Methods for treating neoplasia with a chemotherapeutic agent and radiation are provided. Radiation therapies used in conduction with a compound described herein presents a synergistic effect in the treatment of cancers. A compound of formula (I): wherein X, Y, Z, R<;SUB>;1 <;/SUB>;and R<;SUB>;2 <;/SUB>;are defined herein, sensitize cells making them more susceptible to radiation therapy.