Lycopene inhibits the growth of normal human prostate epithelial cells in vitro

Lycopene has repeatedly been shown to inhibit the growth of human prostate cells in vitro. However, previous studies with lycopene have focused on cancer specimens, and it is still unclear whether this carotenoid affects the growth of normal human prostate cells as well. Therefore, we investigated the effects of lycopene on normal human prostate epithelial cells (PrEC) by treating them with synthetic all-E-lycopene (up to 5 micromol/L) and assessing proliferation via [3H]thymidine incorporation. The effects of lycopene on cell cycle progression were investigated via flow cytometry. To elucidate whether lycopene modulates cyclins involved in cell cycle progression, protein expressions of cyclins D1 and E were analyzed. The results show that lycopene significantly inhibited the growth of PrEC in a dose-dependent fashion. Flow cytometry revealed a significant cell cycle arrest in the G0/G1 phase. This effect was confirmed by inhibition of cyclin D1 protein expression, whereas cyclin E levels remained unchanged. The results demonstrate that lycopene inhibits growth of nonneoplastic PrEC in vitro. We hypothesize that lycopene might likewise inhibit the growth of prostatic epithelial cells in vivo. This might have an effect on prostate development and/or on enlargement of prostate tissue as found in benign prostate hyperplasia, a potential precursor of prostate cancer.