Use of γH2AX and other biomarkers of double-strand breaks during radiotherapy

Targeting CK2-mediated phosphorylation of p53R2 sensitizes BRCA-proficient cancer cells to PARP inhibitors

Poly[ADP-ribose] polymerase (PARP) inhibitors, which selectively kills homologous recombination (HR) repair-deficient cancer cells, are widely employed to treat cancer patients harboring BRCA1/2 mutations. However, they display limited efficacy in tumors with wild-type (WT) BRCA1/2. Thus, it is crucial to identify new druggable HR repair regulators and improve the therapeutic efficacy of PARP inhibitors via combination therapies in BRCA1/2-WT tumors. Here, we show that the depletion of ribonucleotide reductase (RNR) subunit p53R2 impairs HR repair and sensitizes BRCA1/2-WT cancer cells to PARP inhibition. We further demonstrate that the loss of p53R2 leads to a decrease of HR repair factor CtIP, as a result of dNTPs shortage-induced ubiquitination of CtIP. Moreover, we identify that casein kinase II (CK2) phosphorylates p53R2 at its ser20, which subsequently activates RNR for dNTPs production. Therefore, pharmacologic inhibition of the CK2-mediated phosphorylation of p53R2 compromises its HR repair capacity in BRCA1/2-WT cancer cells, which renders these cells susceptible to PARP inhibition in vitro and in vivo. Therefore, our study reveals a novel strategy to inhibit HR repair activity and convert BRCA1/2-proficient cancers to be susceptible to PARP inhibitors via synthetic lethal combination.

Predictive Biomarkers of Pathological Response to Neoadjuvant Chemoradiotherapy for Locally Advanced Soft Tissue Sarcomas

BACKGROUND

Marginally resectable and unresectable soft tissue sarcomas (STS) remain a therapy challenge due to the lack of highly active treatment. The aim of the study was to identify a biomarker to predict the pathological response (PR) to preplanned treatment of these STSs.

METHODS

In the phase II clinical trial (NCT03651375), locally advanced STS patients received preoperative treatment with a combination of doxorubicin-ifosfamide chemotherapy and 5 × 5 Gy radiotherapy. PR to the treatment was classified using the European Organization for Research and Treatment of Cancer-Soft Tissue and Bone Sarcoma Group recommendations. We have chosen HIF-1α, CD163, CD68, CD34, CD105, and γH2AFX proteins, rendering different biological phenomena, for biomarker study.

RESULTS

Nineteen patients were enrolled and in four cases a good PR was reported. The high expression of HIF-1α before surgery showed a negative correlation with PR, which means a poor response to therapy. Furthermore, the samples after surgery had decreased expression of HIF-1α, which confirmed the correlation with PR. However, high expression of γH2AFX positively correlated with PR, which provides better PR. The high number of positive-staining TAMs and the high IMVD did not correlate with PR.

CONCLUSIONS

HIF1α and γH2AFX could be potential biomarkers for PR prediction after neoadjuvant treatment in STS.

Non-linear dose response of DNA double strand breaks in response to chronic low dose radiation in individuals from high level natural radiation areas of Kerala coast

BACKGROUND

The human population living in high level natural radiation areas (HLNRAs) of Kerala coast provide unique opportunities to study the biological effects of low dose and low dose rate ionizing radiation below 100 mGy. The level of radiation in this area varies from < 1.0 to 45 mGy/year. The areas with ≤ 1.50 mGy/year are considered as normal level natural radiation areas (NLNRA) and > 1.50 mGy/year, as high level natural radiation areas (HLNRA). The present study evaluated dose response relationship between DNA double strand breaks (DSBs) and background radiation dose in individuals residing in Kerala coast. Venous blood samples were collected from 200 individuals belonging to NLNRA (n = 50) and four dose groups of HLNRA; 1.51-5.0 mGy/year (n = 50), 5.01-10.0 mGy/year (n = 30), 10.01-15.0 mGy/year (n = 33), > 15.0 mGy/year (n = 37) with written informed consent. The mean dose of NLNRA and four HLNRA dose groups studied are 1.21 ± 0.21 (range: 0.57-1.49), 3.02 ± 0.95 (range: 1.57-4.93), 7.43 ± 1.48 (range: 5.01-9.75), 12.22 ± 1.47 (range: 10.21-14.99), 21.64 ± 6.28 (range: 15.26-39.88) mGy/year, respectively. DNA DSBs were quantified using γH2AX as a marker, where foci were counted per cell using fluorescence microscopy.

RESULTS

Our results revealed that the frequency of γH2AX foci per cell was 0.090 ± 0.051 and 0.096 ± 0.051, respectively in NLNRA and HLNRA individuals, which were not significantly different (t₁₉₈ = 0.33; P = 0.739). The frequency of γH2AX foci was observed to be 0.090 ± 0.051, 0.096 ± 0.051, 0.076 ± 0.036, 0.087 ± 0.042, 0.108 ± 0.046 per cell, respectively in different dose groups of ≤ 1.50, 1.51-5.0, 5.01-10.0, 10.01-15.0, > 15.0mGy/year (ANOVA, F_4,195 = 2.18, P = 0.072) and suggested non-linearity in dose response. The frequency of γH2AX foci was observed to be 0.098 ± 0.042, 0.078 ± 0.037, 0.084 ± 0.042, 0.099 ± 0.058, 0.097 ± 0.06 and 0.114 ± 0.033 per cell in the age groups of ≤ 29, 30-34, 35-39, 40-44, 45-49 and ≥ 50 years, respectively (ANOVA, F_5,194 = 2.17, P = 0.059), which suggested marginal influence of age on the baseline of DSBs. Personal habits such as smoking (No v/s Yes: 0.092 ± 0.047 v/s 0.093 ± 0.048, t₁₉₈ = 0.13; P = 0.895) and drinking alcohol (No v/s Yes: 0.096 ± 0.052 v/s 0.091 ± 0.045, t₁₉₈ = 0.62; P = 0.538) did not show any influence on DSBs in the population.

CONCLUSION

The present study did not show any increase in DSBs in different dose groups of HLNRA compared to NLNRA, however, it suggested a non-linear dose response between DNA DSBs and chronic low dose radiation.

Screen identifies fasudil as a radioprotector on human fibroblasts

Background

Radioprotectors safeguard biological system exposed to ionizing radiation (IR) by protecting normal cells from radiation damage during radiotherapy. Due to the toxicity and limited clinical utility of the present radioprotectors, it prompts us to identify novel radioprotectors that could alleviate IR-induced cytotoxicity of normal tissues.

Aims and Methods

To identify new radioprotectors, we screened a chemical molecular library comprising 253 compounds in normal human fibroblasts (HFs) or 16HBE cells upon IR by CCK-8 assays and clonogenic survival assays. Fasudil was identified as a potential effective radioprotector.

Results

The results indicated that Fasudil exerts radioprotective effects on HFs against IR-induced DNA double-strand breaks (DSBs) through the regulation of DSB repair. Fasudil increased homologous recombination (HR) repair by 45.24% and decreased non-homologous end-joining (NHEJ) by 63.88% compared with untreated cells, without affecting changes to cell cycle profile. We further found that fasudil significantly facilitated the expression and foci formation of HR core proteins such as Rad51 and BRCA1 upon IR, and decreased the expression of NHEJ-associated proteins such as DNA-PKcs at 24 h post-IR.

Conclusion

Our study identified fasudil as a novel radioprotector that exert radioprotective effects on normal cells through regulation of DSB repair by promoting HR repair.

A deep learning model (FociRad) for automated detection of γ-H2AX foci and radiation dose estimation

DNA double-strand breaks (DSBs) are the most lethal form of damage to cells from irradiation. γ-H2AX (phosphorylated form of H2AX histone variant) has become one of the most reliable and sensitive biomarkers of DNA DSBs. However, the γ-H2AX foci assay still has limitations in the time consumed for manual scoring and possible variability between scorers. This study proposed a novel automated foci scoring method using a deep convolutional neural network based on a You-Only-Look-Once (YOLO) algorithm to quantify γ-H2AX foci in peripheral blood samples. FociRad, a two-stage deep learning approach, consisted of mononuclear cell (MNC) and γ-H2AX foci detections. Whole blood samples were irradiated with X-rays from a 6 MV linear accelerator at 1, 2, 4 or 6 Gy. Images were captured using confocal microscopy. Then, dose-response calibration curves were established and implemented with unseen dataset. The results of the FociRad model were comparable with manual scoring. MNC detection yielded 96.6% accuracy, 96.7% sensitivity and 96.5% specificity. γ-H2AX foci detection showed very good F1 scores (> 0.9). Implementation of calibration curve in the range of 0-4 Gy gave mean absolute difference of estimated doses less than 1 Gy compared to actual doses. In addition, the evaluation times of FociRad were very short (< 0.5 min per 100 images), while the time for manual scoring increased with the number of foci. In conclusion, FociRad was the first automated foci scoring method to use a YOLO algorithm with high detection performance and fast evaluation time, which opens the door for large-scale applications in radiation triage.

The genotoxic potential of mixed nitrosamines in drinking water involves oxidative stress and Nrf2 activation

Nitrosamine by-products in drinking water are designated as probable human carcinogens by the IARC, but the health effects of simultaneous exposure to multiple nitrosamines in drinking water remain unknown. Genotoxicity assays were used to assess the effects of both individual and mixed nitrosamines in finished drinking water produced by a large water treatment plant in Shanghai, China. Cytotoxicity and genotoxicity were measured at 1, 10-, 100- and 1000-fold actual concentrations by the Ames test, Comet assay, γ-H2AX assay, and the cytokinesis-block micronuclei assay; oxidative stress and the Nrf2 pathway were also assessed. Nitrosamines detected in drinking water included NDMA (36.45 ng/L), NDPA (44.68 ng/L), and NEMA (37.27 ng/L). Treatment with a mixture of the three nitrosamines at 1000-fold actual drinking-water concentration induced a doubling of revertants in Salmonella typhimurium strain TA100, DNA and chromosome damage in HepG2 cells, while 1-1000-fold concentrations of compounds applied singly lacked these effects. Treatment with 100- and 1000-fold concentrations increased ROS, GSH, and MDA and decreased SOD activity. Thus, nitrosamine mixtures showed greater genotoxic potential than that of the individual compounds. N-Acetylcysteine protected against the nitrosamine-induced chromosome damage, and Nrf2 pathway activation suggested that oxidative stress played pivotal roles in the genotoxic property of the nitrosamine mixtures.

DAB2IP predicts treatment response and prognosis of ESCC patients and modulates its radiosensitivity through enhancing IR-induced activation of the ASK1-JNK pathway

Background

Disabled homolog 2 interacting protein (DAB2IP) plays a tumor-suppressive role in several types of human cancers. However, the molecular status and function of the DAB2IP gene in esophageal squamous cell carcinoma (ESCC) patients who received definitive chemoradiotherapy is rarely reported.

Methods

We examined the expression dynamics of DAB2IP by immunohistochemistry (IHC) in 140 ESCC patients treated with definitive chemoradiotherapy. A series of in vivo and in vitro experiments were performed to elucidate the effect of DAB2IP on the chemoradiotherapy (CRT) response and its underlying mechanisms in ESCC.

Results

Decreased expression of DAB2IP in ESCCs correlated positively with ESCC resistance to CRT and was a strong and independent predictor for short disease-specific survival (DSS) of ESCC patients. Furthermore, the therapeutic sensitivity of CRT was substantially increased by ectopic overexpression of DAB2IP in ESCC cells. In addition, knockdown of DAB2IP dramatically enhanced resistance to CRT in ESCC. Finally, we demonstrated that DAB2IP regulates ESCC cell radiosensitivity through enhancing ionizing radiation (IR)-induced activation of the ASK1-JNK signaling pathway.

Conclusions

Our data highlight the molecular etiology and clinical significance of DAB2IP in ESCC, which may represent a new therapeutic strategy to improve therapy and survival for ESCC patients.

Clinical Applications of Biological Dosimetry in Patients Exposed to Low Dose Radiation Due to Radiological, Imaging or Nuclear Medicine Procedures

Radiation dosimetric biomarkers have found applications beyond radiation protection area and now are actively introduced into clinical practice. Cytogenetic assays appeared to be a valuable tool for individualized quantifying radiation effects in patients, with high capability for assessing genotoxicity of various medical exposure modalities and providing meaningful radiation dose estimates for prognoses of radiation-related cancer risk. This review summarized current data on the use of biological dosimetry methods in patients undergoing various medical irradiations to low doses. The highlighted topics include basic aspects of biological dosimetry and its limitations in the range of low radiation doses, and main patterns of in vivo induction of radiation biomarkers in clinical exposure scenarios, occurring in X-ray diagnostics, computed tomography, interventional radiology, low dose radiotherapy, and nuclear medicine (internally administered ¹³¹I and other radiopharmaceuticals). Additionally, several specific issues, examined by biodosimetry techniques, are analysed, such as contrast media effect, radiation response in pediatric patients, impact of magnetic resonance imaging, evaluation of radioprotectors, detection of patients' abnormal intrinsic radiosensitivity and dose estimation in persons involved in medical radiation incidents. A prognosis of possible directions for further improvements in this area includes the automation of cytogenetic analysis, introduction of molecular biodosimeters and development of multiparametric biodosimetry platforms. A potential approach to the advanced biodosimetry of internal exposure and/or low dose external irradiation is suggested; this can be a multiparametric platform based on the combination of the γ-H2AX foci, dicentric, and translocation assays, each applied in the optimum postexposure time range, with the amalgamation of the dose estimates. The study revealed the necessity of further research, which might clarify medical radiation safety concerns for patients via using stringent biodosimetry methodology.

Translation of DNA Damage Response Inhibitors as Chemoradiation Sensitizers From the Laboratory to the Clinic

Combination therapies with agents targeting the DNA damage response (DDR) offer an opportunity to selectively enhance the therapeutic index of chemoradiation or eliminate use of chemotherapy altogether. The successful translation of DDR inhibitors to clinical use requires investigating both their direct actions as (chemo)radiosensitizers and their potential to stimulate tumor immunogenicity. Beginning with high-throughput screening using both viability and DNA damage-reporter assays, followed by validation in gold-standard radiation colony-forming assays and in vitro assessment of mechanistic effects on the DDR, we describe proven strategies and methods leading to the clinical development of DDR inhibitors both with radiation alone and in combination with chemoradiation. Beyond these in vitro studies, we discuss the impact of key features of human xenograft and syngeneic mouse models on the relevance of in vivo tumor efficacy studies, particularly with regard to the immunogenic effects of combined therapy with radiation and DDR inhibitors. Finally, we describe recent technological advances in radiation delivery (using the small animal radiation research platform) that allow for conformal, clinically relevant radiation therapy in mouse models. This overall approach is critical to the successful clinical development and ultimate Food and Drug Administration approval of DDR inhibitors as (chemo)radiation sensitizers.

Plasmonic AuPt@CuS Heterostructure with Enhanced Synergistic Efficacy for Radiophotothermal Therapy

Integrating multifunctional nanostructures capable of radiotherapy and photothermal ablation is an emerging alternative in killing cancer cells. In this work, we report a novel plasmonic heterostructure formed by decorating AuPt nanoparticles (NPs) onto the surfaces of CuS nanosheets (AuPt@CuS NSs) as a highly effective nanotheranostic toward dual-modal photoacoustic/computed tomography imaging and enhanced synergistic radiophotothermal therapy. These heterostructures can confer higher photothermal conversion efficiency via the local electromagnetic enhancement as well as a greater radiation dose deposition in the form of glutathione depletion and reactive oxygen species generation. As a result, the depth of tissue penetration is improved, and hypoxia of the tumor microenvironment is alleviated. With synergistic enhancement in the efficacy of photothermal ablation and radiotherapy, the tumor can be eliminated without later recurrence. It is believed that these multifunctional heterostructures will play a vital role in future oncotherapy with the enhanced synergistic effects of radiotherapy and photothermal ablation under the guided imaging of a potential dual-modality system.

Radiation-Induced Osteocyte Senescence Alters Bone Marrow Mesenchymal Stem Cell Differentiation Potential via Paracrine Signaling

Cellular senescence and its senescence-associated secretory phenotype (SASP) are widely regarded as promising therapeutic targets for aging-related diseases, such as osteoporosis. However, the expression pattern of cellular senescence and multiple SASP secretion remains unclear, thus leaving a large gap in the knowledge for a desirable intervention targeting cellular senescence. Therefore, there is a critical need to understand the molecular mechanism of SASP secretion in the bone microenvironment that can ameliorate aging-related degenerative pathologies including osteoporosis. In this study, osteocyte-like cells (MLO-Y4) were induced to cellular senescence by 2 Gy γ-rays; then, senescence phenotype changes and adverse effects of SASP on bone marrow mesenchymal stem cell (BMSC) differentiation potential were investigated. The results revealed that 2 Gy irradiation could hinder cell viability, shorten cell dendrites, and induce cellular senescence, as evidenced by the higher expression of senescence markers p16 and p21 and the elevated formation of senescence-associated heterochromatin foci (SAHF), which was accompanied by the enhanced secretion of SASP markers such as IL-1α, IL-6, MMP-3, IGFBP-6, resistin, and adiponectin. When 0.8 μM JAK1 inhibitors were added to block SASP secretion, the higher expression of SASP was blunted, but the inhibition in osteogenic and adipogenic differentiation potential of BMSCs co-cultured with irradiated MLO-Y4 cell conditioned medium (CM- 2 Gy) was alleviated. These results suggest that senescent osteocytes can perturb BMSCs’ differential potential via the paracrine signaling of SASP, which was also demonstrated by in vivo experiments. In conclusion, we identified the SASP factor partially responsible for the degenerative differentiation of BMSCs, which allowed us to hypothesize that senescent osteocytes and their SASPs may contribute to radiation-induced bone loss.

Complete response to neoadjuvant chemoradiotherapy in rectal cancer is associated with RAS/AKT mutations and high tumour mutational burden

BACKGROUND

Pathological complete response (pathCR) in rectal cancer is beneficial, as up to 75% of patients do not experience regrowth of the primary tumour, but it is poorly understood. We hypothesised that the changes seen in the pre-treatment biopsies of pathCR but not seen in residual tumour after chemoradiotherapy were the determinants of responsiveness.

METHODS

Two groups of patients with either complete response (pathCR group, N = 24) or no response (poor response group, N = 24) were retrieved. Pre-treatment biopsies of cancers from these patients underwent high read depth amplicon sequencing for a targeted panel, exome sequencing, methylation profiling and immunohistochemistry for DNA repair pathway proteins.

RESULTS

Twenty four patients who underwent pathCR and twenty-four who underwent poor response underwent molecular characterisation. Patients in the pathCR group had significantly higher tumour mutational burden and neoantigen load, frequent copy number alterations but fewer structural variants and enrichment for driver mutations in the PI3K/AKT/mTOR signalling pathway. There were no significant differences in tumour heterogeneity as measured by MATH score. Methylation analysis demonstrated enrichment for hypomethyation in the PI3K/AKT/mTOR signalling pathway.

DISCUSSION

The phenomenon of pathCR in rectal cancer may be related to immunovisibility caused by a high tumour mutational burden phenotype. Potential therapy resistance mechanisms involve the PI3K/AKT/mTOR signalling pathway, but tumour heterogeneity does not seem to play a role in resistance.

CDCA2 promotes tumorigenesis and induces radioresistance in oesophageal squamous cell carcinoma cells

Cell division cycle‑associated 2 (CDCA2) overexpression has been demonstrated to serve a significant role in tumorigenesis in certain types of cancer. Nevertheless, its role in tumour proliferation and radioresistance in oesophageal squamous cell carcinoma (ESCC) remains to be elucidated. Thus, the present study aimed to elucidate these roles. Data were downloaded from The Cancer Genome Atlas (TCGA) to compare the gene expression profiles. The expression of CDCA2 was higher in ESCC tissues compared with normal tissues. Gene set enrichment analysis was performed based on the ESCC cohorts in TCGA database. This demonstrated that higher expression of CDCA2 was significantly associated with the expression of related components of the cell cycle phase transition and G2/M phase transition pathways. Collectively, the results revealed that CDCA2 could serve as an underlying target to regulate tumour growth and radioresistance among patients with ESCC.

Evaluation of DNA double-strand break repair capacity in human cells: Critical overview of current functional methods

DNA double-strand breaks (DSBs) are highly deleterious lesions, responsible for mutagenesis, chromosomal translocation or cell death. DSB repair (DSBR) is therefore a critical part of the DNA damage response (DDR) to restore molecular and genomic integrity. In humans, this process is achieved through different pathways with various outcomes. The balance between DSB repair activities varies depending on cell types, tissues or individuals. Over the years, several methods have been developed to study variations in DSBR capacity. Here, we mainly focus on functional techniques, which provide dynamic information regarding global DSB repair proficiency or the activity of specific pathways. These methods rely on two kinds of approaches. Indirect techniques, such as pulse field gel electrophoresis (PFGE), the comet assay and immunofluorescence (IF), measure DSB repair capacity by quantifying the time-dependent decrease in DSB levels after exposure to a DNA-damaging agent. On the other hand, cell-free assays and reporter-based methods directly track the repair of an artificial DNA substrate. Each approach has intrinsic advantages and limitations and despite considerable efforts, there is currently no ideal method to quantify DSBR capacity. All techniques provide different information and can be regarded as complementary, but some studies report conflicting results. Parameters such as the type of biological material, the required equipment or the cost of analysis may also limit available options. Improving currently available methods measuring DSBR capacity would be a major step forward and we present direct applications in mechanistic studies, drug development, human biomonitoring and personalized medicine, where DSBR analysis may improve the identification of patients eligible for chemo- and radiotherapy.

FMS-Related Tyrosine Kinase 3 Ligand Promotes Radioresistance in Esophageal Squamous Cell Carcinoma

Aim: The FMS-related tyrosine kinase 3 ligand (FL) has an important role in regulating FMS-related tyrosine kinase 3 (Flt-3) activity. Serum FL levels are markedly increased among patients with hematopoietic disease. However, its role in radiation treatment remains unclear. In this study, we investigated the effects of FL on radiotherapy for esophageal squamous cell carcinoma (ESCC).

Methods: KYSE150 and KYSE450 cells were stimulated with FL (200 ng/ml). mRNA expression was analyzed using qRT-PCR. Cell viability was checked using CCK-8 assay kits. Proliferation was determined using the EdU assay. Radiosensitivity was detected through a colony-forming assay. Flow cytometry was used to evaluate cell apoptosis. The number of γH2AX foci was verified using an immunofluorescence assay. The change in relative proteins was determined by western blot analysis. The growth of transplanted tumors was demonstrated in nude mice.

Results: Our results showed that FL increased the radiation resistance of ESCC cells by promoting clone formation, increasing EdU incorporation, enhancing DNA damage repair, and inhibiting apoptosis. Moreover, the Flt-3 receptor expression significantly increased in ESCC cells after radiation, which may have been an important factor in their radioresistance.

Conclusion: Our results suggest that FL increases the radioresistance of esophageal cancer cells and that FL-Flt-3 could be a potential target for enhancing radiosensitivity in ESCC.

Potential application of γ-H2AX as a biodosimetry tool for radiation triage

Radiation triage and biological dosimetry are two initial steps in the medical management of exposed individuals following radiological accidents. Well established biodosimetry methods such as the dicentric (DC) assay, micronucleus (MN) assay, and fluorescence in-situ hybridization (FISH) translocation assay (for residual damage) have been used for this purpose for several decades. Recent advances in scoring methodology and networking among established laboratories have increased triage capacity; however, these methods still have limitations in analysing large sample numbers, particularly because of the ∼ 48 h minimum culture time required prior to analysis. Hence, there is a need for simple, and high throughput markers to identify exposed individuals in case of radiological/nuclear emergencies. In recent years, a few markers were identified, one being phosphorylated histone 2AX (γ-H2AX), which measured a nuclear foci or nuclear staining intensity that was found to be suitable for triage. Measurement of γ-H2AX foci formed at and around the sites of DNA double-strand breaks is a rapid and sensitive biodosimetry method which does not require culturing and is thus promising for the analysis of a large number of samples. In this review, we have summarized the recent developments of γ-H2AX assay in radiation triage and biodosimetry, focusing chiefly on: i) the importance of baseline frequency and reported values among different laboratories, ii) the influence of known and unknown variables on dose estimation, iii) quality assurance such as inter-laboratory comparison between scorers and scoring methods, and iv) current limitations and potential for future development.

The ATPase subunit of ATP6V1C1 inhibits autophagy and enhances radiotherapy resistance in esophageal squamous cell carcinoma

Radiotherapy is one of the primary therapeutic modalities for patients diagnosed esophageal squamous cell carcinoma(ESCC). Previous studies have shown that chemotherapy resistance could be linked with the overexpression vascular ATPases(V-ATPase) subunits genes. However, it is unknown whether V-ATPase subunits genes play a role in radiotherapy resistance. The aim of this study was to investigate the effect of the ATP6V1C1 in radiotherapy resistance. siRNA and plasmids were used to transfect low expression of ATP6V1C1 in TE13 (human ESCC cell) and high expressed in ECA109 (human ESCC cell), respectively. To observe proliferation, radiosensitivity, apoptosis and DNA-damage response, colony formation assays, EDU assays, flow cytometry and γH2AX assay were used with or without radiation exposure, separately. The quantities of the autophagosomes and autolysosomes by immunofluorescence were calculated. Autophagic microstructure were discovered by transmission electron microscopy, and the study also repeated in vivo by nude mice. Western blot assay was applied to prove changes in relative proteins. We found that suppressing ATP6V1C1 increased the sensitivity of ESCC cells after RT. Silencing ATP6V1C1 with IR suppressed the tumor growth and promoted autophagy. Besides, the underlying mechanism of ATP6V1C1, which is not fatally disrupted, is that ATP6V1C1 with ionizing radiation (IR)decreased apoptosis and inhibited autophagy may by activating mTOR signaling to suppress radiosensitivity for ESCC cells. Thus, we first reported that the ATP6V1C1 may represent a potential radiotherapeutic target by effect on radiation sensitivity for ESCC.

Developing a clinically relevant radiosensitizer for temozolomide-resistant gliomas

The prognosis for patients with glioblastoma (GB) remains grim. Concurrent temozolomide (TMZ) radiation—the cornerstone of glioma control—extends the overall median survival of GB patients by only a few months over radiotherapy alone. While these survival gains could be partly attributed to radiosensitization, this benefit is greatly minimized in tumors expressing O⁶-methylguanine DNA methyltransferase (MGMT), which specifically reverses O⁶-methylguanine lesions. Theoretically, non-O⁶-methylguanine lesions (i.e., the N-methylpurine adducts), which represent up to 90% of TMZ-generated DNA adducts, could also contribute to radiosensitization. Unfortunately, at concentrations attainable in clinical practice, the alkylation capacity of TMZ cannot overwhelm the repair of N-methylpurine adducts to efficiently exploit these lesions. The current therapeutic application of TMZ therefore faces two main obstacles: (i) the stochastic presence of MGMT and (ii) a blunted radiosensitization potential at physiologic concentrations. To circumvent these limitations, we are developing a novel molecule called NEO212—a derivatization of TMZ generated by coupling TMZ to perillyl alcohol. Based on gas chromatography/mass spectrometry and high-performance liquid chromatography analyses, we determined that NEO212 had greater tumor cell uptake than TMZ. In mouse models, NEO212 was more efficient than TMZ at crossing the blood-brain barrier, preferentially accumulating in tumoral over normal brain tissue. Moreover, in vitro analyses with GB cell lines, including TMZ-resistant isogenic variants, revealed more potent cytotoxic and radiosensitizing activities for NEO212 at physiologic concentrations. Mechanistically, these advantages of NEO212 over TMZ could be attributed to its enhanced tumor uptake presumably leading to more extensive DNA alkylation at equivalent dosages which, ultimately, allows for N-methylpurine lesions to be better exploited for radiosensitization. This effect cannot be achieved with TMZ at clinically relevant concentrations and is independent of MGMT. Our findings establish NEO212 as a superior radiosensitizer and a potentially better alternative to TMZ for newly diagnosed GB patients, irrespective of their MGMT status.

Ralaniten Sensitizes Enzalutamide-Resistant Prostate Cancer to Ionizing Radiation in Prostate Cancer Cells that Express Androgen Receptor Splice Variants

Blocking androgen receptor (AR) transcriptional activity by androgen deprivation therapy (ADT) improves the response to radiotherapy for intermediate and high risk prostate cancer. Unfortunately, ADT, antiandrogens, and abiraterone increase expression of constitutively active splice variants of AR (AR-Vs) which regulate DNA damage repair leading to resistance to radiotherapy. Here we investigate whether blocking the transcriptional activities of full-length AR and AR-Vs with ralaniten leads to enhanced sensitivity to radiotherapy. Combination therapies using ralaniten with ionizing radiation were evaluated for effects on proliferation, colony formation, cell cycle, DNA damage, and Western blot analyses in human prostate cancer cells that express both full-length AR and AR-Vs. Ralaniten and a potent next-generation analog (EPI-7170) decreased expression of DNA repair genes whereas enzalutamide had no effect. FACS analysis revealed a dose-dependent decrease of BrdU incorporation with increased accumulation of γH2AX with a combination of ionizing radiation with ralaniten. An additive inhibitory effect on proliferation of enzalutamide-resistant cells was achieved with a combination of ralaniten compounds with ionizing radiation. Ralaniten and EPI-7170 sensitized prostate cancer cells that express full-length AR and AR-Vs to radiotherapy whereas enzalutamide had no added benefit.

Irradiation-induced senescence of bone marrow mesenchymal stem cells aggravates osteogenic differentiation dysfunction via paracrine signaling

The role of cellular senescence induced by radiation in bone loss has attracted much attention. As one of the common complications of anticancer radiotherapy, irradiation-induced bone deterioration is common and clinically significant, but the pathological mechanism has not been elucidated. This study was performed to explore the cellular senescence and senescence-associated secretory phenotype (SASP) induction of bone marrow-derived mesenchymal stem cells (BMSCs) by irradiation and its role in osteogenic differentiation dysfunction. It was observed that irradiated BMSCs lost typical fibroblast-like morphology, exhibited suppressed viability and differentiation potential accompanied with senescence phenotypes, including an increase in senescence-associated β-galactosidase (SA-β-gal) staining-positive cells, and upregulated senescence-related genes p53/p21, whereas no changes happened to p16. Additionally, DNA damage γ-H2AX foci, G0/G1 phase of cell cycle arrest, and cellular and mitochondrial reactive oxygen species (ROS) increased in an irradiation dose-dependent manner. Meanwhile, the JAK1/STAT3 pathway was activated and accompanied by an increase in SASP secretion, such as IL-6, IL-8, and matrix metalloproteinase-9 (MMP9), whereas 0.8 μM JAK1 inhibitor (JAKi) treatment effectively inhibited the JAK pathway and SASP production. Furthermore, conditioned medium (CM) from irradiation-induced senescent (IRIS) BMSCs exhibited a markedly reduced ability in osteogenic differentiation and marker gene expression of osteoblasts, whereas CM with JAKi intervention may effectively improve these deterioration effects. In conclusion, irradiation could provoke BMSC senescence and SASP secretion and further aggravate osteogenic differentiation dysfunction via paracrine signaling, whereas SASP targeting may be a possible intervention strategy for alleviating irradiation-induced bone loss.

DNA Strand Break Properties of Protoporphyrin IX by X-Ray Irradiation against Melanoma

Recent reports have suggested that 5-aminolevulinic acid (5-ALA), which is a precursor to protoporphyrin IX (PpIX), leads to selective accumulation of PpIX in tumor cells and acts as a radiation sensitizer in vitro and in vivo in mouse models of melanoma, glioma, and colon cancer. In this study, we investigated the effect of PpIX under X-ray irradiation through ROS generation and DNA damage. ROS generation by the interaction between PpIX and X-ray was evaluated by two kinds of probes, 3′-(p-aminophenyl) fluorescein (APF) for hydroxyl radical (•OH) detection and dihydroethidium (DHE) for superoxide (O₂^•-). •OH showed an increase, regardless of the dissolved oxygen. Meanwhile, the increase in O₂^•- was proportional to the dissolved oxygen. Strand breaks (SBs) of DNA molecule were evaluated by gel electrophoresis, and the enhancement of SBs was observed by PpIX treatment. We also studied the effect of PpIX for DNA damage in cells by X-ray irradiation using a B16 melanoma culture. X-ray irradiation induced γH2AX, DNA double-strand breaks (DSBs) in the context of chromatin, and affected cell survival. Since PpIX can enhance ROS generation even in a hypoxic state and induce DNA damage, combined radiotherapy treatment with 5-ALA is expected to improve therapeutic efficacy for radioresistant tumors.

A class of Pt(iv) triple-prodrugs targeting nucleic acids, thymidylate synthases and histone deacetylases

A Pt(iv)-triple-prodrug, comprising VPA, 5-FU, regulated TS, HDAC, and γH2AX, showing higher efficiency and lower toxicity than cisplatin.

Verification of 5-Aminolevurinic Radiodynamic Therapy Using a Murine Melanoma Brain Metastasis Model

Melanoma is a highly aggressive cancer with a propensity for brain metastases. These can be treated by radiotherapy, but the radiation-resistant nature of melanoma makes the prognosis for melanoma patients with brain metastases poor. Previously, we demonstrated that treatment of mice with subcutaneous melanoma with 5-aminolevurinic acid (5-ALA) and X-rays in combination, (“radiodynamic therapy (RDT)”), instead of with 5-ALA and laser beams (“photodynamic therapy”), improved tumor suppression in vivo. Here, using the B16-Luc melanoma brain metastasis model, we demonstrate that 5-ALA RDT effectively treats brain metastasis. We also studied how 5-ALA RDT damages cells in vitro using a B16 melanoma culture. Cell culture preincubated with 5-ALA alone increased intracellular photosensitizer protoporphyrin IX. On X-ray irradiation, the cells enhanced their ∙OH radical generation, which subsequently induced γH2AX, a marker of DNA double-strand breaks in their nuclei, but decreased mitochondrial membrane potential. After two days, the cell cycle was arrested. When 5-ALA RDT was applied to the brain melanoma metastasis model in vivo, suppression of tumor growth was indicated. Therapeutic efficacy in melanoma treatment has recently been improved by molecular targeted drugs and immune checkpoint inhibitors. Treatment with these drugs is now expected to be combined with 5-ALA RDT to further improve therapeutic efficacy.

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

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

DNA Damage Focus Formation Assay

Advanced techniques allow investigating cellular DNA damage measurements. Ionizing radiation produces multiple DNA damages. Among them, DNA double strand breaks are most toxic to cells. DSBs can form mutations, chromosome aberrations, and cell killing. Although DSBs in cells can be detected directly by neutral elution, pulse field gel electrophoresis, and premature chromosome condensation, recent technologies like cellular immunocytochemistry-based fluorescence detection allow us to visualize the DSBs in cells. Here, we describe gamma-H2AX and Rad51 focus formation assay, which play an important role in DNA damage responses.

CHTOP in Chemoresistant Epithelial Ovarian Cancer: A Novel and Potential Therapeutic Target

Objective: Chemoresistance is a major challenge in epithelial ovarian cancer (EOC) treatment. Chromatin target of protein arginine methyltransferase (CHTOP) was identified as a potential biomarker in chemoresistant EOC cell lines using label-free LC-MS/MS quantitative proteomics. Thus, the aim of this study is to investigate the role of CHTOP in chemoresistant EOC and the underlying mechanism.

Methods: The expression of CHTOP in human ovarian cancer cells and tissues was detected using immunofluorescence (IF), western blot (WB), and immunohistochemistry (IHC), respectively. Flow cytometry and TUNEL assay were employed to detect the effect of CHTOP knockdown (KD) in chemoresistant EOC cell apoptosis, while colony and sphere formation assays were used to evaluate its effect on cell stemness. The association of CHTOP with cell metastasis was determined using Matrigel invasion and wound-healing assays.

Results: The higher level expression of CHTOP protein was found in chemoresistant EOC cells as compared to their sensitive parental cells or normal epithelial ovarian cells. Results from IHC and bioinformatic analysis showed CHTOP was highly expressed in human ovarian cancer tissues and associated with a poor progression-free survival in patients. In addition, CHTOP KD significantly enhanced cisplatin-induced apoptosis, reduced the stemness of chemoresistant EOC cells, and decreased their metastatic potential.

Conclusion: Our findings suggest that CHTOP is associated with apoptosis, stemness, and metastasis in chemoresistant EOC cells and might be a promising target to overcome chemoresistance in EOC treatment.

Methanol Extract of Aerial Parts of Pavetta indica L. Enhances the Cytotoxic Effect of Doxorubicin and Induces Radiation Sensitization in MDA-MB-231 Triple-Negative Breast Cancer Cells

Pavetta indica L. is used in traditional medicine for the treatment of various diseases including hemorrhoids, headache, urinary conditions, ulcerated nose, and dropsy. However, no study has evaluated the anticancer effect of P. indica L. In this study, we found that a methanol extract of the leaves and branches of P. indica L. (MEPI) caused cellcycle arrest at the sub-G1 phase and induced apoptosis, as indicated by the activation of caspase-8, -3, -7, and c-PARP. Western blotting revealed that MEPI significantly reduced the levels of markers of the epithelial-mesenchymal transition, such as Vimentin, Snail, Slug, and matrix metallopeptidase 9. Notably, the expression of multidrug resistance-associated protein 1 in triple negative breast cancer (TNBC) was significantly decreased by MEPI. Moreover, the co-treatment with MEPI and doxorubicin resulted in a synergistic reduction in cell viability. MEPI also induced radiation sensitization of TNBC cells. Gas chromatography-mass spectrometry analysis revealed that 5,6-dehydrokawain (DK) is the major constituent of MEPI. Interestingly, DK exerted significant anti-invasive and anti-metastatic effects. Our results provide a strong rationale for investigating the molecular mechanisms of action of MEPI in TNBC.

Fuplatin: An Efficient and Low-Toxic Dual-Prodrug

As FDA-approved chemotherapeutic agents, cisplatin, oxaliplatin, and 5-fluorouracil are widely used in clinic but limited by severe side-effects. To ameliorate their respective defects, a series of "dual-prodrug" by linking oxoplatin and 5-FU were designed and synthesized. The assembled compounds 10-17, named Fuplatin, exhibited much higher cytotoxicity against the tested cancer cells while lower cytotoxicity toward the human normal lung cells than free drugs or their combinations. Among them, 14 enhanced cellular accumulation with 62- and 825-fold amount of oxaliplatin and 8 at 9 h, respectively, significantly induced DNA damage and cell apoptosis, and inhibited migration and invasion in HCT-116 cells. Compound 14 arrested the cell cycle at S and G2 phases and up-regulated thymidylate synthase and p53, consistent with the results of the combination, suggesting 14 adopted a collaborative mode of 5-FU and oxaliplatin to kill cancer cells. In vivo, compound 14 showed high antitumor effect and no observable toxicity in NOD/SCID mice bearing HCT-116 tumors.

Protein phosphatase 2A inhibition enhances radiation sensitivity and reduces tumor growth in chordoma

Background

Standard therapy for chordoma consists of surgical resection followed by high-dose irradiation. Protein phosphatase 2A (PP2A) is a ubiquitously expressed serine/threonine phosphatase involved in signal transduction, cell cycle progression, cell differentiation, and DNA repair. LB100 is a small-molecule inhibitor of PP2A designed to sensitize cancer cells to DNA damage from irradiation and chemotherapy. A recently completed phase I trial of LB100 in solid tumors demonstrated its safety. Here, we show the therapeutic potential of LB100 in chordoma.

Methods

Three patient-derived chordoma cell lines were used: U-CH1, JHC7, and UM-Chor1. Cell proliferation was determined with LB100 alone and in combination with irradiation. Cell cycle progression was assessed by flow cytometry. Quantitative γ-H2AX immunofluorescence and immunoblot evaluated the effect of LB100 on radiation-induced DNA damage. Ultrastructural evidence for nuclear damage was investigated using Raman imaging and transmission electron microscopy. A xenograft model was established to determine potential clinical utility of adding LB100 to irradiation.

Results

PP2A inhibition in concert with irradiation demonstrated in vitro growth inhibition. The combination of LB100 and radiation also induced accumulation at the G2/M phase of the cell cycle, the stage most sensitive to radiation-induced damage. LB100 enhanced radiation-induced DNA double-strand breaks. Animals implanted with chordoma cells and treated with the combination of LB100 and radiation demonstrated tumor growth delay.

Conclusions

Combining LB100 and radiation enhanced DNA damage-induced cell death and delayed tumor growth in an animal model of chordoma. PP2A inhibition by LB100 treatment may improve the effectiveness of radiation therapy for chordoma.

Enhancement of radiotherapeutic efficacy for esophageal cancer by paclitaxel-loaded red blood cell membrane nanoparticles modified by the recombinant protein anti-EGFR-iRGD

Paclitaxel is widely used as a radiosensitizer for various tumors, including esophageal cancer, but its therapeutic effect remains to be improved. In this study, we constructed a novel nano-radiosensitizer, anti-EGFR-iRGD-conjugated (iE)-PRNPs, by conjugating the recombinant protein anti-epidermal growth factor receptor (EGFR)-internalizing arginine-glycine-aspartic (iRGD) to the surface of paclitaxel-loaded red blood cell membrane nanoparticles (PRNPs). The iE-PRNPs were confirmed to possess tumor-targeting, high penetrability, and sustained release properties that free paclitaxel does not possess. Compared with that of paclitaxel, the sensitizer enhancement ratio of iE-PRNPs was significantly increased (1.32-fold and 1.25-fold) in esophageal cancer cells with high and low expression levels of EGFR, respectively. Additionally, compared with that of unmodified PRNPs, the sensitizer enhancement ratio of iE-PRNPs in EGFR-overexpressing esophageal cancer cells was significantly increased (1.27-fold), while that of PRNPs in esophageal cancer cells with a low EGFR expression level increased slightly (1.06-fold). The improved radiosensitization effect was associated with enhanced G2/M arrest, increased reactive oxygen species, and more effective induction of DNA double-strand breaks. In summary, iE-PRNPs appear to be a novel type of radiosensitizer with the potential to overcome the bottleneck of esophageal cancer radiotherapeutic efficacy.

A Novel Compound, "FA-1" Isolated from Prunus mume, Protects Human Bronchial Epithelial Cells and Keratinocytes from Cigarette Smoke Extract-Induced Damage

Extract of the Japanese apricot (JAE) has biological properties as an antioxidant and anti-inflammatory agent. We hypothesized that JAE might exert therapeutic effects on cigarette smoke (CS)-induced DNA damage and cytotoxicity. In this study, we found that concentrated JAE protects against cigarette smoke extract (CSE)-induced cytotoxicity and DNA damage accompanied by increased levels of aldehyde dehydrogenase (ALDH)2, 3A1, and Werner's syndrome protein (WRN) in immortalized human bronchial epithelial cells (HBEC2) and normal human epidermal keratinocytes (NHEK). Using the centrifugal partition chromatography (CPC) method, we identified an undescribed compound, 5-hydroxymethyl-2-furaldehyde bis(5-formylfurfuryl) acetal (which we named FA-1), responsible for the protective effects against CSE. This chemical structure has not been reported from a natural source to date. Protective effects of isolated FA-1 against CSE were observed in both HBEC2 and NHEK cells. The studies described herein suggest that FA-1 isolated from JAE protects against CSE-induced DNA damage and apoptosis by augmenting multiple isozymes of ALDH and DNA repair and reducing oxidative stress.

Biological effects of radiation on cancer cells

With the development of radiotherapeutic oncology, computer technology and medical imaging technology, radiation therapy has made great progress. Research on the impact and the specific mechanism of radiation on tumors has become a central topic in cancer therapy. According to the traditional view, radiation can directly affect the structure of the DNA double helix, which in turn activates DNA damage sensors to induce apoptosis, necrosis, and aging or affects normal mitosis events and ultimately rewires various biological characteristics of neoplasm cells. In addition, irradiation damages subcellular structures, such as the cytoplasmic membrane, endoplasmic reticulum, ribosome, mitochondria, and lysosome of cancer cells to regulate various biological activities of tumor cells. Recent studies have shown that radiation can also change the tumor cell phenotype, immunogenicity and microenvironment, thereby globally altering the biological behavior of cancer cells. In this review, we focus on the effects of therapeutic radiation on the biological features of tumor cells to provide a theoretical basis for combinational therapy and inaugurate a new era in oncology.

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

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

Nanostructure of DNA repair foci revealed by superresolution microscopy

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

Niclosamide sensitizes nasopharyngeal carcinoma to radiation by downregulating Ku70/80 expression

The aim of the present study was to investigate whether niclosamide could sensitize the nasopharyngeal carcinoma cells to radiation and further explore the underlying mechanisms. CCK-8 assay was used to determine the effect of niclosamide on the proliferation of NPC cells. Colony formation assay was used to evaluate the radiosensitizing effect of niclosamide on NPC cells. Flow cytometry analysis was used to determine the apoptosis of NPC cells induced by niclosamide. Immunofluorescent staining was used to detect the formation of γ-H2AX foci and the localization of Ku70/80 proteins in NPC cells. Real-time PCR quantification analysis was used to examine the level of Ku70/80 mRNA. DNA damage repair-related proteins were detected by western blot analysis. Our results showed that niclosamide markedly suppressed the proliferation of NPC cells. Niclosamide pretreatment followed by irradiation reduced the colony forming ability of NPC cells. Niclosamide in combination with irradiation significantly increased the apoptotic rate of NPC cells. Niclosamide significantly reduced the transcriptional level of K70/80 but not the translocation of Ku70/80 protein induced by irradiation. In conclusion, our study demonstrated that niclosamide could inhibit the growth of NPC cells and sensitize the NPC cells to radiation via suppressing the transcription of Ku70/80.

Combined treatment of pancreatic cancer xenograft with 90Y-ITGA6B4-mediated radioimmunotherapy and PI3K/mTOR inhibitor

AIM

To investigate the therapeutic effect of combined integrin α₆β₄-targeted radioimmunotherapy (RIT) and PI3K/mTOR inhibitor BEZ235 in a pancreatic cancer model.

METHODS

Phosphorylation of Akt, mTOR, the downstream effectors eukaryotic initiation factor 4E binding protein 1 (4EBP1) and S6 ribosomal protein (S6) were evaluated in BxPC-3 human pancreatic cancer cells treated with Yttrium-90 (⁹⁰Y) labeled anti-integrin α₆β₄ antibody (ITGA6B4) and BEZ235 by western blotting. The cytotoxic effect of BEZ235 was investigated using a colony formation assay. Therapeutic efficacy enhancement by oral BEZ235 administration was assessed using mice bearing BxPC-3 xenograft tumors. Tumor volume measurements and immunohistochemical analyses (cell proliferation marker Ki-67, DNA damage marker p-H2AX and p-4EBP1 staining) of tumors were performed for evaluation of combined treatment with ⁹⁰Y-ITGA6B4 plus BEZ235, or each arm alone.

RESULTS

We found that phosphorylation of Akt (p-Akt), 4EBP1 (p-4EBP1) and S6 (p-S6) was inhibited by BEZ235. Colony formation in BxPC-3 cells was additively suppressed by the combination of ⁹⁰Y-ITGA6B4 and BEZ235. Pretreatment with BEZ235 before ⁹⁰Y-ITGA6B4 exposure resulted in significant reduction of cells plating efficiency (PE) (0.54 ± 0.11 vs 2.81 ± 0.14 with 185 kBq/mL ⁹⁰Y-ITGA6B4 exposure, P < 0.01; 0.39 ± 0.08 vs 1.88 ± 0.09 with 370 kBq/mL ⁹⁰Y-ITGA6B4 exposure, P < 0.01) when 5 × 10³ cells per dish were plated. In vivo, the combined treatment with ⁹⁰Y-ITGA6B4 plus BEZ235 enhanced the inhibition of tumor growth and statistically significant differences of relative tumor volume were observed for 27 d after the treatment start date when compared with the ⁹⁰Y-ITGA6B4 single injection treatment (1.03 ± 0.38 vs 1.5 ± 0.15 at Day 27, P < 0.05), and for 41 d when compared with the BEZ235 treatment alone (1.8 ± 0.7 vs 3.14 ± 1.19 at Day 41, P < 0.05). Tumors from treatment groups showed reduction in volumes, decreased Ki-67-positive cells, increased p-H2AX-positive cells and decreased p-4EBP1 expression.

CONCLUSION

The therapeutic efficacy of ⁹⁰Y-ITGA6B4-RIT can be improved by combining with dual PI3K and mTOR inhibitor, BEZ235, in a pancreatic cancer model suggesting potential clinical application.

A novel automatic quantification method for high-content screening analysis of DNA double strand-break response

High-content screening is commonly used in studies of the DNA damage response. The double-strand break (DSB) is one of the most harmful types of DNA damage lesions. The conventional method used to quantify DSBs is γH2AX foci counting, which requires manual adjustment and preset parameters and is usually regarded as imprecise, time-consuming, poorly reproducible, and inaccurate. Therefore, a robust automatic alternative method is highly desired. In this manuscript, we present a new method for quantifying DSBs which involves automatic image cropping, automatic foci-segmentation and fluorescent intensity measurement. Furthermore, an additional function was added for standardizing the measurement of DSB response inhibition based on co-localization analysis. We tested the method with a well-known inhibitor of DSB response. The new method requires only one preset parameter, which effectively minimizes operator-dependent variations. Compared with conventional methods, the new method detected a higher percentage difference of foci formation between different cells, which can improve measurement accuracy. The effects of the inhibitor on DSB response were successfully quantified with the new method (p = 0.000). The advantages of this method in terms of reliability, automation and simplicity show its potential in quantitative fluorescence imaging studies and high-content screening for compounds and factors involved in DSB response.

Downregulation of Mitochondrial Single Stranded DNA Binding Protein (SSBP1) Induces Mitochondrial Dysfunction and Increases the Radiosensitivity in Non-Small Cell Lung Cancer Cells

Radiotherapy is one of the major therapeutic strategies for human non-small cell lung cancer (NSCLC), but intrinsic radioresistance of cancer cells makes a further improvement of radiotherapy for NSCLC challenging. Mitochondrial function is frequently dysregulated in cancer cells for adaptation to the changes of tumor microenvironment after exposure to radiation. Therefore, targeting mitochondrial biogenesis and bioenergetics is an attractive strategy to sensitize cancer cells to radiation therapy. In this study, we found that downregulation of single-strand DNA-binding protein 1 (SSBP1) in H1299 cells was associated with inducing mitochondrial dysfunction and increasing radiosensitivity to ionizing radiation. Mechanistically, SSBP1 loss induced mitochondrial dysfunction via decreasing mitochondrial DNA copy number and ATP generation, enhancing the mitochondrial-derived ROS accumulation and downregulating key glycolytic enzymes expression. SSBP1 knockdown increased the radiosensitivity of H1299 cells by inducing increased apoptosis, prolonged G2/M phase arrest and defective homologous recombination repair of DNA double-strand breaks. Our findings identified SSBP1 as a radioresistance-related protein, providing potential novel mitochondrial target for sensitizing NSCLC to radiotherapy.

Sulforaphene enhances radiosensitivity of hepatocellular carcinoma through suppression of the NF-κB pathway

Sulforaphene (SFE), a naturally occurring isothiocyanate found in cruciferous vegetables, has attracted increasing attention for its anti-cancer effect in many cancers, including hepatocellular carcinoma (HCC). However, the precise role of SFE in the radiosensitivity of HCC is still unclear. Here, cell proliferation and apoptosis were detected by MTT and flow cytometry assay, respectively. The activity of NF-κB was further evaluated by ELISA. We also observed the effect of SFE and/or radiation on tumor growth. The results showed that SFE inhibited cell proliferation and induced apoptosis in HCC cells. Radiation increased NF-kB activity, while PDTC, a NF-kB inhibitor, enhanced radiation-induced cell death. SFE inhibited NF-kB activity and the downstream gene expressions of the NF-kB pathway in HCC cells. Moreover, SFE enhanced the inhibitory effect of radiation on tumor growth both in vitro and in vivo. This study indicated that SFE sensitized the radiosensitivity of HCC by blocking the NF-kB pathway.

Castration radiosensitizes prostate cancer tissue by impairing DNA double-strand break repair

Chemical castration improves responses to radiotherapy in prostate cancer, but the mechanism is unknown. We hypothesized that this radiosensitization is caused by castration-mediated down-regulation of nonhomologous end joining (NHEJ) repair of DNA double-strand breaks (DSBs). To test this, we enrolled 48 patients with localized prostate cancer in two arms of the study: either radiotherapy first or radiotherapy after neoadjuvant castration treatment. We biopsied patients at diagnosis and before and after castration and radiotherapy treatments to monitor androgen receptor, NHEJ, and DSB repair in verified cancer tissue. We show that patients receiving neoadjuvant castration treatment before radiotherapy had reduced amounts of the NHEJ protein Ku70, impaired radiotherapy-induced NHEJ activity, and higher amounts of unrepaired DSBs, measured by γ-H2AX foci in cancer tissues. This study demonstrates that chemical castration impairs NHEJ activity in prostate cancer tissue, explaining the improved response of patients with prostate cancer to radiotherapy after chemical castration.

Evaluating biomarkers to model cancer risk post cosmic ray exposure

Robust predictive models are essential to manage the risk of radiation-induced carcinogenesis. Chronic exposure to cosmic rays in the context of the complex deep space environment may place astronauts at high cancer risk. To estimate this risk, it is critical to understand how radiation-induced cellular stress impacts cell fate decisions and how this in turn alters the risk of carcinogenesis. Exposure to the heavy ion component of cosmic rays triggers a multitude of cellular changes, depending on the rate of exposure, the type of damage incurred and individual susceptibility. Heterogeneity in dose, dose rate, radiation quality, energy and particle flux contribute to the complexity of risk assessment. To unravel the impact of each of these factors, it is critical to identify sensitive biomarkers that can serve as inputs for robust modeling of individual risk of cancer or other long-term health consequences of exposure. Limitations in sensitivity of biomarkers to dose and dose rate, and the complexity of longitudinal monitoring, are some of the factors that increase uncertainties in the output from risk prediction models. Here, we critically evaluate candidate early and late biomarkers of radiation exposure and discuss their usefulness in predicting cell fate decisions. Some of the biomarkers we have reviewed include complex clustered DNA damage, persistent DNA repair foci, reactive oxygen species, chromosome aberrations and inflammation. Other biomarkers discussed, often assayed for at longer points post exposure, include mutations, chromosome aberrations, reactive oxygen species and telomere length changes. We discuss the relationship of biomarkers to different potential cell fates, including proliferation, apoptosis, senescence, and loss of stemness, which can propagate genomic instability and alter tissue composition and the underlying mRNA signatures that contribute to cell fate decisions. Our goal is to highlight factors that are important in choosing biomarkers and to evaluate the potential for biomarkers to inform models of post exposure cancer risk. Because cellular stress response pathways to space radiation and environmental carcinogens share common nodes, biomarker-driven risk models may be broadly applicable for estimating risks for other carcinogens.

Validation of a flow cytometry-based detection of γ-H2AX, to measure DNA damage for clinical applications

BACKGROUND

The nucleosomal histone protein H2AX is specifically phosphorylated (γ-H2AX) adjacent to DNA double-strand breaks (DSBs) and is used for quantifying DSBs. Many chemotherapies and ionizing radiation (IR) used in cancer treatment result in DSBs. Therefore, γ-H2AX has a significant potential as a biomarker in evaluating patient sensitivity and responsiveness to IR and chemotherapy.

METHODS

Here, we report a flow cytometry-based quantification of γ-H2AX (FCM-γ-H2AX assay) customized for clinical practice.

RESULTS

We validated that our method is able to detect DNA damage in peripheral blood mononuclear cells (PBMCs) treated with DSB inducing agents. The method also detected the DNA repair deficiency in PBMCs treated with DNA repair inhibitors, as well as the deficiency in DNA repair signaling in PBMCs from two ataxia telangiectasia patients.

CONCLUSIONS

The FCM-γ-H2AX assay has sufficient analytical sensitivity and precision to measure levels of DNA damage and DNA repair for clinical purposes. © 2016 International Clinical Cytometry Society.

Mean frequency and relative fluorescence intensity measurement of γ-H2AX foci dose response in PBL exposed to γ-irradiation: An inter- and intra-laboratory comparison and its relevance for radiation triage

Measurement of γ-H2AX protein changes in the peripheral blood lymphocytes (PBL) of individuals exposed to ionizing radiation is a simple, sensitive, and rapid assay for radiation triage and early marker of dose estimation. The qualitative and quantitative measurements of the protein changes were examined using flow cytometry and microscopy. Whole blood and isolated lymphocytes were exposed in vitro between 0.1 and 5 Gy doses of (60) Co γ-radiation at a dose rate of 1 Gy/min. Radiation induced γ-H2AX foci frequency (n = 3) and relative fluorescence intensity (n = 7) in PBL was measured at 0.5 and 2 hrs postexposure. The observed dose response for γ-H2AX foci frequency at both time points, for whole blood and isolated lymphocytes did not show any significant (P > 0.05) differences. However, when compared with γ-H2AX foci frequency scored manually (microscopy), the semiautomated analysis (captured images) showed a better correlation (r(2) = 0.918) than that obtained with automated (Metafer) scoring (r(2) = 0.690). It is noteworthy to mention that, the γ-H2AX foci frequency quantified using microscopy showed a dose dependent increase up to 2 Gy and the relative fluorescence intensity (RFI) measured with flow cytometry revealed an increase up to 5 Gy in the PBL exposed in vitro. Moreover, a better correlation was observed between the γ-H2AX foci frequency obtained by manual scoring and RFI (r(2) = 0.910). Kinetic studies showed that the γ-H2AX foci remain more or less unchanged up to 4 hrs and reduces gradually over 48 hrs of postexposure at 37°C. Further, inter and intra-laboratory comparisons showed consistency in the scoring of γ-H2AX foci frequency by manual and semiautomated scoring. The overall results suggest that measurement of γ-H2AX (microscopy and flow cytometry) should be employed within 4 to 6 hrs for a reliable dosimetry either by sharing the work load between the laboratories or investing more manpower; however, triage can be possible even up to 48 hrs of postirradiation.

Correlation between radiation dose and p53 protein expression levels in human lymphocytes

The aim of this research was to evaluate the relationship between p53 protein levels and absorbed doses from in vitro irradiated human lymphocytes. For this, samples of blood from 23 donors were irradiated with 0.5; 1; 2; and 4 Gy from a Cobalt-60 source, and the percentages of lymphocytes expressing p53 were scored using Flow Cytometry. The subjects were divided into 3 groups, in accordance with the p53 levels expressed per radiation dose: low (Group I), high (Group II), and excessive levels (Group III). For all groups, the analyses showed that the p53 expression levels increase with the absorbed dose. Particularly for groups I and II, the correlation between this protein expression and the dose follows the linear-quadratic model, such as for radioinduced chromosomal aberrations. In conclusion, our findings indicate possible applications of this approach in evaluating individual radiosensitivity prior to radiotherapeutical procedures as well as in medical surveillance of occupationally exposed workers. Furthermore, due to the rapidity of flow-cytometric analyses, the methodology here employed would play an important role in emergency responses to a large-scale radiation incident where many people may have been exposed.

Residual γH2AX foci after ex vivo irradiation of patient samples with known tumour-type specific differences in radio-responsiveness

PURPOSE

To apply our previously published residual ex vivo γH2AX foci method to patient-derived tumour specimens covering a spectrum of tumour-types with known differences in radiation response. In addition, the data were used to simulate different experimental scenarios to simplify the method.

MATERIALS AND METHODS

Evaluation of residual γH2AX foci in well-oxygenated tumour areas of ex vivo irradiated patient-derived tumour specimens with graded single doses was performed. Immediately after surgical resection, the samples were cultivated for 24h in culture medium prior to irradiation and fixed 24h post-irradiation for γH2AX foci evaluation. Specimens from a total of 25 patients (including 7 previously published) with 10 different tumour types were included.

RESULTS

Linear dose response of residual γH2AX foci was observed in all specimens with highly variable slopes among different tumour types ranging from 0.69 (95% CI: 1.14-0.24) to 3.26 (95% CI: 4.13-2.62) for chondrosarcomas (radioresistant) and classical seminomas (radiosensitive) respectively. Simulations suggest that omitting dose levels might simplify the assay without compromising robustness.

CONCLUSION

Here we confirm clinical feasibility of the assay. The slopes of the residual foci number are well in line with the expected differences in radio-responsiveness of different tumour types implying that intrinsic radiation sensitivity contributes to tumour radiation response. Thus, this assay has a promising potential for individualized radiation therapy and prospective validation is warranted.