Characterization of Salicylates as Novel Catalytic Inhibitors of Human DNA Topoisomerase II Alpha
Abstract
Topoisomerase II (topo II) is a ubiquitous enzyme required for the maintenance of DNA topology. Due to its essential nature, many pharmaceuticals have been found to or developed to target the enzyme for both laboratory and clinical uses. Topo II poisons, such as doxorubicin and etoposide, are commonly used in cancer chemotherapy regimens and are cytotoxic due to their ability to covalently trap topo II on cleaved DNA, leading to the accumulation of DNA double-stranded breaks. In contrast, compounds that inhibit topo II catalytic activity without generating DNA double-stranded breaks are classified as catalytic inhibitors and impair enzyme function at a number of stages in the catalytic cycle, including DNA binding, DNA cleavage, ATP hydrolysis, and enzyme dissociation. Some catalytic inhibitors have been found to counter the DNA damaging effects of topo II poisons. This thesis describes work identifying salicylate as a novel catalytic inhibitor of topo II. It demonstrates that pretreatment of cells with salicylate, prior to treatment with topo II poisons, attenuates poison-induced DNA damage signaling mediated by the ATM protein kinase. This is associated with a concomitant loss of poison-induced DNA double- stranded breaks and consequently decreased cytotoxicity following treatment with topo II poisons. This work also demonstrates that salicylate does not block topo II-DNA binding, or trap the enzyme as a closed clamp on DNA. Rather, salicylate blocks DNA cleavage and enzyme-mediated ATP hydrolysis is impaired in a non-competitive manner. Furthermore, salicylate-mediated inhibition of topo II catalytic activity is selective for the alpha isoform of topo II. In investigating the structural determinants modulating potency of topo II inhibition, many compounds with structural similarities to salicylate, including the salicylate-based pharmaceuticals sulfasalazine and diflunisal, were found to also act as catalytic inhibitors of topo II. It was determined that potency is determined by modifications at the 2’-position that are electronegative and capable of donating a hydrogen bond, but that these effects are further influenced by substitutions at the 5’-position. Considered together, the data presented in this thesis establish a new role for a long-established drug.
Description
Keywords
Biology--Molecular, Medicine and Surgery, Pharmacology
Citation
Bau, J. (2014). Characterization of Salicylates as Novel Catalytic Inhibitors of Human DNA Topoisomerase II Alpha (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25289