Natural Compounds in Pomegranates May Prevent Growth of Hormone-Dependent Breast Cancer

Eating fruit, such as pomegranates, that contain anti-aromatase phytochemicals reduces the incidence of hormone-dependent breast cancer, according to results of a study published in the January issue of Cancer Prevention Research, a journal of the American Association for Cancer Research.

Pomegranate is enriched in a series of compounds known as ellagitannins that, as shown in this study, appear to be responsible for the anti-proliferative effect of the pomegranate.
"Phytochemicals suppress estrogen production that prevents the proliferation of breast cancer cells and the growth of estrogen-responsive tumors," said principal investigator Shiuan Chen, Ph.D., director of the Division of Tumor Cell Biology and co-leader of the Breast Cancer Research Program at City of Hope in Duarte, Calif.
Previous research has shown that pomegranate juice -- punica granatum L -- is high in antioxidant activity, which is generally attributed to the fruit's high polyphenol content. Ellagic acid found in pomegranates inhibits aromatase, an enzyme that converts androgen to estrogen. Aromatase plays a key role in breast carcinogenesis; therefore, the growth of breast cancer is inhibited.
Chen, along with Lynn Adams, Ph.D., a research fellow at Beckman Research Institute of City of Hope, and colleagues, evaluated whether phytochemicals in pomegranates can suppress aromatase and ultimately inhibit cancer growth.
After screening and examining a panel of 10 ellagitannin-derived compounds in pomegranates, the investigators found that those compounds have the potential to prevent estrogen-responsive breast cancers. Urolithin B, which is a metabolite produced from ellagic acid and related compounds, significantly inhibited cell growth.
"We were surprised by our findings," said Chen. "We previously found other fruits, such as grapes, to be capable of the inhibition of aromatase. But, phytochemicals in pomegranates and in grapes are different."
According to Gary Stoner, Ph.D., professor in the Department of Internal Medicine at Ohio State University, additional studies will be needed to confirm the chemopreventive action of Urolithin B against hormone-dependent breast cancer.
"This is an in vitro study in which relatively high levels of ellagitannin compounds were required to demonstrate an anti-proliferative effect on cultured breast cancer cells," said Stoner, who is not associated with this study. "It's not clear that these levels could be achieved in animals or in humans because the ellagitannins are not well absorbed into blood when provided in the diet."
Stoner believes these results are promising enough to suggest that more experiments with pomegranate in animals and humans are warranted.
Powel Brown, M.D., Ph.D., medical oncologist and chairman of the Clinical Cancer Prevention Department at the University of Texas M. D. Anderson Cancer Center, agreed with Stoner's sentiments and said these results are intriguing. He recommended that future studies focus on testing pomegranate juice for its effect on estrogen levels, menopausal symptoms, breast density or even as a cancer preventive agent.
"More research on the individual components and the combination of chemicals is needed to understand the potential risks and benefits of using pomegranate juice or isolated compounds for a health benefit or for cancer prevention," Brown said. "This study does suggest that studies of the ellagitannins from pomegranates should be continued."
Until then, Stoner said people "might consider consuming more pomegranates to protect against cancer development in the breast and perhaps in other tissues and organs."

Flower Power May Reduce Resistance to Breast Cancer Drug Tamoxifen

Feverfew plant used in herbal medicines.

Combining tamoxifen, the world's most prescribed breast cancer agent, with a compound found in the flowering plant feverfew may prevent initial or future resistance to the drug, say researchers at Georgetown Lombardi Comprehensive Cancer Center.
The finding, reported online Feb. 12 in The FASEB Journal, provides new insight into the biological roots of that resistance, and also tests a novel way to get around it.
"A solution to tamoxifen resistance is sorely needed, and if a strategy like this can work, it would make a difference in our clinical care of breast cancer," says the study's lead investigator, Robert Clarke, PhD, DSc, a professor of oncology and physiology & biophysics at Lombardi, a part of Georgetown University Medical Center (GUMC). Clarke is also the interim director of GUMC's Biomedical Graduate Research Organization.
Clarke added that the purified research chemical they tested, parthenolide, a derivative of feverfew, is being tested by other scientists as treatment for a variety of cancers, as well as other health conditions. Feverfew has long been a staple of natural medicine, and is particularly known for its effects on headaches and arthritis. Latin for "fever reducer," feverfew is a common garden bush with small daisy-like flowers.
"The chemical clearly has potential, and we ought to be able to figure out fairly quickly if it can help solve tamoxifen's resistance problem," Clarke says.
Tamoxifen is a treatment of choice for breast cancer that is estrogen receptor positive (ER+), meaning that the hormone estrogen drives cancer growth. Most newly diagnosed breast cancers -- about 70 percent -- fall into that category. But about half of these cancers do not initially respond to tamoxifen, which is designed to block the hormone from binding to the cell's protein receptor, and many patients that do respond are at risk for developing resistance and cancer relapse.
In this study, Clarke and a team of researchers set out to study if, as previous research had suggested, tamoxifen resistance is regulated by the protein complex NF-κB (nuclear factor kappa B), which is often found to be over-expressed in ER+ breast cancer. NF-κB is known to help cells survive when damaged. The researchers had earlier discovered that NF-κB is over-expressed in cells that are resistant to tamoxifen, and they had found that resistance to another tamoxifen-like drug, fulvestrant, was controlled by a protein (Bcl2) that is, itself, regulated by NF-κB.
"Our scientific quest was to see if blocking NF-?B affects tamoxifen resistance, and if it does, why?" says Clarke.
They conducted a variety of tests using parthenolide, which has been shown to act on NF-κB. They found that in resistant breast cancer cells, the chemical blocked the activity of NF-κB, making the cells sensitive once again to tamoxifen. They then silenced NF-B in tamoxifen resistant cells, and found that this had the same effect as using parthenolide.
They further found that increased activation of NF-κB can alter sensitivity of tamoxifen by modulating the protein CASP8, which is involved in programmed cell death. That then affects Bcl2, which also helps push a damaged cell to die.
"When you give tamoxifen to a breast cancer cell, that is essentially a pro-death signal, because you are blocking the cell's access to estrogen, and the cell recognizes this is a mortal blow," Clarke says. "Such a damaged cell uses CASP8 and Bcl2 to trigger the cell machinery needed for dying.
"But the cell has ways to counteract the pro-death signal, and one important one is to activate NF-κB, which can control expression of genes necessary for survival," he says. "Now the cell thinks it should be living, not dying."
Because NF-κB controls CASP8 and Bcl2, it can turn those proteins essentially off, Clarke says. "The pro-survival signals override the pro-death signals."
Still, as much as this study advances the understanding of tamoxifen resistance, there is much that is not understood, he adds. "We don't know when NF-κB becomes over-expressed in the transformation of tamoxifen-sensitive to a tamoxifen-resistant breast cancer cells, and we don't know of other adaptations the cell may have made," he says. "It is probably fair to say this is a hideously complex process."
To that end, Clarke cannot predict how many women who try a combination of tamoxifen and parthenolide will benefit. He says the science is much too early to make any recommendations and strongly warns women against adding feverfew supplements to their cancer treatment.
Still, he is hopeful. "Every breast tumor slightly different, but we know many do use NF-κB because excess amounts of the protein are found in these cancers," he says. "That suggests they may be sensitive to targeted approaches that shut down this pro-survival signal."
The study was funded by grants from the U.S. Department of Defense, the Army Medical Research and Material Command, and the National Institutes of Health. The authors disclose no potential financial conflicts.