The schedule-dependent enhanced cytotoxic activity of 7-ethyl-10-hydroxy-camptothecin (SN-38) in combination with Gefitinib (Iressa, ZD1839)

Biochem Pharmacol. 2004 Jul 1;68(1):135-44. doi: 10.1016/j.bcp.2004.03.014.


The combination of the topoisomerase I (Topo I) inhibitor CPT-11 with the anti-epidermal growth factor receptor (EGFR) agent Gefitinib (Iressa, ZD1839) represents a promising medical approach for colorectal cancer patients. In this report, we provide pre-clinical evidences for their optimal combination schedule in HT-29 and LoVo human colon cancer cell lines. We analyzed the different effects that three different combination schedules of SN-38 (the active CPT-11 metabolite) and Gefitinib (Gefitinib before; Gefitinib simultaneously; Gefitinib after SN-38) have on cell growth, cell cycle, apoptosis, and expression/phosphorylation of EGFR, Topo I and some steps of the signal transduction pathway. We first determined the IC(50) of each drug choosing the 5 days exposure for Gefitinib (0.6 and 3.8 microM for LoVo and HT-29 cells, respectively) and 1 day exposure for SN-38 (0.31 and 0.5 microM for LoVo and HT-29 cells, respectively). The different drug combination schedules were tested in various concentrations by using equiactive concentrations of the two drugs. The cytotoxicity of Gefitinib and SN-38 combination was schedule- and concentration-dependent but not cell line-specific. The most synergistic schedule was Gefitinib given after SN-38, with combination indexes (CI) of 0.007 and 0.454 in HT-29 and LoVo, respectively. Analysis of bio-molecular targets showed that Gefitinib was able to modulate SN-38 ability to inhibit Topo I, to accumulate cells in S-phase, and to induce apoptosis. Interestingly, SN-38 was able to activate EGFR and its signal transduction pathway. Confirming preliminary clinical experience of Gefitinib with other cytotoxic drugs, it seems that Gefitinib after SN-38 represents the best cytotoxic combination schedule but the biomolecular basis for this synergism remain to be completely elucidated.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / administration & dosage
  • Antineoplastic Agents / pharmacology*
  • Apoptosis*
  • Camptothecin / administration & dosage
  • Camptothecin / analogs & derivatives
  • Camptothecin / pharmacology*
  • Cell Cycle / drug effects
  • Cell Division / drug effects
  • Colonic Neoplasms / pathology
  • DNA Topoisomerases, Type I / metabolism
  • Drug Synergism
  • ErbB Receptors / metabolism
  • Gefitinib
  • HT29 Cells
  • Humans
  • Irinotecan
  • Quinazolines / administration & dosage
  • Quinazolines / pharmacology*
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Tumor Cells, Cultured


  • Antineoplastic Agents
  • Quinazolines
  • Irinotecan
  • ErbB Receptors
  • DNA Topoisomerases, Type I
  • Gefitinib
  • Camptothecin