title: The novel Chk1 inhibitor MK-8776 sensitizes human leukemia cells to HDAC inhibitors by targeting the intra-S checkpoint and DNA replication and repair.
abstract: Interactions between the novel Chk1 inhibitor MK-8776 and the histone deacetylase (HDAC) inhibitor (HDACI) vorinostat were examined in human leukemia cells harboring wild-type (wt) or deficient p53. MK-8776 synergistically potentiated vorinostat-mediated apoptosis in various p53-wt or -deficient leukemia cell lines, whereas p53 knockdown by short hairpin RNA (shRNA) sensitized p53-wt cells to lethality of this regimen. Leukemia cell lines carrying FLT3-ITD were also sensitive to the MK-8776/vorinostat regimen. Synergistic interactions were associated with inhibition of Chk1 activity, interference with the intra-S-phase checkpoint, disruption of DNA replication, and downregulation of proteins involved in DNA replication (e.g., Cdt1) and repair (e.g., CtIP and BRCA1), resulting in sharp increases in DNA damage, reflected by enhanced γ-H2A.X formation, and apoptosis. Moreover, leukemia cells expressing kinase-dead Chk1 (D130A) or Chk1 shRNA were significantly more sensitive to HDACIs compared with their wt counterparts and displayed downregulation of CtIP and BRCA1 phosphorylation following HDACI exposure. Finally, the MK-8776/vorinostat regimen was active in primary acute myelogenous leukemia (AML) blasts, particularly against the CD34(+)/CD38(-)/CD123(+) population enriched for leukemia-initiating cells. In contrast, identical regimens were relatively sparing toward normal cord blood CD34(+) cells. Together, these findings indicate that the novel Chk1 inhibitor MK-8776 markedly potentiates HDACI lethality in leukemia cells displaying various genetic backgrounds through mechanisms involving disruption of the intra-S checkpoint, DNA replication, and DNA repair. They also argue that leukemic cells, including those bearing oncogenic mutations associated with poor prognosis, for example, p53 deletion/mutation or FLT3-ITD, may also be susceptible to this strategy.
authors.affiliation: Division of Hematology/Oncology, Department of Medicine, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Shuang
authors.initials: S
authors.lastname: Chen
authors.forename: Maciej
authors.initials: M
authors.lastname: Kmieciak
authors.forename: Liang
authors.initials: L
authors.lastname: Zhou
authors.forename: Hui
authors.initials: H
authors.lastname: Lin
authors.forename: Xin-Yan
authors.initials: XY
authors.lastname: Pei
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage; D017209:Apoptosis / Q000187:drug effects*; D001854:Bone Marrow Cells / Q000473:pathology; D002478:Cells, Cultured; D000071877:Checkpoint Kinase 1; D004260:DNA Repair / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D015973:Gene Expression Regulation, Leukemic; D056572:Histone Deacetylase Inhibitors / Q000008:administration & dosage*; D006655:Histone Deacetylases / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000008:administration & dosage; D007938:Leukemia / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D011720:Pyrazoles / Q000008:administration & dosage; D011743:Pyrimidines / Q000008:administration & dosage; D059807:S Phase Cell Cycle Checkpoints / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors; D000077337:Vorinostat
chemical_list: D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; C559815:MK-8776; D011720:Pyrazoles; D011743:Pyrimidines; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D000077337:Vorinostat; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D006655:Histone Deacetylases
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