Stimulation of topoisomerase II-mediated DNA cleavage by benzene metabolites

Benzene is a human carcinogen that induces hematopoietic malignancies. It is believed that benzene does not initiate leukemias directly, but rather generates DNA damage through a series of phenolic and quinone-based metabolites, especially 1,4-benzoquinone. Since the DNA damage induced by 1,4-benzoquinone is consistent with that of topoisomerase II-targeted drugs, it has been proposed that the compound initiates specific types of leukemia by acting as a topoisomerase 11 poison. This hypothesis, however, was not supported by initial in vitro studies. While 1,4-benzoquinone inhibited topoisomerase 11 catalysis, increases in enzyme-mediated DNA cleavage were not observed. Because of the potential involvement of topoisomerase 11 in benzene-induced leukemias, we re-examined the effects of benzene metabolites (including 1,4-benzoquinone, 1,4-hydroquinone, catechol, 1,2,4-benzenetriol, 2,2'-biphenol, and 4,4'-biphenol) on DNA cleavage mediated by human topoisomerase II alpha. In contrast to previous reports, we found that 1,4-benzoquinone was a strong topoisomerase 11 poison and was more potent in vitro than the anticancer drug etoposide. Other metabolites displayed considerably less activity. DNA cleavage enhancement by 1,4benzoquinone was unseen in previous studies due to the presence of reducing agents and the incubation of 1,4-benzoquinone with the enzyme prior to the addition of DNA. Unlike anticancer drugs such as etoposide that interact with topoisomerase II alpha in a noncovalent manner, the actions of 1,4-benzoquinone appear to involve a covalent attachment to the enzyme. Finally, 1,4-benzoquinone stimulated DNA cleavage by topoisomerase net in cultured human cells. These findings are consistent with the hypothesis that topoisomerase II alpha plays a role in the initiation of some benzene-induced leukemias. 0 2005 Elsevier Ireland Ltd. All rights reserved.