Quercetin exerts synergetic anti-cancer activity with 10-hydroxy camptothecin

Quercetin (Qu) is known as a dietary antioxidant with numerous bioactivities, but its function in anti-cancer has not been fully investigated. Here, we show that Qu at low doses (≤10μM) significantly enhances the inhibition of 10-hydroxy camptothecin (HCPT) on the proliferation of MCF7, BGC823 and HepG2 cells. A plasmid DNA relaxation assay indicates that the inhibition of HCPT on the catalytic activity of topoisomerase I (Topo I) is increased by Qu at 10μM. Compared to the treatment by Qu or HCPT alone, phosphorylation at Ser139 of γH2A.X in MCF7 cells starts to increase significantly (P