezomib/HA14-1-mediated JNK activation, upregulation of p53 and Bax, and release of cytochrome c and Smac/DIABLO. Finally, bortezomib/HA14-1-mediated apoptosis was unaffected by exogenous IL-6. Together, these findings indicate that sequential exposure of myeloma cells to proteasome and small molecule Bcl-2 inhibitors such as HA14-1 may represent a novel therapeutic strategy in myeloma.
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000502:physiology*; D001897:Boronic Acids / Q000633:toxicity*; D000069286:Bortezomib; D002455:Cell Division / Q000187:drug effects; D003546:Cysteine Endopeptidases; D003574:Cytochrome c Group / Q000032:analysis; D003907:Dexamethasone / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D009101:Multiple Myeloma; D011480:Protease Inhibitors / Q000633:toxicity*; D046988:Proteasome Endopeptidase Complex; D011719:Pyrazines / Q000633:toxicity*; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; D003574:Cytochrome c Group; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D011719:Pyrazines; D000069286:Bortezomib; D003907:Dexamethasone; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex