Bark takes bite out of cancer
The road to ancient herbal remedies in northeastern China began, for Addanki Pratap Kumar, Ph.D., almost 10 years ago. Dr. Kumar, a professor of urology in the
School of Medicine at the UT Health Science Center, was interested in the fact that
prostate cancer rates are much higher in Western populations than in Asian ones —
at least until Asian men had been living in Western countries for five or six years.
After Dr. Kumar published a paper examining some of the differences in Asian and Western diets, a provider of extract from the bark of the Amur cork tree (Phellodendron amurense) told him that some men who took it reported that their PSA levels dropped.
Native to the Amur River watershed in northeastern China and far western Russia, the cork tree has a bark that has long been used in Chinese herbal medicine as an anti-inflammatory and treatment for digestive problems. PSA, or prostate-specific antigen, is secreted by the prostate gland, and elevated levels of it have been linked to the presence of prostate cancer, although it is not considered a definitive test.
Dr. Kumar was intrigued enough by the possibility of a link to start a laboratory study of the substance. He wanted to see if an extract of the cork tree’s bark killed prostate cancer cells in tissue samples, and then in animal models. The studies, supported by grants from the National Cancer Institute and the U.S. Department of Veterans Affairs, were successful.
Building on that success, Dr. Kumar launched a limited clinical trial for men who were patients at the South Texas Veterans Health Care System. As co-leader of the Cancer Prevention and Population Science program at the Health Science Center’s Cancer Therapy & Research Center (CTRC), he was able to network with clinicians who could oversee the patient arms of the study.
The study for VA patients with prostate cancer is divided into two sections: those who receive surgery and those who receive radiation therapy.
The men in the radiation arm, like Joe Covert, take the drug each day throughout the course of their therapy. Covert, a patient at the CTRC, said he had to get used to taking the required thrice-daily dose, but that it hasn’t caused him any trouble. Covert also said he doesn’t expect a miracle — he decided to participate in the early-stage study out of a wish to help other men with prostate cancer in the future.
But unlike in the case of many drugs that are first being tested on humans, researchers are not worried that the cork tree bark will have toxic side effects in study participants, since it has been used as a medicine for hundreds of years.
“It’s never been toxic, so we would be incredibly surprised if there was an interaction,” said William “Trey” Jones, M.D., assistant professor of radiation oncology at the UT Health Science Center, who is leading the radiation therapy arm of the study.
What they are hoping to find from this first small study is that the drug works in humans the way it worked in the lab: sensitizing cancer cells to the point that they succumb more completely to radiation.
“We’re hoping to find that it provides much higher levels of cell kill,” Dr. Jones said.
That could lead to using lower levels of radiation in therapy, said Joseph W. Basler, M.D., Ph.D., professor of urology at the UT Health Science Center.
“There are still significant side effects to radiation therapy,” Basler said, “so if you have a medicine that can sensitize the tumor, you can reduce the amount of radiation given to the patient.”
Even better, and eventually, “Our hope is to find a drug that could treat small tumors and maybe avoid surgery or radiation in the future.”
Dr. Basler’s patients in the surgery arm take the bark extract, which comes in small yellow capsules, for 30 to 80 days before their operations. The tissue that is removed during the operation can then be examined for tumor markers and compared to the initial biopsy tissue.
Dr. Basler noted that the way Dr. Kumar coordinated with physicians to move the study of the bark extract from the lab to the clinic happened in a relatively brief time period compared to other medical research studies.
“It’s a good example of translational medicine,” Dr. Basler said.
Dr. Kumar has his eye on the next step.
“If the patients even moderately respond, we will try to take the study to other cancers,” he said, adding that he has already talked with CTRC specialists in the areas of bladder cancer, pancreatic cancer and melanoma.