title: The schedule-dependent enhanced cytotoxic activity of 7-ethyl-10-hydroxy-camptothecin (SN-38) in combination with Gefitinib (Iressa, ZD1839).
abstract: 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.
authors.affiliation: Clinical Experimental Oncology Laboratory, National Cancer Institute, Bari, Italy.
authors.forename: Amalia
authors.initials: A
authors.lastname: Azzariti
authors.forename: Jian-Ming
authors.initials: JM
authors.lastname: Xu
authors.forename: Letizia
authors.initials: L
authors.lastname: Porcelli
authors.forename: Angelo
authors.initials: A
authors.lastname: Paradiso
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D017209:Apoptosis; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D003110:Colonic Neoplasms / Q000473:pathology; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004357:Drug Synergism; D066246:ErbB Receptors / Q000378:metabolism; D000077156:Gefitinib; D019073:HT29 Cells; D006801:Humans; D000077146:Irinotecan; D011799:Quinazolines / Q000008:administration & dosage / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D011799:Quinazolines; D000077146:Irinotecan; D066246:ErbB Receptors; D004264:DNA Topoisomerases, Type I; D000077156:Gefitinib; D002166:Camptothecin