title: Determinants of CPT-11 and SN-38 activities in human lung cancer cells.
abstract: Irinotecan (CPT-11) is a semisynthetic camptothecin derivative with a broad spectrum of anti-tumour activity. Carboxylesterase (CE) catalyses the conversion of CPT-11 to SN-38 (7-ethyl-10-hydroxycamptothecin), the active form of CPT-11. The antiproliferative effects of CPT-11 and SN-38, CE-activity and topoisomerase I protein expression were investigated in five human small-cell lung cancer (SCLC) cell lines and four human non-small-cell lung cancer (NSCLC) cell lines. Antiproliferative activity, expressed as IC50 values, was determined using the MTT assay. CPT-11 was significantly more active in SCLC than in NSCLC cell lines (P = 0.0036), whereas no significant difference between histological types was observed with SN-38. A significant correlation (r2 = 0.52, P = 0.028) was observed between CE activity and chemosensitivity to CPT-11 but not to SN-38, and significantly higher CE activity was observed in SCLC compared with NSCLC cell lines (P = 0.025). Western blotting experiments showed topoisomerase I protein expressions within a factor of 2, and a granular nuclear staining was detectable in all cell lines by immunocytochemistry of cytospins. No correlation was observed between protein expression and sensitivity to CPT-11 or SN-38. Cellular and medium concentrations of CPT-11 and SN-38 were measured by high-performance liquid chromatography (HPLC) in one SCLC cell line with high CE activity and high sensitivity to CPT-11, and one NSCLC cell line with low sensitivity to CPT-11 and CE activity. Intracellular concentrations of CPT-11 and SN-38 were higher in the SCLC cell line, and this was associated with an increase in cellular uptake of CPT-11 compared with the medium, and an increased intracellular formation of SN-38. In conclusion, CE activity appears to be associated with higher sensitivity to CPT-11 in human lung cancer cell lines and may partly explain the difference in the in vitro sensitivity to CPT-11 between SCLC and NSCLC cells. The assessment of CE activity in clinical material of lung cancer patients undergoing treatment with CPT-11 may be warranted. However, other mechanisms may influence sensitivity to CPT-11, possibly including drug transport.
authors.affiliation: University Hospital Vrije Universiteit, Department of Medical Oncology, Amsterdam, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: van Ark-Otte
authors.forename: M A
authors.initials: MA
authors.lastname: Kedde
authors.forename: W J
authors.initials: WJ
authors.lastname: van der Vijgh
authors.forename: A M
authors.initials: AM
authors.lastname: Dingemans
authors.forename: W J
authors.initials: WJ
authors.lastname: Jansen
authors.forename: H M
authors.initials: HM
authors.lastname: Pinedo
authors.forename: E
authors.initials: E
authors.lastname: Boven
authors.forename: G
authors.initials: G
authors.lastname: Giaccone
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D018288:Carcinoma, Small Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000096:biosynthesis / Q000378:metabolism; D004354:Drug Screening Assays, Antitumor; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D000077146:Irinotecan; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004791:Enzyme Inhibitors; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D002265:Carboxylic Ester Hydrolases; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin