Synergistic cytotoxicity of topoisomerse I inhibitors with alkylating agents and etoposide in human brain tumor cell lines

Anna J. Janss, Avital Cnaan, Huaqing Zhao, Arkady Shpilsky, Cindy Levow, Leslie Sutton, Peter C. Phillips

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


To evaluate potential synergistic interactions between topoisomerase I (Topo I) inhibitors, i.e. camptothecin (CPT) and topotecan (TPT), and chemotherapeutic agents known to be active in treatment of brain tumors, in vitro studies were conducted with human glioma and medulloblastoma cell lines. Tumor cells were exposed to CPT or TPT alone or in combination with cisplatin, 4-hydroperoxycyclophosphamide (4-HC), BCNU or etoposide (VP-16). Cytotoxicity was assessed by colony formation assays. Drug interactions were evaluated by means of a novel analytical model which permits statistical evaluation over a range of dose combination. Experimental results were corroborated by published models of drug interaction. Our findings indicate that in vitro cytotoxic interactions in brain tumor cells between Topo I inhibitors and alkylating agents or etoposide depend on drug dose, dose schedule and tumor cell line. Treatment of DAOY medulloblastoma cells with CPT and either cisplatin, 4-HC or VP-16 produced significant synergistic cytotoxicity over a wide range of dose combinations. When VP-16 was administered after CPT, synergy was reduced to a narrow range of dose combinations. For U251 glioma cells, incubation with OPT and cisplatin or 4HC also produced synergistic cytotoxicity over a broad range of dose combinations. By contrast, antagonistic interactions were observed after administration of CPT with BCNU or VP-16. Treatment of U251 cells with CPT and cisplatin produced synergistic or antagonistic cytotoxicity depending on the dose combination used. These findings support a role for pharmacokinetic analysis in multiagent phase II trials involving Topo I Inhibitors and have important implications for clinical trial design strategies.

Original languageEnglish
Pages (from-to)641-652
Number of pages12
JournalAnti-Cancer Drugs
Issue number7
StatePublished - 1998
Externally publishedYes


  • Brain tumor cell lines
  • Camptothecin
  • Cisplatin
  • Etoposide
  • Synergy
  • Topoisomerase I inhibitor


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