TY - JOUR T1 - Salicylate, a Catalytic Inhibitor of Topoisomerase II, Inhibits DNA Cleavage and is Selective for the Alpha Isoform JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.113.088963 SP - mol.113.088963 AU - Jason T Bau AU - Zhili Kang AU - Caroline A Austin AU - Ebba U Kurz Y1 - 2013/01/01 UR - http://molpharm.aspetjournals.org/content/early/2013/11/12/mol.113.088963.abstract N2 - Topoisomerase II (topo II) is a ubiquitous enzyme that is essential for cell survival through its role in regulating DNA topology and chromatid separation. Topo II can be poisoned by common chemotherapeutics (such as doxorubicin and etoposide), leading to the accumulation of cytotoxic enzyme-linked DNA double-stranded breaks. In contrast, non-break-inducing topo II catalytic inhibitors have also been described and have more limited use in clinical chemotherapy. These agents, however, may alter the efficacy of regimens incorporating topo II poisons. We previously identified salicylate, the primary metabolite of aspirin, as a novel catalytic inhibitor of topo II. We have now determined the mechanism by which salicylate inhibits topo II. As catalytic inhibitors can act at a number of steps in the topo II catalytic cycle, we used multiple independent, biochemical approaches to interrogate the catalytic cycle. Furthermore, as mammalian cells express two isoforms of topo II (α and β), we examined whether salicylate was isoform selective. Our results demonstrate that salicylate is unable to intercalate DNA, does not prevent enzyme-DNA interaction, nor does it promote stabilization of topo IIα in closed clamps on DNA. While salicylate decreased topo IIα ATPase activity in a dose-dependent non-competitive manner, this was secondary to salicylate-mediated inhibition of DNA cleavage. Surprisingly, comparison of salicylate's effects using purified human topo IIα and topo IIβ revealed that salicylate selectively inhibits the alpha isoform. These findings provide a definitive mechanism for salicylate-mediated inhibition of topo IIα and provide support for further studies determining the basis for its isoform selectivity. ER -