Gamma histone 2AX (γ-H2AX)as a predictive tool in radiation oncology

Predicting Radiation-Induced Lung Injury in Patients With Lung Cancer: Challenges and Opportunities

Radiation-induced lung injury (RILI) is one of the main dose-limiting toxicities in radiation therapy (RT) for lung cancer. Approximately 10% to 20% of patients show signs of RILI of variable severity. The reason for the wide range of RILI severity and the mechanisms underlying its development are only partially understood. A number of clinical risk factors have been identified that can aid in clinical decision making. Technological advancements in RT and the use of strict organ-at-risk dose constraints have helped to reduce RILI. Predicting patients at risk for RILI may be further improved with a combination of cytokine assessments, γH2AX-assays in leukocytes, or epigenetic markers. A complicating factor is the lack of an objective definition of RILI. Tools such as computed tomography densitometry, fluorodeoxyglucose-positron emission tomography uptake, changes in lung function measurements, and exhaled breath analysis can be implemented to better define and quantify RILI. This can aid in the search for new biomarkers, which can be accelerated by omics techniques, single-cell RNA sequencing, mass cytometry, and advances in patient-specific in vitro cell culture models. An objective quantification of RILI combined with these novel techniques can aid in the development of biomarkers to better predict patients at risk and allow personalized treatment decisions.

Potent anti-cancer activity of Sphaerocoryne affinis fruit against cervical cancer HeLa cells via inhibition of cell proliferation and induction of apoptosis

BACKGROUND

Cervical cancer remains a significant global health issue, highlighting the need for effective therapeutic strategies. Given that Sphaerocoryne affinis (SA) has shown potential anti-cancer activity in several cancer types, herein, we investigate the effects of SA fruit (SAF) on human cervical cancer HeLa cells and their underlying mechanisms of action.

METHODS

SAF extract cytotoxicity was assessed in various cancer cell lines. The effects of the hexane fraction (SAF-Hex) on HeLa cell viability, cell cycle protein expression, apoptosis, and DNA damage were evaluated using cytotoxicity assays, Western blotting, quantitative PCR, 4',6-diamidino-2-phenylindole (DAPI) staining, and a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay.

RESULTS

SAF-Hex selectively inhibited HeLa cell viability with an IC50 of 4.20 ± 0.36 µg/mL and a selectivity index of 5.11 ± 0.58. The time-dependent cytotoxicity assay showed decreased cell survival after 48 h of treatment, accompanied by morphological changes and apoptotic bodies in HeLa cells. SAF-Hex also suppressed HeLa cell cycle proteins (Cyclin E, CDK2, and CDK1), reduced PCNA transcription, and diminished AKT and mTOR activation, thus inhibiting cell proliferation. The increased γH2AX expression, DNA fragmentation, and caspases-3 and -9 activation indicated SAF-Hex-induced DNA damage and apoptosis. However, the BAX/BCL-2 ratio remained unchanged, and BAX and BCL2 expression was attenuated.

CONCLUSION

SAF-Hex effectively inhibits HeLa cell proliferation and induces DNA damage in that cervical cancer cell line activating apoptosis through the intrinsic pathway. Interestingly, the BAX/BCL-2 ratio remained unchanged while BAX and BCL2 transcription was attenuated. Hence, further research is required to explore this unexpected finding and facilitate the development of novel therapies targeting cervical cancer HeLa cells.

JNC-1043, a Novel Podophyllotoxin Derivative, Exerts Anticancer Drug and Radiosensitizer Effects in Colorectal Cancer Cells

The objective of this study was to determine whether (5S)-5-(4-benzyloxy-3,5-dimethoxy-phenyl)-5,9-dihydro-8H-furo [3’,4’:6,7] naphtho [2,3-d] [1,3]dioxol-6-one (JNC-1043), which is a novel chemical derivative of β-apopicropodophyllin, acts as a novel potential anticancer reagent and radiosensitizer in colorectal cancer (CRC) cells. Firstly, we used MTT assays to assess whether JNC-1043 could inhibit the cell proliferation of HCT116 and DLD-1 cells. The IC50 values of these cell lines were calculated as 114.5 and 157 nM, respectively, at 72 h of treatment. Using doses approximating the IC50 values, we tested whether JNC-1043 had a radiosensitizing effect in the CRC cell lines. Clonogenic assays revealed that the dose-enhancement ratios (DER) of HCT116 and DLD-1 cells were 1.53 and 1.25, respectively. Cell-counting assays showed that the combination of JNC-1043 and γ-ionizing radiation (IR) enhanced cell death. Treatment with JNC-1043 or IR alone induced cell death by 50~60%, whereas the combination of JNC-1043 and IR increased this cell death by more than 20~30%. Annexin V-propidium iodide assays showed that the combination of JNC-1043 and IR increased apoptosis by more 30~40% compared to that induced by JNC-1043 or IR alone. DCFDA- and MitoSOX-based assays revealed that mitochondrial ROS production was enhanced by the combination of JNC-1043 and IR. Finally, we found that suppression of ROS by N-acetylcysteine (NAC) blocked the apoptotic cell death induced by the combination of JNC-1043 and IR. The xenograft model also indicated that the combination of JNC-1043 and IR increased apoptotic cell death in tumor mass. These results collectively suggest that JNC-1043 acts as a radiosensitizer and exerts anticancer effects against CRC cells by promoting apoptosis mediated by mitochondrial ROS.

Chrysin impairs genomic stability by suppressing DNA double-strand break repair in breast cancer cells

Chrysin, a natural compound isolated from various plants, such as the blue passion flower (Passiflora caerulea L.), exhibits multiple pharmacological activities, such as antitumor, anti-inflammatory and antioxidant activities. Accumulating evidence shows that chrysin inhibits cancer cell growth by inducing apoptosis and regulating cell cycle arrest. However, whether chrysin is involved in regulating genomic stability and its underlying mechanisms in breast cancer cells have not been determined. Here, we demonstrated that chrysin impairs genomic stability in MCF-7 and BT474 cells, inhibits cell survival and enhances the sensitivity of MCF-7 cells to chemotherapeutic drugs. Further experiments revealed that chrysin impairs DNA double-strand break (DSB) repair, resulting in accumulation of DNA damage. Mechanistic studies showed that chrysin inhibits the recruitment of the key NHEJ factor 53BP1 and delays the recruitment of the HR factor RAD51. Thus, we elucidated novel regulatory mechanisms of chrysin in DSB repair and proposed that a combination of chrysin and chemotherapy has curative potential in breast cancers.

Radiosensitizer Effect of β-Apopicropodophyllin against Colorectal Cancer via Induction of Reactive Oxygen Species and Apoptosis

β-apopicropodophyllin (APP), a derivative of podophyllotoxin (PPT), has been identified as a potential anti-cancer drug. This study tested whether APP acts as an anti-cancer drug and can sensitize colorectal cancer (CRC) cells to radiation treatment. APP exerted an anti-cancer effect against the CRC cell lines HCT116, DLD-1, SW480, and COLO320DM, with IC50 values of 7.88 nM, 8.22 nM, 9.84 nM, and 7.757 nM, respectively, for the induction of DNA damage. Clonogenic and cell counting assays indicated that the combined treatment of APP and γ-ionizing radiation (IR) showed greater retardation of cell growth than either treatment alone, suggesting that APP sensitized CRC cells to IR. Annexin V–propidium iodide (PI) assays and immunoblot analysis showed that the combined treatment of APP and IR increased apoptosis in CRC cells compared with either APP or IR alone. Results obtained from the xenograft experiments also indicated that the combination of APP and IR enhanced apoptosis in the in vivo animal model. Apoptosis induction by the combined treatment of APP and IR resulted from reactive oxygen species (ROS). Inhibition of ROS by N-acetylcysteine (NAC) restored cell viability and decreased the induction of apoptosis by APP and IR in CRC cells. Taken together, these results indicate that a combined treatment of APP and IR might promote apoptosis by inducing ROS in CRC cells.

Metabolism of cancer cells commonly responds to irradiation by a transient early mitochondrial shutdown

Cancer bioenergetics fuel processes necessary to maintain viability and growth under stress conditions. We hypothesized that cancer metabolism supports the repair of radiation-induced DNA double-stranded breaks (DSBs). We combined the systematic collection of metabolic and radiobiological data from a panel of irradiated cancer cell lines with mathematical modeling and identified a common metabolic response with impact on the DSB repair kinetics, including a mitochondrial shutdown followed by compensatory glycolysis and resumption of mitochondrial function. Combining ionizing radiation (IR) with inhibitors of the compensatory glycolysis or mitochondrial respiratory chain slowed mitochondrial recovery and DNA repair kinetics, offering an opportunity for therapeutic intervention. Mathematical modeling allowed us to generate new hypotheses on general and individual mechanisms of the radiation response with relevance to DNA repair and on metabolic vulnerabilities induced by cancer radiotherapy. These discoveries will guide future mechanistic studies for the discovery of metabolic targets for overcoming intrinsic or therapy-induced radioresistance.

3D Breast Tumor Models for Radiobiology Applications

Breast cancer is a leading cause of cancer-associated death in women. The clinical management of breast cancers is normally carried out using a combination of chemotherapy, surgery and radiation therapy. The majority of research investigating breast cancer therapy until now has mainly utilized two-dimensional (2D) in vitro cultures or murine models of disease. However, there has been significant uptake of three-dimensional (3D) in vitro models by cancer researchers over the past decade, highlighting a complimentary model for studies of radiotherapy, especially in conjunction with chemotherapy. In this review, we underline the effects of radiation therapy on normal and malignant breast cells and tissues, and explore the emerging opportunities that pre-clinical 3D models offer in improving our understanding of this treatment modality.

Disulfiram Alone Functions as a Radiosensitizer for Pancreatic Cancer Both In Vitro and In Vivo

The prognosis of pancreatic cancer remains very poor worldwide, partly due to the lack of specificity of early symptoms and innate resistance to chemo-/radiotherapy. Disulfiram (DSF), an anti-alcoholism drug widely used in the clinic, has been known for decades for its antitumor effects when simultaneously applied with copper ions, including pancreatic cancer. However, controversy still exists in the context of the antitumor effects of DSF alone in pancreatic cancer and related mechanisms, especially in its potential roles as a sensitizer for cancer radiotherapy. In the present study, we focused on whether and how DSF could facilitate ionizing radiation (IR) to eliminate pancreatic cancer. DSF alone significantly suppressed the survival of pancreatic cancer cells after exposure to IR, both in vitro and in vivo. Additionally, DSF treatment alone caused DNA double-strand breaks (DSBs) and further enhanced IR-induced DSBs in pancreatic cancer cells. In addition, DSF alone boosted IR-induced cell cycle G2/M phase arrest and apoptosis in pancreatic cancer exposed to IR. RNA sequencing and bioinformatics analysis results suggested that DSF could trigger cell adhesion molecule (CAM) signaling, which might be involved in its function in regulating the radiosensitivity of pancreatic cancer cells. In conclusion, we suggest that DSF alone may function as a radiosensitizer for pancreatic cancer, probably by regulating IR-induced DNA damage, cell cycle arrest and apoptosis, at least partially through the CAM signaling pathway.

Histone Variants: Guardians of Genome Integrity

Chromatin integrity is key for cell homeostasis and for preventing pathological development. Alterations in core chromatin components, histone proteins, recently came into the spotlight through the discovery of their driving role in cancer. Building on these findings, in this review, we discuss how histone variants and their associated chaperones safeguard genome stability and protect against tumorigenesis. Accumulating evidence supports the contribution of histone variants and their chaperones to the maintenance of chromosomal integrity and to various steps of the DNA damage response, including damaged chromatin dynamics, DNA damage repair, and damage-dependent transcription regulation. We present our current knowledge on these topics and review recent advances in deciphering how alterations in histone variant sequence, expression, and deposition into chromatin fuel oncogenic transformation by impacting cell proliferation and cell fate transitions. We also highlight open questions and upcoming challenges in this rapidly growing field.

Effect of epigallocatechin-3-gallate (EGCG) on embryos inseminated with oxidative stress-induced DNA damage sperm

Cryopreservation can induce damage in human spermatozoa through reactive oxygen species (ROS) generation. To reduce the potential risk of oxidative stress-induced sperm DNA damage, addition of different epigallocatechin-3-gallate (EGCG) concentrations were performed to determine the optimum concentration which was beneficial for IVF outcome for both fresh and frozen-thawed sperm. Next, the mouse sperm model exhibiting oxidative stress-induced DNA damage by exogenously treating with H₂O₂ but overcoming the low fertilization rate of frozen-thawed sperm was used to investigate the effect of EGCG on the embryonic development and the potential EGCG-mediated effects on ataxia telangiectasia mutated (ATM) pSer-1981 in zygotes, the latter was known for leading to the activation of major kinases involved in the DNA repair pathway and the cell cycle checkpoint pathway. We found the fertilization and embryonic development of embryos inseminated with frozen-thawed sperm was impaired compared to fresh sperm. EGCG promoted the development of embryos inseminated with both types of sperm at optimum concentration. In embryos inseminated with the H₂O₂ sperm, fertilization, embryonic development, and the time at which the cleavage rate of one-cell embryos reached ≥95% were not affected by EGCG treatment. However, the EGCG-treated group required less time to achieve 50% cleavage rate of one-cell embryos, and the EGCG-treated zygotes showed enhanced expression of ATM (pSer-1981) than the untreated group. EGCG at optimum concentrations may exert beneficial effects by modulating the ATM activation and moving up the time to enter into mitotic (M) phase.

ABBREVIATIONS

ROS: reactive oxygen species; EGCG: epigallocatechin-3-gallate; ATM: ataxia telangiectasia mutated; M: mitotic.

The kinetics of γ-H2AX during radiotherapy of head and neck cancer potentially allow for prediction of severe mucositis

Background

The aim of the study was to evaluate the changes in γ-H2AX expression in peripheral blood lymphocytes (PBL) according to severity of radiation-induced mucositis.

Patients and method

Fifty patients with head and neck cancer treated with radiotherapy (RT) or chemoradiation were included in the study. Blood samples were collected before treatment to measure baseline γ-H2AX levels. Second sample was taken 45 minutes after the first RT fraction and then once a week, 45 min after irradiation. In patients treated with chemoradiation the blood sample was taken the day after chemotherapy. Mucositis was evaluated once a week and reported according to CTCAE v4 and RTOG/EORTC scales. PBL were analyzed with flow cytometry and level of H2AX phosphorylation at every time point was evaluated.

Results

In 35 patients mild to moderate (grade 1–2) mucositis was observed and 15 patients developed severe (grade 3) mucositis. No cases of grade 4 mucositis were observed. The difference in baseline levels of γ-H2AX between groups with mild and severe mucositis was statistically insignificant (p = 0.25). The statistically significant difference in γ-H2AX level was observed in week 7 of treatment (p = 0.01). No significant differences in γ-H2AX level were found neither between group treated with concomitant chemoradiation or RT alone neither between groups with and without common comorbidities. In the analysis of the kinetics of γ-H2AX during treatment, a statistically significant difference (p = 0.0088) between groups with mild and severe mucositis was observed. After fourth week of treatment levels of γ-H2AX decreased significantly in the group with severe mucositis and increased in patients with mild side effects. The observed difference was not caused by the decrease in peripheral lymphocyte count, which was similar in both groups.

Conclusions

Presented results indicate that severity of radiation-induced mucositis does not correlate directly with γ-H2AX levels measured in vivo in PBL. Prediction of mucositis grade based on γ-H2AX level is not yet possible, either before treatment or early during treatment, but preliminary results, indicating significant differences in γ-H2AX kinetics between groups, encourage further studies.

Immunohistochemical detection of senescence markers in human sarcomas

INTRODUCTION

Senescent cells in tumors are not inert cells but exert bystander effects by developing secretory phenotypes affecting the extracellular matrix and interfering the biological behavior of adjacent tumor cells.

MATERIALS AND METHODS

We assessed putative senescent cell content in a series of human sarcomas, using in parallel markers related to cell proliferation (Ki67), DNA damage (γH2Ax), lipofuscin detection (SenTraGor®) and two cyclin-dependent kinase CDK-inhibitors (p16/INK4a and p21/cip/waf21).

RESULTS

Necrosis was directly linked with the size of tumors (p = 0.02, r = 0.25), number of mitosis (p = 0.05, r = 0.21) and inversely with the expression of γH2Ax (p = 0.01, r = 0.28). Smaller tumors (less than 3 cm) had a higher p16 expression (p = 0.07); Moreover, in group analysis, tumors with lack of expression of p16 had significantly higher necrosis score (p = 0.03). Linear regression analysis showed that p21 expression was strongly and directly related with MIB1 (p < 0.0001, r = 0.44) and with Lipofuscin expression (p = 0.02, r = 0.26).

CONCLUSION

Senescence markers are extensively expressed in human sarcomas and correlated with histopathological features. However, p16, p21 and Lipofuscin expression show different patterns, suggesting that these markers may detect different senescence phenotypes. In addition, our data suggest that the novel marker SenTraGor® may detect phenotypes of senescent cells involving p21 activation.

Apoptosis Induction by Pseudorabies Virus via Oxidative Stress and Subsequent DNA Damage Signaling

BACKGROUND

Pseudorabies virus (PRV) infection induces apoptosis in swine cells both in vitro and in vivo; however, the mechanism associated with host-cell signaling has not been studied. This study investigated the role of free radicals caused by cellular oxidative stress after viral infection and examined whether the DNA damage response plays an important role in PRV-induced apoptosis.

METHODS

Several apoptosis assays and western blotting confirmed PRV-induced apoptosis. PRV-mediated oxidative stress was evaluated by reactive oxygen species (ROS) assay.

RESULTS

Our results showed that PRV caused apoptosis in a porcine kidney cell line, PK15, and induced expressions of proapoptotic Bcl family proteins in a dose- and time-dependent manner. Expressions of specific DNA damage sensors and phosphorylation of histone H2AX were also significantly increased, which subsequently activated the expressions of checkpoint kinase 1/2 and proapoptotic p53. Caffeine, a known DNA damage inhibitor, was found to inhibit caspase-3 activation and protect cells from PRV-induced apoptosis. Additionally, the antioxidant N-acetyl-L-cysteine was shown to prevent the production of cellular ROS, protecting DNA from cleavage.

CONCLUSIONS

Our results confirmed that oxidative stress and free radicals arising from PRV infection cause DNA damage, which consequently triggers apoptosis.

A Roberts Syndrome Individual With Differential Genotoxin Sensitivity and a DNA Damage Response Defect

PURPOSE

Roberts syndrome (RBS) is a rare, recessively transmitted developmental disorder characterized by growth retardation, craniofacial abnormalities, and truncation of limbs. All affected individuals to date have mutations in the ESCO2 (establishment of cohesion 2) gene, a key regulator of the cohesin complex, which is involved in sister chromatid cohesion and DNA double-strand break (DSB) repair. Here we characterize DNA damage responses (DDRs) for the first time in an RBS-affected family.

METHODS AND MATERIALS

Lymphoblastoid cell lines were established from an RBS family, including the proband and parents carrying ESCO2 mutations. Various DDR assays were performed on these cells, including cell survival, chromosome break, and apoptosis assays; checkpoint activation indicators; and measures of DNA breakage and repair.

RESULTS

Cells derived from the RBS-affected individual showed sensitivity to ionizing radiation (IR) and mitomycin C-induced DNA damage. In this ESCO2 compound heterozygote, other DDRs were also defective, including enhanced IR-induced clastogenicity and apoptosis; increased DNA DSB induction; and a reduced capacity for repairing IR-induced DNA DSBs, as measured by γ-H2AX foci and the comet assay.

CONCLUSIONS

In addition to its developmental features, RBS can be, like ataxia telangiectasia, considered a DDR-defective syndrome, which contributes to its cellular, molecular, and clinical phenotype.

The antitumor effect of cisplatin-loaded thermosensitive chitosan hydrogel combined with radiotherapy on nasopharyngeal carcinoma

Cisplatin-based chemo-radiotherapy (RT) is the most effective treatment in patients with loco-regionally advanced nasopharyngeal carcinoma (NPC). However, traditional chemotherapy drugs have low bioavailability and targeting ability, which reduce their antitumor effects. Therefore, we developed a chitosan/ cis-dichlorodiamineplatinum (CS/DDP) hydrogel-based drug delivery system for the in situ treatment of NPC in combination with RT, and investigated their synergistic antitumor efficacy and underlying mechanism of action. CS/DDP hydrogel remarkably prolonged the survival time (81 days) when combined with RT compared to the control group (P < 0.01). The main mechanism was likely the increase in cancer cell apoptosis (76.23 ± 1.13%, p < 0.01). Furthermore, the CS/DDP hydrogel in combination with RT also increased X-ray-induced DSBs and γ-H2AX foci, induced G2/M phase arrest, inhibited cell proliferation by blocking Ki-67, and decreased CD31+ micro-vessel density (MVD). These results underscore the therapeutic potential of the combination of CS/DDP hydrogel and RT for localized NPC.

Ionizing radiation-induced cellular senescence promotes tissue fibrosis after radiotherapy. A review

Ionizing radiation-exposure induces a variety of cellular reactions, such as senescence and apoptosis. Senescence is a permanent arrest state of the cell division, which can be beneficial or detrimental for normal tissue via an inflammatory response and senescence-associated secretion phenotype. Damage to healthy cells and their microenvironment is considered as an important source of early and late complications with an increased risk of morbidity in patients after radiotherapy (RT). In addition, the benefit/risk ratio may depend on the radiation technique/dose used for cancer eradication and the irradiated volume of healthy tissues. For radiation-induced fibrosis risk, the knowledge of mechanisms and potential prevention has become a crucial point to determining radiation parameters and patients' intrinsic radiosensitivity. This review summarizes our understanding of ionizing radiation-induced senescent cell in fibrogenesis. This mechanism may provide new insights for therapeutic modalities for better risk/benefit ratios after RT in the new era of personalized treatments.

CD44 collaborates with ERBB2 mediate radiation resistance via p38 phosphorylation and DNA homologous recombination pathway in prostate cancer

CD44, a glycoprotein, has been reported to have relationship with resistance to radiation in prostate cancer (Cap) cells. However, its molecular mechanism remains unknown. In this study, we demonstrated that inhibited CD44 enhanced the radiosentivity in Cap cells. It has been hypothesized that CD44 combine with ERBB2 and activate downstream phosphated protein to mediate DNA damage repair. Therefore, we conducted a detailed analysis of effects of radiation by clonogenic assay and immunofluorescence stain for p-H2AX foci. The downstream of CD44/ERBB2 and DNA damage repair proteins was detected by western blot. The results reveal that CD44 interacted with ERBB2, the downstream of CD44/ERBB2 was p-p38 when Cap cells were irradiated. Among the pathways, homologous recombination (HR) related proteins Mre11 and Rad50 were involved in CD44/ERBB2/p-p38 mediated radioresistance in Cap. In conclusion, CD44 could stabilize ERBB2 and co-activate p-p38 expression then promote the DNA damage repair by HR pathway, which finally contribute to the radioresistance of CaP.

Advantages of evaluating γH2AX induction in non-clinical drug development

γH2AX, the phosphorylated form of a histone variant H2AX at Ser 139, is already widely used as a biomarker to research the fundamental biology of DNA damage and repair and to assess the risk of environmental chemicals, pollutants, radiation, and so on. It is also beginning to be used in the early non-clinical stage of pharmaceutical drug development as an in vitro tool for screening and for mechanistic studies on genotoxicity. Here, we review the available information on γH2AX-based test systems that can be used to develop drugs and present our own experience of practically applying these systems during the non-clinical phase of drug development. Furthermore, the potential application of γH2AX as a tool for in vivo non-clinical safety studies is also discussed.

Post-Translational Modifications of H2A Histone Variants and Their Role in Cancer

Histone variants are chromatin components that replace replication-coupled histones in a fraction of nucleosomes and confer particular characteristics to chromatin. H2A variants represent the most numerous and diverse group among histone protein families. In the nucleosomal structure, H2A-H2B dimers can be removed and exchanged more easily than the stable H3-H4 core. The unstructured N-terminal histone tails of all histones, but also the C-terminal tails of H2A histones protrude out of the compact structure of the nucleosome core. These accessible tails are the preferential target sites for a large number of post-translational modifications (PTMs). While some PTMs are shared between replication-coupled H2A and H2A variants, many modifications are limited to a specific histone variant. The present review focuses on the H2A variants H2A.Z, H2A.X, and macroH2A, and summarizes their functions in chromatin and how these are linked to cancer development and progression. H2A.Z primarily acts as an oncogene and macroH2A and H2A.X as tumour suppressors. We further focus on the regulation by PTMs, which helps to understand a degree of context dependency.

Radiation-resistant cancer stem-like cell properties are regulated by PTEN through the activity of nuclear β-catenin in nasopharyngeal carcinoma

Radiotherapy is the primary and most important treatment for nasopharyngeal carcinoma (NPC). Cancer stem-like cells (CSCs) have been shown to be resistant to radiation. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) tumor suppressor gene has been suggested to play a role in stem cell self-renewal. In the present study, we sorted PTEN−/+ cells using a flow cytometer. The clone formation assay showed that PTEN− cells were more radioresistant than PTEN+ NPC cells. We found that PTEN− cells demonstrated a significant increase in tumorsphere formation and CSCs markers compared with PTEN+ cells. Silencing the expression of PTEN with siRNA resulted in increased expression of p-AKT, active β-catenin and Nanog. siPTEN cells irradiated showed more radioresistant and DNA damage than parental cells. We also confirmed that down-regulation of β-catenin expression with shRNA resulted in a reduced percentage of side population cells and expression of Nanog. shβ-catenin cells significantly decreased survivin expression at 4 Gy irradiation in PTEN− cells compared with PTEN+ cells. In siPTEN cells, β-catenin staining shifted from the cytoplasmic membrane to the nucleus. Furthermore, immunofluorescence showed that following irradiation of PTEN− cells, at 4 Gy, active β-catenin was mainly found in the nucleus. Immunohistochemistry analysis also demonstrated that the PTEN−/p-AKT+/β-catenin+/Nanog+ axis may indicate poor prognosis and radioresistance in clinical NPC specimens. Thus, our findings strongly suggest that PTEN− cells have CSCs properties that are resistant to radiation in NPC. PTEN exerts these effects through the downstream effector PI3K/AKT/β-catenin/Nanog axis which depends on nuclear β-catenin accumulation.

A Short-Term Biological Indicator for Long-Term Kidney Damage after Radionuclide Therapy in Mice

Folate receptor (FR)-targeted radionuclide therapy using folate radioconjugates is of interest due to the expression of the FR in a variety of tumor types. The high renal accumulation of radiofolates presents, however, a risk of radionephropathy. A potential option to address this challenge would be to use radioprotectants, such as amifostine. Methods for early detection of kidney damage that—in this case—cannot be predicted based on dose estimations, would facilitate the development of novel therapies. The aim of this study was, therefore, to assess potentially changing levels of plasma and urine biomarkers and to determine DNA damage at an early stage after radiofolate application. The identification of an early indicator for renal damage in mice would be useful since histological changes become apparent only several months after treatment. Mice were injected with different quantities of ¹⁷⁷Lu-folate (10 MBq, 20 MBq and 30 MBq), resulting in mean absorbed kidney doses of ~23 Gy, ~46 Gy and ~69 Gy, respectively, followed by euthanasia two weeks (>85% of the mean renal radiation dose absorbed) or three months later. Whereas all investigated biomarkers remained unchanged, the number of γ-H2AX-positive nuclei in the renal cortex showed an evident dose-dependent increase as compared to control values two weeks after treatment. Comparison with the extent of kidney injury determined by histological changes five to eight months after administration of the same ¹⁷⁷Lu-folate activities suggested that the quantitative assessment of double-strand breaks can be used as a biological indicator for long-term radiation effects in the kidneys. This method may, thus, enable faster assessment of radiopharmaceuticals and protective measures by preventing logistically challenging long-term investigations to detect kidney damage.

XLF-mediated NHEJ activity in hepatocellular carcinoma therapy resistance

Background

DNA repair pathways are used by cancer cells to overcome many standard anticancer treatments, causing therapy resistance. Here, we investigated the role of XRCC4-like factor (XLF), a core member of the non-homologous end joining (NHEJ) repair pathway, in chemoresistance in hepatocellular carcinoma (HCC).

Methods

qRT-PCR analysis and western blotting were performed to detect expression levels of genes and proteins related to NHEJ. NHEJ repair capacity was assessed in vitro (cell-free) and in vivo by monitoring the activity of the NHEJ pathway. Cell viability and IC50 assays were used to measure sensitivity to drug therapy. A xenograft HCC model was used to develop methods of targeting XLF-induced chemosensitization. Clinicopathological analysis was conducted on patients with HCC treated with transarterial chemoembolization (TACE).

Results

Many conventional cancer chemotherapeutics induce DNA double-strand breaks (DSBs). HCC cells respond to these breaks by increasing their NHEJ activity, resulting in resistance. XLF-knockdown cells show an inhibition of NHEJ activity in both cell-free and live-cell assays as well as a high level of unrepaired cellular DSBs. These results indicate that XLF facilitates DNA end-joining and therefore promotes NHEJ activity in cancer cells. Consequently, knockdown of XLF significantly chemosensitized resistant cells both in vitro and in xenograft tumors. A low rate of XLF genomic alteration was found in patients with primary HCC, but XLF expression was induced after drug treatment. Clinically, a high level of XLF expression is significantly associated with advanced HCC and shorter overall survival.

Conclusion

Chemotherapy-induced overexpression of XLF and XLF-mediated enhancements in NHEJ activity contribute to chemoresistance in HCC cells and patients with HCC. Targeting XLF to modulate DSB repair could enhance drug sensitivity and may be a therapeutically useful addition to conventional therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3345-y) contains supplementary material, which is available to authorized users.

Impact of CD44 expression on radiation response for bladder cancer

Background Identification of potential factors that can stratify tumors' response to specific therapies will aid in the selection of cancer therapy. Radioresistance is the major obstacles to positive outcomes in bladder cancer patients after definite chemotherapy. CD44, a cancer stem cell surface marker, is relevant in treatment resistance. In the present study, we examined the role of CD44 in bladder cancer.

Methods We retrospectively analyzed the clinical outcomes of 85 bladder cancer patients treated with definite chemoradiotherapy, and correlated the expressions of CD44 with IL-6 and treatment response. Furthermore, the bladder cancer cell lines HT1197 and MB49 were selected for cellular and animal experiments to investigate the links between the CD44, IL-6 and radiation response.

Results Analyzing the clinical specimen, the staining of CD44 was significantly linked with higher clinical stage, lower complete response rates, higher loco-regional failure rate and lower survival rate with intact bladder for patients treated with definite CCRT. In addition, the frequency of CD44 immunoreactivity was significantly higher in IL-6-positive bladder cancer specimens. By cellular experiments, the expression of CD44 was stimulated by IL-6 and linked with the cancer stem cell-like property. As demonstrated through in vitro and animal experiments using immunocompromised and immunocompetent hosts, CD44+ bladder cancer cells appeared more resistant to irradiation, associated with less RT-induced cell death.

Conclusions Our findings suggested that CD44 is important in predicting the radiation response of bladder tumor cells. If overexpressed CD44 and/or IL-6 were noted in pre-surgical specimens, radical cystectomy is more likely to be preferred.

gamma-H2AX: Can it be established as a classical cancer prognostic factor?

Double-strand breaks are among the first procedures taking place in cancer formation and progression as a result of endogenic and exogenic factors. The histone variant H2AX undergoes phosphorylation at serine 139 due to double-strand breaks, and the gamma-H2AX is formatted as a result of genomic instability. The detection of gamma-H2AX can potentially serve as a biomarker for transformation of normal tissue to premalignant and consequently to malignant tissues. gamma-H2AX has already been investigated in a variety of cancer types, including breast, lung, colon, cervix, and ovary cancers. The prognostic value of gamma-H2AX is indicated in certain cancer types, such as breast or endometrial cancer, but further investigation is needed to establish gamma-H2AX as a prognostic marker. This review outlines the role of gamma-H2AX in cell cycle, and its formation as a result of DNA damage. We investigate the role of gamma-H2AX formation in several cancer types and its correlation with other prognostic factors, and we try to find out whether it fulfills the requirements for its establishment as a classical cancer prognostic factor.

Ionizing radiation biomarkers in epidemiological studies - An update

Recent epidemiology studies highlighted the detrimental health effects of exposure to low dose and low dose rate ionizing radiation (IR): nuclear industry workers studies have shown increased leukaemia and solid tumour risks following cumulative doses of <100mSv and dose rates of <10mGy per year; paediatric patients studies have reported increased leukaemia and brain tumours risks after doses of 30-60mGy from computed tomography scans. Questions arise, however, about the impact of even lower doses and dose rates where classical epidemiological studies have limited power but where subsets within the large cohorts are expected to have an increased risk. Further progress requires integration of biomarkers or bioassays of individual exposure, effects and susceptibility to IR. The European DoReMi (Low Dose Research towards Multidisciplinary Integration) consortium previously reviewed biomarkers for potential use in IR epidemiological studies. Given the increased mechanistic understanding of responses to low dose radiation the current review provides an update covering technical advances and recent studies. A key issue identified is deciding which biomarkers to progress. A roadmap is provided for biomarker development from discovery to implementation and used to summarise the current status of proposed biomarkers for epidemiological studies. Most potential biomarkers remain at the discovery stage and for some there is sufficient evidence that further development is not warranted. One biomarker identified in the final stages of development and as a priority for further research is radiation specific mRNA transcript profiles.

Fractionated exposure to low doses of ionizing radiation results in accumulation of DNA damage in mouse spleen tissue and activation of apoptosis in a p53/Atm-independent manner

PURPOSE

While the effects of high doses of ionizing radiation (IR) are relatively well characterized, the molecular mechanisms underlying cellular responses to prolonged exposure to low doses of radiation remain largely under-investigated.

MATERIALS AND METHODS

Here, we addressed the DNA damage and apoptotic response in the spleen tissue of C57BL/6 male mice after fractionated exposure to X-rays within the 0.1-0.5 Gy dose range.

RESULTS

The response to initial exposure to 0.1 Gy of IR was characterized by increased DNA damage and elevated levels of apoptosis. Subsequent exposures (cumulative doses of 0.2 and 0.3 Gy) resulted in adaptive response-like changes, represented as increased proliferation and apoptotic response. Cumulative doses of 0.4 and 0.5 Gy were characterized by accumulation of DNA damage and reactivation of apoptosis and apoptosis-related proteins. Additionally, spleen cells with irreversible damage caused by radiation can undergo apoptosis via activation of p38, which does not necessarily involve the Atm/p53 pathway.

CONCLUSIONS

Fractionated exposure to low doses of X-rays resulted in accumulation of DNA damage in the murine spleen and induction of apoptotic response in p53/Atm-independent manner. Further studies are needed to understand the outcomes and molecular mechanisms underlying cellular responses and early induction of p38 in response to prolonged exposure to IR.

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.

Endoplasmic reticulum protein 29 (ERp29) confers radioresistance through the DNA repair gene, O(6)-methylguanine DNA-methyltransferase, in breast cancer cells

Resistance of cancer cells to radiotherapy is a major clinical problem in cancer treatment. Therefore, understanding the molecular basis of cellular resistance to radiotherapy and identification of novel targets are essential for improving treatment efficacy for cancer patients. Our previous studies have demonstrated a significant role of ERp29 in breast cancer cell survival against doxorubicin-induced genotoxic stress. We here reported that ERp29 expression in the triple negative MDA-MB-231 breast cancer cells significantly increased cell survival against ionizing radiation. Methylation PCR array analysis identified that ERp29 expression increased promoter hypomethylation of the DNA repair gene, O⁶-methylguanine DNA-methyltransferase (MGMT), by downregulating DNA methyltransferase 1. Knockdown of MGMT in the ERp29-transfected cancer cells increased radiosensitivity, leading to a decreased post-irradiation survival. In addition, radiation treatment in the MGMT-knockdown cells elevated phosphorylation of γ-H2AX and cleavage of caspase 3, indicating that depletion of MGMT facilitates DNA double strands breaks and increases cell apoptosis. Hence, our studies prove a novel function of ERp29\MGMT in cancer cell survival against radiation. Targeting ERp29\MGMT axis may be useful for providing better treatment efficacy in combination with radiotherapy in breast cancer.

Evaluation of Severe Combined Immunodeficiency and Combined Immunodeficiency Pediatric Patients on the Basis of Cellular Radiosensitivity

Pediatric patients with severe or nonsevere combined immunodeficiency have increased susceptibility to severe, life-threatening infections and, without hematopoietic stem cell transplantation, may fail to thrive. A subset of these patients have the radiosensitive (RS) phenotype, which may necessitate conditioning before hematopoietic stem cell transplantation, and this conditioning includes radiomimetic drugs, which may significantly affect treatment response. To provide statistical criteria for classifying cellular response to ionizing radiation as the measure of functional RS screening, we analyzed the repair capacity and survival of ex vivo irradiated primary skin fibroblasts from five dysmorphic and/or developmentally delayed pediatric patients with severe combined immunodeficiency and combined immunodeficiency. We developed a mathematical framework for the analysis of γ histone 2A isoform X foci kinetics to quantitate DNA-repair capacity, thus establishing crucial criteria for identifying RS. The results, presented in a diagram showing each patient as a point in a 2D RS map, were in agreement with findings from the assessment of cellular RS by clonogenic survival and from the genetic analysis of factors involved in the nonhomologous end-joining repair pathway. We provide recommendations for incorporating into clinical practice the functional assays and genetic analysis used for establishing RS status before conditioning. This knowledge would enable the selection of the most appropriate treatment regimen, reducing the risk for severe therapy-related adverse effects.

DNA damage foci: Meaning and significance

The discovery of DNA damage response proteins such as γH2AX, ATM, 53BP1, RAD51, and the MRE11/RAD50/NBS1 complex, that accumulate and/or are modified in the vicinity of a chromosomal DNA double-strand break to form microscopically visible, subnuclear foci, has revolutionized the detection of these lesions and has enabled studies of the cellular machinery that contributes to their repair. Double-strand breaks are induced directly by a number of physical and chemical agents, including ionizing radiation and radiomimetic drugs, but can also arise as secondary lesions during replication and DNA repair following exposure to a wide range of genotoxins. Here we aim to review the biological meaning and significance of DNA damage foci, looking specifically at a range of different settings in which such markers of DNA damage and repair are being studied and interpreted.

Survival Fraction at 2 Gy and γH2AX Expression Kinetics in Peripheral Blood Lymphocytes From Cancer Patients: Relationship With Acute Radiation-Induced Toxicities

PURPOSE

Predictive assays for acute radiation toxicities would be clinically relevant in radiation oncology. We prospectively examined the predictive role of the survival fraction at 2 Gy (SF2) and of γH2AX (double-strand break [DSB] DNA marker) expression kinetics in peripheral blood mononuclear cells (PBMCs) from cancer patients before radiation therapy.

METHODS AND MATERIALS

SF2 was measured with Trypan Blue assay in the PBMCs from 89 cancer patients undergoing radiation therapy at 4 hours (SF2[4h]) and 24 hours (SF2[24h]) after ex vivo irradiation. Using Western blot analysis and band densitometry, we further assessed the expression of γH2AX in PBMC DNA at 0 hours, 30 minutes, and 4 hours (33 patients) and 0 hour, 4 hours, and 24 hours (56 patients), following ex vivo irradiation with 2 Gy. Appropriate ratios were used to characterize each patient, and these were retrospectively correlated with early radiation therapy toxicity grade.

RESULTS

The SF2(4h) was inversely correlated with the toxicity grade (P=.006). The γH2AX-ratio(30min) (band density of irradiated/non-irradiated cells at 30 minutes) revealed, similarly, a significant inverse association (P=.0001). The DSB DNA repair rate from 30 minutes to 4 hours, calculated as the relative RγH2AX-ratio (γH2AX-ratio(4h)/γH2AX-ratio(30min)) showed a significant direct association with high toxicity grade (P=.01).

CONCLUSIONS

Our results suggest that SF2 is a significant radiation sensitivity index for patients undergoing radiation therapy. γH2AX Western blot densitometry analysis provided 2 important markers of normal tissue radiation sensitivity. Low γH2AX expression at 30 minutes was linked with high toxicity grade, suggesting that poor γH2AX repair activity within a time frame of 30 minutes after irradiation predicts for poor radiation tolerance. On the other hand, rapid γH2AX content restoration at 4 hours after irradiation, compatible with efficient DSB repair ability, predicts for increased radiation tolerance.

DNA damage at respiratory distress, but not acute time-points, correlates with tissue fibrosis following thoracic radiation exposure in mice

PURPOSE

Radiation exposure can result in DNA damage but whether the extent of DNA damage correlates with the radiation-induced tissue injury in the lung is not known. We aimed to determine whether numbers of γH2AX foci, representing histone H2AX phosphorylation a marker of DNA damage, measured within days of radiation exposure, correlated with known later lung injury responses in eight inbred mouse strains.

MATERIALS AND METHODS

Mice received 18 Gy pulmonary irradiation and numbers of γH2AX positive nuclei in the lung were immunohistochemically determined.

RESULTS

Numbers of γH2AX foci, assessed up to seven days post irradiation did not correlate with pulmonary fibrosis. γH2AX counts from mice in respiratory distress, however, significantly correlated with fibrosis and lungs from mice treated with a fibrosis-reducing antagonist had fewer γH2AX foci.

CONCLUSIONS

Acute response measures of pulmonary DNA damage did not predict for pathology, but levels of this marker in distressed mice were correlative of fibrosis.