An ancient Chinese herbal remedy is being tested in a clinical trial as a prostate cancer treatment drug, U.S. researchers say. Adanki Pratap Kumar, a professor of urology in the University of Texas School of Medicine at the Health Science Center in San Antonio, discovered in his laboratory that there was something special about the extract -- from the bark of the Amur cork tree in China -- in combination with radiation treatments that seemed to make both work much better. Kumar and colleagues are testing the supplement with radiation treatments against prostate cancer in patients. The study, open only to biopsy-proven prostate cancer patients in the South Texas Veterans Health Care Systems, is divided into two sections -- those who get surgery and those who get radiation. The men who get radiation take the supplement three times a day. Since the supplement has been used in traditional Chinese medicine for hundreds of years there is not much fear the tree bark will have toxic side effects in study participants. \"It\'s never been toxic, so we would be incredibly surprised if there was an interaction,\" Dr. William \"Trey\" Jones, a radiation oncologist, said in a statement. \"We\'re hoping to find that it provides a much higher level of cancer cell kill.\"