AG14361 is a potent inhibitor of PARP1 with Ki of <5 nM. It is at least 1000-fold more potent than the benzamides. AG14361 treatment before irradiation statistically significantly increases the sensitivity to radiation therapy. AG14361 enhances the growth-inhibitory and cytotoxic effects of topoisomerase I poisons and increases the persistence of camptothecin-induced DNA single-strand breaks.