Noncovalent Fragments vs WRN

Key Takeaways

• 1,020 fluorinated fragments screened via 19F NMR T2 CPMG.
• Seven primary hits led to three crystal structures.
• SPR screen of 500 fragments added three more crystal hits.
• Initial fragments lacked activity in WRN enzymatic assays.
• Optimized compound 4 showed SPR affinity and functional inhibition.

Pulse Analysis

The Werner syndrome helicase (WRN) has emerged as a high‑value synthetic‑lethal target for cancers harboring defects in homologous recombination or mismatch repair. Because WRN relies on ATP‑driven domain motions to unwind DNA, its multidomain architecture samples a wide range of conformations, complicating traditional high‑throughput screening. While covalent inhibitors have reached clinical stages, noncovalent ligands promise reversible modulation and broader chemical space, yet they must overcome the protein’s structural plasticity and the prevalence of assay artefacts that have plagued earlier efforts.

To sidestep false‑positive enzymatic readouts, Merck and Proteros deployed a biophysical‑first strategy. A library of 1,020 fluorine‑tagged fragments was interrogated by 19F‑NMR T2 CPMG, yielding 31 initial hits; subsequent deconvolution and three orthogonal ligand‑detected NMR assays narrowed the set to seven candidates, three of which produced crystal structures. A parallel surface‑plasmon‑resonance (SPR) screen of 500 non‑fluorinated fragments added three more crystallographic hits. Strikingly, the bound fragments induced pronounced domain rearrangements, highlighting WRN’s conformational adaptability.

The structural snapshots guided a focused medicinal‑chemistry campaign that expanded the primary fragment into a 17‑member virtual library. Among these, compound 4 displayed the strongest SPR‑derived affinity and, uniquely, measurable inhibition in a functional helicase assay—an early proof‑of‑concept that noncovalent chemistry can engage WRN productively. This work underscores the necessity of integrating NMR, SPR, and crystallography when tackling flexible enzymes, and it sets a template for future synthetic‑lethal programs seeking reversible inhibitors with improved safety profiles.