Effects of novel inhibitors of poly(ADP-ribose) polymerase-1 and the DNA-dependent protein kinase on enzyme activities and DNA repair

Oncogene. 2004 Sep 23;23(44):7322-9. doi: 10.1038/sj.onc.1207984.


DNA-dependent protein kinase (DNA-PK) and poly (ADP-ribose) polymerase-1 (PARP-1) participate in nonhomologous end joining and base excision repair, respectively, and are key determinants of radio- and chemo-resistance. Both PARP-1 and DNA-PK have been identified as therapeutic targets for anticancer drug development. Here we investigate the effects of specific inhibitors on enzyme activities and DNA double-strand break (DSB) repair. The enzyme activities were investigated using purified enzymes and in permeabilized cells. Inhibition, or loss of activity, was compared using potent inhibitors of DNA-PK (NU7026) and PARP-1 (AG14361), and cell lines proficient or deficient for DNA-PK or PARP-1. Inactive DNA-PK suppressed the activity of PARP-1 and vice versa. This was not the consequence of simple substrate competition, since DNA ends were provided in excess. The inhibitory effect of DNA-PK on PARP activity was confirmed in permeabilized cells. Both inhibitors prevented ionizing radiation-induced DSB repair, but only AG14361 prevented single-strand break repair. An increase in DSB levels caused by inhibition of PARP-1 was shown to be caused by a decrease in DSB repair, and not by the formation of additional DSBs. These data point to combined inhibition of PARP-1 and DNA-PK as a powerful strategy for tumor radiosensitization.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Azulenes
  • Benzodiazepines / pharmacology
  • Binding, Competitive
  • Cell Line
  • Cell Line, Tumor
  • Chromones / chemical synthesis
  • Chromones / pharmacology
  • DNA Repair / drug effects*
  • DNA-Activated Protein Kinase
  • DNA-Binding Proteins*
  • Enzyme Inhibitors / pharmacology
  • Humans
  • Mice
  • Morpholines / chemical synthesis
  • Morpholines / pharmacology
  • Nuclear Proteins
  • Phosphorylation
  • Poly(ADP-ribose) Polymerase Inhibitors*
  • Poly(ADP-ribose) Polymerases
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*


  • 1-(4-dimethylaminomethylphenyl)-8,9-dihydro-7H-2,7,9a-benzo(cd)azulen-6-one
  • 2-(morpholin-4-yl)benzo(h)chromen-4-one
  • Azulenes
  • Chromones
  • DNA-Binding Proteins
  • Enzyme Inhibitors
  • Morpholines
  • Nuclear Proteins
  • Poly(ADP-ribose) Polymerase Inhibitors
  • Benzodiazepines
  • PARP2 protein, human
  • Poly(ADP-ribose) Polymerases
  • DNA-Activated Protein Kinase
  • PRKDC protein, human
  • Protein-Serine-Threonine Kinases