title: Antagonistic effect of aclarubicin on the cytotoxicity of etoposide and 4'-(9-acridinylamino)methanesulfon-m-anisidide in human small cell lung cancer cell lines and on topoisomerase II-mediated DNA cleavage.
abstract: The effect of combinations of the anthracycline aclarubicin and the topoisomerase II targeting drugs 4'-demethylepipodophyllotoxin-9-(4,6-O-ethylidene-beta-D-glucopyra noside) (VP-16) and 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) was investigated in a clonogenic assay. The cytotoxicity of VP-16 was almost completely antagonized by preincubating cells with nontoxic concentrations of aclarubicin. The inhibition of cytotoxicity was not seen when the cells were exposed to aclarubicin after exposure to VP-16. The inhibition was significant over a wide range of aclarubicin concentrations (3 nM to 0.4 microM), above which the toxicity of aclarubicin became apparent. A similar effect was seen on the toxicity of m-AMSA. In contrast to aclarubicin, preincubation with Adriamycin did not antagonize the effect of VP-16. With purified topoisomerase II and naked DNA, aclarubicin did not stimulate the formation of cleavable complexes between topoisomerase II and DNA. Aclarubicin concentrations above 1 microM inhibited the baseline formation of cleavable complexes elicited with the enzyme alone. Low (1 to 10 nM) aclarubicin concentrations increased the formation of cleavable complexes obtained with VP-16 and m-AMSA; however, at aclarubicin concentrations above 1 microM an antagonistic effect was obtained. In cells, the m-AMSA- and VP-16-induced, protein-concealed DNA strand breaks were completely inhibitable by aclarubicin preincubation with no synergic dose levels. Our results suggest that aclarubicin inhibits topoisomerase II-mediated DNA cleavage. This inhibition could represent the mechanism of action of the drug and explain the lack of cross-resistance to the classical anthracyclines. The observed antagonism could have consequences for scheduling of aclarubicin with topoisomerase II-active anticancer drugs.
authors.affiliation: Department of Oncology, Finsen Institute, Copenhagen, Denmark.
authors.forename: P B
authors.initials: PB
authors.lastname: Jensen
authors.forename: B S
authors.initials: BS
authors.lastname: Sørensen
authors.forename: E J
authors.initials: EJ
authors.lastname: Demant
authors.forename: M
authors.initials: M
authors.lastname: Sehested
authors.forename: P S
authors.initials: PS
authors.lastname: Jensen
authors.forename: L
authors.initials: L
authors.lastname: Vindeløv
authors.forename: H H
authors.initials: HH
authors.lastname: Hansen
mesh_terms: D015250:Aclarubicin / Q000494:pharmacology*; D000677:Amsacrine / Q000037:antagonists & inhibitors* / Q000633:toxicity; D018288:Carcinoma, Small Cell / Q000188:drug therapy* / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000187:drug effects*; D004317:Doxorubicin / Q000494:pharmacology; D005047:Etoposide / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000633:toxicity; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000235:genetics; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
chemical_list: D004273:DNA, Neoplasm; D059005:Topoisomerase II Inhibitors; D000677:Amsacrine; D005047:Etoposide; D015250:Aclarubicin; D004317:Doxorubicin