Researchers identify synthetic lethal TYMS inhibitor effective against ATRX-deficient cells
Scientists developed a 'phenotype-first' screening approach that identified a covalent chemical fragment, PP12, which selectively kills cells lacking the ATRX tumor suppressor gene by inhibiting the enzyme thymidylate synthase (TYMS). ATRX mutations are found in several cancers, including gliomas and pediatric brain tumors, making synthetic lethal strategies — where a second vulnerability is exploited in cells already carrying a specific mutation — a promising therapeutic avenue. The findings establish a reusable workflow for linking covalent fragment phenotypes to specific molecular targets, potentially accelerating the discovery of precision cancer therapies.
A study posted to bioRxiv describes a new drug-discovery workflow that combines covalent fragment screening, chemoproteomics, and genetic tools to identify cancer-specific vulnerabilities. Using isogenic cell lines that differ only in ATRX status, researchers screened roughly 500 cysteine-reactive chemical fragments and found that PP12, a chloroacetamide fragment, selectively impairs the viability of ATRX-deficient cells. By integrating competitive click-chemoproteomics with genome-wide CRISPR synthetic lethal datasets, the team pinpointed thymidylate synthase (TYMS) as the functionally relevant target of PP12. Target engagement was confirmed through X-ray crystallography, competition experiments with the established TYMS inhibitor 5-fluorouracil, and direct measurement of impaired dTMP synthesis in cells. Mechanistically, TYMS inhibition triggers replication stress that proves selectively lethal in ATRX-deficient cells, with the proteins FAM111A and SLFN11 identified as key mediators of this effect. The authors argue the approach is generalizable and could be applied to other genetically defined cancer contexts to identify new synthetic lethal drug targets.
What's missing
As a preprint, this work has not yet undergone peer review, so findings should be interpreted with caution. The study relies on a single haploid cell line model (eHAP); whether the synthetic lethal relationship between ATRX loss and TYMS inhibition holds in diploid, patient-derived, or in vivo cancer models is not yet established. The therapeutic window and potential toxicity of PP12 or optimized analogs in normal ATRX-expressing tissues are not addressed.
What different sources said
- bioRxivCenter
Phenotype-first covalent fragment screening identifies a synthetic lethal TYMS inhibitor in ATRX-deficient cells
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