Inhibition of PNKP phosphatase activity in cells with concentrations of A12B4C3 and A83B4C63 in the same range of 1 to 10 μM inhibits the repair of single and double-stranded DNA breaks and sensitizes cancer cells to the topoisomerase poison camptothecin and gamma irradiation (65, –, 70). Here, PNKP is linked to cancer.