More reasons to eat your veggies

[Guest guest]

Chemical in Broccoli Blocks Growth of Human Prostate Cancer Cells, Report UC

Berkeley Researchers

 

12 May 2003

Sarah Yang

   

 

 

Berkeley - Those seeking yet another reason to eat their veggies, take note.

Researchers at the University of California, Berkeley, have found that a

chemical produced when digesting such greens as broccoli and kale can stifle the

growth of human prostate cancer cells.

 

The findings show that 3,3'-diindolylmethane (DIM), which is obtained by

eating cruciferous vegetables in the Brassica genus, acts as a powerful

anti-androgen that inhibits the proliferation of human prostate cancer cells in

culture

tests.

" As far as we know, this is the first plant-derived chemical discovered that

acts as an anti-androgen, " said Leonard Bjeldanes, professor and chair of

nutritional sciences and toxicology at UC Berkeley's College of Natural

Resources

and principal investigator of the study. " This is of considerable interest in

the development of therapeutics and preventive agents for prostate cancer. "

Vegetables such as broccoli, Brussels sprouts, kale and cauliflower are rich

sources of indole-3-carbinol (I3C), which the body converts into DIM during

digestion. Over the years, Bjeldanes has been researching the anti-cancer

properties of dietary indoles with co-author Gary Firestone, UC Berkeley

professor

of molecular and cell biology.

The new study will be published in the June 6 issue of the Journal of

Biological Chemistry, but is now available online.

Androgen is an important hormone for the normal development and function of

the prostate, but it also plays a key role in the early stages of prostate

cancer, which is typically treated with anti-androgen drugs.

In most cases of prostate cancer, the cancer cells develop resistance to

androgen and grow independently of the hormone in later stages of the disease.

In the new study, the researchers conducted a series of tests comparing the

effects of DIM on androgen-dependent human prostate cancer cells as well as on

their androgen-independent counterparts.

They found that androgen-dependent cancer cells treated with a solution of

DIM grew 70 percent less than the same type of cancer cells that had been left

untreated. The same solution had no effect on the growth of

androgen-independent cells, pointing to androgen inhibition as the key mechanism

by which the

DIM is acting.

This was confirmed with further tests showing that DIM inhibits the actions

of dihydrotestosterone (DHT), the primary androgen involved in prostate

cancer. DHT stimulates the expression of prostate specific antigen (PSA), which

acts

as a growth factor for prostate cancer. When androgen-dependent cells were

treated with DIM, the researchers found a drop in the level of PSA.

" There are lots of things that can stop growth, but the fact that DIM

decreases the expression of PSA shows that it is functioning at a gene

expression

level, " said Bjeldanes.

Comparisons of the molecular conformation of DIM show that it is similar to

Casodex, a synthetic anti-androgen on the market. " DIM works by binding to the

same receptor that DHT uses, so it's essentially blocking the androgen from

triggering the growth of the cancer cells, " said Hien Le, lead author of the

study and a former graduate student in Bjeldanes' lab.

" DIM is chemically different than Casodex, but it behaves similarly in how

it blocks the effects of androgen, " said Le, who received her PhD in molecular

and biochemical nutrition in 2002.

These latest findings appear to add new burnish for this class of chemicals

that has already shown promise in prior studies as a therapeutic agent for

breast and endometrial cancer. For instance, a 1998 study by Bjeldanes and

Firestone showed that I3C keeps breast cancer cells from duplicating.

" We are investigating the potential use of indoles in combination with

current anti-cancer drugs on the market, " said Firestone. " The advantage of

combination therapy is that you can back off on the dose of a single agent and

thereby reduce potential side effects. "

Prostate cancer is the second leading cause of cancer deaths in American

men. One in 10 men in the United States will develop signs of prostate cancer in

his life, and more than 100,000 new cases are reported each year.

Le pointed out that the incidence of prostate cancer among men in Asia -

where consumption of vegetables is higher - is significantly lower than that for

men in the United States. However, the risk for Asian immigrants rises to

levels comparable to American men the longer they stay in the United States,

suggesting that factors such as diet and lifestyle play a role in the

development

of prostate cancer.

" There are already plenty of health reasons for consuming more vegetables

such as broccoli, " said Le. " This study suggests that there are even more

benefits to a diet rich in these phytochemicals when it comes to preventing

prostate

cancer. "

The study was also co-authored by Charlene Schaldach, a former PhD student

in the Bjeldanes lab.

The research is supported by the California Cancer Research Project and the

National Institute of Environmental Health Sciences, part of the National

Institutes of Health.