Inhibition of Human Topoisomerase II in Vitro by Bioactive Benzene Metabolites

Abstract

Benzene is a clastogenic and carcinogenic agent that induces acute myelogenous leukemia in humans and multiple of tumors in animals. Previous research has indicated that benzene must first be metabolized to one or more bioactive species to exert its myelotoxic and genotoxic effects. To better understand the possible role of individual benzene metabolites in the leukemogenic process, as well as to further investigate inhibition of topoisomerase II by benzene metabolites, a series of known and putative benzene metabolites, phenol, 4,4'-biphenol, 2,2'-biphenol, hydroquinone, catechol, 1,2,4-benzenetriol, 1,4-benzoquinone, and trans-trans-muconaldehyde were tested for inhibitory effects in vitro on the human topoisomerase II enzyme. With minor modifications of the standard assay conditions, 1,4-benzoquinone and trans-trans-muconaldehyde were shown to be directly inhibitory, whereas all of the phenolic metabolites were shown to inhibit enzymatic activity following bioactivation using a peroxidase activation system. The majority of compounds tested inhibited topoisomerase II at concentrations at or below 10 microM. These results confirm and expand upon previous findings from our laboratory and indicate that many of the metabolites of benzene could potentially interfere with topoisomerase II. Since other inhibitors of topoisomerase II have been shown to induce leukemia in humans, inhibition of this enzyme by benzene metabolites may also play a role in the carcinogenic effects of benzene.

The Nature of Chromosomal Aberrations Detected in Humans Exposed to Benzene

“…This is of interest because, as mentioned above, t(11q23) is associated with leukemia caused by topoisomerase II inhibitors that form cleavable complexes, such as etoposide and adriamycin (Pui et al, 1991). Benzene metabolites are inhibitors of topoisomerase II, but do not form cleavable complexes (Chen and Eastmond, 1995;Frantz et al, 1996). In this respect they are similar to bimolane, which induces leukemias with t(21q22).…”

In vitro assessment of the cytotoxic, DNA damaging, and cytogenetic effects of hydroquinone in human peripheral blood lymphocytes

“…This was sustained by the significantly higher values of all comet assay parameters measured in the sample treated with 8 µg mL -1 compared to the other two hydroquinone-treated samples. Also, findings by Frantz et al (66) suggest that 1,4-benzoquinone inhibited topoisomerase II in in vitro conditions at concentrations of ≥10 µmol L -1…”

“…As another important mechanism of hydroquinone action at DNA level, the available literature suggests the inhibition of topoisomerase II enzyme (66)(67)(68) and induction of oxidative stress (33,65), resulting in a significant amount of DNA breaks. According to Andreoli et al (33), hydroquinone produces significantly more primary DNA damage in isolated human lymphocytes than in the whole blood leukocyte population.…”

Acute leukemia in early childhood

“…Topo-II inhibitors include chemotherapeutic agents, benzene metabolites (such as benzoquinone), isoflavones, flavonoids, lignans, podophyllin resin, quinolone antibiotics, and some pesticides. Specific fruits and vegetables that contain quercetin, soybeans (genistein), tea, cocoa, wine (catechins), and caffeine have all been related to an increased risk of infant AML (36,(38)(39)(40). Thus, to better understand the environmental exposures to damaging agents that give rise to these genetic changes in utero, infants represent a more accurate group than older children, since the window of exposure is limited and known (shortly before or during pregnancy).…”