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 types 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 11 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-transmuconaldehyde were tested for inhibitory effects in vitro on the human topoisomerase 11 enzyme. With minor modifications of the standard assay conditions, 1,4-benzoquinone and transtrans-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 11 at concentrations at or below 10 pM. 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 11. Since other inhibitors of topoisomerase 11 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. Environ Health Perspect 104(Suppl 6): 1319-1323 (1996)

Benzene and lymphohematopoietic malignancies in humans†

“…Some of the cytogenetic abnormalities observed (e.g., long arm deletions of chromosomes 5 and 7, aneuploidy in chromosomes 8 and 21) are similar to those observed in patients with secondary leukemias induced by alkylating agents and topoisomerase II inhibitor chemotherapy drugs [van Leeuwen, 1996;Felix, 1998], and by persons developing solvent-induced leukemias [Crane et al, 1996;Davico et al, 1998]. Several activated benzene metabolites (including phenol, 4,4 H -biphenol, 2,2 H -biphenol, hydroquinone, catechol, 1,2,4-benzenetriol, 1,4-benzenequinone, and trans-trans-muconaldehyde) have been shown to inhibit topoisomerase II, an enzyme critical in DNA replication and repair [Chen and Eastmond, 1995;Frantz et al, 1996;Eastmond et al, 2000]. Studies in animals and humans have shown that benzene induces deletions and other large-scale chromosomal alterations [Schiestl et al, 1997;Zhang et al, 1998;Eastmond et al, 2000], translocations [Aksoy, 1988;Chen et al, 1994;Eastmond et al, 2000], and aneuploidy [Chen et al, 1994;Zhang et al, 1996;Zhang et al, 1998].…”

Quinone-Induced Enhancement of DNA Cleavage by Human Topoisomerase IIα: Adduction of Cysteine Residues 392 and 405

“…The quinone-based topoisomerase II poisons differ from "classic" topoisomerase II poisons (such as etoposide and bioflavonoids) in two ways. First, quinones are mixed-function inhibitors of the type II enzyme: they increase DNA scission when added to a topoisomerase II-DNA complex, but inhibit scission when incubated with the enzyme prior to the addition of nucleic acids (36)(37)(38)(39)(50)(51)(52)(53)(54). Second, in contrast to compounds like etoposide (which interact with topoisomerase II in a non-covalent manner), quinones act by covalently attaching to the protein (35)(36)(37)(38)(39)53).…”

Analysis of glutathione and vitamin C effects

“…Using an antikinetochore antibody-based micronucleus assay and FISH techniques in HL-60 cells, BT was found to produce mainly aneugenic effects by disrupting microtubules [13,14]. Moreover, in vitro inhibition of enzymes involved in DNA replication and repair, as topoisomerase enzymes, by BT and other benzene metabolites represents a potential mechanism for the formation of chromosomal aberrations and may contribute to the leukemogenic effect of benzene [43,44].…”