title: Evaluation of topoisomerase I catalytic activity as determinant of drug response in human cancer cell lines.
abstract: The prognostic value of topoisomerase I (Topo I) catalytic activity and expression of the multidrug resistance (MDR) marker P-glycoprotein (Pgp) and multidrug resistance protein (MRP) for in vitro sensitivity to Topo I interactive agents were evaluated. The efficacy of short term (2 h) and long term (24 h) exposures of camptothecin (CPT), two CPT derivatives (SN-22, SN-38) and the indolocarbazole compound NB-506, was determined against human ovarian carcinoma (A2780 and A2780 DX5), human fibrosarcoma (HT1080 and IIT1080/DR4) and human ileocecal carcinoma (HCT-8). For each cell line the Topo I protein levels and catalytic activity were determined and correlated with drug-induced cytotoxicity. In general, the Topo I protein levels correlated with Topo I catalytic activity. Drug-induced cytotoxicity increased significantly with prolongation of the exposure time. With the 2 h exposure, the multidrug resistant A2780 DX5 cell line (Pgp+, MRP-) was moderately resistant to all four drugs compared to its parental cell line. In case of CPT and SN-22 but not for SN-38 and NB-506, this resistance was no longer detectable following 24 h drug exposure. No resistance was detectable for the multidrug resistant HT1080/DR4 (Pgp-, MRP+) cell line when compared to its parental cell line. With short term exposures a strong trend was observed toward increased cytotoxicity with increased Topo I catalytic activity, especially if this correlation was studied between derivative cell lines (A2780 vs. A2780 DX5 and HT1080 vs. HT1080/DR4). This correlation weakened when all 5 cell lines and both exposure conditions were considered. Thus, although overall the correlation between Topo I catalytic activity and sensitivity to Topo I interactive drugs between different cell lines is weak, this correlation may be stronger when comparing derivative cell lines. For CPT and SN-22 but not for SN-38 and NB-506, the moderate resistance levels observed in the Pgp-expressing cell line could be negated by prolongation of exposure duration. MRP expression did not effect drug efficacy. The data demonstrate that the importance of Topo I catalytic activity as single prognostic factor for drug response to Topo I interactive agents is weak and that additional mechanisms affecting drug response have to be taken into consideration.
authors.affiliation: Martin-Luther-Universität Halle-Wittenberg, Klinikum Kröllwitz, Department of Hematology/Oncology, Halle/Saale, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Voigt
authors.forename: U
authors.initials: U
authors.lastname: Vanhoefer
authors.forename: M B
authors.initials: MB
authors.lastname: Yin
authors.forename: H
authors.initials: H
authors.lastname: Minderman
authors.forename: H J
authors.initials: HJ
authors.lastname: Schmoll
authors.forename: Y M
authors.initials: YM
authors.lastname: Rustum
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology*; D002227:Carbazoles / Q000494:pharmacology; D002384:Catalysis; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005960:Glucosides / Q000494:pharmacology; D006801:Humans; D000077146:Irinotecan; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D002227:Carbazoles; D004791:Enzyme Inhibitors; D005960:Glucosides; C092476:NB 506; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; C051891:7-ethylcamptothecin; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin