Identification and Characterization of Small Molecule Inhibitors of Polynucleotide Kinase 3'-Phosphatase

DNA lesions arise constantly in cells and are repaired by a variety of DNA repair pathways. Polynucleotide kinase 3’-phosphatase (PNKP) aids repair by phosphorylating 5’-hydroxyl DNA termini and dephosphorylating 3’-phosphate DNA termini for the completion of repair by DNA ligases. This activity is critical in vivo because DNA breaks do not usually possess ligatable termini. PNKP knockdown sensitizes cells to several DNA damaging agents, including the topoisomerase I (TOP1) inhibitor camptothecin - analogs of which are being developed into chemotherapeutic drugs - because the resolution of stalled TOP1-DNA complexes requires processing by PNKP. We hypothesize that small molecule inhibitors of PNKP could bolster the effects of radio- and chemotherapies on cancer cells. I have identified eight compounds that effectively inhibit human PNKP and, with reduced potency, T4 PNK in vitro. These compounds act by reversibly inhibiting the substrate-enzyme interaction but they do not appear to sensitize U2OS cells to camptothecin.MAS