title: Cytokinetically quiescent (G0/G1) human multiple myeloma cells are susceptible to simultaneous inhibition of Chk1 and MEK1/2.
abstract: Effects of Chk1 and MEK1/2 inhibition were investigated in cytokinetically quiescent multiple myeloma (MM) and primary CD138(+) cells. Coexposure to the Chk1 and MEK1/2 inhibitors AZD7762 and selumetinib (AZD6244) robustly induced apoptosis in various MM cells and CD138(+) primary samples, but spared normal CD138(-) and CD34(+) cells. Furthermore, Chk1/MEK1/2 inhibitor treatment of asynchronized cells induced G(0)/G(1) arrest and increased apoptosis in all cell-cycle phases, including G(0)/G(1). To determine whether this regimen is active against quiescent G(0)/G(1) MM cells, cells were cultured in low-serum medium to enrich the G(0)/G(1) population. G(0)/G(1)-enriched cells exhibited diminished sensitivity to conventional agents (eg, Taxol and VP-16) but significantly increased susceptibility to Chk1 ± MEK1/2 inhibitors or Chk1 shRNA knock-down. These events were associated with increased γH2A.X expression/foci formation and Bim up-regulation, whereas Bim shRNA knock-down markedly attenuated lethality. Immunofluorescent analysis of G(0)/G(1)-enriched or primary MM cells demonstrated colocalization of activated caspase-3 and the quiescent (G(0)) marker statin, a nuclear envelope protein. Finally, Chk1/MEK1/2 inhibition increased cell death in the Hoechst-positive (Hst(+)), low pyronin Y (PY)-staining (2N Hst(+)/PY(-)) G(0) population and in sorted small side-population (SSP) MM cells. These findings provide evidence that cytokinetically quiescent MM cells are highly susceptible to simultaneous Chk1 and MEK1/2 inhibition.
authors.affiliation: Division of Hematology/Oncology, Department of Medicine, Virginia Commonwealth University, Richmond, 23298, USA.
authors.forename: Xin-Yan
authors.initials: XY
authors.lastname: Pei
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Leena E
authors.initials: LE
authors.lastname: Youssefian
authors.forename: Shuang
authors.initials: S
authors.lastname: Chen
authors.forename: Wesley W
authors.initials: WW
authors.lastname: Bodie
authors.forename: Yukie
authors.initials: Y
authors.lastname: Takabatake
authors.forename: Jessica
authors.initials: J
authors.lastname: Felthousen
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Almenara
authors.forename: Lora B
authors.initials: LB
authors.lastname: Kramer
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001562:Benzimidazoles / Q000008:administration & dosage / Q000627:therapeutic use; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D016193:G1 Phase; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors*; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors*; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage / Q000627:therapeutic use*; D011494:Protein Kinases / Q000378:metabolism*; D016192:Resting Phase, Cell Cycle; D053668:Syndecan-1 / Q000378:metabolism; D013876:Thiophenes / Q000008:administration & dosage / Q000627:therapeutic use; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000627:therapeutic use
chemical_list: C532363:3-(carbamoylamino)-5-(3-fluorophenyl)-N-(3-piperidyl)thiophene-2-carboxamide; C517975:AZD 6244; D001562:Benzimidazoles; C508600:IL6 protein, human; D015850:Interleukin-6; D047428:Protein Kinase Inhibitors; C508241:SDC1 protein, human; D053668:Syndecan-1; D013876:Thiophenes; D014508:Urea; D011494:Protein Kinases; C482128:MAP2K2 protein, human; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human