Zhengqiang Bao

DNA-PKcs and PARP1 Bind to Unresected Stalled DNA Replication Forks Where They Recruit XRCC1 to Mediate Repair

A series of critical pathways are responsible for the detection, signaling, and restart of replication forks that encounter blocks during S-phase progression. Small base lesions may obstruct replication fork progression and processing, but the link between repair of small lesions and replication forks is unclear. In this study, we investigated a hypothesized role for DNA-PK, an important enzyme in DNA repair, in cellular responses to DNA replication stress. The enzyme catalytic subunit DNA-PKcs was phosphorylated on S2056 at sites of stalled replication forks in response to short hydroxyurea treatment. Using DNA fiber experiments, we found that catalytically active DNA-PK was required for efficient replication restart of stalled forks. Furthermore, enzymatically active DNA-PK was also required for PARP-dependent recruitment of XRCC1 to stalled replication forks. This activity was enhanced by preventing Mre11-dependent DNA end resection, suggesting that XRCC1 must be recruited early to an unresected stalled fork. We also found that XRCC1 was required for effective restart of a subset of stalled replication forks. Overall, our work suggested that DNA-PK and PARP-dependent recruitment of XRCC1 is necessary to effectively protect, repair, and restart stalled replication forks, providing new insight into how genomic stability is preserved.

Effectiveness and safety of poly (ADP-ribose) polymerase inhibitors in cancer therapy: A systematic review and meta-analysis

Poly (ADP-ribose) polymerase (PARP) inhibitors are a class of small-molecule drugs suppressing PARP enzymes activity, inducing the death of cells deficient in homologous recombination repair (HRR). HRR deficiency is common in tumor cells with BRCA gene mutation. Since their first clinical trial in 2003, PARP inhibitors have shown benefit in the treatment of HRR-deficient tumors. Recently, several randomized clinical trials (RCTs) have been conducted to investigate the potential benefit of administration of PARP inhibitors in cancer patients. However, the results remain controversial. To evaluate the efficiency and safety of PARP inhibitors in patients with cancer, we performed a comprehensive meta-analysis of RCTs. According to our study, PARP inhibitors could clearly improve progression-free survival (PFS), especially in patients with BRCA mutation. However, our study showed no significant difference in overall survival (OS) between the PARP inhibitors and controls, even in the BRCA mutation group. Little toxicity was reported in the rate of treatment correlated adverse events (AEs) in PARP inhibitor group compared with controls. In conclusion, PARP inhibitors do well in improving PFS with little toxicity, especially in patients with BRCA deficiency.

Effectiveness and safety of PD-1/PD-L1 inhibitors in the treatment of solid tumors: a systematic review and meta-analysis

BACKGROUND PD-1/PD-L1 inhibitors have been implicated as potentially effective anti-cancer therapies. Some clinical randomized controlled trials (RCTs) have been completed for a variety of PD-1/PD-L1 inhibitors to treat various malignancies, and more RCTs are still under way. We carried out this systematic meta-analysis to evaluate the efficacy and safety of PD-1/PD-L1 inhibitors in the treatment of solid tumors. METHODS We searched PubMed, EMBASE, clinical trial registers, conference reports, and related reviews. Eligible RCTs that compared PD-1/PD-L1 inhibitors with other chemotherapy agents or placebo in solid tumor patients were included. For each RCT, progression-free survival (PFS), overall survival (OS), objective response rate (ORR), disease control rate (DCR), stable disease rate (SDR), progressive disease rate (PDR), and adverse events (AEs) were pooled for meta-analysis. FINDINGS Based on an analysis of 10 eligible RCTs, PD-1/PD-L1 inhibitors were found to significantly improve PFS (Hazard ratio (HR), 0.65; 95% confidence interval (CI) 0.53 to 0.79, P<0.001), OS (HR, 0.69; 95%CI 0.62 to 0.76, P<0.001), and ORR (Risk Ratio (RR) 2.92; 95% confidence interval (CI) 2.06 to 4.15, P<0.00001) in all populations, including melanoma and NSCLC subgroups. However, they failed to increase the DCR of cancer patients (RR 1.15; 95%CI 0.91 to 1.45, P=0.25). Furthermore, less AEs were observed in the PD-1/PD-L1 inhibitor groups than the control groups. INTERPRETATION PD-1 inhibitors are more effective for improving the PFS, OS, and ORR of cancer patients with little toxicity, despite having little effect on increasing of the DCR.Background PD-1/PD-L1 inhibitors have been implicated as potentially effective anti-cancer therapies. Some clinical randomized controlled trials (RCTs) have been completed for a variety of PD-1/PD-L1 inhibitors to treat various malignancies, and more RCTs are still under way. We carried out this systematic meta-analysis to evaluate the efficacy and safety of PD-1/PD-L1 inhibitors in the treatment of solid tumors. Methods We searched PubMed, EMBASE, clinical trial registers, conference reports, and related reviews. Eligible RCTs that compared PD-1/PD-L1 inhibitors with other chemotherapy agents or placebo in solid tumor patients were included. For each RCT, progression-free survival (PFS), overall survival (OS), objective response rate (ORR), disease control rate (DCR), stable disease rate (SDR), progressive disease rate (PDR), and adverse events (AEs) were pooled for meta-analysis. Findings Based on an analysis of 10 eligible RCTs, PD-1/PD-L1 inhibitors were found to significantly improve PFS (Hazard ratio (HR), 0.65; 95% confidence interval (CI) 0.53 to 0.79, P<0.001), OS (HR, 0.69; 95%CI 0.62 to 0.76, P<0.001), and ORR (Risk Ratio (RR) 292; 95% confidence interval (CI) 2.06 to 4.15, P<0.00001) in all populations, including melanoma and NSCLC subgroups. However, they failed to increase the DCR of cancer patients (RR 1.15; 95%CI 0.91 to 1.45, P=0.25). Furthermore, less AEs were observed in the PD-1/PD-L1 inhibitor groups than the control groups. Interpretation PD-1 inhibitors are more effective for improving the PFS, OS, and ORR of cancer patients with little toxicity, despite having little effect on increasing of the DCR.

Bcl-2 inhibitors reduce steroid-insensitive airway inflammation

Background Asthmatic inflammation is dominated by accumulation of either eosinophils, neutrophils, or both in the airways. Disposal of these inflammatory cells is the key to disease control. Eosinophilic airway inflammation is responsive to corticosteroid treatment, whereas neutrophilic inflammation is resistant and increases the burden of global health care. Corticosteroid‐resistant neutrophilic asthma remains mechanistically poorly understood and requires novel effective therapeutic strategies. Objective We sought to explore the underlying mechanisms of airway inflammation persistence, as well as corticosteroid resistance, and to investigate a new strategy of effective treatment against corticosteroid‐insensitive neutrophilic asthma. Methods Mouse models of either eosinophil‐dominated or neutrophil‐dominated airway inflammation were used in this study to test corticosteroid sensitivity in vivo and in vitro. We also used vav–Bcl‐2 transgenic mice to confirm the importance of granulocytes apoptosis in the clearance of airway inflammation. Finally, the Bcl‐2 inhibitors ABT‐737 or ABT‐199 were tested for their therapeutic effects against eosinophilic or neutrophilic airway inflammation and airway hyperresponsiveness. Results Overexpression of Bcl‐2 protein was found to be responsible for persistence of granulocytes in bronchoalveolar lavage fluid after allergic challenge. This was important because allergen‐induced airway inflammation aggravated and persisted in vav–Bcl‐2 transgenic mice, in which nucleated hematopoietic cells were overexpressed with Bcl‐2 and resistant to apoptosis. The Bcl‐2 inhibitors ABT‐737 or ABT‐199 play efficient roles in alleviation of either eosinophilic or corticosteroid‐resistant neutrophilic airway inflammation by inducing apoptosis of immune cells, such as eosinophils, neutrophils, TH2 cells, TH17 cells, and dendritic cells. Moreover, these inhibitors were found to be more efficient than steroids to induce granulocyte apoptosis ex vivo from patients with severe asthma. Conclusion Apoptosis of inflammatory cells is essential for clearance of allergen‐induced airway inflammation. The Bcl‐2 inhibitors ABT‐737 or ABT‐199 might be promising drugs for the treatment of airway inflammation, especially for corticosteroid‐insensitive neutrophilic airway inflammation.

Genomic instability in chronic airway inflammatory diseases.

Chronic airway inflammatory diseases are life-threatening conditions, including bronchial asthma, chronic obstructive pulmonary disease (COPD), and so on. However, as the disease etiology remains largely unclear, current treatments that target chronic airway inflammatory diseases are still not satisfactory. DNA damage response (DDR), regarded as one of the many causes of apoptosis and cell senescence, as well as a factor involved in carcinogenesis, has recently begun to attract attention as a source of chronic inflammation. Considering that COPD and allergic asthma inflammation enhance DNA damage, measures related with DNA repair should be taken so as to reduce the injuries caused by these airway diseases. Small molecule inhibitors specifically against various DNA repair proteins have been developed over the last decade to fight against chronic diseases. Poly(ADP-ribose) polymerase (PARP) inhibitor, for example, has already shown its potential in asthma animal models to block airway inflammation. In this review, we highlight the roles of DDR in chronic airway inflammatory diseases, and try to have a better understanding of these diseases. We also discuss the possibilities of targeting DDR signaling to develop potential novel treatments against these conditions.

Proteomic analysis of sputum reveals novel biomarkers for various presentations of asthma

AbstractBackgroundIt is now recognized that asthma can present in different forms. Typically, asthma present with symptoms of wheeze, breathlessness and cough. Atypical forms of asthma such as cough variant asthma (CVA) or chest tightness variant asthma (CTVA) do not wheeze. We hypothesize that these different forms of asthma may have distinctive cellular and molecular features.Methods30 patients with typical or classical asthma (CA), 27 patients with CVA, 30 patients with CTVA, and 30 healthy control adults were enrolled in this prospective study. We measured serum IgE, lung function, sputum eosinophils, nitric oxide in exhaled breath (FeNO). We performed proteomic analysis of induced-sputum supernatants by mass spectrometry.ResultsThere were no significant differences in atopy and FEV1 among patients with CA, CVA, and CTVA. Serum IgE, sputum eosinophil percentages, FeNO, anxiety and depression scores were significantly increased in the three presentations of asthmatic patients as compared with healthy controls but there was no difference between the asthmatic groups. Comprehensive mass spectrometric analysis revealed more than a thousand proteins in the sputum from patients with CA, CVA, and CTVA, among which 23 secreted proteins were higher in patients than that in controls.ConclusionsPatients with CA, CVA, or CTVA share common clinical characteristics of eosinophilic airway inflammation. And more importantly, their sputum samples were composed with common factors with minor distinctions. These findings support the concept that these three different presentations of asthma have similar pathogenetic mechanism in terms of an enhanced Th2 associated with eosinophilia. In addition, this study identified a pool of novel biomarkers for diagnosis of asthma and to label its subtypes. Trial registrationhttp://www.chictr.org.cn (ChiCTR-OOC-15006221)

Unrepaired DNA damage in macrophages causes elevation of particulate matter- induced airway inflammatory response

The inflammatory cascade can be initiated with the recognition of damaged DNA. Macrophages play an essential role in particulate matter (PM)-induced airway inflammation. In this study, we aim to explore the PM induced DNA damage response of macrophages and its function in airway inflammation. The DNA damage response and inflammatory response were assessed using bone marrow–derived macrophages following PM treatment and mouse model instilled intratracheally with PM. We found that PM induced significant DNA damage both in vitro and in vivo and simultaneously triggered a rapid DNA damage response, represented by nuclear RPA, 53BP1 and γH2AX foci formation. Genetic ablation or chemical inhibition of the DNA damage response sensor amplified the production of cytokines including Cxcl1, Cxcl2 and Ifn-γ after PM stimulation in bone marrow–derived macrophages. Similar to that seen in vitro, mice with myeloid-specific deletion of RAD50 showed higher levels of airway inflammation in response to the PM challenge, suggesting a protective role of DNA damage sensor during inflammation. These data demonstrate that PM exposure induces DNA damage and activation of DNA damage response sensor MRN complex in macrophages. Disruption of MRN complex lead to persistent, unrepaired DNA damage that causes elevated inflammatory response.

Oleandrin induces DNA damage responses in cancer cells by suppressing the expression of Rad51

Oleandrin is a monomeric compound extracted from leaves and seeds of Nerium oleander. It had been reported that oleandrin could effectively inhibit the growth of human cancer cells. However, the specific mechanisms of the oleandrin-induced anti-tumor effects remain largely unclear. Genomic instability is one of the main features of cancer cells, it can be the combined effect of DNA damage and tumour-specific DNA repair defects. DNA damage plays important roles during tumorigenesis. In fact, most of the current chemotherapy agents were designed to kill cancer cells by inducing DNA damage. In this study, we found that oleandrin was effective to induce apoptosis in cancer cells, and cause rapid DNA damage response, represented by nuclear RPA (Replication Protein A, a single strand DNA binding protein) and γH2AX(a marker for DNA double strand breaks) foci formation. Interestingly, expression of RAD51, a key protein involved in homologous recombination (HR), was suppressed while XRCC1 was up-regulated in oleandrin treated cancer cells. These results suggested that XRCC1 may play a predominant role in repairing oleandrin-induced DNA damage. Collectively, oleandrin may be a potential anti-tumor agent by suppressing the expression of Rad51.