Abstract C39: Catalytic inhibition of human DNA topoisomerase II α by salicylate and related nonsteroidal anti-inflammatory drugs
Authors: Bau Jason T. , Kurz Ebba U. 
Published: June 2012

Abstract
Salicylate-based drugs, including aspirin (acetylsalicylic acid), have long been used in the treatment of mild to moderate cancer pain and have been shown in population-based studies to have cancer chemopreventive properties. Several mechanisms have been hypothesized to underlie these effects, including the inhibition of cyclooxygenases and the inhibition of the transcription factor NF-\#954;B. We have recently demonstrated, however, that salicylate, the primary metabolite of aspirin, is a novel catalytic inhibitor of human DNA topoisomerase IIα (topo II), a nuclear enzyme essential for cell proliferation and division and the target of several widely used anti-cancer chemotherapeutics. As a consequence of this inhibition, and independent of its capacity to inhibit cyclooxygenases and NF-\#954;B, we have demonstrated that a brief pretreatment of human breast cancer cells with salicylate attenuates the cytotoxicity of the topo II poisons, doxorubicin and etoposide. We have observed that salicylate prevents doxorubicin-induced DNA double-strand break generation, which is attributable to salicylate-mediated inhibition of doxorubicin-stabilized topo II-DNA cleavable complex formation in vivo. Together, these data suggest that co-administration of salicylates could negatively impact the efficacy of cancer treatment regimens incorporating topo II-targeting therapeutics.
We have now extended our investigation of salicylate, using a biochemical approach to determine the mechanism whereby salicylate inhibits the catalytic activity of topo II. As the inhibition of topo II can occur at one of several stages in its catalytic cycle, we have undertaken multiple independent approaches, including an examination of DNA binding, DNA intercalation, measurement of ATPase activity and evaluation of salicylate's capacity to stabilize topo II in a closed clamp formation without causing DNA double-strand breaks. In addition to delineating the mechanism of salicylate-mediated inhibition of topo II, we have investigated whether common salicylate- and non-salicylate-based non-steroidal anti-inflammatory drugs (NSAIDs) possess similar topo II inhibitory properties, initially by examining the effects of short-term exposure on doxorubicin-induced DNA damage signaling followed by a direct examination of their effects on topo II catalytic activity. Our experiments demonstrate that inhibition of topo II is readily observed with multiple salicylate-based therapies at clinically achieved concentrations.
These investigations identify a novel cellular target of salicylate and will inform future studies that may reveal evidence warranting the discouragement of NSAID co-administration in patients undergoing treatment for any of the broad-reaching malignancies using topo II poisons in their therapeutics regimen.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C39.