title: Antagonistic effect of aclarubicin on daunorubicin-induced cytotoxicity in human small cell lung cancer cells: relationship to DNA integrity and topoisomerase II.
abstract: The effect of combinations of the anthracyclines aclarubicin and daunorubicin was investigated in a clonogenic assay using the human small cell lung cancer cell line OC-NYH and a multidrug-resistant (MDR) murine subline of Ehrlich ascites tumor (EHR2/DNR+). It was found that the cytotoxicity of daunorubicin in OC-NYH cells was antagonized by simultaneous exposure to nontoxic concentrations of aclarubicin. Coordinately, aclarubicin inhibited the formation of daunorubicin-induced protein-concealed DNA single-strand breaks and DNA-protein cross-links in OC-NYH cells when assayed by the alkaline elution technique. Aclarubicin had no influence on the accumulation of daunorubicin in these cells. In contrast, the accumulation of daunorubicin in EHR2/DNR+ cells was enhanced by more than 300% when the cells were simultaneously incubated with the MDR modulator verapamil, aclarubicin, or the two agents combined. Yet the cytotoxicity of daunorubicin was potentiated significantly only by verapamil. The increased cytotoxicity of daunorubicin in the presence of verapamil was completely antagonized when aclarubicin was used together with the MDR modulator. Finally, the effect of daunorubicin on the DNA cleavage activity of purified topoisomerase II in the presence and absence of aclarubicin was examined. It was found that daunorubicin stimulated DNA cleavage by topoisomerase II at specific DNA sites. The addition of aclarubicin completely inhibited the daunorubicin-induced stimulation of DNA cleavage. Taken together, these data indicate that aclarubicin-mediated inhibition of daunorubicin-induced cytotoxicity is due mainly to a drug interaction with the nuclear enzyme topoisomerase II. This antagonism at the nuclear level explains why aclarubicin is a poor modulator of daunorubicin resistance even though aclarubicin is able to increase the intracellular accumulation of daunorubicin in a MDR cell line.
authors.affiliation: Department of Oncology, Finsen Institute, Copenhagen, Denmark.
authors.forename: P B
authors.initials: PB
authors.lastname: Jensen
authors.forename: P S
authors.initials: PS
authors.lastname: Jensen
authors.forename: E J
authors.initials: EJ
authors.lastname: Demant
authors.forename: E
authors.initials: E
authors.lastname: Friche
authors.forename: B S
authors.initials: BS
authors.lastname: Sørensen
authors.forename: M
authors.initials: M
authors.lastname: Sehested
authors.forename: K
authors.initials: K
authors.lastname: Wassermann
authors.forename: L
authors.initials: L
authors.lastname: Vindeløv
authors.forename: O
authors.initials: O
authors.lastname: Westergaard
authors.forename: H H
authors.initials: HH
authors.lastname: Hansen
mesh_terms: D015250:Aclarubicin / Q000494:pharmacology*; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D002286:Carcinoma, Ehrlich Tumor / Q000188:drug therapy; D018288:Carcinoma, Small Cell / Q000188:drug therapy*; D003114:Colony-Forming Units Assay; D004247:DNA / Q000187:drug effects*; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000187:drug effects; D003630:Daunorubicin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004336:Drug Antagonism; D006801:Humans; D066298:In Vitro Techniques; D008175:Lung Neoplasms / Q000188:drug therapy*; D051379:Mice; D014700:Verapamil / Q000494:pharmacology
chemical_list: D015250:Aclarubicin; D004247:DNA; D014700:Verapamil; D004250:DNA Topoisomerases, Type II; D003630:Daunorubicin