title: Combination drug scheduling defines a "window of opportunity" for chemopotentiation of gemcitabine by an orally bioavailable, selective ChK1 inhibitor, GNE-900.
abstract: Checkpoint kinase 1 (ChK1) is a serine/threonine kinase that functions as a central mediator of the intra-S and G2-M cell-cycle checkpoints. Following DNA damage or replication stress, ChK1-mediated phosphorylation of downstream effectors delays cell-cycle progression so that the damaged genome can be repaired. As a therapeutic strategy, inhibition of ChK1 should potentiate the antitumor effect of chemotherapeutic agents by inactivating the postreplication checkpoint, causing premature entry into mitosis with damaged DNA resulting in mitotic catastrophe. Here, we describe the characterization of GNE-900, an ATP-competitive, selective, and orally bioavailable ChK1 inhibitor. In combination with chemotherapeutic agents, GNE-900 sustains ATR/ATM signaling, enhances DNA damage, and induces apoptotic cell death. The kinetics of checkpoint abrogation seems to be more rapid in p53-mutant cells, resulting in premature mitotic entry and/or accelerated cell death. Importantly, we show that GNE-900 has little single-agent activity in the absence of chemotherapy and does not grossly potentiate the cytotoxicity of gemcitabine in normal bone marrow cells. In vivo scheduling studies show that optimal administration of the ChK1 inhibitor requires a defined lag between gemcitabine and GNE-900 administration. On the refined combination treatment schedule, gemcitabine's antitumor activity against chemotolerant xenografts is significantly enhanced and dose-dependent exacerbation of DNA damage correlates with extent of tumor growth inhibition. In summary, we show that in vivo potentiation of gemcitabine activity is mechanism based, with optimal efficacy observed when S-phase arrest and release is followed by checkpoint abrogation with a ChK1 inhibitor.
authors.affiliation: Corresponding Authors: Elizabeth Blackwood and Shiva Malek, Genentech, 1 DNA Way, South San Francisco, CA 94080. eblack@gene.com.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Blackwood
authors.forename: Jennifer
authors.initials: J
authors.lastname: Epler
authors.forename: Ivana
authors.initials: I
authors.lastname: Yen
authors.forename: Michael
authors.initials: M
authors.lastname: Flagella
authors.forename: Tom
authors.initials: T
authors.lastname: O'Brien
authors.forename: Marie
authors.initials: M
authors.lastname: Evangelista
authors.forename: Stephen
authors.initials: S
authors.lastname: Schmidt
authors.forename: Yang
authors.initials: Y
authors.lastname: Xiao
authors.forename: Jonathan
authors.initials: J
authors.lastname: Choi
authors.forename: Kaska
authors.initials: K
authors.lastname: Kowanetz
authors.forename: Judi
authors.initials: J
authors.lastname: Ramiscal
authors.forename: Kenton
authors.initials: K
authors.lastname: Wong
authors.forename: Diana
authors.initials: D
authors.lastname: Jakubiak
authors.forename: Sharon
authors.initials: S
authors.lastname: Yee
authors.forename: Gary
authors.initials: G
authors.lastname: Cain
authors.forename: Lewis
authors.initials: L
authors.lastname: Gazzard
authors.forename: Karen
authors.initials: K
authors.lastname: Williams
authors.forename: Jason
authors.initials: J
authors.lastname: Halladay
authors.forename: Peter K
authors.initials: PK
authors.lastname: Jackson
authors.forename: Shiva
authors.initials: S
authors.lastname: Malek
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols; D017209:Apoptosis / Q000187:drug effects; D059447:Cell Cycle Checkpoints / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D004249:DNA Damage / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D006801:Humans; D008938:Mitosis / Q000187:drug effects / Q000235:genetics; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage*; D011494:Protein Kinases / Q000378:metabolism*; D011725:Pyridines / Q000008:administration & dosage*; D011758:Pyrroles / Q000008:administration & dosage*; D000093542:Gemcitabine
chemical_list: C588399:3-(4-(1-piperidinylmethyl)phenyl)-9H-pyrrolo(2,3-b-5,4-c')dipyridine-6-carbonitrile; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D011758:Pyrroles; D003841:Deoxycytidine; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D000093542:Gemcitabine