A screen for the identification of inhibitors of tyrosyl-DNA phosphodiesterase 1

Abstract

Tyrosyl-DNA Phosphodiesterase (Tdp1) is crucial for cleavage of the covalent topoisomerase-DNA complex, an intermediate in DNA repair. Tdp1 also plays a role in reversing inhibition of topoisomerase I by camptothecins (CPT), a series of potent and effective inhibitors used in the treatment of colo-rectal carcinomas, and, for ovarian and small cell lung cancers. It is thought that inhibition of Tdp1 activity may reverse this resistance mechanism, restoring CPT sensitivity in tumors displaying resistance by this mechanism. To date, there are few published inhibitors of Tdp1 activity. Here, we describe the design, development and execution of a novel assay to identify and characterize inhibitors of Tdp1 from natural product extracts. A total of 227,905 purified molecules, pre-fractionated extracts and crude natural product extracts were screened. This yielded 534 initial positives (0.23%). Rigorous confirmation reduced this number to 117 (0.05% final hit rate). From these initial hits, several novel inhibitors have been identified showing micromolar inhibition of Tdp1.