Genistein potentiates the radiation effect on prostate carcinoma cells

We have shown previously that genistein, the major isoflavone in soybean, i nhibited the growth of human prostate cancer cells irt vitro by affecting t he cell cycle and inducing apoptosis, To augment the effect of radiation fo r prostate carcinoma, we have now tested the combination of genistein with photon and neutron radiation on prostate carcinoma cells in vitro, The effe cts of photon or neutron radiation alone or genistein alone or both combine d mere evaluated on DNA synthesis, cell growth, and cell ability to form co lonies. We found that neutrons were more effective than photons for the kil ling of prostate carcinoma cells irt vitro, resulting in a relative biologi cal effectiveness of 2.6 when compared with photons. Genistein at 15 muM ca used a significant inhibition in DNA synthesis, cell growth, and colony for mation in the range of 40-60% and potentiated the effect of low doses of 20 0-300 cGy photon or 100-150 cGy neutron radiation. The effect of the combin ed treatment was more pronounced than with genistein or radiation alone. Ou r data indicate that genistein combined with radiation inhibits DNA synthes is, resulting in inhibition of cell division and growth. Genistein can augm ent the effect of neutrons at doses similar to2-fold lower than photon dose s required to observe the same efficacy. These studies suggest a potential of combining genistein with radiation far the treatment of localized prosta te carcinoma.