Inhibition of human tyrosyl-DNA phosphodiesterase (Tdp1) by neomycin and aminoglycoside antibiotics

Proc Amer Assoc Cancer Res, Volume 46, 2005 2391 DNA topoisomerase I (Top1) is the target of camptothecin and novel Top1 inhibitors are in development (Meng et al., Curr Topics Med Chem, 3: 305-320, 2003). Top1 inhibitors induce DNA damage by trapping covalent complexes between the Top1 catalytic tyrosine and the 3’-end of the broken DNA. Recently tyrosyl-DNA phosphodiesterase (Tdp1) was identified as an important enzyme hydrolyzing the tyrosyl-DNA bond thereby generating DNA 3’-phosphate ends. Inhibiting Tdp1 has the potential to enhance the therapeutic effects of Top1 inhibitors (Pommier et al., Mutat Res, 532: 173-203, 2003) ( ). In the present study we report biochemical assays for Tdp1 activity using recombinant Tdp1 enzyme and model substrate oligonucleotides. Neomycin shows stronger inhibition of Tdp1 than its related chemicals paromomycin and lividomycin A. Inhibition of Tdp1 by neomycin is dependent both on the DNA substrate structure and on Tdp1 concentration. Inhibition is stronger with partial duplex DNA than single-stranded DNA substrates. Inhibition by neomycin can be overcome with excess Tdp1. Schiff base assays suggest that neomycin inhibits Tdp1 by interfering with the formation of Tdp1-DNA complexes. To our knowledge, neomycin and aminoglycoside antibiotics are the first Tdp1 inhibitors reported to date. They may be used as leads for further development of Tdp1 inhibitors in combination with Top1 inhibitors.