A novel use for the comet assay: Detection of topoisomerase II inhibitors

Background: The simple and quick comet assay can quantitatively detect DNA cleavage in cells. This study aimed to determine whether the comet assay co uld be used to detect topoisomerase (topo) II inhibitors. Materials and Met hods: HT-29 colon cancer cells wets pre-incubated with aclarubicin, a topo II antagonist, then treated with topo II poisons: etoposide (VP-16), tenipo side (VM-26), 4'-(acridinylamino) methansulfon-manisidide (m-AMSA) and adri amycin (doxorubicin). We also tested a topo I poison (camptothecin) and a m icrotubule depolymerization inhibitor (taxol). Results: Aclarubicin signifi cantly reduced DNA cleavage induced by topo II poisons, but not that induce d by camptothecin. In HL-60/MX2 cells (containing no topo LIP and reduced t opo IIa), DNA breakage induced by topo II poisons was lower. Also, aclarubi cin antagonized topo I-mediated camptothecin-induced DNA cleavage in these resistant cells. Conclusions: The comet assay can be used to detect topo II poisons in cultured cells. Also, aclarubicin has a dual topo I and topo II antagonism, with "preferential antagonism" of topo II when topo II beta ca talytic activity is normally expressed.