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

Amalia Azzariti, Jian Ming Xu, Letizia Porcelli, Angelo Paradiso

Research output: Contribution to journalArticle


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 IC50 of each drug choosing the 5 days exposure for Gefitinib (0.6 and 3.8 μM for LoVo and HT-29 cells, respectively) and 1 day exposure for SN-38 (0.31 and 0.5 μM 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.

Original languageEnglish
Pages (from-to)135-144
Number of pages10
JournalBiochemical Pharmacology
Issue number1
Publication statusPublished - Jul 1 2004


  • 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide
  • 5-fluorouracil
  • 5-FU
  • CI
  • combination index
  • dimethyl sulfoxide
  • DMSO
  • EDTA
  • EGFR
  • epidermal growth factor receptor
  • ethylenediaminetetraacetic acid
  • MTT
  • NB
  • neutralizing buffer
  • PBS

ASJC Scopus subject areas

  • Pharmacology

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