Rapamycin Prevents Side Effects Of Radiation Therapy By Protecting Stem Cells

Radiation therapy is very heavily used to treat many different types of cancer. Unfortunately, radiation damages normal cells and tissues and can have horrible side effects that debilitate patients. However, a class of drugs known as inhibitors of mTOR, which stands for mammalian target of rapamycin, can prevent the tissue damage normally caused by radiation. These drugs protect against radiation-induced damage by protecting normal stem cells. Since these stem cells help repair the damaged tissues, these drugs speed recovery and improve outcomes. These results come from a preclinical study published in the September issue of the journal Cell Stem Cell.

The senior author of this study, J. Silvio Gutking of the National Institute of Dental and Craniofacial Research, made this comment about his study: “We can exploit the emerging findings for the development of new preventive strategies and more effective treatment option for patients suffering this devastating disease.”

After undergoing radiation therapy, cancer patients often suffer from a painful condition called mucositis. Mucositis is characterized by the swelling of tissues in the mouth, and this swelling can prevent patients from drinking and the pain of this condition drives them to heavily rely on narcotic pain killers. Mucositis and other types of radiation-induced tissue damage are induced by depletion of stem cells capable of repairing damaged tissue.

In their study, Gutkind and his team discovered that an mTOR inhibitor called rapamycin protects stem cells extracted from the mouths of healthy individuals against radiation-induced damage. Fortuitously, rapamycin does not convey the same protections to cancer cells. The drug extended the lifespans of normal stem cells and allowed them to grow after irradiation. Rapamycin exerted its protective effects by preventing the accumulation of harmful molecules called reactive oxygen species (ROS). Also mice that received rapamycin during radiation treatment did not develop mucositis.

Rapamycin is already approved by the Food and Drug Administration and is currently under investigation in clinical trials as a cancer prevention agent and a potential treatment of various kinds of cancer. These novel findings could have immediate and important implications for a many different cancer patients.

According to Gutkind: “Mucositis prevention would have a remarkable impact on the quality of life and recovery of cancer patients and at the same time would reduce the cost of treatment. Our study provides the basis for further testing in humans, and we hope that these findings can be translated rapidly into the clinic.”