A study by Dutch and German researchers has provided evidence that lycopene may be able to inhibit the growth of prostate tumours and that its effect may be enhanced if it is combined with vitamin E.
A number of epidemiological studies have already indicated that high intake of lycopene – a carotinoid that gives the red colour to tomatoes and other fruits – is associated with a reduced risk of prostate cancer.
But, these observational findings have now been underpinned by new research demonstrating a beneficial effect in human prostate tumours grown in mice. A Phase II study testing the compounds in cancer patients is now under way.
The findings of the animal study are being reported by Dutch research scientist Dr. Jacqueline Limpens at the EORTC-NCI-AACR Symposium on Molecular Targets and Cancer Therapeutics in Geneva.
The study involved testing one low and one high dose of synthetic lycopene alone, one low and one high dose of synthetic vitamin E alone and a combination of low dose synthetic lycopene and vitamin E or a placebo. The researchers injected human tumour cells into the prostate of mice to see what effect the lycopene and vitamin supplements would have on the tumour growth and PSA (prostate specific antigen) and to compare any effects against the placebo.
Dr. Limpens, who is from the Department of Urology at the Josephine Nefkins Institute at the Erasmus Medical Center in Rotterdam, said: "We found that low dose lycopene suppressed the growth of the human prostate tumours by over half (at day 42 of the study), extending the tumour doubling time accordingly, while all other single treatments had no significant effect. However, the combination of low-dose lycopene and vitamin E produced the greatest tumour inhibition – 73% (at day 42). Importantly, we also saw that the doubling time of PSA values matched the tumour responses in all the experimental groups. This means that we can use PSA values as a surrogate marker in short phase II/III human trials as it is clear that PSA values are accurately reflecting the inhibiting activity of the lycopene and vitamin E on tumour growth.
"What was particularly marked was that it was the low dose of both lycopene and vitamin E that was the most effective, demonstrating that ‘more does not necessarily equal better’. Many pharmacological agents and natural compounds follow a bell-shaped dose response curve, which means that very low or high doses may not work and that there is an optimal dose between the two extremes."
The study showed that the lycopene and vitamin E were effectively taken up in the mice prostates in the same form as they are in humans, said Dr. Limpens.
Dr. Limpens said the findings seem promising, but it was early days yet and the Phase II trial in Germany was designed to verify whether a similar treatment to that used in the mice could alter the course of minimal clinical disease in patients. The lycopene product used (LycoVit®), has received the Generally Recognized as Safe (GRAS) status from the United States Food and Drug Administration (FDA) and can be used to fortify foods.
It was too early, said Dr. Limpens, to say whether lycopene and vitamin E could ever be used to prevent prostate cancer in healthy individuals. The first step was to see the results from the studies on men with prostate cancer: changes may, for example, be necessary to optimise the treatment. And before any preventative trials could even be considered it would be essential to verify the compound’s potential to really prevent the development of cancer in a mouse model.
"However, our data fit in with the general picture that lycopene and vitamin E may have chemopreventative effects on prostate cancer. Therefore we would certainly recommend that all men regularly eat lycopene and vitamin E-rich foods: for example, all kinds of processed tomato products, papayas, pink grapefruit and watermelon, wheat germs, whole grains, mangoes, leafy green vegetables, nuts and olive oils. Of course, this needs to be part of an all-round healthy lifestyle and diet with plenty of vegetables and other healthy foods. Regular consumption of supplements and fortified foods may help to obtain adequate amounts of lycopene and vitamin E, which may otherwise be difficult to obtain while maintaining a balanced diet."