A new animal study has added to a body of research suggesting that soy could prove helpful in the fight against prostate cancer spreading to other parts of the body.
The same research team from Northwestern University previously established the mechanism by which genistein, an antioxidant from soy, inhibits detachment of cancer cells from a primary prostate tumour and represses cell invasion: by blocking activation of p38 MAP kinases molecules.
The results of the new study, which appears in the March 15 issue of Cancer Research, give a new basis for hope that genistein could help prevent the spread of prostate cancer in patients, said senior investigator Raymond Bergan, MD.
Bergan and his team fed genistein to several groups of mice, and then implanted them with an aggressive form of prostate cancer. The amount of genistein included in the creatures' chow was no higher than that which a human would consume as part of a diet that includes lots of soy.
While the genistein did not seem to affect the size of prostate tumours in the mice, it did appear to completely stop lung metastasis (the spreading of cancer cells to other locations in the body). Metastases were seen to be decreased by 96 per cent.
When Bergan examined the animals' tissue, measuring the size of the nuclei, he found that the cells had flattened out in order to spread. This, he said, demonstrates that the genistein has a primary effect on metastasis.
In addition, the mice fed genistein were seen to express higher levels of genes involved in cancer cell migration.
While this may seem to counter the study's overall conclusions, Bergan explained this as follows:
"What we think is happening here is that the cells we put in the mice normally like to move. When genisten restricted their ability to do so, they tried to compensate by producing more protein involved in migration. But genistein prevented those proteins from being activated."
There are limitations to the study, which Bergan noted.
He said it may be that the effects of the compound in people who have eaten soy all their lives could be greater than in that seen in people who have only just started to eat genistein.
The only real way to establish the potential of genistein, he said, is by conducting clinical trials.
"Studies of antimetastatic efficacy in man are warranted and are under way," he wrote in his conclusion.
Over half a million news cases of prostate cancer are diagnosed every year world wide, and the cancer is the direct cause of over 200,000 deaths. More worryingly, the incidence of the disease is increasing with a rise of 1.7 per cent over 15 years.
Previous studies have indicated that men with a high risk of prostate cancer could benefit from a higher intake of soy isoflavones. For instance, a recent study published in the Journal of Nutrition (Vol 137, Pages 2258) investigated the potential of isoflavones to increase the excretion of two oestrogen metabolites suggested to initiate hormone-related cancers.
Another study published in the same journal (Vol. 137, pp. 1974-1979) and in Cancer Epidemiol Biomarkers Prev (Vol. 16, pp. 538-545) claimed to be the first prospective study to report an inverse association between isoflavone and prostate cancer in Japanese men.
Cancer Research 2008;68(6):2024-32
"Dietary Genistein Inhibits Metastasis of Human Prostate Cancer in Mice"
Authors: Minalini Lakshman, Li Xu, Vijayalakshmi Ananthanarayanan, Joshua Cooper, Chris H. Takimoto, Irene Helenowski, Jill Pelling and Raymond Bergan