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Role of the 20-hydroxyl group in camptothecin binding by the topoisomerase I-DNA binary complex

X Wang1, X Zhou, S M Hecht

  • 1Department of Chemistry, University of Virginia, Charlottesville 22901, USA.

Biochemistry
|April 9, 1999
PubMed

Insights

Camptothecin analogues lacking a 20-OH group still effectively inhibit DNA topoisomerase I. This challenges existing models of inhibitor binding to the DNA-topoisomerase I complex, suggesting alternative interactions are involved.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Enzymology

Background:

  • DNA topoisomerase I is a crucial enzyme in DNA replication and repair.
  • Camptothecin is a known inhibitor of DNA topoisomerase I.
  • Existing models propose the 20-OH group of camptothecin is essential for binding via hydrogen bonds.

Purpose of the Study:

  • To evaluate camptothecin analogues with modifications at the C-20 position for their ability to inhibit DNA topoisomerase I.
  • To investigate the role of the C-20 substituent in the binding of camptothecin to the DNA-topoisomerase I binary complex.

Main Methods:

  • Synthesis of five camptothecin analogues differing only at the C-20 position.
  • Assay of the binding affinity of these analogues to the DNA-topoisomerase I binary complex.
  • Assessment of their enzyme inhibitory function.

Main Results:

  • Analogues with 20-chloro and 20-bromo substituents bound effectively to the DNA-topoisomerase I binary complex.
  • These halogenated analogues exhibited similar binding efficacy as 20-amino camptothecin.
  • Inhibition of enzyme function was observed despite the absence of a hydrogen bond donor at C-20.

Conclusions:

  • The 20-OH group of camptothecin is not essential for binding to the DNA-topoisomerase I binary complex.
  • Alternative binding interactions, beyond donor hydrogen bonds involving the 20-OH group, likely contribute to inhibitor efficacy.
  • These findings necessitate a revision of current models for camptothecin-DNA topoisomerase I interactions.

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