Compounds found in soybeans can make radiation treatment of lung cancer tumors more effective while helping to preserve normal tissue.

A team of scientists led by Gilda Hillman, PhD, professor of radiation oncology at Wayne State University’s (WSU; Detroit, MI, USA) School of Medicine and the Barbara Ann Karmanos Cancer Institute (Detroit, MI, USA), had earlier demonstrated that soy isoflavones, a natural, nontoxic component of soybeans, increase the ability of radiation to destroy cancer cells in prostate tumors by blocking DNA repair processes and molecular survival pathways, which are activated by the cancer cells to survive the damage radiation causes. At the same time, isoflavones act to reduce damage caused by radiation to surrounding cells of normal, noncancerous tissue. This was shown in a clinical trial conducted at WSU for prostate cancer patients treated with radiotherapy and soy tablets.

In findings published in the journal Nutrition and Cancer in 2010, those patients experienced reduced radiation toxicity to surrounding organs; fewer problems with incontinence and diarrhea; and better sexual organ function. Dr. Hillman’s preclinical research in the prostate tumor model led to the design of that clinical trial.

Soy isoflavones can make cancer cells more vulnerable to ionizing radiation by inhibiting survival pathways that are activated by radiation in cancer cells but not in normal cells. In normal tissues, soy isoflavones also can act as antioxidants, protecting those tissues from radiation-induced toxicity.

During 2010, the investigators achieved similar results in non-small-cell lung cancer cells in vitro. Dr. Hillman recently received a two-year, USD 347,000 grant from the US National Cancer Institute, part of the National Institutes of Health (Bethesda, MD, USA), to examine whether those findings also were sustained for non-small cell lung tumors in mice, and has found that they do. Her findings, which she called “substantial” and “very promising,” were published in the November 2011 issue of the journal Radiotherapy and Oncology.

Dr. Hillman stressed that soy supplements alone are not a substitute for traditonal cancer treatment, and that doses of soy isoflavones must be medically administered in combination with conventional cancer treatments to have the desired effects. “Preliminary studies indicate that soy could cause radioprotection,” she said. “It is important to show what is happening in the lung tissue.”

The next phase, according to Dr. Hillman, is to assess the effects of soy isoflavones in mouse lung-tumor models to determine the conditions that will maximize the tumor-killing and normal tissue-protecting effects during radiation therapy. “If we succeed in addressing preclinical issues in the mouse lung cancer model showing the benefits of this combined treatment, we could design clinical protocols for non-small-cell lung cancer to improve the radiotherapy of lung cancer,” Dr. Hillman said. “We also could improve the secondary effects of radiation, for example, improving the level of breathing in the lungs.”

Once protocols are developed, according to Dr. Hillman, clinicians can begin utilizing soy isoflavones combined with radiation therapy in humans, a process they believe will yield both therapeutic and economic benefits. “In contrast to drugs, soy is very, very safe,” Dr. Hillman said. “It’s also readily available, and it’s cheap. The excitement here is that if we can protect the normal tissue from radiation effects and improve the quality of life for patients who receive radiation therapy, we will have achieved an important goal.”

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