Modulation of DNA repair by various inhibitors of DNA synthesis following 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induced DNA damage

Chem Biol Interact. 1998 Mar 12;110(1-2):7-25. doi: 10.1016/s0009-2797(97)00114-2.


The tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is present in tobacco smoke and is hepatocarcinogenic in rats. Its bioactivation in rat hepatocytes leads to methylation and pyridyloxobutylation of DNA. Rat hepatocytes were cultured in serum-free William medium E on collagen-coated dishes. We demonstrated that some enzymes of the base and/or excision-repair pathways were involved in repair of NNK-induced DNA damage, measured by [methyl-3H] thymidine incorporation. Unscheduled DNA synthesis (UDS) induced by N-methyl-N-nitrosourea (MNU), NNK, N'-nitrosonornicotine (NNN) and 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNKOAc) increased 2.9-, 2.8-, 1.5- and 3.5-fold, respectively, suggesting that methylated and/or pyridyloxobutylated-DNA by these four nitroso compounds is repaired by the excision pathway. Moreover, levels of NNK-induced UDS were dose (1-3 mM) and time (1-18 h) dependent. Enzymes involved in the excision repair pathways were selectively inhibited. Inhibitors of DNA topoisomerase I (camptothecin) and topoisomerase II (etoposide, nalidixic acid) did not decrease the induction of UDS, suggesting that topoisomerases are not involved in the repair of NNK-induced damage. While aphidicolin and arabinocytidine (DNA polymerase alpha, delta, epsilon inhibitors) totally inhibited NNK- and NNKOAc-induced UDS, dideoxythymidine (DNA polymerase beta inhibitor) inhibited NNK- and NNKOAc-induced UDS by 40 and 33%, respectively. We conclude that DNA polymerase alpha, delta or epsilon and to a lesser degree polymerase beta are involved in the repair of pyridyloxobutylated DNA. Previous studies showed that inhibition of poly(ADP-ribosyl) polymerase (PARP) by 3-aminobenzamide (3-ab) facilitated DNA ligation. Our results demonstrate that 3-ab increased NNK-induced UDS, but does not affect NNKOAc-induced UDS. These observations suggest that the ligation step is rate limiting in the repair of methylated DNA but not of pyridyloxobutylated DNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carcinogens / toxicity*
  • Cells, Cultured / drug effects
  • DNA Damage*
  • DNA Methylation
  • DNA Repair / drug effects*
  • Liver / drug effects*
  • Liver Neoplasms, Experimental / chemically induced
  • Male
  • Methylnitrosourea / toxicity
  • Nitrosamines / toxicity*
  • Nucleic Acid Synthesis Inhibitors* / pharmacology*
  • Pyridines / toxicity
  • Rats
  • Rats, Inbred F344
  • Tobacco Smoke Pollution / adverse effects
  • Topoisomerase I Inhibitors*


  • Carcinogens
  • Nitrosamines
  • Nucleic Acid Synthesis Inhibitors
  • Pyridines
  • Tobacco Smoke Pollution
  • Topoisomerase I Inhibitors
  • 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone
  • Methylnitrosourea
  • 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone
  • N'-nitrosonornicotine