Inhibition of topoisomerase II by phase II metabolites of resveratrol in human colon cancer cells.

Abstract

The cytotoxic and genotoxic potential of phase II metabolites of resveratrol (RSV) was investigated in human colon cells with special emphasis on human topoisomerase (TOP) II. Cell-free screening of topoisomerase II (TOPII) inhibition by the decatenation assay showed inhibitory potential for RSV (≥200 μM) and for the first time for the three human phase II metabolites RSV-3-sulfate (≥200 μM), RSV-3-glucuronide (≥100 μM) and RSV-disulfate (≥100 μM). Conjugation at the C4'-position (RSV-4'-sulfate and RSV-4'-glucuronide) resulted in loss of the inhibitory potential in this assay. Cell-based experiments with RSV and the most abundant metabolite in humans, RSV-3-Sulf, revealed no TOP poisoning in HT29 and Caco-2 cells up to 250 μM. Further, the phase II metabolite exhibited only minor effects in the comet assay and showed negligible cytotoxic effects and apoptotic potential after 1 and 24 h incubation. Fluorescence microscopy and HPLC-DAD analysis identified cellular uptake of RSV and of RSV-3-Sulf although to a lesser extent when compared to RSV. Furthermore, within the cells fractional deconjugation of RSV-3-Sulf to the parent compound was observed. Sulfate- and glucuronide-phase II metabolites might contribute to the genotoxic potential of RSV by inhibition of TOPII activity. By deconjugation at the target site RSV-3-Sulf might serve as a pool of the parent compound.