A recently completed study at two UCHealth locations suggests that a commonly used, relatively inexpensive product, grape seed extract, could benefit some men with prostate cancer.

Grape seed extract is readily available in pill, capsule and liquid form on the aisles of health food and grocery stores. Many people take it as a dietary supplement – it contains antioxidants and may help to reduce inflammation and lower blood pressure, although studies of those benefits are sparse.

By contrast, grape seed extract has been the subject of National Institutes of Health-funded studies for well over a decade at the Skaggs School of Pharmacy and Pharmaceutical Sciences on the University of Colorado Anschutz Medical Campus. There, Drs. Chapla Agarwal and Rajesh Agarwal and their research colleagues isolated a specific compound in grape seed extract that not only inhibits the growth of prostate cancer tumors but also causes the cells that drive the growth to die.

That success, published in 2014, followed many years of lab work by the Agarwals that established the cancer-fighting properties of grape seed extract in cell cultures and in mice. For example, in 2009, they published a study summarizing evidence from their own studies and others that grape seed extract administered to mice was effective in slowing the growth of not only prostate but also skin, colorectal and breast cancers.

From bench to bedside: Grape seed extract for prostate cancer

This and other work provided the foundation for the current study, led by Dr. Paul Maroni, associate professor of Surgery-Urology at the University of Colorado School of Medicine. Maroni met with Rajesh Agarwal about the feasibility of a clinical trial that would test the effectiveness of grape seed extract in treating human patients with prostate cancer. They put together a trial protocol, based not on hope, but on the years of evidence the Agarwals had developed.

“The basic science suggested that grape seed extract might slow down the progression of prostate cancer,” Maroni said.

In a relatively speedy seven-month period, the trial recruited 20 patients from UCHealth University of Colorado Hospital on the Anschutz Medical Campus and UCHealth Cancer Care and Hematology Clinic – Harmony Campus in Fort Collins. The subjects were men who had previously completed surgery, radiation treatment or both for their prostate cancer. They also had to have slowly increasing PSA (prostate specific antigen) numbers – a key marker for prostate cancer tumors – despite lacking evidence through imaging or other tests that the cancer had metastasized, or spread.

Slowing the next treatment step for prostate cancer

The idea was to see if taking 150 milligrams of grape seed extract twice a day for a year could slow the progression of the disease, as measured by the time it took for the patient’s PSA level to double, Maroni said. The longer that period, the longer providers could hold off on administering androgen deprivation therapy (ADT), which suppresses the hormones that drive prostate cancer.

ADT can blunt the cancer’s spread, but it also comes with a host of serious side effects, including hot flashes, fatigue, weight gain, weakened bones and increased risk for metabolic problems, heart disease and fractures, Maroni said.

Of course, some patients need that therapy to slow the spread of cancer to other parts of the body, he stressed.

“We don’t mind if a treatment gives patients side effects if there is a lot of value for them in terms of a longer life or a decreased burden of treatment later,” Maroni said. “But if the PSA is rising slowly, a patient may go for years before there are symptoms or detectable metastasis.”

In that case, the strategy is to watch and wait, and if grape seed extract lengthens that period, that’s a plus. The study suggests that the supplement treatment achieved at least partial success and deserves further study, Maroni said.

Using grape seed extract: posting the results

The American Association for Cancer Research accepted the findings of the study for a poster presentation, and Maroni summarized them in a recorded address at a June 22 virtual meeting of the organization. (View that poster presentation here.)

As Maroni and his study colleagues noted in the poster presentation, the “observation period” for patients with non-metastatic prostate cancer “presents an opportunity to treat patients with compounds that have a favorable side effect profile with the hope of delaying progression of disease” and the need for ADT.

The primary objective of the trial was for patients’ PSA doubling time to increase by 30% or more. Nine of the 20 enrollees met that goal. Three patients saw their PSA levels decrease, Maroni added. Overall, the PSA doubling time rose from 5.4 months to 6.4 months – slightly less than 20% — suggesting the grape seed extract helped to slow the production of cancer cells.

The poster presentation noted that eight patients withdrew from the study because their PSA levels doubled in less than three months, requiring more aggressive therapy. There were some “adverse events” recorded in patients, notably hypertension and dehydration, but the researchers added that patients generally tolerated grape seed extract well.

More research needed for using grape seed extract to slow cancer

The team concluded with a call for more research into the potential benefits of the supplement for patients with non-metastatic prostate cancer who have otherwise exhausted their treatment options. That’s now in the works, Maroni said, with the aim of recruiting another cohort of 20 patients.

“We want to see if we can replicate the data from this study,” Maroni said, adding that he is reasonably optimistic that the new patient recruitment phase can begin in August.

Rajesh Agarwal emphasized that whatever the ultimate findings of the trials, grape seed extract is not a stand-alone treatment for cancer of any kind and is never a substitute for standard medical care. The same goes for other natural substances with potential cancer-fighting properties that he has researched, including silibinin (a compound from milk thistle) and bitter melon juice, which shows promise in targeting pancreatic cancer cells.

“If you are on any kind of treatment regimen, don’t do anything else without first consulting with your physician,” he added.

But he is hopeful that the recent study leads to more options for clinicians treating prostate cancer patients.

“Grape seed extract is important because it is non-toxic and there is science and data behind using it,” Agarwal said. “We hope to drive more research and produce more evidence. Our goal at the end of the day is to help patients.”

For his part, Maroni said that he is encouraged that patients with slowly progressing prostate cancer may be able to avoid therapies with challenging side effects for longer periods of time, a boon for their quality of life.

“I like to think there is a lot of opportunity there,” Maroni concluded.