The folate metabolism enzyme MTHFD2 (methylenetetrahydrofolate dehydrogenase/cyclohydrolase) is consistently overexpressed in cancer but its roles are not fully characterized, and current candidate inhibitors have limited potency for clinical development. In the present study, we demonstrate a role for MTHFD2 in DNA replication and genomic stability in cancer cells, and perform a drug screen to identify potent and selective nanomolar MTHFD2 inhibitors; protein cocrystal structures demonstrated binding to the active site of MTHFD2 and target engagement. MTHFD2 inhibitors reduced replication fork speed and induced replication stress followed by S-phase arrest and apoptosis of acute myeloid leukemia cells in vitro and in vivo, with a therapeutic window spanning four orders of magnitude compared with nontumorigenic cells. Mechanistically, MTHFD2 inhibitors prevented thymidine production leading to misincorporation of uracil into DNA and replication stress. Overall, these results demonstrate a functional link between MTHFD2-dependent cancer metabolism and replication stress that can be exploited therapeutically with this new class of inhibitors.

The aim of this work was to elucidate the oxidative folding mechanism of the macrocyclic cystine knot protein MCoTI-II. We aimed to investigate how the six-cysteine residues distributed on the circular backbone of the reduced unfolded peptide recognize their correct partner and join up to form a complex cystine-knotted topology. To answer this question, we studied the oxidative folding of the naturally occurring peptide using a range of spectroscopic methods. Although it is widely accepted that the folding of proteins is governed exclusively by their amino acid sequence (1), the prediction of the threedimensional structure of a biologically active protein from its primary sequence remains an unsolved challenge. The importance of protein folding is highlighted by the causes of debilitating diseases such as Alzheimer disease, cystic fibrosis, and Creutzfeld-Jakob disease (2, 3), which are attributed to the loss of biological functions of specific proteins due to their inability to either fold or remain correctly folded. An understanding of protein folding should provide a greater opportunity to devise novel approaches for the treatment of these and other protein misfolding diseases.In proteins containing cysteine residues, the oxidative formation of native disulfide bonds is an integral part of the folding process. In such proteins, conformational folding is coupled with disulfide formation in the process of oxidative folding. Because disulfide bonds play key roles in the stabilization of three-dimensional structures in vivo but their formation in a cellular environment is poorly understood, the study of oxidative folding in vitro offers a valuable tool to understand the complex pathways by which native disulfide formation takes place. In particular, the study of oxidative folding is facilitated by the ability to isolate discrete (disulfide-bonded) intermediates, something that cannot be achieved in studies of conformational folding of non-disulfide-containing proteins.Model studies of oxidative folding of cysteine-rich proteins, such as bovine pancreatic trypsin inhibitor (4, 5) and ribonuclease A (6, 7) have established a basis for understanding this process. Most oxidative folding studies reported to date have involved the isolation of stable intermediates by liquid chromatographic purification of acid-quenched folding reactions followed by structural elucidation and disulfide connectivity analysis. The oxidative folding pathways analyzed so far can be classified in terms of the number and types (i.e. native or nonnative) of disulfide bonds present in the intermediate species. Interestingly, different combinations of intermediates have been found for different proteins, and it is not clear how the primary amino acid sequence or a particular three-dimensional fold relates to a particular type of oxidative folding pathway. Thus there is a need for detailed studies on specific protein classes, and in this paper, we report on a class where the final disulfide network is particularly interesting in that it forms a "...

Supplementary methods for the article "Pharmacological targeting of MTHFD2 suppresses acute myeloid leukemia by inducing thymidine depletion and replication stress".