Abstract

BACKGROUNDWe developed MTH1 inhibitors (MTH1i) TH588 and TH1579 showing broad anti-cancer activity, while structurally distinct MTH1i fail to kill cancer cells. Here, we describe a new role of MTH1 in mitosis and the detailed mechanism of action of TH1579 (karonudib) and other structurally distinct MTH1i.\n\nMATERIALS AND METHODSCancer cell lines or zebrafish embryos were treated with MTH1i or siRNA targeting MTH1 and analysed primarily by live cell and immunofluorescence microscopy, survival assays, DNA fibre or COMET assays. MTH1 and tubulin interactions were analysed in vitro using co-immunoprecipitation and tubulin polymerisation assays.\n\nRESULTSHere, we describe a mitotic role for the MTH1 protein, which binds to tubulin, is required for microtubule polymerisation, correct spindle assembly, mitosis progression and suppression reactive oxygen species (ROS) generation in mitosis. Potent MTH1i display differential abilities to break the MTH1-tubulin interaction and cause mitotic arrest, demonstrating 8-oxodGTPase and mitotic function of MTH1 are mechanistically distinct. TH588 and TH1579 have more profound effect on mitotic arrest than other MTH1i explained by additional direct inhibition of tubulin polymerisation. MTH1i only inhibiting 8-oxodGTPase activity synergize with mitotic poisons.\n\nCONCLUSIONSEfficient MTH1 have a dual mechanism of action: inhibiting mitosis (to generate ROS) and promoting 8-oxodGTP incorporation into DNA during mitotic replication, dependent on ROS generation. Direct inhibition of tubulin polymerisation of TH588 and TH1579 increase their ability to arrest cells and generate ROS in mitosis. Furthermore, non-cytotoxic MTH1 can become effective and increase incorporation of oxidised nucleotides into DNA when combined with sub-therapeutic concentrations of mitotic inhibitors or challenged directly by 8-oxodGTP.