Evaluation of the DNA damage response (DDR) network as predictor of nivolumab efficacy in head and neck squamous cell carcinoma (HNSCC)

We have previously shown that Peripheral Blood Mononuclear Cells (PBMCs) from HNSCC patients, at diagnosis, exhibit deregulated DDR-related parameters and higher levels of oxidative stress compared to healthy individuals. Herein, we tested the hypothesis that aberrations in DDR signals of the patients' PBMCs may predict therapeutic benefit from PD-1 checkpoint blockade in HNSCC. Oxidative stress, DDR associated parameters, including endogenous DNA damage and basal DNA repair mechanisms, namely nucleotide excision repair (NER) and double-strand breaks (DSBs) repair, were evaluated in PBMCs from 50 recurrent/metastatic HNSCC patients who participated in a phase II nivolumab trial (NCT03652142) and 26 healthy controls (HC). PBMCs were obtained at baseline, after 4 weeks of nivolumab treatment, and at progression. Per our previous findings, we verified that PBMCs from patients at baseline showed significantly higher levels of endogenous DNA damage compared with HC. Using alkaline comet assay measuring single-strand breaks and/or double-strand breaks, we found that lower endogenous DNA damage was associated with longer PFS (P=0.006), OS (P=0.002), and higher likelihood for response (P=0.03) and clinical benefit from nivolumab (P=0.015). Using γH2AX immunofluorescence staining for the evaluation of DSBs, we found that lower DSBs burden at baseline was also associated with statistically significant improvement of PFS, OS, and higher likelihood for response and clinical benefit (all p < 0.002). Moreover, PBMCs which exhibited lower levels of oxidative stress were correlated with a better clinical benefit (P=0.011). More importantly, lower NER and DSBs repair capacities of patients’ PBMCs were associated with better PFS and OS and a higher likelihood for response and clinical benefit (all P<0.004). Oxidative stress and DDR-related aberrations, measured in PBMCs from HNSCC patients correlated with the response to PD-1 immune checkpoint blockade. These results provide a proof of concept that DDR-based measurements could be used as a potential non-invasive biomarker to select HNSCC patients for treatment with PD-1 checkpoint inhibitors.