Inhibition by 4-(4-Bromo-2-oxo-3-benzimidazol-1-yl)--(4-iodophenyl)piperidine-1-carboxamide (TH5487) of the Activity of Human 8-Oxoguanine DNA Glycosylase-1 (OGG1) for the Excision of 2,6-Diamino-4-hydroxy-5-formamidopyrimidine, 4,6-Diamino-5-formamidopyrimidine, and 8-Oxoguanine from Oxidatively Damaged DNA.

DNA glycosylases of the base excision repair pathway have become clinically validated drug targets for the treatment of several diseases. Human OGG1 (hOGG1) is specific for the removal of the highly mutagenic 8-oxoguanine (8-oxo-Gua) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) from damaged DNA. To develop clinically approved drugs, various small-molecule inhibitors of hOGG1 have been developed to inhibit its glycosylase and lyase activities, with 4-(4-bromo-2-oxo-3H-benzimidazol-1-yl)--(4-iodophenyl)piperidine-1-carboxamide (TH5487) shown to be a potent inhibitor. The inhibition of hOGG1 by TH5487 has been shown to suppress cancer cell growth, pulmonary inflammation, and lung fibrosis and sensitize cancer cells to ionizing radiation, confirming hOGG1 as a target for pharmaceutical intervention. While the assays that identified TH5487 utilized an oligodeoxynucleotide with the target substrate being 8-hydroxyadenine mispaired with cytosine, measurements of TH5487-mediated inhibition of the release of 8-oxo-Gua and FapyGua have not been reported. In the present work, we investigated the inhibition of hOGG1 by TH5487 using genomic DNA with multiple lesions and gas chromatography-tandem mass spectrometry with isotope dilution to measure inhibition of hOGG1-catalyzed DNA base lesion removal from DNA. An oligodeoxynucleotide containing 8-oxo-Gua was also used to measure the half-maximal inhibitory concentration (IC), which is 0.800 μmol/L ± 0.061 μmol/L. We show that TH5487 efficiently inhibits the excision of both 8-oxo-Gua and FapyGua, and a minor substrate 4,6-diamino-5-formamidopyrimidine (FapyAde) from DNA with the IC values of 1.6 μmol/L, 3.1 μmol/L, and 3.1 μmol/L, respectively. The results suggest that the approach used in the present work may be applied for future studies of hOGG1 inhibition by TH5487 on cellular and animal disease models.