Differential stabilization of eukaryotic DNA topoisomerase I cleavable complexes by camptothecin derivatives

Biochemistry. 1995 May 30;34(21):7200-6. doi: 10.1021/bi00021a035.


Camptothecins belong to a group of anticancer agents with a specific mechanism of action: stabilization and trapping of eukaryotic DNA topoisomerase I (top1) cleavable complexes. Two water-soluble camptothecin derivatives are in clinical trial, and their anticancer activity appears promising: topotecan and CPT-11. The latter is hydrolyzed to its active metabolite, SN-38. We have previously reported that SN-38 is among the most cytotoxic camptothecin derivatives and that the cleavable complexes induced by SN-38 are more stable than those induced by CPT in human colon carcinoma cells [Tanizawa et al. (1994) J. Natl. Cancer Inst, 86, 836-842]. Top1 inhibition was further investigated by determining the salt-induced religation rates of top1-cleavable complexes in fragments from the top1 cDNA. Religation depended on both the local DNA base sequence and the drug structure. Cleavable complexes induced by SN-38 and 10,11-methylenedioxycamptothecin were markedly more stable (less rapidly reversible) than those induced by CPT, topotecan, and 9-aminocamptothecin. The stability of 10-hydroxycamptothecin-induced cleavable complexes was intermediate to those of CPT and SN-38, indicating that both the 10-hydroxy and the 7-ethyl group of SN-38 probably interact with the drug binding site of top1-cleavable complexes. A DNA oligonucleotide containing a single top1 cleavage site was also used to compare the camptothecin derivatives. The salt stability of drug-induced cleavable complexes in the top1 oligonucleotide was correlated with the drug potencies to induce top1 cleavage. Cell killing requires that trapped cleavable complexes be converted to DNA damage as a result of replication fork collision.(ABSTRACT TRUNCATED AT 250 WORDS)

MeSH terms

  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Base Sequence
  • Camptothecin / analogs & derivatives*
  • Camptothecin / pharmacology
  • DNA
  • DNA Topoisomerases, Type I / metabolism
  • Enzyme Stability
  • Hydrolysis
  • Molecular Sequence Data
  • Osmolar Concentration
  • Salts
  • Topoisomerase I Inhibitors*


  • Antineoplastic Agents, Phytogenic
  • Salts
  • Topoisomerase I Inhibitors
  • DNA
  • DNA Topoisomerases, Type I
  • Camptothecin