Cancer Research | WRN Helicase Targeting Induces Antitumor Immunity in Microsatellite Unstable Colorectal Cancer through eccDNA Release

This study reveals a novel mechanism by which WRN inhibition in microsatellite unstable tumors activates immune responses via eccDNA, providing solid experimental evidence for designing combination therapies with PD-1 blockade. It particularly inspires translational strategies leveraging immunogenic cell death as a biomarker.

 

Literature Overview

This paper, 'Targeting WRN Helicase in Microsatellite Instable Colorectal Cancer Induces Antitumor Immunity through Extrachromosomal Circular DNA Release,' published in the journal Cancer Research, systematically investigates the antitumor immune mechanisms triggered by targeting the DNA helicase WRN in microsatellite unstable colorectal cancer (MSI CRC). The study finds that WRN deficiency not only causes DNA damage and apoptosis but also activates innate immune pathways through the release of extrachromosomal circular DNA (eccDNA), enhancing dendritic cell (DC) function and T-cell infiltration. This discovery expands our understanding of the immune effects of synthetic lethality strategies and offers new insights into overcoming resistance to immune checkpoint inhibitors (ICIs).

Background Knowledge

Microsatellite instability (MSI) colorectal cancer accounts for approximately 10–15% of all CRC cases and is driven by defective DNA mismatch repair (MMR), resulting in a high tumor mutational burden (TMB) and abundant neoantigens. This makes MSI CRC relatively sensitive to PD-1 blockade therapy. However, a significant proportion of patients exhibit primary or acquired resistance to ICIs, and treatment-related immune toxicities limit dose escalation, representing an unmet clinical need. In recent years, WRN has been identified as a synthetic lethal target in MSI cancers, where its inhibition causes severe genomic instability in MSI cells. Yet, whether WRN inhibitors exert their efficacy in preclinical models through immune system engagement remains unclear. This study focuses on whether WRN loss not only kills tumor cells but also induces immunogenic cell death (ICD), thereby enhancing antitumor immunity. Notably, eccDNA has emerged as an immunostimulatory molecule, generated from apoptotic cells in a LIG3-dependent manner and recognized by the cGAS-STING pathway. Therefore, the authors systematically evaluated the role of eccDNA in immune activation induced by WRN inhibition, uncovering a novel pathway linking DNA damage to innate immunity.

 

 

Research Methods and Experiments

The study employed multiple human and murine MSI CRC cell lines, including HCT116, RKO, LoVo, and Mlh1-knockout CT26 cells generated via CRISPR/Cas9, along with CH3+5 cells with homologous recombination deficiency as MSS controls. WRN was targeted using siRNA knockdown or small-molecule inhibitors (ML216, HRO761) to assess cell viability, apoptosis, and DNA damage markers (e.g., γH2AX, p53, PUMA). eccDNA was isolated using a modified alkaline lysis method combined with silica-column purification, and its circular structure was confirmed by gel electrophoresis and enzymatic digestion. To investigate immune effects, the authors co-cultured tumor cells with dendritic cells derived from human peripheral blood mononuclear cells (PBMCs), measuring phagocytic activity and DC maturation markers (CD83, CD86, HLA-DR). In vivo, immunocompetent BALB/c mice were implanted with Mlh1-KO CT26 tumors to evaluate the efficacy of WRN inhibitors alone or in combination with anti–PD-1, with tumor-infiltrating lymphocytes analyzed by flow cytometry. Additionally, patient-derived colorectal cancer organoids (PDOs) were used in an air-liquid interface (ALI) system to validate therapeutic effects, preserving the original tumor immune microenvironment.

Key Conclusions and Perspectives

• WRN deficiency selectively induces p53/PUMA-dependent apoptosis in MSI CRC cells, accompanied by eccDNA release, a phenomenon not significantly observed in MSS cells, highlighting the specificity of the synthetic lethality mechanism. [Data discovery] + [guidance for subsequent experimental directions]
• eccDNA generation depends on nuclear ligase LIG3; its knockout completely blocks cytokine release (e.g., TNF-α, IFN-β) and DC activation triggered by WRN inhibition, identifying LIG3 as a key molecule linking DNA damage to immune responses. [Data discovery] + [guidance for subsequent experimental directions]
• The immunostimulatory activity in conditioned media is resistant to linear DNAse (Plasmid-Safe DNase) and mtDNAse (PacI), but abolished by the broad-spectrum nuclease benzonase, confirming that the circular structure of eccDNA underlies its immunogenicity. [Data discovery] + [guidance for subsequent experimental directions]
• In mouse models, WRN inhibitors (ML216, HRO761) significantly suppress MSI tumor growth in a LIG3- and CD8+ T-cell–dependent manner, and synergize with anti–PD-1 therapy to enhance antitumor immunity, evidenced by increased T-cell infiltration and DC activation. [Data discovery] + [guidance for subsequent experimental directions]
• In patient-derived organoid models, combining WRN inhibition with anti–PD-1 significantly enhances CD8+ T-cell infiltration and IFN-γ secretion, validating the translational potential of this strategy in clinically relevant models. [Data discovery] + [guidance for subsequent experimental directions]

Research Significance and Prospects

This study extends the role of WRN inhibition beyond direct cytotoxicity to include immune modulation, offering a new dimension for developing more effective therapies for MSI cancers. Targeting WRN not only directly kills tumor cells but also 'ignites' the immune microenvironment via eccDNA release, converting 'cold' tumors into 'hot' ones, thereby enhancing responsiveness to ICIs. This provides a rational combination strategy to overcome primary or acquired resistance, particularly beneficial for patients intolerant to high-dose PD-1 blockade. Furthermore, eccDNA may serve as a liquid biopsy biomarker to predict the efficacy of WRN inhibitors, advancing the development of precision immunotherapy.

 

 

Conclusion

This study establishes the dual role of targeting WRN in microsatellite unstable colorectal cancer: directly inducing DNA damage–mediated cell death and triggering innate immune activation through eccDNA release. This mechanism relies on LIG3-mediated eccDNA generation and ultimately promotes CD8+ T-cell–dependent antitumor immunity. In preclinical models, WRN inhibitors combined with anti–PD-1 antibodies show significantly enhanced efficacy, validated in patient-derived organoids. These findings offer new perspectives on the treatment paradigm for MSI CRC, leveraging synthetic lethality not only to eliminate tumor cells but also to reshape the immune microenvironment. Moving forward, advancing WRN inhibitors into clinical trials, particularly in combination with ICIs, holds promise for improving current immunotherapy response rates and offering new options for resistant patients. Moreover, this mechanism may apply to other MSI-high tumor types, such as gastric and endometrial cancers, demonstrating broad translational potential. From bench to bedside, this discovery could become a cornerstone in optimizing immunotherapy strategies for MSI cancers, driving the development of personalized combination therapies.

 

Suisui Hao, Yoshiaki Sato, Zhaojin Liu, Jian Yu, and Lin Zhang. Targeting WRN Helicase in Microsatellite Instable Colorectal Cancer Induces Antitumor Immunity through Extrachromosomal Circular DNA Release. Cancer research.