The life and death of DNA-PK

TOX High Mobility Group Box Family Member 4 Promotes DNA Double Strand Break Repair via Non-Homologous End Joining

Non-homologous end joining (NHEJ) is a pivotal mechanism in the repair of DNA double-strand breaks (DSBs). Central to NHEJ is the DNA-dependent protein kinase (DNA-PK) complex, comprising the KU heterodimer and the catalytic subunit, DNA-PKcs. In this study, we characterize TOX High Mobility Group Box Family Member 4 (TOX4) as a factor recruited to both laser-induced DNA damage and endonuclease-induced DNA DSBs. Depletion of TOX4 leads to accumulation of DNA damage, which is epistatic to DNA-PKcs. Consistently, TOX4 depletion substantially reduces NHEJ efficiency measured using both intrachromosomal and extrachromosomal repair assays. Our proteomic and biochemical analyses reveal TOX4 association with DNA-PK that is required for DNA-PKcs activation. Furthermore, we show that TOX4 coordinates with Phosphatase 1 Nuclear-Targeting Subunit (PNUTS) in NHEJ. PNUTS, previously shown to protect DNA-PKcs phosphorylation from protein phosphatase 1 (PP1)-mediated dephosphorylation, binds DNA-PK in a TOX4-dependent manner. In line with its role in DNA repair, TOX4 emerges as a promising target for anti-cancer drug development, and its targeting enhances tumor cell sensitivity to DNA damage in head and neck cancer and other malignancies.

Impact of glycolysis enzymes and metabolites in regulating DNA damage repair in tumorigenesis and therapy

Initially, it was believed that glycolysis and DNA damage repair (DDR) were two distinct biological processes that independently regulate tumor progression. The former metabolic reprogramming rapidly generates energy and generous intermediate metabolites, supporting the synthetic metabolism and proliferation of tumor cells. While the DDR plays a pivotal role in preserving genomic stability, thus resisting cellular senescence and cell death under both physiological and radio-chemotherapy conditions. Recently, an increasing number of studies have shown closely correlation between these two biological processes, and then promoting tumor progression. For instance, lactic acid, the product of glycolysis, maintains an acidic tumor microenvironment that not only fosters cell proliferation and invasion but also facilitates DDR by enhancing AKT activity. Here, we provide a comprehensive overview of the enzymes and metabolites involved in glycolysis, along with the primary methods for DDR. Meanwhile, this review explores existing knowledge of glycolysis enzymes and metabolites in regulating DDR. Moreover, considering the significant roles of glycolysis and DDR in tumor development and radio-chemotherapy resistance, the present review discusses effective direct or indirect therapeutic strategies targeted to glycolysis and DDR.

A Novel Dual ATM/DNA-PK Inhibitor, XRD-0394, Potently Radiosensitizes and Potentiates PARP and Topoisomerase I Inhibitors

A majority of patients with cancer receive radiotherapy as part of their treatment regimens whether using external beam therapy or locally-delivered radioisotopes. While often effective, some tumors are inadequately controlled with radiation and radiotherapy has significant short-term and long-term toxicities for cancer survivors. Insights into molecular mechanisms involved in cellular responses to DNA breaks introduced by radiation or other cancer therapies have been gained in recent years and approaches to manipulate these responses to enhance tumor cell killing or reduce normal tissue toxicity are of great interest. Here, we report the identification and initial characterization of XRD-0394, a potent and specific dual inhibitor of two DNA damage response kinases, ATM and DNA-PKcs. This orally bioavailable molecule demonstrates significantly enhanced tumor cell kill in the setting of therapeutic ionizing irradiation in vitro and in vivo. XRD-0394 also potentiates the effectiveness of topoisomerase I inhibitors in vitro. In addition, in cells lacking BRCA1/2 XRD-0394 shows single-agent activity and synergy in combination with PARP inhibitors. A phase Ia clinical trial (NCT05002140) with XRD-0394 in combination with radiotherapy has completed. These results provide a rationale for future clinical trials with XRD-0394 in combination with radiotherapy, PARP inhibitors, and targeted delivery of topoisomerase I inhibitors.

Discovery of Novel Heterotricyclic Compounds as DNA-Dependent Protein Kinase (DNA-PK) Inhibitors with Enhanced Chemosensitivity, Oral Bioavailability, and the Ability to Potentiate Cancer Immunotherapy

In this work, a novel series of heterotricyclic DNA-PK inhibitors were rationally designed, synthesized, and assessed for their biological activity. In the DNA-PK biochemical assay, most compounds displayed potent enzymatic activity, with IC50 values between 0.11 and 71.5 nM. Among them, SK10 exhibited the most potent DNA-PK-inhibitory activity (IC50 = 0.11 nM). Studies of the mechanism of action indicated that SK10 could lower γH2A.X expression levels and demonstrate optimal synergistic antiproliferative activity against Jurkat cells (IC50 = 25 nM) when combined with doxorubicin. Importantly, in CT26 and B16-F10 tumor-bearing mouse models, the combination therapies of SK10 with chemotherapeutic drug doxorubicin, a PD-L1 antibody, and SWS1 (a potent PD-L1 small-molecule inhibitor) demonstrated superior synergistic anticancer and potential immunomodulatory effects. Furthermore, SK10 possessed favorable in vivo pharmacokinetic properties [e.g., oral bioavailability (F) = 31.8%]. Taken together, SK10 represents a novel heterotricyclic DNA-PK inhibitor with antitumor immune effects and favorable pharmacokinetics.

Comparative analysis of basal and etoposide-induced alterations in gene expression by DNA-PKcs kinase activity

Background: Maintenance of the genome is essential for cell survival, and impairment of the DNA damage response is associated with multiple pathologies including cancer and neurological abnormalities. DNA-PKcs is a DNA repair protein and a core component of the classical nonhomologous end-joining pathway, but it also has roles in modulating gene expression and thus, the overall cellular response to DNA damage. Methods: Using cells producing either wild-type (WT) or kinase-inactive (KR) DNA-PKcs, we assessed global alterations in gene expression in the absence or presence of DNA damage. We evaluated differential gene expression in untreated cells and observed differences in genes associated with cellular adhesion, cell cycle regulation, and inflammation-related pathways. Following exposure to etoposide, we compared how KR versus WT cells responded transcriptionally to DNA damage. Results: Downregulated genes were mostly involved in protein, sugar, and nucleic acid biosynthesis pathways in both genotypes, but enriched biological pathways were divergent, again with KR cells manifesting a more robust inflammatory response compared to WT cells. To determine what major transcriptional regulators are controlling the differences in gene expression noted, we used pathway analysis and found that many master regulators of histone modifications, proinflammatory pathways, cell cycle regulation, Wnt/β-catenin signaling, and cellular development and differentiation were impacted by DNA-PKcs status. Finally, we have used qPCR to validate selected genes among the differentially regulated pathways to validate RNA sequence data. Conclusion: Overall, our results indicate that DNA-PKcs, in a kinase-dependent fashion, decreases proinflammatory signaling following genotoxic insult. As multiple DNA-PK kinase inhibitors are in clinical trials as cancer therapeutics utilized in combination with DNA damaging agents, understanding the transcriptional response when DNA-PKcs cannot phosphorylate downstream targets will inform the overall patient response to combined treatment.

Tumor targeted alpha particle therapy with an actinium-225 labelled antibody for carbonic anhydrase IX

Selective antibody targeted delivery of α particle emitting actinium-225 to tumors has significant therapeutic potential. This work highlights the design and synthesis of a new bifunctional macrocyclic diazacrown ether chelator, H2MacropaSqOEt, that can be conjugated to antibodies and forms stable complexes with actinium-225. The macrocyclic diazacrown ether chelator incorporates a linker comprised of a short polyethylene glycol fragment and a squaramide ester that allows selective reaction with lysine residues on antibodies to form stable vinylogous amide linkages. This new H2MacropaSqOEt chelator was used to modify a monoclonal antibody, girentuximab (hG250), that binds to carbonic anhydrase IX, an enzyme that is overexpressed on the surface of cancers such as clear cell renal cell carcinoma. This new antibody conjugate (H2MacropaSq-hG250) had an average chelator to antibody ratio of 4 : 1 and retained high affinity for carbonic anhydrase IX. H2MacropaSq-hG250 was radiolabeled quantitatively with [225Ac]AcIII within one minute at room temperature with micromolar concentrations of antibody and the radioactive complex is stable in human serum for >7 days. Evaluation of [225Ac]Ac(MacropaSq-hG250) in a mouse xenograft model, that overexpresses carbonic anhydrase IX, demonstrated a highly significant therapeutic response. It is likely that H2MacropaSqOEt could be used to modify other antibodies providing a readily adaptable platform for other actinium-225 based therapeutics.

Biological effects of ionizing radiation on aquatic biota - A critical review

Ionizing radiation from radionuclides impacts marine aquatic biota and the scope of investigation must be wider than just invertebrates. We intend to detail and illustrate numerous biological effects that occur in both aquatic vertebrates and invertebrates, at various dose rates from all three kinds of ionizing radiation. The characteristics of radiation sources and dosages that would most effectively generate the intended effects in the irradiated organism were assessed once the biological differentiation between vertebrates and invertebrates was determined through multiple lines of evidence. We contend that invertebrates are still more radiosensitive than vertebrates, due to their small genome size, rapid reproduction rates and lifestyle, which help them to compensate for the effects of radiation induced declines in fecundity, life span and individual health. We also identified various research gaps in this field and suggest future directions to be investigated to remedy the lack of data available in this area.

Linking Benzene, in Utero Carcinogenicity and Fetal Hematopoietic Stem Cell Niches: A Mechanistic Review

Previous research reported that prolonged benzene exposure during in utero fetal development causes greater fetal abnormalities than in adult-stage exposure. This phenomenon increases the risk for disease development at the fetal stage, particularly carcinogenesis, which is mainly associated with hematological malignancies. Benzene has been reported to potentially act via multiple modes of action that target the hematopoietic stem cell (HSCs) niche, a complex microenvironment in which HSCs and multilineage hematopoietic stem and progenitor cells (HSPCs) reside. Oxidative stress, chromosomal aberration and epigenetic modification are among the known mechanisms mediating benzene-induced genetic and epigenetic modification in fetal stem cells leading to in utero carcinogenesis. Hence, it is crucial to monitor exposure to carcinogenic benzene via environmental, occupational or lifestyle factors among pregnant women. Benzene is a well-known cause of adult leukemia. However, proof of benzene involvement with childhood leukemia remains scarce despite previously reported research linking incidences of hematological disorders and maternal benzene exposure. Furthermore, accumulating evidence has shown that maternal benzene exposure is able to alter the developmental and functional properties of HSPCs, leading to hematological disorders in fetus and children. Since HSPCs are parental blood cells that regulate hematopoiesis during the fetal and adult stages, benzene exposure that targets HSPCs may induce damage to the population and trigger the development of hematological diseases. Therefore, the mechanism of in utero carcinogenicity by benzene in targeting fetal HSPCs is the primary focus of this review.

DNA Damage and Its Role in Cancer Therapeutics

DNA damage is a double-edged sword in cancer cells. On the one hand, DNA damage exacerbates gene mutation frequency and cancer risk. Mutations in key DNA repair genes, such as breast cancer 1 (BRCA1) and/or breast cancer 2 (BRCA2), induce genomic instability and promote tumorigenesis. On the other hand, the induction of DNA damage using chemical reagents or radiation kills cancer cells effectively. Cancer-burdening mutations in key DNA repair-related genes imply relatively high sensitivity to chemotherapy or radiotherapy because of reduced DNA repair efficiency. Therefore, designing specific inhibitors targeting key enzymes in the DNA repair pathway is an effective way to induce synthetic lethality with chemotherapy or radiotherapy in cancer therapeutics. This study reviews the general pathways involved in DNA repair in cancer cells and the potential proteins that could be targeted for cancer therapeutics.

Elevated Levels of Lamin A Promote HR and NHEJ-Mediated Repair Mechanisms in High-Grade Ovarian Serous Carcinoma Cell Line

Extensive research for the last two decades has significantly contributed to understanding the roles of lamins in the maintenance of nuclear architecture and genome organization which is drastically modified in neoplasia. It must be emphasized that alteration in lamin A/C expression and distribution is a consistent event during tumorigenesis of almost all tissues of human bodies. One of the important signatures of a cancer cell is its inability to repair DNA damage which befalls several genomic events that transform the cells to be sensitive to chemotherapeutic agents. This genomic and chromosomal instability is the most common feature found in cases of high-grade ovarian serous carcinoma. Here, we report elevated levels of lamins in OVCAR3 cells (high-grade ovarian serous carcinoma cell line) in comparison to IOSE (immortalised ovarian surface epithelial cells) and, consequently, altered damage repair machinery in OVCAR3. We have analysed the changes in global gene expression as a sequel to DNA damage induced by etoposide in ovarian carcinoma where lamin A is particularly elevated in expression and reported some differentially expressed genes associated with pathways conferring cellular proliferation and chemoresistance. We hereby establish the role of elevated lamin A in neoplastic transformation in the context of high-grade ovarian serous cancer through a combination of HR and NHEJ mechanisms.

Molecular targets that sensitize cancer to radiation killing: From the bench to the bedside

Radiotherapy is a standard cytotoxic therapy against solid cancers. It uses ionizing radiation to kill tumor cells through damage to DNA, either directly or indirectly. Radioresistance is often associated with dysregulated DNA damage repair processes. Most radiosensitizers enhance radiation-mediated DNA damage and reduce the rate of DNA repair ultimately leading to accumulation of DNA damages, cell-cycle arrest, and cell death. Recently, agents targeting key signals in DNA damage response such as DNA repair pathways and cell-cycle have been developed. This new class of molecularly targeted radiosensitizing agents is being evaluated in preclinical and clinical studies to monitor their activity in potentiating radiation cytotoxicity of tumors and reducing normal tissue toxicity. The molecular pathways of DNA damage response are reviewed with a focus on the repair mechanisms, therapeutic targets under current clinical evaluation including ATM, ATR, CDK1, CDK4/6, CHK1, DNA-PKcs, PARP-1, Wee1, & MPS1/TTK and potential new targets (BUB1, and DNA LIG4) for radiation sensitization.

Cancer and Radiosensitivity Syndromes: Is Impaired Nuclear ATM Kinase Activity the Primum Movens?

There are a number of genetic syndromes associated with both high cancer risk and clinical radiosensitivity. However, the link between these two notions remains unknown. Particularly, some cancer syndromes are caused by mutations in genes involved in DNA damage signaling and repair. How are the DNA sequence errors propagated and amplified to cause cell transformation? Conversely, some cancer syndromes are caused by mutations in genes involved in cell cycle checkpoint control. How is misrepaired DNA damage produced? Lastly, certain genes, considered as tumor suppressors, are not involved in DNA damage signaling and repair or in cell cycle checkpoint control. The mechanistic model based on radiation-induced nucleoshuttling of the ATM kinase (RIANS), a major actor of the response to ionizing radiation, may help in providing a unified explanation of the link between cancer proneness and radiosensitivity. In the frame of this model, a given protein may ensure its own specific function but may also play additional biological role(s) as an ATM phosphorylation substrate in cytoplasm. It appears that the mutated proteins that cause the major cancer and radiosensitivity syndromes are all ATM phosphorylation substrates, and they generally localize in the cytoplasm when mutated. The relevance of the RIANS model is discussed by considering different categories of the cancer syndromes.

FOXOs: masters of the equilibrium

Forkhead box O (FOXO) transcription factors (TFs) are a subclass of the larger family of forkhead TFs. Mammalians express four members FOXO1, FOXO3, FOXO4, and FOXO6. The interest in FOXO function stems mostly from their observed role in determining lifespan, where in model organisms, increased FOXO activity results in extended lifespan. FOXOs act as downstream of several signaling pathway and are extensively regulated through post-translational modifications. The transcriptional program activated by FOXOs in various cell types, organisms, and under various conditions has been described and has shed some light on what the critical transcriptional targets are in mediating FOXO function. At the cellular level, these studies have revealed a role for FOXOs in cell metabolism, cellular redox, cell proliferation, DNA repair, autophagy, and many more. The general picture that emerges hereof is that FOXOs act to preserve equilibrium, and they are important for cellular homeostasis. Here, we will first briefly summarize the general knowledge of FOXO regulation and possible functions. We will use genomic stability to illustrate how FOXOs ensure homeostasis. Genomic stability is critical for maintaining genetic integrity, and therefore preventing disease. However, genomic mutations need to occur during lifetime to enable evolution, yet their accumulation is believed to be causative to aging. Therefore, the role of FOXO in genomic stability may underlie its role in lifespan and aging. Finally, we will come up with questions on some of the unknowns in FOXO function, the answer(s) to which we believe will further our understanding of FOXO function and ultimately may help to understand lifespan and its consequences.

Green synthesized nickel doped cobalt ferrite nanoparticles exhibit antibacterial activity and induce reactive oxygen species mediated apoptosis in MCF-7 breast cancer cells through inhibition of PI3K/Akt/mTOR pathway

This study aimed to synthesize the nickel (Ni) doped cobalt ferrite (CFO) nanoparticles and to determine its anticancer effect on breast cancer MCF-7 cells. The various concentrations of Ni (0.2%, 0.4%, 0.6%, 0.8%, and 1%) doped CFO nanoparticles were synthesized using Coriandrum sativum extracts by precipitation technique. The synthesized Ni-CFO was characterized by X-ray diffraction, Fourier transform infrared spectroscopic, transmission electron microscopy, and vibrating sample magnetometer analyses. The results show that 0.8% Ni-CFO nanoparticles showed good magnetic properties and antioxidant activity than other concentrations of Ni-CFO. The results showed that the administration of 0.8% Ni-CFO nanoparticles promoted apoptosis, and reduced cell adhesion and migration of MCF-7 cells, as demonstrated by increased lipid peroxidation, decreased antioxidant levels such as superoxide dismutase, catalase, and glutathione peroxidase, and increased formation of reactive oxygen species. Moreover, administration of 0.8% Ni-CFO nanoparticles decreased the Bcl-2 expression while activating the expression of p53, Bax, and cleaved caspase 3, 8 and 9 protein expression. Notably, 0.8% Ni-CFO treatment reduced phospho-PI3K, phospho-Akt, and phospho-mTOR expression levels. As a result, via altering apoptotic related proteins, 0.8% Ni-CFO induced cell death. Therefore, the 0.8% Ni-CFO could be utilized to treat breast cancer.

Silver nanoparticles synthesized by Euphorbia hirta exhibited antibacterial activity and induced apoptosis through downregulation of PI3Kγ mediated PI3K/Akt/mTOR/p70S6K in human lung adenocarcinoma A549 cells

Plant extracts were successfully applied to synthesize nanoparticles, and expected such biological processes of effective for chemotherapeutic applications and safe for human use. Our study planned to evaluate the anticancer efficacy of silver nanoparticles (AgNPs) synthesized by Euphorbia hirta on human lung adenocarcinoma A549 cells. The E. hirta synthesized Eh-AgNPs was investigated by UV-spectroscopy, X-ray diffraction, transmission electron microscopy, and Fourier-transform infrared spectroscopy examination. The bactericidal efficacy of Eh-AgNPs was studied by the agar well method, and the cytotoxicity on A549 cells was assessed by MTT assay. Results showed that Eh-AgNPs exhibited effective antibacterial activity against bacterial pathogens, established dose-dependent cytotoxicity on A549 cells, and persuaded apoptosis, as evidenced by increased lipid peroxidation and decreased levels of antioxidants. Eh-AgNPs significantly increased the early apoptosis in A549 cells in a concentration-dependent way. The Eh-AgNPs administration reduced the Bcl-2 expression; however, it increased the expression of p53, Bax, cleaved caspase-3 and -9 apoptotic members. Eh-AgNPs treatment reduced PI3Kγ, phospho-PI3K, phospho-Akt, phospho-mTOR, and p70S6K levels. The obtained results demonstrated that the Eh-AgNPs induce reactive oxygen species-mediated apoptosis by expressing p53, Bax, and inhibiting PI3K/Akt/mTOR/p70S6K signaling pathway.

Enhancing anti-tumour innate immunity by targeting the DNA damage response and pattern recognition receptors in combination with radiotherapy

Radiotherapy is one of the most effective and frequently used treatments for a wide range of cancers. In addition to its direct anti-cancer cytotoxic effects, ionising radiation can augment the anti-tumour immune response by triggering pro-inflammatory signals, DNA damage-induced immunogenic cell death and innate immune activation. Anti-tumour innate immunity can result from recruitment and stimulation of dendritic cells (DCs) which leads to tumour-specific adaptive T-cell priming and immunostimulatory cell infiltration. Conversely, radiotherapy can also induce immunosuppressive and anti-inflammatory mediators that can confer radioresistance. Targeting the DNA damage response (DDR) concomitantly with radiotherapy is an attractive strategy for overcoming radioresistance, both by enhancing the radiosensitivity of tumour relative to normal tissues, and tipping the scales in favour of an immunostimulatory tumour microenvironment. This two-pronged approach exploits genomic instability to circumvent immune evasion, targeting both hallmarks of cancer. In this review, we describe targetable DDR proteins (PARP (poly[ADP-ribose] polymerase); ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), DNA-PKcs (DNA-dependent protein kinase, catalytic subunit) and Wee1 (Wee1-like protein kinase) and their potential intersections with druggable immunomodulatory signalling pathways, including nucleic acid-sensing mechanisms (Toll-like receptors (TLR); cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and retinoic acid-inducible gene-I (RIG-I)-like receptors), and how these might be exploited to enhance radiation therapy. We summarise current preclinical advances, recent and ongoing clinical trials and the challenges of therapeutic combinations with existing treatments such as immune checkpoint inhibitors.

Current clinical landscape of oncolytic viruses as novel cancer immunotherapeutic and recent preclinical advancements

Oncolytic viruses (OVs) have been gaining attention in the pharmaceutical industry as a novel immunotherapeutic and therapeutic adjuvant due to their ability to induce and boost antitumor immunity through multiple mechanisms. First, intrinsic mechanisms of OVs that enable exploitation of the host immune system (e.g., evading immune detection) can nullify the immune escape mechanism of tumors. Second, many types of OVs have been shown to cause direct lysis of tumor cells, resulting in an induction of tumor-specific T cell response mediated by release of tumor-associated antigens and danger signal molecules. Third, armed OV-expressing immune stimulatory therapeutic genes could be highly expressed in tumor tissues to further improve antitumor immunity. Last, these OVs can inflame cold tumors and their microenvironment to be more immunologically favorable for other immunotherapeutics. Due to these unique characteristics, OVs have been tested as an adjuvant of choice in a variety of therapeutics. In light of these promising attributes of OVs in the immune-oncology field, the present review will examine OVs in clinical development and discuss various strategies that are being explored in preclinical stages for the next generation of OVs that are optimized for immunotherapy applications.

Discovery of novel 7,8-dihydropteridine-6(5H)-one-based DNA-PK inhibitors as potential anticancer agents via scaffold hopping strategy

DNA-dependent protein kinase (DNA-PK) is an essential element in the DNA damage response (DDR) pathway and has been regarded as a druggable target for antineoplastic agents. Starting from AZD-7648, a potent DNA-PK inhibitor being investigated in phase II clinical trials for advanced cancer treatment, two series of DNA-PK inhibitors were rationally designed via scaffold hopping strategy, synthesized, and assessed for their biological activity. Most compounds exhibited potent biochemical activity on DNA-PK enzymatic assay with IC₅₀ values below 300 nM. Among these compounds, DK1 showed the best DNA-PK-inhibitory potency (IC₅₀ = 0.8 nM), slightly better than that of AZD-7648 (IC₅₀ = 1.58 nM). Mode of action studies revealed that compound DK1 decreased the expression levels of γH2A.X and demonstrated synergistic antiproliferative activity against a series of cancer cell lines when used in combination with doxorubicin. Moreover, DK1 showed reasonable in vitro drug-like properties and favorable in vivo pharmacokinetics as an oral drug candidate. Importantly, the combination therapy of DK1 with DNA double-strand break (DSB)-inducing agent doxorubicin showed synergistic anticancer efficacy in the HL-60 xenograft model with a tumor growth inhibition (TGI) of 52.4% and 62.4% for tumor weight and tumor volume, respectively. In conclusion, DK1 is a novel DNA-PK inhibitor with great promise for further study.

Atractylodin induces oxidative stress-mediated apoptosis and autophagy in human breast cancer MCF-7 cells through inhibition of the P13K/Akt/mTOR pathway

This study aimed to determine the apoptosis and autophagy-inducing mechanism of atractylodin in human breast cancer MCF-7 cells. The molecular mechanism of anticancer activity of atractylodin was confirmed by assessing the levels of reactive oxygen species (ROS) level, lipid peroxidation (LPO), antioxidants activity, dual staining, and comet assay. Moreover, cleaved caspases 3, 8, and 9, and signaling proteins, such as p53, Bcl-2, and Bax, phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin(P13K/Akt/mTOR), LC3I and LC3II, and beclin-1 were analyzed. In MCF-7 cells treated with atractylodin, the concentration-dependent toxicity, increased LPO, increased production of ROS, and decreased activity of superoxide dismutase, catalase, and glutathione peroxidasewere observed. In MCF-7 cells, atractylodin administration decreased Bcl-2 expression while activating the expression of p53, Bax, cleaved caspase-3, caspase-8, and caspase-9 apoptotic members. Furthermore, atractylodin blocked the P13K/Akt/mTOR signaling pathway, increased the conversion of LC3I to its lipidated form of LC3II, and increased beclin-1 expression, whereas downregulated the p62 expression in MCF-7 cells. As a result, altering apoptotic and autophagy-related biomarkers, atractylodin triggered apoptosis and autophagy in MCF-7 cells. As a result, atractylodin could be utilized to treat human breast cancer after the proper clinical trial.

β-Caryophyllene promotes oxidative stress and apoptosis in KB cells through activation of mitochondrial-mediated pathway - An in-vitro and in-silico study

Beta-caryophyllene (BCP), are natural bicyclic sesquiterpenes which are present in numerous plants worldwide. BCP has antioxidant, antimicrobial, and antifungal properties. Here, we studied its anticancer, anti-inflammatory, and cytotoxic effects. Cells treated with BCP, in a dose-dependent manner, exhibited morphological changes, showed lower cell growth, underwent apoptosis and lost the ability to metastasis through the suppression of NF-ҡ B via PI3K/AKT signalling pathway. These results elucidate that the inhibition of NF-ҡ B and PI3K/AKT is one of the most important mechanism by which BCP suppresses cancer cell proliferation and enhances apoptosis.

Effects of fecal microbiota transplant on DNA methylation in subjects with metabolic syndrome

Accumulating evidence shows that microbes with their theater of activity residing within the human intestinal tract (i.e., the gut microbiome) influence host metabolism. Some of the strongest results come from recent fecal microbial transplant (FMT) studies that relate changes in intestinal microbiota to various markers of metabolism as well as the pathophysiology of insulin resistance. Despite these developments, there is still a limited understanding of the multitude of effects associated with FMT on the general physiology of the host, beyond changes in gut microbiome composition. We examined the effect of either allogenic (lean donor) or autologous FMTs on the gut microbiome, plasma metabolome, and epigenomic (DNA methylation) reprogramming in peripheral blood mononuclear cells in individuals with metabolic syndrome measured at baseline (pre-FMT) and after 6 weeks (post-FMT). Insulin sensitivity was determined with a stable isotope-based 2 step hyperinsulinemic clamp and multivariate machine learning methodology was used to uncover discriminative microbes, metabolites, and DNA methylation loci. A larger gut microbiota shift was associated with an allogenic than with autologous FMT. Furthemore, the data results of the the allogenic FMT group data indicates that the introduction of new species can potentially modulate the plasma metabolome and (as a result) the epigenome. Most notably, the introduction of Prevotella ASVs directly correlated with methylation of AFAP1, a gene involved in mitochondrial function, insulin sensitivity, and peripheral insulin resistance (Rd, rate of glucose disappearance). FMT was found to have notable effects on the gut microbiome but also on the host plasma metabolome and the epigenome of immune cells providing new avenues of inquiry in the context of metabolic syndrome treatment for the manipulation of host physiology to achieve improved insulin sensitivity.

DNA-PKcs promotes sepsis-induced multiple organ failure by triggering mitochondrial dysfunction

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DNA-PKcs inhibition attenuates sepsis-related MODS by preserving mitochondrial function and homeostasis.

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Organ-specific deletion of DNA-PKcs sustained myocardial contraction, liver function, and kidney performance in LPS-challenged mice.

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DNA-PKcs deficiency supported cardiomyocyte function through improving mitochondrial respiration.

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DNA-PKcs deficiency alleviated liver dysfunction by inhibiting LPS-induced mitochondrial oxidative stress and apoptosis.

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DNA-PKcs deficiency attenuated kidney dysfunction by normalizing mitochondrial dynamics and biogenesis, as well as mitophagy.

Introduction

Multiple organ failure is the commonest cause of death in septic patients.

Objectives

This study was undertaken in an attempt to elucidate the functional importance of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) on mitochondrial dysfunction associated with the development and progression of sepsis-related multiple organ dysfunction syndrome (MODS).

Methods

Cardiomyocyte-specific DNA-PKcs knockout (DNA-PKcs^CKO) mice, liver-specific DNA-PKcs knockout (DNA-PKcs^LKO) mice, and kidney tubular cell-specific DNA-PKcs knockout (DNA-PKcs^TKO) mice were used to generate an LPS-induced sepsis model. Echocardiography, serum biochemistry, and tissue microscopy were used to analyze organ damage and morphological changes induced by sepsis. Mitochondrial function and dynamics were determined by qPCR, western blotting, ELISA, and mt-Keima and immunofluorescence assays following siRNA-mediated DNA-PKCs knockdown in cardiomyocytes, hepatocytes, and kidney tubular cells.

Results

DNA-PKcs deletion attenuated sepsis-mediated myocardial damage through improving mitochondrial metabolism. Loss of DNA-PKcs protected the liver against sepsis through inhibition of mitochondrial oxidative damage and apoptosis. DNA-PKcs deficiency sustained kidney function upon LPS stress through normalization of mitochondrial fission/fusion events, mitophagy, and biogenesis.

Conclusion

We conclude that strategies targeting DNA-PKcs expression or activity may be valuable therapeutic options to prevent or reduce mitochondrial dysfunction and organ damage associated with sepsis-induced MODS.

Genomic Instability and Replicative Stress in Multiple Myeloma: The Final Curtain?

Simple Summary

Genomic instability is recognized as a driving force in most cancers as well as in the haematological cancer multiple myeloma and remains among the leading cause of drug resistance. Several evidences suggest that replicative stress exerts a fundamental role in fuelling genomic instability. Notably, cancer cells rely on a single protein, ATR, to cope with the ensuing DNA damage. In this perspective, we provide an overview depicting how replicative stress represents an Achilles heel for multiple myeloma, which could be therapeutically exploited either alone or in combinatorial regimens to preferentially ablate tumor cells.

Abstract

Multiple Myeloma (MM) is a genetically complex and heterogeneous hematological cancer that remains incurable despite the introduction of novel therapies in the clinic. Sadly, despite efforts spanning several decades, genomic analysis has failed to identify shared genetic aberrations that could be targeted in this disease. Seeking alternative strategies, various efforts have attempted to target and exploit non-oncogene addictions of MM cells, including, for example, proteasome inhibitors. The surprising finding that MM cells present rampant genomic instability has ignited concerted efforts to understand its origin and exploit it for therapeutic purposes. A credible hypothesis, supported by several lines of evidence, suggests that at the root of this phenotype there is intense replicative stress. Here, we review the current understanding of the role of replicative stress in eliciting genomic instability in MM and how MM cells rely on a single protein, Ataxia Telangiectasia-mutated and Rad3-related protein, ATR, to control and survive the ensuing, potentially fatal DNA damage. From this perspective, replicative stress per se represents not only an opportunity for MM cells to increase their evolutionary pool by increasing their genomic heterogeneity, but also a vulnerability that could be leveraged for therapeutic purposes to selectively target MM tumor cells.

DNA repair protein DNA-PK protects PC12 cells from oxidative stress-induced apoptosis involving AKT phosphorylation

Background

Emerging evidence suggest that DNA-PK complex plays a role in the cellular response to oxidative stress, in addition to its function of double strand break (DSB) repair. In this study we evaluated whether DNA-PK participates in oxidative stress response and whether this role is independent of its function in DNA repair.

Methods and results

We used a model of H₂O₂-induced DNA damage in PC12 cells (rat pheochromocytoma), a well-known neuronal tumor cell line. We found that H₂O₂ treatment of PC12 cells induces an increase in DNA-PK protein complex levels, along with an elevation of DNA damage, measured both by the formation of γΗ2ΑX foci, detected by immunofluorescence, and γH2AX levels detected by western blot analysis. After 24 h of cell recovery, γΗ2ΑX foci are repaired both in the absence and presence of DNA-PK kinase inhibitor NU7026, while an increase of apoptotic cells is observed when DNA-PK activity is inhibited, as revealed by counting pycnotic nuclei and confirmed by FACS analysis. Our results suggest a role of DNA-PK as an anti-apoptotic factor in proliferating PC12 cells under oxidative stress conditions. The anti-apoptotic role of DNA-PK is associated with AKT phosphorylation in Ser473. On the contrary, in differentiated PC12 cells, were the main pathway to repair DSBs is DNA-PK-mediated, the inhibition of DNA-PK activity causes an accumulation of DNA damage.

Conclusions

Taken together, our results show that DNA-PK can protect cells from oxidative stress induced-apoptosis independently from its function of DSB repair enzyme.

Graphical Abstract

DNAPK Inhibition Preferentially Compromises the Repair of Radiation-induced DNA Double-strand Breaks in Chronically Hypoxic Tumor Cells in Xenograft Models

Radiation-induced DNA double-strand breaks (DSBs) can be repaired by homologous recombination (HR) and nonhomologous end joining (NHEJ). Recently, it has been found that chronic tumor hypoxia compromises HR repair of DNA DSBs but activates the NHEJ protein DNAPK. We therefore hypothesized that inhibition of DNAPK can preferentially potentiate the sensitivity of chronically hypoxic cancer cells to radiation through contextual synthetic lethality in vivo In this study, we investigated the impact of DNAPK inhibition by a novel selective DNAPK inhibitor, NU5455, on the repair of radiation-induced DNA DSBs in chronically hypoxic and nonhypoxic cells across a range of xenograft models. We found that NU5455 inhibited DSB repair following radiation in both chronically hypoxic and nonhypoxic tumor cells. Most importantly, the inhibitory effect was more pronounced in chronically hypoxic tumor cells than in nonhypoxic tumor cells. This is the first in vivo study to indicate that DNAPK inhibition may preferentially sensitize chronically hypoxic tumor cells to radiotherapy, suggesting a broader therapeutic window for transient DNAPK inhibition combined with radiotherapy.

Recent Advances in Therapeutic Application of DNA Damage Response Inhibitors against Cancer

DNA integrity is continuously challenged by intrinsic cellular processes and environmental agents. To overcome this genomic damage, cells have developed multiple signaling pathways collectively named as DNA damage response (DDR) and composed of three components: (i) sensor proteins, which detect DNA damage, (ii) mediators that relay the signal downstream and recruit the repair machinery, and (iii) the repair proteins, which restore the damaged DNA. A flawed DDR and failure to repair the damage lead to the accumulation of genetic lesions and increased genomic instability, which is recognized as a hallmark of cancer. Cancer cells tend to harbor increased mutations in DDR genes and often have fewer DDR pathways than normal cells. This makes cancer cells more dependent on particular DDR pathways and thus become more susceptible to compounds inhibiting those pathways compared to normal cells, which have all the DDR pathways intact. Understanding the roles of different DDR proteins in the DNA damage response and repair pathways and identification of their structures have paved the way for the development of their inhibitors as targeted cancer therapy. In this review, we describe the major participants of various DDR pathways, their significance in carcinogenesis, and focus on the inhibitors developed against several key DDR proteins.

Natural Progression of Non-Alcoholic Steatohepatitis to Hepatocellular Carcinoma

Non-alcoholic steatohepatitis (NASH) is a chronic and progressive form of non-alcoholic fatty liver disease (NAFLD). Its global incidence is increasing which makes NASH an epidemic and a public health threat. Due to repeated insults to the liver, patients are at risk for developing hepatocellular carcinoma (HCC). The progression of NASH to HCC was initially defined according to a two-hit model which involved the development of steatosis, followed by lipid peroxidation and inflammation. However, current research defines a "multi-hit" or "multi-parallel hit" model which synthesizes several contributing pathways involved in progressive fibrosis and oncogenesis. This perspective considers the effects of cellular, genetic, immunologic, metabolic, and endocrine pathways leading up to HCC which underscores the complexity of this condition. This article will provide an updated review of the pathogenic mechanisms leading from NASH to HCC as well as an exploration of the role of biomarkers and screening.

Zinc oxide nanoparticles synthesized from Aspergillus terreus induces oxidative stress-mediated apoptosis through modulating apoptotic proteins in human cervical cancer HeLa cells

OBJECTIVES

This study was aimed to analyze the cytotoxicity of biogenic zinc oxide nanoparticles (ZnO NPs) in human cervical epithelial cancer HeLa.

METHODS

The ZnO NPs was synthesized from the culture filtrated of Aspergillus terreus, and examined by UV-spectroscopy, X-ray diffraction (XRD), transmission electron microscope (TEM), energy-dispersive X-ray (EDX) and Fourier transform infrared (FTIR) analysis. The cytotoxicity of synthesized ZnO NPs was analyzed by the MTT assay, and the expression of apoptotic proteins was examined by Western blot analyses.

KEY FINDINGS

The ZnO NPs exhibited concentration-dependent cytotoxicity on HeLa cells and induced the apoptosis as evidenced by reduced superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) levels, and increased reactive oxygen species (ROS) and diminished mitochondrial membrane potential (MMP) was noticed in ZnO NPs treated HeLa cells. Western blot analyses explored that the Bcl-2 expression was significantly downregulated, whereas, the expression of p53, Bax, Caspase-3, Caspase-9 and Cytochrome-c were significantly upregulated in ZnO NPs treated cells.

CONCLUSION

Consequently, the mycosynthesized ZnO NPs induces apoptosis in HeLa cells by persuading oxidative damage and modulating the apoptotic proteins. Therefore, A. terreus synthesized ZnO NPs could be used as an effective chemotherapeutic agent for cervical cancer treatment.

Tampering of Viruses and Bacteria with Host DNA Repair: Implications for Cellular Transformation

A reduced ability to properly repair DNA is linked to a variety of human diseases, which in almost all cases is associated with an increased probability of the development of cellular transformation and cancer. DNA damage, that ultimately can lead to mutations and genomic instability, is due to many factors, such as oxidative stress, metabolic disorders, viral and microbial pathogens, excess cellular proliferation and chemical factors. In this review, we examine the evidence connecting DNA damage and the mechanisms that viruses and bacteria have evolved to hamper the pathways dedicated to maintaining the integrity of genetic information, thus affecting the ability of their hosts to repair the damage(s). Uncovering new links between these important aspects of cancer biology might lead to the development of new targeted therapies in DNA-repair deficient cancers and improving the efficacy of existing therapies. Here we provide a comprehensive summary detailing the major mechanisms that viruses and bacteria associated with cancer employ to interfere with mechanisms of DNA repair. Comparing these mechanisms could ultimately help provide a common framework to better understand how certain microorganisms are involved in cellular transformation.

Dual mTOR/DNA-PK Inhibitor CC-115 Induces Cell Death in Melanoma Cells and Has Radiosensitizing Potential

CC-115 is a dual inhibitor of the mechanistic target of rapamycin (mTOR) kinase and the DNA-dependent protein kinase (DNA-PK) that is currently being studied in phase I/II clinical trials. DNA-PK is essential for the repair of DNA-double strand breaks (DSB). Radiotherapy is frequently used in the palliative treatment of metastatic melanoma patients and induces DSBs. Melanoma cell lines and healthy-donor skin fibroblast cell lines were treated with CC‑115 and ionizing irradiation (IR). Apoptosis, necrosis, and cell cycle distribution were analyzed. Colony forming assays were conducted to study radiosensitizing effects. Immunofluorescence microscopy was performed to determine the activity of homologous recombination (HR). In most of the malign cell lines, an increasing concentration of CC-115 resulted in increased cell death. Furthermore, strong cytotoxic effects were only observed in malignant cell lines. Regarding clonogenicity, all cell lines displayed decreased survival fractions during combined inhibitor and IR treatment and supra-additive effects of the combination were observable in 5 out of 9 melanoma cell lines. CC-115 showed radiosensitizing potential in 7 out of 9 melanoma cell lines, but not in healthy skin fibroblasts. Based on our data CC-115 treatment could be a promising approach for patients with metastatic melanoma, particularly in the combination with radiotherapy.

DNA-PK: gatekeeper for IKKγ/NEMO nucleocytoplasmic shuttling in genotoxic stress-induced NF-kappaB activation

The transcription factors of the nuclear factor κB (NF-κB) family play a pivotal role in the cellular response to DNA damage. Genotoxic stress-induced activation of NF-κB differs from the classical canonical pathway by shuttling of the NF-κB Essential Modifier (IKKγ/NEMO) subunit through the nucleus. Here, we show that DNA-dependent protein kinase (DNA-PK), an enzyme involved in DNA double-strand break (DSB) repair, triggers the phosphorylation of NEMO by genotoxic stress, thereby enabling shuttling of NEMO through the nucleus with subsequent NF-κB activation. We identified serine 43 of NEMO as a DNA-PK phosphorylation site and point mutation of this serine to alanine led to a complete block of NF-κB activation by ionizing radiation (IR). Blockade of DNA-PK by a specific shRNA or by DNA-PKcs-deficient cells abrogated NEMO entry into the nucleus, as well. Accordingly, SUMOylation of NEMO, a prerequisite of nuclear NEMO, was abolished. Based on these observations, we propose a model in which NEMO phosphorylation by DNA-PK provides the first step in the nucleocytoplasmic trafficking of NEMO.

Beta Human Papillomavirus 8E6 Attenuates Non-Homologous End Joining by Hindering DNA-PKcs Activity

Cutaneous viral infections occur in a background of near continual exposure to environmental genotoxins, like UV radiation in sunlight. Failure to repair damaged DNA is an established driver of tumorigenesis and substantial cellular resources are devoted to repairing DNA lesions. Beta-human papillomaviruses (β-HPVs) attenuate DNA repair signaling. However, their role in human disease is unclear. Some have proposed that β-HPV promotes tumorigenesis, while others suggest that β-HPV protects against skin cancer. Most of the molecular evidence that β-HPV impairs DNA repair has been gained via characterization of the E6 protein from β-HPV 8 (β-HPV 8E6). Moreover, β-HPV 8E6 hinders DNA repair by binding and destabilizing p300, a transcription factor for multiple DNA repair genes. By reducing p300 availability, β-HPV 8E6 attenuates a major double strand DNA break (DSB) repair pathway, homologous recombination. Here, β-HPV 8E6 impairs another DSB repair pathway, non-homologous end joining (NHEJ). Specifically, β-HPV 8E6 acts by attenuating DNA-dependent protein kinase (DNA-PK) activity, a critical NHEJ kinase. This includes DNA-PK activation and the downstream of steps in the pathway associated with DNA-PK activity. Notably, β-HPV 8E6 inhibits NHEJ through p300 dependent and independent means. Together, these data expand the known genome destabilizing capabilities of β-HPV 8E6.

Inhibition of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) stimulates osteoblastogenesis by potentiating bone morphogenetic protein 2 (BMP2) responses

The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) is a pleiotropic enzyme involved in DNA repair, cell cycle control, and transcription regulation. A potential role for DNA-PKcs in the regulation of osteoblastogenesis remains to be established. We show that pharmacological inhibition of DNA-PKcs kinase activity or gene silencing of Prkdc (encoding DNA-PKcs) in murine osteoblastic MC3T3-E1 cells and human adipose-derived mesenchymal stromal cells markedly enhanced osteogenesis and the expression of osteoblast differentiation marker genes. Inhibition of DNA-PKcs inhibited cell cycle progression and increased osteogenesis by significantly enhancing the bone morphogenetic protein 2 response in osteoblasts and other mesenchymal cell types. Importantly, in vivo pharmacological inhibition of the kinase enhanced bone biomechanical properties. Bones from osteoblast-specific conditional Prkdc-knockout mice exhibited a similar phenotype of increased stiffness. In conclusion, DNA-PKcs negatively regulates osteoblast differentiation, and therefore DNA-PKcs inhibitors may have therapeutic potential for bone regeneration and metabolic bone diseases.

Effects of the scid mutation on X-ray-induced deletions in the brain and spleen of gpt delta mice

Background

DNA-dependent protein kinase (DNA-PK), consisting of a Ku heterodimer (Ku70/80) and a large catalytic subunit (DNA-PKcs), plays an important role in the repair of DNA double-strand breaks via non-homologous end-joining (NHEJ) in mammalian cells. Severe combined immunodeficient (scid) mice carry a mutation in the gene encoding DNA-PKcs and are sensitive to ionizing radiation. To examine the roles of DNA-PKcs in the generation of deletion mutations in vivo, we crossed scid mice with gpt delta transgenic mice for detecting mutations.

Results

The scid and wild-type (WT) gpt delta transgenic mice were irradiated with a single X-ray dose of 10 Gy, and Spi⁻ mutant frequencies (MFs) were determined in the brain and spleen 2 days after irradiation. Irradiation with X-rays significantly enhanced Spi⁻ MF in both organs in the scid and WT mice. The MFs in the brain of irradiated scid mice were significantly lower than those in WT mice, i.e., 2.9 ± 1.0 × 10^− 6 versus 5.0 ± 1.1 × 10^− 6 (P < 0.001), respectively. In the spleen, however, both mouse strains exhibited similar MFs, i.e., 4.1 ± 1.8 × 10^− 6 versus 4.8 ± 1.4 × 10^− 6. Unirradiated scid and WT mice did not exhibit significant differences in MFs in either organ.

Conclusions

DNA-PKcs is unessential for the induction of deletion mutations in the spleen, while it plays a role in this in the brain. Therefore, the contribution of DNA-PKcs to NHEJ may be organ-specific.

DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer

Radiotherapy is one of the most common countermeasures for treating a wide range of tumors. However, the radioresistance of cancer cells is still a major limitation for radiotherapy applications. Efforts are continuously ongoing to explore sensitizing targets and develop radiosensitizers for improving the outcomes of radiotherapy. DNA double-strand breaks are the most lethal lesions induced by ionizing radiation and can trigger a series of cellular DNA damage responses (DDRs), including those helping cells recover from radiation injuries, such as the activation of DNA damage sensing and early transduction pathways, cell cycle arrest, and DNA repair. Obviously, these protective DDRs confer tumor radioresistance. Targeting DDR signaling pathways has become an attractive strategy for overcoming tumor radioresistance, and some important advances and breakthroughs have already been achieved in recent years. On the basis of comprehensively reviewing the DDR signal pathways, we provide an update on the novel and promising druggable targets emerging from DDR pathways that can be exploited for radiosensitization. We further discuss recent advances identified from preclinical studies, current clinical trials, and clinical application of chemical inhibitors targeting key DDR proteins, including DNA-PKcs (DNA-dependent protein kinase, catalytic subunit), ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), the MRN (MRE11-RAD50-NBS1) complex, the PARP (poly[ADP-ribose] polymerase) family, MDC1, Wee1, LIG4 (ligase IV), CDK1, BRCA1 (BRCA1 C terminal), CHK1, and HIF-1 (hypoxia-inducible factor-1). Challenges for ionizing radiation-induced signal transduction and targeted therapy are also discussed based on recent achievements in the biological field of radiotherapy.

Targeting hallmarks of cancer to enhance radiosensitivity in gastrointestinal cancers

Radiotherapy is used in the treatment of approximately 50% of all malignancies including gastrointestinal cancers. Radiation can be given prior to surgery (neoadjuvant radiotherapy) to shrink the tumour or after surgery to kill any remaining cancer cells. Radiotherapy aims to maximize damage to cancer cells, while minimizing damage to healthy cells. However, only 10-30% of patients with rectal cancer or oesophageal cancer have a pathological complete response to neoadjuvant chemoradiation therapy, with the rest suffering the negative consequences of toxicities and delays to surgery with no clinical benefit. Furthermore, in pancreatic cancer, neoadjuvant chemoradiation therapy results in a pathological complete response in only 4% of patients and a partial pathological response in only 31%. Resistance to radiation therapy is polymodal and associated with a number of biological alterations both within the tumour itself and in the surrounding microenvironment including the following: altered cell cycle; repopulation by cancer stem cells; hypoxia; altered management of oxidative stress; evasion of apoptosis; altered DNA damage response and enhanced DNA repair; inflammation; and altered mitochondrial function and cellular energetics. Radiosensitizers are needed to improve treatment response to radiation, which will directly influence patient outcomes in gastrointestinal cancers. This article reviews the literature to identify strategies - including DNA-targeting agents, antimetabolic agents, antiangiogenics and novel immunotherapies - being used to enhance radiosensitivity in gastrointestinal cancers according to the hallmarks of cancer. Evidence from radiosensitizers from in vitro and in vivo models is documented and the action of radiosensitizers through clinical trial data is assessed.

Identification and characterization of novel SCR7-based small-molecule inhibitor of DNA end-joining, SCR130 and its relevance in cancer therapeutics

Targeting DNA repair with small-molecule inhibitors is an attractive strategy for cancer therapy. Majority of DNA double-strand breaks in mammalian cells are repaired through nonhomologous end-joining (NHEJ). It has been shown that small-molecule inhibitors of NHEJ can block efficient repair inside cancer cells, leading to cell death. Previously, we have reported that SCR7, an inhibitor of NHEJ can induce tumor regression in mice. Later studies have shown that different forms of SCR7 can inhibit DNA end-joining in Ligase IV-dependent manner. Recently, we have derivatized SCR7 by introducing spiro ring into core structure. Here, we report the identification of a novel inhibitor of NHEJ, named SCR130 with 20-fold higher efficacy in inducing cytotoxicity in cancer cell lines. SCR130 inhibited DNA end-joining catalyzed by rat tissue extract. Specificity analysis revealed that while SCR130 was specific to Ligase IV, it showed minimal or no effect on Ligase III and Ligase I mediated joining. Importantly, SCR130 exhibited the least cytotoxicity in Ligase IV-null cell line as compared with wild type, confirming Ligase IV-specificity. Furthermore, we demonstrate that SCR130 can potentiate the effect of radiation in cancer cells when used in combination with γ-radiation. Various cellular assays in conjunction with Western blot analysis revealed that treatment with SCR130 led to loss of mitochondrial membrane potential leading to cell death by activating both intrinsic and extrinsic pathways of apoptosis. Thus, we describe a novel inhibitor of NHEJ with higher efficacy and may have the potential to be developed as cancer therapeutic.

Radiation resistance in head and neck squamous cell carcinoma: dire need for an appropriate sensitizer

Radiation is a significant treatment for patients with head and neck cancer. Despite advances to improve treatment, many tumors acquire radiation resistance resulting in poor survival. Radiation kills cancer cells by inducing DNA double-strand breaks. Therefore, radiation resistance is enhanced by efficient repair of damaged DNA. Head and neck cancers overexpress EGFR and have a high frequency of p53 mutations, both of which enhance DNA repair. This review discusses the clinical criteria for radiation resistance in patients with head and neck cancer and summarizes how cancer cells evade radiation-mediated apoptosis by p53- and epidermal growth factor receptor (EGFR)-mediated DNA repair. In addition, we explore the role of cancer stem cells in promoting radiation resistance, and how the abscopal effect provides rationale for combination strategies with immunotherapy.

Selective DNA-PKcs inhibition extends the therapeutic index of localized radiotherapy and chemotherapy

Potentiating radiotherapy and chemotherapy by inhibiting DNA damage repair is proposed as a therapeutic strategy to improve outcomes for patients with solid tumors. However, this approach risks enhancing normal tissue toxicity as much as tumor toxicity, thereby limiting its translational impact. Using NU5455, a newly identified highly selective oral inhibitor of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity, we found that it was indeed possible to preferentially augment the effect of targeted radiotherapy on human orthotopic lung tumors without influencing acute DNA damage or a late radiation-induced toxicity (fibrosis) to normal mouse lung. Furthermore, while NU5455 administration increased both the efficacy and the toxicity of a parenterally administered topoisomerase inhibitor, it enhanced the activity of doxorubicin released locally in liver tumor xenografts without inducing any adverse effect. This strategy is particularly relevant to hepatocellular cancer, which is treated clinically with localized drug-eluting beads and for which DNA-PKcs activity is reported to confer resistance to treatment. We conclude that transient pharmacological inhibition of DNA-PKcs activity is effective and tolerable when combined with localized DNA-damaging therapies and thus has promising clinical potential.

High drug efflux pump capacity and low DNA damage response induce doxorubicin resistance in canine hemangiosarcoma cell lines

Canine hemangiosarcoma (HSA) is an aggressive malignant endothelial tumor in dogs and characterized by poor prognosis because of its high invasiveness, high metastatic potential, and poor responsiveness to anti-cancer drugs. Although doxorubicin-based chemotherapy is regularly conducted after surgical treatment, its effects on survival rates are limited. Acquisition of drug resistance is one of the causes of this problem, but the underlying mechanisms remain unclear. In the present study, we aimed to identify the drug-resistance mechanism in canine HSA by establishing doxorubicin-resistant (DR) HSA cell lines. HSA cell lines were exposed to doxorubicin at gradually increasing concentrations. When the cells were able to grow in the presence of a 16-fold higher doxorubicin concentration compared with the initial culture, they were designated DR-HSA cell lines. Characterization of these DR-HSA cell lines revealed higher drug efflux pump capacity compared with the parental cell lines. Furthermore, the DR-HSA cell lines did not show activation of the DNA damage response despite carrying high DNA damage burdens, meaning that apoptosis was not strongly induced. In conclusion, canine HSA cell lines acquired doxorubicin resistance by increasing their drug efflux pump capacity and decreasing the DNA damage response. This study provides useful findings to promote further research on the drug-resistance mechanisms in canine HSA.

Evidence for a novel mechanism of influenza A virus host adaptation modulated by PB2-627

Influenza virus cross-species transmission is restricted by the host, but viruses overcome this restriction by accumulating mutations which allow them to adapt to a new host. Among the many factors which facilitate virus host adaptation, polymerase basic protein 2 (PB2) 627 plays an important role, although the underlying molecular mechanism has not been fully understood. In a previous study, we found that histone H1.2 (encoded by HIST1H1C) regulates human or avian influenza virus replication in different ways, indicating that it might be involved in virus host adaptation. Herein, we found that HIST1H1C expression, phosphorylation and methylation levels are decreased when infected with H1N1 influenza virus and increased when infected with H5N1 influenza virus. Overexpressing the eight gene segments of the influenza virus, we found that only PB2 significantly affects HIST1H1C expression and modifications. Since the 627 site is different between the H5N1 and H1N1 influenza viruses we constructed PB2-627E (avian variant) and PB2-627K (human variant) mutant viruses, and observed that the effects of the wild-type and the mutant viruses on HIST1H1C expression and modifications are the opposite of one another. Further analysis showed that influenza virus PB2-627 regulates HIST1H1C expression via Sp1, and specifically that PB2-627K down-regulates Sp1 and HIST1H1C while PB2-627E up-regulates Sp1 and HIST1H1C. In addition, HIST1H1C can feedback regulate DNA-dependent protein kinase and euchromatic histone-lysine N-methyltransferase 1/2, leading to altered HIST1H1C phosphorylation and methylation levels, and affecting influenza virus replication accordingly. In summary, this study illustrates the mechanism of PB2-627E/K-mediated regulation of influenza virus host adaptation.

From NASH to HCC: current concepts and future challenges

Caloric excess and sedentary lifestyle have led to a global epidemic of obesity and metabolic syndrome. The hepatic consequence of metabolic syndrome and obesity, nonalcoholic fatty liver disease (NAFLD), is estimated to affect up to one-third of the adult population in many developed and developing countries. This spectrum of liver disease ranges from simple steatosis to nonalcoholic steatohepatitis (NASH) and cirrhosis. Owing to the high prevalence of NAFLD, especially in industrialized countries but also worldwide, and the consequent burden of progressive liver disease, there is mounting epidemiological evidence that NAFLD has rapidly become a leading aetiology underlying many cases of hepatocellular carcinoma (HCC). In this Review, we discuss NAFLD-associated HCC, including its epidemiology, the key features of the hepatic NAFLD microenvironment (for instance, adaptive and innate immune responses) that promote hepatocarcinogenesis and the management of HCC in patients with obesity and associated metabolic comorbidities. The challenges and future directions of research will also be discussed, including clinically relevant biomarkers for early detection, treatment stratification and monitoring as well as approaches to therapies for both prevention and treatment in those at risk or presenting with NAFLD-associated HCC.

Reactivation of heat-inactivated Ku proteins by heat shock cognate protein HSC73

PURPOSE

Mouse double-stranded DNA-dependent protein kinase (DNA-PK) activity is heat sensitive. Recovery of heat-inactivated DNA repair activity is a problem after combination therapy with radiation and heat. We investigated the mechanism of recovery of heat-inactivated DNA-PK activity.

METHODS

Hybrid cells containing a fragment of human chromosome 8 in scid cells (RD13B2) were used. DNA-PK activity was measured by an in vitro assay. Immunoprecipitation of the nuclear extract was performed with an anti-Ku80 antibody. Proteins co-precipitated with Ku80 were separated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and detected by Western blotting using anti-heat shock protein (HSP)72 and anti-heat shock cognate protein (HSC)73 antibodies. HSC73 was overexpressed with the pcDNA3.1 vector. Short hairpin (sh)RNA was used to downregulate HSC73 and HSP72.

RESULTS

The activity of heat-inactivated DNA-PK recovered to about 50% of control during an additional incubation at 37 °C after heat treatment at 44 °C for 15 min in the presence of cycloheximide (which inhibits de novo protein synthesis). Maximal recovery was observed within 3 h of incubation at 37 °C after heat treatment. Constitutively expressed HSC73, which folds newly synthesized proteins, reached maximal levels 3 h after heat treatment using a co-immunoprecipitation assay with the Ku80 protein. Inhibiting HSC73, but not HSP72, expression with shRNA decreased the recovery of DNA-PK activity after heat treatment.

CONCLUSIONS

These results suggest that de novo protein synthesis is unnecessary for recovery of some heat-inactivated DNA-PK. Rather, it might be reactivated by the molecular chaperone activity of HSC73, but not HSP72.

DNA Repair: Translation to the Clinic

It has been well established that an accumulation of mutations in DNA, whether caused by external sources (e.g. ultraviolet light, radioactivity) or internal sources (e.g. metabolic by-products, such as reactive oxygen species), has the potential to cause a cell to undergo carcinogenesis and increase the risk for the development of cancer. Therefore, it is critically important for a cell to have the capacity to properly respond to and repair DNA damage as it occurs. The DNA damage response (DDR) describes a collection of DNA repair pathways that aid in the protection of genomic integrity by detecting myriad types of DNA damage and initiating the correct DNA repair pathway. In many instances, a deficiency in the DDR, whether inherited or spontaneously assumed, can increase the risk of carcinogenesis and ultimately tumorigenesis through the accumulation of mutations that fail to be properly repaired. Interestingly, although disruption of the DDR can lead to the initial genomic instability that can ultimately cause carcinogenesis, the DDR has also proven to be an invaluable target for anticancer drugs and therapies. Making matters more complicated, the DDR is also involved in the resistance to first-line cancer therapy. In this review, we will consider therapies already in use in the clinic and ongoing research into other avenues of treatment that target DNA repair pathways in cancer.

Activation of EGFR-DNA-PKcs pathway by IGFBP2 protects esophageal adenocarcinoma cells from acidic bile salts-induced DNA damage

Background

The incidence of esophageal adenocarcinoma (EAC) is rising rapidly in the US and Western countries. The development of Barrett’s esophagus (BE) and its progression to EAC have been linked to chronic gastroesophageal reflux disease (GERD). Exposure of BE and EAC cells to acidic bile salts (ABS) in GERD conditions induces high levels of oxidative stress and DNA damage. In this study, we investigated the role of insulin-like growth factor binding protein 2 (IGFBP2) in regulating ABS-induced DNA double-strand breaks.

Methods

Real-time RT-PCR, western blot, immunohistochemistry, immunofluorescence, co-immunoprecipitation, flow cytometry, and cycloheximide (CHX) chase assays were used in this study. To mimic GERD conditions, a cocktail of acidic bile salts (pH 4) was used in 2D and 3D organotypic culture models. Overexpression and knockdown of IGFBP2 in EAC cells were established to examine the functional and mechanistic roles of IGFBP2 in ABS-induced DNA damage.

Results

Our results demonstrated high levels of IGFBP2 mRNA and protein in EAC cell lines as compared to precancerous Barrett’s cell lines, and IGFBP2 is frequently overexpressed in EACs (31/57). Treatment of EAC cells with ABS, to mimic GERD conditions, induced high levels of IGFBP2 expression. Knocking down endogenous IGFBP2 in FLO1 cells (with constitutive high levels of IGFBP2) led to a significant increase in DNA double-strand breaks and apoptosis, following transient exposure to ABS. On the other hand, overexpression of exogenous IGFBP2 in OE33 cells (with low endogenous levels of IGFBP2) had a protective effect against ABS-induced double-strand breaks and apoptosis. We found that IGFBP2 is required for ABS-induced nuclear accumulation and phosphorylation of EGFR and DNA-PKcs, which are necessary for DNA damage repair activity. Using co-immunoprecipitation assay, we detected co-localization of IGFBP2 with EGFR and DNA-PKcs, following acidic bile salts treatment. We further demonstrated, using cycloheximide chase assay, that IGFBP2 promotes EGFR protein stability in response to ABS exposure.

Conclusions

IGFBP2 protects EAC cells against ABS-induced DNA damage and apoptosis through stabilization and activation of EGFR - DNA-PKcs signaling axis.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-1021-y) contains supplementary material, which is available to authorized users.

DNA-dependent protein kinase: Epigenetic alterations and the role in genomic stability of cancer

DNA-dependent protein kinase (DNA-PK), a member of phosphatidylinositol-kinase family, is a key protein in mammalian DNA double-strand break (DSB) repair that helps to maintain genomic integrity. DNA-PK also plays a central role in immune cell development and protects telomerase during cellular aging. Epigenetic deregulation due to endogenous and exogenous factors may affect the normal function of DNA-PK, which in turn could impair DNA repair and contribute to genomic instability. Recent studies implicate a role for epigenetics in the regulation of DNA-PK expression in normal and cancer cells, which may impact cancer progression and metastasis as well as provide opportunities for treatment and use of DNA-PK as a novel cancer biomarker. In addition, several small molecules and biological agents have been recently identified that can inhibit DNA-PK function or expression, and thus hold promise for cancer treatments. This review discusses the impact of epigenetic alterations and the expression of DNA-PK in relation to the DNA repair mechanisms with a focus on its differential levels in normal and cancer cells.

Nanostructure of DNA repair foci revealed by superresolution microscopy

Induction of DNA double-strand breaks (DSBs) by ionizing radiation leads to formation of micrometer-sized DNA-repair foci, whose organization on the nanometer-scale remains unknown because of the diffraction limit (∼200 nm) of conventional microscopy. Here, we applied diffraction-unlimited, direct stochastic optical-reconstruction microscopy ( dSTORM) with a lateral resolution of ∼20 nm to analyze the focal nanostructure of the DSB marker histone γH2AX and the DNA-repair protein kinase (DNA-PK) in irradiated glioblastoma multiforme cells. Although standard confocal microscopy revealed substantial colocalization of immunostained γH2AX and DNA-PK, in our dSTORM images, the 2 proteins showed very little (if any) colocalization despite their close spatial proximity. We also found that γH2AX foci consisted of distinct circular subunits ("nanofoci") with a diameter of ∼45 nm, whereas DNA-PK displayed a diffuse, intrafocal distribution. We conclude that γH2AX nanofoci represent the elementary, structural units of DSB repair foci, that is, individual γH2AX-containing nucleosomes. dSTORM-based γH2AX nanofoci counting and distance measurements between nanofoci provided quantitative information on the total amount of chromatin involved in DSB repair as well as on the number and longitudinal distribution of γH2AX-containing nucleosomes in a chromatin fiber. We thus estimate that a single focus involves between ∼0.6 and ∼1.1 Mbp of chromatin, depending on radiation treatment. Because of their ability to unravel the nanostructure of DSB-repair foci, dSTORM and related single-molecule localization nanoscopy methods will likely emerge as powerful tools in biology and medicine to elucidate the effects of DNA damaging agents in cells.-Sisario, D., Memmel, S., Doose, S., Neubauer, J., Zimmermann, H., Flentje, M., Djuzenova, C. S., Sauer, M., Sukhorukov, V. L. Nanostructure of DNA repair foci revealed by superresolution microscopy.