the SOY story (not TOY STORY) GETS MORE INTERESTING...

[Lani]

Soy Isoflavones May Boost Efficacy of Radiotherapy for Prostate Cancer


By Will Boggs, MD

NEW YORK (Reuters Health) Jun 14 - Soy isoflavones enhance radiotherapy effects in a mouse model of metastatic prostate cancer, according to a report in the June 1st International Journal of Cancer.

Soy isoflavones "enhance the susceptibility of cancer cells to radiation effects by inhibiting molecular survival pathways induced by radiation," Dr. Gilda G. Hillman told Reuters Health.

Dr. Hillman from Wayne State University School of Medicine, Detroit, Michigan and colleagues previously found that the soy isoflavone genistein potentiated radiation induced killing of tumor cells in vitro but increased lymph node metastases in vivo.

The researcher therefore investigated whether the presence of three isoflavones -- daidzein, glycitein, and genistein -- is effective at radiosensitization of prostate tumors while protecting against the increased metastasis caused by pure genistein.

In vitro, soy isoflavones dose-dependently increased the killing of prostate cancer cells alone and when combined with radiation, the authors report. The combined treatment downregulated antiapoptotic molecules and upregulated proapoptotic molecules.

In the xenograft orthotopic model of prostate cancer in mice, soy isoflavones inhibited prostate tumor growth more significantly than genistein alone, the results indicate, and combination with radiation caused a further inhibition of primary prostate tumor growth.

"Interestingly, treatment with soy isoflavones did not increase metastasis to para-aortic lymph nodes," the researchers note.

"We strongly feel that the use of dietary agents to enhance the antitumor activity of conventional radiotherapy has a great therapeutic potential," Dr. Hillman said.

"We are currently investigating the effect of other isoflavones found in the soybeans formulation to determine which components of soybeans protect against the adverse metastatic effects of pure genistein," Dr. Hillman said. "We are also studying molecular mechanisms of metastasis that could be enhanced by genistein and not by soy isoflavone mixture."

"Our research program investigating the radiosensitization effect of soy isoflavones for prostate cancer is a successful and dynamic program including scientists and clinicians at the Karmanos Cancer Institute and Wayne State University School of Medicine," Dr. Hillman explained. "However, due to limited funds available at the national level, the success and continuation of this program is dependent upon raising funds from private donors."

Int J Cancer 2007;120:2491-2498.