Herbal extracts sensitize tumor cells to ionizing radiation by inducing cellular oxidative stress

Ionizing radiation has been widely used in treatment of cancer for the past many decades. However, the success of cancer radiotherapy is limited due to commonly observed adverse effects of radiation on normal tissues. To overcome this limitation, researchers have actively been investigating for developing new approaches to selectively kill the cancer cells without significantly harming the normal cells. Recent researches have aided to considerable improvement in delivering the radiation dose to diseased tissues but technical limitations yet pose the induction of secondary cancer following the radiation treatment. A promising strategy that holds potential in improving treatment of cancer patients consists in search for compounds from natural sources which may cause selective toxicity to tumor cells. Research from our group has shown that some natural compounds from plants remarkably sensitize tumor cells with no or minimal effects on normal cells. The mechanisms seem to involve induction of oxidative stress resulting in generation of reactive oxygen species (ROS) inside tumor cells. It is further found that increased ROS trigger apoptosis (cellular suicide) in tumor cells. We have found that that the bioactive compounds of natural origin are largely rich in polyphenols, flavonoids, alkaloids and exhibit radiosensitizing properties. The observed lower normal cell toxicity, high water solubility and selective toxicity to tumor cells in vitro are being examined to develop new drugs for possible improvement of radiation cancer treatment. (author)