Isoflavonoids inhibit catabolism of vitamin D in prostate cancer cells.

The high ingestion of soybean products in Asian countries has been suggested to be responsible for a reduced incidence of prostate cancer. The mechanism of action, however, is unknown. Our data demonstrate that genistein and some isoflavone metabolites reduce the activity of 25-D3-24-hydroxylase (CYP24) in the human prostate cancer-derived cell line DU-145. CYP24 is also responsible for degradation of the active vitamin D metabolite 1,25-dihydroxyvitamin D3 which is known to be antimitotic and prodifferentiating in prostate cancer cells. High levels of CYP24 frequently found in prostate cancer cells may thus degrade the active metabolite. This could be prevented by ingestion of genistein-containing food such as soybeans.