E-7016 is an inhibitor of poly(ADP-ribose) polymerase, is being developed for anticancer therapy. Tumor cell lines exposed to E7016 preirradiation yielded an increase in radiosensitivity with dose enhancement factors at a surviving fraction of 0.1 from 1.4 to 1.7. To assess DNA double-strand breaks repair, gammaH2AX measured at 24 hours postirradiation had significantly more foci per cell in the E7016/irradiation group versus irradiation alone. Mice treated with E7016/irradiation/temozolomide had an additional growth delay of six days compared with the combination of temozolomide and irradiation. E-7016 can enhance tumor cell radiosensitivity in vitro and in vivo through the inhibition of DNA repair. Enhanced growth delay with the addition of E-7016 to temozolomide and radiotherapy in a glioma mouse model suggests a potential role for this drug in the treatment of glioblastoma multiforme.