Tomato extract retards the growth of hormone independent human prostate cancer (DU145) xenografts in immune deficient mice

Epidemiologic studies suggest that diets rich in tomato products and therefore lycopene are associated with reduced risk of prostate cancer. In vitro studies indicate that lycopene can inhibit the proliferation of PC3, DU145, and LNCaP human prostate adenocarcinoma cell lines. We examined the growth of prostate tumors in 8 week old athymic male Swiss nu/nu mice fed either an AIN76A diet supplemented with 10% solvent extracted tomato oleoresin containing 5% lycopene (gift of LycoRed Natural Products Industries. Ltd, Beer-Sheva Israel) or supplemented with 6% cottonseed and 1% linseed oils to mimic the fatty acid profile of the tomato oleoresin. After a 14 day prefeeding period, animals received subcutaneous injections of DU145 cells (1.5×10⁶) bilaterally on the flank. We observed a slight, but significant, delay in tumor growth. For example, by day 13 after inoculation, bilateral tumors were present in 100% of the control mice compared to only 71 % of the tomato-fed mice (p<0.05 by Chisquare). 100 % of controls and 93 % of the tomato-fed mice developed tumors by day 26 after inoculation. Livers from mice fed tomato oleoresin accumulated 2.86 ± 0.59 nmoles/g total lycopene while the tumors contained 0.65 ± 0.25 nmoles/g. All-trans lycopene accounted for 33.0 ± 7.3 % of total lycopene in both tissues, although the diet contained 52% all trans lycopene. This study suggests that increased tomato consumption will not have a major impact upon advanced hormone refractory prostate cancer in humans. Additional studies are necessary to establish the role of tomato products in earlier stages of prostate carcinogenesis.