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

Abstract

Background: The simple and quick comet assay can quantitatively detect DNA cleavage in cells. This study aimed to determine whether the comet assay could be used to detect topoisomerase (topo) II inhibitors. Materials and Methods: HT-29 colon cancer cells were pre-incubated with aclarubicin, a topo II antagonist, then treated with topo II poisons: etoposide (VP-16), teniposide (VM-26), 4'-(acridinylamino) methansulfon-manisidide (m-AMSA) and adriamycin (doxorubicin). We also tested a topo I poison (camptothecin) and a microtubule depolymerization inhibitor (taxol). Results: Aclarubicin significantly reduced DNA cleavage induced by topo II poisons, but not that induced by camptothecin. In HL-60/MX2 cells (containing no topo IIβ and reduced topo IIα), DNA breakage induced by topo II poisons was lower. Also, aclarubicin 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 IIβ catalytic activity is normally expressed.