title: Inhibition of Chk1 by CEP-3891 accelerates mitotic nuclear fragmentation in response to ionizing Radiation.
abstract: The human checkpoint kinase Chk1 has been suggested as a target for cancer treatment. Here, we show that a new inhibitor of Chk1 kinase, CEP-3891, efficiently abrogates both the ionizing radiation (IR)-induced S and G(2) checkpoints. When the checkpoints were abrogated by CEP-3891, the majority (64%) of cells showed fragmented nuclei at 24 hours after IR (6 Gy). The formation of nuclear fragmentation in IR-treated human cancer cells was directly visualized by time-lapse video microscopy of U2-OS cells expressing a green fluorescent protein-tagged histone H2B protein. Nuclear fragmentation occurred as a result of defective chromosome segregation when irradiated cells entered their first mitosis, either prematurely without S and G(2) checkpoint arrest in the presence of CEP-3891 or after a prolonged S and G(2) checkpoint arrest in the absence of CEP-3891. The nuclear fragmentation was clearly distinguishable from apoptosis because caspase activity and nuclear condensation were not induced. Finally, CEP-3891 not only accelerated IR-induced nuclear fragmentation, it also increased the overall cell killing after IR as measured in clonogenic survival assays. These results demonstrate that transient Chk1 inhibition by CEP-3891 allows premature mitotic entry of irradiated cells, thereby leading to accelerated onset of mitotic nuclear fragmentation and increased cell death.
authors.affiliation: Department of Cell Cycle and Cancer and Apoptosis Laboratory, Institute of Cancer Biology, Danish Cancer Society, Copenhagen, Denmark.
authors.forename: Randi G
authors.initials: RG
authors.lastname: Syljuåsen
authors.forename: Claus Storgaard
authors.initials: CS
authors.lastname: Sørensen
authors.forename: Jesper
authors.initials: J
authors.lastname: Nylandsted
authors.forename: Claudia
authors.initials: C
authors.lastname: Lukas
authors.forename: Jiri
authors.initials: J
authors.lastname: Lukas
authors.forename: Jiri
authors.initials: J
authors.lastname: Bartek
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D001859:Bone Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology / Q000532:radiotherapy; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects* / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D000071877:Checkpoint Kinase 1; D016195:G2 Phase / Q000187:drug effects* / Q000528:radiation effects; D006801:Humans; D008938:Mitosis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D012516:Osteosarcoma / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology / Q000532:radiotherapy; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011494:Protein Kinases / Q000378:metabolism*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D016196:S Phase / Q000187:drug effects* / Q000528:radiation effects
chemical_list: D047428:Protein Kinase Inhibitors; D011838:Radiation-Sensitizing Agents; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1