WITHAFERIN-A - A NEW RADIOSENSITIZER FROM THE INDIAN MEDICINAL PLANT WITHANIA-SOMNIFERA

Withaferin A, a steroidal lactone isolated from the roots of the India n medicinal plant Withania somnifera, reduced survival of V79 cells in a dose-dependent manner. LD(50) for survival was 16 mu M. One-hour tr eatment with a non-toxic dose of 2.1 mu M before irradiation significa ntly enhanced cell killing, giving a sensitizer enhancement ratio (SER ) of 1.5 for 37% survival and 1.4 for 10% survival. SER increased with drug dose, but at higher doses the increased lethality appears to be due to two effects-drug toxicity and radiosensitization. The drug indu ced a G(2)/M block, with a maximum accumulation of cells in G(2)-M pha se at h after treatment with 10.5 mu M withaferin A for 1 h. The appli cability of this drug as a radiosensitizer in cancer therapy needs to be explored.