Targeting WRN Helicase in Microsatellite Instable Colorectal Cancer Induces Antitumor Immunity through Extrachromosomal Circular DNA Release

Colorectal cancer (CRC) with microsatellite instability (MSI) is often treated with immune checkpoint inhibitors (ICIs), such as anti-PD-1 antibodies. However, a substantial fraction of MSI CRCs do not respond to ICIs. Recent studies have identified the DNA helicase WRN as a synthetic lethal target in MSI cancer cells, leading to the development of several small-molecule WRN inhibitors that are currently in clinical trials. In this study, we found that targeting WRN in MSI CRC cells triggered a robust antitumor immune response. Cell death induced by WRN inhibition was selective in MSI CRC cells and led to the release of extrachromosomal circular DNA (eccDNA), which directly stimulated immune cell activation and cytokine production. The deletion of nuclear ligase LIG3, a key mediator of eccDNA biogenesis, abolished the antitumor and immunogenic effects of WRN inhibition in MSI CRC cells and tumors. Furthermore, WRN inhibition potentiated anti-PD-1 therapy in MSI CRC models, including syngeneic mouse tumors and patient-derived tumor organoids. Together, these results reveal eccDNA-mediated immunogenic effects of WRN inhibition in MSI CRC, further strengthening the rationale for combining WRN inhibitors with ICIs.