The impact of lycopene and non-lycopene-containing tomato extracts on in vitro prostate cancer cell growth

High tomato diets have been observed to significantly reduce the risk of prostate cancer; however, the causal agents within tomato that produce this effect are uncertain. Lycopene, the principle and highly abundant carotenoid within tomato fruit, has been suggested to be the major causative agent due to its in vitro antioxidant and anti-carcinogenic effects; however, in vivo evidence is inconclusive, with whole tomato supplementation being more protective than pure lycopene. This implicates the involvement of other tomato nutrients and carotenoids in the protective effect. This was investigated by applying hexane extracts of tomatoes with or without all-trans-lycopene as their principal fruit carotenoid, dissolved in tetrahydrofuran to PC3 prostate cancer cells. High performance liquid chromatography and photodiode array analysis verified that orange grape (RO) and tangerine (TAN) tomatoes had almost exclusively β-carotene and tetra-cis-lycopene as their principal carotenoid, respectively. In contrast, red grape (RR), tangerine wild-type (TWT), and commercial truss (TRUSS) tomatoes contained predominantly all-trans-lycopene. An MTT cell inhibition assay revealed that the TAN tomato extract treatment had a barely significant inhibitory effect upon PC3 cells compared with the control, while β-carotene tomato extracts had no significant impact on PC3 proliferation. When the tomato lines with all-trans-lycopene as their predominant carotenoid were pooled, a similar inhibition of prostate cancer cell growth was observed, with a tendency for TAN tomato extract to inhibit growth slightly better. This preliminary study demonstrates that tetra-cis-lycopene as well as all-trans lycopene may both have an anti-carcinogenic effect on prostate cancer cells.