The discovery and optimisation of small-molecule inhibitors of human 5’-tyrosyl DNA phosphodiesterase (Tdp2)

Topoisomerases (topo) regulate DNA topology by the transient cleavage and re-ligation of DNA during transcription and replication. 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, TTRAP, EAPII) is a recently discovered human 5’-tyrosyl DNA phosphodiesterase which repairs this topo-mediated DNA damage, therefore 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. It has therefore been proposed that selective pharmacological inhibition of Tdp2 may be a novel approach to overcome intrinsic or acquired resistance to topo II targeted drug therapy. To date, no known drug-like inhibitors of Tdp2 have been identified. We have recently reported a robust ‘mix and read’ HTS compatible assay and this was used to screen a diverse chemical library of approximately 92,000 compounds. From this, 2 distinct hit series have been identified. Following further chemical exploration of the original hit compounds small molecule inhibitors of Tdp2 with sub-100nM potencies have been identified. This poster will describe our preliminary results in this area.