Activated RAS GTPase signalling is a critical driver of oncogenic transformation and malignant disease. Cellular models of RAS-dependent cancers have been used to identify experimental small molecules, such as SCH51344, but their molecular mechanism of action remains generally unknown. Here, using a chemical proteomic approach, we identify the target of SCH51344 as the human mutT homologue MTH1 (also known as NUDT1), a nucleotide pool sanitizing enzyme. Loss-of-function of MTH1 impaired growth of KRAS tumour cells, whereas MTH1 overexpression mitigated sensitivity towards SCH51344. Searching for more drug-like inhibitors, we identified the kinase inhibitor crizotinib as a nanomolar suppressor of MTH1 activity. Surprisingly, the clinically used (R)-enantiomer of the drug was inactive, whereas the (S)-enantiomer selectively inhibited MTH1 catalytic activity. Enzymatic assays, chemical proteomic profiling, kinome-wide activity surveys and MTH1 co-crystal structures of both enantiomers provide a rationale for this remarkable stereospecificity. Disruption of nucleotide pool homeostasis via MTH1 inhibition by (S)-crizotinib induced an increase in DNA single-strand breaks, activated DNA repair in human colon carcinoma cells, and effectively suppressed tumour growth in animal models. Our results propose (S)-crizotinib as an attractive chemical entity for further pre-clinical evaluation, and small-molecule inhibitors of MTH1 in general as a promising novel class of anticancer agents.
Ras致癌基因的突变与不良预后有关。过去人们知道，MTH1 (在防止受损的碱基被结合到DNA内部中所涉及的一种蛋白) 的过度表达会防止发生由Ras诱导的衰老。在寻求了解受损的脱氧核苷酸 (dNTPs)怎样促进癌症的过程中，Thomas Helleday及同事发现，MTH1的活性是被改变细胞的存活所必需的，同时他们还分离出了两个小分子MTH1抑制因子，即TH287 和 TH588。在这些水解酶抑制因子存在的情况下，受损的核苷酸只被结合到癌细胞的DNA中，造成细胞毒性，并在小鼠异种移植癌症模型中引发一个有益的反应。在第二项研究中，Giulio Superti-Furga及同事寻求识别一个小分子(即SCH51344，是针对依赖于Ras的癌症研发的)的作用目标，发现它能使MTH1失去活性。这使得他们识别出了MTH1的一个新的、具有对映选择性的强效抑制因子，即(S)-crizotinib。在有该药物存在的情况下，肿瘤生长在结肠癌动物模型中受到抑制。