title: Differential cytotoxicity of clinically important camptothecin derivatives in P-glycoprotein-overexpressing cell lines.
abstract: Camptothecin and its derivatives are specific inhibitors of eukaryotic topoisomerase I (top1) and are active in cancer patients against a variety of refractory solid tumors and leukemia.
  
  
  OBJECTIVE
  The present study further investigated the relationship between multidrug resistance (MDR) mediated by P-glycoproteinMDR and potential resistance to camptothecin derivatives using two experimental systems: (1) MDR KB-V1 cells selected for vinblastine resistance, and (2) NIH3T3 cells transfected with a plasmid expressing wildtype P-glycoproteinMDR multidrug transporter (NIH-MDR-G185).
  
  
  RESULTS
  We found that both KBV-1 and NIH-MDR-G185 cells were resistant to topotecan, and that topotecan-induced cleavable complexes were reduced in KB-V1 cells, consistent with a role of P-glycoproteinMDR in cellular resistance to topotecan. By contrast, no significant resistance to camptothecin, 9-aminocamptothecin, 10, 11-methylenedioxycamptothecin, or SN-38 (the active metabolite of CPT-11) was observed in NIH-MDR-G185 cells, while KB-V1 cells were cross-resistant to these compounds but produced cleavable complexes similar to those produced by parental KB-3-1 cells.
  
  
  CONCLUSIONS
  These results suggest that topotecan is the only camptothecin tested with significant susceptibility to MDR in cell culture, and that multidrug resistant cells such as KBV1 probably exhibit additional resistance mechanisms to camptothecins besides P-glycoproteinMDR overexpression.
authors.affiliation: Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Hoki
authors.forename: A
authors.initials: A
authors.lastname: Fujimori
authors.forename: Y
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000187:drug effects; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D015152:Blotting, Northern; D015153:Blotting, Western; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004264:DNA Topoisomerases, Type I / Q000187:drug effects; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D007624:KB Cells; D013997:Time Factors; D019772:Topotecan; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D019772:Topotecan; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin