title: Altered DNA-cleavage activity of topoisomerase II from WEHI-3B leukemia cells with specific resistance to ciprofloxacin.
abstract: In order to investigate the mechanisms of drug resistance arising in tumor cells, we investigated the capacity of fluoroquinolones to inhibit the in vitro growth of WEHI-3B monomyelocytic leukemia cells and then we established a variant of this line (currently maintained in the absence of drug). The line, named WEHI-3B/CPX, expresses a specific resistance to ciprofloxacin (CPX; resistance index=17.3+/-2.2), and does not show cross-resistance with other fluoroquinolones, camptothecin and topoisomerase II inhibitors such as doxorubicin, etoposide and teniposide. Although a little decrease in intracellular accumulation of CPX is observed in WEHI-3B/CPX cells, these cells do not express MDR or LRP markers, and the resistance is not circumvented by verapamil. Purified nuclear extracts from WEHI-3B and WEHI-3B/CPX cells were tested for topoisomerase I catalytic activity and checking in vitro topoisomerase I sensitivity to CPX and camptothecin inhibition, but no difference was observed. As the treatment with CPX showed that the resistant cell line suffers a significantly lower number of breaks in the DNA molecule we also addressed our investigations to the topoisomerase II-dependent DNA cleavage that, in the resistant clone, was found dramatically less susceptible to be enhanced by CPX both in pre-strand and post-strand DNA passage conditions. WEHI-3B/CPX cells do not express any character of multidrug resistance and represent a rare case of specific drug resistance to CPX. The specific resistance to CPX observed in these cells is related to a functional decrease of topoisomerase II cleavage activity. It could be consequent to a decreased binding affinity of CPX for the topoisomerase II--DNA complex or to a decreased affinity or specificity of topoisomerase II for its DNA cleavage sites.
authors.affiliation: Institute of Microbiology, Faculty of Medicine, University of Milan, 20133 Milan, Italy. pessinaa@mailserver.unimi.it
authors.forename: A
authors.initials: A
authors.lastname: Pessina
authors.forename: A
authors.initials: A
authors.lastname: Raimondi
authors.forename: C
authors.initials: C
authors.lastname: Croera
authors.forename: M
authors.initials: M
authors.lastname: Acchini
authors.forename: E
authors.initials: E
authors.lastname: Mineo
authors.forename: P
authors.initials: P
authors.lastname: Foti
authors.forename: M G
authors.initials: MG
authors.lastname: Neri
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D002166:Camptothecin / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002939:Ciprofloxacin / Q000494:pharmacology*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D015479:Leukemia, Myelomonocytic, Acute / Q000201:enzymology*; D014407:Tumor Cells, Cultured / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology
chemical_list: D000890:Anti-Infective Agents; D000972:Antineoplastic Agents, Phytogenic; D004273:DNA, Neoplasm; D002939:Ciprofloxacin; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin