TH287 is a potent and selective inhibitor of MTH1, with an IC50 of 0.8 nM. TH287 is highly selective towards MTH1, with no relevant inhibition of MTH2, NUDT5, NUDT12, NUDT14, NUDT16, dCTPase, dUTPase and ITPA at 100 μM. TH287 could act as a chemotherapeutic agent for cancer research.