Abstract A174: High-throughput screening for natural product inhibitors of human tyrosyl-DNA-phosphodiesterase (Tdp-1)

Abstract

Abstract Tyrosyl-DNA-phosphodiesterase I (Tdp-1) is part of the DNA repair complex that resolves irreversible topoisomerase I (Top1)-DNA cleavage complexes by catalyzing the hydrolysis of 3′-phosphotyrosyl bonds. A point mutation in the Tdp1 gene causes a neurological disorder called spinocerebellar ataxia with axonal neuropathy (SCAN1) (Takashima, 2002). SCAN1 cells display hypersensitivity to camptothecin (CPT), a potent Topoisomerase 1 inhibitor. Additionally, overexpression of a human Tdp1 fusion protein alleviates some of the effects of CPT treatment (Barthelmes, 2004). These observations suggest that inhibitors of Tdp1 could act synergistically with CPT in a combined therapeutic treatment for certain cancers. Despite attempts to identify synthetic small molecule inhibitors of Tdp-1, there are few verified inhibitors of this enzyme activity and none currently in clinical trials. While previous screening efforts have focused mainly upon compounds of synthetic origin (Antony, 2007), little effort has been directed towards the discovery of natural product derived inhibitors. The Molecular Targets Development Program (MTDP) at NCI-Frederick has developed a fluorescence-based assay for the rapid identification and characterization of natural product derived inhibitors of Tdp1 enzyme activity. Initial high-throughput screening work has identified several unique extracts showing potent inhibition of enzyme activity. Follow up work is currently underway to evaluate the molecular mechanism of isolated active natural compounds. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A174.