Cellular homeostasis is dependent on a balance between DNA damage and DNA repair mechanisms. Cells are constantly assaulted by both exogenous and endogenous stimuli leading to high levels of
reactive oxygen species (ROS) that cause oxidation of the
nucleotide dGTP to
8-oxodGTP. If this base is incorporated into
DNA and goes unrepaired, it can result in G > T transversions, leading to genomic DNA damage. MutT Homolog 1 (MTH1) is a
nucleoside diphosphate X (Nudix)
pyrophosphatase that can remove
8-oxodGTP from the
nucleotide pool before it is incorporated into
DNA by hydrolyzing it into 8-oxodGMP. MTH1 expression has been shown to be elevated in many
cancer cells and is thought to be a survival mechanism by which a
cancer cell can stave off the effects of high ROS that can result in cell senescence or death. It has recently become a target of interest in
cancer because it is thought that inhibiting MTH1 can increase genotoxic damage and cytotoxicity. Determining the role of MTH1 in normal and
cancer cells is confounded by an inability to reliably and directly measure its native enzymatic activity. We have used the chimeric
ATP-releasing
guanine-oxidized (ARGO) probe that combines
8-oxodGTP and
ATP to measure MTH1 enzymatic activity in
colorectal cancer (CRC),
non-small cell lung cancer (NSCLC) and pancreatic ductal
adenocarcinoma (PDAC) along with patient-matched normal tissue. MTH1
8-oxodGTPase activity is significantly increased in
tumors across all three tissue types, indicating that MTH1 is a marker of
cancer. MTH1 activity measured by ARGO assay was compared to
mRNA and
protein expression measured by RT-qPCR and Western blot in the CRC tissue pairs, revealing a positive correlation between ARGO assay and Western blot, but little correlation with RT-qPCR in these samples. The adoption of the ARGO assay will help in establishing the level of MTH1 activity in model systems and in assessing the effects of MTH1 modulation in the treatment of
cancer.