title: Identification of ATR-Chk1 pathway inhibitors that selectively target p53-deficient cells without directly suppressing ATR catalytic activity.
abstract: Resistance to DNA-damaging chemotherapy is a barrier to effective treatment that appears to be augmented by p53 functional deficiency in many cancers. In p53-deficient cells in which the G1-S checkpoint is compromised, cell viability after DNA damage relies upon intact intra-S and G2-M checkpoints mediated by the ATR (ataxia telangiectasia and Rad3 related) and Chk1 kinases. Thus, a logical rationale to sensitize p53-deficient cancers to DNA-damaging chemotherapy is through the use of ATP-competitive inhibitors of ATR or Chk1. To discover small molecules that may act on uncharacterized components of the ATR pathway, we performed a phenotype-based screen of 9,195 compounds for their ability to inhibit hydroxyurea-induced phosphorylation of Ser345 on Chk1, known to be a critical ATR substrate. This effort led to the identification of four small-molecule compounds, three of which were derived from known bioactive library (anthothecol, dihydrocelastryl, and erysolin) and one of which was a novel synthetic compound termed MARPIN. These compounds all inhibited ATR-selective phosphorylation and sensitized p53-deficient cancer cells to DNA-damaging agents in vitro and in vivo. Notably, these compounds did not inhibit ATR catalytic activity in vitro, unlike typical ATP-competitive inhibitors, but acted in a mechanistically distinct manner to disable ATR-Chk1 function. Our results highlight a set of novel molecular probes to further elucidate druggable mechanisms to improve cancer therapeutic responses produced by DNA-damaging drugs.
authors.affiliation: Division of Dermatology, Department of Medicine, University of Washington, Seattle, Washington. kawasumi@uw.edu pnghiem@uw.edu.
authors.forename: Masaoki
authors.initials: M
authors.lastname: Kawasumi
authors.affiliation: The Broad Institute of MIT and Harvard, Cambridge, Massachusetts. Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts. Department of Medicine, Harvard Medical School, Boston, Massachusetts.
authors.forename: James E
authors.initials: JE
authors.lastname: Bradner
authors.affiliation: The Broad Institute of MIT and Harvard, Cambridge, Massachusetts.
authors.forename: Nicola
authors.initials: N
authors.lastname: Tolliday
authors.affiliation: Division of Dermatology, Department of Medicine, University of Washington, Seattle, Washington.
authors.forename: Renee
authors.initials: R
authors.lastname: Thibodeau
authors.affiliation: Division of Dermatology, Department of Medicine, University of Washington, Seattle, Washington.
authors.forename: Heather
authors.initials: H
authors.lastname: Sloan
authors.affiliation: University of Pittsburgh Center for Chemical Methodologies and Library Development, Pittsburgh, Pennsylvania.
authors.forename: Kay M
authors.initials: KM
authors.lastname: Brummond
authors.affiliation: Division of Dermatology, Department of Medicine, University of Washington, Seattle, Washington. Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, Washington. kawasumi@uw.edu pnghiem@uw.edu.
authors.forename: Paul
authors.initials: P
authors.lastname: Nghiem
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D002384:Catalysis / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D000071877:Checkpoint Kinase 1; D004249:DNA Damage / Q000187:drug effects; D059565:G2 Phase Cell Cycle Checkpoints; D006367:HeLa Cells; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D011494:Protein Kinases / Q000096:biosynthesis* / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D054852:Small Molecule Libraries / Q000008:administration & dosage; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*
chemical_list: D054852:Small Molecule Libraries; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1