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