# WRN inhibitors: a second synthetic-lethal win for mismatch-repair cancers

Source: https://onco.cc/ideas/idea-bio1-wrn-msi-programme/  
OnCo record `idea-bio1-wrn-msi-programme` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Cancers with faulty DNA proof-reading depend on one particular unwinding enzyme to survive. Blocking it kills them and spares normal cells.

## Summary

Microsatellite-unstable cancers accumulate expanded TA repeats that form secondary structures requiring WRN helicase to resolve; WRN loss is selectively lethal in MSI-high lines, one of the strongest synthetic-lethal signals from CRISPR screens. WRN inhibitors and degraders have entered early clinical trials. The strategic proposal is to test WRN inhibition specifically in MSI-high tumours that have failed immunotherapy, a group with no good options.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: WRN inhibition produces objective responses in MSI-high tumours that have progressed on checkpoint blockade, at a rate materially higher than that of available chemotherapy.
- Rationale: The dependency is genotype-defined, near-binary and reproducible across laboratories, which is rare; MSI status is already tested routinely, so patient selection needs no new diagnostic.
- Proposed test: Tumour-agnostic phase 2 in MSI-high, immunotherapy-refractory cancers with a pre-specified response threshold and paired biopsies for target engagement.
- Maturity: early-clinical
- Actor: industry

## Sources

- Bottleneck evidence (The undruggable drivers): Dang et al., Drugging the 'undruggable' cancer targets (Nature Reviews Cancer 2017): https://doi.org/10.1038/nrc.2017.36

## Connected records

- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Endometrial cancer](https://onco.cc/cancers/endometrial/), [Mismatch-repair deficient (MSI-high) colorectal cancer](https://onco.cc/cancers/msi-high-colorectal/), [Mismatch-repair-deficient endometrial cancer](https://onco.cc/cancers/endometrial-mmr-deficient/)
- technologies: [CRISPR functional genomics](https://onco.cc/technologies/crispr-screens/), [Synthetic lethality approaches](https://onco.cc/technologies/synthetic-lethality-approaches/)
- terms: [Microsatellite instability (MSI-H) / mismatch repair deficiency (dMMR)](https://onco.cc/terms/msi/), [Synthetic lethality](https://onco.cc/terms/synthetic-lethality/), [Tumour-agnostic (tissue-agnostic) approval](https://onco.cc/terms/tumour-agnostic/)
- bottlenecks: [Acquired resistance to every therapy](https://onco.cc/bottlenecks/b-resistance/), [The undruggable drivers](https://onco.cc/bottlenecks/b-undruggable-targets/)
- key papers: [Drugging the 'undruggable' cancer targets](https://onco.cc/key-papers/paper-dang-nat-rev-cancer/)

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