PU-H71 HCl (Zelavespib HCl) is a novel Hsp90 inhibitor, a novel purine-based analog, and a radiosensitizer that may be a promising agent for CIRT. PU-H71 HCL shows antitumor activity in many preclinical models of malignancy. PU-H71 HCL has an inhibitory effect on the protein expression levels of Rad51 and Ku70, which may be associated with the double chain break repair in the homologous recombination pathway and non-homologous end-joining pathway.