The DNA damage response (DDR) system is a complicated network of signaling pathways that detects and repairs DNA damage or induces apoptosis. Critical regulators of the DDR network include the DNA damage kinases ataxia telangiectasia mutated Rad3-related kinase (ATR) and ataxia-telangiectasia mutated (ATM). The ATR pathway coordinates processes such as replication stress response, stabilization of replication forks, cell cycle arrest, and DNA repair. ATR inhibition disrupts these functions, causing a reduction of DNA repair, accumulation of DNA damage, replication fork collapse, inappropriate mitotic entry, and mitotic catastrophe. Recent data have shown that the inhibition of ATR can lead to synthetic lethality in ATM-deficient malignancies. In addition, ATR inhibition plays a significant role in the activation of the immune system by increasing the tumor mutational burden and neoantigen load as well as by triggering the accumulation of cytosolic DNA and subsequently inducing the cGAS-STING pathway and the type I IFN response. Taken together, we review stimulating data showing that ATR kinase inhibition can alter the DDR network, the immune system, and their interplay and, therefore, potentially provide a novel strategy to improve the efficacy of antitumor therapy, using ATR inhibitors as monotherapy or in combination with genotoxic drugs and/or immunomodulators.

Aging is characterized by the progressive deregulation of homeostatic mechanisms causing the accumulation of macromolecular damage, including DNA damage, progressive decline in organ function and chronic diseases. Since several features of the aging phenotype are closely related to defects in the DNA damage response (DDR) network, we have herein investigated the relationship between chronological age and DDR signals in peripheral blood mononuclear cells (PBMCs) from healthy individuals. DDR-associated parameters, including endogenous DNA damage (single-strand breaks and double-strand breaks (DSBs) measured by the alkaline comet assay (Olive Tail Moment (OTM); DSBs-only by γH2AX immunofluorescence staining), DSBs repair capacity, oxidative stress, and apurinic/apyrimidinic sites were evaluated in PBMCs of 243 individuals aged 18–75 years, free of any major comorbidity. While OTM values showed marginal correlation with age until 50 years (r_s = 0.41, p = 0.11), a linear relationship was observed after 50 years (r = 0.95, p < 0.001). Moreover, individuals older than 50 years showed increased endogenous DSBs levels (γH2Ax), higher oxidative stress, augmented apurinic/apyrimidinic sites and decreased DSBs repair capacity than those with age lower than 50 years (all p < 0.001). Results were reproduced when we examined men and women separately. Prospective studies confirming the value of DNA damage accumulation as a biomarker of aging, as well as the presence of a relevant agethreshold, are warranted.

The DNA damage response (DDR) system is a complicated network of signaling pathways that detects and repairs DNA damage or induces apoptosis. Critical regulators of the DDR network include the DNA damage kinases ataxia telangiectasia mutated Rad3-related kinase (ATR) and ataxia-telangiectasia mutated (ATM). The ATR pathway coordinates processes such as replication stress response, stabilization of replication forks, cell cycle arrest, and DNA repair. ATR inhibition disrupts these functions, causing reduction of DNA repair, accumulation of DNA damage, replication fork collapse, inappropriate mitotic entry and mitotic catastrophe. Recent data have shown that the inhibition of ATR can lead to synthetic lethality in ATM-deficient malignancies. In addition, ATR inhibition plays a significant role in the activation of the immune system by increasing the tumor mutational burden and neoantigen load as well as by triggering the accumulation of cytosolic DNA and subsequently inducing the cGAS-STING pathway and the type I IFN response. Taken together, we review stimulating data showing that ATR kinase inhibition can alter the DDR network, the immune system and their interplay and therefore potentially provide a novel strategy to improve the efficacy of antitumor therapy, using ATR inhibitors as monotherapy or in combination with genotoxic drugs and/or immunomodulators.

Background/Objectives: DNA damage response (DDR) is a network of molecular pathways associated with the pathogenesis and progression of several diseases, as well as the outcome of chemotherapy. Moreover, the intracellular redox status is essential for maintaining cell viability and controlling cellular signaling. Herein, we analyzed DDR signals and redox status in peripheral blood mononuclear cells (PBMCs) from patients with lung cancer with different response rates to platinum-based chemotherapy. Methods: Several DDR-associated signals and redox status, expressed as the GSH/GSSG ratio, were measured in two lung cancer cell lines (A549, H1299), two normal fibroblast cell lines (WS1, 1BR3hT), and PBMCs from 20 healthy controls and 32 patients with lung cancer at baseline (17 responders and 15 non-responders to subsequent platinum-based chemotherapy). Results: Higher levels of endogenous/baseline DNA damage, decreased GSH/GSSG ratios, and augmented apurinic/apyrimidinic sites, as well as lower nucleotide excision repair (NER) and increased interstrand cross-links (ICLs) repair efficiencies, were observed in lung cancer cell lines compared with normal ones (all p < 0.05). Moreover, PBMCs from patients with lung cancer showed reduced GSH/GSSG ratios, augmented apurinic/apyrimidinic sites, decreased NER and ICL repair capacities, and lower apoptosis rates, compared with healthy controls (all p < 0.001). Interestingly, PBMCs from patients who are responders are characterized by reduced GSH/GSSG ratios, augmented apurinic/apyrimidinic sites, decreased NER and ICL repair capacities, and higher apoptosis rates compared with patients who are non-responders (all p < 0.01). Conclusions: Together, DDR-associated parameters and redox status measured in PBMCs from patients with lung cancer at baseline are associated with the therapeutic benefit of platinum-based chemotherapy.

Accumulation of evidence highlighted the crosstalk between DNA damage repair and the immune system. Herein, we tested the hypothesis that in head and neck squamous cell carcinoma (HNSCC), the DNA repair capacity of patients’ PBMCs correlates with therapeutic response to immune checkpoint blockade. Following in vitro UVC irradiation, oxidative stress, apurinic/apyrimidinic (AP) lesions, endogenous/baseline DNA damage, and DNA damage repair efficiency were evaluated in three HNSCC (UM-SCC-11A, Cal-33, BB49) and two normal cell lines (RPMI-1788, 1BR-3h-T), as well as in peripheral blood mononuclear cells (PBMCs) from 15 healthy controls (HC) and 49 recurrent/metastatic HNSCC patients at baseline (8 responders, 41 non-responders to subsequent nivolumab therapy). HNSCC cell lines showed lower DNA repair efficiency, increased oxidative stress, and higher AP sites than normal ones (all p < 0.001). Moreover, patients’ PBMCs exhibited increased endogenous/baseline DNA damage, decreased DNA repair capacity, augmented oxidative stress, and higher AP sites than PBMCs from HC (all p < 0.001). Importantly, PBMCs from responders to nivolumab therapy showed lower endogenous/baseline DNA damage, higher DNA repair capacities, decreased oxidative stress, and reduced AP sites than non-responders (all p < 0.05). Together, we demonstrated that oxidative stress status and DNA repair efficiency in PBMCs from HNSCC patients are correlated with the response to immune checkpoint blockade.

Accumulation of evidence highlights the crosstalk between the DNA damage repair and the immune system. Herein, we tested the hypothesis that in Head and Neck Squamous Cell Carcinoma (HNSCC), DNA repair capacity of patients’ PBMCs correlates with therapeutic response to immune checkpoint blockade. Following in vitro UVC irradiation, oxidative stress, apurinic/apyrimidinic (AP) lesions, endogenous/baseline DNA damage and DNA damage repair efficiency were evaluated in three HNSCC (UM-SCC-11A, Cal-33, BB49) and two normal cell lines (RPMI-1788, 1BR-3h-T), as well as in peripheral blood mononuclear cells (PBMCs) from 15 healthy controls (HC) and 49 recurrent/metastatic HNSCC patients at baseline (8 responders, 41 non-responders to subsequent nivolumab therapy). HNSCC cell lines showed lower DNA repair efficiency, increased oxidative stress and higher AP-sites than normal ones (all P < 0.001). Moreover, patients’ PBMCs exhibited increased endogenous/baseline DNA damage, decreased DNA repair capacity, augmented oxidative stress and higher AP-sites than PBMCs from HC (all P < 0.001). Importantly, PBMCs from responders to nivolumab therapy showed lower endogenous/baseline DNA damage, higher DNA repair capacities, decreased oxidative stress and reduced AP-sites than non-responders (all P < 0.05). Together, we demonstrate that oxidative stress status and DNA repair efficiency evaluated in PBMCs from HNSCC patients correlate with response to immune checkpoint blockade.