The mammalian lignan enterolactone is a major metabolite of plant-based lignans that has been shown to inhibit the growth and development of prostate cancer. However, little is known about the mechanistic basis for its anticancer activity. In this study, we report that enterolactone selectively suppresses the growth of LNCaP prostate cancer cells by triggering apoptosis. Mechanistic studies showed that enterolactone-induced apoptosis was characterized by a dose-dependent loss of mitochondrial membrane potential, release of cytochrome c and cleavage of procaspase-3 and poly(ADP-ribose)-polymerase (PARP). Caspase dependencewas indicated by the ability of the pancaspase inhibitor z-VAD-fmk to attenuate enterolactonemediated apoptosis. Mechanistic studies suggested roles for Akt, GSK-3β, MDM2, and p53 in enterolactone-dependent apoptosis. Our findings encourage further studies of enterolactone as a promising chemopreventive agent against prostate cancer. Copyright © 2007 American Association for Cancer Research.