title: Heat shock protein 90 inhibition sensitizes acute myelogenous leukemia cells to cytarabine.
abstract: Previous studies demonstrated that ataxia telangiectasia mutated- and Rad3-related (ATR) kinase and its downstream target checkpoint kinase 1 (Chk1) facilitate survival of cells treated with nucleoside analogs and other replication inhibitors. Recent results also demonstrated that Chk1 is depleted when cells are treated with heat shock protein 90 (Hsp90) inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG). The present study examined the effects of 17-AAG and its major metabolite, 17-aminogeldanamycin (17-AG), on Chk1 levels and cellular responses to cytarabine in human acute myelogenous leukemia (AML) cell lines and clinical isolates. Cytarabine, at concentrations as low as 30 nM, caused activating phosphorylation of Chk1, loss of the phosphatase Cdc25A, and S-phase slowing. Conversely, treatment with 100 to 300 nM 17-AAG for 24 hours caused Chk1 depletion that was accompanied by diminished cytarabine-induced S-phase accumulation, decreased Cdc25A degradation, and enhanced cytotoxicity as measured by inhibition of colony formation and induction of apoptosis. Additional studies demonstrated that small inhibitory RNA (siRNA) depletion of Chk1 also sensitized cells to cytarabine, whereas disruption of the phosphatidylinositol 3-kinase (PI3k) signaling pathway, which is also blocked by Hsp90 inhibition, did not. Collectively, these results suggest that treatment with 17-AAG might represent a means of reversing checkpoint-mediated cytarabine resistance in AML.
authors.affiliation: Division of Hematology, Department of Medicine, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
authors.forename: Ruben A
authors.initials: RA
authors.lastname: Mesa
authors.forename: David
authors.initials: D
authors.lastname: Loegering
authors.forename: Heather L
authors.initials: HL
authors.lastname: Powell
authors.forename: Karen
authors.initials: K
authors.lastname: Flatten
authors.forename: Sonnet J H
authors.initials: SJ
authors.lastname: Arlander
authors.forename: Nga T
authors.initials: NT
authors.lastname: Dai
authors.forename: Michael P
authors.initials: MP
authors.lastname: Heldebrant
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Vroman
authors.forename: B Douglas
authors.initials: BD
authors.lastname: Smith
authors.forename: Judith E
authors.initials: JE
authors.lastname: Karp
authors.forename: Cynthia J Ten
authors.initials: CJ
authors.lastname: Eyck
authors.forename: Charles
authors.initials: C
authors.lastname: Erlichman
authors.forename: Scott H
authors.initials: SH
authors.lastname: Kaufmann
authors.forename: Larry M
authors.initials: LM
authors.lastname: Karnitz
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D016227:Benzoquinones; D000071877:Checkpoint Kinase 1; D003561:Cytarabine / Q000494:pharmacology*; D004357:Drug Synergism; D018922:HL-60 Cells; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D047029:Lactams, Macrocyclic; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D017828:Rifabutin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D016196:S Phase / Q000187:drug effects
chemical_list: D000964:Antimetabolites, Antineoplastic; D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D034741:RNA, Small Interfering; D003561:Cytarabine; D017828:Rifabutin; C112765:tanespimycin; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1