Topoisomerase inhibitors induce irreversible fragmentation of replicated DNA in concanavalin A stimulated splenocytes

• Published in: Biochemistry (Easton) 1988-01, Vol.27 (1), p.95-99
• Main Authors: Jaxel, Christine, Taudou, Georges, Portemer, Christiane, Mirambeau, Gilles, Panijel, Jacques, Duguet, Michel
• Format: Article
• Language: English
• Subjects: Animals; Camptothecin - pharmacology; Concanavalin A - pharmacology; DNA - drug effects; DNA Replication - drug effects; DNA Topoisomerases, Type II - isolation & purification; Etoposide - pharmacology; Lymphocyte Activation; Lymphocytes - drug effects; Lymphocytes - enzymology; Lymphocytes - immunology; Mice; Mice, Inbred C57BL; Novobiocin - pharmacology; Phenylmethylsulfonyl Fluoride - pharmacology; Spleen - immunology; Sulfones - pharmacology; Topoisomerase II Inhibitors
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00401a016

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.