Soy substances slow prostate cancer growth in animals

October 26, 1999

COLUMBUS, Ohio -- Substances present in dietary soy products may slow the growth of prostate cancer, a new animal study has shown. But cancer researchers warn against rushing to use them as diet supplements.

The finding suggests that substances known as soy isoflavones are probably responsible for the anti-cancer effect.

"The study strongly supports the need for clinical trials to assess the potential role of soy in reducing the incidence and progression of human prostate cancer," said Steven Clinton, associate professor of internal medicine at Ohio State University.

However, Clinton cautions against taking soy phytochemicals or dietary supplements enriched with soy isoflavones at this time.

"Soy phytochemicals are potent compounds. Plants use them to regulate genes during growth and development and as poisons to ward off predators," said Clinton, who is also director of the Cancer Prevention and Control Program at Ohio StateÆs Arthur G. James Cancer Hospital and Richard J. Solove Research Institute. "Some of these chemicals may even enhance or promote the growth of some other types of tumors.

"Our results do suggest that including soy-based foods in the diet is reasonable for a number of health benefits. For example, consumption of soy protein has been shown to reduce blood cholesterol levels," he said.

"The bottom line is that proper clinical studies need to be done to identify the benefits and potential side effects of these compounds."

The study, which was led by Clinton and involved a team of researchers, was published in the September issue of the Journal of Nutrition.

It tested the ability of two types of soy extract, soy protein isolate and soy phytochemical concentrate, to inhibit the growth of human prostate cancer cells transplanted into mice.

Soy protein isolate is a high quality protein made from whole soy; it contains a very small amount of isoflavones. Soy phytochemical concentrate is an extract of soy that is rich in isoflavones (the amount is about 85 times greater than that found in soy protein isolate).

The study involved 48 mice divided into six groups. All the animals had been injected with a human prostate-cancer cells, which grow to form a tumor under the skin.

Three of the groups were fed soy protein isolate as their protein source. The remaining three groups, which formed the second arm of the study, received casein (milk protein) as their protein source.

One group in each arm was also fed an amount of soy phytochemical concentrate at a level equivalent to 0.2 percent of their diet; a second group in each arm was fed an amount equal to 1.0 percent of their diet.

After three weeks, the volumes of the tumors were compared in all the groups.

"We found that as the amount of isoflavones went up, the amount of tumor growth went down," said Clinton.

For example, mice fed soy protein and no phytochemical concentrate had tumors that were 11 percent smaller than did the control mice that received casein only. Mice that received the highest level of isoflavones -- those fed soy protein plus 1 percent phytochemical concentrate -- had tumors that were 40 percent smaller than those in the casein-fed controls.

The researchers also attempted to learn how soy isoflavones retarded prostate tumor growth. They identified three possible mechanisms.

First, tumors receiving the highest levels of soy phytochemical concentrate had a lower rate of cell proliferation and higher numbers of cells undergoing programmed cell death, or apoptosis.

Second, there was a lower number of blood vessels in these tumors. This may reflect the ability of isoflavones to inhibit the growth of new blood vessels in the tumor (that is, they have antiangiogenic properties).

Third, animals fed isoflavones had lower levels of insulin-like growth factor 1, a hormone that stimulates the growth of prostate cancer.

This work was supported by grants from the National Institutes of Health and the Harvard Clinical Nutrition Research Center.
-end-
Contact: Steven Clinton, M.D., Ph.D., 614-293-8396; Clinton-1@medctr.osu.edu
Written by Darrell E. Ward, 614-292-8456; Ward.25@osu.edu

Ohio State University

Related Prostate Cancer Articles from Brightsurf:

Low risk of cancer spread on active surveillance for early prostate cancer
Men undergoing active surveillance for prostate cancer have very low rates - one percent or less - of cancer spread (metastases) or death from prostate cancer, according to a recent study published in the Journal of Urology®, an Official Journal of the American Urological Association (AUA).

ESMO 2020: Breast cancer drug set to transform prostate cancer treatment
A drug used to treat breast and ovarian cancer can extend the lives of some men with prostate cancer and should become a new standard treatment for the disease, concludes a major trial which is set to change clinical practice.

Major trial shows breast cancer drug can hit prostate cancer Achilles heel
A drug already licensed for the treatment of breast and ovarian cancers is more effective than targeted hormone therapy at keeping cancer in check in some men with advanced prostate cancer, a major clinical trial reports.

The Lancet: Prostate cancer study finds molecular imaging could transform management of patients with aggressive cancer
Results from a randomised controlled trial involving 300 prostate cancer patients find that a molecular imaging technique is more accurate than conventional medical imaging and recommends the scans be introduced into routine clinical practice.

Common genetic defect in prostate cancer inspires path to new anti-cancer drugs
Researchers found that, in prostate cancer, a mutation leading to the loss of one allele of a tumor suppressor gene known as PPP2R2A is enough to worsen a tumor caused by other mutations.

First prostate cancer therapy to target genes delays cancer progression
For the first time, prostate cancer has been treated based on the genetic makeup of the cancer, resulting in delayed disease progression, delayed time to pain progression, and potentially extending lives in patients with advanced, metastatic prostate cancer, reports a large phase 3 trial.

Men taking medications for enlarged prostate face delays in prostate cancer diagnosis
University of California San Diego School of Medicine researchers report that men treated with medications for benign prostatic hyperplasia (enlarged prostate) experienced a two-year delay in diagnosis of their prostate cancer and were twice as likely to have advanced disease upon diagnosis.

CNIO researchers confirm links between aggressive prostate cancer and hereditary breast cancer
The study has potential implications for families with members suffering from these types of tumours who are at an increased risk of developing cancer.

Distinguishing fatal prostate cancer from 'manageable' cancer now possible
Scientists at the University of York have found a way of distinguishing between fatal prostate cancer and manageable cancer, which could reduce unnecessary surgeries and radiotherapy.

Researchers find prostate cancer drug byproduct can fuel cancer cells
A genetic anomaly in certain men with prostate cancer may impact their response to common drugs used to treat the disease, according to new research at Cleveland Clinic.

Read More: Prostate Cancer News and Prostate Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.