Glucosylated isoflavones as DNA topoisomerase II poisons

Since topoisomerase poisons allow the enzyme to cut and covalently bind to DNA but abort the subsequent rejoining of the molecule after relieving the torsional stress. To study their action we have made use of a supercoiled f orm of the pRYG plasmid that bears a specific topoisomerase recognition and binding region. The conversion of the supercoiled circular double-stranded DNA to the linear and open circle forms in the presence of a topoisomerase II poison and a denaturation step by proteinase K-SDS is indicative of the efficiency of our test agents to stabilize the cleavable complex. Using th is system, three glucosylated isoflavones (6'-methoxypseudobaptigenin-7-O-b eta-glucoside, genistin, and daidzin) isolated from cytotoxic chloroform an d ethyl acetate extracts of Retama sphaerocarpa Boissier, were found to hav e the ability to stabilize the cleavage complex human DNA topoisomerase II.