title: A novel inhibitor of DNA polymerase beta enhances the ability of temozolomide to impair the growth of colon cancer cells.
abstract: The recent emerging concept to sensitize cancer cells to DNA-alkylating drugs is by inhibiting various proteins in the base excision repair (BER) pathway. In the present study, we used structure-based molecular docking of DNA polymerase beta (Pol-beta) and identified a potent small molecular weight inhibitor, NSC-666715. We determined the specificity of this small molecular weight inhibitor for Pol-beta by using in vitro activities of APE1, Fen1, DNA ligase I, and Pol-beta-directed single-nucleotide and long-patch BER. The binding specificity of NSC-666715 with Pol-beta was also determined by using fluorescence anisotropy. The effect of NSC-666715 on the cytotoxicity of the DNA-alkylating drug temozolomide (TMZ) to colon cancer cells was determined by in vitro clonogenic and in vivo xenograft assays. The reduction in tumor growth was higher in the combination treatment relative to untreated or monotherapy treatment. NSC-666715 showed a high specificity for blocking Pol-beta activity. It blocked Pol-beta-directed single-nucleotide and long-patch BER without affecting the activity of APE1, Fen1, and DNA ligase I. Fluorescence anisotropy data suggested that NSC-666715 directly and specifically interacts with Pol-beta and interferes with binding to damaged DNA. NSC-666715 drastically induces the sensitivity of TMZ to colon cancer cells both in in vitro and in vivo assays. The results further suggest that the disruption of BER by NSC-666715 negates its contribution to drug resistance and bypasses other resistance factors, such as mismatch repair defects. Our findings provide the "proof-of-concept" for the development of highly specific and thus safer structure-based inhibitors for the prevention of tumor progression and/or treatment of colorectal cancer.
authors.affiliation: Department of Anatomy and Cell Biology and University of Florida Shands Cancer Center, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Aruna S
authors.initials: AS
authors.lastname: Jaiswal
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Banerjee
authors.forename: Harekrushna
authors.initials: H
authors.lastname: Panda
authors.forename: Charles D
authors.initials: CD
authors.lastname: Bulkin
authors.forename: Tadahide
authors.initials: T
authors.lastname: Izumi
authors.forename: Fazlul H
authors.initials: FH
authors.lastname: Sarkar
authors.forename: David A
authors.initials: DA
authors.lastname: Ostrov
authors.forename: Satya
authors.initials: S
authors.lastname: Narayan
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001665:Binding Sites; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000201:enzymology / Q000473:pathology*; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism; D053843:DNA Mismatch Repair / Q000187:drug effects; D019951:DNA Polymerase beta / Q000037:antagonists & inhibitors*; D004273:DNA, Neoplasm / Q000378:metabolism; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000378:metabolism; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D045585:Flap Endonucleases; D006801:Humans; D051379:Mice; D009711:Nucleotides / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D000077204:Temozolomide; D023041:Xenograft Model Antitumor Assays
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D004791:Enzyme Inhibitors; C000607892:LIG1 protein, human; D009711:Nucleotides; D003606:Dacarbazine; D019951:DNA Polymerase beta; D045585:Flap Endonucleases; C468317:FEN1 protein, human; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D011088:DNA Ligases; D000072481:DNA Ligase ATP; D000077204:Temozolomide