The group found that the drug rapamycin appeared to prevent radiation-induced tissue damage in mice by protecting normal stem cells that are crucial for tissue repair. Although this study was preclinical, rapamycin has already been cleared by the U.S. Food and Drug Administration (FDA) and is currently in use in clinical trials (Cell Stem Cell, September 7, 2012, Vol. 11:3, pp. 401-414).

Ramiro Iglesias-Bartolome, a postdoctoral fellow specializing in cell biology at the National Institutes of Health's (NIH) Oral and Pharyngeal Cancer Branch, and colleagues were initially trying to determine whether adding a class of drugs known as mammalian target of rapamycin (mTOR) inhibitors would sensitize head and neck cancer.

Instead, the researchers discovered that the mTOR inhibitor rapamycin protects stem cells taken from the mouths of healthy individuals from DNA damage and radiation-induced death. The drug extended the life span of these normal stem cells and allowed them to grow. Rapamycin exerted these protective effects by preventing the accumulation of harmful molecules called reactive oxygen species (ROS).

Mice that received rapamycin during radiation treatment did not develop mucositis. Specifically, the rapamycin treatment effectively limited the loss of proliferative basal oral epithelial stem cells upon irradiation, thereby enhancing their tissue repopulating capacity and preventing the appearance of ulcers.

In a commentary on the research, Dr. Toren Finkel, PhD, from the National Heart, Lung, and Blood Institute, acknowledged that systematic rapamycin use is known to cause significant toxicities (Cell Stem Cell, September 7, 2012, Vol. 11:3, pp. 287-288). He suggested, however, that it might be possible to develop a mouthwash or gel that could regulate the levels of reactive oxygen species, preserve the tissue repopulating capacity of the epithelial stem cells, and provide targeted relief from radiation-induced mucositis.

Reducing or preventing mucositis could have profound effects, both in terms of cost and in enabling patients to complete their cancer treatment. Clinical studies have repeatedly shown that some patients do not complete chemotherapy and/or radiation therapy because of this condition.