In this JCO Precision Oncology Article Insights episode, Dr. Jiasen He summarizes JCO PO article "Synthetic Lethal Co-Mutations in DNA Damage Response Pathways Predict Response to Immunotherapy in Pan-Cancer" by Hua Zhong et al.

TRANSCRIPT

Jiasen He: Hello and welcome to the JCO Precision Oncology Article Insights. I am your host, Jiasen He, and today we will be discussing the JCO Precision Oncology article, "Synthetic Lethal Co-mutations in DNA Damage Response Pathway Predict Response to Immunotherapy in Pan-Cancer" by Dr. Zhang and colleagues.

Immunotherapy has emerged as a groundbreaking treatment option for many types of cancer. However, the overall response rate to immunotherapy is low, around 10% to 30%. This highlights the critical need to identify which patients are most likely to benefit from immunotherapy. Two of the most extensively studied biomarkers are PD-L1 expression and tumor mutation burden (TMB). High levels of PD-L1 and TMB have been associated with better response to immune checkpoint inhibitors, which are now widely used in clinical practice. The predictive value of these markers is inconsistent across all settings. Some tumors with high PD-L1 or TMB still respond poorly to immunotherapy.

One reason is that TMB reflects new antigen production, but recent studies suggest that new antigen levels do not always correlate with tumor immunogenicity. Many new antigens are not effectively recognized by T cells, limiting the immune response. Emerging evidence indicates that mutations in the DNA damage response (DDR) pathway play a critical role in moderating tumor immune interactions. Tumors harboring DDR pathways frequently exhibit increased genome instability, which may enhance their sensitivity to immune checkpoint inhibitors. While all these pathways are under active investigation, the optimal DDR pathway biomarkers for patient selection remain unclear.

Notably, tumor cells with a defect in one DDR pathway may acquire greater reliance on alternative DDR pathways. Recent studies suggest that synthetic lethal co-mutations within DDR pathways are associated with immune-inflamed or hot tumor microenvironments. Based on this rationale, Dr. Zhang is investigating if synthetic lethal co-mutations in DDR pathway response pathway can serve as a treatment biomarker for immune checkpoint inhibitors. To address this question, Dr. Zhang and colleagues first utilized SynLethDB 2.0, a comprehensive database that integrated multiple data sets.

Synthetic lethal (SL) gene pairs in this resource are identified through both experimental and computational approaches, with confidence scores assigned to each pair. These SL pairs were then mapped to gene sequencing results from several clinical cohorts. SL co-mutation status was defined as positive when both genes in a synthetic lethal pair were mutated. From this, SL co-mutation pairs specifically involving DDR pathway genes were selected. Patients were classified as DDR co-mutation positive if both genes in a synthetic lethal pair, each belonging to the defined DDR pathways, were mutated.

In total, 431 DDR-related SL pairs were identified and matched to sequencing data from clinical cohorts. Clinical information was extracted from the cBioPortal, while further analysis of immune infiltration was performed using DNA mutation and RNA expression data from The Cancer Genome Atlas (TCGA) pan-cancer data set. The author first examined the correlation between SL co-mutation status and response to ICI therapy. They discovered that patients with SL co-mutation showed significantly improved outcome to ICI therapy across various clinical cohorts.

Notably, in patients who did not receive ICI treatment, patients with SL co-mutation showed markedly compromised overall survival. Further analysis focused on the predictive value of SL co-mutation within DDR pathway genes. The author found that patients with DDR SL co-mutation had a longer overall survival compared to those with mutations in a single DDR gene, implying that SL co-mutations may be more effective biomarkers within the DDR pathway.

To explore this further, in the TMB-MSKCC cohort, the author found that patients with DDR co-mutation constituted approximately 20% of various cancer types, including non-small cell lung cancer, melanoma, and bladder cancer. These patients demonstrated significantly better survival outcomes and disease control rates when treated with ICIs compared to DDR co-mutation negative patients. Notably, the TMB level was substantially higher in patients with DDR co-mutation, a finding consistent with data from the Miao-lung cohort.

Furthermore, in cohorts not treated with ICIs, patients with DDR co-mutation had a shorter overall survival compared to their counterparts. Upon stratifying by PD-L1 expression, the author observed that patients with DDR co-mutation who were also PD-L1 positive derived the greatest clinical benefit from ICI therapy. Upon analyzing the frequency of co-mutation within the DDR pathway, the authors found that patients with SL co-mutation in the CPF-CPF pathway experienced remarkable survival benefit from ICIs. Within this group, one of the most common co-mutation combinations was TP53-ATM, observed in approximately 45% of cases, which was associated with a better response to ICI therapy.

Further analysis of immune cell infiltration revealed that patients with TP53-ATM co-mutation exhibited a distinct tumor immune microenvironment. As the authors stated, the study's main limitation lies in the nature of retrospective analysis, which lacked the control over confounding variables and was subject to non-random sampling. For instance, patients with both SL co-mutations and DDR SL co-mutations exhibited high TMB, and TMB was known to be associated with improved response to ICI therapy itself. So, these findings require validation through prospective studies, and immune infiltration analysis needs confirmation via laboratory experiments.

In conclusion, the authors found that patients with SL co-mutations in DDR pathways showed favorable clinical response and prolonged survival following ICI therapy. They also identified TP53-ATM co-mutations as a clinically relevant biomarker for predicting ICI treatment response.

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