title: Characterization of sequence-dependent synergy between ZD1839 ("Iressa") and oxaliplatin.
abstract: ZD1839 ("Iressa"), a selective epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), is currently undergoing preclinical and clinical evaluation in several solid tumors. The present study aimed to assess the effect of ZD1839 in combination with oxaliplatin in the colon cancer cell lines HT-29 and LoVo. For in vitro chemosensitivity testing, cells were treated with serial dilutions of each drug sequentially at a fixed ratio of doses that corresponded to 1/20, 1/10, 1/5, 1/2, 1, 1.5 and 2 times the individual IC(50) values. Oxaliplatin followed by ZD1839 produced a synergistic effect. In contrast, oxaliplatin following ZD1839 exhibited an additive effect at best. Mass spectrometry examination revealed that ZD1839 modestly enhanced cellular oxaliplatin accumulation and platinum-DNA (Pt-DNA) adducts (P>0.05). In additional studies, high-performance liquid chromatography revealed that oxaliplatin had no effect on ZD1839 accumulation. In contrast, ZD1839 markedly inhibited removal of Pt-DNA adducts (P<0.05). With oxaliplatin treatment (1 day) followed by ZD1839 (1 day), then incubation with drug-free medium (1 day), 90% of Pt-DNA adducts remained. Apoptosis examination revealed that oxaliplatin-induced apoptosis was prolonged by sequential oxaliplatin followed by ZD1839 treatment compared with oxaliplatin alone. Further experiments revealed that ZD1839 decreased cellular gamma-glutamyltransferase activity.
  
  
  CONCLUSIONS
  The above observations provide a mechanistic explanation for the synergy of oxaliplatin followed by ZD1839, and suggest that this treatment combination warrants further preclinical and clinical investigation.
authors.affiliation: Beijing 307 Hospital Cancer Center, Beijing 100039, China.
authors.forename: Jian-Ming
authors.initials: JM
authors.lastname: Xu
authors.forename: Amalia
authors.initials: A
authors.lastname: Azzariti
authors.forename: Montemuro
authors.initials: M
authors.lastname: Severino
authors.forename: Bing
authors.initials: B
authors.lastname: Lu
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Colucci
authors.forename: Angelo
authors.initials: A
authors.lastname: Paradiso
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D018736:DNA Adducts / Q000378:metabolism; D004357:Drug Synergism; D066246:ErbB Receptors / Q000378:metabolism; D000077156:Gefitinib; D019073:HT29 Cells; D006801:Humans; D009944:Organoplatinum Compounds / Q000008:administration & dosage / Q000494:pharmacology*; D000077150:Oxaliplatin; D010766:Phosphorylation; D010984:Platinum / Q000378:metabolism; D011799:Quinazolines / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D005723:gamma-Glutamyltransferase / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D018736:DNA Adducts; D009944:Organoplatinum Compounds; D011799:Quinazolines; D000077150:Oxaliplatin; D010984:Platinum; D005723:gamma-Glutamyltransferase; D066246:ErbB Receptors; D000077156:Gefitinib