Rescue effects: irradiated cells helped by unirradiated bystander cells

Radiation-induced rescue effect on human breast carcinoma cells is regulated by macrophages

The susceptibility of cancer cells to DNA damages is influenced by their microenvironment. For example, unirradiated neighbors of irradiated cells can produce signals that reduce DNA damages. This phenomenon, known as Radiation-Induced Rescue Effect (RIRE), has profound implications on the efficacy of radiotherapy. Using bystander cells co-cultured with mock-irradiated cells as a control, we demonstrated, for the first time, two types of RIRE. Conditioned medium from naïve by stander cells, i.e., cells not exposed to irradiated cells, could mitigate UV-induced DNA damages in human breast carcinoma MCF7 cells, as judged by phospho-H2AX and 53BP1 immunostaining. This protective effect could be further enhanced by the prior treatment of bystander cells with factors from UV-irradiated cells. We named the former effect "basal RIRE" and the latter "active RIRE" which were cell type-dependent. As bystanders, MCF7 showed a significant active RIRE, whereas THP1-derived macrophages showed a strong basal RIRE but no active RIRE. Interestingly, RIRE of macrophages could further be modulated by polarisation. The basal RIRE of macrophages was abolished by M1 polarisation, while M2 and Tumour Associated Macrophages (TAM) demonstrated pronounced basal and active RIRE. When mixtures of MCF7 cells and polarised macrophages were used as bystanders, the overall RIRE was dictated by macrophage phenotypes: RIRE was suppressed by M1 macrophages but significantly enhanced by M2 and TAM. This study shows a previously unappreciated role of the innate immune system in RIRE. Depending on polarised phenotypes, macrophages in the tumour microenvironment can interfere with the effectiveness of radiotherapy by adjusting the RIRE magnitudes.

Population Studies and Molecular Mechanisms of Human Radioadaptive Capabilities: Is It Time to Rethink Radiation Safety Standards?

The evolution of man on Earth took place under conditions of constant exposure to background ionizing radiation (IR). From this point of view, it would be reasonable to hypothesize the existence of adaptive mechanisms that enable the human organism to safely interact with IR at levels approximating long-term natural background levels. In some situations, the successful operation of molecular mechanisms of protection against IR is observed at values significantly exceeding the natural background level, for example, in cancer cells. In 15-25% of cancer patients, cancer cells develop a phenotype that is resistant to high doses of IR. While further investigations are warranted, the current evidence suggests a strong probability of observing positive health effects, including an increased lifespan, a reduced cancer risk, and a decreased incidence of congenital pathologies, precisely at low doses of ionizing radiation. This review offers arguments primarily based on a phenomenological approach and critically reconsidering existing methodologies for assessing the biological risks of IR to human health. Currently, in the most economically developed countries, there are radiation safety rules that interpret low-dose radiation as a clearly negative environmental factor. Nowadays, this approach may pose significant challenges to the advancement of radiomedicine and introduce complexities in the regulation of IR sources. The review also examines molecular mechanisms that may play a key role in the formation of the positive effects of low-dose IR on human radioadaptive capabilities.

Effects of spatial variation in dose delivery: what can we learn from radon-related lung cancer studies?

Exposure to radon progeny results in heterogeneous dose distributions in many different spatial scales. The aim of this review is to provide an overview on the state of the art in epidemiology, clinical observations, cell biology, dosimetry, and modelling related to radon exposure and its association with lung cancer, along with priorities for future research. Particular attention is paid on the effects of spatial variation in dose delivery within the organs, a factor not considered in radiation protection. It is concluded that a multidisciplinary approach is required to improve risk assessment and mechanistic understanding of carcinogenesis related to radon exposure. To achieve these goals, important steps would be to clarify whether radon can cause other diseases than lung cancer, and to investigate radon-related health risks in children or persons at young ages. Also, a better understanding of the combined effects of radon and smoking is needed, which can be achieved by integrating epidemiological, clinical, pathological, and molecular oncology data to obtain a radon-associated signature. While in vitro models derived from primary human bronchial epithelial cells can help to identify new and corroborate existing biomarkers, they also allow to study the effects of heterogeneous dose distributions including the effects of locally high doses. These novel approaches can provide valuable input and validation data for mathematical models for risk assessment. These models can be applied to quantitatively translate the knowledge obtained from radon exposure to other exposures resulting in heterogeneous dose distributions within an organ to support radiation protection in general.

Radiation-Induced Rescue Effect: Insights from Microbeam Experiments

The present paper reviews a non-targeted effect in radiobiology known as the Radiation-Induced Rescue Effect (RIRE) and insights gained from previous microbeam experiments on RIRE. RIRE describes the mitigation of radiobiological effects in targeted irradiated cells after they receive feedback signals from co-cultured non-irradiated bystander cells, or from the medium previously conditioning those co-cultured non-irradiated bystander cells. RIRE has established or has the potential of establishing relationships with other non-traditional new developments in the fields of radiobiology, including Radiation-Induced Bystander Effect (RIBE), Radiation-Induced Field Size Effect (RIFSE) and ultra-high dose rate (FLASH) effect, which are explained. The paper first introduces RIRE, summarizes previous findings, and surveys the mechanisms proposed for observations. Unique opportunities offered by microbeam irradiations for RIRE research and some previous microbeam studies on RIRE are then described. Some thoughts on future priorities and directions of research on RIRE exploiting unique features of microbeam radiations are presented in the last section.

Low Dose Ionising Radiation-Induced Hormesis: Therapeutic Implications to Human Health

The concept of radiation-induced hormesis, whereby a low dose is beneficial and a high dose is detrimental, has been gaining attention in the fields of molecular biology, environmental toxicology and radiation biology. There is a growing body of literature that recognises the importance of hormetic dose response not only in the radiation field, but also with molecular agents. However, there is continuing debate on the magnitude and mechanism of radiation hormetic dose response, which could make further contributions, as a research tool, to science and perhaps eventually to public health due to potential therapeutic benefits for society. The biological phenomena of low dose ionising radiation (LDIR) includes bystander effects, adaptive response, hypersensitivity, radioresistance and genomic instability. In this review, the beneficial and the detrimental effects of LDIR-induced hormesis are explored, together with an overview of its underlying cellular and molecular mechanisms that may potentially provide an insight to the therapeutic implications to human health in the future.

HMGB1 knockdown increases the radiosensitivity of esophageal squamous cell carcinoma by regulating the expression of molecules involved in DNA repair

Radiotherapy is an effective therapeutic strategy in esophageal squamous cell carcinoma (ESCC). However, acquired radioresistance of cancer cells leads to radiotherapy failure. The present study aimed to investigate the mechanisms of the effect of high mobility group box 1 (HMGB1) on the radiation sensitivity of ESCC. Small interfering RNA (si) transfection was used to generate three groups of TE-1 cells (TE-1, negative control and TE-1+siHMGB1), and the protein expression levels of HMGB1 in TE-1 cells were detected by western blotting. These groups of TE-1 cells were irradiated with different doses (0, 2, 4, 6 and 8 Gy) of X-rays after transfection. Subsequently, the viability of TE-1 cells was detected using an MTT assay, and the survival fraction of TE-1 cells was observed using a colony formation assay. The apoptotic rate, reactive oxygen species (ROS) content and levels of phosphorylated (p)-histone H2AX at S139 (p-γH2AX) of the cells were detected by flow cytometry. The alterations in mRNA expression levels of nicotinamide adenine nucleotide phosphate oxidase (NOX)1 and NOX5 were detected by reverse transcription-quantitative PCR, while the changes in protein levels of caspase-3, poly(ADP-ribose) polymerase, p-p38, p-ERK1/2 and p-JNK were detected by western blotting. The results revealed that HMGB1 knockdown significantly decreased cell viability, and the apoptosis rate of TE-1 cells transfected with siHMGB1 combined with radiation treatment was increased compared with that in cells with either siHMGB1 transfection or radiation treatment alone. HMGB1 knockdown increased nicotinamide adenine nucleotide phosphate oxidase-mediated ROS production and induced DNA damage via the MAPK signaling pathway, which may promote apoptosis and radiosensitivity after radiation in TE-1 cells. In conclusion, targeting HMGB1 may represent a promising strategy to increase the efficacy of radiation therapy for ESCC.

4-Methylumbelliferone administration enhances radiosensitivity of human fibrosarcoma by intercellular communication

Hyaluronan synthesis inhibitor 4-methylumbelliferone (4-MU) is a candidate of radiosensitizers which enables both anti-tumour and anti-metastasis effects in X-ray therapy. The curative effects under such 4-MU administration have been investigated in vitro; however, the radiosensitizing mechanisms remain unclear. Here, we investigated the radiosensitizing effects under 4-MU treatment from cell experiments and model estimations. We generated experimental surviving fractions of human fibrosarcoma cells (HT1080) after 4-MU treatment combined with X-ray irradiation. Meanwhilst, we also modelled the pharmacological effects of 4-MU treatment and theoretically analyzed the synergetic effects between 4-MU treatment and X-ray irradiation. The results show that the enhancement of cell killing by 4-MU treatment is the greatest in the intermediate dose range of around 4 Gy, which can be reproduced by considering intercellular communication (so called non-targeted effects) through the model analysis. As supposed to be the involvement of intercellular communication in radiosensitization, the oxidative stress level associated with reactive oxygen species (ROS), which leads to DNA damage induction, is significantly higher by the combination of 4-MU treatment and irradiation than only by X-ray irradiation, and the radiosensitization by 4-MU can be suppressed by the ROS inhibitors. These findings suggest that the synergetic effects between 4-MU treatment and irradiation are predominantly attributed to intercellular communication and provide more efficient tumour control than conventional X-ray therapy.

Field size effects on DNA damage and proliferation in normal human cell populations irradiated with X-ray microbeams

To clarify the health risks of internal radiation exposure, it is important to investigate the radiological effects of local exposure at cell levels from radioactive materials taken up by organs. Focusing on the response of cell populations post-irradiation, X-ray microbeams are very effective at reproducing the effects of local exposure within an internal exposure in vitro. The present study aims to clarify the effects of local exposure by investigating the response of normal human cell (MRC-5) populations irradiated with X-ray microbeams of different beam sizes to DNA damage. The populations of MRC-5 were locally irradiated with X-ray microbeams of 1 Gy at 0.02-1.89 mm2 field sizes, and analyzed whether the number of 53BP1 foci as DSB (DNA double strand break) per cell changed with the field size. We found that even at the same dose, the number of DSB per cell increased depending on the X-irradiated field size on the cell population. This result indicated that DNA damage repair of X-irradiated cells might be enhanced in small size fields surrounded by non-irradiated cells. This study suggests that X-irradiated cells received some signal (a rescue signal) from surrounding non-irradiated cells may be involved in the response of cell populations post-irradiation.

Collagen-Based Materials Modified by Phenolic Acids-A Review

Collagen-based biomaterials constitute one of the most widely studied types of materials for biomedical applications. Low thermal and mechanical parameters are the main disadvantages of such structures. Moreover, they present low stability in the case of degradation by collagenase. To improve the properties of collagen-based materials, different types of cross-linkers have been researched. In recent years, phenolic acids have been studied as collagen modifiers. Mainly, tannic acid has been tested for collagen modification as it interacts with a polymeric chain by strong hydrogen bonds. When compared to pure collagen, such complexes show both antimicrobial activity and improved physicochemical properties. Less research reporting on other phenolic acids has been published. This review is a summary of the present knowledge about phenolic acids (e.g., tannic, ferulic, gallic, and caffeic acid) application as collagen cross-linkers. The studies concerning collagen-based materials with phenolic acids are summarized and discussed.

RADIATION-INDUCED BYSTANDER EFFECT - MODELING, MANIFESTATION, MECHANISMS, PERSISTENCE, CANCER RISKS (literature review)

The review summarizes and analyzes the data of world scientific literature and the results of the own research con- cerning one of the main non-targeted effects of ionizing radiation - the radiation induced bystander effect (RIBE) - the ability of irradiated target cells to induce secondary biological changes in non-irradiated receptor cells. The his- tory of studies of this phenomenon is presented - it described under various names since 1905, began to study from the end of the twentieth century when named as RIBE and caused particular interest in the scientific community during recent decades. It is shown that the development of biological science and the improvement of research methods allowed to get new in-depth data on the development of RIBE not only at the level of the whole organism, but even at the genome level. The review highlights the key points of numerous RIBE investigations including mod- eling; methodological approaches to studying; classification; features of interaction between irradiated and intact cells; the role of the immune system, oxidative stress, cytogenetic disorders, changes in gene expression in the mechanism of development of RIBE; rescue effect, abscopal effect, persistence, modification, medical effects. It is emphasized that despite the considerable amount of research concerning the bystander response as the universal phenomenon and RIBE as one of its manifestations, there are still enough «white spots» in determining the mech- anisms of the RIBE formation and assessing the possible consequences of its development for human health.

Role of PARP1 regulation in radiation-induced rescue effect

Radiation-induced rescue effect (RIRE) in cells refers to the phenomenon where irradiated cells (IRCs) receive help from feedback signals produced by partnered bystander unirradiated cells (UIRCs) or from the conditioned medium (CM) that has previously conditioned the UIRCs. In the present work, we explored the role of poly (ADP-ribose) polymerase 1 (PARP1) regulation in RIRE and the positive feedback loop between PARP1 and nuclear factor-kappa-light-chain-enhancer of activated B cell (NF-κB) in RIRE using various cell lines, including HeLa, MCF7, CNE-2 and HCT116 cells. We first found that when the IRCs (irradiated with 2 Gy X-ray) were treated with CM, the relative mRNA expression levels of both tumor suppressor p53-binding protein 1 (53BP1) and PARP1, the co-localization factor between 53BP1 and γH2AX as well as the fluorescent intensity of PARP1 were reduced. We also found that IRCs treated with the PARP1 inhibitor, Olaparib (AZD2281) had a higher 53BP1 expression. These results illustrated that PARP1 was involved in RIRE transcriptionally and translationally. We further revealed that treatment of IRCs with CM together with Olaparib led to significantly lower mRNA expression levels and fluorescent intensities of NF-κB, while treatment of IRCs with CM together the NF-κB inhibitor BAY-11-7082 led to significantly lower mRNA expression levels as well as fluorescent intensities of PARP1. These results illustrated that PARP1 and NF-κB were involved in the positive feedback loop transcriptionally and translationally. Thus, the results supported the occurrence of a PARP1-NF-κB positive feedback loop in RIRE. The present work provided insights into potential exploitation of inhibition of PARP1 and/or the PARP1-NF-κB positive feedback loop in designing adjuncts to cancer radiotherapeutics.

Multiple Stressor Effects of Radon and Phthalates in Children: Background Information and Future Research

The present paper reviews available background information for studying multiple stressor effects of radon (222Rn) and phthalates in children and provides insights on future directions. In realistic situations, living organisms are collectively subjected to many environmental stressors, with the resultant effects being referred to as multiple stressor effects. Radon is a naturally occurring radioactive gas that can lead to lung cancers. On the other hand, phthalates are semi-volatile organic compounds widely applied as plasticizers to provide flexibility to plastic in consumer products. Links of phthalates to various health effects have been reported, including allergy and asthma. In the present review, the focus on indoor contaminants was due to their higher concentrations and to the higher indoor occupancy factor, while the focus on the pediatric population was due to their inherent sensitivity and their spending more time close to the floor. Two main future directions in studying multiple stressor effects of radon and phthalates in children were proposed. The first one was on computational modeling and micro-dosimetric studies, and the second one was on biological studies. In particular, dose-response relationship and effect-specific models for combined exposures to radon and phthalates would be necessary. The ideas and methodology behind such proposed research work are also applicable to studies on multiple stressor effects of collective exposures to other significant airborne contaminants, and to population groups other than children.

Coupling of cell fate selection model enhances DNA damage response and may underlie BE phenomenon

Double-strand break-induced (DSB) cells send signal that induces DSBs in neighbour cells, resulting in the interaction among cells sharing the same medium. Since p53 network gives oscillatory response to DSBs, such interaction among cells could be modelled as an excitatory coupling of p53 network oscillators. This study proposes a plausible coupling model of three-mode two-dimensional oscillators, which models the p53-mediated cell fate selection in globally coupled DSB-induced cells. The coupled model consists of ATM and Wip1 proteins as variables. The coupling mechanism is realised through ATM variable via a mean-field modelling the bystander signal in the intercellular medium. Investigation of the model reveals that the coupling generates more sensitive DNA damage response by affecting cell fate selection. Additionally, the authors search for the cause-effect relationship between coupled p53 network oscillators and bystander effect (BE) endpoints. For this, they search for the possible values of uncertain parameters that may replicate BE experiments' results. At certain parametric regions, there is a correlation between the outcomes of cell fate and endpoints of BE, suggesting that the intercellular coupling of p53 network may manifest itself as the form of observed BEs.

The Radiation-Induced Bystander Effect (RIBE) and its Connections with the Hallmarks of Cancer

Radiation therapy is one of the pillars of cancer treatment, with approximately one half of all cancer patients receiving it as part of their standard of care. Emerging evidence indicates that the biological effects of radiation are not limited to targeted cells. The radiation-induced bystander effect (RIBE) refers to the plethora of biological phenomena occurring in nonirradiated cells as a result of signal transmission from an irradiated cell. Experimental evidence has linked RIBE to numerous hallmarks of cancer including resisting cell death, tumor immune evasion, genomic instability, deregulated cellular energetics, tumor-promoting inflammation and sustained proliferative signaling as well as enhanced radioresistance, thus highlighting the potential role of RIBE events in patient treatment response. The mechanisms underlying RIBE events in vivo are poorly understood. However, elucidating the molecular mechanisms involved in their manifestation may reveal novel therapeutic targets to improve radiation response in cancer patients.

Current status of space radiobiological studies in China

After successfully launching two space laboratories, namely, Tiangong-1 and Tiangong-2, China has announced her next plan of constructing the Chinese Space Station (CSS) in 2022. The CSS will provide not only platforms for Chinese scientists to carry out experimental studies in outer space but also opportunities for open international cooperation. In this article, we review the development of China's manned space exploration missions and the preliminary plan for CSS. Additionally, China has initiated space radiation research decades ago with both ground-based simulation research platform and space vehicles and has made noticeable progresses in several aspects. These include studies on human health risk assessment using mammalian cell cultures and animals as models. Furthermore, there have been numerous studies on assessing the space environment in plant breeding.

Intensity Modulated Radiation Fields Induce Protective Effects and Reduce Importance of Dose-Rate Effects

In advanced radiotherapy, intensity modulated radiation fields and complex dose-delivery are utilized to prescribe higher doses to tumours. Here, we investigated the impact of modulated radiation fields on radio-sensitivity and cell recovery during dose delivery. We generated experimental survival data after single-dose, split-dose and fractionated irradiation in normal human skin fibroblast cells (AGO1522) and human prostate cancer cells (DU145). The dose was delivered to either 50% of the area of a T25 flask containing the cells (half-field) or 100% of the flask (uniform-field). We also modelled the impact of dose-rate effects and intercellular signalling on cell-killing. Applying the model to the survival data, it is found that (i) in-field cell survival under half-field exposure is higher than uniform-field exposure for the same delivered dose; (ii) the importance of sub-lethal damage repair (SLDR) in AGO1522 cells is reduced under half-field exposure; (iii) the yield of initial DNA lesions measured with half-field exposure is smaller than that with uniform-field exposure. These results suggest that increased cell survival under half-field exposure is predominantly attributed not to rescue effects (increased SLDR) but protective effects (reduced induction of initial DNA lesions). In support of these protective effects, the reduced DNA damage leads to modulation of cell-cycle dynamics, i.e., less G₁ arrest 6 h after irradiation. These findings provide a new understanding of the impact of dose-rate effects and protective effects measured after modulated field irradiation.

Radiation-induced rescue effect

Radiation-induced rescue effect (RIRE) refers to the phenomenon in which detrimental effects in targeted irradiated cells are reduced upon receiving feedback signals from partnered non-irradiated bystander cells, or from the medium previously conditioning these partnered non-irradiated bystander cells. For convenience, in the current review we define two types of RIRE: (i) Type 1 RIRE (reduced detrimental effects in targeted cells upon receiving feedback signals from bystander cells) and (ii) Type 2 RIRE (exacerbated detrimental effects in targeted cells upon receiving feedback signals from bystander cells). The two types of RIRE, as well as the associated mechanisms and chemical messengers, have been separately reviewed. The recent report on the potential effects of RIRE on the traditional colony-formation assays has also been reviewed. Finally, future priorities and directions for research into RIRE are discussed.

Monte Carlo studies on photon interactions in radiobiological experiments

X-ray and γ-ray photons have been widely used for studying radiobiological effects of ionizing radiations. Photons are indirectly ionizing radiations so they need to set in motion electrons (which are a directly ionizing radiation) to perform the ionizations. When the photon dose decreases to below a certain limit, the number of electrons set in motion will become so small that not all cells in an "exposed" cell population can get at least one electron hit. When some cells in a cell population are not hit by a directly ionizing radiation (in other words not irradiated), there will be rescue effect between the irradiated cells and non-irradiated cells, and the resultant radiobiological effect observed for the "exposed" cell population will be different. In the present paper, the mechanisms underlying photon interactions in radiobiological experiments were studied using our developed NRUphoton computer code, which was benchmarked against the MCNP5 code by comparing the photon dose delivered to the cell layer underneath the water medium. The following conclusions were reached: (1) The interaction fractions decreased in the following order: 16O > 12C > 14N > 1H. Bulges in the interaction fractions (versus water medium thickness) were observed, which reflected changes in the energies of the propagating photons due to traversals of different amount of water medium as well as changes in the energy-dependent photon interaction cross-sections. (2) Photoelectric interaction and incoherent scattering dominated for lower-energy (10 keV) and high-energy (100 keV and 1 MeV) incident photons. (3) The fractions of electron ejection from different nuclei were mainly governed by the photoelectric effect cross-sections, and the fractions from the 1s subshell were the largest. (4) The penetration fractions in general decreased with increasing medium thickness, and increased with increasing incident photon energy, the latter being explained by the corresponding reduction in interaction cross-sections. (5) The areas under the angular distribution curves of photons exiting the medium layer and subsequently undergoing interactions within the cell layer became smaller for larger incident photon energies. (6) The number of cells suffering at least one electron hit increased with the administered dose. For larger incident photon energies, the numbers of cells suffering at least one electron hit became smaller, which was attributed to the reduction in the photon interaction cross-section. These results highlighted the importance of the administered dose in radiobiological experiments. In particular, the threshold administered doses at which all cells in the exposed cell array suffered at least one electron hit might provide hints on explaining the intriguing observation that radiation-induced cancers can be statistically detected only above the threshold value of ~100 mSv, and thus on reconciling controversies over the linear no-threshold model.

Induction of autophagy and interleukin 6 secretion in bystander cells: metabolic cooperation for radiation-induced rescue effect?

We hypothesized that radiation-induced rescue effect (RIRE) shared similar mechanisms with 'metabolic cooperation', in which nutrient-deprived cancer cells prompted normal cells to provide nutrients. Our data demonstrated that X-ray irradiation induced autophagy in HeLa cells, which could last at least 18 h, and proved that the irradiated cells (IRCs) resorted to breaking down their own intracellular components to supply the molecules required for cell-repair enhancement (e.g. to activate the NF-κB pathway) in the absence of support from bystander unirradiated cells (UICs). Furthermore, autophagy accumulation in IRCs was significantly reduced when they were partnered with UICs, and more so with UICs with pre-induced autophagy before partnering (through starvation using Earle's Balanced Salt Solution), which showed that the autophagy induced in UICs supported the IRCs. Our results also showed that interleukin 6 (IL-6) was secreted by bystander UICs, particularly the UICs with pre-induced autophagy, when they were cultured in the medium having previously conditioned irradiated HeLa cells. It was established that autophagy could activate the signal transducer and activator of transcription 3 (STAT3) that was required for the IL-6 production in the autophagy process. Taken together, the metabolic cooperation of RIRE was likely initiated by the bystander factors released from IRCs, which induced autophagy and activated STAT3 to produce IL-6 in bystander UICs, and was finally manifested in the activation of the NF-κB pathway in IRCs by the IL-6 secreted by the UICs.

Alpha-particle fluence in radiobiological experiments

Two methods were proposed for determining alpha-particle fluence for radiobiological experiments. The first involved calculating the probabilities of hitting the target for alpha particles emitted from a source through Monte Carlo simulations, which when multiplied by the activity of the source gave the fluence at the target. The second relied on the number of chemically etched alpha-particle tracks developed on a solid-state nuclear track detector (SSNTD) that was irradiated by an alpha-particle source. The etching efficiencies (defined as percentages of latent tracks created by alpha particles from the source that could develop to become visible tracks upon chemical etching) were computed through Monte Carlo simulations, which when multiplied by the experimentally counted number of visible tracks would also give the fluence at the target. We studied alpha particles with an energy of 5.486 MeV emitted from an 241Am source, and considered the alpha-particle tracks developed on polyallyldiglycol carbonate film, which is a common SSNTD. Our results showed that the etching efficiencies were equal to one for source-film distances of from 0.6 to 3.5 cm for a circular film of radius of 1 cm, and for source-film distances of from 1 to 3 cm for circular film of radius of 2 cm. For circular film with a radius of 3 cm, the etching efficiencies never reached 1. On the other hand, the hit probability decreased monotonically with increase in the source-target distance, and fell to zero when the source-target distance was larger than the particle range in air.

Zebrafish as an In Vivo Model to Assess Epigenetic Effects of Ionizing Radiation

Exposure to ionizing radiations (IRs) is ubiquitous in our environment and can be categorized into “targeted” effects and “non-targeted” effects. In addition to inducing deoxyribonucleic acid (DNA) damage, IR exposure leads to epigenetic alterations that do not alter DNA sequence. Using an appropriate model to study the biological effects of radiation is crucial to better understand IR responses as well as to develop new strategies to alleviate exposure to IR. Zebrafish, Danio rerio, is a scientific model organism that has yielded scientific advances in several fields and recent studies show the usefulness of this vertebrate model in radiation biology. This review briefly describes both “targeted” and “non-targeted” effects, describes the findings in radiation biology using zebrafish as a model and highlights the potential of zebrafish to assess the epigenetic effects of IR, including DNA methylation, histone modifications and miRNA expression. Other in vivo models are included to compare observations made with zebrafish, or to illustrate the feasibility of in vivo models when the use of zebrafish was unavailable. Finally, tools to study epigenetic modifications in zebrafish, including changes in genome-wide DNA methylation, histone modifications and miRNA expression, are also described in this review.

CHK1 and RAD51 activation after DNA damage is regulated via urokinase receptor/TLR4 signaling

Mechanisms of DNA damage and repair signaling are not completely understood that hinder the efficiency of cancer therapy. Urokinase-type plasminogen activator receptor (PLAUR) is highly expressed in most solid cancers and serves as a marker of poor prognosis. We show that PLAUR actively promotes DNA repair in cancer cells. On the contrary, downregulation of PLAUR expression results in delayed DNA repair. We found PLAUR to be essential for activation of Checkpoint kinase 1 (CHK1); maintenance of cell cycle arrest after DNA damage in a TP53-dependent manner; expression, nuclear import and recruitment to DNA-damage foci of RAD51 recombinase, the principal protein involved in the homologous recombination repair pathway. Underlying mechanism implies auto-/paracrine signaling of PLAUR/TLR4 receptor complex leading to activation of CHK1 and DNA repair. The signaling is induced by a danger molecule released by DNA-damaged cells and mediates, at least partially, activation of DNA-damage response. This study describes a new mechanism of DNA repair activation initiated by auto-/paracrine signaling of membrane receptors PLAUR/TLR4. It adds to the understanding of role of PLAUR in cancer and provides a rationale for therapeutic targeting of PLAUR/TLR4 interaction in TP53-positive cancers.

Signaling factors and pathways of α-particle irradiation induced bilateral bystander responses between Beas-2B and U937 cells

Although radiation induced bystander effects (RIBE) have been investigated for decades for their potential health risk, the underlying gene regulation is still largely unclear, especially the roles of immune system and inflammatory response in RIBE. In the present study, macrophage U937 cells and epithelial Beas-2B cells were co-cultured to disclose the cascades of bystander signaling factors and intercellular communications. After α-particle irradiation, both ERK and p38 pathways were activated in Beas-2B cells and were associated with the autocrine and paracrine signaling of TNF-α and IL-8, resulting in direct damage to the irradiated cells. Similar upregulation of TNF-α and IL-8 was induced in the bystander U937 cells after co-culture with α-irradiated Beas-2B cells. This upregulation was dependent on the activation of NF-κB pathway and was responsible for the enhanced damage of α-irradiated Beas-2B cells. Interestingly, the increased expressions of TNF-α and IL-8 mRNAs in the bystander U937 cells were clearly relayed on the activated ERK and p38 pathways in the irradiated Beas-2B cells, and the upregulation of TNF-α and IL-8 mRNAs in co-cultured Beas-2B cells was also partly due to the activated NF-κB pathway in the bystander U937 cells. With the pretreatment of U0126 (MEK1/2 inhibitor), SB203580 (p38 inhibitor) or BAY 11-7082 (NF-κB inhibitor), the aggravated damage in the α-irradiated Beas-2B cells could be largely alleviated. Our results disclosed novel signaling cascades of macrophage-mediated bilateral bystander responses that the release of TNF-α and IL-8 regulated by MAPK and NF-κB pathways synergistically increased cellular injury after α-particle irradiation.

Modulation of NF-κB in rescued irradiated cells

Studies by different groups on the rescue effect, where unirradiated bystander cells mitigated the damages in the irradiated cells, since its discovery by the authors' group in 2011 were first reviewed. The properties of the rescue effect were then examined using a novel experimental set-up to physically separate the rescue signals from the bystander signals. The authors' results showed that the rescue effect was mediated through activation of the nuclear factor-κB (NF-κB) response pathway in the irradiated cells, and that the NF-κB activation inhibitor BAY-11-7082 did not affect the activation of this response pathway in the irradiated cells induced by direct irradiation.

Rescue of Targeted Nonstem-Like Cells from Bystander Stem-Like Cells in Human Fibrosarcoma HT1080

Cancer stem-like cells (CSCs) have been suggested to be the principal cause of tumor radioresistance, dormancy and recurrence after radiotherapy. However, little is known about CSC behavior in response to clinical radiotherapy, particularly with regard to CSC communication with bulk cancer cells. In this study, CSCs and nonstem-like cancer cells (NSCCs) were co-cultured, and defined cell types were chosen and irradiated, respectively, with proton microbeam. The bidirectional rescue effect in the combinations of the two cell types was then investigated. The results showed that out of all four combinations, only the targeted, proton irradiated NSCCs were protected by bystander CSCs and showed less accumulation of 53BP1, which is a widely used indicator for DNA double-strand breaks. In addition, supplementation with c-PTIO, a specific nitric oxide scavenger, can show a similar effect on targeted NSCCs. These results, showed that the rescue effect of CSCs on targeted NSCCs involves nitric oxide in the process, suggesting that the cellular communication between CSCs and NSCCs may be important in determining the survival of tumor cells after radiation therapy. To our knowledge, this is the first report demonstrating a rescue effect of CSCs to irradiated NSCCs that may help us better understand CSC behavior in response to cancer radiotherapy.

The different radiation response and radiation-induced bystander effects in colorectal carcinoma cells differing in p53 status

Radiation-induced bystander effect, appearing as different biological changes in cells that are not directly exposed to ionizing radiation but are under the influence of molecular signals secreted by irradiated neighbors, have recently attracted considerable interest due to their possible implication for radiotherapy. However, various cells present diverse radiosensitivity and bystander responses that depend, inter alia, on genetic status including TP53, the gene controlling the cell cycle, DNA repair and apoptosis. Here we compared the ionizing radiation and bystander responses of human colorectal carcinoma HCT116 cells with wild type or knockout TP53 using a transwell co-culture system. The viability of exposed to X-rays (0-8 Gy) and bystander cells of both lines showed a roughly comparable decline with increasing dose. The frequency of micronuclei was also comparable at lower doses but at higher increased considerably, especially in bystander TP53-/- cells. Moreover, the TP53-/- cells showed a significantly elevated frequency of apoptosis, while TP53+/+ counterparts expressed high level of senescence. The cross-matched experiments where irradiated cells of one line were co-cultured with non-irradiated cells of opposite line show that both cell lines were also able to induce bystander effects in their counterparts, however different endpoints revealed with different strength. Potential mediators of bystander effects, IL-6 and IL-8, were also generated differently in both lines. The knockout cells secreted IL-6 at lower doses whereas wild type cells only at higher doses. Secretion of IL-8 by TP53-/- control cells was many times lower than that by TP53+/+ but increased significantly after irradiation. Transcription of the NFκBIA was induced in irradiated TP53+/+ mainly, but in bystanders a higher level was observed in TP53-/- cells, suggesting that TP53 is required for induction of NFκB pathway after irradiation but another mechanism of activation must operate in bystander cells.