Topoisomerase II Inhibition and Altered Kinetics of Formation and Repair of Nitrosourea and Cisplatin-induced DNA Interstrand Cross-Links and Cytotoxicity in Human Glioblastoma Cells

Francis Ali-Osman, Sriram Rajagopal, Mitchel S. Berger, Alexander Spence, Robert B. Livingston

Research output: Contribution to journalArticle

62 Scopus citations

Abstract

By altering the accessibility of DNA sequences for alkylation or platination, and/or for subsequent repair, topoisomerase II can potentially affect the level of DNA interstrand cross-links induced in cells by bifunctional agents. In this study, we investigated the extent to which inhibition of topoisomerase H activity in a human glioblastoma multiforme cell line alters the kinetics of both the formation and the repair of total genomic DNA interstrand cross-links, as well as the sensitivity of the tumor cells to cis-diamminedichloroplatinum II (cis-DDP) and l,3-bis(2-chloroethyl)-l-nitrosourea (BCNU). Cells were incubated with and without 200 m novobiocin, a known topoisomerase II inhibitor, for 24 h, followed by exposure to 50 M BCNU and 25 M cis-DDP. DNA interstrand cross-linking was determined at various time points over 72 h, using a modified ethidium bromide-DNA binding assay. Sensitivity of the cells to cis-DDP and BCNU was also determined with and without novobiocin pretreatment with 200 m novobiocin. This concentration of novobiocin showed no significant direct cytoxicity, although it inhibited topoisomerase II activity in tumor cell nuclear extracts by 73%. A significant decrease in the rate of repair of both cis-DDP and BCNU induced DNA interstrand cross-links, with a corresponding decrease in the clonogenic survival of the cells, was observed following novobiocin exposure. Although the peak cross-link indices of novobiocin-treated cells relative to controls were not significantly increased, residual DNA cross-linking in the cells after 72 h was increased by 1.4-fold for BCNU and 3-fold for cells treated with cis-DDP, thus, indicating a greater effect of topoisomerase U on cross-link repair than on cross-link formation. These data suggest that inhibition of topoisomerase II may provide a potentially effective clinical strategy for sensitizing human brain tumors, and possibly other tumors as well, to DNA cross-linking anticancer agents.

Original languageEnglish (US)
Pages (from-to)5663-5668
Number of pages6
JournalCancer Research
Volume53
Issue number23
StatePublished - Dec 1993

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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