title: Altered formation of topotecan-stabilized topoisomerase I-DNA adducts in human leukemia cells.
abstract: Topotecan (TPT) is a topoisomerase I (topo I) poison that has shown promising antineoplastic activity in solid tumors and acute leukemia. In the present study, a band depletion assay was used to evaluate the ability of TPT to stabilize topo I-DNA adducts in human leukemia cell lines and in clinical leukemia samples ex vivo. This assay showed that 50% of the cellular topo I in HL-60 human myelomonocytic leukemia cells became covalently bound to DNA at an extracellular TPT concentration of 4 micromol/L. In contrast, in 13 clinical specimens of human leukemia harvested before treatment of patients with TPT, the TPT concentration required to stabilize 50% of the cellular topo I in topo I-DNA complexes ranged from 3 to greater than 100 micromol/L (median, 30 micromol/ L). Flow microfluorimetry showed that cellular TPT accumulation varied over only a twofold range and failed to provide evidence for transport-mediated resistance in the clinical samples. These observations raise the possibility that formation of topo I-DNA adducts is diminished in many specimens of refractory/relapsed acute leukemia by a mechanism that might alter topo I sensitivity to TPT.
authors.affiliation: Division of Oncology Research, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: S H
authors.initials: SH
authors.lastname: Kaufmann
authors.forename: P A
authors.initials: PA
authors.lastname: Svingen
authors.forename: S D
authors.initials: SD
authors.lastname: Gore
authors.forename: D K
authors.initials: DK
authors.lastname: Armstrong
authors.forename: Y C
authors.initials: YC
authors.lastname: Cheng
authors.forename: E K
authors.initials: EK
authors.lastname: Rowinsky
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D018736:DNA Adducts / Q000187:drug effects* / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000187:drug effects / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D006801:Humans; D007938:Leukemia / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism; D011446:Prospective Studies; D019772:Topotecan
chemical_list: D000970:Antineoplastic Agents; D018736:DNA Adducts; D004273:DNA, Neoplasm; D019772:Topotecan; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin