Provided herein is the compound RK-33, or a salt, solvate, stereoisomer, or derivative thereof, which is shown to be an inhibitor if the DEAD box helicase DDX3, in mammalian cells. RK-33 is also provided herein for use as a radiation dose sensitizer in a subject suffering from a proliferative disease and undergoing radiation therapy. Methods of treatment of proliferative diseases, such as cancer with a combination of RK-33 and radiotherapy methods such as stereotactic ablative radiotherapy (SABR) are also provided.
