The ATM-Chk2 and ATR-Chk1 pathways in DNA damage signaling and cancer

The R337C mutation in the p53 oligomerization domain affects the regulatory domain and its ability to bind response elements: Evidence based on structural and biophysical studies

The homotetrameric form of p53 is critical for performing essential functions like maintaining genomic stability and preventing uncontrolled cell proliferation. In part, these crucial functions are mediated by the p53 C-terminal region (CTR) containing the tetramerization/oligomerization domain (TD/OD) and regulatory domain (RD), responsible for maintaining the protein's oligomeric state and regulating its function. Mutations in the tetramerization domain reduce the transactivation potential and alter the transactivation specificity of p53. This study investigates the effect of high-frequency tetramerization missense mutation p53R337C on protein stability, oligomeric state, and its ability to bind the DNA response elements. For the first time using CD and FTIR spectroscopy, we have shown that the p53 regulatory domain (residues 363-393) and oligomerization domain (residues 327-355) possess a characteristic alpha helix secondary structure, which is enhanced upon binding to DNA, implicating stabilization of the domain. The mutation R337C in the OD impacts the secondary and tertiary structure of p53 CTR, leading to the loss of secondary structure and the formation of unstable tetramers, as shown by CD and DSC thermal studies. Surprisingly, the secondary structure of mutant p53 CTR partially stabilized upon binding to the DNA sequence. Our data suggests that the unstable p53R337C tetramer exhibits weaker binding to the DNA promoter sequence with decreased transcription activity, consistent with previous cell-based assays. Our study conclude that the loss of salt-bridge interactions between Arg337 and Asp352 in the intra-dimer of p53 leads to the formation of unstable tetramers, and the DNA-binding ability of the regulatory domain.

CD8+ T cells in patients with hypopharyngeal squamous cell carcinoma are susceptible to radiation-induced damage

Radiotherapy (RT) is a commonly used clinical management for hypopharyngeal squamous cell carcinoma (HPSCC), which represents the most unfavorable prognosis among all subtypes of head and neck squamous cell carcinoma. However, radiation may cause lymphopenia, a significantly adverse event with detrimental prognostic implications for patients. While CD8+ T cells are vital in tumor immunity, the specific effects of RT on CD8+ T cells as well as the underlying mechanisms have not been clearly elucidated. Here we found that subpopulations of peripheral T lymphocytes exhibited differential profiles in patients with HPSCC compared to healthy individuals both pre- and post-irradiation. Importantly, CD8+ T cells from HPSCC patients showed greater reduction of cytokine production, more severe proliferation defect, and increased apoptosis compared to those from healthy individuals after in vitro irradiation. Mechanistically, the ATM-Chk2 pathway mediated the enhanced apoptosis of CD8+ T lymphocytes from HPSCC patients upon irradiation. Therefore, our study demonstrated that CD8+ T cells in patients with HPSCC exhibit a higher susceptibility to radiation-induced damage compared to those in healthy individuals. The ATM-Chk2 pathway represents a potential immunotherapeutic target for safeguarding CD8+ T cells in HPSCC patients against radiation-induced apoptosis.

Small molecule as potent hepatocellular carcinoma progression inhibitor through stabilizing G-quadruplex DNA to activate replication stress responded DNA damage

G-quadruplex (G4) DNA, prevalent in tumor cells, offers a potential anticancer target. This study examined TA-1, a tanshinone IIA derivative, for its antitumor activity against liver cancer. We found that TA-1 binds and stabilizes multiple G4 DNA,triggering DNA damage, suppressing the angiogenesis in vitro and in vivo and leading to cancer cell death. Notably, we confirmed TA-1's inhibitory effect on liver cancer cells and explored its mechanism, which involves stabilizing G4 DNA to mediate replication-stress-dependent DNA damage. Furthermore, TA-1 promotes 53BP1 expression, activating toxic NHEJ repair and leading to apoptotic cell death via the ATM-Chk2-p53 pathway. In vivo studies further supported these findings. In summary, TA-1 is a potent VEGF G-quadruplex stabilizer that inhibits liver cancer progression.

Discovery of 4-(2-(methylamino)thiazol-5-yl)pyrimidin-2-amine derivatives as novel cyclin-dependent kinase 12 (CDK12) inhibitors for the treatment of esophageal squamous cell carcinoma

The transcriptional cyclin-dependent protein kinase 12 (CDK12), a potential target in various cancers, was recently discovered with a dramatic amplification in esophageal cancer (EC). In this study, we conducted an online database analysis that revealed CDK12 to be overexpressed in esophageal squamous cell carcinoma (ESCC) tissue samples from patients. Furthermore, survival analysis indicated that CDK12 can serve as a prognostic indicator for ESCC patients. In addition, CDK12 knockdown had been shown to reduce the proliferation of ESCC cells. The present study also details the design, synthesis, and biological evaluation of new CDK12 inhibitors which bear the scaffold of 4-(2-(methylamino)thiazol-5-yl)pyrimidin-2-amine. Among the synthesized compounds, H63 has been identified as a potent inhibitor of CDK12 with excellent anti-ESCC activity. Mechanistically, H63 blocked transcription elongation, downregulated the G1-phase core genes to induce cell cycle arrest, and altered the CDK12-ATM/ATR-CHEK1/CHEK2 signaling axis to cause DNA damage. In addition, H63 exhibited favorable pharmacokinetic properties, good safety, and prominent anti-ESCC activity in vivo. The present study suggests that CDK12 is a promising target for ESCC treatment, and H63 is a promising candidate for further clinical development as an anti-ESCC drug.

Mitochondrial fission surveillance is coupled to Caenorhabditis elegans DNA and chromosome segregation integrity

Mitochondrial fission and fusion are tightly regulated to specify mitochondrial abundance, localization, and arrangement during cell division as well as in the diverse differentiated cell types and physiological states. However, the regulatory pathways for such mitochondrial dynamics are less explored than the mitochondrial fission and fusion components. Here we report a large-scale screen for genes that regulate mitochondrial fission. Mitochondrial fission defects cause a characteristic uneven fluorescent pattern in embryos carrying mitochondrial stress reporter genes. Using this uneven activation, we performed RNAi screens that identified 3 kinase genes from a ~ 500-kinase library and another 11 genes from 3,300 random genes that function in mitochondrial fission. Many of these identified genes play roles in chromosome segregation. We found that chromosome missegregation and genome instability lead to dysregulation of mitochondrial fission, possibly independent of DRP-1. ATL-1, the C. elegans ATR orthologue, plays a potentially protective role in alleviating the mitochondrial fission defect caused by chromosome missegregation. This establishes a screening paradigm for identifying mitochondrial fission regulators, which reveals the potential role of ATR in surveilling mitochondrial fission to mitigate dysregulation caused by improper chromosome segregation.

Replication stress response and radioresistance in lung cancer: Mechanistic insights and advanced therapeutic approaches

Lung cancer, the leading cause of cancer mortality globally, comprises mainly non-small cell lung cancer and small cell lung cancer. Its pathogenesis involves genetic mutations, environmental exposures, chronic inflammation, and tumor microenvironment interactions. Critical genes like TP53, RB1, KRAS, and EGFR often mutate, driving uncontrolled cell growth. Radiation therapy, a primary treatment, faces challenges with radioresistance due to DNA repair mechanisms and replication stress responses. Emerging therapeutic strategies target DNA repair pathways, cell cycle checkpoints, and immune responses to enhance radiosensitivity and counteract resistance. Promising approaches include PARP inhibitors, CDK inhibitors, EGFR blockers, and immunotherapies combined with radiation. Advances in understanding these mechanisms are crucial for developing targeted therapies to improve lung cancer patient outcomes. The present review focuses on elucidating the intricate mechanisms of lung cancer pathogenesis and radioresistance, while highlighting novel therapeutic strategies designed to overcome these challenges and improve treatment efficacy.

Ganoderic acid a potentiates cisplatin's cytotoxicity on gallbladder cancer cells by promoting DNA damage and inhibiting cell stemness

BACKGROUND

Ganoderma acid A (GAA), a triterpenoid compound from Ganoderma lucidum, has gained attention for its anti-tumor properties. Herein, we hypothesized that GAA may enhance cisplatin's (DDP) anticancer effect in gallbladder cancer (GBC) cells by promoting DNA damage response, particularly through upregulation of DNA damage markers such as γH2AX, p-ATM, p-ATR, and p-p53, and reducing cell stemness by downregulating stemness markers like SOX2, Oct4, and NANOG.

MATERIALS AND METHODS

The human GBC cell line GBC-SD and human gallbladder epithelial cell line HGBEC were cultured in RPMI-1640 and DMEM/F12 media with 10% fetal bovine serum. Cells were treated with 2 µM DDP and 60 µM GAA for 24 h. To evaluate the toxicity of GAA in normal cells, HGBEC cells were treated under the same conditions. Cell viability was assessed by CCK-8 assay, and colony formation was measured in 6-well plates. Apoptosis was evaluated by TUNEL assay, and DNA damage was assessed using comet assay. Stemness was analyzed by spheroid formation and CD44 immunofluorescence staining. Western blot analysis was performed to evaluate the expression of apoptotic, stemness, and DNA damage markers (Bax/Bcl-2, cleaved-caspase 3, SOX2, Oct4, NANOG, γH2AX, p-ATM, p-ATR, p-p53).

RESULTS

The results showed that GAA significantly reduced GBC-SD cell viability in a concentration-dependent manner (p < 0.05). The combined treatment of GAA and DDP further decreased cell viability, with the DDP IC50 value reduced from 8.98 µM to 4.07 µM (p < 0.05). Colony formation was significantly inhibited (p < 0.05), and apoptosis increased, as assessed by TUNEL assay (p < 0.05). Western blot analysis revealed increased pro-apoptotic proteins Bax/Bcl-2 and cleaved-caspase 3(p < 0.05). The expression of stemness markers SOX2, Oct4, NANOG, and DNA damage markers γH2AX, p-ATM, p-ATR, and p-p53 was significantly altered (p < 0.05). Specifically, p53 expression was significantly increased, indicating enhanced DNA damage response (p < 0.05).

CONCLUSION

GAA can significantly enhance the anticancer effects of DDP on GBC cells by inhibiting DNA damage response and cell stemness, supporting GAA as an adjuvant treatment for GBC and warrants further validatory preclinical studies.

Enhancing radiotherapy techniques for Triple-Negative breast cancer treatment

Breast cancer is the most prevalent cancer among women worldwide, with various subtypes that require distinct treatment approaches. Among these, Triple-Negative Breast Bancer (TNBC) is recognized as the most aggressive form, often associated with poor prognosis due to its lack of targeted therapeutic options. This review specifically focuses on Radiotherapy (RT) as a treatment modality for TNBC, evaluating recent advancements and ongoing challenges, particularly the issue of radioresistance. RT remains an essential part in the management of breast cancer, including TNBC. Over the years, multiple improvements have been made to enhance RT effectiveness and minimize resistance. The introduction of advanced techniques such as Stereotactic Body Radiation Therapy (SBRT) and Stereotactic Radiosurgery (SRS) has significantly improved precision and reduced toxicity. More recently, proton radiation therapy, a novel RT modality, has been introduced, offering enhanced dose distribution and reducing damage to surrounding healthy tissues. Despite these technological advancements, a subset of TNBC patients continues to exhibit resistance to RT, leading to recurrence and poor treatment outcomes. To overcome radioresistance, there is an increasing interest in combining RT with targeted therapeutic agents that sensitize cancer cells to radiation. Radiosensitizing drugs have been explored to enhance the efficacy of RT by making cancer cells more susceptible to radiation-induced damage. Potential candidates include DNA damage repair inhibitors, immune checkpoint inhibitors, and small-molecule targeted therapies that interfere with key survival pathways in TNBC cells. In conclusion, while RT remains a crucial modality for TNBC treatment, radioresistance remains a significant challenge. Future research should focus on optimizing RT techniques while integrating radiosensitizing agents to improve treatment efficacy. By combining RT with targeted drug therapy, a more effective and personalized treatment approach can be developed, ultimately improving patient outcomes and reducing recurrence rates in TNBC.

Perspectives on cancer therapy-synthetic lethal precision medicine strategies, molecular mechanisms, therapeutic targets and current technical challenges

In recent years, synthetic lethality has become an important theme in the field of targeted cancer therapy. Synthetic lethality refers to simultaneous defects in two or more genes leading to cell death, whereas defects in any single gene do not lead to cell death. Taking advantage of the genetic vulnerability that exists within cancer cells, it theoretically has no negative impact on healthy cells and has fewer side effects than non-specific chemotherapy. Currently, targeted cancer therapies focus on inhibiting key pathways in cancer. However, it has been found that over-activation of oncogenic-related signaling pathways can also induce cancer cell death, which is a major breakthrough in the new field of targeted therapies. In this review, we summarize the conventional gene targets in synthetic lethality (PARP, ATR, ATM, WEE1, PRMT) and provide an in-depth analysis of their latest potential mechanisms. We explore the impact of over-activation of pathways such as PI3K/AKT, MAPK, and WNT on cancer cell survival, and present the technical challenges of current research. Important theoretical foundations and insights are provided for the application of synthetic lethal strategies in cancer therapy, as well as future research directions.

Heat shock transcription factor-mediated thermal tolerance and cell size plasticity in marine diatoms

Diatoms are a crucial component of marine ecosystems, recognized for their broad environmental adaptability and wide temperature tolerance. However, the molecular mechanisms underlying their adaptability to diverse temperatures are unknown. In this study, we discover that heat shock transcription factors (HSFs) are potentially important for thermal tolerance in diatoms. Our study focuses on PtHSF2, annotated as HSF2 in Phaeodactylum tricornutum's genome, which is ubiquitous in diatoms. Overexpression of PtHSF2 markedly enhances thermal tolerance and increases cell size; causes significant differential expression of several genes, including cell division cycle protein 45-like (PtCdc45-like), ATM (ataxia telangiectasia mutated), ATR (ataxia telangiectasia and Rad3-related), light-harvesting complex protein 2 (Lhcx2), and fatty acid desaturase. Cleavage Under Targets and Tagmentation (CUT&Tag) and CUT&Tag-qPCR analyses demonstrate that PtHSF2 directly targets and upregulates PtCdc45-like and Lhcx2 while downregulating ATP-binding cassette transporter. Functional validation of PtCdc45-like shows that its overexpression results in larger cell size, enhances antioxidant capacity, and improves cell survival at elevated temperatures. Collectively, our findings elucidate the molecular mechanism by which PtHSF2 mediates high-temperature tolerance in diatoms and validate the functions of its target gene PtCdc45-like. These results highlight the importance of HSFs in diatom temperature adaptation and provide insights into temperature acclimation in microalgae.

Synthetic selenomelanin nanoparticles radio-sensitize non-melanocytic lung cancer (A549) cells by promoting G2/M arrest

Recent studies have postulated the natural existence of selenomelanin and its role in the radio-protection of healthy cells. The present study aimed to understand its radio-modulatory activity in non-melanocytic cancerous (A549) cells of lung origin. Briefly, selenomelanin was synthesized under laboratory conditions following the previously reported methodology. The various spectroscopic (electron paramagnetic resonance, X-ray photoelectron spectroscopy, atomic absorption spectroscopy, transmission electron microscopy and dynamic light scattering) analyses confirmed the formation of selenomelanin nanoparticles. The short-term (72 h) and long-term (14 days) toxicity profiling of selenomelanin by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) and clonogenic assays respectively revealed its half maximal inhibitory concentrations (IC50) of 72.03 ± 7.13 μg/ml and 0.85 ± 0.16 μg/ml respectively in A549 cells and of 81.56 ± 1.63 μg/ml and > 5 μg/ml respectively in healthy lung fibroblast (WI26) cells. Further, pre-treatment of selenomelanin (at concentrations non-toxic for WI26 cells) selectively augmented the radiosensitivity of A549 cells. Finally, mechanistic investigations in A549 cells revealed that selenomelanin increased the levels of reactive oxygen species, DNA damage and modulated the phospho-levels of CHK1 and CHK2 (effectors of cell cycle arrest) in the irradiated cells to favour G2/M arrest followed by cleavage of caspase 3 (effector of apoptosis). Together, the present study proposes the novel application of selenomelanin as a radiosensitizer to enhance the efficacy of radiotherapy in cancerous cells of lung origin.

How human papillomavirus (HPV) targets DNA repair pathways for viral replication: from guardian to accomplice

SUMMARYHuman papillomaviruses (HPVs) are small DNA viruses that are responsible for significant disease burdens worldwide, including cancers of the cervix, anogenital tract, and oropharynx. HPVs infect stratified epithelia at a variety of body locations and link their productive life cycles to the differentiation of the host cell. These viruses have evolved sophisticated mechanisms to exploit cellular pathways, such as DNA damage repair (DDR), to regulate their life cycles. HPVs activate key DDR pathways such as ATM, ATR, and FA, which are critical for maintaining genomic integrity but are often dysregulated in cancers. Importantly, these DDR pathways are essential for HPV replication in undifferentiated cells and amplification upon differentiation. The ability to modulate these DDR pathways not only enables HPV persistence but also contributes to cellular transformation. In this review, we discuss the recent advances in understanding the mechanisms by which HPV manipulates the host DDR pathways and how these depend upon enhanced topoisomerase activity and R-loop formation. Furthermore, the strategies to manipulate DDR pathways utilized by high-risk HPVs are compared with those used by other DNA viruses that exhibit similarities and distinct differences.

The Clinical Pathological Characteristics and Prognostic Relevance of Homologous Recombination Repair Gene Mutations in Ovarian Cancer Patients: A Prospective Cohort Study

Backgrouds: Whether homologous recombination repair (HRR) mutation has a differential effect on the prognosis has not been confirmed by current studies. The purpose of this study was to explore the clinical importance, prognostic value, and frequency of pathogenic changes in HRR genes in patients with ovarian cancer (OC). Methods: We analyze information including HRR mutation and clinical prognosis of OC patients both in our cohort and in the TCGA-OV database. Blood and/or tumor samples from 98 women admitted to Shanghai General Hospital between January 2021 and May 2024, and DNA sequencing was performed on these samples for all patients included in this retrospective study. Testing was performed for HRR mutations, including germline BRCA1/2 mutations, and defects in HRR were defined as detrimental mutations within relevant genes. Comprehensive medical records were gathered for all patients, with a follow-up period recorded for 74 of them. Results: HRR pathway genes, including BRCA1/2, CDK12, RAD54L, RAD51, ATM, MRE11, and BRIP2, are highly expressed in FIGO Stages I-II OCs among 482 patients in the TCGA-OV database, and 95.06% samples presented mutations. The alignment diagram analyzed by logistic and Cox regression was derived to investigate HRR genes on overall survival (OS < 763 days) of OC patients. A total of 98 patients were enrolled in our study, with 70 harboring HRR mutations (HRRmt) and 28 having the HRR wild-type (HRRwt). The predominant pathological type across all four patient groups was high-grade serous adenocarcinoma, with similar prevalence in HRRmt (84.30%) versus HRRwt (75%, p=0.360) and BRCAmt (94.20%) versus BRCAwt (74.60%, p=0.151) groups. Survival prediction data were collected from 74 patients, and the HRRmt group (n = 50) exhibited a numerically longer PFS compared to the HRRwt group (n = 24), with 23 months versus 17 months, respectively. A significant disparity was noted in the percentage of patients administered PARPi medication between the HRRmt and HRRwt groups (58.00% vs. 20.20%; p=0.003). Patients in both the HRRmt group (p=0.049) and the BRCAwt group (p=0.046) receiving PARPi treatment have extended PFS. Significant differences were identified between HRRmt and HRRwt groups in the size of the initial debulking surgery achieving R0 status (p=0.005), low CA125 levels (< 1000 U/mL) at diagnosis (p=0.015), and the use of PARP inhibitors (PARPi) (p=0.024) and antiangiogenic drugs (p < 0.001). For patients with HRR mutations, the use of PARPi significantly impacted PFS (p=0.049), and achieving R0 status (p=0.005) significantly influenced PFS. Conclusions: This study indicates that mutations in the HRR gene possess significant potential as a prognostic marker in OC. Our aim was to comprehensively explore how HRR gene mutations, including but not limited to BRCA, might influence the clinical course and survival of patients, shedding light on potential new avenues for personalized treatment strategies.

ADAM9 mediates Cisplatin resistance in gastric cancer cells through DNA damage response pathway

Gastric cancer is one of the most common malignant tumors in the world. The occurrence of chemotherapy resistance seriously affects the survival and prognosis of middle and advanced patients. Enhancing DNA repair ability is one of the important mechanisms of chemotherapy resistance. ADAM9, a member of the disintegrin and metalloproteinase family, is involved in many biological processes, such as tumor cells proliferation, apoptosis, invasion and migration, vascular invasion, and drug resistance. In this study, we found that the high expression of ADAM9 in gastric cancer tissues was associated with a variety of clinicopathological factors and poor prognosis in patients. Gastric cancer cells with high ADAM9 expression reduced sensitivity to Cisplatin, decreased DNA damage, increased expression of ATM and CHK2, the key proteins in DNA damage repair pathway, and improved cancer cells survival rate. Further studies showed that the expression of ADAM9 was selectively interfered with gastric cancer cells, the expression levels of ATM and CHK2 were decreased, while the expression of damage protein γ-H2AX was significantly increased, the degree of DNA damage was increased, and the sensitivity of gastric cancer cells to Cisplatin was significantly enhanced. It is suggested that ADAM9 is involved in Cisplatin resistance in gastric cancer cells, and its mechanism is related to the activation of ATM-CHK2 pathway in DNA damage repair. These data demonstrate that ADAM9 plays a pro-cancer role and mediates Cisplatin resistance in gastric cancer, which may be a new target to overcome chemotherapy resistance.

Poly (ADP-ribose) polymerase inhibitors in cancer therapy

Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPis) have emerged as critical agents for cancer therapy. By inhibiting the catalytic activity of PARP enzymes and trapping them in the DNA, PARPis disrupt DNA repair, ultimately leading to cell death, particularly in cancer cells with homologous recombination repair deficiencies, such as those harboring BRCA mutations. This review delves into the mechanisms of action of PARPis in anticancer treatments, including the inhibition of DNA repair, synthetic lethality, and replication stress. Furthermore, the clinical applications of PARPis in various cancers and their adverse effects as well as their combinations with other therapies and the mechanisms underlying resistance are summarized. This review provides comprehensive insights into the role and mechanisms of PARP and PARPis in DNA repair, with a particular focus on the potential of PARPi-based therapies in precision medicine for cancer treatment.

Signaling pathway dysregulation in breast cancer

This article provides a comprehensive analysis of the signaling pathways implicated in breast cancer (BC), the most prevalent malignancy among women and a leading cause of cancer-related mortality globally. Special emphasis is placed on the structural dynamics of protein complexes that are integral to the regulation of these signaling cascades. Dysregulation of cellular signaling is a fundamental aspect of BC pathophysiology, with both upstream and downstream signaling cascade activation contributing to cellular process aberrations that not only drive tumor growth, but also contribute to resistance against current treatments. The review explores alterations within these pathways across different BC subtypes and highlights potential therapeutic strategies targeting these pathways. Additionally, the influence of specific mutations on therapeutic decision-making is examined, underscoring their relevance to particular BC subtypes. The article also discusses both approved therapeutic modalities and ongoing clinical trials targeting disrupted signaling pathways. However, further investigation is necessary to fully elucidate the underlying mechanisms and optimize personalized treatment approaches.

Computational Analysis of Non-synonymous SNPs in ATM Kinase: Structural Insights, Functional Implications, and Inhibitor Discovery

Ataxia telangiectasia-mutated (ATM) protein kinase, a key player in cellular integrity regulation, is known for its role in DNA damage response. This study investigates the broader impact of ATM on cellular processes and potential clinical manifestations arising from mutations, aiming to expand our understanding of ATM's diverse functions beyond conventional roles. The research employs a comprehensive set of computational techniques for a thorough analysis of ATM mutations. The mutation data are curated from dbSNP and HuVarBase databases. A meticulous assessment is conducted, considering factors such as deleterious effects, protein stability, oncogenic potential, and biophysical characteristics of the identified mutations. Conservation analysis, utilizing diverse computational tools, provides insights into the evolutionary significance of these mutations. Molecular docking and dynamic simulation analyses are carried out for selected mutations, investigating their interactions with Y2080D, AZD0156, and quercetin inhibitors to gauge potential therapeutic implications. Among the 419 mutations scrutinized, five (V1913C, Y2080D, L2656P, C2770G, and C2930G) are identified as both disease causing and protein destabilizing. The study reveals the oncogenic potential of these mutations, supported by findings from the COSMIC database. Notably, Y2080D is associated with haematopoietic and lymphoid cancers, while C2770G shows a correlation with squamous cell carcinomas. Molecular docking and dynamic simulation analyses highlight strong binding affinities of quercetin for Y2080D and AZD0156 for C2770G, suggesting potential therapeutic options. In summary, this computational analysis provides a comprehensive understanding of ATM mutations, revealing their potential implications in cellular integrity and cancer development. The study underscores the significance of Y2080D and C2770G mutations, offering valuable insights for future precision medicine targeting-specific ATM. Despite informative computational analyses, a significant research gap exists, necessitating essential in vitro and in vivo studies to validate the predicted effects of ATM mutations on protein structure and function.

Phospholipid Biosynthesis: An Unforeseen Modulator of Nuclear Metabolism

Glycerophospholipid biosynthesis is crucial not only for providing structural components required for membrane biogenesis during cell proliferation but also for facilitating membrane remodeling under stress conditions. The biosynthetic pathways for glycerophospholipid tails, glycerol backbones, and diverse head group classes intersect with various other metabolic processes, sharing intermediary metabolites. Recent studies have revealed intricate connections between glycerophospholipid synthesis and nuclear metabolism, including metabolite-mediated crosstalk with the epigenome, signaling pathways that govern genome integrity, and CTP-involved regulation of nucleotide and antioxidant biosynthesis. This review highlights recent advances in understanding the functional roles of glycerophospholipid biosynthesis beyond their structural functions in budding yeast and mammalian cells. We propose that glycerophospholipid biosynthesis plays an integrative role in metabolic regulation, providing a new perspective on lipid biology.

Transcription coupled repair occurrence in Trypanosoma cruzi mitochondria

Although several proteins involved in DNA repair systems have been identified in the T. cruzi mitochondrion, limited information is available regarding the specific DNA repair mechanisms responsible for kinetoplast DNA (kDNA) maintenance. The kDNA, contained within a single mitochondrion, exhibits a highly complex replication mechanism compared to the mitochondrial DNA of other eukaryotes. The absence of additional mitochondria makes the proper maintenance of this single mitochondrion essential for parasite viability. Trypanosomatids possess a distinct set of proteins dedicated to kDNA organization and metabolism, known as kinetoplast-associated proteins (KAPs). Despite studies identifying the localization of these proteins, their functions remain largely unclear. Here, we demonstrate that TcKAP7 is involved in the repair of kDNA lesions induced by UV radiation and cisplatin. TcKAP7 mutant cells exhibited phenotypes similar to those observed in Angomonas deanei following the deletion of this gene. This monoxenic trypanosomatid colonizes the gastrointestinal tract of insects and possesses a kinetoplast with a distinct shape and kDNA topology compared to T. cruzi, making it a suitable comparative model in this study. Additionally, we observed that DNA damage can trigger distinct signaling pathways leading to cell death. Furthermore, we elucidated the involvement of CSB in this response, suggesting a potential interaction between TcKAP7 and CSB proteins in transcription-coupled DNA repair. The results presented here describe, for the first time, the mechanism of mitochondrial DNA repair in trypanosomatids following exposure to UV radiation and cisplatin.

TOPBP1 as a potential predictive biomarker for enhanced combinatorial efficacy of olaparib and AZD6738 in PDAC

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive and often lethal malignancy, requiring the development of enhanced therapeutic approaches. The DNA damage response (DDR) pathway is frequently altered during PDAC development, leading to an increased occurrence of DNA damage. DNA topoisomerase II-binding protein 1 (TOPBP1) plays a supportive role in regulating the DDR pathway, and its overexpression has been linked to the tumorigenesis of various cancers. This study investigated the biological role of TOPBP1 in PDAC pathogenesis and evaluated its clinical relevance in guiding treatment regimens. We examined the relationship between TOPBP1 expression, DDR pathway modulation, and therapeutic response in PDAC cell lines, primary cells, and subcutaneous mouse models. We found that elevated TOPBP1 expression was positively correlated with increased histologic grade and reduced patient survival in PDAC. TOPBP1 knockdown increased the sensitivity of PDAC cells to olaparib treatment and improved therapeutic efficacy in both PDAC cell lines and subcutaneous mouse models. Combination treatment with olaparib and AZD6738 effectively induced P53-dependent apoptosis via inhibiting the ATR pathway and enhancing signaling through the ATM pathway, which significantly reduced the viability of pancreatic cell lines. Notably, this combination therapy was more effective in PDAC cell lines exhibiting high TOPBP1 expression, indicating that TOPBP1 may serve as a useful predictive biomarker. In conclusion, TOPBP1 is a potential marker for optimizing the olaparib and AZD6738 combination therapy in PDAC. This study highlights the clinical significance of TOPBP1 in the treatment of PDAC and emphasizes the potential implications for a broader population of patients.

Homoharringtonine: mechanisms, clinical applications and research progress

Homoharringtonine is a natural alkaloid with significant pharmacological potential that has demonstrated promising efficacy in the treatment of hematological malignancies in recent years. This article systematically reviews the pharmacological mechanisms of Homoharringtonine, focusing on its key roles in inducing apoptosis, inhibiting cell cycle progression, and reducing cell migration and invasion. Additionally, HHT exhibits multiple biological activities, including immunomodulation, antiviral effects, and anti-fibrotic properties, with recent studies also revealing its potential neuroprotective functions. In clinical trials, Homoharringtonine has demonstrated promising efficacy in the treatment of hematological malignancies, particularly in various types such as acute myeloid leukemia and chronic myeloid leukemia. Despite the significant antitumor effects observed in clinical applications, its low bioavailability and potential side effects remain major challenges that limit its widespread use. This article details the latest research advancements aimed at enhancing the bioavailability of Homoharringtonine, including various drug delivery systems such as nanoparticles and liposomes, as well as chemical modification strategies. These approaches not only improve HHT's bioavailability in vivo but also enhance its targeting ability while reducing toxicity to normal cells. Furthermore, the combination of HHT with other drugs presents broader prospects for clinical treatment. By exploring the diverse pharmacological activities of Homoharringtonine in depth, this article aims to provide a foundation for developing novel therapeutic approaches based on natural products, thereby advancing HHT's application research in cancer treatment and other fields.

Genomic instability in ovarian cancer: Through the lens of single nucleotide polymorphisms

Ovarian cancer (OC) is the deadliest gynecological malignancy among all female reproductive cancers. It is characterized by high mortality rate and poor prognosis. Genomic instability caused by mutations, single nucleotide polymorphisms (SNPs), copy number variations (CNVs), microsatellite instability (MSI), and chromosomal instability (CIN) are associated with OC predisposition. SNPs, which are highly prevalent in the general population, show a greater relative risk contribution, particularly in sporadic cancers. Understanding OC etiology in terms of genetic basis can increase the use of molecular diagnostics and provide promising approaches for designing novel treatment modalities. This will help deliver personalized medicine to OC patients, which may soon be within reach. Given the pivotal impact of SNPs in cancers, the primary emphasis of this review is to shed light on their prevalence in key caretaker genes that closely monitor genomic integrity, viz., DNA damage response, repair, cell cycle checkpoints, telomerase maintenance, and apoptosis and their clinical implications in OC. We highlight the current challenges faced in different SNP-based studies. Various computational methods and bioinformatic tools employed to predict the functional impact of SNPs have also been comprehensively reviewed concerning OC research. Overall, this review identifies that variants in the DDR and HRR pathways are the most studied, implying their critical role in the disease. Conversely, variants in other pathways, such as NHEJ, MMR, cell cycle, apoptosis, telomere maintenance, and PARP genes, have been explored the least.

Extensive homologous recombination safeguards oocyte genome integrity in mammals

Meiosis in mammalian oocytes is interrupted by a prolonged arrest at the germinal vesicle stage, during which oocytes have to repair DNA lesions to ensure genome integrity or otherwise undergo apoptosis. The FIRRM/FLIP-FIGNL1 complex dissociates RAD51 from the joint DNA molecules in both homologous recombination (HR) and DNA replication. However, as a type of non-meiotic, non-replicative cells, whether this RAD51-dismantling mechanism regulates genome integrity in oocytes remains elusive. Here, we show that FIRRM/FLIP is required for disassembly of RAD51-filaments and maintenance of genome integrity in oocytes. Deletion of FIRRM in oocytes leads to formation of massive nuclear RAD51 foci in oocytes of primordial follicles and activated follicles in mice. These RAD51 foci colocalize with the sites of DNA damage repair, as indicated by RPA2 and EdU, suggesting substantial DNA damage and extensive HR in oocytes. Especially in fully-grown FIRRM-deleted oocytes, RAD51 forms a net-like structure. As a consequence, FIRRM-deleted females are infertile due to aberrant homologous chromosome segregation at metaphase I and primordial follicle insufficiency at young adulthood. Hence, our study demonstrates the physiological importance of HR in maintaining genome integrity in oocytes.

Riluzole Enhancing Anti-PD-1 Efficacy by Activating cGAS/STING Signaling in Colorectal Cancer

Colorectal cancer is the second leading cause of cancer mortality in the United States. Although immune checkpoint blockade therapies including anti-PD-1/PD-L1 have been successful in treating a subset of patients with colorectal cancer, the response rates remain low. We have found that riluzole, a well-tolerated FDA-approved oral medicine for treating amyotrophic lateral sclerosis, increased intratumoral CD8+ T cells and suppressed tumor growth of colon cancer cells in syngeneic immune-competent mice. Riluzole-mediated tumor suppression was dependent on the presence of CD8+ T cells. Riluzole activates the cytosolic DNA sensing cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway in colon cancer cells, resulting in increased expression of IFNβ and IFNβ-regulated genes including CXCL10. Inhibition of ataxia telangiectasia mutated (ATM), but not ATM-related, resulted in a synergistic increase in IFNβ expression, suggesting that riluzole induces ATM-mediated damage response that contributes to cGAS/STING activation. Depletion of cGAS or STING significantly attenuated riluzole-induced expression of IFNβ and CXCL10 as well as increase of intratumoral CD8+ T cells and suppression of tumor growth. These results indicate that riluzole-mediated tumor infiltration of CD8+ T cells and attenuation of tumor growth is dependent on tumor cell-intrinsic STING activation. To determine whether riluzole treatment primes the tumor microenvironment for immune checkpoint modulation, riluzole was combined with anti-PD-1 treatment. This combination showed greater efficacy than either single agent and strongly suppressed tumor growth in vivo. Taken together, our studies indicate that riluzole activates cGAS/STING-mediated innate immune responses, which might be exploited to sensitize colorectal tumors to anti-PD-1/PD-L1 therapies.

Protein Phosphatase 2ACα Regulates ATR-Mediated Endogenous DNA Damage Response Against Microcephaly

Protein phosphatase 2A (PP2A) is an abundant heterotrimeric holoenzyme in eukaryotic cells coordinating with specific kinases to regulate spatial-temporal protein dephosphorylation in various biological processes. However, the function of PP2A in cortical neurogenesis remains largely unknown. Here, we report that neuronal-specific deletion of Pp2acα in mice displayed microcephaly, with significantly smaller brains and defective learning and memory ability. Mechanistically, neuronal Pp2acα deficiency resulted in elevated endogenous DNA damage and activation of ATR/CHK1 signaling. It was further induced by the loss of direct interaction between PP2AC and ATR as well as the function of PP2AC to dephosphorylate ATR. Importantly, ATR/CHK1 signaling dysregulation altered both the expression and activity of several critical downstream factors including P53, P21, Bcl2, and Bax, which led to decreased proliferation of cortical progenitor cells and increased apoptosis in developing cortical neurons. Taken together, our results indicate an essential function of PP2ACα in endogenous DNA damage response-mediated ATR signaling during neurogenesis, and defective PP2ACα in neurons contributes to microcephaly.

Guarding against digestive-system cancers: Unveiling the role of Chk2 as a potential therapeutic target

Digestive-system cancers represent major threats to human health; however, the mechanisms underlying tumorigenesis and radiochemotherapy resistance have remained elusive. Therefore, an urgent need exists for identifying key drivers of digestive system tumorigenesis and novel targeted therapeutics. The checkpoint kinase 2 (Chk2) regulates cell-cycle progression, and Chk2 dysregulation or Chk2 mutations can lead to the development of various cancers, which makes Chk2 an important research topic. This review summarizes the roles of Chk2 in DNA-damage responses, cell-cycle regulation, autophagy, and homeostasis maintenance. We describe relationships between tumorigenesis and cell-cycle dysregulation induced by Chk2 mutations. In addition, we summarize evidence indicating that Chk2 can serve as a novel therapeutic target, based on its contributions to radiochemotherapy-resistance reversion and progress made in developing antitumor agents against Chk2. The prevailing evidence supports the conclusion that further research on Chk2 will provide a deeper understanding of digestive-system tumorigenesis and should suggest novel therapeutic targets.

ATM/ATR-Mediated DNA Damage Response Facilitates SARS-CoV-2 Spike Protein-Induced Syncytium Formation

Multinucleated cells are present in lung tissues of patients infected by SARS-CoV-2. Although the spike protein can cause the fusion of infected cells and ACE2-expressing cells to form syncytia and induce damage, how host cell responses to this damage and the role of DNA damage response (DDR) signals in cell fusion are still unclear. Therefore, we investigated the effect of SARS-CoV-2 spike protein on the fusion of homologous and heterologous cells expressing ACE2 in vitro models, focusing on the protein levels of ATR and ATM, the major kinases responding to DNA damage, and their substrates CHK1 and CHK2. We found that both homologous and heterologous cell fusion activated the ATR-CHK1 and ATM-CHK2 signaling axis and induced the aggregation of γH2AX, 53BP1 and RAD51 in syncytia. In addition, siRNA or inhibitors of ATM and ATR suppressed syncytia formation by decreasing the level of S protein. These results showed the important role of DDR in stabilizing the S protein and in favoring its induction of cell fusion and syncytium formation, suggesting that the virus exploits the host DDR to facilitate its spread among infected cells.

PrimPol-mediated repriming elicits gap-filling by template switching and promotes cellular tolerance to cidofovir

A nucleoside analog, Cidofovir (CDV), is used for the treatment of viral diseases such as cytomegalovirus retinitis and herpes virus infection. CDV converts to its active diphosphate metabolite (CDVpp) through cellular kinases and acts as a competitive inhibitor for viral polymerase thereby interfering with viral replication. However, the effect of this drug on the replication of healthy host cells and the mechanisms involved in the cellular tolerance to CDV are yet to be fully understood. In this study, we explored the mechanisms underlying cellular tolerance to CDV by screening mutant cell lines exhibiting hypersensitivity to CDV from a collection of DT40 mutants deficient in various genome maintenance systems. We identified Rad17 and PrimPol as critical factors for CDV tolerance. We found that Rad17 plays a pivotal role in activating intra-S phase checkpoint by the phosphorylation of Chk1, a vital checkpoint mediator. We showed that PrimPol, a factor involved in the release of stalled replication, plays critical roles in CDV tolerance in tandem with Rad17. We found that PrimPol deficient cells showed slower replication on the CDV-incorporated template strand than did wild-type cells, indicating a critical role of PrimPol in the continuous replication fork progression on the CDV-incorporated damaged template. PrimPol releases replication arrest with its DNA-damage bypass function and its repriming function, we thus investigated which PrimPol function is involved in CDV tolerance using the separation of function mutant genes of PRIMPOL. The CDV hypersensitive phenotype of PrimPol deficient cells was restored by PRIMPOLY89D (primase active / reduced polymerase activity), indicating that the repriming function of PrimPol is required for maintaining replication on the CDV-damaged template. Moreover, we found that the number of sister chromatid exchange (SCE) was reduced in PrimPol-deficient cells. These data indicate that gaps generated by PrimPol-mediated repriming on CDV-damaged templates promote post-replicative gap-filing by template switching.

STEAP4 with copper reductase activity suppresses tumorigenesis by regulating the cell cycle in hepatocellular carcinoma cells

BACKGROUND

Abnormal expression of six-transmembrane epithelial antigen of prostate 4 (STEAP4) has been implicated in the carcinogenesis of hepatocellular carcinoma (HCC). However, the biological role and regulatory mechanisms of STEAP4 in HCC remain unclear.

METHODS AND RESULTS

Here, we analyzed STEAP4 expression levels and differentially expressed genes (DEGs) between STEAP4 high- and low-expression groups using multiple databases. Proliferation assays, 5-ethynyl-2'-deoxyuridine (EdU) assays, propidium iodide (PI) flow cytometry, and colony formation assays were conducted to assess the effects of STEAP4 on HCC cell proliferation, cell cycle progression, and clonogenic capacity. STEAP4 was downregulated in HCC tumor tissues, with lower expression associated with poorer overall survival (OS) and disease-free survival (DFS) in patients. Functional network analysis suggested that STEAP4 regulates cell cycle signaling, with tumor sections showing a negative correlation between STEAP4 and cell cycle proteins. Overexpression of STEAP4, combined with non-cytotoxic copper exposure in the HepG2 cell line, reduced proliferation and clonogenicity, induced cell cycle arrest, and downregulated the mRNA and protein levels of cell cycle-regulating genes. A predictive model based on STEAP4 and cell cycle gene demonstrated prognostic value in HCC patients.

CONCLUSIONS

Our results lay a foundation for further study of the cell cycle regulatory role of STEAP4 with Cu2+ reductase activity in HCC, indicating that STEAP4 may be a promising therapeutic target for HCC.

Identification of new hub- ferroptosis-related genes in Lupus Nephritis

Background: Lupus Nephritis (LN) is the primary causation of kidney injury in systemic lupus erythematosus (SLE). Ferroptosis is a programmed cell death. Therefore, understanding the crosstalk between LN and ferroptosis is still a significant challenge. Methods: We obtained the expression profile of LN kidney biopsy samples from the Gene Expression Omnibus database and utilised the R-project software to identify differentially expressed genes (DEGs). Then, we conducted a functional correlation analysis. Ferroptosis-related genes (FRGs) and differentially expressed genes (DEGs) crossover to select FRGs with LN. Afterwards, we used CIBERSORT to assess the infiltration of immune cells in both LN tissues and healthy control samples. Finally, we performed immunohistochemistry on LN human renal tissue. Results: 10619 DEGs screened from the LN biopsy tissue were identified. 22 hub-ferroptosis-related genes with LN (FRGs-LN) were screened out. The CIBERSORT findings revealed that there were significant statistical differences in immune cells between healthy control samples and LN tissues. Immunohistochemistry further demonstrated a significant difference in HRAS, TFRC, ATM, and SRC expression in renal tissue between normal and control groups. Conclusion: We developed a signature that allowed us to identify 22 new biomarkers associated with FRGs-LN. These findings suggest new insights into the pathology and therapeutic potential of LN ferroptosis inhibitors and iron chelators.

Harnessing Bioluminescence: A Comprehensive Review of In Vivo Imaging for Disease Monitoring and Therapeutic Intervention

The technique of using naturally occurring light-emitting reactants (photoproteins and luciferases] that have been extracted from a wide range of animals is known as bioluminescence imaging, or BLI. This imaging offers important details on the location and functional state of regenerative cells inserted into various disease-modeling animals. Reports on gene expression patterns, cell motions, and even the actions of individual biomolecules in whole tissues and live animals have all been made possible by bioluminescence. Generally speaking, bioluminescent light in animals may be found down to a few centimetres, while the precise limit depends on the signal's brightness and the detector's sensitivity. We can now spatiotemporally visualize cell behaviors in any body region of a living animal in a time frame process, including proliferation, apoptosis, migration, and immunological responses, thanks to BLI. The biological applications of in vivo BLI in nondestructively monitoring biological processes in intact small animal models are reviewed in this work, along with some of the advancements that will make BLI a more versatile molecular imaging tool.

Myriad factors and pathways influencing tumor radiotherapy resistance

Radiotherapy is a cornerstone in the treatment of various tumors, yet radioresistance often leads to treatment failure and tumor recurrence. Several factors contribute to this resistance, including hypoxia, DNA repair mechanisms, and cancer stem cells. This review explores the diverse elements that drive tumor radiotherapy resistance. Historically, resistance has been attributed to cellular repair and tumor repopulation, but recent research has expanded this understanding. The tumor microenvironment - characterized by hypoxia, immune evasion, and stromal interactions - further complicates treatment. Additionally, molecular mechanisms such as aberrant signaling pathways, epigenetic modifications, and non-B-DNA structures play significant roles in mediating resistance. This review synthesizes current knowledge, highlighting the interplay of these factors and their clinical implications. Understanding these mechanisms is crucial for developing strategies to overcome resistance and improve therapeutic outcomes in cancer patients.

New Synthetic Analogs of Natural 5Z,9Z-Dienoic Acids-Hybrid Molecules Based on Oleanolic Acid: Synthesis and Study of Antitumor Activity

Objectives: A series of synthetic analogs of natural (5Z,9Z)-diene acids were synthesized for the first time in the form of hybrid molecules containing an oleanolic acid fragment. This fragment was simultaneously linked by an amide bond to various hetero- and carbocyclic amines and a complex ester bond to (5Z,9Z)-tetradeca-5,9-dienecarboxylic acid, which was synthesized by a new reaction of Ti-catalyzed homocyclomagnification of 1,2-dienes. Results: Among the synthesized hybrids, the highest cytotoxic activity was observed for compound 9a in the series of Jurkat, K562, U937, and HEK293, with IC50 values of 4.5; 3.1; 2.8; and 26.17 μM/L, respectively. Furthermore, the synthesized compound 9a has been observed to induce apoptosis and exhibit genotoxicity in Jurkat culture, which suggests that it may be a promising candidate for further investigation as an antitumor agent.

The unique Pt(II)-induced nucleolar stress response and its deviation from DNA damage response pathways

The mechanisms of action for the platinum compounds cisplatin and oxaliplatin have yet to be fully elucidated, despite the worldwide use of these drugs. Recent studies suggest that the two compounds may be working through different mechanisms, with cisplatin inducing cell death via the DNA damage response (DDR) and oxaliplatin utilizing a nucleolar stress-based cell death pathway. While cisplatin-induced DDR has been subject to much research, the mechanisms for oxaliplatin's influence on the nucleolus are not well understood. Prior work has outlined structural parameters for Pt(II) derivatives capable of nucleolar stress induction. In this work, we gain insight into the nucleolar stress response induced by these Pt(II) derivatives by investigating potential correlations between this unique pathway and DDR. Key findings from this study indicate that Pt(II)-induced nucleolar stress occurs when DDR is inhibited and works independently of the ATM/ATR-dependent DDR pathway. We also determine that Pt(II)-induced stress may be linked to the G1 cell cycle phase, as cisplatin can induce nucleolar stress when cell cycle inhibition occurs at the G1/S checkpoint. Finally, we compare Pt(II)-induced nucleolar stress with other small-molecule nucleolar stress-inducing compounds Actinomycin D, BMH-21, and CX-5461 and find that Pt(II) compounds cause irreversible nucleolar stress, whereas the reversibility of nucleolar stress induced by small-molecules varies. Taken together, these findings contribute to a better understanding of Pt(II)-induced nucleolar stress, its deviation from ATM/ATR-dependent DDR, and the possible influence of cell cycle on the ability of Pt(II) compounds to cause nucleolar stress.

RAD18- and BRCA1-dependent pathways promote cellular tolerance to the nucleoside analog ganciclovir

Ganciclovir (GCV) is a clinically important drug as it is used to treat viral infections. GCV is incorporated into the DNA during replication, where it interferes with subsequent replication on GCV-incorporated templates. However, the effects of GCV on the host genome and the mechanisms underlying cellular tolerance to GCV remain unclear. In this study, we explored these mechanisms using a collection of mutant DT40 cells. We identified RAD17/-, BRCA1-/-, and RAD18-/- cells as highly GCV-sensitive. RAD17, a component of the alternative checkpoint-clamp loader RAD17-RFC, was required for the activation of the intra-S checkpoint following GCV treatment. BRCA1, a critical factor for promoting homologous recombination (HR), was required for suppressing DNA double-strand breaks (DSBs). Moreover, RAD18, an E3-ligase involved in DNA repair, was critical in suppressing the aberrant ligation of broken chromosomes caused by GCV. We found that BRCA1 suppresses DSBs through HR-mediated repair and template switching (TS)-mediated damage bypass. Moreover, the strong GCV sensitivity of BRCA1-/- cells was rescued by the loss of 53BP1, despite the only partial restoration in the sister chromatid exchange events which are hallmarks of HR. These results indicate that BRCA1 promotes cellular tolerance to GCV through two mechanisms, TS and HR-mediated repair.

Targeting the DNA damage response in cancer

DNA damage response (DDR) pathway is the coordinated cellular network dealing with the identification, signaling, and repair of DNA damage. It tightly regulates cell cycle progression and promotes DNA repair to minimize DNA damage to daughter cells. Key proteins involved in DDR are frequently mutated/inactivated in human cancers and promote genomic instability, a recognized hallmark of cancer. Besides being an intrinsic property of tumors, DDR also represents a unique therapeutic opportunity. Indeed, inhibition of DDR is expected to delay repair, causing persistent unrepaired breaks, to interfere with cell cycle progression, and to sensitize cancer cells to several DNA-damaging agents, such as radiotherapy and chemotherapy. In addition, DDR defects in cancer cells have been shown to render these cells more dependent on the remaining pathways, which could be targeted very specifically (synthetic lethal approach). Research over the past two decades has led to the synthesis and testing of hundreds of small inhibitors against key DDR proteins, some of which have shown antitumor activity in human cancers. In parallel, the search for synthetic lethality interaction is broadening the use of DDR inhibitors. In this review, we discuss the state-of-art of ataxia-telangiectasia mutated, ataxia-telangiectasia-and-Rad3-related protein, checkpoint kinase 1, Wee1 and Polθ inhibitors, highlighting the results obtained in the ongoing clinical trials both in monotherapy and in combination with chemotherapy and radiotherapy.

Tumour-intrinsic PDL1 signals regulate the Chk2 DNA damage response in cancer cells and mediate resistance to Chk1 inhibitors

BACKGROUND

Aside from the canonical role of PDL1 as a tumour surface-expressed immune checkpoint molecule, tumour-intrinsic PDL1 signals regulate non-canonical immunopathological pathways mediating treatment resistance whose significance, mechanisms, and therapeutic targeting remain incompletely understood. Recent reports implicate tumour-intrinsic PDL1 signals in the DNA damage response (DDR), including promoting homologous recombination DNA damage repair and mRNA stability of DDR proteins, but many mechanistic details remain undefined.

METHODS

We genetically depleted PDL1 from transplantable mouse and human cancer cell lines to understand consequences of tumour-intrinsic PDL1 signals in the DNA damage response. We complemented this work with studies of primary human tumours and inducible mouse tumours. We developed novel approaches to show tumour-intrinsic PDL1 signals in specific subcellular locations. We pharmacologically depleted tumour PDL1 in vivo in mouse models with repurposed FDA-approved drugs for proof-of-concept clinical translation studies.

RESULTS

We show that tumour-intrinsic PDL1 promotes the checkpoint kinase-2 (Chk2)-mediated DNA damage response. Intracellular but not surface-expressed PDL1 controlled Chk2 protein content post-translationally and independently of PD1 by antagonising PIRH2 E3 ligase-mediated Chk2 polyubiquitination and protein degradation. Genetic tumour PDL1 depletion specifically reduced tumour Chk2 content but not ATM, ATR, or Chk1 DDR proteins, enhanced Chk1 inhibitor (Chk1i) synthetic lethality in vitro in diverse human and murine tumour models, and improved Chk1i efficacy in vivo. Pharmacologic tumour PDL1 depletion with cefepime or ceftazidime replicated genetic tumour PDL1 depletion by reducing tumour Chk2, inducing Chk1i synthetic lethality in a tumour PDL1-dependent manner, and reducing in vivo tumour growth when combined with Chk1i.

CONCLUSIONS

Our data challenge the prevailing surface PDL1 paradigm, elucidate important and previously unappreciated roles for tumour-intrinsic PDL1 in regulating the ATM/Chk2 DNA damage response axis and E3 ligase-mediated protein degradation, suggest tumour PDL1 as a biomarker for Chk1i efficacy, and support the rapid clinical potential of pharmacologic tumour PDL1 depletion to treat selected cancers.

Panobinostat Synergizes with Chemotherapeutic Agents and Improves Efficacy of Standard-of-Care Chemotherapy Combinations in Ewing Sarcoma Cells

Background: The survival rate of patients with Ewing sarcoma (EWS) has seen very little improvement over the past several decades and remains dismal for those with recurrent or metastatic disease. HDAC2, ALK, JAK1, and CDK4 were identified as potential targets using RNA sequencing performed on EWS patient tumors with the bioinformatic analysis of gene expression. Methods/Results: The pan-HDAC inhibitor Panobinostat was cytotoxic to all the Ewing sarcoma cell lines tested. Mechanistically, Panobinostat decreases the expression of proteins involved in the cell cycle, including Cyclin D1 and phospho-Rb, and DNA damage repair, including CHK1. Further, Panobinostat induces a G1 cell cycle arrest. The combination of Panobinostat with Doxorubicin or Etoposide, both of which are used as standard of care in upfront treatment, leads to a synergistic effect in EWS cells. The combination of Panobinostat and Doxorubicin induces an accumulation of DNA damage, a decrease in the expression of DNA damage repair proteins CHK1 and CHK2, and an increase in caspase 3 cleavage. The addition of Panobinostat to standard-of-care chemotherapy combinations significantly reduces cell viability compared to that of chemotherapy alone. Conclusions: Overall, our data indicate that HDAC2 is overexpressed in many EWS tumor samples and HDAC inhibition is effective in targeting EWS cells, alone and in combination with standard-of-care chemotherapy agents. This work suggests that the addition of an HDAC inhibitor to upfront treatment may improve response.

Cell cycle checkpoint revolution: targeted therapies in the fight against malignant tumors

Malignant tumors are among the most important causes of death worldwide. The pathogenesis of a malignant tumor is complex and has not been fully elucidated. Studies have shown that such pathogenesis is related to abnormal cell cycle progression. The expression levels of cyclins, cyclin-dependent kinases (CDKs), and CDK inhibitors as well as functions of the cell cycle checkpoints determine whether the cell cycle progression is smooth. Cell-cycle-targeting drugs have the advantages of high specificity, low toxicity, low side effects, and low drug resistance. Identifying drugs that target the cell cycle and applying them in clinical treatments are expected to promote chemotherapeutic developments against malignant tumors. This article aims to review drugs targeted against the cell cycle and their action mechanisms.

Tryptanthrin targets GSTP1 to induce senescence and increases the susceptibility to apoptosis by senolytics in liver cancer cells

Targeting senescence has emerged as a promising strategy for liver cancer treatment. However, the lack of a safe agent capable of inducing complete senescence and being combined with senolytics poses a limitation. Here, we screened a natural product library and identified tryptanthrin (TRYP) as a potent inducer of cellular senescence in liver cancer cells both in vitro and in vivo. Mechanistically, Glutathione S-transferase P1 (GSTP1), a key regulator for redox homeostasis, was identified as a target protein for TRYP-induced senescence. TRYP directly bound to GSTP1 and inhibited its enzymatic activity, mediating reactive oxygen species (ROS) accumulation, followed by DNA damage response (DDR), consequently contributing to initiating primary senescence. Furthermore, TRYP triggered DNA damage-dependent activation of NF-κB pathway, which evoked senescence-associated secretory phenotype (SASP), thereby leading to senescence reinforcement. Importantly, TRYP exposed the vulnerability of tumor cells and sensitized senescent cells to apoptosis induced by senolytic agent ABT263, a Bcl2 inhibitor. Taken together, our findings reveal that TRYP induces cellular senescence via GSTP1/ROS/DDR/NF-κB/SASP axis, providing a novel potential application in synergizing with senolytic therapy in liver cancer.

Therapeutic effect of three-dimensional hanging drop cultured human umbilical cord mesenchymal stem cells on osteoarthritis in rabbits

BACKGROUND

Mesenchymal stem cells (MSCs) have shown a positive effect on Osteoarthritis (OA), but the efficacy is still not significant in clinical. Conventional two-dimensional (2D) monolayer culture method is prone to cause MSCs undergoing replication senescence, which may affect the functions of MSCs. Three-dimensional (3D) culture strategy can sustain cell proliferative capacity and multi-differentiation potential. This study aimed to investigate the therapeutic potential of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) cultured by 3D hanging drop method on OA.

METHODS

hUC-MSCs were isolated from umbilical cord and cultured by 3D hanging drop method for 48 h. Scanning electron microscopy (SEM) was used to observe gross morphology 2D and 3D hUC-MSCs. Transcriptome comparison of gene expression differences between 2D and 3D hUC-MSCs. GO enrichment analysis, KEGG pathway enrichment analysis and GSEA enrichment analysis were used to analyze the impact of 3D hanging drop culture on the biological functions of hUC-MSCs. Female New Zealand rabbits (n = 12) were divided into 4 groups: Normal group, Model group, 2D hUC-MSCs treatment group and 3D hUC-MSCs treatment group. After 8 weeks, the gross and histological appearance of the cartilage was evaluated by safranin O-fast green staining and Mankin scoring system. The expression of type I collagen and type II collagen was detected by immunohistochemistry. The levels of IL-6, IL-7, TNFα, TGFβ1 and IL-10 in the knee joint fluid were tested by ELISA.

RESULTS

3D hanging drop culture changed cell morphology but did not affect phenotype. The MSCs transcriptome profiles showed that 3D hanging drop culture method enhanced cell-cell contact, improved cell responsiveness to external stimuli and immunomodulatory function. The animal experiment results showed that hUC-MSCs could promote cartilage regeneration compared with Model group. 3D hUC-MSCs treatment group had a higher histological score and significantly increased type II collagen secretion. In addition, 3D hUC-MSCs treatment group increased the expression of anti-inflammatory factors TGFβ1 and IL-10.

CONCLUSION

The above experimental results illustrated that 3D hanging drop culture method could enhance the therapeutic effect of hUC-MSCs, and showed a good clinical application prospect in the treatment of OA.

Cigarette smoke extract induces malignant transformation and DNA damage via c-MET phosphorylation in human bronchial epithelial cells

Cigarette smoke, a complex mixture produced by tobacco combustion, contains a variety of carcinogens and can trigger DNA damage. Overactivation of c-MET, a receptor tyrosine kinase, may cause cancer and cellular DNA damage, but the underlying mechanisms are unknown. In this work, we investigated the mechanisms of cigarette smoke extract (CSE) induced malignant transformation and DNA damage in human bronchial epithelial cells (BEAS-2B). The results demonstrated that CSE treatment led to up-regulated mRNA expression of genes associated with the c-MET signaling pathway, increased expression of the DNA damage sensor protein γ-H2AX, and uncontrolled proliferation in BEAS-2B cells. ATR, ATR, and CHK2, which are involved in DNA damage repair, as well as the phosphorylation of c-MET and a group of kinases (ATM, ATR, CHK1, CHK2) involved in the DNA damage response were all activated by CSE. In addition, CSE activation promotes the phosphorylation modification of ATR, CHK1 proteins associated with DNA damage repair. The addition of PHA665752, a specific inhibitor of c-MET, or knock-down with c-MET both attenuated DNA damage, while overexpression of c-MET exacerbated DNA damage. Thus, c-MET phosphorylation may be involved in CSE-induced DNA damage, providing a potential target for intervention in the prevention and treatment of smoking-induced lung diseases.

Arabidopsis cryptochromes interact with SOG1 to promote the repair of DNA double-strand breaks

Cryptochromes (CRYs) are blue light (BL) photoreceptors to regulate a variety of physiological processes including DNA double-strand break (DSB) repair. SUPPRESSOR OF GAMMA RADIATION 1 (SOG1) acts as the central transcription factor of DNA damage response (DDR) to induce the transcription of downstream genes, including DSB repair-related genes BRCA1 and RAD51. Whether CRYs regulate DSB repair by directly modulating SOG1 is unknown. Here, we demonstrate that CRYs physically interact with SOG1. Disruption of CRYs and SOG1 leads to increased sensitivity to DSBs and reduced DSB repair-related genes' expression under BL. Moreover, we found that CRY1 enhances SOG1's transcription activation of DSB repair-related gene BRCA1. These results suggest that the mechanism by which CRYs promote DSB repair involves positive regulation of SOG1's transcription of its target genes, which is likely mediated by CRYs-SOG1 interaction.

Critical role of checkpoint kinase 1 in spinal cord injury-induced motor dysfunction in mice

Spinal cord injury (SCI) is a devastating neurotraumatic condition characterized by severe motor dysfunction and paralysis. Accumulating evidence suggests that DNA damage is involved in SCI pathology. However, the underlying mechanisms remain elusive. Although checkpoint kinase 1 (Chk1)-regulated DNA damage is involved in critical cellular processes, its role in SCI regulation remains unclear. This study aimed to explore the role and potential mechanism of Chk1 in SCI-induced motor dysfunction. Adult female C57BL/6J mice subjected to T9-T10 spinal cord contusions were used as models of SCI. Western blotting, immunoprecipitation, histomorphology, and Chk1 knockdown or overexpression achieved by adeno-associated virus were performed to explore the underlying mechanisms. Levels of p-Chk1 and γ-H2AX (a cellular DNA damage marker) were upregulated, while ferroptosis-related protein levels, including glutathione peroxidase 4 (GPX4) and x-CT were downregulated, in the spinal cord and hippocampal tissues of SCI mice. Functional experiments revealed increased Basso Mouse Scale (BMS) scores, indicating that Chk1 downregulation promoted motor function recovery after SCI, whereas Chk1 overexpression aggravated SCI-induced motor dysfunction. In addition, Chk1 downregulation reversed the SCI-increased levels of GPX4 and x-CT expression in the spinal cord and hippocampus, while immunoprecipitation assays revealed strengthened interactions between p-Chk1 and GPX4 in the spinal cord after SCI. Finally, Chk1 downregulation promoted while Chk1 overexpression inhibited NeuN cellular immunoactivity in the spinal cord after SCI, respectively. Collectively, these preliminary results imply that Chk1 is a novel regulator of SCI-induced motor dysfunction, and that interventions targeting Chk1 may represent promising therapeutic targets for neurotraumatic diseases such as SCI.

PROTAC-mediated conditional degradation of the WRN helicase as a potential strategy for selective killing of cancer cells with microsatellite instability

Multiple studies have demonstrated that cancer cells with microsatellite instability (MSI) are intolerant to loss of the Werner syndrome helicase (WRN), whereas microsatellite-stable (MSS) cancer cells are not. Therefore, WRN represents a promising new synthetic lethal target for developing drugs to treat cancers with MSI. Given the uncertainty of how effective inhibitors of WRN activity will prove in clinical trials, and the likelihood of tumours developing resistance to WRN inhibitors, alternative strategies for impeding WRN function are needed. Proteolysis-targeting chimeras (PROTACs) are heterobifunctional small molecules that target specific proteins for degradation. Here, we engineered the WRN locus so that the gene product is fused to a bromodomain (Bd)-tag, enabling conditional WRN degradation with the AGB-1 PROTAC specific for the Bd-tag. Our data revealed that WRN degradation is highly toxic in MSI but not MSS cell lines. In MSI cells, WRN degradation caused G2/M arrest, chromosome breakage and ATM kinase activation. We also describe a multi-colour cell-based platform for facile testing of selective toxicity in MSI versus MSS cell lines. Together, our data show that a degrader approach is a potentially powerful way of targeting WRN in MSI cancers and paves the way for the development of WRN-specific PROTAC compounds.

Inhibition of Aberrantly Overexpressed Polo-like Kinase 4 Is a Potential Effective Treatment for DNA Damage Repair-Deficient Uterine Leiomyosarcoma

PURPOSE

Uterine leiomyosarcoma (LMS) is an aggressive sarcoma and a subset of which exhibits DNA repair defects. Polo-like kinase 4 (PLK4) precisely modulates mitosis, and its inhibition causes chromosome missegregation and increased DNA damage. We hypothesize that PLK4 inhibition is an effective LMS treatment.

EXPERIMENTAL DESIGN

Genomic profiling of clinical uterine LMS samples was performed, and homologous recombination (HR) deficiency scores were calculated. A PLK4 inhibitor (CFI-400945) with and without an ataxia telangiectasia mutated (ATM) inhibitor (AZD0156) was tested in vitro on gynecologic sarcoma cell lines SK-UT-1, SKN, and SK-LMS-1. Findings were validated in vivo using the SK-UT-1 xenograft model in the Balb/c nude mouse model. The effects of CFI-400945 were also evaluated in a BRCA2-knockout SK-UT-1 cell line. The mechanisms of DNA repair were analyzed using a DNA damage reporter assay.

RESULTS

Uterine LMS had a high HR deficiency score, overexpressed PLK4 mRNA, and displayed mutations in genes responsible for DNA repair. CFI-400945 demonstrated effective antitumor activity in vitro and in vivo. The addition of AZD0156 resulted in drug synergism, largely due to a preference for nonhomologous end-joining DNA repair. Compared with wild-type cells, BRCA2 knockouts were more sensitive to PLK4 inhibition when both HR and nonhomologous end-joining repairs were impaired.

CONCLUSIONS

Uterine LMS with DNA repair defects is sensitive to PLK4 inhibition because of the effects of chromosome missegregation and increased DNA damage. Loss-of-function BRCA2 alterations or pharmacologic inhibition of ATM enhanced the efficacy of the PLK4 inhibitor. Genomic profiling of an advanced-stage or recurrent uterine LMS may guide therapy.

DNA lesions that block transcription induce the death of Trypanosoma cruzi via ATR activation, which is dependent on the presence of R-loops

Trypanosoma cruzi is the etiological agent of Chagas disease and a peculiar eukaryote with unique biological characteristics. DNA damage can block RNA polymerase, activating transcription-coupled nucleotide excision repair (TC-NER), a DNA repair pathway specialized in lesions that compromise transcription. If transcriptional stress is unresolved, arrested RNA polymerase can activate programmed cell death. Nonetheless, how this parasite modulates these processes is unknown. Here, we demonstrate that T. cruzi cell death after UV irradiation, a genotoxic agent that generates lesions resolved by TC-NER, depends on active transcription and is signaled mainly by an apoptotic-like pathway. Pre-treated parasites with α-amanitin, a selective RNA polymerase II inhibitor, become resistant to such cell death. Similarly, the gamma pre-irradiated cells are more resistant to UV when the transcription processes are absent. The Cockayne Syndrome B protein (CSB) recognizes blocked RNA polymerase and can initiate TC-NER. Curiously, CSB overexpression increases parasites' cell death shortly after UV exposure. On the other hand, at the same time after irradiation, the single-knockout CSB cells show resistance to the same treatment. UV-induced fast death is signalized by the exposition of phosphatidylserine to the outer layer of the membrane, indicating a cell death mainly by an apoptotic-like pathway. Furthermore, such death is suppressed in WT parasites pre-treated with inhibitors of ataxia telangiectasia and Rad3-related (ATR), a key DDR kinase. Signaling for UV radiation death may be related to R-loops since the overexpression of genes associated with the resolution of these structures suppress it. Together, results suggest that transcription blockage triggered by UV radiation activates an ATR-dependent apoptosis-like mechanism in T. cruzi, with the participation of CSB protein in this process.

Distinct regulation of ATM signaling by DNA single-strand breaks and APE1

In response to DNA double-strand breaks or oxidative stress, ATM-dependent DNA damage response (DDR) is activated to maintain genome integrity. However, it remains elusive whether and how DNA single-strand breaks (SSBs) activate ATM. Here, we provide direct evidence in Xenopus egg extracts that ATM-mediated DDR is activated by a defined SSB structure. Our mechanistic studies reveal that APE1 promotes the SSB-induced ATM DDR through APE1 exonuclease activity and ATM recruitment to SSB sites. APE1 protein can form oligomers to activate the ATM DDR in Xenopus egg extracts in the absence of DNA and can directly stimulate ATM kinase activity in vitro. Our findings reveal distinct mechanisms of the ATM-dependent DDR activation by SSBs in eukaryotic systems and identify APE1 as a direct activator of ATM kinase.

Correlation between Molecular Docking and the Stabilizing Interaction of HOMO-LUMO: Spirostans in CHK1 and CHK2, an In Silico Cancer Approach

Checkpoint kinases 1 and 2 (CHK1 and CHK2) are enzymes that are involved in the control of DNA damage. At the present time, these enzymes are some of the most important targets in the fight against cancer since their inhibition produces cytotoxic effects in carcinogenic cells. This paper proposes the use of spirostans (Sp), natural compounds, as possible inhibitors of the enzymes CHK1 and CHK2 from an in silico analysis of a database of 155 molecules (S5). Bioinformatics studies of molecular docking were able to discriminate between 13 possible CHK1 inhibitors, 13 CHK2 inhibitors and 1 dual inhibitor for both enzymes. The administration, distribution, metabolism, excretion and toxicity (ADMETx) studies allowed a prediction of the distribution and metabolism of the potential inhibitors in the body, as well as determining the excretion routes and the appropriate administration route. The best inhibition candidates were discriminated by comparing the enzyme-substrate interactions from 2D diagrams and molecular docking. Specific inhibition candidates were obtained, in addition to studying the dual inhibitor candidate and observing their stability in dynamic molecular studies. In addition, Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital (HOMO-LUMO) interactions were analyzed to study the stability of interactions between the selected enzymes and spirostans resulting in the predominant gaps from HOMOCHKs to LUMOSp (Highest Occupied Molecular Orbital of CHKs-Lowest Unoccupied Molecular Orbital of spirostan). In brief, this study presents the selection inhibitors of CHK1 and CHK2 as a potential treatment for cancer using a combination of molecular docking and dynamics, ADMETx predictons, and HOMO-LUMO calculation for selection.

Deciphering the role of post-translational modifications in fanconi anemia proteins and their influence on tumorigenesis

Fanconi anemia (FA) is an autosomal or X-linked human disease, characterized by bone marrow failure, cancer susceptibility and various developmental abnormalities. So far, at least 22 FA genes (FANCA-W) have been identified. Germline inactivation of any one of these FA genes causes FA symptoms. Proteins encoded by FA genes are involved in the Fanconi anemia pathway, which is known for its roles in DNA inter-strand crosslinks (ICLs) repair. Besides, its roles in genome maintenance upon replication stress has also been reported. Post-translational modifications (PTMs) of FA proteins, particularly phosphorylation and ubiquitination, emerge as critical determinants in the activation of the FA pathway during ICL repair or replication stress response. Consequent inactivation of the FA pathway engenders heightened chromosomal instability, thereby constituting a genetic susceptibility conducive to cancer predisposition and the exacerbation of tumorigenesis. In this review, we have combined recent structural analysis of FA proteins and summarized knowledge on the functions of different PTMs in regulating FA pathways, and discuss potential contributions stemming from mutations at PTMs to the genesis and progression of tumorigenesis.