Potent inhibition of werner and bloom helicases by DNA minor groove binding drugs.

Maintenance of genomic integrity is vital to all organisms. A number of human genetic disorders, including Werner Syndrome, Bloom Syndrome and Rothmund-Thomson Syndrome, exhibit genomic instability with some phenotypic characteristics of premature aging and cancer predisposition. Presumably the aberrant cellular and clinical phenotypes in these disorders arise from defects in important DNA metabolic pathways such as replication, recombination or repair. These syndromes are all characterized by defects in a member of the RecQ family of DNA helicases. To obtain a better understanding of how these enzymes function in DNA metabolic pathways that directly influence chromosomal integrity, we have examined the effects of non-covalent DNA modifications on the catalytic activities of purified Werner (WRN) and Bloom (BLM) DNA helicases. A panel of DNA-binding ligands displaying unique properties for interacting with double helical DNA was tested for their effects on the unwinding activity of WRN and BLM helicases on a partial duplex DNA substrate. The levels of inhibition by a number of these compounds were distinct from previously reported values for viral, prokaryotic and eukaryotic helicases. The results demonstrate that BLM and WRN proteins exhibit similar sensitivity profiles to these DNA-binding ligands and are most potently inhibited by the structurally related minor groove binders distamycin A and netropsin (K(i) </=1 microM). The distinct inhibition of WRN and BLM helicases by the minor groove binders suggest that these helicases unwind double-stranded DNA by a related mechanism.