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

Colorectal cancer with microsatellite instability (MSI) is often treated with immune checkpoint inhibitors (ICI), such as anti-PD-1 antibodies. However, a substantial fraction of MSI colorectal cancers do not respond to ICIs. Recent studies have identified the DNA helicase Werner (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 colorectal cancer cells triggered a robust antitumor immune response. Cell death induced by WRN inhibition was selective in MSI colorectal cancer 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 colorectal cancer cells and tumors. Furthermore, WRN inhibition potentiated anti-PD-1 therapy in MSI colorectal cancer models, including syngeneic mouse tumors and patient-derived tumor organoids. Together, these results reveal the eccDNA-mediated immunogenic effects of WRN inhibition in MSI colorectal cancer, further strengthening the rationale for combining WRN inhibitors with ICIs. SIGNIFICANCE: Extrachromosomal circular DNA release induced by WRN inhibition in colorectal cancer cells with microsatellite instability stimulates immune cell activation and cytokine production, which can be leveraged to enhance the efficacy of immunotherapy.