Free Zn2+ enhances inhibitory effects of EGCG on the growth of PC‐3 cells

Abstract Epigallocatechin‐3‐gallate (EGCG), a major component of green tea, has both preventive and therapeutic beneficial actions in prostate cancer. In the present study, we compared the growth inhibitory effects and the antioxidant and ability to modify cell membrane permeation of zinc‐EGCG complex and Zn 2+ /EGCG mixture on androgen‐insensitive prostate cancer (PC‐3) cells. It was noted that free Zn 2+ enhanced the growth inhibitory effects of EGCG on PC‐3 cells at 160 μmol/L concentration, whereas zinc‐EGCG complex was ineffective. EGCG showed potent free radical scavenging ability in the presence of Zn 2+ . EGCG in the presence of Zn 2+ was more effective than EGCG alone in enhancing the permeability of the cell membrane, whereas zinc‐EGCG complex had no effect on PC‐3 cell membrane permeability. These results indicate that though Zn 2+ enhanced the action of EGCG on PC‐3 cells, zinc‐EGCG complex is highly unlikely to be formed in the presence of Zn 2+ and EGCG to explain the potentiating action of Zn 2+ on the growth inhibitory property of EGCG on PC‐3 cells.