title: Combined treatment with the checkpoint abrogator UCN-01 and MEK1/2 inhibitors potently induces apoptosis in drug-sensitive and -resistant myeloma cells through an IL-6-independent mechanism.
abstract: The effects of combined exposure to the checkpoint abrogator UCN-01 and pharmacologic MEK1/2 inhibitors were examined in human multiple myeloma (MM) cell lines. Treatment of RPMI8226, NCI-H929, and U266 MM cells with a minimally toxic concentration of UCN-01 (150 nM) for 24 hours resulted in mitogen-activated protein (MAP) kinase activation, an effect that was blocked by coadministration of the MEK1/2 inhibitor PD184352. These events were accompanied by enhanced activation of p34(cdc2) and a marked increase in mitochondrial damage (loss of DeltaPsim; cytochrome c and Smac/DIABLO (direct IAP binding protein with low pI) release), poly(ADP-ribose) polymerase (PARP) cleavage, and apoptosis. PD184352/UCN-01 also dramatically reduced clonogenic survival in each of the MM cell lines. In contrast to As(2)0(3), apoptosis induced by PD184352/UCN-01 was not blocked by the free-radical scavenger N-acetyl-L-cysteine. Whereas exogenous interleukin 6 substantially prevented dexamethasone-induced lethality in MM cells, it was unable to protect them from PD184352/UCN-01-induced apoptosis despite enhancing Akt activation. Insulinlike growth factor 1 (IGF-1) also failed to diminish apoptosis induced by this drug regimen. MM cell lines selected for a high degree of resistance to doxorubicin, melphalan, or dexamethasone, or displaying resistance secondary to fibronectin-mediated adherence, remained fully sensitive to PD184352/UCN-01-induced cell death. Finally, primary CD138(+) MM cells were also susceptible to UCN-01/MEK inhibitor-mediated apoptosis. Together, these findings suggest that simultaneous disruption of cell cycle and MEK/MAP kinase signaling pathways provides a potent stimulus for mitochondrial damage and apoptosis in MM cells, and also indicate that this strategy bypasses the block to cell death conferred by several other well-described resistance mechanisms.
authors.affiliation: Division of Hematology/Oncology, Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Terry H
authors.initials: TH
authors.lastname: Landowski
authors.forename: Steven T
authors.initials: ST
authors.lastname: Rosen
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides / Q000494:pharmacology; D001854:Bone Marrow Cells / Q000187:drug effects / Q000473:pathology; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002448:Cell Adhesion / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects*; D003907:Dexamethasone / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology / Q000502:physiology; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008558:Melphalan / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000032:analysis; D008928:Mitochondria / Q000187:drug effects / Q000473:pathology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology; D009101:Multiple Myeloma / Q000201:enzymology / Q000473:pathology*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology; D011509:Proteoglycans / Q000032:analysis; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019311:Staurosporine / Q000031:analogs & derivatives; D053668:Syndecan-1; D053667:Syndecans; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000473:pathology; D014410:Tumor Stem Cell Assay
chemical_list: C120227:2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide; D000470:Alkaloids; D001549:Benzamides; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D015850:Interleukin-6; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D011509:Proteoglycans; D011518:Proto-Oncogene Proteins; C508241:SDC1 protein, human; D053668:Syndecan-1; D053667:Syndecans; D007334:Insulin-Like Growth Factor I; C054852:7-hydroxystaurosporine; D003907:Dexamethasone; D004317:Doxorubicin; C482128:MAP2K2 protein, human; D011505:Protein-Tyrosine Kinases; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D016203:CDC2 Protein Kinase; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D019311:Staurosporine; D008558:Melphalan