# Inhibition by 4-(4-Bromo-2-oxo-3H-benzimidazol-1-yl)-N-(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

## TL;DR

This study shows that TH5487 strongly inhibits the DNA repair enzyme hOGG1, which could lead to new treatments for cancer and lung diseases.

## Contribution

The study reports the first measurement of TH5487's inhibition of hOGG1 activity on multiple DNA lesions using genomic DNA and mass spectrometry.

## Key findings

- TH5487 inhibits hOGG1-catalyzed excision of 8-oxo-Gua with an IC50 of 0.8 μmol/L.
- TH5487 also inhibits excision of FapyGua and FapyAde with IC50 values of 3.1 μmol/L.
- The inhibition was measured using genomic DNA and gas chromatography-tandem mass spectrometry.

## Abstract

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)-N-(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 (IC50), 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 IC50 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.