Juice May Slow Prostate Cancer Growth [Sci News]
Janet Raloff
Week of Aug. 12, 2006; Vol. 170, No. 7
Prostate cancer will claim the lives of an estimated 30,000 men in the United States this year. The second leading cause of cancer death in men, its incidence climbs with age. In Western countries, the disease is reaching nearly epidemic proportions among the elderly. However, the cancer can grow so slowly that many men with prostate cancer will die of something else first.
A mystery has always been what factors might improve a man's odds of having a slow-growing malignancy. A new study suggests that drinking pomegranate juice might be one of them.
FRUIT OR JUICE? Men in the new study drank a commercially marketed brand of juice, POM Wonderful—Wonderful being the name of this California-grown cultivated variety. Although the juicy fruit that surrounds each seed is rich in antioxidants, the commercial juice contains even more, the manufacturer notes, because it's made by crushing the whole fruit. This collects antioxidants also present in the rind and membrane.
Several studies have associated diets high in plant-derived polyphenols—principally, the deeply pigmented antioxidants in many fruits and vegetables—with lower risks of malignancies including prostate cancer. Because the blood-red juice of pomegranates is especially rich in such compounds, Allan J. Pantuck of the David Geffen School of Medicine at the University of California, Los Angeles and his colleagues decided to test it against metastatic prostate cancer. These are malignancies that have spread beyond the gland, which in these men had been removed or destroyed, along with tumors, by radiation.
Over time, the presence of these residual cancer cells was confirmed by rising concentrations of a protein in the men's blood: prostate-specific antigen (PSA). Because PSA is made by prostate cells—usually cancerous ones—and because these men no longer had intact prostates, the presence of the substance indicated that cancerous prostate cells continued to exist in the men's' bodies, Pantuck explains.
The researchers calculated that the men's average doubling time in PSA concentrations—a rough gauge of cancer growth—was 15 months. After men drank a glass of juice a day, their average doubling time more than tripled. In nearly one-third of men, Pantuck notes, PSA values actually fell—in a few cases, dramatically.
Although this is just one study and the juice showed no sign of curing the disease, Pantuck says it shows that pomegranate juice might be a beneficial adjunct to other therapies in men with this potentially lethal disease.
A glass a day
Last fall, researchers at the University of Wisconsin–Madison reported related laboratory data. They incubated cells from an aggressive form of prostate cancer with pomegranate-fruit extract. The higher the concentration of the extract the greater the inhibition of the cancer cells' growth, notes team leader Hasan Mukhtar.
The team also injected human–prostate-cancer cells into lab mice. The cells grew into tumors, but the rate was reduced in animals fed pomegranate extract, his team reported in the Oct. 11 Proceedings of the National Academy of Sciences. The team confirmed the juice's effect by measuring PSA concentrations in the animals' blood.
The new study extends these trials into people. Pantuck's group recruited 46 men who, despite having undergone prostate-cancer surgery, were exhibiting rising PSA values, as measured over a 6-month period. Concentrations of the protein at the start of the study ranged from 0.2 to 5 nanograms per liter of blood, indicative of small residues of cancer cells. These men had no medical sign of metastatic disease except for the PSA concentrations and were on no anticancer drugs or other therapies.
All recruits were then assigned to drink an 8-ounce bottle of pomegranate juice daily. PSA and other cancer indicators were measured every 3 months, and men were removed from the trial if they showed signs that their disease was advancing rapidly. By 33 months into the trial, PSA values had changed measurably in enough men to allow the researchers to calculate the concentration's new doubling time. On average, that figure was then about 54 months.
Overall, "more than 80 percent [of recruits] had a prolongation in their PSA doubling time," says Pantuck. "This means [that] for the majority of patients, their cancer's growth slowed."
PSA concentrations decreased in about a third of the study participants, the team reports in the July 1 Clinical Cancer Research. Most such decreases were small, but four men exhibited declines in the cancer indicator of more than 50 percent while taking the juice. One man's PSA concentration dropped a whopping 85 percent, Pantuck says. Once PSA becomes detectable, the urologist explains, it tends to rise inexorably—"you don't expect it to spontaneously decrease."
The researchers also conducted a few biochemical tests. For instance, they grew standard cultures of human-prostate cells in test tubes and fed the cells blood serum taken from the recruits at the beginning and end of the trial. The procedure was intended to reveal whether something changed in the men's blood that might affect cancer growth. Pantuck's group found that the cells' growth rate was 12 percent slower when the lab cultures were fed serum from the men after they had been drinking the juice.
The men's blood also tended to be less vulnerable to oxidation—a chemical reaction that can damage cells—once pomegranate-juice supplementation began.
What's next?
In this trial, no one was treated with a placebo instead of pomegranate juice. Such a study design is the gold standard for medical trials, because it rules out the possibility that just the idea of treatment—or some other factor—might be responsible for any effect that emerges from the study.
That's why Pantuck's group and others at institutions around the nation recently began just such a placebo-controlled, follow-up trial of pomegranate juice. The researchers' goal is to recruit some 350 patients with prostate cancer. Some men will receive pomegranate juice containing 570 milligrams of polyphenols per 8 ounces. Others will get juice with twice that quantity of polyphenols, and some men will receive a pomegranate substitute with no polyphenols.
Even if it turns out that the juice doesn't affect prostate growth in the new trial, there are plenty of reasons to enjoy this fruit. A growing library of published studies show that its antioxidant-rich flesh and juice inhibit cholesterol oxidation in human blood, lower blood pressure, retard the development of atherosclerosis, and even slow progression of Alzheimer's disease.
People in sunny climes may derive yet another unexpected benefit from pomegranate consumption: skin protection from the sun's harmful ultraviolet rays. Earlier this year, Mukhtar's group showed that treating cultured skin cells with a pomegranate extract minimized the development of precancerous changes when those cells were later irradiated with ultraviolet light. The scientists reported their findings in the March Photochemistry and Photobiology.
You say you don't like pomegranates? There may still be ways to fight prostate cancer naturally, via the diet—such as by drinking tea.
At a meeting 2 years ago, Suzanne Henning of the University of California, Los Angeles and her colleagues reported that polyphenols in tea appear to make men's blood less nourishing to prostate cancer cells. Moreover, drinking tea prior to prostate cancer surgery made noticeable changes in the tissue's cells. Those cells were less susceptible to runaway growth, a hallmark of cancer, in men who drank tea than in those who didn't. Her team's findings have now been formally published, in the July Journal of Nutrition.
Other evidence suggests that soy and aged garlic inhibit prostate cancer, as might foods rich in selenium (such as certain grains)—or boron (such as grapes and red wine). Indeed, Mukhtar argues, the best approach is always to strive for diversity in the diet, especially plenty of products made from different fruits and vegetables.
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