• Generation of assays and antibodies to facilitate the study of human 5'-tyrosyl DNA phosphodiesterase.

      Thomson, Graeme J; Watson, Amanda J; Caldecott, K; Denneny, Olive; Depledge, Paul; Hamilton, Nicola S; Hopkins, Gemma V; Jordan, Allan M; Morrow, Christopher J; Raoof, Ali; et al. (2013-02-12)
      Topoisomerases regulate DNA topology by the transient cleavage and re-ligation of DNA during transcription and replication. Topoisomerase II (Topo II) poisons such as etoposide can induce abortive DNA strand breaks in which Topo II remains covalently bound to a 5' DNA strand terminus via a phosphotyrosyl linker. Tyrosyl DNA phosphodiesterase 2 (Tdp2) is a recently discovered human 5'-tyrosyl DNA phosphodiesterase which repairs this topoisomerase-mediated DNA damage, thus playing a central role in maintaining normal DNA topology in cells. Cellular depletion of Tdp2 has been shown to result in an increased susceptibility and sensitivity to Topo II-induced DNA double strand breaks, thereby revealing Tdp2 as a potentially attractive anti-cancer target. No drug-like inhibitors of Tdp2 have been identified to date and assays suitable for high throughput screening (HTS) have not been widely reported. Here we have identified a new and effective chromogenic substrate for Tdp2 and developed a homogenous and robust HTS assay. A second novel Tdp2 assay was also developed to cross-validate hit matter identified from an HTS. Additionally, a new and specific Tdp2 antibody is described. Together these new tools will aid in the identification of novel Tdp2 inhibitors and the investigation of the role of Tdp2 in cancer.
    • Mode of action of DNA-competitive small molecule inhibitors of tyrosyl DNA phosphodiesterase 2.

      Hornyak, P; Askwith, T; Walker, S; Komulainen, E; Paradowski, M; Pennicott, L; Bartlett, E; Brissett, N; Raoof, Ali; Watson, Mandy; et al. (2016-04-20)
      TDP2 is a 5'-tyrosyl DNA phosphodiesterase important for the repair of DNA adducts generated by non-productive (abortive) activity of topoisomerase II. TDP2 facilitates therapeutic resistance to topoisomerase poisons, which are widely used in the treatment of a range of cancer types. Consequently, TDP2 is an interesting target for the development of small molecule inhibitors that could restore sensitivity to topoisomerase-directed therapies. Previous studies identified a class of deazaflavin-based molecules that showed inhibitory activity against TDP2 at therapeutically useful concentrations, but their mode of action was uncertain. We have confirmed that the deazaflavin series inhibits TDP2 enzyme activity in a fluorescence-based assay, suitable for HTS-screening.  We have gone on to determine crystal structures of these compounds bound to a 'humanised' form of murine TDP2. The structures reveal their novel mode of action as competitive ligands for the binding site of an incoming DNA substrate, and point the way to generating novel and potent inhibitors of TDP2.