title: Attenuated topoisomerase II content directly correlates with a low level of drug resistance in a Chinese hamster ovary cell line.
abstract: A new multiple drug-resistant Chinese hamster ovary cell line, CHO-SMR5, has been isolated which demonstrates a direct correlation between reduced cellular topoisomerase II activity (5-fold reduction) and a low level of resistance (3- to 7-fold) to topoisomerase II inhibitors. This cell line, initially selected for resistance to 9-(4,6-O-ethylidene-beta-D-glucopyranosyl)-4'-demethylepipodophylloto xin, exhibits cross-resistance to other topoisomerase II inhibitors including 4'-(9-acridinylamino)methanesulfon-m-anisidide, doxorubicin, and mitoxantrone. The resistant cells show a 4.5-fold decrease in topoisomerase II by immunoblotting when compared to wild-type cells. Drug uptake studies reveal equivalent equilibrium intracellular concentrations of [3H]9-(4,6-O-ethylidene-beta-D-glucopyranosyl)-4'-demethyepipodophyll otoxin in the resistant and parental cells. The catalytic activity of topoisomerase II (decatenation of kinetoplast DNA) is 5-fold less in the drug-resistant cell line relative to wild-type Chinese hamster ovary cells. Drug-induced DNA damage, measured as either formation of DNA double-strand breaks or covalent DNA-enzyme complexes, is 4-fold less in the resistant cell line. Finally, Northern blot analysis demonstrates a 5-fold reduction in topoisomerase II mRNA isolated from log phase CHO-SMR5 cells. These findings suggest that a reduced level of topoisomerase II is likely to be the sole mechanism of drug resistance in this novel cell line.
authors.affiliation: James Graham Brown Cancer Center, University of Louisville, Kentucky 40292.
authors.forename: C D
authors.initials: CD
authors.lastname: Webb
authors.forename: M D
authors.initials: MD
authors.lastname: Latham
authors.forename: R B
authors.initials: RB
authors.lastname: Lock
authors.forename: D M
authors.initials: DM
authors.lastname: Sullivan
mesh_terms: D000818:Animals; D001692:Biological Transport; D015152:Blotting, Northern; D015153:Blotting, Western; D016466:CHO Cells; D002467:Cell Nucleus / Q000201:enzymology; D006224:Cricetinae; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004278:DNA, Superhelical / Q000378:metabolism; D004351:Drug Resistance; D005047:Etoposide / Q000494:pharmacology*; D015870:Gene Expression; D012333:RNA, Messenger / Q000235:genetics; D059005:Topoisomerase II Inhibitors
chemical_list: D004278:DNA, Superhelical; D012333:RNA, Messenger; D059005:Topoisomerase II Inhibitors; D005047:Etoposide; D004250:DNA Topoisomerases, Type II