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Position-specific trapping of topoisomerase II by benzo[a]pyrene diol epoxide adducts: implications for interactions

Qasim A Khan1, Glenda Kohlhagen, Richard Marshall

  • 1Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, National Institutes of Health/DHHS, Building 37, Bethesda, MD 20892, USA.

Proceedings of the National Academy of Sciences of the United States of America
|October 3, 2003
PubMed

Insights

DNA topoisomerase II (Top2) is targeted by anticancer drugs. Intercalating polycyclic aromatic hydrocarbons near Top2 cleavage sites can trap the enzyme, potentially explaining their carcinogenicity.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Medicinal Chemistry

Background:

  • DNA topoisomerase II (Top2) is a crucial enzyme in DNA replication and transcription.
  • Top2 is a validated target for numerous anticancer drugs, particularly DNA intercalators.
  • Understanding drug-DNA-enzyme interactions is key to developing effective cancer therapies.

Purpose of the Study:

  • To investigate how intercalating ligands at specific positions affect human Topoisomerase II alpha (Top2α) DNA cleavage.
  • To correlate the position and orientation of benzo[a]pyrene DE dA adducts with Top2 trapping.
  • To elucidate the mechanism of Top2 poisoning by bulky polycyclic aromatic hydrocarbons.

Main Methods:

  • Synthesis of oligodeoxynucleotides with specific benzo[a]pyrene DE dA adducts.
  • NMR structural analysis of DNA-ligand complexes.
  • Assays to detect Top2 cleavage complex formation and DNA cleavage activity.

Main Results:

  • Top2 cleavage complexes are trapped by intercalation at or near staggered Top2 cleavage sites.
  • The position of the adduct influences whether Top2 cleavage is concerted or non-concerted.
  • Intercalation outside the cleavage site suppresses Top2-mediated DNA cleavage.

Conclusions:

  • Specific binding sites for intercalators that trap Top2 have been identified.
  • Top2 poisoning by bulky polycyclic aromatic hydrocarbon DE adducts is a potential mechanism for their carcinogenic activity.
  • These findings provide insights into the design of Top2-targeting anticancer agents and understanding chemical carcinogenesis.

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