In this work, the authors demonstrate very nicely the mode of action of emodin, an active anthraquinone natural product from plants and fungi (and used as a laxative). This widely used drug is genotoxic and is a carcinogen. Its mode of action is unclear and this work defines it as a topo II inhibitor and poison. They propose a mechanism involving both cleavage stabilization and inhibition of ATP hydrolysis. The key experiments involved using the ICE bioassay to examine in vivo relevance of the drug in cells.
TopoGEN offers the In Vivo Link Kit for topoisomerase I, II (a and b) which is instrumental in proving the mode of action of this particular drug.
Article Source: PubMed
Emodin Triggers DNA Double-Strand Breaks by Stabilizing Topoisomerase II-DNA Cleavage Complexes and by Inhibiting ATP Hydrolysis of Topoisomerase II
Emodin, an anthraquinone derived from a plant and fungi, has been reported to possess potential genotoxicity, but the mechanism is not entirely clear. Here, we report that emodin causes DNA double-strand breaks (DSBs) through stabilization of topoisomerase (Topo) II-DNA cleavage complexes and inhibition of ATP hydrolysis. In our study, emodin did not induce mutagenecity in the salmonella mutation assay but caused genotoxicity in the thymidine kinase gene mutation assay and in the micronucleus test. Moreover, emodin induced DNA DSBs demonstrated by induction of comet tails, the expression of phosphorylated histone H2AX, and phosphorylation of ataxia telangiectasia mutated. Our studies also revealed that emodin exerted strong inhibitory activity against Topo II in the supercoiled pBR322 relaxation assay and in Topo II–mediated kinetoplast DNA decatenation, similar to the previous report. We also showed that the inhibitory effect of emodin on Topo II was because of its ability to stabilize Topo II-DNA complexes and to inhibit the ATP hydrolysis of Topo II. Furthermore, emodin was found to trigger DNA DSBs in a Topo II–dependent manner using the Topo II catalytic inhibitor aclarubicin and in Topo II–deficient mitoxantrone-resistant variant HL-60/MX2 cells. Together, these results suggest that in emodin-induced DNA DSBs and genotoxicity, stabilization of Topo II-DNA cleavage complexes and inhibition of ATP
hydrolysis play an important role.
TOXICOLOGICAL SCIENCES 118(2), 435–443 (2010)