Ellagic acid and its derivates as catalytic inhibitors of human topoisomerase II

Ellagitannins (ETs) are natural compounds abundant in some fruits and nuts with a large variety of molecular structures. They are among the main pharmacologically active substances in several traditional herbal products used in folk medicine [1], and their metabolites are reported by several authors to be responsible for anti-viral, anti-oxidant, anti-peroxidating, anti-foodborn pathogens, anti-mutagenic, antiproliferative and proapoptotic activities [2-4]. The main product of the ETs degradation is the ellagic acid (EA), which is further biodegradated in urolithins by the colonic microflora [5]. EA inhibits the human topoisomerase II [4] but its mechanism of action has not been elucidated in details. To elucidate its distinct antitumor properties and to obtain structure-activity relationship (SAR) information, we have characterized the effects of EA and several synthetic derivates on human topo II using enzymatic assays, and on cellular culture using the two lines MCF-7 and HT-29. Four bilactones (EA, 1179, 1183 and 1186) and two urolithins (1182 and 1185) were highly active on the human topo II, both in isoforms α and β, with IC50 ≤1µM. The results for these six active compounds point out to the importance of the number and relative position of hydroxyl groups on both EA and urolithin scaffold to gain activity on human topo II. These six potent inhibitors of the human topos II were slightly cytotoxic on MCF-7 breast cancer cells. The data collected with the RP-HPLC about the LogPow show that all the compounds with activity on human topo II had the lowest LogP, suggesting low penetration of the cell membrane. Further competitive inhibition tests aimed at elucidating the mechanism of inhibition toward topo II, demonstrated that ATP competitively and dose-dependently influences the inhibition of active compounds on human topo II. The results suggest that ellagic acid and its derivates are catalytic inhibitors of the human enzyme, and may share a common binding site with ATP.