title: Identification and evaluation of a potent novel ATR inhibitor, NU6027, in breast and ovarian cancer cell lines.
abstract: BACKGROUND
  The ataxia telangiectasia mutated and Rad3-related kinase (ATR) has a key role in the signalling of stalled replication forks and DNA damage to cell cycle checkpoints and DNA repair. It has long been recognised as an important target for cancer therapy but inhibitors have proved elusive. As NU6027, originally developed as a CDK2 inhibitor, potentiated cisplatin in a CDK2-independent manner we postulated that it may inhibit ATR.
  
  
  METHODS
  Cellular ATR kinase activity was determined by CHK1 phosphorylation in human fibroblasts with inducible dominant-negative ATR-kinase dead expression and human breast cancer MCF7 cells. Cell cycle effects and chemo- and radiopotentiation by NU6027 were determined in MCF7 cells and the role of mismatch repair and p53 was determined in isogenically matched ovarian cancer A2780 cells.
  
  
  RESULTS
  NU6027 is a potent inhibitor of cellular ATR activity (IC(50)=6.7 μM) and enhanced hydroxyurea and cisplatin cytotoxicity in an ATR-dependent manner. NU6027 attenuated G2/M arrest following DNA damage, inhibited RAD51 focus formation and increased the cytotoxicity of the major classes of DNA-damaging anticancer cytotoxic therapy but not the antimitotic, paclitaxel. In A2780 cells sensitisation to cisplatin was greatest in cells with functional p53 and mismatch repair (MMR) and sensitisation to temozolomide was greatest in p53 mutant cells with functional MMR. Importantly, NU6027 was synthetically lethal when DNA single-strand break repair is impaired either through poly(ADP-ribose) polymerase (PARP) inhibition or defects in XRCC1.
  
  
  CONCLUSIONS
  NU6027 inhibits ATR, impairing G2/M arrest and homologous recombination thus increasing sensitivity to DNA-damaging agents and PARP inhibitors. It provides proof of concept data for clinical development of ATR inhibitors.
authors: Newcastle University, Northern Institute for Cancer Research, Newcastle upon Tyne NE2 4HH, UK.
authors: A
authors: A
authors: Peasland
authors: L-Z
authors: LZ
authors: Wang
authors: E
authors: E
authors: Rowling
authors: S
authors: S
authors: Kyle
authors: T
authors: T
authors: Chen
authors: A
authors: A
authors: Hopkins
authors: W A
authors: WA
authors: Cliby
authors: J
authors: J
authors: Sarkaria
authors: G
authors: G
authors: Beale
authors: R J
authors: RJ
authors: Edmondson
authors: N J
authors: NJ
authors: Curtin
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D064007:Ataxia Telangiectasia Mutated Proteins; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors*; D045744:Cell Line, Tumor; D004249:DNA Damage / Q000187:drug effects; D053843:DNA Mismatch Repair / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D005260:Female; D016158:Genes, p53; D006801:Humans; D007939:Leukemia L1210; D051379:Mice; D009603:Nitroso Compounds / Q000627:therapeutic use*; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000235:genetics; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D011743:Pyrimidines / Q000627:therapeutic use*
chemical_list: C475622:4-cyclohexylmethoxy-5-nitrosopyrimidine-2,6-diamine; D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D009603:Nitroso Compounds; D011743:Pyrimidines; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases