Search Results (759)

DNA double-strand breaks (DSBs), caused by various endogenous and exogenous factors, pose a significant threat to genomic stability. Several conserved repair pathways address DSBs, with homologous recombination (HR) being the only mechanism capable of accurately restoring the original DNA sequence. The BRCA1 gene plays a critical role in HR and is involved in maintaining genomic stability, cell cycle regulation, transcription, and tumor angiogenesis. Germline mutations in BRCA1 are strongly associated with increased risks of breast, ovarian, and other cancers. Dysfunction of BRCA1 leads to homologous recombination deficiency (HRD), forcing cells to rely on error-prone repair pathways, which promotes genomic instability and tumorigenesis. Besides hereditary mutations, HRD can also arise in sporadic cancers through epigenetic mechanisms such as promoter hypermethylation and reduced BRCA1 expression. Although BRCA1 deficiency is uncommon in lung cancer, BRCA1 status is considered a potential biomarker for sensitivity to platinum-based chemotherapy and other cytotoxic agents used in lung cancer treatment. However, the impact of BRCA1 on treatment response and prognosis in lung cancer remains controversial and not fully understood. This review summarizes current evidence on the role of BRCA1 in modulating chemotherapy response and disease outcomes in lung cancer patients, highlighting its potential as a biomarker for personalized therapy selection. Thus, in this context, the key unresolved issues critical for the development of personalized treatment strategies for lung cancer associated with BRCA1 alterations include the identification of molecular biomarkers most reliably associated with tumor sensitivity to chemotherapy. In addition, the development of methods for identifying patients with homologous recombination deficiency specifically in lung tumors appears to be of considerable importance, as does a better understanding of how the biological and therapeutic implications of BRCA1-related parameters in lung cancer differ from those observed in other tumor types. Addressing these challenges could substantially improve the efficacy of chemotherapy and patient outcomes, while also expanding the opportunities for a personalized approach to treatment selection in patients with lung cancer. Full article

Alterations in the redox status and the DNA damage response (DDR) parameters are early, mechanistically interconnected drivers of carcinogenesis. Herein, we investigated whether such alterations, arising during the progression of Multiple Myeloma (MM), are systemically reflected in peripheral blood mononuclear cells (PBMCs). Redox status, expressed as the GSH/GSSG ratio, and DDR-related parameters, including baseline DNA damage, efficiency of key DNA repair pathways, namely nucleotide excision repair (NER) and double-strand break repair (DSB/R), as well as apoptotic sensitivity, were evaluated in PBMCs from 17 patients with Monoclonal Gammopathy of Undetermined Significance (MGUS), 20 with smoldering MM (SMM), and 19 with MM. PBMCs from 20 healthy controls (HCs) were analyzed in parallel. Baseline DNA damage levels and DNA repair capacities across all examined pathways increased progressively in the following order: HC < MGUS < SMM < MM (p < 0.001). This progression was accompanied by a gradual increase in chromatin relaxation. Conversely, the GSH/GSSG ratio and apoptotic sensitivity declined during disease progression (p < 0.001). Collectively, malignant transformation in MM is associated with progressive dysregulation of DDR pathways and redox status in PBMCs. The identification of these molecular perturbations in an easily accessible tissue, such as peripheral blood, underscores their potential utility for early detection and prognostic assessment of MM. Full article

Background: Head and neck squamous cell carcinoma (HNSCC) remains a highly aggressive malignancy with poor clinical outcomes. Although poly(ADP-ribose) polymerase (PARP) inhibitors have shown promising activity in tumors with homologous recombination deficiency, their efficacy in BRCA wild-type HNSCC remains limited. Reactive oxygen species (ROS)-induced DNA damage may increase cellular dependence on DNA repair pathways and thereby enhance sensitivity to PARP inhibition. This study investigated whether ROS-mediated DNA damage could sensitize BRCA wild-type HNSCC cells to the PARP inhibitor olaparib. Methods: BRCA wild-type HSC-3 and SCC-25 HNSCC cell lines were exposed to H₂O₂ to induce oxidative stress. Intracellular ROS levels were quantified using DCFDA assays, DNA double-strand breaks were evaluated by γ-H2AX ELISA, PARP activity was assessed by ELISA, and cell viability was determined using MTT assays. Expression levels of DNA repair genes (PARP1, PARP2, BRCA1, BRCA2, RAD51, and MLH1), checkpoint kinases (ATM, ATR, and CHK1), the homologous recombination regulator FANCD2, and redox defense genes (NQO1, GPX4, and SLC7A11) were analyzed by qRT-PCR. Therapeutic selectivity was assessed using HGF-1 normal human gingival fibroblasts as a normal cell control. Apoptosis was measured through caspase-3/7 activity assays, and drug interactions were evaluated using the Chou–Talalay method. Results: H₂O₂ treatment increased intracellular ROS levels in both cell lines, accompanied by significant induction of DNA damage as demonstrated by elevated γ-H2AX levels. ROS induction markedly enhanced olaparib sensitivity, significantly reducing IC₅₀ values in both HSC-3 and SCC-25 cells. Combined H₂O₂ and olaparib treatment produced strong synergistic cytotoxicity, suppressed DNA repair, checkpoint kinase, and redox defense gene expression, and increased caspase-3/7 activity compared with control cells. Importantly, the combination demonstrated selective cytotoxicity toward cancer cells, with normal HGF-1 cells retaining significantly higher viability. Conclusions: ROS-induced DNA damage significantly enhances the anti-tumor activity of olaparib in BRCA wild-type HNSCC cells through a functional synthetic lethal-like interaction involving the simultaneous collapse of DNA repair capacity, checkpoint activation, and oxidative stress buffering, culminating in apoptosis induction. These findings support the rationale for combining ROS-generating therapies with PARP inhibitors in HNSCC treatment. Full article

Ribonucleotides are frequently incorporated into DNA during the replication of genetic information and, if missed during ribonucleotide excision repair, they may undergo phosphodiester bond rearrangement or cleavage. These changes can in turn lead to deformation of the spatial geometry of the local double helix and potentially interfere with charge transfer through ds-DNA. This process is believed to support long-range communication between proteins involved in genome replication and repair. This study theoretically explores how a single embedded riboadenosine (A₃) affects the structure, electronic properties, and charge-transfer properties of double-stranded DNA ([A₁G₂A₃G₄A₅]*[T₅C₄T₃C₂T₁]). In particular, the study focuses on four products formed at the ribonucleotide site: native 3′,5′-linkage (R-DNA), the 2′,3′-cyclic phosphate intermediate (IM-R-DNA), rearranged 2′,5-linked (RE-R-DNA), and the single-strand-break cleavage product (SSB-R-DNA). This theoretical investigation was performed at the M06-2X/6-31++G**//M06-2X/D95** level of theory in the aqueous phase. Significant spatial geometry perturbations were found at the central part of ds-oligonucleotides, i.e., the A₃T₃|G₄C₂ region, where the modified linkage affected the base overlap and stacking interactions most strongly; in the rearranged and cleaved forms, stacking at this site decreased by about 7 kcal•mol⁻¹ relative to native DNA. Global electronic analysis showed that R-DNA had the highest ionisation potential and the lowest electron affinity, whereas SSB-R-DNA displayed the lowest adiabatic ionisation potential and the highest adiabatic electron affinity, indicating a much greater tendency to stabilise excess charge. At the base-pair level, G₂C₄ was usually the preferred hole sink, except in RE-R-DNA, where G₄C₂ was favoured. In contrast, electron localisation was generally favoured at G₄C₂, while, in SSB-R-DNA, the A₃T₃ pair became the most favourable electron-accepting site. Overall, the results show that even a single ribonucleotide, depending on its linkage chemistry, can substantially reshape charge migration through ds-DNA and may therefore influence lesion recognition, repair efficiency, and genome stability. Full article

Chromosomal rearrangements that lead to the formation of oncogenic gene fusions, such as EML4-ALK, are thought to arise from incorrect repair of double-strand breaks in DNA. However, the mechanisms and factors driving rearrangement formation remain poorly understood, and analysis of these processes is limited by detection methods that are labor-intensive, low-throughput, and not readily quantitative at single-cell resolution. Here, we developed a genetically encoded ALK reporter based on A549 lung adenocarcinoma cells, created by inserting an ALK-P2A-mCherry cassette into the endogenous ALK locus, so that induced EML4-ALK fusion activated mCherry fluorescence. Reporter activation yielded a readily quantifiable mCherry-positive subpopulation that could be measured and enriched by flow cytometry and correlated with EML4-ALK levels. Using this platform, we combined CRISPR-mediated rearrangement induction with knockdown of DNA repair factors using RNA interference. Of the factors involved in base excision repair, homologous recombination-related pathways and canonical non-homologous end joining, knockdown of the APEX1 gene encoding apurinic endonuclease 1 (APE1) selectively increased EML4-ALK levels both in the reporter cell line and in parental A549 cells. Together, this work provides a sensitive, single-cell A549-based ALK reporter platform and a framework for future studies aimed at identifying cellular and environmental factors that modulate oncogenic EML4-ALK rearrangement formation. Full article

Endogenous gene tagging using CRISPR has changed the understanding of the role played by different proteins due to the ability to track and study proteins in their natural state. With CRISPR-based gene tagging, it is possible to insert fluorescent, luminescent, epitope, affinity, and proximity labels into the target protein at its endogenous genomic location without affecting its physiological expression and dynamics. Here, we discuss the DNA-repair mechanisms employed in endogenous gene tagging, including homology-dependent repair, NHEJ-based integration, and alternative approaches that can be used with challenging cell types. Key aspects of efficient CRISPR tagging experiments are also described. Additionally, we review recent advances in the increasing array of protein tag technologies, including fluorescent proteins, split-reporter technologies, NanoLuc/HiBiT, peptide epitopes, and proximity biotinylation enzymes. Lastly, we review the scalability of endogenous tagging approaches using multiplex editing, atlas-scale proteome tagging, iPSC-based disease modeling, and drug discovery platforms for assessing target engagement, protein degradation, phenotype screening, and mechanism of action of compounds. Although difficult in primary and pluripotent cells, new methods based on avoiding double-strand breaks, such as prime editing, PASTE, and CRISPR associated transposases, will drive the future expansion of endogenous tagging approaches. Such developments firmly set up CRISPR gene tagging as a fundamental technology in quantitative cell biology and translational pharmacology. Full article

Background/Objective: Ultraviolet A and B (UVAB) radiation is a major environmental factor that induces DNA damage and upregulates programmed death-ligand 1 (PD-L1) expression in skin cells, thereby contributing to immune evasion and impaired tissue repair. This study evaluated the protective effects of two purified compounds, Cinnamtannin B1 (CTB-1) and Cinnamtannin D1 (CTD-1), as well as cinnamon extract, in UVAB-irradiated human keratinocyte HaCaT cells. Methods: HaCaT cells were exposed to low (20 kJ/m² UVA, 1.3 kJ/m² UVB), medium (30 kJ/m² UVA, 2 kJ/m² UVB), and high (40 kJ/m² UVA, 2.7 kJ/m² UVB) UVAB doses of UVAB radiation. Dose-dependent effects of CTB-1 and CTD-1 (0, 5, 10, 25, and 50 µg/ mL) and cinnamon extract (0, 5, 10, 50, and 100 µg/mL), as well as time-dependent effects (12, 24, and 72 h), were evaluated by measuring PD-L1 expression, cell viability, and DNA damage. Results: CTD-1 was the most effective compound, significantly reducing UVAB-induced PD-L1 expression and DNA double-strand breaks without compromising cell viability. CTB-1 also demonstrated protective effects at specific doses and time points; however, higher concentrations reduced cell viability. Cinnamon extract was protective at low concentrations but cytotoxic at higher doses. Conclusions: CTD-1, CTB-1, and cinnamon extract attenuated UVAB-induced cellular damage in HaCaT cells, with CTD-1 demonstrating the most favorable protective profile. These findings support the potential of cinnamon-derived compounds as therapeutic candidates for preventing UVAB-induced skin damage and immune dysregulation. Full article

Background/Objectives: Disruption of cellular redox balance and DNA damage response (DDR) signals represents a key driver of cancer development, influencing tumor progression and therapeutic response. Here, we investigated the interplay between DDR-related parameters and oxidative stress in relation to treatment response in patients with multiple myeloma (MM). Methods: Oxidative stress and DDR signals were evaluated in primary cells, including peripheral blood mononuclear cells (PBMCs) and bone marrow plasma cells (BMPCs), collected at diagnosis from MM patients who were subsequently classified as responders (n = 35) or non-responders (n = 41) to melphalan-based therapy. Results: PBMCs and BMPCs from non-responders exhibited a distinct biological profile characterized by lower baseline DNA damage, reduced oxidative stress, increased nucleotide excision repair and double-strand break repair capacity, and reduced apoptotic sensitivity compared with responders (all p < 0.001). In addition, non-responders displayed increased chromatin relaxation. Differential gene expression patterns involving DDR-related pathways further distinguished BMPCs between the two clinical outcome groups. Conclusions: Collectively, these findings indicate that alterations in oxidative stress and DDR signals play a crucial role in determining response to melphalan-based therapy in MM. The identification of these molecular alterations in an easily accessible tissue, such as peripheral blood, underscores their potential clinical relevance and warrants further validation. Full article

Ataxia–telangiectasia is a rare, autosomal recessive primary immunodeficiency caused by mutations in the ATM gene on chromosome 11, which encodes a serine–threonine kinase essential for the recognition and repair of DNA double-strand breaks. The disease is characterized by progressive neurological impairment, immunological dysfunction, and an increased susceptibility to recurrent infections and malignancies. Pulmonary involvement represents a major source of morbidity and frequently arises from chronic infections, aspiration, and impaired airway clearance, ultimately leading to the development of bronchiectasis. The case of a 15-year-old adolescent with a history of recurrent aspiration pneumonias, neuropsychomotor developmental delay, and severe malnutrition is reported, who was admitted for evaluation of chronic productive cough, fever, and dysphagia. Comprehensive clinical assessment and ancillary investigations revealed recurrent respiratory infections, gastroesophageal reflux, and typical features of ataxia–telangiectasia, including cerebellar ataxia, oculomotor apraxia, and conjunctival telangiectasias. Additionally, bronchiectasis was identified as a secondary consequence of the underlying neurological and immunological impairment. This case highlights the diagnostic challenges posed by ataxia–telangiectasia in pediatric patients presenting with chronic respiratory symptoms and emphasizes the importance of early recognition of the underlying systemic disorder. A multidisciplinary approach is essential for accurate diagnosis and optimized management, aiming to address both the primary disease and its pulmonary complications. Full article

Radiotherapy is one of the most effective methods of cancer treatment. New, more effective, and safer radiotherapy methods can be developed thanks to selective radioprotectors. In our study, we investigated the antioxidant and radiomodulatory activity of sodium aminodihydrophthalazinedione (the drug Tameron^®) on human mesenchymal stem cells (MSCs) and human osteosarcoma cells of the MNNG/Hos line in vitro. We have shown that sodium aminodihydrophthalazinedione effectively scavenged radiation-induced hydrogen peroxide in aqueous solution in a concentration-dependent manner after X-ray irradiation. We also showed that sodium aminodihydrophthalazinedione (0.25 mM and above) effectively protects human MSCs from the damaging effects of X-rays, reducing the level of intracellular ROS and the number of apoptotic cells after irradiation, enhancing the restoration of double-stranded DNA breaks and clonogenic activity. Meanwhile, the effect of sodium aminodihydrophthalazinedione on human osteosarcoma MNNG/Hos cells was different: it increased the number of apoptotic cells and reduced the rate of repair of double-stranded DNA breaks. Transcriptomic studies on both cell culture types using nanopore sequencing technology after X-ray irradiation and sodium aminodihydrophthalazinedione pretreatment revealed a significant level of modulation of key genes responsible for DNA repair, antioxidant activity, and genome stability. Our data show that sodium aminodihydrophthalazinedione may be a promising therapeutic agent for modulating the cellular effects of radiation exposure. Full article

Background/Objectives: Schisandrin B (Sch B), a bioactive lignan of Schisandra chinensis has been commonly investigated for its antitumor activities, yet its radiosensitizing effect and mechanism remain unclear. This study was conducted to investigate the radiosensitizing effects of Sch B in breast cancer (BC) and elucidate its molecular mechanisms, with a specific focus on the gut microbiota–immune axis. Methods: In vitro, CCK-8, colony formation, and 3D spheroid assays were used to evaluate the effects of Sch B on proliferation inhibition and radiosensitization, flow cytometry and immunofluorescence were used to elucidate the mechanisms involved. In vivo, 4T1 tumor-bearing mice were treated with Sch B, and 16S rDNA sequencing and LC-MS/MS were used to analyze the gut microbiota and short-chain fatty acid (SCFA) metabolism. IHC and qPCR detected antitumor immune responses. Results: Sch B inhibited the proliferation of BC cells in a time- and dose-dependent manner with negligible toxicity to the mammary epithelial cell line MCF-10A. Furthermore, Sch B enhanced the radiosensitivity (sensitization enhancement ratio: 1.20~1.77) of BC by inducing G1 phase cell cycle arrest and delaying radiation-induced DNA double-strand break repair. In vivo, Sch B suppressed BC growth in BALB/c mice without causing obvious systemic toxicity. Sch B reversed tumor-induced gut microbiota dysbiosis (restoring species abundance and the Firmicutes/Bacteroidetes ratio, enriching beneficial genera such as Lactobacillus and Butyrobacter) and normalized SCFA profiles (correlative evidence). Furthermore, Sch B modulated systemic immune responses by increasing the expression of Ifng, Cxcl10, Ddx58 and promoting CD3⁺ and CD8⁺ T-cell infiltration in tumors. Conclusions: Sch B exerts BC radiosensitization through dual mechanisms, direct regulation of the cell cycle and DNA repair, and indirect modulation of the gut microbiota-immune axis (correlative evidence), highlighting it as a safe and effective candidate for improving the efficacy of BC radiotherapy. Full article

Germline loss-of-function mutations in BRCA1 and BRCA2 markedly increase susceptibility to breast, ovarian, and other cancers. Mechanistically, BRCA2 facilitates RAD51 recruitment to sites of DNA damage, whereas BRCA1 regulates homologous recombination repair (HRR) through double-strand break resection and broader DNA damage response signaling. These insights underpin targeted therapies such as poly (ADP-ribose) polymerase inhibitors (PARPis), which induce synthetic lethality in homologous recombination-deficient tumors. Clinically, PARPis have demonstrated significant benefit in BRCA1/2-mutated breast, ovarian, pancreatic, and prostate cancers. However, resistance remains a major obstacle, with secondary intragenic BRCA1/2 mutations restoring partial protein function representing a prominent mechanism. Despite therapeutic advances, critical gaps persist in understanding how specific BRCA1/2 domains and residual protein activities contribute to tumorigenesis and treatment response. In this review, we summarize the structural and functional domains of BRCA1/2, their pathogenic mutation profiles, and therapeutic strategies targeting BRCA1/2-deficient cancers. Despite therapeutic advances, critical gaps persist in understanding how specific BRCA1/2 domains and residual protein activities contribute to tumorigenesis and treatment response. This review emphasizes the need for functional studies of BRCA1/2 variants to refine risk prediction and develop mutation-tailored therapies. Full article

Locally advanced rectal cancer is commonly treated using total neoadjuvant therapy (TNT), which integrates radiotherapy with systemic chemotherapy to improve tumor downstaging, local control, and long-term oncologic outcomes. Despite its central role in treatment, responses to radiotherapy remain highly heterogeneous. While some tumors undergo complete regression, others exhibit intrinsic or acquired treatment resistance, resulting in incomplete tumor control while experiencing treatment-related toxicity. Understanding the biological determinants that govern radiation sensitivity in rectal cancer, therefore, represents a major clinical challenge. Ionizing radiation induces tumor cell death primarily through the generation of reactive oxygen species (ROS) and DNA damage, particularly DNA double-strand breaks. In addition to nuclear DNA injury, radiation-induced oxidative stress can initiate lipid peroxidation within cellular membranes. When lipid peroxide accumulation exceeds the capacity of cellular antioxidant systems, this process can trigger ferroptosis, an iron-dependent form of regulated cell death driven by phospholipid oxidation. Ferroptotic susceptibility is regulated by interconnected metabolic pathways, including cystine transport through system Xc⁻ (SLC7A11/SLC3A2), glutathione synthesis, glutathione peroxidase-4 (GPX4) activity, iron metabolism, and membrane lipid remodeling. Recent evidence further indicates that ferroptosis intersects with antitumor immunity. Ferroptotic tumor cells release oxidized lipid mediators and damage-associated molecular signals that can influence immune activation, while interferon-γ produced by activated CD8⁺ T cells during immune checkpoint blockade suppresses SLC7A11 expression, limiting cystine uptake and promoting ferroptotic tumor cell death. These findings suggest that ferroptosis represents a mechanistic interface between tumor metabolic vulnerability and immune-mediated cytotoxicity. This interaction is particularly relevant in colorectal cancer biology, where immune checkpoint inhibitors demonstrate clinical benefit primarily in tumors with deficient mismatch repair or microsatellite instability-high (MSI-H) status. The vast majority of rectal cancers are microsatellite stable (MSS) and exhibit limited responsiveness to immunotherapy due to reduced immunogenicity and immune exclusion within the tumor microenvironment. Strategies capable of increasing tumor immunogenicity in this setting are therefore of considerable interest. In this review, we examine the molecular mechanisms linking radiation-induced oxidative stress to ferroptosis and tumor immunity in colorectal cancer, while focusing on the clinical context of radiotherapy in rectal cancer. We discuss how lipid metabolism, iron homeostasis, cysteine-dependent antioxidant systems, and immune signaling pathways converge to regulate ferroptotic vulnerability and radiation response. We further explore the therapeutic potential of integrating radiotherapy, ferroptosis-targeting strategies, and immunotherapy to overcome radioresistance and improve treatment outcomes in colorectal cancer. Full article

The use of proton beam therapy (PBT), as a more precision-targeted radiotherapy technique, is increasing in the treatment of head and neck squamous cell carcinoma (HNSCC). PBT benefits from the precise delivery of the radiation dose to the tumour via the Bragg peak. However, challenges still remain in the treatment of HNSCC with radiotherapy, particularly with tumour radioresistance and recurrence, requiring strategies leading to radiosensitisation. There are added complexities with the use of PBT given the increase in linear energy transfer (LET) at and around the Bragg peak, which can cause an altered cellular response compared to low-LET radiation. Nevertheless, targeting the cellular DNA damage response is considered an important strategy to enhance tumour cell killing caused by radiotherapy. Therefore, using specific inhibitors against the protein kinases ataxia telangiectasia mutated (ATM), ataxia telangiectasia and Rad3-related (ATR) and the DNA-dependent protein kinase catalytic subunit (DNA-Pkcs), we investigated their impact in radiosensitising HPV-negative HNSCC cells to PBT of increasing LET. We demonstrate that inhibitors against ATR (AZD6738), and particularly ATM (AZD1390) and DNA-Pkcs (AZD7648), could significantly decrease clonogenic survival of HNSCC cell lines following PBT at both low and relatively high LET (~2 keV/µm and ~8 keV/µm, respectively). We confirmed that the inhibitors in combination with PBT led to DSB persistence through neutral comet assays and monitoring γH2AX/53BP1 foci. We also show that this strategy can enhance the sensitivity of patient-derived organoids of HNSCC to PBT of both low and high LET, highlighting this as a strategy which should be exploited further. Full article

We aimed to clarify how the priming dose and the experimental design could affect the development of an adaptive response (AR) induced by low-dose Zeocin (Zeo) in Saccharomyces cerevisiae strains with differing genetic constitution. Constant-field gel electrophoresis was used for measuring double-strand breaks (DSBs) induction and DNA rejoining; for microbiological experiments, Zimmermann’s test was used for measuring survival fraction and genetic events. Favorable experimental conditions for the induction of AR in both D7ts1 and 551 strains were determined: the priming dose inducing about 20% lethality or at least a 1.5-fold increased DSB level, 45 min inter-treatment time, and recovery time of 30–45 min. Both strains developed well-expressed AR, measured by increased cell survival, but differed in their ability to develop AR, measured by reduction in DSBs. This discrepancy could be due to different DSBs rejoining rather than different DNA susceptibility, and the partial contribution of DSB repair to cell survival in the split-dose experiments. The frequency of mutagenic and recombinogenic events and DSB levels were lower in split-dose treatment. The development of AR depends on several factors: the magnitude of the priming dose, DNA susceptibility, the duration of the ITT window, the duration of recovery time, as well as genetic constitution of strains. Full article