VA Tennessee Valley Healthcare System, Nashville, Tennessee 37212, United States.
Chem Res Toxicol. 2021 Apr 19;34(4):1082-1090. doi: 10.1021/acs.chemrestox.0c00492. Epub 2021 Mar 24.
1,2-Naphthoquinone, a secondary metabolite of naphthalene, is an environmental pollutant found in diesel exhaust particles that displays cytotoxic and genotoxic properties. Because many quinones have been shown to act as topoisomerase II poisons, the effects of this compound on DNA cleavage mediated by human topoisomerase IIα and IIβ were examined. The compound increased the levels of double-stranded DNA breaks generated by both enzyme isoforms and did so better than a series of naphthoquinone derivatives. Furthermore, 1,2-naphthoquinone was a more efficacious poison against topoisomerase IIα than IIβ. Topoisomerase II poisons can be classified as interfacial (which interact noncovalently at the enzyme-DNA interface and increase DNA cleavage by blocking ligation) or covalent (which adduct the protein and increase DNA cleavage by closing the N-terminal gate of the enzyme). Therefore, experiments were performed to determine the mechanistic basis for the actions of 1,2-naphthoquinone. In contrast to results with etoposide (an interfacial poison), the activity of 1,2-naphthoquinone against topoisomerase IIα was abrogated in the presence of sulfhydryl and reducing agents. Moreover, the compound inhibited cleavage activity when incubated with the enzyme prior to the addition of DNA and induced virtually no cleavage with the catalytic core of the enzyme. It also induced stable covalent topoisomerase IIα-DNA cleavage complexes and was a partial inhibitor of DNA ligation. Findings were also consistent with 1,2-naphthoquinone acting as a covalent poison of topoisomerase IIβ; however, mechanistic studies with this isoform were less conclusive. Whereas the activity of 1,2-naphthoquinone was blocked in the presence of a sulfhydryl reagent, it was much less sensitive to the presence of a reducing agent. Furthermore, the reduced form of 1,2-naphthoquinone, 1,2-dihydroxynaphthalene, displayed high activity against the β isoform. Taken together, results suggest that 1,2-naphthoquinone increases topoisomerase II-mediated double-stranded DNA scission (at least in part) by acting as a covalent poison of the human type II enzymes.
1,2-萘醌是萘的一种次生代谢物，是柴油废气颗粒中的一种环境污染物，具有细胞毒性和遗传毒性。由于许多醌类化合物已被证明可以作为拓扑异构酶 II 抑制剂，因此研究了该化合物对人拓扑异构酶 IIα和 IIβ介导的 DNA 切割的影响。该化合物增加了两种酶同工型产生的双链 DNA 断裂水平，并且比一系列萘醌衍生物更好。此外，1,2-萘醌对拓扑异构酶 IIα的毒性比 IIβ更强。拓扑异构酶 II 抑制剂可分为界面型（与酶-DNA 界面非共价相互作用，通过阻断连接增加 DNA 切割）或共价型（与蛋白质结合，通过关闭酶的 N 端门增加 DNA 切割）。因此，进行了实验以确定 1,2-萘醌作用的机制基础。与依托泊苷（界面型抑制剂）的结果相反，在存在巯基和还原剂的情况下，1,2-萘醌对拓扑异构酶 IIα的活性被阻断。此外，该化合物在与酶孵育后加入 DNA 时抑制了切割活性，并与酶的催化核心几乎没有诱导切割。它还诱导稳定的共价拓扑异构酶 IIα-DNA 切割复合物，并部分抑制 DNA 连接。这些发现也与 1,2-萘醌作为拓扑异构酶 IIβ的共价抑制剂一致；然而，该同工型的机制研究不太确定。虽然 1,2-萘醌的活性在巯基试剂存在下被阻断，但它对还原剂的敏感性要低得多。此外，1,2-萘醌的还原形式 1,2-二羟基萘对β同工型具有很高的活性。总之，结果表明，1,2-萘醌通过作为人 II 型酶的共价抑制剂增加拓扑异构酶 II 介导的双链 DNA 断裂（至少部分如此）。
