Inhibition of human DNA topoisomerase IB by a cyclometalated gold III compound: analysis on the different steps of the enzyme catalytic cycle.
A gold(III) compound [Au(C^N^C)(IMe)]CF(3)SO(3) (Gold III) has been reported to have anticancer properties as it is able to reduce topoisomerase IB activity in vitro and suppress tumor growth in nude mice model. Here we have investigated the mechanism of inhibition of human topoisomerase IB activity by this compound, analyzing the various steps of the catalytic cycle. DNA supercoiled relaxation and the cleavage reaction are inhibited, but Gold III does not perturb the religation reaction, in contrast to what has been observed for camptothecin. Pre-incubation of enzyme with the inhibitor before adding DNA substrate increases the inhibitory effect. In addition, when Gold III is preincubated with the enzyme it prevents the stabilization of the cleavable complex by camptothecin. The analysis of the DNA-topoisomerase binding reaction indicates that the compound acts as a topoisomerase I inhibitor by preventing the enzyme-DNA interaction.
Department of Biology, University of Rome Tor Vergata, Italy.
Silvia
S
Castelli
Oscar
O
Vassallo
Prafulla
P
Katkar
Chi-Ming
CM
Che
Raymond Wai-Yin
RW
Sun
Alessandro
A
Desideri
D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology; D002384:Catalysis; D004247:DNA / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000187:drug effects* / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D007700:Kinetics; D051379:Mice; D050607:Organogold Compounds / Q000737:chemistry / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D013379:Substrate Specificity; D059004:Topoisomerase I Inhibitors / Q000737:chemistry / Q000494:pharmacology*
D000970:Antineoplastic Agents; D050607:Organogold Compounds; D011994:Recombinant Proteins; D059004:Topoisomerase I Inhibitors; D004247:DNA; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human