DNA-PKcs: A Multi-Faceted Player in DNA Damage Response

UBE2D3 facilitates NHEJ by orchestrating ATM signalling through multi-level control of RNF168

Maintenance of genome integrity requires tight control of DNA damage response (DDR) signalling and repair, with phosphorylation and ubiquitination representing key elements. How these events are coordinated to achieve productive DNA repair remains elusive. Here we identify the ubiquitin-conjugating enzyme UBE2D3 as a regulator of ATM kinase-induced DDR that promotes non-homologous end-joining (NHEJ) at telomeres. UBE2D3 contributes to DDR-induced chromatin ubiquitination and recruitment of the NHEJ-promoting factor 53BP1, both mediated by RNF168 upon ATM activation. Additionally, UBE2D3 promotes NHEJ by limiting RNF168 accumulation and facilitating ATM-mediated phosphorylation of KAP1-S824. Mechanistically, defective KAP1-S824 phosphorylation and telomeric NHEJ upon UBE2D3-deficiency are linked to RNF168 hyperaccumulation and aberrant PP2A phosphatase activity. Together, our results identify UBE2D3 as a multi-level regulator of NHEJ that orchestrates ATM and RNF168 activities. Moreover, they reveal a negative regulatory circuit in the DDR that is constrained by UBE2D3 and consists of RNF168- and phosphatase-mediated restriction of KAP1 phosphorylation.

BUB1 regulates non-homologous end joining pathway to mediate radioresistance in triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer subtype often treated with radiotherapy (RT). Due to its intrinsic heterogeneity and lack of effective targets, it is crucial to identify novel molecular targets that would increase RT efficacy. Here we demonstrate the role of BUB1 (cell cycle Ser/Thr kinase) in TNBC radioresistance and offer a novel strategy to improve TNBC treatment.

METHODS

Gene expression analysis was performed to look at genes upregulated in TNBC patient samples compared to other subtypes. Cell proliferation and clonogenic survivals assays determined the IC50 of BUB1 inhibitor (BAY1816032) and radiation enhancement ratio (rER) with pharmacologic and genomic BUB1 inhibition. Mammary fat pad xenografts experiments were performed in CB17/SCID. The mechanism through which BUB1 inhibitor sensitizes TNBC cells to radiotherapy was delineated by γ-H2AX foci assays, BLRR, Immunoblotting, qPCR, CHX chase, and cell fractionation assays.

RESULTS

BUB1 is overexpressed in BC and its expression is considerably elevated in TNBC with poor survival outcomes. Pharmacological or genomic ablation of BUB1 sensitized multiple TNBC cell lines to cell killing by radiation, although breast epithelial cells showed no radiosensitization with BUB1 inhibition. Kinase function of BUB1 is mainly accountable for this radiosensitization phenotype. BUB1 ablation also led to radiosensitization in TNBC tumor xenografts with significantly increased tumor growth delay and overall survival. Mechanistically, BUB1 ablation inhibited the repair of radiation-induced DNA double strand breaks (DSBs). BUB1 ablation stabilized phospho-DNAPKcs (S2056) following RT such that half-lives could not be estimated. In contrast, RT alone caused BUB1 stabilization, but pre-treatment with BUB1 inhibitor prevented stabilization (t1/2, ~8 h). Nuclear and chromatin-enriched fractionations illustrated an increase in recruitment of phospho- and total-DNAPK, and KAP1 to chromatin indicating that BUB1 is indispensable in the activation and recruitment of non-homologous end joining (NHEJ) proteins to DSBs. Additionally, BUB1 staining of TNBC tissue microarrays demonstrated significant correlation of BUB1 protein expression with tumor grade.

CONCLUSIONS

BUB1 ablation sensitizes TNBC cell lines and xenografts to RT and BUB1 mediated radiosensitization may occur through NHEJ. Together, these results highlight BUB1 as a novel molecular target for radiosensitization in women with TNBC.

GCN5 mediates DNA-PKcs crotonylation for DNA double-strand break repair and determining cancer radiosensitivity

BACKGROUND

DNA double-strand break (DSB) induction and repair are important events for determining cell survival and the outcome of cancer radiotherapy. The DNA-dependent protein kinase (DNA-PK) complex functions at the apex of DSBs repair, and its assembly and activity are strictly regulated by post-translation modifications (PTMs)-associated interactions. However, the PTMs of the catalytic subunit DNA-PKcs and how they affect DNA-PKcs's functions are not fully understood.

METHODS

Mass spectrometry analyses were performed to identify the crotonylation sites of DNA-PKcs in response to γ-ray irradiation. Co-immunoprecipitation (Co-IP), western blotting, in vitro crotonylation assays, laser microirradiation assays, in vitro DNA binding assays, in vitro DNA-PK assembly assays and IF assays were employed to confirm the crotonylation, identify the crotonylase and decrotonylase, and elucidate how crotonylation regulates the activity and function of DNA-PKcs. Subcutaneous xenografts of human HeLa GCN5 WT or HeLa GCN5 siRNA cells in BALB/c nude mice were generated and utilized to assess tumor proliferation in vivo after radiotherapy.

RESULTS

Here, we reveal that K525 is an important site of DNA-PKcs for crotonylation, and whose level is sharply increased by irradiation. The histone acetyltransferase GCN5 functions as the crotonylase for K525-Kcr, while HDAC3 serves as its dedicated decrotonylase. K525 crotonylation enhances DNA binding activity of DNA-PKcs, and facilitates assembly of the DNA-PK complex. Furthermore, GCN5-mediated K525 crotonylation is indispensable for DNA-PKcs autophosphorylation and the repair of double-strand breaks in the NHEJ pathway. GCN5 suppression significantly sensitizes xenograft tumors of mice to radiotherapy.

CONCLUSIONS

Our study defines K525 crotonylation of DNA-PKcs is important for the DNA-PK complex assembly and DSBs repair activity via NHEJ pathway. Targeting GCN5-mediated K525 Kcr of DNA-PKcs may be a promising therapeutic strategy for improving the outcome of cancer radiotherapy.

Post-translational modification-dependent oligomerization switch in regulation of global transcription and DNA damage repair during genotoxic stress

Mechanisms of functional cross-talk between global transcriptional repression and efficient DNA damage repair during genotoxic stress are poorly known. In this study, using human AF9 as representative of Super Elongation Complex (SEC) components, we delineate detailed mechanisms of these processes. Mechanistically, we describe that Poly-Serine domain-mediated oligomerization is pre-requisite for AF9 YEATS domain-mediated TFIID interaction-dependent SEC recruitment at the promoter-proximal region for release of paused RNA polymerase II. Interestingly, during genotoxic stress, CaMKII-mediated phosphorylation-dependent nuclear export of AF9-specific deacetylase HDAC5 enhances concomitant PCAF-mediated acetylation of K339 residue. This causes monomerization of AF9 and reduces TFIID interaction for transcriptional downregulation. Furthermore, the K339 acetylation-dependent enhanced AF9-DNA-PKc interaction leads to phosphorylation at S395 residue which reduces AF9-SEC interaction resulting in transcriptional downregulation and efficient repair of DNA damage. After repair, nuclear re-entry of HDAC5 reduces AF9 acetylation and restores its TFIID and SEC interaction to restart transcription.

The NDR family of kinases: essential regulators of aging

Aging is defined as a progressive decline of cognitive and physiological functions over lifetime. Since the definition of the nine hallmarks of aging in 2013 by López-Otin, numerous studies have attempted to identify the main regulators and contributors in the aging process. One interesting group of proteins whose participation has been implicated in several aging hallmarks are the nuclear DBF2-related (NDR) family of serine-threonine AGC kinases. They are one of the core components of the Hippo signaling pathway and include NDR1, NDR2, LATS1 and LATS2 in mammals, along with its highly conserved metazoan orthologs; Trc in Drosophila melanogaster, SAX-1 in Caenorhabditis elegans, CBK1, DBF20 in Saccharomyces cerevisiae and orb6 in Saccharomyces pombe. These kinases have been independently linked to the regulation of widely diverse cellular processes disrupted during aging such as the cell cycle progression, transcription, intercellular communication, nutrient homeostasis, autophagy, apoptosis, and stem cell differentiation. However, a comprehensive overview of the state-of-the-art knowledge regarding the post-translational modifications of and by NDR kinases in aging has not been conducted. In this review, we summarize the current understanding of the NDR family of kinases, focusing on their relevance to various aging hallmarks, and emphasize the growing body of evidence that suggests NDR kinases are essential regulators of aging across species.

BUB1 regulates non-homologous end joining pathway to mediate radioresistance in triple-negative breast cancer

Background

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer subtype often treated with radiotherapy (RT). Due to its intrinsic heterogeneity and lack of effective targets, it is crucial to identify novel molecular targets that would increase RT efficacy. Here we demonstrate the role of BUB1 (cell cycle Ser/Thr kinase) in TNBC radioresistance and offer a novel strategy to improve TNBC treatment.

Methods

Gene expression analysis was performed to look at genes upregulated in TNBC patient samples compared to other subtypes. Cell proliferation and clonogenic survivals assays determined the IC 50 of BUB1 inhibitor (BAY1816032) and radiation enhancement ratio (rER) with pharmacologic and genomic BUB1 inhibition. Mammary fat pad xenografts experiments were performed in CB17/SCID. The mechanism through which BUB1 inhibitor sensitizes TNBC cells to radiotherapy was delineated by γ-H2AX foci assays, BLRR, Immunoblotting, qPCR, CHX chase, and cell fractionation assays.

Results

BUB1 is overexpressed in BC and its expression is considerably elevated in TNBC with poor survival outcomes. Pharmacological or genomic ablation of BUB1 sensitized multiple TNBC cell lines to cell killing by radiation, although breast epithelial cells showed no radiosensitization with BUB1 inhibition. Kinase function of BUB1 is mainly accountable for this radiosensitization phenotype. BUB1 ablation also led to radiosensitization in TNBC tumor xenografts with significantly increased tumor growth delay and overall survival. Mechanistically, BUB1 ablation inhibited the repair of radiation-induced DNA double strand breaks (DSBs). BUB1 ablation stabilized phospho-DNAPKcs (S2056) following RT such that half-lives could not be estimated. In contrast, RT alone caused BUB1 stabilization, but pre-treatment with BUB1 inhibitor prevented stabilization (t 1/2 , ∼8 h). Nuclear and chromatin-enriched fractionations illustrated an increase in recruitment of phospho- and total-DNAPK, and KAP1 to chromatin indicating that BUB1 is indispensable in the activation and recruitment of non-homologous end joining (NHEJ) proteins to DSBs. Additionally, BUB1 staining of TNBC tissue microarrays demonstrated significant correlation of BUB1 protein expression with tumor grade.

Conclusions

BUB1 ablation sensitizes TNBC cell lines and xenografts to RT and BUB1 mediated radiosensitization may occur through NHEJ. Together, these results highlight BUB1 as a novel molecular target for radiosensitization in women with TNBC.

High-efficiency transgene integration by homology-directed repair in human primary cells using DNA-PKcs inhibition

Therapeutic applications of nuclease-based genome editing would benefit from improved methods for transgene integration via homology-directed repair (HDR). To improve HDR efficiency, we screened six small-molecule inhibitors of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a key protein in the alternative repair pathway of non-homologous end joining (NHEJ), which generates genomic insertions/deletions (INDELs). From this screen, we identified AZD7648 as the most potent compound. The use of AZD7648 significantly increased HDR (up to 50-fold) and concomitantly decreased INDELs across different genomic loci in various therapeutically relevant primary human cell types. In all cases, the ratio of HDR to INDELs markedly increased, and, in certain situations, INDEL-free high-frequency (>50%) targeted integration was achieved. This approach has the potential to improve the therapeutic efficacy of cell-based therapies and broaden the use of targeted integration as a research tool.

Inactivation of VRK1 sensitizes ovarian cancer to PARP inhibition through regulating DNA-PK stability

Ovarian cancer is the leading cause of gynecologic cancer death. Among the most innovative anti-cancer approaches, the genetic concept of synthetic lethality is that mutations in multiple genes work synergistically to effect cell death. Previous studies found that although vaccinia-related kinase-1 (VRK1) associates with DNA damage repair proteins, its underlying mechanisms remain unclear. Here, we found high VRK1 expression in ovarian tumors, and that VRK1 depletion can significantly promote apoptosis and cell cycle arrest. The effect of VRK1 knockdown on apoptosis was manifested by increased DNA damage, genomic instability, and apoptosis, and also blocked non-homologous end joining (NHEJ) by destabilizing DNA-PK. Further, we verified that VRK1 depletion enhanced sensitivity to a PARP inhibitor (PARPi), olaparib, promoting apoptosis through DNA damage, especially in ovarian cancer cell lines with high VRK1 expression. Proteins implicated in DNA damage responses are suitable targets for the development of new anti-cancer therapeutic strategies, and their combination could represent an alternative form of synthetic lethality. Therefore, normal protective DNA damage responses are impaired by combining olaparib with elimination of VRK1 and could be used to reduce drug dose and its associated toxicity. In summary, VRK1 represents both a potential biomarker for PARPi sensitivity, and a new DDR-associated therapeutic target, in ovarian cancer.

Therapeutic Targeting of DNA Repair Pathways in Pediatric Extracranial Solid Tumors: Current State and Implications for Immunotherapy

DNA damage is fundamental to tumorigenesis, and the inability to repair DNA damage is a hallmark of many human cancers. DNA is repaired via the DNA damage repair (DDR) apparatus, which includes five major pathways. DDR deficiencies in cancers give rise to potential therapeutic targets, as cancers harboring DDR deficiencies become increasingly dependent on alternative DDR pathways for survival. In this review, we summarize the DDR apparatus, and examine the current state of research efforts focused on identifying vulnerabilities in DDR pathways that can be therapeutically exploited in pediatric extracranial solid tumors. We assess the potential for synergistic combinations of different DDR inhibitors as well as combinations of DDR inhibitors with chemotherapy. Lastly, we discuss the immunomodulatory implications of targeting DDR pathways and the potential for using DDR inhibitors to enhance tumor immunogenicity, with the goal of improving the response to immune checkpoint blockade in pediatric solid tumors. We review the ongoing and future research into DDR in pediatric tumors and the subsequent pediatric clinical trials that will be critical to further elucidate the efficacy of the approaches targeting DDR.

DNA-PK and ATM drive phosphorylation signatures that antagonistically regulate cytokine responses to herpesvirus infection or DNA damage

The DNA-dependent protein kinase, DNA-PK, is an essential regulator of DNA damage repair. DNA-PK-driven phosphorylation events and the activated DNA damage response (DDR) pathways are also components of antiviral intrinsic and innate immune responses. Yet, it is not clear whether and how the DNA-PK response differs between these two forms of nucleic acid stress-DNA damage and DNA virus infection. Here, we define DNA-PK substrates and the signature cellular phosphoproteome response to DNA damage or infection with the nuclear-replicating DNA herpesvirus, HSV-1. We establish that DNA-PK negatively regulates the ataxia-telangiectasia-mutated (ATM) DDR kinase during viral infection. In turn, ATM blocks the binding of DNA-PK and the nuclear DNA sensor IFI16 to viral DNA, thereby inhibiting cytokine responses. However, following DNA damage, DNA-PK enhances ATM activity, which is required for IFN-β expression. These findings demonstrate that the DDR autoregulates cytokine expression through the opposing modulation of DDR kinases.

Functional screening in human HSPCs identifies optimized protein-based enhancers of Homology Directed Repair

Homology Directed Repair (HDR) enables precise genome editing, but the implementation of HDR-based therapies is hindered by limited efficiency in comparison to methods that exploit alternative DNA repair routes, such as Non-Homologous End Joining (NHEJ). In this study, we develop a functional, pooled screening platform to identify protein-based reagents that improve HDR in human hematopoietic stem and progenitor cells (HSPCs). We leverage this screening platform to explore sequence diversity at the binding interface of the NHEJ inhibitor i53 and its target, 53BP1, identifying optimized variants that enable new intermolecular bonds and robustly increase HDR. We show that these variants specifically reduce insertion-deletion outcomes without increasing off-target editing, synergize with a DNAPK inhibitor molecule, and can be applied at manufacturing scale to increase the fraction of cells bearing repaired alleles. This screening platform can enable the discovery of future gene editing reagents that improve HDR outcomes.

Regulation of ferroptosis by PI3K/Akt signaling pathway: a promising therapeutic axis in cancer

The global challenge posed by cancer, marked by rising incidence and mortality rates, underscores the urgency for innovative therapeutic approaches. The PI3K/Akt signaling pathway, frequently amplified in various cancers, is central in regulating essential cellular processes. Its dysregulation, often stemming from genetic mutations, significantly contributes to cancer initiation, progression, and resistance to therapy. Concurrently, ferroptosis, a recently discovered form of regulated cell death characterized by iron-dependent processes and lipid reactive oxygen species buildup, holds implications for diseases, including cancer. Exploring the interplay between the dysregulated PI3K/Akt pathway and ferroptosis unveils potential insights into the molecular mechanisms driving or inhibiting ferroptotic processes in cancer cells. Evidence suggests that inhibiting the PI3K/Akt pathway may sensitize cancer cells to ferroptosis induction, offering a promising strategy to overcome drug resistance. This review aims to provide a comprehensive exploration of this interplay, shedding light on the potential for disrupting the PI3K/Akt pathway to enhance ferroptosis as an alternative route for inducing cell death and improving cancer treatment outcomes.

Trypanosoma cruzi infection induces DNA double-strand breaks and activates DNA damage response pathway in host epithelial cells

Trypanosoma cruzi, the etiological agent of Chagas disease, invades many cell types affecting numerous host-signalling pathways. During the T. cruzi infection, we demonstrated modulations in the host RNA polymerase II activity with the downregulation of ribonucleoproteins affecting host transcription and splicing machinery. These alterations could be a result of the initial damage to the host DNA caused by the presence of the parasite, however, the mechanisms are not well understood. Herein, we examined whether infection by T. cruzi coincided with enhanced DNA damage in the host cell. We studied the engagement of the DNA damage response (DDR) pathways at the different time points (0-24 h post-infection, hpi) by T. cruzi in LLC-MK2 cells. In response to double-strand breaks (DSB), maximum phosphorylation of the histone variant H2AX is observed at 2hpi and promotes recruitment of the DDR p53-binding protein (53BP1). During T. cruzi infection, Ataxia-telangiectasia mutated protein (ATM) and DNA-PK protein kinases remained active in a time-dependent manner and played roles in regulating the host response to DSB. The host DNA lesions caused by the infection are likely orchestrated by the non-homologous end joining (NHEJ) pathway to maintain the host genome integrity.

Transplantation of Neural Stem Cells-Overexpressed Ku70 Improves Neurological Deficits in a Mice Model of Cerebral Ischemia Stroke

Cerebral ischemic stroke is a cerebrovascular disease, which is related to DNA damage. Many researches have shown that Ku70 is a key regulator for DNA damage. Here, we aimed to explore Ku70 roles in cerebral ischemic stroke and its potential molecular mechanism. In our study, neural stem cells (NSCs) were induced by oxygen-glucose deprivation/reoxygenation (OGD/R) for constructing cerebral ischemic stroke cell model. CCK8 assay, Brdu/GFP staining, flow cytometry and TUNEL staining were performed to examine cell proliferation, cell cycle and apoptosis, respectively. Relative mRNA and protein levels were detected by quantitative real-time PCR and western blot analysis, respectively. Ku70 positive cells were examined by immunofluorescence staining. Comet assay was employed to determine DNA damage. Animal experiments were performed to assess the effect of transplanting NSCs and Ku70-overexpressed NSCs on neurological deficits, infarct volume, brain edema and blood‒brain barrier (BBB) integrity in middle cerebral artery occlusion (MCAO) model. Our data found that Ku70 expression was decreased in NSCs after OGD/R. Overexpression of Ku70 reduced DNA damage and apoptosis of OGD/R-induced NSCs. Knockdown of Ku70 promoted the activity of ATM/p53. Moreover, KU60019 (ATM-specific inhibitor) reversed the promoting effects of Ku70 silencing on DNA damage and apoptosis in OGD/R-induced NSCs. In animal experiments, transplantation of NSCs-overexpressed Ku70 enhanced cell survival, improved motor function, reduced infarct volume, relieved brain edema and alleviated BBB dysfunction in MCAO mice models. In conclusion, Ku70 overexpression repressed the DNA damage and apoptosis in OGD/R-induced NSCs by regulating ATM/p53 pathway, and transplantation of NSCs-overexpressed Ku70 played neuroprotective effects in MCAO mice models.

The crosstalk between telomeres and DNA repair mechanisms: an overview to mammalian somatic cells, germ cells, and preimplantation embryos

Telomeres are located at the ends of linear chromosomes and play a critical role in maintaining genomic stability by preventing premature activation of DNA repair mechanisms. Because of exposure to various genotoxic agents, telomeres can undergo shortening and genetic changes. In mammalian cells, the basic DNA repair mechanisms, including base excision repair, nucleotide excision repair, double-strand break repair, and mismatch repair, function in repairing potential damages in telomeres. If these damages are not repaired correctly in time, the unfavorable results such as apoptosis, cell cycle arrest, and cancerous transition may occur. During lifespan, mammalian somatic cells, male and female germ cells, and preimplantation embryos experience a number of telomeric damages. Herein, we comprehensively reviewed the crosstalk between telomeres and the DNA repair mechanisms in the somatic cells, germ cells, and embryos. Infertility development resulting from possible defects in this crosstalk is also discussed in the light of existing studies.

New Discoveries on Protein Recruitment and Regulation during the Early Stages of the DNA Damage Response Pathways

Maintaining genomic stability and properly repairing damaged DNA is essential to staying healthy and preserving cellular homeostasis. The five major pathways involved in repairing eukaryotic DNA include base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), non-homologous end joining (NHEJ), and homologous recombination (HR). When these pathways do not properly repair damaged DNA, genomic stability is compromised and can contribute to diseases such as cancer. It is essential that the causes of DNA damage and the consequent repair pathways are fully understood, yet the initial recruitment and regulation of DNA damage response proteins remains unclear. In this review, the causes of DNA damage, the various mechanisms of DNA damage repair, and the current research regarding the early steps of each major pathway were investigated.

Advances in DNA damage response inhibitors in colorectal cancer therapy

One potential cause of cancer is genomic instability that arises in normal cells due to years of DNA damage in the body. The clinical application of radiotherapy and cytotoxic drugs to treat cancer is based on the principle of damaging the DNA of cancer cells. However, the benefits of these treatments also have negative effects on normal tissue. While there have been notable advancements in molecular-driven therapy and immunotherapy for colorectal cancer (CRC), a considerable portion of patients with advanced CRC do not experience any benefits from these treatments, leading to a poor prognosis. In recent years, targeted therapy aimed at suppressing the DNA damage response (DDR) in cancer cells has emerged as a potential treatment option for CRC patients, offering them more choices for treatment. Currently, the integration of DDR and clinical intervention remains in the exploratory phase. This review primarily elucidates the fundamental principles of DDR inhibitors, provides an overview of their current clinical application status in CRC, and discusses the advancements as well as limitations observed in relevant studies.

Phase 1b study of enzalutamide plus CC-115, a dual mTORC1/2 and DNA-PK inhibitor, in men with metastatic castration-resistant prostate cancer (mCRPC)

BACKGROUND

CC-115, a dual mTORC1/2 and DNA-PK inhibitor, has promising antitumour activity when combined with androgen receptor (AR) inhibition in pre-clinical models.

METHODS

Phase 1b multicentre trial evaluating enzalutamide with escalating doses of CC-115 in AR inhibitor-naive mCRPC patients (n = 41). Primary endpoints were safety and RP2D. Secondary endpoints included PSA response, time-to-PSA progression, and radiographic progression.

RESULTS

Common adverse effects included rash (31.7% Grades 1-2 (Gr); 31.7% Gr 3), pruritis (43.9% Gr 1-2), diarrhoea (37% Gr 1-2), and hypertension (17% Gr 1-2; 9.8% Gr 3). CC-115 RP2D was 5 mg twice a day. In 40 evaluable patients, 80% achieved ≥50% reduction in PSA (PSA50), and 58% achieved ≥90% reduction in PSA (PSA90) by 12 weeks. Median time-to-PSA progression was 14.7 months and median rPFS was 22.1 months. Stratification by PI3K alterations demonstrated a non-statistically significant trend towards improved PSA50 response (PSA50 of 94% vs. 67%, p = 0.08). Exploratory pre-clinical analysis suggested CC-115 inhibited mTOR pathway strongly, but may be insufficient to inhibit DNA-PK at RP2D.

CONCLUSIONS

The combination of enzalutamide and CC-115 was well tolerated. A non-statistically significant trend towards improved PSA response was observed in patients harbouring PI3K pathway alterations, suggesting potential predictive biomarkers of response to a PI3K/AKT/mTOR pathway inhibitor.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02833883.

FAM21 interacts with Ku to promote the localization of WASH to DNA double strand break sites

Cytoplasmic FAM21 works as a guiding protein in Wiskott-Aldrich Syndrome Protein and SCAR Homolog (WASH) complex by linking WASH complex to endosomes through its interaction with retromer. Recently, we have reported that nuclear WASH localizes to DNA double strand break (DSB) sites to promote DNA repair through non-homologous end-joining (NHEJ). However, whether FAM21, the close partner of WASH, is involved in the nuclear WASH localization and DNA repair remains to be clarified. Here, we show that FAM21 interacts with Ku and the interaction between C-terminal FAM21 and Ku is essential for its recruitment to DSB sites. Moreover, FAM21 depletion led to decreases in WASH recruitment to damaged DNA and repair capacity upon DNA damage. Taken together, these results reveal that FAM21 promotes DNA repair by orchestrating the recruitment of WASH to DSB sites, providing a mechanistic insight into WASH-dependent DNA DSB repair.

Inhibitors of phosphoinositide 3-kinase (PI3K) and phosphoinositide 3-kinase-related protein kinase family (PIKK)

Phosphoinositide 3-kinases (PI3K) and phosphoinositide 3-kinase-related protein kinases (PIKK) are two structurally related families of kinases that play vital roles in cell growth and DNA damage repair. Dysfunction of PIKK members and aberrant stimulation of the PI3K/AKT/mTOR signalling pathway are linked to a plethora of diseases including cancer. In recent decades, numerous inhibitors related to the PI3K/AKT/mTOR signalling have made great strides in cancer treatment, like copanlisib and sirolimus. Notably, most of the PIKK inhibitors (such as VX-970 and M3814) related to DNA damage response have also shown good efficacy in clinical trials. However, these drugs still require a suitable combination therapy to overcome drug resistance or improve antitumor activity. Based on the aforementioned facts, we summarised the efficacy of PIKK, PI3K, and AKT inhibitors in the therapy of human malignancies and the resistance mechanisms of targeted therapy, in order to provide deeper insights into cancer treatment.

Synergistic cytotoxicity of fludarabine, clofarabine, busulfan, vorinostat and olaparib in AML cells

Combinations of nucleoside analog(s) and DNA alkylating agent(s) are used for cancer treatment as components of pre-transplant regimens used in hematopoietic stem cell transplantation. Their efficacies are enhanced by combining drugs with different mechanisms of action, which also allows a reduction in the individual drug dosages and thus potentially in toxicity to the patient. We hypothesized that addition of SAHA and olaparib, an HDAC- and a PARP-inhibitor, respectively, to the established combination of fludarabine, clofarabine and busulfan would enhance AML cell cytotoxicity. Exposure of the AML cell lines KBM3/Bu2506, MV4-11, MOLM14 and OCI-AML3 to the 5-drug combination resulted in synergistic cytotoxicity with combination indexes < 1. Increased protein acetylation and decreased poly(ADP-ribosyl)ation were observed, as expected. Activation of apoptosis was suggested by cleavage of Caspase 3 and PARP1, DNA fragmentation, increased reactive oxygen species, and decreased mitochondrial membrane potential. The reduction in poly(ADP-ribosyl)ation was independent of caspase activation. Several proteins involved in DNA damage response and repair were downregulated, which may be contributing factors for the observed synergism. The increased phosphorylation of DNAPKcs suggests inhibition of its kinase activity and diminution of its role in DNA repair. A similar synergism was observed in patient-derived cell samples. These findings will be important in designing clinical trials using these drug combinations as pre-transplant conditioning regimens for AML patients.

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) drives angiotensin II-induced vascular remodeling through regulating mitochondrial fragmentation

BACKGROUND

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a novel instigator for mitochondrial dysfunction, and plays an important role in the pathogenesis of cardiovascular diseases. However, the role and mechanism of DNA-PKcs in angiotensin II (Ang II)-induced vascular remodeling remains obscure.

METHODS

Rat aortic smooth muscle cells (SMC) and VSMC-specific DNA-PKcs knockout (DNA-PKcsΔVSMC) mice were employed to examine the role of DNA-PKcs in vascular remodeling and the underlying mechanisms. Blood pressure of mice was monitored using the tail-cuff and telemetry methods. The role of DNA-PKcs in vascular function was evaluated using vascular relaxation assessment.

RESULTS

In the tunica media of remodeled mouse thoracic aortas, and renal arteries from hypertensive patients, elevated DNA-PKcs expression was observed along with its cytoplasmic translocation from nucleus, suggesting a role for DNA-PKcs in vascular remodeling. We then infused wild-type (DNA-PKcsfl/fl) and DNA-PKcsΔVSMC mice with Ang II for 14 days to establish vascular remodeling, and demonstrated that DNA-PKcsΔVSMC mice displayed attenuated vascular remodeling through inhibition of dedifferentiation of VSMCs. Moreover, deletion of DNA-PKcs in VSMCs alleviated Ang II-induced vasodilation dysfunction and hypertension. Mechanistic investigations denoted that Ang II-evoked rises in cytoplasmic DNA-PKcs interacted with dynamin-related protein 1 (Drp1) at its TQ motif to phosphorylate Drp1S616, subsequently promoting mitochondrial fragmentation and dysfunction, as well as reactive oxygen species (ROS) production. Treatment of irbesartan, an Ang II type 1 receptor (AT1R) blocker, downregulated DNA-PKcs expression in VSMCs and aortic tissues following Ang II administration.

CONCLUSION

Our data revealed that cytoplasmic DNA-PKcs in VSMCs accelerated Ang II-induced vascular remodeling by interacting with Drp1 at its TQ motif and phosphorylating Drp1S616 to provoke mitochondrial fragmentation. Maneuvers targeting DNA-PKcs might be a valuable therapeutic option for the treatment of vascular remodeling and hypertension.

Design and Synthesis of Ketenimine Sulfonamide Conjugates through Multicomponent Reactions; A Combined Cytotoxic Analysis and Computational Exploration

Multicomponent reactions involving zwitterion generated from dimethyl acetylenedicarboxylate, aryl sulfonamide, and isocyanide to generate sulfonamide-conjugated ketenimines is reported. The synthetic strategy adopted is highly atom economical and stereoselective. Ketenimine sulfonamide analogues are key intermediates for further synthetic conversions to generate a combinatorial library of compounds. Furthermore, sulfonamide compounds are known to possess a broad spectrum of biological applications. All the novel molecules synthesized exhibit the potential to target the nonhomologous DNA end-joining (NHEJ) pathway with cytotoxic ability. Computational studies compliment the in vitro biological assays of the 8 small-molecule inhibitors. DNA double-strand breaks (DSBs) are considered as the most lethal among different DNA damages. NHEJ repairs about 70% of the DSBs generated in cells within mammals. The DNA-dependent protein kinase catalytic subunit is one of the PI3 kinases associated with NHEJ. Compounds DK01-DK08 were investigated for their ability to induce cancer cell death by treating with two leukemic cell lines where NHEJ is high. Results showed that bromoaryl (DK04)- and nitroaryl (DK05)-conjugated molecules showed excellent biological activity, having IC50 values of ∼2 μM in Nalm6 cell lines.

Structure and mechanism in non-homologous end joining

DNA double-stranded breaks (DSBs) are a particularly challenging form of DNA damage to repair because the damaged DNA must not only undergo the chemical reactions responsible for returning it to its original state, but, additionally, the two free ends can become physically separated in the nucleus and must be bridged prior to repair. In nonhomologous end joining (NHEJ), one of the major pathways of DSB repair, repair is carried out by a number of repair factors capable of binding to and directly joining DNA ends. It has been unclear how these processes are carried out at a molecular level, owing in part to the lack of structural evidence describing the coordination of the NHEJ factors with each other and a DNA substrate. Advances in cryo-Electron Microscopy (cryo-EM), allowing for the structural characterization of large protein complexes that would be intractable using other techniques, have led to the visualization several key steps of the NHEJ process, which support a model of sequential assembly of repair factors at the DSB, followed by end-bridging mediated by protein-protein complexes and transition to full synapsis. Here we examine the structural evidence for these models, devoting particular attention to recent work identifying a new NHEJ intermediate state and incorporating new NHEJ factors into the general mechanism. We also discuss the evolving understanding of end-bridging mechanisms in NHEJ and DNA-PKcs's role in mediating DSB repair.

Structure and function of the apical PIKKs in double-strand break repair

Members of the phosphatidylinositol 3' kinase (PI3K)-related kinases (PIKKs) family, including DNA-dependent protein kinase catalytic subunit (DNA-PKcs), ataxia telangiectasia mutated (ATM), ataxia-telangiectasia mutated and Rad3-related (ATR), mammalian target of rapamycin (mTOR), suppressor with morphological effect on genitalia 1 (SMG1), and transformation/transcription domain-associated protein 1 (TRRAP/Tra1), participate in a variety of physiological processes, such as cell-cycle control, metabolism, transcription, replication, and the DNA damage response. In eukaryotic cells, DNA-PKcs, ATM, and ATR-ATRIP are the main sensors and regulators of DNA double-strand break repair. The purpose of this review is to describe recent structures of DNA-PKcs, ATM, and ATR, as well as their functions in activation and phosphorylation in different DNA repair pathways.

A new wave of innovations within the DNA damage response

Genome instability has been identified as one of the enabling hallmarks in cancer. DNA damage response (DDR) network is responsible for maintenance of genome integrity in cells. As cancer cells frequently carry DDR gene deficiencies or suffer from replicative stress, targeting DDR processes could induce excessive DNA damages (or unrepaired DNA) that eventually lead to cell death. Poly (ADP-ribose) polymerase (PARP) inhibitors have brought impressive benefit to patients with breast cancer gene (BRCA) mutation or homologous recombination deficiency (HRD), which proves the concept of synthetic lethality in cancer treatment. Moreover, the other two scenarios of DDR inhibitor application, replication stress and combination with chemo- or radio- therapy, are under active clinical exploration. In this review, we revisited the progress of DDR targeting therapy beyond the launched first-generation PARP inhibitors. Next generation PARP1 selective inhibitors, which could maintain the efficacy while mitigating side effects, may diversify the application scenarios of PARP inhibitor in clinic. Albeit with unavoidable on-mechanism toxicities, several small molecules targeting DNA damage checkpoints (gatekeepers) have shown great promise in preliminary clinical results, which may warrant further evaluations. In addition, inhibitors for other DNA repair pathways (caretakers) are also under active preclinical or clinical development. With these progresses and efforts, we envision that a new wave of innovations within DDR has come of age.

Review of possible mechanisms of radiotherapy resistance in cervical cancer

Radiotherapy is one of the main treatments for cervical cancer. Early cervical cancer is usually considered postoperative radiotherapy alone. Radiotherapy combined with cisplatin is the standard treatment for locally advanced cervical cancer (LACC), but sometimes the disease will relapse within a short time after the end of treatment. Tumor recurrence is usually related to the inherent radiation resistance of the tumor, mainly involving cell proliferation, apoptosis, DNA repair, tumor microenvironment, tumor metabolism, and stem cells. In the past few decades, the mechanism of radiotherapy resistance of cervical cancer has been extensively studied, but due to its complex process, the specific mechanism of radiotherapy resistance of cervical cancer is still not fully understood. In this review, we discuss the current status of radiotherapy resistance in cervical cancer and the possible mechanisms of radiotherapy resistance, and provide favorable therapeutic targets for improving radiotherapy sensitivity. In conclusion, this article describes the importance of understanding the pathway and target of radioresistance for cervical cancer to promote the development of effective radiotherapy sensitizers.

Aloe-Emodin Overcomes Anti-Cancer Drug Resistance to Temozolomide and Prevents Colony Formation and Migration in Primary Human Glioblastoma Cell Lines NULU and ZAR

Glioblastoma, the most dangerous and aggressive type of CNS tumor, appears resistant to many chemotherapy drugs. In the patient-derived glioma cell lines NULU and ZAR, which exhibit drug-resistant phenotypes, we investigated the effect of combined AE (Aloe-emodin) and TMZ (temozolomide) and found a significant additive inhibitory effect on cell growth and a promising cytotoxic effect on both cell lines compared to treatment with single agents. We also examined the effect of combined AE and TMZ treatment on the drug-resistance protein MGMT. The results suggest that using AE combined with traditional drugs restores drug resistance in both primary resistant cell lines (NULU and ZAR). Furthermore, migration assays and scratch tests showed that the combined use of AE and TMZ can slow down the colony formation and migration of glioblastoma cells. These convincing results suggest that AE could be a natural adjuvant agent to potentiate the effects of traditional drugs (TMZ) and overcome drug resistance in glioblastoma cells.

Advances in radiotherapy and immunity in hepatocellular carcinoma

Primary liver cancer is one of the most common malignant tumours worldwide; it caused approximately 830,000 deaths in 2020. Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer, accounting for over 80% of all cases. Various methods, including surgery, chemotherapy, radiotherapy, and radiofrequency ablation, have been widely used in the treatment of HCC. With the advancement of technology, radiotherapy has become increasingly important in the comprehensive treatment of HCC. However, due to the insufficient sensitivity of tumour cells to radiation, there are still multiple limitation in clinical application of radiotherapy. In recent years, the role of immunotherapy in cancer has been increasingly revealed, and more researchers have turned their attention to the combined application of immunotherapy and radiotherapy in the hope of achieving better treatment outcomes. This article reviews the progress on radiation therapy in HCC and the current status of its combined application with immunotherapy, and discusses the prospects and value of radioimmunotherapy in HCC.

Cross-talk between DNA damage response and the central carbon metabolic network underlies selective vulnerability of Purkinje neurons in ataxia-telangiectasia

Cerebellar ataxia is often the first and irreversible outcome in the disease of ataxia-telangiectasia (A-T), as a consequence of selective cerebellar Purkinje neuronal degeneration. A-T is an autosomal recessive disorder resulting from the loss-of-function mutations of the ataxia-telangiectasia-mutated ATM gene. Over years of research, it now becomes clear that functional ATM-a serine/threonine kinase protein product of the ATM gene-plays critical roles in regulating both cellular DNA damage response and central carbon metabolic network in multiple subcellular locations. The key question arises is how cerebellar Purkinje neurons become selectively vulnerable when all other cell types in the brain are suffering from the very same defects in ATM function. This review intended to comprehensively elaborate the unexpected linkages between these two seemingly independent cellular functions and the regulatory roles of ATM involved, their integrated impacts on both physical and functional properties, hence the introduction of selective vulnerability to Purkinje neurons in the disease will be addressed.

DNA-PKcs regulates myogenesis in an Akt-dependent manner independent of induced DNA damage

Skeletal muscle regeneration relies on muscle stem (satellite) cells. We previously demonstrated that satellite cells efficiently and accurately repair radiation-induced DNA double-strand breaks (DSBs) via the DNA-dependent kinase DNA-PKcs. We show here that DNA-PKcs affects myogenesis independently of its role in DSB repair. Consequently, this process does not require the accumulation of DSBs and it is also independent of caspase-induced DNA damage. We report that in myogenic cells DNA-PKcs is essential for the expression of the differentiation factor Myogenin in an Akt2-dependent manner. DNA-PKcs interacts with the p300-containing complex that activates Myogenin transcription. We show also that SCID mice that are deficient in DNA-PKcs, and are used for transplantation and muscle regeneration studies, display altered myofiber composition and delayed myogenesis upon injury. These defects are exacerbated after repeated injury/regeneration events resulting in reduced muscle size. We thus identify a novel, caspase-independent, regulation of myogenic differentiation, and define a differentiation phase that does not involve the DNA damage/repair process.

RUNX3 regulates the susceptibility against EGFR-targeted non-small cell lung cancer therapy using 47Sc-conjugated cetuximab

BACKGROUND

Radioimmunotherapy with cetuximab and conjugates with various radioisotopes is a feasible treatment option for different tumor models. Scandium-47 (⁴⁷Sc), one of several β^--particle-emitting radioisotopes, displays favorable physical and chemical properties for conjugation to monoclonal antibodies. However, the therapeutic efficacy of ⁴⁷Sc in preclinical and clinical studies is largely unknown. Given that intrinsic alterations in tumors greatly contribute to resistance to anti-epidermal growth factor receptor (EGFR)-targeted therapy, research on overcoming resistance to radioimmunotherapy using cetuximab is required.

METHODS

⁴⁷Sc was produced by irradiation of a CaCO₃ target at the HANARO research reactor in KAERI (Korea Atomic Energy Research Institute) and prepared by chromatographic separation of the irradiated target. Cetuximab was conjugated with ⁴⁷Sc using the bifunctional chelating agent DTPA. Radiochemical purity was determined using instant thin-layer chromatography. The immunoreactivity of ⁴⁷Sc-DTPA-cetuximab was evaluated using the Lindmo method and an in vitro cell-binding assay. The inhibitory effects of cetuximab and ⁴⁷Sc-DTPA-cetuximab were confirmed using cell growth inhibition and BrdU cell proliferation assays. Differences in protein expression levels between cetuximab- and ⁴⁷Sc-DTPA-cetuximab-treated cells were confirmed using western blotting. Complex formation between RUNX3 and DNA repair components was confirmed using immunoprecipitation and western blotting.

RESULTS

Cetuximab induces cell cycle arrest and cell death in EGFR-overexpressing NSCLC cells. Radiolabeling of cetuximab with ⁴⁷Sc led to increased therapeutic efficacy relative to cetuximab alone. Application of ⁴⁷Sc-DTPA-cetuximab induced DNA damage responses, and activation of RUNX3 significantly enhanced the therapeutic efficacy of ⁴⁷Sc-DTPA-cetuximab. RUNX3 mediated susceptibility to EGFR-targeted NSCLC therapy using ⁴⁷Sc-DTPA-cetuximab via interaction with components of the DNA damage and repair machinery.

CONCLUSIONS

⁴⁷Sc-DTPA-cetuximab promoted cell death in EGFR-overexpressing NSCLC cells by targeting EGFR and inducing DNA damage as a result of β irradiation emitted from the conjugated ⁴⁷Sc. Activation of RUNX3 played a key role in DNA damage and repair processes in response to the ionizing radiation and inhibited cell growth, thus leading to more effective tumor suppression. RUNX3 can potentially moderate susceptibility to ⁴⁷Sc-conjugated cetuximab by modulating DNA damage and repair process mechanisms.

ARIH1 activates STING-mediated T-cell activation and sensitizes tumors to immune checkpoint blockade

Despite advances in cancer treatment, immune checkpoint blockade (ICB) only achieves complete response in some patients, illustrating the need to identify resistance mechanisms. Using an ICB-insensitive tumor model, here we discover cisplatin enhances the anti-tumor effect of PD-L1 blockade and upregulates the expression of Ariadne RBR E3 ubiquitin-protein ligase 1 (ARIH1) in tumors. Arih1 overexpression promotes cytotoxic T cell infiltration, inhibits tumor growth, and potentiates PD-L1 blockade. ARIH1 mediates ubiquitination and degradation of DNA-PKcs to trigger activation of the STING pathway, which is blocked by the phospho-mimetic mutant T68E/S213D of cGAS protein. Using a high-throughput drug screen, we further identify that ACY738, less cytotoxic than cisplatin, effectively upregulates ARIH1 and activates STING signaling, sensitizing tumors to PD-L1 blockade. Our findings delineate a mechanism that tumors mediate ICB resistance through the loss of ARIH1 and ARIH1-DNA-PKcs-STING signaling and indicate that activating ARIH1 is an effective strategy to improve the efficacy of cancer immunotherapy.

CRISPR/Cas9 as a therapeutic tool for triple negative breast cancer: from bench to clinics

Clustered regularly interspaced short palindromic repeats (CRISPR) is a third-generation genome editing method that has revolutionized the world with its high throughput results. It has been used in the treatment of various biological diseases and infections. Various bacteria and other prokaryotes such as archaea also have CRISPR/Cas9 systems to guard themselves against bacteriophage. Reportedly, CRISPR/Cas9-based strategy may inhibit the growth and development of triple-negative breast cancer (TNBC) via targeting the potentially altered resistance genes, transcription, and epigenetic regulation. These therapeutic activities could help with the complex issues such as drug resistance which is observed even in TNBC. Currently, various methods have been utilized for the delivery of CRISPR/Cas9 into the targeted cell such as physical (microinjection, electroporation, and hydrodynamic mode), viral (adeno-associated virus and lentivirus), and non-viral (liposomes and lipid nano-particles). Although different models have been developed to investigate the molecular causes of TNBC, but the lack of sensitive and targeted delivery methods for in-vivo genome editing tools limits their clinical application. Therefore, based on the available evidences, this review comprehensively highlighted the advancement, challenges limitations, and prospects of CRISPR/Cas9 for the treatment of TNBC. We also underscored how integrating artificial intelligence and machine learning could improve CRISPR/Cas9 strategies in TNBC therapy.

Harnessing the cooperation between DNA-PK and cGAS in cancer therapies: The cooperation between DNA-PK and cGAS shapes tumour immunogenicity

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is central for the initiation of anti-tumoural immune responses. Enormous effort has been made to optimise the design and administration of STING agonists to stimulate tumour immunogenicity. However, in certain contexts the cGAS-STING axis fuels tumourigenesis. Here, we review recent findings on the regulation of cGAS expression and activity. We particularly focus our attention on the DNA-dependent protein kinase (DNA-PK) complex, that recently emerged as an activator of inflammatory responses in tumour cells. We propose that stratification analyses on cGAS and DNA-PK expression/activation status should be carried out to predict treatment efficacy. We herein also provide insights into non-canonical functions borne by cGAS and cGAMP, highlighting how they may influence tumourigenesis. All these parameters should be taken into consideration concertedly to choose strategies aiming to effectively boost tumour immunogenicity.

Molecular portraits of cell cycle checkpoint kinases in cancer evolution, progression, and treatment responsiveness

Cell cycle dysregulation is prerequisite for cancer formation. However, it is unknown whether the mode of dysregulation affects disease characteristics. Here, we conduct comprehensive analyses of cell cycle checkpoint dysregulation using patient data and experimental investigations. We find that ATM mutation predisposes the diagnosis of primary estrogen receptor (ER)+/human epidermal growth factor (HER)2- cancer in older women. Conversely, CHK2 dysregulation induces formation of metastatic, premenopausal ER+/HER2- breast cancer (P = 0.001) that is treatment-resistant (HR = 6.15, P = 0.01). Lastly, while mutations in ATR alone are rare, ATR/TP53 co-mutation is 12-fold enriched over expected in ER+/HER2- disease (P = 0.002) and associates with metastatic progression (HR = 2.01, P = 0.006). Concordantly, ATR dysregulation induces metastatic phenotypes in TP53 mutant, not wild-type, cells. Overall, we identify mode of cell cycle dysregulation as a distinct event that determines subtype, metastatic potential, and treatment responsiveness, providing rationale for reconsidering diagnostic classification through the lens of the mode of cell cycle dysregulation..

Combination Therapy as a Promising Way to Fight Oral Cancer

Oral cancer is a highly aggressive tumor with invasive properties that can lead to metastasis and high mortality rates. Conventional treatment strategies, such as surgery, chemotherapy, and radiation therapy, alone or in combination, are associated with significant side effects. Currently, combination therapy has become the standard practice for the treatment of locally advanced oral cancer, emerging as an effective approach in improving outcomes. In this review, we present an in-depth analysis of the current advancements in combination therapies for oral cancer. The review explores the current therapeutic options and highlights the limitations of monotherapy approaches. It then focuses on combinatorial approaches that target microtubules, as well as various signaling pathway components implicated in oral cancer progression, namely, DNA repair players, the epidermal growth factor receptor, cyclin-dependent kinases, epigenetic readers, and immune checkpoint proteins. The review discusses the rationale behind combining different agents and examines the preclinical and clinical evidence supporting the effectiveness of these combinations, emphasizing their ability to enhance treatment response and overcome drug resistance. Challenges and limitations associated with combination therapy are discussed, including potential toxicity and the need for personalized treatment approaches. A future perspective is also provided to highlight the existing challenges and possible resolutions toward the clinical translation of current oral cancer therapies.

CRISPR-based gene editing of non-homologous end joining factors biases DNA repair pathway choice toward single-strand annealing in Aedes aegypti

To maintain genome stability, eukaryotic cells orchestrate DNA repair pathways to process DNA double-strand breaks (DSBs) that result from diverse developmental or environmental stimuli. Bias in the selection of DSB repair pathways, either non-homologous end joining (NHEJ) or homology-directed repair (HDR), is also critical for efficient gene editing and for homing-based gene drive approaches developed for the control of disease-transmitting vector mosquitoes. However, little is understood about DNA repair homeostasis in the mosquito genome. Here, we utilized CRISPR/Cas9 to generate indel mutant strains for core NHEJ factors ku80, DNA ligase IV (lig4), and DNA-PKcs in the mosquito Aedes aegypti and evaluated the corresponding effects on DNA repair. In a plasmid-based assay, disruption of ku80 or lig4, but not DNA-PKcs, reduced both NHEJ and SSA. However, a transgenic reporter strain-based test revealed that those mutations significantly biased DNA repair events toward SSA. Interestingly, ku80 mutation also significantly increased the end joining rate by a yet-characterized mechanism in males. Our study provides evidence that the core NHEJ factors have an antagonistic effect on SSA-based DSB repair of the Ae. aegypti genome. Down-modulating the NHEJ pathway can enhance the efficiency of nuclease-based genetic control approaches, as most of those operate by homology-based repair processes along with extensive DNA end resection that is antagonized by NHEJ.

The mechanism and clinical application of DNA damage repair inhibitors combined with immune checkpoint inhibitors in the treatment of urologic cancer

Urologic cancers such as kidney, bladder, prostate, and uroepithelial cancers have recently become a considerable global health burden, and the response to immunotherapy is limited due to immune escape and immune resistance. Therefore, it is crucial to find appropriate and effective combination therapies to improve the sensitivity of patients to immunotherapy. DNA damage repair inhibitors can enhance the immunogenicity of tumor cells by increasing tumor mutational burden and neoantigen expression, activating immune-related signaling pathways, regulating PD-L1 expression, and reversing the immunosuppressive tumor microenvironment to activate the immune system and enhance the efficacy of immunotherapy. Based on promising experimental results from preclinical studies, many clinical trials combining DNA damage repair inhibitors (e.g., PARP inhibitors and ATR inhibitors) with immune checkpoint inhibitors (e.g., PD-1/PD-L1 inhibitors) are underway in patients with urologic cancers. Results from several clinical trials have shown that the combination of DNA damage repair inhibitors with immune checkpoint inhibitors can improve objective rates, progression-free survival, and overall survival (OS) in patients with urologic tumors, especially in patients with defective DNA damage repair genes or a high mutational load. In this review, we present the results of preclinical and clinical trials of different DNA damage repair inhibitors in combination with immune checkpoint inhibitors in urologic cancers and summarize the potential mechanism of action of the combination therapy. Finally, we also discuss the challenges of dose toxicity, biomarker selection, drug tolerance, drug interactions in the treatment of urologic tumors with this combination therapy and look into the future direction of this combination therapy.

DNA Ligase 4 Contributes to Cell Proliferation against DNA-PK Inhibition in MYCN-Amplified Neuroblastoma IMR32 Cells

Identifying the vulnerability of altered DNA repair machinery that displays synthetic lethality with MYCN amplification is a therapeutic rationale in unfavourable neuroblastoma. However, none of the inhibitors for DNA repair proteins are established as standard therapy in neuroblastoma. Here, we investigated whether DNA-PK inhibitor (DNA-PKi) could inhibit the proliferation of spheroids derived from neuroblastomas of MYCN transgenic mice and MYCN-amplified neuroblastoma cell lines. DNA-PKi exhibited an inhibitory effect on the proliferation of MYCN-driven neuroblastoma spheroids, whereas variable sensitivity was observed in those cell lines. Among them, the accelerated proliferation of IMR32 cells was dependent on DNA ligase 4 (LIG4), which comprises the canonical non-homologous end-joining pathway of DNA repair. Notably, LIG4 was identified as one of the worst prognostic factors in patients with MYCN-amplified neuroblastomas. It may play complementary roles in DNA-PK deficiency, suggesting the therapeutic potential of LIG4 inhibition in combination with DNA-PKi for MYCN-amplified neuroblastomas to overcome resistance to multimodal therapy.

DNA-Dependent Protein Kinase Catalytic Subunit (DNA-PKcs): Beyond the DNA Double-Strand Break Repair

DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a member of the phosphatidylinositol 3-kinase related kinase family is a well-known player in repairing DNA double strand break through non-homologous end joining pathway. This mechanism has allowed us to understand its critical role in T and B cell development through V(D)J recombination and class switch recombination, respectively. We have also learned that the defects in these mechanisms lead to severely combined immunodeficiency (SCID). Here we highlight some of the latest evidence where DNA-PKcs has been shown to localize not only in the nucleus but also in the cytoplasm, phosphorylating various proteins involved in cellular metabolism and cytokine production. While it is an exciting time to unveil novel functions of DNA-PKcs, one should carefully choose experimental models to study DNA-PKcs as the experimental evidence has been shown to differ between cells of defective DNA-PKcs and those of DNA-PKcs knockout. Moreover, while there are several DNA-PK inhibitors currently being evaluated in the clinical trials in attempt to increase the efficacy of radiotherapy or chemotherapy, multiple functions and subcellular localization of DNA-PKcs in various types of cells may further complicate the effects at the cellular and organismal level.

DNA‑PKcs phosphorylation specific inhibitor, NU7441, enhances the radiosensitivity of clinically relevant radioresistant oral squamous cell carcinoma cells

Radioresistant cancer cells lead to poor prognosis after radiotherapy. However, the mechanisms underlying cancer cell radioresistance have not been fully elucidated. Thus, the DNA damage response of clinically relevant radioresistant oral squamous cell carcinoma HSC2-R cells, established by long-term exposure of parental HSC2 cells to fractionated radiation, was investigated. The DNA double-strand break (DSB) repair protein-specific inhibitor, NU7441, which targets DNA-dependent protein kinase catalytic subunit (DNA-PKcs) phosphorylation, and IBR2, which targets Rad51, were administered to HSC2 and HSC2-R cells. NU7441 administration eliminated colony formation in both cell lines under 6 Gy X-ray irradiation, whereas IBR2 did not affect colony formation. NU7441 and IBR2 significantly enhanced 6 Gy X-ray irradiation-induced apoptosis in HSC2-R cells. In HSC2-R cells, cell cycle arrest released earlier than in HSC2 cells, and phosphorylated-H2A histone family member X (γH2AX) expression rapidly decreased. Following NU7441 administration, γH2AX expression and the cell percentages of the G2/M phase were not decreased at 48 h after treatment in HSC2-R cells. DNA-PKcs has been demonstrated to regulate non-homologous end-joining (NHEJ) and homologous recombination (HR) repair, and the later phase of DSB repair is dominated by HR. Therefore, the results of the present study indicated that the DSB repair mechanism in HSC2-R cells strongly depends on NHEJ and loss of HR repair function. The present study revealed a potential mechanism underlying the acquired radioresistance and therapeutic targets in radioresistant cancer cells.

Doxorubicin-An Agent with Multiple Mechanisms of Anticancer Activity

Doxorubicin (DOX) constitutes the major constituent of anti-cancer treatment regimens currently in clinical use. However, the precise mechanisms of DOX's action are not fully understood. Emerging evidence points to the pleiotropic anticancer activity of DOX, including its contribution to DNA damage, reactive oxygen species (ROS) production, apoptosis, senescence, autophagy, ferroptosis, and pyroptosis induction, as well as its immunomodulatory role. This review aims to collect information on the anticancer mechanisms of DOX as well as its influence on anti-tumor immune response, providing a rationale behind the importance of DOX in modern cancer therapy.

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.

Integrative multi-omics networks identify PKCδ and DNA-PK as master kinases of glioblastoma subtypes and guide targeted cancer therapy

Despite producing a panoply of potential cancer-specific targets, the proteogenomic characterization of human tumors has yet to demonstrate value for precision cancer medicine. Integrative multi-omics using a machine-learning network identified master kinases responsible for effecting phenotypic hallmarks of functional glioblastoma subtypes. In subtype-matched patient-derived models, we validated PKCδ and DNA-PK as master kinases of glycolytic/plurimetabolic and proliferative/progenitor subtypes, respectively, and qualified the kinases as potent and actionable glioblastoma subtype-specific therapeutic targets. Glioblastoma subtypes were associated with clinical and radiomics features, orthogonally validated by proteomics, phospho-proteomics, metabolomics, lipidomics and acetylomics analyses, and recapitulated in pediatric glioma, breast and lung squamous cell carcinoma, including subtype specificity of PKCδ and DNA-PK activity. We developed a probabilistic classification tool that performs optimally with RNA from frozen and paraffin-embedded tissues, which can be used to evaluate the association of therapeutic response with glioblastoma subtypes and to inform patient selection in prospective clinical trials.

UBA1 inhibition contributes radiosensitization of glioblastoma cells via blocking DNA damage repair

Glioblastoma multiforme (GBM) is a brain tumor with high mortality and recurrence rate. Radiotherapy and chemotherapy after surgery are the main treatment options available for GBM. However, patients with glioblastoma have a grave prognosis. The major reason is that most GBM patients are resistant to radiotherapy. UBA1 is considered an attractive potential anti-tumor therapeutic target and a key regulator of DNA double-strand break repair and genome replication in human cells. Therefore, we hypothesized that TAK-243, the first-in-class UBA1 inhibitor, might increase GBM sensitivity to radiation. The combined effect of TAK-243 and ionizing radiation on GBM cell proliferation, and colony formation ability was detected using CCK-8, colony formation, and EdU assays. The efficacy of TAK-243 combined with ionizing radiation for GBM was further evaluated in vivo, and the mechanism of TAK-243 sensitizing radiotherapy was preliminarily discussed. The results showed that TAK-243, in combination with ionizing radiation, significantly inhibited GBM cell proliferation, colony formation, cell cycle arrest in the G2/M phase, and increased the proportion of apoptosis. In addition, UBA1 inhibition by TAK-243 substantially increased the radiation-induced γ-H2AX expression and impaired the recruitment of the downstream effector molecule 53BP1. Therefore, TAK-243 inhibited the radiation-induced DNA double-strand break repair and thus inhibited the growth of GBM cells. Our results provided a new therapeutic strategy for improving the radiation sensitivity of GBM and laid a theoretical foundation and experimental basis for further clinical trials.

DNA damage repair kinase DNA-PK and cGAS synergize to induce cancer-related inflammation in glioblastoma

Cytosolic DNA promotes inflammatory responses upon detection by the cyclic GMP-AMP (cGAMP) synthase (cGAS). It has been suggested that cGAS downregulation is an immune escape strategy harnessed by tumor cells. Here, we used glioblastoma cells that show undetectable cGAS levels to address if alternative DNA detection pathways can promote pro-inflammatory signaling. We show that the DNA-PK DNA repair complex (i) drives cGAS-independent IRF3-mediated type I Interferon responses and (ii) that its catalytic activity is required for cGAS-dependent cGAMP production and optimal downstream signaling. We further show that the cooperation between DNA-PK and cGAS favors the expression of chemokines that promote macrophage recruitment in the tumor microenvironment in a glioblastoma model, a process that impairs early tumorigenesis but correlates with poor outcome in glioblastoma patients. Thus, our study supports that cGAS-dependent signaling is acquired during tumorigenesis and that cGAS and DNA-PK activities should be analyzed concertedly to predict the impact of strategies aiming to boost tumor immunogenicity.

Tissue Reactions and Mechanism in Cardiovascular Diseases Induced by Radiation

The long-term survival rate of cancer patients has been increasing as a result of advances in treatments and precise medical management. The evidence has accumulated that the incidence and mortality of non-cancer diseases have increased along with the increase in survival time and long-term survival rate of cancer patients after radiotherapy. The risk of cardiovascular disease as a radiation late effect of tissue damage reactions is becoming a critical challenge and attracts great concern. Epidemiological research and clinical trials have clearly shown the close association between the development of cardiovascular disease in long-term cancer survivors and radiation exposure. Experimental biological data also strongly supports the above statement. Cardiovascular diseases can occur decades post-irradiation, and from initiation and development to illness, there is a complicated process, including direct and indirect damage of endothelial cells by radiation, acute vasculitis with neutrophil invasion, endothelial dysfunction, altered permeability, tissue reactions, capillary-like network loss, and activation of coagulator mechanisms, fibrosis, and atherosclerosis. We summarize the most recent literature on the tissue reactions and mechanisms that contribute to the development of radiation-induced cardiovascular diseases (RICVD) and provide biological knowledge for building preventative strategies.

Recent progress of the tumor microenvironmental metabolism in cervical cancer radioresistance

Radiotherapy is widely used as an indispensable treatment option for cervical cancer patients. However, radioresistance always occurs and has become a big obstacle to treatment efficacy. The reason for radioresistance is mainly attributed to the high repair ability of tumor cells that overcome the DNA damage caused by radiotherapy, and the increased self-healing ability of cancer stem cells (CSCs). Accumulating findings have demonstrated that the tumor microenvironment (TME) is closely related to cervical cancer radioresistance in many aspects, especially in the metabolic processes. In this review, we discuss radiotherapy in cervical cancer radioresistance, and focus on recent research progress of the TME metabolism that affects radioresistance in cervical cancer. Understanding the mechanism of metabolism in cervical cancer radioresistance may help identify useful therapeutic targets for developing novel therapy, overcome radioresistance and improve the efficacy of radiotherapy in clinics and quality of life of patients.