Up-regulation of DNA-dependent protein kinase correlates with radiation resistance in oral squamous cell carcinoma

LncRNA LINC01664 promotes cancer resistance through facilitating homologous recombination-mediated DNA repair

The intracellular responses to DNA double-strand breaks (DSB) repair are crucial for genomic stability and play an essential role in cancer resistance. In addition to canonical DSB repair proteins, long non-coding RNAs (lncRNAs) have been found to be involved in this sophisticated network. In the present study, we performed a loss-of-function screen for a customized siRNA Premix Library to identify lncRNAs that participate in homologous recombination (HR) process. Among the candidates, we identified LINC01664 as a novel lncRNA required for HR repair. Furthermore, LINC01664 knockdown significantly increased the sensitivity of cancer cells to DNA damage agents such as ionizing radiation and genotoxic drugs. Mechanistically, LINC01664 interacted with Sirt1 promoter and then activated Sirt1 transcription, which contributed to HR-mediated DNA damage repair. In summary, our findings revealed a new mechanism of LINC01664 in DNA damage repair, providing evidence for a potential therapeutic strategy for eliminating the treatment bottlenecks caused by cancer resistance to chemotherapy and radiotherapy.

Prognostic and Potential Therapeutic Roles of PRKDC Expression in Lung Cancer

PRKDC is a key factor involved in the ligation step of the non-homologous end joining pathway. Its dysfunction has proven to be a biomarker for radiosensitivity of cancer cells. However, the prognostic value of PRKDC and its underlying mechanisms have not been clarified yet. In this study, we found that PRKDC overexpressed in lung adenocarcinoma (LUAD) and is significantly related to unfavorable survival, while downregulation of PRKDC is link to inflamed tumor immune signature. Our further in vitro results also showed a potent antitumor efficacy of PRKDC inhibitors alone or combined with cisplatin in human lung cancer cells. This study demonstrated that PRKDC is a potential prognostic biomarker, immunotherapy target, and promising combination candidate for chemotherapy for lung cancer, and highlighted the potential of PRKDC-targeted inhibitors for the treatment of lung cancer.

Inhibition of key DNA double strand break repair protein kinases enhances radiosensitivity of head and neck cancer cells to X-ray and proton irradiation

Ionising radiation (IR) is widely used in cancer treatment, including for head and neck squamous cell carcinoma (HNSCC), where it induces significant DNA damage leading ultimately to tumour cell death. Among these lesions, DNA double strand breaks (DSBs) are the most threatening lesion to cell survival. The two main repair mechanisms that detect and repair DSBs are non-homologous end joining (NHEJ) and homologous recombination (HR). Among these pathways, the protein kinases ataxia telangiectasia mutated (ATM), ataxia telangiectasia and Rad3-related (ATR) and the DNA dependent protein kinase catalytic subunit (DNA-Pkcs) play key roles in the sensing of the DSB and subsequent coordination of the downstream repair events. Consequently, targeting these kinases with potent and specific inhibitors is considered an approach to enhance the radiosensitivity of tumour cells. Here, we have investigated the impact of inhibition of ATM, ATR and DNA-Pkcs on the survival and growth of six radioresistant HPV-negative HNSCC cell lines in combination with either X-ray irradiation or proton beam therapy, and confirmed the mechanistic pathway leading to cell radiosensitisation. Using inhibitors targeting ATM (AZD1390), ATR (AZD6738) and DNA-Pkcs (AZD7648), we observed that this led to significantly decreased clonogenic survival of HNSCC cell lines following both X-ray and proton irradiation. Radiosensitisation of HNSCC cells grown as 3D spheroids was also observed, particularly following ATM and DNA-Pkcs inhibition. We confirmed that the inhibitors in combination with X-rays and protons led to DSB persistence, and increased micronuclei formation. Cumulatively, our data suggest that targeting DSB repair, particularly via ATM and DNA-Pkcs inhibition, can exacerbate the impact of ionising radiation in sensitising HNSCC cell models.

Shaping DNA damage responses: Therapeutic potential of targeting telomeric proteins and DNA repair factors in cancer

Shelterin proteins regulate genomic stability by preventing inappropriate DNA damage responses (DDRs) at telomeres. Unprotected telomeres lead to persistent DDR causing cell cycle inhibition, growth arrest, and apoptosis. Cancer cells rely on DDR to protect themselves from DNA lesions and exogenous DNA-damaging agents such as chemotherapy and radiotherapy. Therefore, targeting DDR machinery is a promising strategy to increase the sensitivity of cancer cells to existing cancer therapies. However, the success of these DDR inhibitors depends on other mutations, and over time, patients develop resistance to these therapies. This suggests the need for alternative approaches. One promising strategy is co-inhibiting shelterin proteins with DDR molecules, which would offset cellular fitness in DNA repair in a mutation-independent manner. This review highlights the associations and dependencies of the shelterin complex with the DDR proteins and discusses potential co-inhibition strategies that might improve the therapeutic potential of current inhibitors.

Breast cancer cells are sensitized by piperine to radiotherapy through estrogen receptor-α mediated modulation of a key NHEJ repair protein- DNA-PK

BACKGROUND

Non-homologous end joining, an important DNA-double-stranded break repair pathway, plays a prominent role in conferring resistance to radiotherapeutic agents, resulting in cancer progression and relapse.

PURPOSE

The molecular players involved in the radio-sensitizing effects of piperine and many other phytocompounds remain evasive to a great extent. The study is designed to assess if piperine, a plant alkaloid can alter the radioresistance by modulating the expression of non-homologous end-joining machinery.

METHODS AND MATERIALS

Estrogen receptor-positive/negative, breast cancer cells were cultured to understand the synergetic effects of piperine with radiotherapy. Cisplatin and Bazedoxifene were used as positive controls. Cells were exposed to γ- radiation using Low Dose gamma Irradiator-2000. The piperine effect on Estrogen receptor modulation, DNA-Damage, DNA-Damage-Response, and apoptosis was done by western blotting, immunofluorescence, yeast-based-estrogen-receptor-LacZ-reporter assay, and nuclear translocation analysis. Micronuclei assay was done for DNA damage and genotoxicity, and DSBs were quantified by γH2AX-foci-staining using confocal microscopy. Flow cytometry analysis was done to determine the cell cycle, mitochondrial membrane depolarization, and Reactive oxygen species generation. Pharmacophore analysis and protein-ligand interaction studies were done using Schrodinger software. Synergy was computed by compusyn-statistical analysis. Standard errors/deviation/significance were computed with GraphPad prism.

RESULTS

Using piperine, we propose a new strategy for overcoming acquired radioresistance through estrogen receptor-mediated modulation of the NHEJ pathway. This is the first comprehensive study elucidating the mechanism of radio sensitizing potential of piperine. Piperine enhanced the radiation-induced cell death and enhanced the expression and activation of Estrogen receptor β, while Estrogen receptor α expression and activation were reduced. In addition, piperine shares common pharmacophore features with most of the known estrogen agonists and antagonists. It altered the estrogen receptor α/β ratio and the expression of estrogen-responsive proteins of DDR and NHEJ pathway. Enhanced expression of DDR proteins, ATM, p53, and P-p53 with low DNA-PK repair complex (comprising of DNA-PKcs/Ku70/Ku80), resulted in the accumulation of radiation-induced DNA double-stranded breaks (as evidenced by MNi and γH2AX-foci) culminating in cell cycle arrest and mitochondrial-pathway of apoptosis.

CONCLUSION

In conclusion, our study for the first time reported that piperine sensitizes breast cancer cells to radiation by accumulating DNA breaks, through altering the expression of DNA-PK Complex, and DDR proteins, via selective estrogen receptor modulation, offering a novel strategy for combating radioresistance.

Targeting the DNA Damage Response for Cancer Therapy

Over the course of long-term evolution, cells have developed intricate defense mechanisms in response to DNA damage; these mechanisms play a pivotal role in maintaining genomic stability. Defects in the DNA damage response pathways can give rise to various diseases, including cancer. The DNA damage response (DDR) system is instrumental in safeguarding genomic stability. The accumulation of DNA damage and the weakening of DDR function both promote the initiation and progression of tumors. Simultaneously, they offer opportunities and targets for cancer therapeutics. This article primarily elucidates the DNA damage repair pathways and the progress made in targeting key proteins within these pathways for cancer treatment. Among them, poly (ADP-ribose) polymerase 1 (PARP1) plays a crucial role in DDR, and inhibitors targeting PARP1 have garnered extensive attention in anticancer research. By delving into the realms of DNA damage and repair, we aspire to explore more precise and effective strategies for cancer therapy and to seek novel avenues for intervention.

Radiation-sensitive genetic prognostic model identifies individuals at risk for radiation resistance in head and neck squamous cell carcinoma

BACKGROUND

The advantages of radiotherapy for head and neck squamous cell carcinoma (HNSCC) depend on the radiation sensitivity of the patient. Here, we established and verified radiological factor-related gene signature and built a prognostic risk model to predict whether radiotherapy would be beneficial.

METHODS

Data from The Cancer Genome Atlas, Gene Expression Omnibus, and RadAtlas databases were subjected to LASSO regression, univariate COX regression, and multivariate COX regression analyses to integrate genomic and clinical information from patients with HNSCC. HNSCC radiation-related prognostic genes were identified, and patients classified into high- and low-risk groups, based on risk scores. Variations in radiation sensitivity according to immunological microenvironment, functional pathways, and immunotherapy response were investigated. Finally, the expression of HNSCC radiation-related genes was verified by qRT-PCR.

RESULTS

We built a clinical risk prediction model comprising a 15-gene signature and used it to divide patients into two groups based on their susceptibility to radiation: radiation-sensitive and radiation-resistant. Overall survival was significantly greater in the radiation-sensitive than the radiation-resistant group. Further, our model was an independent predictor of radiotherapy response, outperforming other clinical parameters, and could be combined with tumor mutational burden, to identify the target population with good predictive value for prognosis at 1, 2, and 3 years. Additionally, the radiation-resistant group was more vulnerable to low levels of immune infiltration, which are significantly associated with DNA damage repair, hypoxia, and cell cycle regulation. Tumor Immune Dysfunction and Exclusion scores also suggested that the resistant group would respond less favorably to immunotherapy.

CONCLUSIONS

Our prognostic model based on a radiation-related gene signature has potential for application as a tool for risk stratification of radiation therapy for patients with HNSCC, helping to identify candidates for radiation therapy and overcome radiation resistance.

Analysis of lncRNA-miRNA-mRNA Expression in the Troxerutin-Mediated Prevention of Radiation-Induced Lung Injury in Mice

Background

Radiation-induced lung injury (RILI) is a critical factor that leads to pulmonary fibrosis and other diseases. LncRNAs and miRNAs contribute to normal tissue damage caused by ionizing radiation. Troxerutin offers protection against radiation; however, its underlying mechanism remains largely undetermined.

Methods

We established a model of RILI in mice pretreated with troxerutin. The lung tissue was extracted for RNA sequencing, and an RNA library was constructed. Next, we estimated the target miRNAs of differentially expressed (DE) lncRNAs, and the target mRNAs of DE miRNAs. Then, functional annotations of these target mRNAs were performed using GO and KEGG.

Results

Compared to the control group, 150 lncRNA, 43 miRNA, and 184 mRNA were significantly up-regulated, whereas, 189 lncRNA, 15 miRNA, and 146 mRNA were markedly down-regulated following troxerutin pretreatment. Our results revealed that the Wnt, cAMP, and tumor-related signaling pathways played an essential role in RILI prevention via troxerutin using lncRNA-miRNA-mRNA network.

Conclusion

These evidences revealed that the abnormal regulation of RNA potentially leads to pulmonary fibrosis. Therefore, targeting lncRNA and miRNA, along with a closer examination of competitive endogenous RNA (ceRNA) networks are of great significance to the identification of troxerutin targets that can protect against RILI.

Identification and characterization of mercaptopyrimidine-based small molecules as inhibitors of nonhomologous DNA end joining

Mercaptopyrimidine derivatives are heterocyclic compounds with potent biological activities including antiproliferative, antibacterial, and anti-inflammatory properties. The present study describes the synthesis and characterization of several mercaptopyrimidine derivatives through condensation of 5,6-diamino-2-mercaptopyrimidin-4-ol with various heterocyclic and aromatic aldehydes. Previous studies have shown that SCR7, synthesized from 5,6-diamino-2-mercaptopyrimidin-4-ol, induced cytotoxicity by targeting cancer cells by primarily inhibiting DNA Ligase IV involved in nonhomologous end joining, one of the major DNA double-strand break repair pathways. Inhibition of DNA repair pathways is considered as an important strategy for cancer therapy. Due to limitations of SCR7 in terms of IC₅₀ in cancer cells, here we have designed, synthesized, and characterized potent derivatives of SCR7 using 5,6-diamino-2-mercaptopyrimidin-4-ol as the starting material. Several synthesized imine compounds exhibited significant improvement in inhibition of end joining and cytotoxicity up to 27-fold lower concentrations than SCR7. Among these, two compounds, SCR116 and SCR132, showed increased cancer cell death in a Ligase IV-dependent manner. Treatment with the compounds also led to reduction in V(D)J recombination efficiency, cell cycle arrest at G2/M phase, accumulation of double-strand breaks inside cells, and improved anti-cancer potential when combined with γ-radiation and radiomimetic drugs. Thus, we describe novel inhibitors of NHEJ with higher efficacy and potential, which can be developed as cancer therapeutics.

DNA Damage Response Mechanisms in Head and Neck Cancer: Significant Implications for Therapy and Survival

Head and neck cancer (HNC) is a term collectively used to describe a heterogeneous group of tumors that arise in the oral cavity, larynx, nasopharynx, oropharynx, and hypopharynx, and represents the sixth most common type of malignancy worldwide. Despite advances in multimodality treatment, the disease has a recurrence rate of around 50%, and the prognosis of metastatic patients remains poor. HNCs are characterized by a high degree of genomic instability, which involves a vicious circle of accumulating DNA damage, defective DNA damage repair (DDR), and replication stress. Nonetheless, the damage that is induced on tumor cells by chemo and radiotherapy relies on defective DDR processes for a successful response to treatment, and may play an important role in the development of novel and more effective therapies. This review summarizes the current knowledge on the genes and proteins that appear to be deregulated in DDR pathways, their implication in HNC pathogenesis, and the rationale behind targeting these genes and pathways for the development of new therapies. We give particular emphasis on the therapeutic targets that have shown promising results at the pre-clinical stage and on those that have so far been associated with a therapeutic advantage in the clinical setting.

Potential value of PRKDC as a therapeutic target and prognostic biomarker in pan-cancer

BACKGROUND

While protein kinase, DNA-activated, catalytic subunit (PRKDC) plays an important role in double-strand break repair to retain genomic stability, there is still no pan-cancer analysis based on large clinical information on the relationship between PRKDC and different tumors. For the first time, this research used numerous databases to perform a pan-cancer review for PRKDC to explore the possible mechanism of PRKDC in the etiology and outcomes in various tumors.

METHODS

PRKDC's expression profile and prognostic significance in pan-cancer were investigated based on various databases and online platforms, including TIMER2, GEPIA2, cBioPortal, CPTAC, and SangerBox. We applied the TIMER to identified the interlink of PRKDC and the immune infiltration in assorted tumors, and the SangerBox online platform was adopted to find out the relevance between PRKDC and immune checkpoint genes, tumor mutation burden, and microsatellite instability in tumors. GeneMANIA tool was employed to create a protein-protein interaction analysis, gene set enrichment analysis was conducted to performed gene enrichment analysis.

RESULTS

Overall, tumor tissue presented a higher degree of PRKDC expression than adjacent normal tissue. Meanwhile, patients with high PRKDC expression have a worse prognosis. PRKDC mutations were present in almost all The Cancer Genome Atlas tumors and might lead to a better survival prognosis. The PRKDC expression level was shown a positive correlation with tumor-infiltrating immune cells. PRKDC high expression cohorts were enriched in "cell cycle" "oocyte meiosis" and "RNA-degradation" signaling pathways.

CONCLUSIONS

This study revealed the potential value of PRKDC in tumor immunology and as a therapeutic target and prognostic biomarker in pan-cancer.

Chrysin impairs genomic stability by suppressing DNA double-strand break repair in breast cancer cells

Chrysin, a natural compound isolated from various plants, such as the blue passion flower (Passiflora caerulea L.), exhibits multiple pharmacological activities, such as antitumor, anti-inflammatory and antioxidant activities. Accumulating evidence shows that chrysin inhibits cancer cell growth by inducing apoptosis and regulating cell cycle arrest. However, whether chrysin is involved in regulating genomic stability and its underlying mechanisms in breast cancer cells have not been determined. Here, we demonstrated that chrysin impairs genomic stability in MCF-7 and BT474 cells, inhibits cell survival and enhances the sensitivity of MCF-7 cells to chemotherapeutic drugs. Further experiments revealed that chrysin impairs DNA double-strand break (DSB) repair, resulting in accumulation of DNA damage. Mechanistic studies showed that chrysin inhibits the recruitment of the key NHEJ factor 53BP1 and delays the recruitment of the HR factor RAD51. Thus, we elucidated novel regulatory mechanisms of chrysin in DSB repair and proposed that a combination of chrysin and chemotherapy has curative potential in breast cancers.

DNA-PK inhibition by M3814 enhances chemosensitivity in non-small cell lung cancer

A significant proportion of non-small cell lung cancer (NSCLC) patients experience accumulating chemotherapy-related adverse events, motivating the design of chemosensitizating strategies. The main cytotoxic damage induced by chemotherapeutic agents is DNA double-strand breaks (DSB). It is thus conceivable that DNA-dependent protein kinase (DNA-PK) inhibitors which attenuate DNA repair would enhance the anti-tumor effect of chemotherapy. The present study aims to systematically evaluate the efficacy and safety of a novel DNA-PK inhibitor M3814 in synergy with chemotherapies on NSCLC. We identified increased expression of DNA-PK in human NSCLC tissues which was associated with poor prognosis. M3814 potentiated the anti-tumor effect of paclitaxel and etoposide in A549, H460 and H1703 NSCLC cell lines. In the four combinations based on two NSCLC xenograft models and two chemotherapy, we also observed tumor regression at tolerated doses in vivo. Moreover, we identified a P53-dependent accelerated senescence response by M3814 following treatment with paclitaxel/etoposide. The present study provides a theoretical basis for the use of M3814 in combination with paclitaxel and etoposide in clinical practice, with hope to aid the optimization of NSCLC treatment.

Targeting DNA repair pathway in cancer: Mechanisms and clinical application

Over the last decades, the growing understanding on DNA damage response (DDR) pathways has broadened the therapeutic landscape in oncology. It is becoming increasingly clear that the genomic instability of cells resulted from deficient DNA damage response contributes to the occurrence of cancer. One the other hand, these defects could also be exploited as a therapeutic opportunity, which is preferentially more deleterious in tumor cells than in normal cells. An expanding repertoire of DDR-targeting agents has rapidly expanded to inhibitors of multiple members involved in DDR pathways, including PARP, ATM, ATR, CHK1, WEE1, and DNA-PK. In this review, we sought to summarize the complex network of DNA repair machinery in cancer cells and discuss the underlying mechanism for the application of DDR inhibitors in cancer. With the past preclinical evidence and ongoing clinical trials, we also provide an overview of the history and current landscape of DDR inhibitors in cancer treatment, with special focus on the combination of DDR-targeted therapies with other cancer treatment strategies.

Target-Based Radiosensitization Strategies: Concepts and Companion Animal Model Outlook

External beam radiotherapy is indicated in approximately 50-60% of human cancer patients. The prescribed dose of ionizing radiation that can be delivered to a tumor is determined by the sensitivity of the normal surrounding tissues. Despite dose intensification provided by highly conformal radiotherapy, durable locoregional tumor control remains a clinical barrier for recalcitrant tumor histologies, and contributes to cancer morbidity and mortality. Development of target-based radiosensitization strategies that selectively sensitizes tumor tissue to ionizing radiation is expected to improve radiotherapy efficacy. While exploration of radiosensitization strategies has vastly expanded with technological advances permitting the precise and conformal delivery of radiation, maximal clinical benefit derived from radiotherapy will require complementary discoveries that exploit molecularly-based vulnerabilities of tumor cells, as well as the assessment of investigational radiotherapy strategies in animal models that faithfully recapitulate radiobiologic responses of human cancers. To address these requirements, the purpose of this review is to underscore current and emerging concepts of molecularly targeted radiosensitizing strategies and highlight the utility of companion animal models for improving the predictive value of radiotherapy investigations.

Role of PRKDC in cancer initiation, progression, and treatment

The PRKDC gene encodes the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) protein. DNA-PKcs plays an important role in nonhomologous end joining (NHEJ) of DNA double-strand breaks (DSBs) and is also closely related to the establishment of central immune tolerance and the maintenance of chromosome stability. The occurrence and development of different types of tumors and the results of their treatment are also influenced by DNA-PKcs, and it may also predict the results of radiotherapy, chemotherapy, and therapy with immune checkpoint inhibitors (ICIs). Here, we discuss and review the structure and mechanism of action of PRKDC and DNA-PKcs and their relationship with cancer.

DNA-PKc inhibition overcomes taxane resistance by promoting taxane-induced DNA damage in prostate cancer cells

BACKGROUND

Overcoming taxane resistance remains a major clinical challenge in metastatic castrate-resistant prostate cancer (mCRPC). Loss of DNA repair proteins is associated with resistance to anti-microtubule agents. We propose that alterations in DNA damage response (DDR) pathway contribute to taxane resistance, and identification of these alterations may provide a potential therapeutic target to resensitize docetaxel-refractory mCRPC to taxane-based therapy.

METHODS

Alterations in DDR gene expression in our prostate cancer cell line model of docetaxel-resistance (DU145-DxR) derived from DU-145 cells were determined by DDR pathway-specific polymerase chain reaction array and immunoblotting. The PRKDC gene encoding DNA-PKc (DNA-dependent protein kinase catalytic unit), was noted to be overexpressed and evaluated for its role in docetaxel resistance. Cell viability and clonogenic survival of docetaxel-treated DU145-DxR cells were assessed after pharmacologic inhibition of DNA-PKc with three different inhibitors-NU7441, LTURM34, and M3814. Response to second-line cytotoxic agents, cabazitaxel and etoposide upon DNA-PKc inhibition was also tested. The impact of DNA-PKc upregulation on DNA damage repair was evaluated by comet assay and analysis of double-strand breaks marker, γH2AX and Rad51. Lastly, DNA-PKc inhibitor's effect on MDR1 activity was assessed by rhodamine 123 efflux assay.

RESULTS

DDR pathway-specific gene profiling revealed significant upregulation of PRKDC and CDK7, and downregulation of MSH3 in DU145-DxR cells. Compared to parental DU145, DU145-DxR cells sustained significantly less DNA damage when exposed to etoposide and docetaxel. Pharmacologic inhibition of DNA-PKc, a component of NHEJ repair machinery, with all three inhibitors, significantly resensitized DU145-DxR cells to docetaxel. Furthermore, DNA-PKc inhibition also resensitized DU145-DxR to cabazitaxel and etoposide, which demonstrated cross-resistance. Inhibition of DNA-PKc led to increased DNA damage in etoposide- and docetaxel-treated DU145-DxR cells. Finally, DNA-PKc inhibition did not affect MDR1 activity, indicating that DNA-PKc inhibitors resensitized taxane-resistant cells via an MDR1-independent mechanism.

CONCLUSION

This study supports a role of DDR genes, particularly, DNA-PKc in promoting resistance to taxanes in mCRPC. Targeting prostatic DNA-PKc may provide a novel strategy to restore taxane sensitivity in taxane-refractory mCRPC.

Understanding the Radiobiology of Vestibular Schwannomas to Overcome Radiation Resistance

Vestibular schwannomas (VS) are benign tumors arising from cranial nerve VIII that account for 8-10% of all intracranial tumors and are the most common tumors of the cerebellopontine angle. These tumors are typically managed with observation, radiation therapy, or microsurgical resection. Of the VS that are irradiated, there is a subset of tumors that are radioresistant and continue to grow; the mechanisms behind this phenomenon are not fully understood. In this review, the authors summarize how radiation causes cellular and DNA injury that can activate (1) checkpoints in the cell cycle to initiate cell cycle arrest and DNA repair and (2) key events that lead to cell death. In addition, we discuss the current knowledge of VS radiobiology and how it may contribute to clinical outcomes. A better understanding of VS radiobiology can help optimize existing treatment protocols and lead to new therapies to overcome radioresistance.

Proteomics-derived basal biomarker DNA-PKcs is associated with intrinsic subtype and long-term clinical outcomes in breast cancer

Precise biomarkers are needed to guide better diagnostics and therapeutics for basal-like breast cancer, for which DNA-dependent protein kinase catalytic subunit (DNA-PKcs) has been recently reported by the Clinical Proteomic Tumor Analysis Consortium as the most specific biomarker. We evaluated DNA-PKcs expression in clinically-annotated breast cancer tissue microarrays and correlated results with immune biomarkers (training set: n = 300; validation set: n = 2401). Following a pre-specified study design per REMARK criteria, we found that high expression of DNA-PKcs was significantly associated with stromal and CD8 + tumor infiltrating lymphocytes. Within the basal-like subtype, tumors with low DNA-PKcs and high tumor-infiltrating lymphocytes displayed the most favourable survival. DNA-PKcs expression by immunohistochemistry identified estrogen receptor-positive cases with a basal-like gene expression subtype. Non-silent mutations in PRKDC were significantly associated with poor outcomes. Integrating DNA-PKcs expression with validated immune biomarkers could guide patient selection for DNA-PKcs targeting strategies, DNA-damaging agents, and their combination with an immune-checkpoint blockade.

SCR7, an inhibitor of NHEJ can sensitize tumor cells to ionization radiation

Nonhomologous end joining (NHEJ), one of the major DNA double-strand break repair pathways, plays a significant role in cancer cell proliferation and resistance to radio and chemotherapeutic agents. Previously, we had described a small molecule inhibitor, SCR7, which inhibited NHEJ in a DNA Ligase IV dependent manner. Here, we report that SCR7 potentiates the effect of γ-radiation (IR) that induces DNA breaks as intermediates to eradicate cancer cells. Dose fractionation studies revealed that coadministration of SCR7 and IR (0.5 Gy) in mice Dalton's lymphoma (DLA) model led to a significant reduction in mice tumor cell proliferation, which was equivalent to that observed for 2 Gy dose when both solid and liquid tumor models were used. Besides, co-treatment with SCR7 and 1 Gy of IR further improved the efficacy. Notably, there was no significant change in blood parameters, kidney and liver functions upon combinatorial treatment of SCR7 and IR. Further, the co-treatment of SCR7 and IR resulted in a significant increase in unrepaired DSBs within cancer cells compared to either of the agent alone. Anatomy, histology, and other studies in tumor models confirmed the cumulative effects of both agents in activating apoptotic pathways to induce cytotoxicity by modulating DNA damage response and repair pathways. Thus, we report that SCR7 has the potential to reduce the side effects of radiotherapy by lowering its effective dose ex vivo and in mice tumor models, with implications in cancer therapy.

Genomic Correlates of DNA Damage in Breast Cancer Subtypes

Simple Summary

Breast cancer (BC) is the most common invasive tumor in women and the second leading cause of cancer-related death. Therefore, identification of druggable targets to improve current therapies and overcome resistance is a major goal. In this work, we performed an in silico analysis of transcriptomic datasets in breast cancer, and focused on those involved in DNA damage, as were clearly upregulated using gene set enrichment analyses (GSEA), particular the following pathways: ATM/ATR, BARD1 and Fanconi Anemia. BHLHE40, RFWD2, BRIP1, PRKDC, NBN, RNF8, FANCD2, RAD1, BLM, DCLRE1C, UBE2T, CSTF1, MCM7, RFC4, YWHAB, YWHAZ, CDC6, CCNE1, and FANCI genes were amplified/overexpressed in BC, and correlated with detrimental prognosis. Finally, we selected the best transcriptomic signature of genes within this function that associated with clinical outcome to identify functional genomic correlates of outcome.

Abstract

Among the described druggable vulnerabilities, acting on the DNA repair mechanism has gained momentum, with the approval of PARP inhibitors in several indications, including breast cancer. However, beyond the mere presence of BRCA1/BRCA2 mutations, the identification of additional biomarkers that would help to select tumors with an extreme dependence on DNA repair machinery would help to stratify therapeutic decisions. Gene set enrichment analyses (GSEA) using public datasets evaluating expression values between normal breast tissue and breast cancer identified a set of upregulated genes. Genes included in different pathways, such as ATM/ATR, BARD1, and Fanconi Anemia, which are involved in the DNA damage response, were selected and confirmed using molecular alterations data contained at cBioportal. Nineteen genes from these gene sets were identified to be amplified and upregulated in breast cancer but only five of them NBN, PRKDC, RFWD2, UBE2T, and YWHAZ meet criteria in all breast cancer molecular subtypes. Correlation of the selected genes with prognosis (relapse free survival, RFS, and overall survival, OS) was performed using the KM Plotter Online Tool. In last place, we selected the best signature of genes within this process whose upregulation can be indicative of a more aggressive phenotype and linked with worse outcome. In summary, we identify genomic correlates within DNA damage pathway associated with prognosis in breast cancer.

Nonhomologous end joining: new accessory factors fine tune the machinery

Nonhomologous DNA end joining (NHEJ) is one of the major DNA double-strand break (DSB) repair pathways in eukaryotes. The well-known critical proteins involved in NHEJ include Ku70/80, DNA-PKcs, Artemis, DNA pol λ/μ, DNA ligase IV-XRCC4, and XLF. Recent studies have added a number of new proteins to the NHEJ repertoire namely paralog of XRCC4 and XLF (PAXX), modulator of retroviral infection (MRI)/ cell cycle regulator of NHEJ (CYREN), transactivation response DNA-binding protein (TARDBP) of 43 kDa (TDP-43), intermediate filament family orphan (IFFO1), ERCC excision repair 6 like 2 (ERCC6L2), and RNase H2. PAXX acts as a stabilizing factor for the main NHEJ components. MRI/CYREN seems to play a dual role stimulating NHEJ in the G1 phase of the cell cycle, while inhibiting the pathway in the S and G2 phases. TDP-43 can recruit the ligase IV-XRCC4 complex to the DSB sites and stimulate ligation in neuronal cells. RNase H2 excises out the ribonucleotides inserted during repair by DNA polymerase μ/TdT. This review provides a brief glimpse into how these new partners were discovered and their contribution to the mechanism and regulation of NHEJ.

Small molecule DNA-PK inhibitors as potential cancer therapy: a patent review (2010-present)

Introduction: DNA-dependent protein kinase (DNA-PK) plays a crucial role in the repair of DSBs via non-homologous end joining (NHEJ). Several DNA-PK inhibitors are being investigated for potential anticancer treatment in clinical trials.Area covered: This review aims to give an overview of patents published since 2010 by analyzing the patent space and structure features of scaffolds used in those patents. It also discusses the recent clinical developments and provides perspectives on future challenges and directions in this field.Expert opinion: As a key component of the DNA damage response (DDR) pathway, DNA-PK appears to be a viable drug target for anticancer therapy. The clinical investigation of a DNA-PK inhibitor employs both a monotherapy and a combination strategy. In the combination strategy, a DNA-PK inhibitor is typically combined with a DSB inducer, radiation, a chemotherapy agent, or a PARP inhibitor, etc. Patent analyses suggest that diverse structures comprising different scaffolds from mono-heteroaryl to bicyclic heteroaryl to tricyclic heteroaryl are capable to achieve good DNA-PK inhibitory activity and good DNA-PK selectivity over other closely related enzymes. Several DNA-PK inhibitors are currently being evaluated in clinics, with the hope to get approval in the near future.

SCR7, a potent cancer therapeutic agent and a biochemical inhibitor of nonhomologous DNA end-joining

Background

DNA double‐strand breaks (DSBs) are harmful to the cell as it could lead to genomic instability and cell death when left unrepaired. Homologous recombination and nonhomologous end‐joining (NHEJ) are two major DSB repair pathways, responsible for ensuring genome integrity in mammals. There have been multiple efforts using small molecule inhibitors to target these DNA repair pathways in cancers. SCR7 is a very well‐studied anticancer molecule that blocks NHEJ by targeting one of the critical enzymes, Ligase IV.

Recent findings

In this review, we have highlighted the anticancer effects of SCR7 as a single agent and in combination with other chemotherapeutic agents and radiation. SCR7 blocked NHEJ effectively both in vitro and ex vivo. SCR7 has been used for biochemical studies like chromosomal territory resetting and in understanding the role of repair proteins in cell cycle phases. Various forms of SCR7 and its derivatives are discussed. SCR7 is also used as a potent biochemical inhibitor of NHEJ, which has found its application in improving genome editing using a CRISPR‐Cas system.

Conclusion

SCR7 is a potent NHEJ inhibitor with unique properties and wide applications as an anticancer agent. Most importantly, SCR7 has become a handy aid for improving genome editing across different model systems.

Inhibition of SETMAR-H3K36me2-NHEJ repair axis in residual disease cells prevents glioblastoma recurrence

BACKGROUND

Residual disease of glioblastoma (GBM) causes recurrence. However, targeting residual cells has failed, due to their inaccessibility and our lack of understanding of their survival mechanisms to radiation therapy. Here we deciphered a residual cell-specific survival mechanism essential for GBM relapse.

METHODS

Therapy resistant residual (RR) cells were captured from primary patient samples and cell line models mimicking clinical scenario of radiation resistance. Molecular signaling of resistance in RR cells was identified using RNA sequencing, genetic and pharmacological perturbations, overexpression systems, and molecular and biochemical assays. Findings were validated in patient samples and an orthotopic mouse model.

RESULTS

RR cells form more aggressive tumors than the parental cells in an orthotopic mouse model. Upon radiation-induced damage, RR cells preferentially activated a nonhomologous end joining (NHEJ) repair pathway, upregulating Ku80 and Artemis while downregulating meiotic recombination 11 (Mre11) at protein but not RNA levels. Mechanistically, RR cells upregulate the Su(var)3-9/enhancer-of-zeste/trithorax (SET) domain and mariner transposase fusion gene (SETMAR), mediating high levels of H3K36me2 and global euchromatization. High H3K36me2 leads to efficiently recruiting NHEJ proteins. Conditional knockdown of SETMAR in RR cells induced irreversible senescence partly mediated by reduced H3K36me2. RR cells expressing mutant H3K36A could not retain Ku80 at double-strand breaks, thus compromising NHEJ repair, leading to apoptosis and abrogation of tumorigenicity in vitro and in vivo. Pharmacological inhibition of the NHEJ pathway phenocopied H3K36 mutation effect, confirming dependency of RR cells on the NHEJ pathway for their survival.

CONCLUSIONS

We demonstrate that the SETMAR-NHEJ regulatory axis is essential for the survival of clinically relevant radiation RR cells, abrogation of which prevents recurrence in GBM.

Synthetic Lethality through the Lens of Medicinal Chemistry

Personalized medicine and therapies represent the goal of modern medicine, as drug discovery strives to move away from one-cure-for-all and makes use of the various targets and biomarkers within differing disease areas. This approach, especially in oncology, is often undermined when the cells make use of alternative survival pathways. As such, acquired resistance is unfortunately common. In order to combat this phenomenon, synthetic lethality is being investigated, making use of existing genetic fragilities within the cancer cell. This Perspective highlights exciting targets within synthetic lethality, (PARP, ATR, ATM, DNA-PKcs, WEE1, CDK12, RAD51, RAD52, and PD-1) and discusses the medicinal chemistry programs being used to interrogate them, the challenges these programs face, and what the future holds for this promising field.

End Processing Factor APLF Promotes NHEJ Efficiency and Contributes to TMZ- and Ionizing Radiation-Resistance in Glioblastoma Cells

Purpose

Glioblastoma (GBM) is the most commonly diagnosed primary brain tumor in adults. Despite a variety of advances in the understanding of GBM cancer biology during recent decades, very few of them were applied into treatment, and the survival rate of GBM patients has not been improved majorly due to the low chemosensitivity to temozolomide (TMZ) or low radiosensitivity. Therefore, it is urgent to elucidate mechanisms of TMZ- and IR-resistance and develop novel therapeutic strategies to improve GBM treatment.

Methods

TMZ- and IR-resistant cell lines were acquired by continuous exposing parental GBM cells to TMZ or IR for 3 months. Cell viability was determined by using Sulforhodamine B (SRB) assay. Protein and mRNA expression were examined by Western blotting assay and quantitative polymerase chain reaction (qPCR) assay, respectively. Homologous recombination (HR) and nonhomologous end joining (NHEJ) efficiency were measured by HR and NHEJ reporter assay. Cell apoptosis was determined by Caspase3/7 activity. Autophagy was analyzed using CYTO-ID^® Autophagy detection kit. Tumor growth was examined by U87 xenograft mice model.

Results

DNA repair efficiency of non-homologous end joining (NHEJ) pathway is significantly increased in TMZ- and IR-resistant GBM cells. Importantly, APLF, which is one of the DNA end processing factors in NHEJ, is upregulated in TMZ- and IR-resistant GBM cells and patients. APLF deficiency significantly decreases NHEJ efficiency and improves cell sensitivity to TMZ and IR both in vitro and in vivo.

Conclusion

Our study provides evidence for APLF serving as a promising, novel target in GBM chemo- and radio-therapy.

Inhibiting Importin 4-mediated nuclear import of CEBPD enhances chemosensitivity by repression of PRKDC-driven DNA damage repair in cervical cancer

Cervical cancer (CC) remains highest in the mortality of female reproductive system cancers, while cisplatin (CDDP) resistance is the one of main reasons for the lethality. Preceding evidence has supported that karyopherins are associated with chemoresistance. In this study, we simultaneously compared CDDP-incomplete responders with CDDP-complete responders of CC patients and CDDP‐insensitive CC cell lines with CDDP‐sensitive group. We finally identified that DNA-PKcs (PRKDC) was related to CDDP sensitivity after overlapping in CC sample tissues and CC cell lines. Further functional assay revealed that targeting PRKDC by shRNA and NU7026 (specific PRKDC inhibitor) could enhance CDDP sensitivity in vitro and in vivo, which was mediated by impairing DNA damage repair pathway in CC. Mechanistically, we found that PRKDC was transcriptionally upregulated by CCAAT/enhancer-binding protein delta (CEBPD), while intriguingly, CDDP treatment strengthened the transcriptional activity of CEBPD to PRKDC. We further disclosed that Importin 4 (IPO4) augmented the nuclear translocation of CEBPD through nuclear localization signals (NLS) to activate PRKDC-mediated DNA damage repair in response to CDDP. Moreover, we demonstrated that IPO4 and CEBPD knockdown improved CDDP-induced cytotoxicity in vitro and in vivo. Together, we shed the novel insight into the role of IPO4 in chemosensitivity and provide a clinical translational potential to enhance CC chemosensitivity since the IPO4-CEBPD-PRKDC axis is actionable via NU7026 (PRKDC inhibitor) or targeting IPO4 in combination with CDDP.

Sublethal Radiation Affects Antigen Processing and Presentation Genes to Enhance Immunogenicity of Cancer Cells

While immunotherapy in cancer is designed to stimulate effector T cell response, tumor-associated antigens have to be presented on malignant cells at a sufficient level for recognition of cancer by T cells. Recent studies suggest that radiotherapy enhances the anti-cancer immune response and also improves the efficacy of immunotherapy. To understand the molecular basis of such observations, we examined the effect of ionizing X-rays on tumor antigens and their presentation in a set of nine human cell lines representing cancers of the esophagus, lung, and head and neck. A single dose of 7.5 or 15 Gy radiation enhanced the New York esophageal squamous cell carcinoma 1 (NY-ESO-1) tumor-antigen-mediated recognition of cancer cells by NY-ESO-1-specific CD8⁺ T cells. Irradiation led to significant enlargement of live cells after four days, and microscopy and flow cytometry revealed multinucleation and polyploidy in the cells because of dysregulated mitosis, which was also revealed in RNA-sequencing-based transcriptome profiles of cells. Transcriptome analyses also showed that while radiation had no universal effect on genes encoding tumor antigens, it upregulated the expression of numerous genes involved in antigen processing and presentation pathways in all cell lines. This effect may explain the immunostimulatory role of cancer radiotherapy.

Targeting DNA-PK in cancer

DNA-dependent protein kinase (DNA-PK) is involved in many cellular pathways. It has a key role in the cellular response to DNA damage, in the repair of DNA double-strand break (DNA-DSBs) and as a consequence an important role in maintaining genomic integrity. In addition, DNA-PK has been shown to modulate transcription, to be involved in the development of the immune system and to protect telomeres. These pleotropic involvements and the fact that its expression is de-regulated in cancer have made DNA-PK an intriguing therapeutic target in cancer therapy, especially when combined with agents causing DNA-DSBs such as topoisomerase II inhibitors and ionizing radiation. Different small molecule inhibitors of DNA-PK have been recently synthesized and some are now being tested in clinical trials. This review discusses what is known about DNA-PK, its role in tumor biology, DNA repair and cancer therapy and critically discusses its inhibition as a potential therapeutic approach.

Differential Expression of DNA Repair Genes in Prognostically-Favorable versus Unfavorable Uveal Melanoma

Expression of DNA repair genes was studied in uveal melanoma (UM) in order to identify genes that may play a role in metastases formation. We searched for genes that are differentially expressed between tumors with a favorable and unfavorable prognosis. Gene-expression profiling was performed on 64 primary UM from the Leiden University Medical Center (LUMC), Leiden, The Netherlands. The expression of 121 genes encoding proteins involved in DNA repair pathways was analyzed: a total of 44 genes differed between disomy 3 and monosomy 3 tumors. Results were validated in a cohort from Genoa and Paris and the The Cancer Genome Atlas (TCGA) cohort. Expression of the PRKDC, WDR48, XPC, and BAP1 genes was significantly associated with clinical outcome after validation. PRKDC was highly expressed in metastasizing UM (p < 0.001), whereas WDR48, XPC, and BAP1 were lowly expressed (p < 0.001, p = 0.006, p = 0.003, respectively). Low expression of WDR48 and XPC was related to a large tumor diameter (p = 0.01 and p = 0.004, respectively), and a mixed/epithelioid cell type (p = 0.007 and p = 0.03, respectively). We conclude that the expression of WDR48, XPC, and BAP1 is significantly lower in UM with an unfavorable prognosis, while these tumors have a significantly higher expression of PRKDC. Pharmacological inhibition of DNA-PKcs resulted in decreased survival of UM cells. PRKDC may be involved in proliferation, invasion and metastasis of UM cells. Unraveling the role of DNA repair genes may enhance our understanding of UM biology and result in the identification of new therapeutic targets.

DNA-dependent protein kinase: effect on DSB repair, G2/M checkpoint and mode of cell death in NSCLC cell lines

Purpose: To evaluate the effect of NU7026, a specific inhibitor of DNA-PKcs, on DNA-double strand break (DSB) repair in a cell cycle specific manner, on the G2/M checkpoint, mitotic progression, apoptosis and clonogenic survival in non-small-cell lung carcinoma (NSCLC) cell lines with different p53 status. Material and methods: Cell cycle progression, and hyperploidy were evaluated using flow cytometry. Polynucleation as a measure for mitotic catastrophe (MC) was evaluated by fluorescence microscopy. DSB induction and repair were measured by constant-gel electrophoresis and γH2AX assay. The efficiency of DSB rejoining during the cell cycle was assessed by distinguishing G1 and G2/M phase cells on the basis of the DNA content in flow cytometry. The overall effect on cell death was determined by apoptosis and the surviving fraction after irradiation with 2 Gy (SF2) assessed by clonogenic survival. Results: DSB signaling upon treatment with NU7026, as measured by γH2AX signaling, was differently affected in G1 and G2/M cells. The background level of γH2AX was significantly higher in G2/M compared to G1 cells, whereas NU7026 had no effect on the background level. The steepness of the initial dose effect relation at 1 h after irradiation was less pronounced in G2/M compared to G1 cells. NU7026 had no significant effect on the initial dose-effect relation of γH2AX signaling. In comparison, NU7026 significantly slowed down the repair kinetics and increased the residual γH2AX signal at 24 h after irradiation in the G1 phase of all cell lines, but was less effective in G2/M cells. NU7026 significantly increased the fraction of G2/M phase cells upon irradiation. Moreover, NU7026 significantly increased mitotic catastrophe and hyperploidy, as a measure for mitotic failure after low irradiation doses of about 4 Gy, but decreased both at higher doses of 20 Gy. In addition, radiation induced apoptosis increased in A549, H520 and H460 but decreased in H661 upon NU7026 treatment, with a significant reduction of SF2 in all NSCLC cell lines. Conclusion: Overall, NU7026 significantly influences the cell cycle progression through the G2- and M-phases and thereby determines the fate of cells. The impairment of DNA-PK upon treatment with NU7026 affects the efficiency of the NHEJ system in a cell cycle dependent manner, which may be of relevance for a clinical application of DNA-PK inhibitors in tumor therapy.

DNA-PK as an Emerging Therapeutic Target in Cancer

The DNA-dependent protein kinase (DNA-PK) plays an instrumental role in the overall survival and proliferation of cells. As a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, DNA-PK is best known as a mediator of the cellular response to DNA damage. In this context, DNA-PK has emerged as an intriguing therapeutic target in the treatment of a variety of cancers, especially when used in conjunction with genotoxic chemotherapy or ionizing radiation. Beyond the DNA damage response, DNA-PK activity is necessary for multiple cellular functions, including the regulation of transcription, progression of the cell cycle, and in the maintenance of telomeres. Here, we review what is currently known about DNA-PK regarding its structure and established roles in DNA repair. We also discuss its lesser-known functions, the pharmacotherapies inhibiting its function in DNA repair, and its potential as a therapeutic target in a broader context.

Carcinogenic role of K-Ras-ERK1/2 signaling in bladder cancer via inhibition of H1.2 phosphorylation at T146

It has been reported that Ras-ERK signaling regulated tumor suppressive genes via epigenetic mechanisms. Herein, we set out to investigate the correlation between K-Ras-ERK1/2 signaling and H1.2 phosphorylation, to provide a better understanding of K-Ras-ERK signaling in cancer. A plasmid for expression of mutated K-Ras was transfected into human bladder carcinoma HT1197 cells. Western blot was carried out for testing the expression changes of ERK1/2 and H1.2. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, soft-agar colony formation assay, and transwell assay were used to test the effects of H1.2 phosphorylation at T146 (H1.2 ^T146ph ) on HT1197 cells growth and migration. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and chromatin immunoprecipitation (ChIP) were performed to test whether H1.2 ^T146ph regulated K-Ras-ERK1/2 downstream genes. Furthermore, how K-Ras-ERK1/2 regulated H1.2 ^T146ph expression was studied. We found that the ERK1/2 was activated when K-Ras was mutated, and H1.2 ^T146ph expression was significantly downregulated by K-Ras mutation. H1.2 ^T146E for mimicking H1.2 ^T146ph significantly attenuated K-Ras mutation induced increases in HT1197 cells viability, colony formation, and relative migration. Besides, H1.2 ^T146ph regulated the transcription of K-Ras-ERK1/2 downstream genes, including NT5E, GDF15, CARD16, CYR61, IGFBP3, and WNT16B. Furthermore, K-Ras-ERK1/2 signaling inhibited H1.2 phosphorylation at T146 through degradation of DNA-PK, and the degraded DNA-PK by K-Ras-ERK1/2 possibly via modulation of MDM2. In conclusion, the activation of K-Ras-ERK1/2 signaling will repress the phosphorylation of H1.2 at T146, and thereby, promoted the growth and migration of bladder cancer cells. K-Ras-ERK1/2 signaling repressed H1.2 phosphorylation possibly by MDM2-mediated degradation of DNA-PK.

Expression of the DNA-dependent protein kinase catalytic subunit is associated with the radiosensitivity of human thyroid cancer cell lines

The prognosis and treatment of thyroid cancer depends on the type and stage of the disease. Radiosensitivity differs among cancer cells owing to their varying capacity for repair after irradiation. Radioactive iodine can be used to destroy thyroid cancer cells. However, patient prognosis and improvement after irradiation varies. Therefore, predictive measures are important for avoiding unnecessary exposure to radiation. We describe a new method for predicting the effects of radiation in individual cases of thyroid cancer based on the DNA-dependent protein kinase (DNA-PK) activity level in cancer cells. The radiation sensitivity, DNA-PK activity, and cellular levels of DNA-PK complex subunits in five human thyroid cancer cell lines were analyzed in vitro. A positive correlation was observed between the D10 value (radiation dose that led to 10% survival) of cells and DNA-PK activity. This correlation was not observed after treatment with NU7441, a DNA-PK-specific inhibitor. A significant correlation was also observed between DNA-PK activity and expression levels of the DNA-PK catalytic subunit (DNA-PKcs). Cells expressing low DNA-PKcs levels were radiation-sensitive, and cells expressing high DNA-PKcs levels were radiation-resistant. Our results indicate that radiosensitivity depends on the expression level of DNA-PKcs in thyroid cancer cell lines. Thus, the DNA-PKcs expression level is a potential predictive marker of the success of radiation therapy for thyroid tumors.

GDC-0084 inhibits cutaneous squamous cell carcinoma cell growth

GDC-0084 is a novel and potent small-molecule PI3K-mTOR dual inhibitor. The present study examined its potential activity in cutaneous squamous cell carcinoma (cSCC) cells. Our results show that GDC-0084 treatment at nanomole concentrations potently inhibited survival and proliferation of established (A431, SCC-13 and SCL-1 lines) and primary human cSCC cells. GDC-0084 induced apoptosis activation and cell cycle arrest in the cSCC cells. It was more efficient than other known PI3K-Akt-mTOR inhibitors in killing cSCC cells, but was non-cytotoxic to the normal human skin fibroblasts/keratinocytes. In A431 cells and primary cSCC cells, GDC-0084 blocked phosphorylation of key PI3K-Akt-mTOR components, including p85, Akt, S6K1 and S6. GDC-0084 also inhibited DNA-PKcs activation in cSCC cells. Significantly, restoring DNA-PKcs activation by a constitutively active-DNA-PKcs (S2056D) partially inhibited GDC-0084-induced cell death and apoptosis in A431 cells. In vivo, GDC-0084 daily gavage potently inhibited A431 xenograft tumor growth in mice. In GDC-0084-treated tumor tissues PI3K-Akt-mTOR and DNA-PKcs activation were significantly inhibited. In summary, GDC-0084 inhibits human cSCC cell growth in vitro and in vivo through blocking PI3K-Akt-mTOR and DNA-PKcs signalings.

Combined ATR and DNA-PK Inhibition Radiosensitizes Tumor Cells Independently of Their p53 Status

Head and neck squamous cell carcinoma (HNSCC) is a significant cause of cancer deaths. Cisplatin-based chemoradiotherapy is a standard of care for locally advanced disease. ATR and DNA-PK inhibition (DNA-PKi) are actively being investigated in clinical trials with preclinical data supporting clinical translation as radiosensitizers. Here, we hypothesized that targeting both ATR and DNA-PK with small molecule inhibitors would increase radiosensitization of HNSCC cell lines. Radiosensitization was assessed by Bliss independence analysis of colony survival data. Strong cell cycle perturbing effects were observed with ATR inhibition reversing the G2/M arrest observed for radiation-DNA-PKi. Increased apoptosis in combination groups was measured by Sub-G1 DNA populations. DNA-PKi increased radiation-induced RAD51 and gamma-H2Ax foci, with the addition of ATR inhibition reducing levels of both. A sharp increase in nuclear fragmentation after aberrant mitotic transit appears to be the main driver of decreased survival due to irradiation and dual ATR/DNA-PKi. Dual inhibition of DNA-PK and ATR represents a novel approach in combination with radiation, with efficacy appearing to be independent of p53 status. Due to toxicity concerns, careful assessment is necessary in any future translation of single or dual radiosensitization approaches. Ongoing clinical trials into the ATR inhibitor AZD6738 plus radiation, and the phenotypically similar combination of AZD6738 and the PARP inhibitor olaparib, are likely to be key in ascertaining the toxicity profile of such combinations.

Tissue and serum expression of TGM-3 may be prognostic marker in patients of oral squamous cell carcinoma undergoing chemo-radiotherapy

Radioresistance is one of the main determinants of treatment outcome in oral squamous cell carcinoma (OSCC), but its prediction is difficult. Several authors aimed to establish radioresistant OSCC cell lines to identify genes with altered expression in response to radioresistance. The development of OSCC is a multistep carcinogenic process that includes activation of several oncogenes and inactivation of tumour suppressor genes. TGM-3 is a tumour suppressor gene and contributes to carcinogenesis process. The aim of this study was to estimate serum and tissue expression of TGM-3 and its correlation with clinico-pathological factors and overall survival in patients of OSCC undergoing chemo-radiotherapy. Tissue expression was observed in formalin fixed tissue biopsies of 96 cases of OSCC and 32 healthy controls were subjected to immunohistochemistry (IHC) by using antibody against TGM-3 and serum level was estimated by ELISA method. mRNA expression was determined by using Real-Time PCR. Patients were followed for 2 year for chemo radiotherapy response. In OSCC, 76.70% cases and in controls 90.62% were positive for TGM-3 IHC expression. TGM-3 expression was cytoplasmic and nuclear staining expressed in keratinized layer, stratum granulosum and stratum spinosum in controls and tumour cells. Mean serum TGM-3 in pre chemo-radiotherapy OSCC cases were 1304.83±573.55, post chemo-radiotherapy samples were 1530.64±669.33 and controls were 1869.16±1377.36, but difference was significant in pre chemo-radiotherapy samples as compared to controls (p<0.018). This finding was also confirmed by real- time PCR analysis in which down regulation (-7.92 fold change) of TGM-3 in OSCC as compared to controls. TGM-3 expression was significantly associated with response to chemo-radiotherapy treatment (p<0.007) and overall survival (p<0.015). Patents having higher level of TGM-3 expression have good response to chemo-radiotherapy and also have better overall survival. TGM-3 may serve as a candidate biomarker for responsiveness to chemo-radiotherapy treatment in OSCC patients.

Expression of DNA-dependent protein kinase catalytic subunit in laryngeal squamous cell carcinoma and its importance

The aim of the present study was to explore the expression and distribution of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) in tumor tissues and adjacent normal mucosa tissues of patients with laryngeal squamous cell carcinoma (LSCC), and further analyze the association between the expression and the clinicopathological parameters of patients with LSCC. Clinical data of tumor tissues and corresponding adjacent normal mucosa tissues of pathologically diagnosed LSCC in 96 cases were collected in the present study. Of these specimens, the mRNA and protein expression levels of DNA-PKcs in LSCC tissues and the adjacent normal mucosa tissues were analyzed via reverse transcription-quantitative polymerase chain reaction and western blot analysis. Immunohistochemistry was used to detect expression and distribution of DNA-PKcs protein in LSCC tissues and corresponding adjacent normal mucosa tissues. The association between DNA-PKcs expression and the specific clinicopathologic features was evaluated by the χ² test. Kaplan-Meier and Cox proportional hazards regression models were used to analyze the data. It was revealed that the expression of DNA-PKcs mRNA and protein was significantly higher in LSCC tissues than the adjacent normal mucosa tissues (P<0.05). DNA-PKcs was expressed predominantly in the nucleus. DNA-PKcs expression showed significant correlation with the differentiation degree of LSCC (P<0.05), and changes of DNA-PKcs expression gradually increased with the decrease of the differentiation degree. However, DNA-PKcs expression was not significantly associated with sex, age, lymph node metastasis or TMN stage (P>0.05). Patients with LSCC exhibited higher DNA-PKcs expression had markedly shorter survival than those with lower DNA-PKcs expression. In conclusion, the present results suggested that the expression levels of DNA-PKcs were significantly increased in LSCC tumor tissues than in adjacent normal mucosa. DNA-PKcs expression was correlated with differentiation of LSCC, and may become a novel prognostic marker for patients with LSCC.

Clinical values of Ku80 upregulation in superficial esophageal squamous cell carcinoma

Ku80 is an important DNA repair protein. Here, this study sought to investigate clinical impacts of Ku80 expression for patients with superficial esophageal squamous cell carcinoma (ESCC). Immunohistochemical analysis of Ku80 expression was carried out in normal esophageal mucosa, squamous epithelial dysplasia, carcinoma in situ, and superficial ESCC. Its relationships with clinicopathological features and survival of superficial ESCC patients were further clarified. Lentivirus-mediated RNA interference was used to silence Ku80 gene in ECA109 and KYSE150 cells. Both quantitative real-time PCR and Western blot were employed to evaluate Ku80 levels. CCK-8 assay, clone formation assay, flow cytometry, and tumorigenesis experiment were performed to evaluate the malignant phenotype of ECA109 and KYSE150 cells. Increased Ku80 expression was observed in dysplastic esophageal mucosa and carcinoma in situ compared to normal esophageal mucosa (P < 0.001, P < 0.001). Ku80 expression was further increased in superficial ESCC in comparison with dysplastic esophageal mucosa and carcinoma in situ (P < 0.001, P = 0.034). In superficial ESCC, Ku80 overexpression was related to tumor differentiation (P = 0.017), T status (P = 0.011), nodal involvement (P = 0.005), TNM stage (P = 0.004), and postoperative recurrence (P = 0.008). Cox proportional hazards regression showed tumor differentiation, T status, nodal involvement, TNM stage, and Ku80 expression were both independent predictors of patients' overall survival and disease-free survival. Ku80 shRNA effectively reduced Ku80 expression, which significantly inhibited proliferation, clone formation, and induced apoptosis in ECA109 and KYSE150 cells. The tumor growth of xenografts was significantly reduced by Ku80 silencing in ECA109 and KYSE150 cells. Ku80 overexpression associates with unfavorable prognosis of superficial ESCC patients, and silencing of Ku80 could inhibit the malignant behavior of ESCC cells. We provide evidence that Ku80 has unrecognized roles in carcinogenesis and development of ESCC.

Gαi3 nuclear translocation causes irradiation resistance in human glioma cells

We have previously shown that Gαi3 is elevated in human glioma, mediating Akt activation and cancer cell proliferation. Here, we imply that Gαi3 could also be important for irradiation resistance. In A172 human glioma cells, Gαi3 knockdown (by targeted shRNAs) or dominant-negative mutation significantly potentiated irradiation-induced cell apoptosis. Reversely, forced over-expression of wild-type or constitutively-active Gαi3 inhibited irradiation-induced A172 cell apoptosis. Irradiation in A172 cells induced Gαi3 translocation to cell nuclei and association with local protein DNA-dependent protein kinase (DNA-PK) catalytic subunit. This association was important for DNA damage repair. Gαi3 knockdown, depletion (using Gαi3 knockout MEFs) or dominant-negative mutation potentiated irradiation-induced DNA damages. On the other hand, expression of the constitutively-active Gαi3 in A172 cells inhibited DNA damage by irradiation. Together, these results indicate a novel function of Gαi3 in irradiation-resistance in human glioma cells.

Studies of lncRNAs in DNA double strand break repair: what is new?

The ‘junk DNA’ that has haunted human genetics for a long time now turns out to hold enormous hidden treasures. As species had their genomes and transcriptomes sequenced, there are an overwhelming number of lncRNA transcripts being reported, however, less than 100 of them have been functionally characterized. DNA damage is recognized and quickly repaired by the cell, with increased expression of numerous genes involved in DNA repair. Most of the time the studies have focused only on proteins involved in these signaling pathways. However, recent studies have implied that lncRNAs can be broadly induced by DNA damage and regulate DNA repair processes by various mechanisms. In this paper, we focus on recent advances in the identification and functional characterization of novel lncRNAs participating in DNA double strand break repair.

DNA-dependent protein kinase modulates the anti-cancer properties of silver nanoparticles in human cancer cells

Silver nanoparticles (Ag-np) were reported to be toxic to eukaryotic cells. These potentially detrimental effects of Ag-np can be advantageous in experimental therapeutics. They are currently being employed to enhance the therapeutic efficacy of cancer drugs. In this study, we demonstrate that Ag-np treatment trigger the activation of DNA-PKcs and JNK pathway at selected doses, presumably as a physiologic response to DNA damage and repair in normal and malignant cells. Ag-np altered the telomere dynamics by disrupting the shelterin complex located at the telomeres and telomere lengths. The genotoxic effect of Ag-np was not restricted to telomeres but the entire genome as Ag-np induced γ-H2AX foci formation, an indicator of global DNA damage. Inhibition of DNA-PKcs activity sensitised the cancer cells towards the cytotoxicity of Ag-np and substantiated the damaging effect of Ag-np at telomeres in human cancer cells. Abrogation of JNK mediated DNA repair and extensive damage of telomeres led to greater cell death following Ag-np treatment in DNA-PKcs inhibited cancer cells. Collectively, this study suggests that improved anti-proliferative and cytotoxic effects of Ag-np treatment in cancer cells can be achieved by the inhibition of DNA-PKcs.

Inhibition of DNA-PK enhances chemosensitivity of B-cell precursor acute lymphoblastic leukemia cells to doxorubicin

DNA damage repair pathways greatly affect the response to genotoxic drugs in cancer cells, so inhibition of such pathways could be a potentially useful strategy to enhance chemosensitivity. DNA-dependent protein kinase (DNA-PK) plays a crucial role in the repair of DNA double-strand breaks (DSBs) that are probably one of the most detrimental types of DNA damage. It has been shown that DNA-PK is highly expressed in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells. Less well appreciated was the effect of DNA-PK inhibition on sensitivity of BCP-ALL cells to DNA-damaging agents. Here, we show that the DNA-PK inhibitor NU7441 increased doxorubicin-induced apoptosis in BCP-ALL cell lines (NALM-6, SUP-B15), correlating with a reduction in DSB repair measured by γ-H2AX foci. NU7441 affected the cell cycle distribution and the cell cycle regulatory molecules in combination with doxorubicin treatment. Doxorubicin-induced DNA-PK phosphorylation was decreased in the presence of NU7441. Apoptosis induction by the combined treatment was associated with marked reduction of Bcl-2 and survivin and a significant increase of Bax mRNA expression levels. In conclusion, our data indicate that inhibition of DNA-PK might be an effective approach to enhance the tumor-cell-killing effects of DNA-damaging agents such as doxorubicin in BCP-ALL and may deliver novel, targeted therapy into the clinic.

The Role of the Core Non-Homologous End Joining Factors in Carcinogenesis and Cancer

DNA double-strand breaks (DSBs) are deleterious DNA lesions that if left unrepaired or are misrepaired, potentially result in chromosomal aberrations, known drivers of carcinogenesis. Pathways that direct the repair of DSBs are traditionally believed to be guardians of the genome as they protect cells from genomic instability. The prominent DSB repair pathway in human cells is the non-homologous end joining (NHEJ) pathway, which mediates template-independent re-ligation of the broken DNA molecule and is active in all phases of the cell cycle. Its role as a guardian of the genome is supported by the fact that defects in NHEJ lead to increased sensitivity to agents that induce DSBs and an increased frequency of chromosomal aberrations. Conversely, evidence from tumors and tumor cell lines has emerged that NHEJ also promotes chromosomal aberrations and genomic instability, particularly in cells that have a defect in one of the other DSB repair pathways. Collectively, the data present a conundrum: how can a single pathway both suppress and promote carcinogenesis? In this review, we will examine NHEJ's role as both a guardian and a disruptor of the genome and explain how underlying genetic context not only dictates whether NHEJ promotes or suppresses carcinogenesis, but also how it alters the response of tumors to conventional therapeutics.

Repurposing DNA repair factors to eradicate tumor cells upon radiotherapy

Cancer is the leading cause of death worldwide. Almost 50% of all cancer patients undergo radiation therapy (RT) during treatment, with varying success. The main goal of RT is to kill tumor cells by damaging their DNA irreversibly while sparing the surrounding normal tissue. The outcome of RT is often determined by how tumors recognize and repair their damaged DNA. A growing body of evidence suggests that tumors often show abnormal expression of DNA double-strand break (DSB) repair genes that are absent from normal cells. Defects in a specific DNA repair pathway make tumor cells overly dependent on alternative or backup pathways to repair their damaged DNA. These tumor cell-specific abnormalities in the DNA damage response (DDR) machinery can potentially be used as biomarkers for treatment outcomes or as targets for sensitization to ionizing radiation (IR). An improved understanding of genetic or epigenetic alterations in the DNA repair pathways specific to cancer cells has paved the way for new treatments that combine pharmacological exploitation of tumor-specific molecular vulnerabilities with IR. Inhibiting DNA repair pathways has the potential to greatly enhance the therapeutic ratio of RT. In this review, we will discuss DNA repair pathways in active cells and how these pathways are deregulated in tumors. We will also describe the impact of targeting cancer-specific aberrations in the DDR as a treatment strategy to improve the efficacy of RT. Finally, we will address the current roadblocks and future prospects of these approaches.