title: Topoisomerase inhibitors induce irreversible fragmentation of replicated DNA in concanavalin A stimulated splenocytes.
abstract: Etoposide, a nonintercalative antitumor drug, is known to inhibit topoisomerase II. Its effects have been tested in concanavalin A stimulated splenocytes, a system of cell proliferation in which topoisomerase II is induced. The primary effect of etoposide was a strong inhibition of DNA synthesis and the production of reversible DNA breaks, presumably associated with topoisomerase II. However, prolonged (20 h) contact with the drug resulted in a secondary fragmentation by irreversible double-strand breaks that yielded unusually small DNA fragments. Surprisingly, the same effect was obtained with novobiocin, which does not produce topoisomerase II associated DNA breaks. Moreover, long-term treatment with camptothecin, a specific inhibitor of topoisomerase I which is known to induce single-strand breaks in vitro and in vivo, also produced double-strand breaks and DNA fragmentation into small pieces. These findings suggest that prolonged treatment of proliferating splenocytes by etoposide and other topoisomerase inhibitors induced DNA fragmentation by a mechanism that does not directly involve topoisomerases.
authors.affiliation: Laboratorie d'Enzymologie des Acides Nucléiques, UA 554 CNRS, Université Pierre et Marie Curie, Paris, France.
authors.forename: C
authors.initials: C
authors.lastname: Jaxel
authors.forename: G
authors.initials: G
authors.lastname: Taudou
authors.forename: C
authors.initials: C
authors.lastname: Portemer
authors.forename: G
authors.initials: G
authors.lastname: Mirambeau
authors.forename: J
authors.initials: J
authors.lastname: Panijel
authors.forename: M
authors.initials: M
authors.lastname: Duguet
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000494:pharmacology*; D003208:Concanavalin A / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects*; D004250:DNA Topoisomerases, Type II / Q000302:isolation & purification; D005047:Etoposide / Q000494:pharmacology*; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D009675:Novobiocin / Q000494:pharmacology*; D010664:Phenylmethylsulfonyl Fluoride / Q000494:pharmacology*; D013154:Spleen / Q000276:immunology; D013450:Sulfones / Q000494:pharmacology*; D059005:Topoisomerase II Inhibitors
chemical_list: D013450:Sulfones; D059005:Topoisomerase II Inhibitors; D003208:Concanavalin A; D009675:Novobiocin; D010664:Phenylmethylsulfonyl Fluoride; D005047:Etoposide; D004247:DNA; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin