Medium-mediated intercellular communication is involved in bystander responses of X-ray-irradiated normal human fibroblasts

Histological and Molecular Biological Changes in Canine Skin Following Acute Radiation Therapy-Induced Skin Injury

Radiation therapy is a crucial cancer treatment, but it can damage healthy tissues, leading to side effects like skin injuries and molecular alterations. This study aimed to elucidate histological and molecular changes in canine skin post-radiation therapy (post-RT) over nine weeks, focusing on inflammation, stem cell activity, angiogenesis, keratinocyte regeneration, and apoptosis. Four male beagles received a cumulative radiation dose of 48 Gy, followed by clinical observations, histological examinations, and an RT-qPCR analysis of skin biopsies. Histological changes correlated with clinical recovery from inflammation. A post-RT analysis revealed a notable decrease in the mRNA levels of Oct4, Sox2, and Nanog from weeks 1 to 9. VEGF 188 levels initially saw a slight increase at week 1, but they had significantly declined by week 9. Both mRNA and protein levels of COX-2 and Keratin 10 significantly decreased over the 9 weeks following RT, although COX-2 expression surged in the first 2 weeks, and Keratin 10 levels increased at weeks 4 to 5 compared to normal skin. Apoptosis peaked at 2 weeks and diminished, nearing normal by 9 weeks. These findings offer insights into the mechanisms of radiation-induced skin injury and provide guidance for managing side effects in canine radiation therapy.

ATR signaling controls the bystander responses of human chondrosarcoma cells by promoting RAD51-dependent DNA repair

PURPOSE

Radiation-induced bystander effect (RIBE) frequently is seen as DNA damage in unirradiated bystander cells, but the repair processes initiated in response to that DNA damage are not well understood. RIBE-mediated formation of micronuclei (MN), a biomarker of persistent DNA damage, was previously observed in bystander normal fibroblast (AG01522) cells, but not in bystander human chondrosarcoma (HTB94) cells. The molecular mechanisms causing this disparity are not clear. Herein, we investigate the role of DNA repair in the bystander responses of the two cell lines.

METHODS

Cells were irradiated with X-rays and immediately co-cultured with un-irradiated cells using a trans-well insert system in which they share the same medium. The activation of DNA damage response (DDR) proteins was detected by immunofluorescence staining or Western blotting. MN formation was examined by the cytokinesis-block MN assay, which is a robust method to detect persistent DNA damage.

RESULTS

Immunofluorescent foci of γH2AX and 53BP1, biomarkers of DNA damage and repair, revealed a greater capacity for DNA repair in HTB94 cells than in AG01522 cells in both irradiated and bystander populations. Autophosphorylation of ATR at the threonine 1989 site was expressed at a greater level in HTB94 cells compared to AG01522 cells at the baseline and in response to hydroxyurea treatment or exposure to 1 Gy of X-rays. An inhibitor of ATR, but not of ATM, promoted MN formation in bystander HTB94 cells. In contrast, no effect of either inhibitor was observed in bystander AG01522 cells, indicating that ATR signaling might be a pivotal pathway to preventing the MN formation in bystander HTB94 cells. Supporting this idea, we found an ATR-dependent increase in the fractions of bystander HTB94 cells with pRPA2 S33 and RAD51 foci. A blocker of RAD51 facilitated MN formation in bystander HTB94 cells.

CONCLUSION

Our results indicate that HTB94 cells were likely more efficient in DNA repair than AG01522 cells, specifically via ATR signaling, which inhibited the bystander signal-induced MN formation. This study highlights the significance of DNA repair efficiency in bystander cell responses.

Next-generation bromodomain inhibitors of the SWI/SNF complex enhance DNA damage and cell death in glioblastoma

Glioblastoma (GBM) is an aggressive brain cancer with a poor prognosis. While surgical resection is the primary treatment, adjuvant temozolomide (TMZ) chemotherapy and radiotherapy only provide slight improvement in disease course and outcome. Unfortunately, most treated patients experience recurrence of highly aggressive, therapy-resistant tumours and eventually succumb to the disease. To increase chemosensitivity and overcome therapy resistance, we have modified the chemical structure of the PFI-3 bromodomain inhibitor of the BRG1 and BRM catalytic subunits of the SWI/SNF chromatin remodelling complex. Our modifications resulted in compounds that sensitized GBM to the DNA alkylating agent TMZ and the radiomimetic bleomycin. We screened these chemical analogues using a cell death ELISA with GBM cell lines and a cellular thermal shift assay using epitope tagged BRG1 or BRM bromodomains expressed in GBM cells. An active analogue, IV-129, was then identified and further modified, resulting in new generation of bromodomain inhibitors with distinct properties. IV-255 and IV-275 had higher bioactivity than IV-129, with IV-255 selectively binding to the bromodomain of BRG1 and not BRM, while IV-275 bound well to both BRG1 and BRM bromodomains. In contrast, IV-191 did not bind to either bromodomain or alter GBM chemosensitivity. Importantly, both IV-255 and IV-275 markedly increased the extent of DNA damage induced by TMZ and bleomycin as determined by nuclear γH2AX staining. Our results demonstrate that these next-generation inhibitors selectively bind to the bromodomains of catalytic subunits of the SWI/SNF complex and sensitize GBM to the anticancer effects of TMZ and bleomycin. This approach holds promise for improving the treatment of GBM.

High-LET-Radiation-Induced Persistent DNA Damage Response Signaling and Gastrointestinal Cancer Development

Ionizing radiation (IR) dose, dose rate, and linear energy transfer (LET) determine cellular DNA damage quality and quantity. High-LET heavy ions are prevalent in the deep space environment and can deposit a much greater fraction of total energy in a shorter distance within a cell, causing extensive DNA damage relative to the same dose of low-LET photon radiation. Based on the DNA damage tolerance of a cell, cellular responses are initiated for recovery, cell death, senescence, or proliferation, which are determined through a concerted action of signaling networks classified as DNA damage response (DDR) signaling. The IR-induced DDR initiates cell cycle arrest to repair damaged DNA. When DNA damage is beyond the cellular repair capacity, the DDR for cell death is initiated. An alternative DDR-associated anti-proliferative pathway is the onset of cellular senescence with persistent cell cycle arrest, which is primarily a defense mechanism against oncogenesis. Ongoing DNA damage accumulation below the cell death threshold but above the senescence threshold, along with persistent SASP signaling after chronic exposure to space radiation, pose an increased risk of tumorigenesis in the proliferative gastrointestinal (GI) epithelium, where a subset of IR-induced senescent cells can acquire a senescence-associated secretory phenotype (SASP) and potentially drive oncogenic signaling in nearby bystander cells. Moreover, DDR alterations could result in both somatic gene mutations as well as activation of the pro-inflammatory, pro-oncogenic SASP signaling known to accelerate adenoma-to-carcinoma progression during radiation-induced GI cancer development. In this review, we describe the complex interplay between persistent DNA damage, DDR, cellular senescence, and SASP-associated pro-inflammatory oncogenic signaling in the context of GI carcinogenesis.

Radiation-induced bystander effect and its clinical implications

For many years, targeted DNA damage caused by radiation has been considered the main cause of various biological effects. Based on this paradigm, any small amount of radiation is harmful to the organism. Epidemiological studies of Japanese atomic bomb survivors have proposed the linear-non-threshold model as the dominant standard in the field of radiation protection. However, there is increasing evidence that the linear-non-threshold model is not fully applicable to the biological effects caused by low dose radiation, and theories related to low dose radiation require further investigation. In addition to the cell damage caused by direct exposure, non-targeted effects, which are sometimes referred to as bystander effects, abscopal effects, genetic instability, etc., are another kind of significant effect related to low dose radiation. An understanding of this phenomenon is crucial for both basic biomedical research and clinical application. This article reviews recent studies on the bystander effect and summarizes the key findings in the field. Additionally, it offers a cross-sectional comparison of bystander effects caused by various radiation sources in different cell types, as well as an in-depth analysis of studies on the potential biological mechanisms of bystander effects. This review aims to present valuable information and provide new insights on the bystander effect to enlighten both radiobiologists and clinical radiologists searching for new ways to improve clinical treatments.

X-rays-Induced Bystander Effect Consists in the Formation of DNA Breaks in a Calcium-Dependent Manner: Influence of the Experimental Procedure and the Individual Factor

Radiation-induced bystander effects (RIBE) describe the biological events occurring in non-targeted cells in the vicinity of irradiated ones. Various experimental procedures have been used to investigate RIBE. Interestingly, most micro-irradiation experiments have been performed with alpha particles, whereas most medium transfers have been done with X-rays. With their high fluence, synchrotron X-rays represent a real opportunity to study RIBE by applying these two approaches with the same radiation type. The RIBE induced in human fibroblasts by the medium transfer approach resulted in a generation of DNA double-strand breaks (DSB) occurring from 10 min to 4 h post-irradiation. Such RIBE was found to be dependent on dose and on the number of donor cells. The RIBE induced with the micro-irradiation approach produced DSB with the same temporal occurrence. Culture media containing high concentrations of phosphates were found to inhibit RIBE, while media rich in calcium increased it. The contribution of the RIBE to the biological dose was evaluated after synchrotron X-rays, media transfer, micro-irradiation, and 6 MeV photon irradiation mimicking a standard radiotherapy session: the RIBE may represent less than 1%, about 5%, and about 20% of the initial dose, respectively. However, RIBE may result in beneficial or otherwise deleterious effects in surrounding tissues according to their radiosensitivity status and their capacity to release Ca2+ ions in response to radiation.

Radiosensitization of Breast Cancer Cells with a 2-Methoxyestradiol Analogue Affects DNA Damage and Repair Signaling In Vitro

Radiation resistance and radiation-related side effects warrant research into alternative strategies in the application of this modality to cancer treatment. Designed in silico to improve the pharmacokinetics and anti-cancer properties of 2-methoxyestradiol, 2-ethyl-3-O-sulfamoyl-estra-1,3,5(10)16-tetraene (ESE-16) disrupts microtubule dynamics and induces apoptosis. Here, we investigated whether pre-exposure of breast cancer cells to low-dose ESE-16 would affect radiation-induced deoxyribonucleic acid (DNA) damage and the consequent repair pathways. MCF-7, MDA-MB-231, and BT-20 cells were exposed to sub-lethal doses of ESE-16 for 24 h before 8 Gy radiation. Flow cytometric quantification of Annexin V, clonogenic studies, micronuclei quantification, assessment of histone H2AX phosphorylation and Ku70 expression were performed to assess cell viability, DNA damage, and repair pathways, in both directly irradiated cells and cells treated with conditioned medium. A small increase in apoptosis was observed as an early consequence, with significant repercussions on long-term cell survival. Overall, a greater degree of DNA damage was detected. Moreover, initiation of the DNA-damage repair response was delayed, with a subsequent sustained elevation. Radiation-induced bystander effects induced similar pathways and were initiated via intercellular signaling. These results justify further investigation of ESE-16 as a radiation-sensitizing agent since pre-exposure appears to augment the response of tumor cells to radiation.

Bystander Response Following High-Dose X-irradiation; Time-dependent Nature of GammaH2AX Foci and Cell Death Consequences

Background

The paradigm shifts in target theory could be defined as the radiation-triggered bystander response in which the radiation deleterious effects occurred in the adjacent cells.

Objective

This study aims to assess bystander response in terms of DNA damage and their possible cell death consequences following high-dose radiotherapy. Temporal characteristics of gH2AX foci as a manifestation of DNA damage were also evaluated.

Material and Methods

In this experimental study, bystander response was investigated in human carcinoma cells of HeLa and HN5, neighboring those that received high doses. Medium transfer was performed from 10 Gy-irradiated donors to 1.5 Gy-irradiated recipients. GammaH2AX foci, clonogenic and apoptosis assays were investigated. The gH2AX foci time-point study was implemented 1, 4, and 24 h after the medium exchange.

Results

DNA damage was enhanced in HeLa and HN5 bystander cells with the ratio of 1.27 and 1.72, respectively, which terminated in more than two-fold clonogenic survival decrease, along with gradual apoptosis increase. GammH2AX foci temporal characterization revealed maximum foci scoring at the 1 h time-point in HeLa, and also 4 h in HN5, which remained even 24 h after the medium sharing in higher level than the control group.

Conclusion

The time-dependent nature of bystander-induced gH2AX foci as a DNA damage surrogate marker was highlighted with the persistent foci at 24 h. considering an outcome of bystander-induced DNA damage, predominant role of clonogenic cell death was also elicited compared to apoptosis. Moreover, the role of high-dose bystander response observed in the current work clarified bystander potential implications in radiotherapy.

HPRT1 Most Suitable Reference Gene for Accurate Normalization of mRNA Expression in Canine Dermal Tissues with Radiation Therapy

Reference genes are crucial in molecular biological studies as an internal control for gene re-search as they exhibit consistent expression patterns across many tissue types. In canines, radiation therapy is the most important therapeutic tool to cure various diseases like cancer. However, when using radiation for therapeutic strategy, radiation exposure to healthy tissues leads to some possible side effects such as acute radiation-induced skin injury and alters gene expression. Therefore, the analysis of a change in reference gene expression during the skin recovery process after radiation therapy is essential in healthy canine tissue. In the present study, we analyzed eight reference genes (ACTB, GAPDH, YWHAZ, GUSB, HPRT1, RPL4, RPS5, and TBP) in canine dermal tissues at 0, 1, 2, 3, 4, 5, 7, and 9 weeks of radiation exposure that affected the skin condition of canines. The stability of reference genes is determined by evaluating radiation therapy’s effect on healthy canine dermal tissue. Epidermal marker, Keratin 10 expression varies each week after irradiation, and HPRT1 is found to be the most suitable for normalization of mRNA expression in radiation-exposed canine dermal tissues. Changes in the gene expression level were evaluated by using a reliable tool such as quantitative real-time polymerase chain reaction (qRT-PCR). In order to achieve a valid qRT-PCR result, the most stable reference genes used for normalization after the radiation exposure process are important. Therefore, the current study was designed to evaluate the most stable reference gene for the post-irradiation canine tissues. After radiation exposure, the alternation of reference gene expression was estimated by three algorithms (geNorm, Normfinder, and Bestkeeper). The RG validation programs (GeNorm and NormFinder) suggested that HPRT1, RPL4, and TBP were suitable for normalization in qRT-PCR. Furthermore, three algorithms suggested that HPRT1 was the most stable reference gene for normalization with qRT-PCR results, regardless of before and after radiation exposure. Whereas GAPDH was found to be the most unstable reference gene. In addition, the use of stable or unstable reference genes for the normalization of Keratin 10 expression showed statistical differences. Therefore, we observed that, to obtain accurate and suitable PCR results of the canine tissues with and without radiation exposure, the HPRT1 reference gene is recommended for normalization with its high stability. Additionally, the use of RGs such as HPRT1, RPL4, and TBP for normalization in qRT-PCR experiments is recommended for post-radiation canine tissues to generate more accurate and reliable data. These results will provide fundamental information regarding internal controls for gene expression studies and can be used for the analysis of gene patterns in regenerative medicine.

The intercellular communications mediating radiation-induced bystander effects and their relevance to environmental, occupational, and therapeutic exposures

PURPOSE

The assumption that traversal of the cell nucleus by ionizing radiation is a prerequisite to induce genetic damage, or other important biological responses, has been challenged by studies showing that oxidative alterations extend beyond the irradiated cells and occur also in neighboring bystander cells. Cells and tissues outside the radiation field experience significant biochemical and phenotypic changes that are often similar to those observed in the irradiated cells and tissues. With relevance to the assessment of long-term health risks of occupational, environmental and clinical exposures, measurable genetic, epigenetic, and metabolic changes have been also detected in the progeny of bystander cells. How the oxidative damage spreads from the irradiated cells to their neighboring bystander cells has been under intense investigation. Following a brief summary of the trends in radiobiology leading to this paradigm shift in the field, we review key findings of bystander effects induced by low and high doses of various types of radiation that differ in their biophysical characteristics. While notable mechanistic insights continue to emerge, here the focus is on the many means of intercellular communication that mediate these effects, namely junctional channels, secreted molecules and extracellular vesicles, and immune pathways.

CONCLUSIONS

The insights gained by studying radiation bystander effects are leading to a basic understanding of the intercellular communications that occur under mild and severe oxidative stress in both normal and cancerous tissues. Understanding the mechanisms underlying these communications will likely contribute to reducing the uncertainty of predicting adverse health effects following exposure to low dose/low fluence ionizing radiation, guide novel interventions that mitigate adverse out-of-field effects, and contribute to better outcomes of radiotherapeutic treatments of cancer. In this review, we highlight novel routes of intercellular communication for investigation, and raise the rationale for reconsidering classification of bystander responses, abscopal effects, and expression of genomic instability as non-targeted effects of radiation.

Direct ionizing radiation and bystander effect in mouse mesenchymal stem cells

Purpose: This study aimed to evaluate the radiation-induced direct and bystander (BYS) responses of mesenchymal stem cells (MSCs) and to characterize these cells radiobiologically.Methods and materials: MSCs were irradiated (IR) and parameters related to DNA damage and cellular signaling were verified in a dose range from 0.5 to 15 Gy; also a transwell insert co-culture system was used to study medium-mediated BYS effects.Results: The main effects on directly IR cells were seen at doses higher than 6 Gy: induction of cell death, cell cycle arrest, upregulation of p21, and alteration of redox status. Irrespective of a specific dose, induction of micronuclei formation, H2AX phosphorylation, and decreased Akt expression also occurred. Thus, mTOR expression, cell senescence, nitric oxide generation, and calcium levels, in general were not significantly modulated by radiation. Data from the linear-quadratic model showed a high alpha/beta ratio, which is consistent with a more exponential survival curve. BYS effects from the unirradiated MSCs placed into companion wells with the directly IR cells, were not observed.Conclusions: The results can be interpreted as a positive outcome, meaning that the radiation damage is restricted to the directed IR MSCs not leading to off-target cell responses.

Non-targeted effects of radiation: a personal perspective on the role of exosomes in an evolving paradigm

PURPOSE

Radiation-induced non-targeted effects (NTE) have implications in a variety of areas relevant to radiation biology. Here we evaluate the various cargo associated with exosomal signalling and how they work synergistically to initiate and propagate the non-targeted effects including Genomic Instability and Bystander Effects.

CONCLUSIONS

Extra cellular vesicles, in particular exosomes, have been shown to carry bystander signals. Exosome cargo may contain nucleic acids, both DNA and RNA, as well as proteins, lipids and metabolites. These cargo molecules have all been considered as potential mediators of NTE. A review of current literature shows mounting evidence of a role for ionizing radiation in modulating both the numbers of exosomes released from affected cells as well as the content of their cargo, and that these exosomes can instigate functional changes in recipient cells. However, there are significant gaps in our understanding, particularly regarding modified exosome cargo after radiation exposure and the functional changes induced in recipient cells.

Exosome-mediated radiosensitizing effect on neighboring cancer cells via increase in intracellular levels of reactive oxygen species

The precise mechanism of intercellular communication between cancer cells following radiation exposure is unclear. Exosomes are membrane‑enclosed small vesicles comprising lipid bilayers and are mediators of intercellular communication that transport a variety of intracellular components, including microRNAs (miRNAs or miRs). The present study aimed to identify novel roles of exosomes released from irradiated cells to neighboring cancer cells. In order to confirm the presence of exosomes in the human pancreatic cancer cell line MIAPaCa‑2, ultracentrifugation was performed followed by transmission electron microscopy and nanoparticle tracking analysis (NanoSight) using the exosome‑specific surface markers CD9 and CD63. Subsequent endocytosis of exosomes was confirmed by fluorescent microscopy. Cell survival following irradiation and the addition of exosomes was evaluated by colony forming assay. Expression levels of miRNAs in exosomes were then quantified by microarray analysis, while protein expression levels of Cu/Zn‑ and Mn‑superoxide dismutase (SOD1 and 2, respectively) enzymes in MIAPaCa‑2 cells were evaluated by western blotting. Results showed that the uptake of irradiated exosomes was significantly higher than that of non‑irradiated exosomes. Notably, irradiated exosomes induced higher intracellular levels of reactive oxygen species (ROS) and a higher frequency of DNA damage in MIAPaCa‑2 cells, as determined by fluorescent microscopy and immunocytochemistry, respectively. Moreover, six up‑ and five downregulated miRNAs were identified in 5 and 8 Gy‑irradiated cells using miRNA microarray analyses. Further analysis using miRNA mimics and reverse transcription‑quantitative PCR identified miR‑6823‑5p as a potential candidate to inhibit SOD1, leading to increased intracellular ROS levels and DNA damage. To the best of our knowledge, the present study is the first to demonstrate that irradiated exosomes enhance the radiation effect via increasing intracellular ROS levels in cancer cells. This contributes to improved understanding of the bystander effect of neighboring cancer cells.

Radiation-Induced Bystander Effect: Loss of Radioprotective Capacity of Rosmarinic Acid In Vivo and In Vitro

In radiation oncology, the modulation of the bystander effect is a target both for the destruction of tumor cells and to protect healthy cells. With this objective, we determine whether the radioprotective capacity of rosmarinic acid (RA) can affect the intensity of these effects. Genoprotective capacity was obtained by determining the micronuclei frequencies in in vivo and in vitro assays and the cell survival was determined by the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay) (MTT) assay in three cell lines (PNT2, TRAMPC1 and B16F10), both in direct exposure to X-rays and after the production of radiation-induced bystander effect. The administration of RA in irradiated cells produced a decrease in the frequency of micronuclei both in vivo and in vitro, and an increase in cell survival, as expression of its radioprotective effect (p < 0.001) attributable to its ability to scavenge radio-induced free radicals (ROS). However, RA does not achieve any modification in the animals receiving serum or in the cultures treated with the irradiated medium, which expresses an absence of radioprotective capacity. The results suggest that ROS participates in the formation of signals in directly irradiated cells, but only certain subtypes of ROS, the cytotoxic products of lipid peroxidation, participate in the creation of lesions in recipient cells.

Role of epigenetic mechanisms in propagating off-targeted effects following radiation based therapies - A review

Despite being an important diagnostic and treatment modality, ionizing radiation (IR) is also known to cause genotoxicity and multiple side effects leading to secondary carcinogenesis. While modern cancer radiation therapy has improved patient recovery and enhanced survival rates, the risk of radiation-related adverse effects has become a growing challenge. It is now well-accepted that IR-induced side effects are not exclusively restricted to exposed cells but also spread to distant 'bystander' cells and even to the unexposed progeny of the irradiated cells. These 'off-targeted' effects involve a plethora of molecular events depending on the type of radiation and tumor tissue background. While the mechanisms by which off-targeted effects arise remain obscure, emerging evidence based on the non-mendelian inheritance of various manifestations of them as well as their persistence for longer periods supports a contribution of epigenetic factors. This review focuses on the major epigenetic phenomena including DNA methylation, histone modifications, and small RNA mediated silencing and their versatile role in the manifestation of IR induced off-targeted effects. As short- and long-range communication vehicles respectively, the role of gap junctions and exosomes in spreading these epigenetic-alteration driven off-targeted effects is also discussed. Furthermore, this review emphasizes the possible therapeutic potentials of these epigenetic mechanisms and how beneficial outcomes could potentially be achieved by targeting various signaling molecules involved in these mechanisms.

Oxidative Stress and Gene Expression Modifications Mediated by Extracellular Vesicles: An In Vivo Study of the Radiation-Induced Bystander Effect

Radiation-induced bystander effect is a biological response in nonirradiated cells receiving signals from cells exposed to ionising radiation. The aim of this in vivo study was to analyse whether extracellular vesicles (EVs) originating from irradiated mice could induce modifications in the redox status and expression of radiation-response genes in bystander mice. C57BL/6 mice were whole-body irradiated with 0.1-Gy and 2-Gy X-rays, and EVs originating from mice irradiated with the same doses were injected into naïve, bystander mice. Lipid peroxidation in the spleen and plasma reactive oxygen metabolite (ROM) levels increased 24 h after irradiation with 2 Gy. The expression of antioxidant enzyme genes and inducible nitric oxide synthase 2 (iNOS2) decreased, while cell cycle arrest-, senescence- and apoptosis-related genes were upregulated after irradiation with 2 Gy. In bystander mice, no significant alterations were observed in lipid peroxidation or in the expression of genes connected to cell cycle arrest, senescence and apoptosis. However, there was a systemic increase in the circulating ROM level after an intravenous EV injection, and EVs originating from 2-Gy-irradiated mice caused a reduced expression of antioxidant enzyme genes and iNOS2 in bystander mice. In conclusion, we showed that ionising radiation-induced alterations in the cellular antioxidant system can be transmitted in vivo in a bystander manner through EVs originating from directly irradiated animals.

Radiation-Induced Bystander Effect can be Transmitted Through Exosomes Using miRNAs as Effector Molecules

The radiation-induced bystander effect (RIBE) is a destructive reaction in nonirradiated cells and is one primary factor in determining the efficacy and success of radiation therapy in the field of cancer treatment. Previously reported studies have shown that the RIBE can be mediated by exosomes that carry miRNA components within. Exosomes, which are one type of cell-derived vesicle, exist in different biological conditions and serve as an important additional pathway for signal exchange between cells. In addition, exosome-derived miRNAs are confirmed to play an important role in RIBE, activating the bystander effect and genomic instability after radiotherapy. After investigating the field of RIBE, it is important to understand the mechanisms and consequences of biological effects as well as the role of exosomes and exosomal miRNAs therein, from different sources and under different circumstances, respectively. More discoveries could help to establish early interventions against RIBE while improving the efficacy of radiotherapy. Meanwhile, measures that would alleviate or even inhibit RIBE to some extent may exist in the near future.

The Role of Low-Dose Radiation in Association with TNF-α on Immunomodulatory Properties of Mesenchymal Stem Cells

Ionizing radiation (IR) is an important medical tool. Despite the effects associated with high-dose radiation during or after treatment, as well as in accidental exposures, the direct or indirect effect of low-dose IR in cells remain poorly documented. IR can affect the tissue microenvironment, including mesenchymal stem cells (MSCs), which have high regenerative and immunomodulatory capacities. This study aimed to investigate the effect of low-dose IR in association with the inflammatory stimuli of TNF-α on the immunomodulatory capacity of MSCs. MSCs were irradiated with a low-dose IR, stimulated with TNF-α, and cultivated in a bystander system with murine spleen cells. The results showed that TNF-R1 is expressed in MSCs and is not affected, even in irradiated MSCs. However, irradiated MSCs produced reduced amounts of IL-6 and increased amounts of IL-10. The levels of PGE₂ and NO^• in MSCs were also increased when stimulated with TNF-α. Furthermore, conditioned media from irradiated MSCs reduced the proliferation of bystander lymphocytes and reduced the metabolic activity of macrophages. In addition, conditioned media from irradiated MSCs modulated the profile of cytokines in bystander spleen cells (lymphocytes and macrophages), reducing inflammatory and increasing anti-inflammatory cytokines, also increasing Treg cells. In conclusion, low-dose IR in association with an inflammatory stimulus affects the immunomodulatory properties of MSCs. In this way, the immunosuppressive capability of MSCs can be explored for several disease treatments where IR usually part of the context of the treatment. However, a complete understanding of the mechanisms underlying these interactions need further investigation. Graphical Abstract.

Astragalus polysaccharide inhibits radiation-induced bystander effects by regulating apoptosis in Bone Mesenchymal Stem Cells (BMSCs)

The purpose of this study was to investigate the effects of astragalus polysaccharides (APS) on the proliferation and apoptosis of bone marrow mesenchymal stem cells (BMSCs) induced by X-ray radiation-induced A549 cells bystander effect (RIBE), and to explore their mechanisms. In this study, APS increased the reduced cell proliferation rate induced by RIBE and inhibiting the apoptosis of bystander cells. In terms of mechanism, APS up-regulates the proteins Bcl-2, Bcl-xl, and down-regulates the proteins Bax and Bak, which induces a decrease in mitochondrial membrane potential, which induces the release of Cyt-c and AIF, which leads to caspase-dependent and caspase-independent pathway to cause apoptosis. In addition, we believe that ROS may be the main cause of these protein changes. APS can inhibit the generation of ROS in bystander cells and thus inhibit the activation of the mitochondrial pathway, further preventing cellular damage caused by RIBE.

Enhanced response of radioresistant carcinoma cell line to heterogeneous dose distribution of grid; the role of high-dose bystander effect

PURPOSE

The classical dogma that restricted the radiation effect to the directly irradiated cells has been challenged by the bystander effect. This off-target phenomenon which was manifested in adjacent cells via signaling of fully exposed cells might be involved in high-dose Grid therapy as well. Here, an in-vitro study was performed to examine the possible extent of carcinoma cells response to the inhomogeneous dose distribution of Grid irradiation in the context of the bystander effect.

MATERIALS AND METHODS

Bystander effect was investigated in human carcinoma cell lines of HeLa and HN5 adjacent to those received high-dose Grid irradiation using 'medium transfer' and 'cell-to-cell contact' strategies. Based on the Grid peak-to-valley dose profile, medium transfer was exerted from 10 Gy uniformly exposed donors to 1.5 Gy uniformly irradiated recipients. Cell-contact bystander was evaluated after nonuniform dose distribution of 10 Gy Grid irradiation using cloning cylinders. GammaH2AX foci, micronucleus and clonogenic assays besides gene expression analysis were performed.

RESULTS

Various parameters (ɑ/β, D37, D50) extracted from survival curve which fitted to the Linear Quadratic model, verified more radioresistance of HN5. Survival fraction at 2 Gy (SF2) indicated as 0.42 ± 0.06 in HeLa and 0.5 ± 0.03 in HN5. The level of survival decrease, DNA damages and micronucleus of cells located in the Grid shielded areas (1.5 Gy cell-to-cell contact bystander cells) were significantly more than the values obtained from cells which were irradiated by merely uniform dose of 1.5 Gy. The gH2AX foci and micronuclei frequencies were enhanced in cell-contact bystander approximately more than 1.8 times. Relative expression of DNA damage repair pathway genes (Xrcc6 and H2afx) in bystander cells increased significantly. The most cell survival reduction (11.6 times) was revealed in the Grid bystander cells of radioresistant cell line (HN5). No statistically significant difference between 10 Gy uniform beam and Grid non-uniform beam was observed.

CONCLUSIONS

Various endpoints confirmed an augmented response of cells in the valley dose region of the Grid block significantly (compared with the cells irradiated by identical dose of uniform beam), suggesting the role of high-dose bystander effect which was more pronounced in resistant carcinoma cell lines. These findings could provide a partial explanation for the Grid beneficial response seen in a number of pre-clinical and clinical studies.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

The dialogue between died and viable cells: in vitro and in vivo bystander effects and 1H-NMR-based metabolic profiling of soluble factors

The bystander effect (BE) is an important biological phenomenon that induces damages in distant and not directly affected by a chemical/physical stress cells. This effect, well known in ionizing radiation treatment, relies on reactive signals released by exposed cells and transmitted via cell–cell interaction or culture medium. In this study, cycloheximide (CHX)-induced apoptotic U937 cells and untreated THP-1 cells were chosen to investigate the chemical-induced BE. The effects of apoptotic U937 cells culture medium, Conditioned Medium (CM), on THP-1 cells were evaluated by morphological and immunohistochemical analysis performed by light microscopy; 1D 1H and 2D J-resolved (JRES) NMR metabolomic analysis has been used to characterize the molecules involved in the BE. In summary, this study indicates that: CM of CHX-treated U937 cells induces a time-dependent induction of toxicity, probably apoptotic cell death, and macrophagic differentiation in THP-1 cells; CM contains different metabolites respect fresh culture medium; CM recruits in vivo activated fibroblasts, endothelial cells, macrophages and mononuclear inflammatory cells in rat calf muscles. These data suggest that CHX exposed cells could cause BE through the release, during the apoptotic process, of soluble factors into the medium that could be exploited in anticancer protocols.

Relevance of Non-Targeted Effects for Radiotherapy and Diagnostic Radiology; A Historical and Conceptual Analysis of Key Players

Non-targeted effects (NTE) such as bystander effects or genomic instability have been known for many years but their significance for radiotherapy or medical diagnostic radiology are far from clear. Central to the issue are reported differences in the response of normal and tumour tissues to signals from directly irradiated cells. This review will discuss possible mechanisms and implications of these different responses and will then discuss possible new therapeutic avenues suggested by the analysis. Finally, the importance of NTE for diagnostic radiology and nuclear medicine which stems from the dominance of NTE in the low-dose region of the dose–response curve will be presented. Areas such as second cancer induction and microenvironment plasticity will be discussed.

miR-27a-containing Exosomes Secreted by Irradiated Skin Keratinocytes Delayed the Migration of Unirradiated Skin Fibroblasts

Radiation-induced bystander effect (RIBE), e.g. the biological response occurring in unirradiated cells when their neighboring cells are irradiated, is the consequence of intercellular communication between irradiated and unirradiated cells and intracellular signal transduction of these two cell populations. Although several miRNAs have been found to play an important role in RIBEs, the evidence for the regulatory effects of miRNAs on RIBEs is still limited. In this study, by using a two cell-line co-culture system, we first found that the migration of unirradiated bystander WS1 skin fibroblasts was inhibited after co-culture with irradiated HaCaT skin keratinocytes. Further study revealed that HaCaT cells exposed to α-particles and X-rays quickly showed an elevated miR-27a expression, which was essential for the induction of the bystander effect, resulting in the secretion of miR-27a-containing exosomes as a major RIBE signaling factor. Upon uptake of these exosomes, the recipient unirradiated WS1 cells displayed oxidative stress and increased miR-27a levels. Elevated levels of miR-27a that targets MMP2 in the recipient WS1 cells then led to slowed cell migration, which was dependent upon the redox status of WS1 cells. To summarize, the present study has revealed a critical role of miR-27a in every step of the induction of bystander migration inhibition of unirradiated WS1 fibroblasts co-cultured with irradiated HaCaT keratinocytes, confirming the important regulatory effects of miRNAs in RIBEs. Additionally, we provided direct evidence that RIBEs could affect wound healing.

What does radiation biology tell us about potential health effects at low dose and low dose rates?

The health risks to humans exposed to low dose and low dose rate ionising radiation remain ambiguous and are the subject of debate. The need to establish risk assessment standards based on the mechanisms underlying low dose/low fluence radiation exposures has been recognised by scholarly and regulatory bodies as critical for reducing the uncertainty in predicting adverse health risks of human exposure to low doses of radiation. Here, a brief review of laboratory-based evidence of molecular and biochemical changes induced by low doses and low dose rates of radiation is presented. In particular, two phenomena, namely bystander effects and adaptive responses that may impact low-level radiation health risks, are discussed together with the need for further studies. The expansion of this knowledge by considering the important variables that affect the radiation response (e.g. genetic susceptibility, time after exposure), and using the latest advances in experimental models and bioinformatics tools, may guide epidemiological studies towards reducing the uncertainty in predicting the potential health hazards of exposure to low-dose radiation.

Intercellular communications-redox interactions in radiation toxicity; potential targets for radiation mitigation

Nowadays, using ionizing radiation (IR) is necessary for clinical, agricultural, nuclear energy or industrial applications. Accidental exposure to IR after a radiation terror or disaster poses a threat to human. In contrast to the old dogma of radiation toxicity, several experiments during the last two recent decades have revealed that intercellular signaling and communications play a key role in this procedure. Elevated level of cytokines and other intercellular signals increase oxidative damage and inflammatory responses via reduction/oxidation interactions (redox system). Intercellular signals induce production of free radicals and inflammatory mediators by some intermediate enzymes such as cyclooxygenase-2 (COX-2), nitric oxide synthase (NOS), NADPH oxidase, and also via triggering mitochondrial ROS. Furthermore, these signals facilitate cell to cell contact and increasing cell toxicity via cohort effect. Nitric oxide is a free radical with ability to act as an intercellular signal that induce DNA damage and changes in some signaling pathways in irradiated as well as non-irradiated adjacent cells. Targeting of these mediators by some anti-inflammatory agents or via antioxidants such as mitochondrial ROS scavengers opens a window to mitigate radiation toxicity after an accidental exposure. Experiments which have been done so far suggests that some cytokines such as IL-1β, TNF-α, TGF-β, IL-4 and IL-13 are some interesting targets that depend on irradiated organs and may help mitigate radiation toxicity. Moreover, animal experiments in recent years indicated that targeting of toll like receptors (TLRs) may be more useful for radioprotection and mitigation. In this review, we aimed to describe the role of intercellular interactions in oxidative injury, inflammation, cell death and killing effects of IR. Moreover, we described evidence on potential mitigation of radiation injury via targeting of these mediators.

Surgical wound fluids from patients treated with intraoperative radiotherapy induce radiobiological response in breast cancer cells

Breast cancer is the most common cancer occurring in women. The standard of breast cancer treatment is based on breast-conserving surgery with administration of adjuvant whole breast radiotherapy. Research shows that in-breast relapse is most likely to occur in the tumour bed, i.e. around the scar. Intraoperative radiotherapy (IORT), in which radiation is delivered to the tumour bed, reduces the risk of local recurrence not only through direct cell killing, but also through modification of local microenvironment. Additionally IORT modifies the composition and biological activity of surgical wound fluid. Since many researchers show that radiation damage is mediated through factors secreted to the environment by irradiated cells, we hypothesized that this radiation-induced bystander effect is partly responsible for the change observed in surgical wound fluids. We collected conditioned medium from irradiated breast cancer cells (CM) and surgical wound fluids from patients who underwent IORT (RT-WF) and from patients after breast-conserving surgery alone (WF). We incubated two breast cancer cell lines (MCF-7 and MDA-MB-468) with WF, RT-WF, CM or WF + CM and measured radiobiological response of cells. We measured the level of double-strand breaks, induction of apoptosis and the changes in expression of genes related to DNA damage repair. We observed that stimulation with RT-WF and with WF + CM-induced double-strand breaks and increased expression of DNA damage repair-related genes, which was not observed after stimulation with WF. These results suggest that IOERT induces secretion of bystander factors mediating the genotoxic effect of ionizing radiation.

Cerium Oxide Nanoparticles Re-establish Cell Integrity Checkpoints and Apoptosis Competence in Irradiated HaCat Cells via Novel Redox-Independent Activity

Cerium oxide nanoparticles (CNPs) are potent radical scavengers protecting cells from oxidative insults, including ionizing radiation. Here we show that CNPs prevent X-ray-induced oxidative imbalance reducing DNA breaks on HaCat keratinocytes, nearly abating mutagenesis. At the same time, and in spite of the reduced damage, CNPs strengthen radiation-induced cell cycle arrest and apoptosis outcome, dropping colony formation; notably, CNPs do not possess any intrinsic toxicity toward non-irradiated HaCat, indicating that they act on damaged cells. Thus CNPs, while exerting their antioxidant action, also reinforce the stringency of damage-induced cell integrity checkpoints, promoting elimination of the “tolerant” cells, being in fact radio-sensitizers. These two contrasting pathways are mediated by different activities of CNPs: indeed Sm-doped CNPs, which lack the Ce³⁺/Ce⁴⁺ redox switch and the correlated antioxidant action, fail to decrease radiation-induced superoxide formation, as expected, but surprisingly maintain the radio-sensitizing ability and the dramatic decrease of mutagenesis. The latter is thus attributable to elimination of damaged cells rather than decreased oxidative damage. This highlights a novel redox-independent activity of CNPs, allowing selectively eliminating heavily damaged cells through non-toxic mechanisms, rather reactivating endogenous anticancer pathways in transformed cells.

The effect of carbon irradiation is associated with greater oxidative stress in mouse intestine and colon relative to γ-rays

Carbon irradiation due to its higher biological effectiveness relative to photon radiation is a concern for toxicity to proliferative normal gastrointestinal (GI) tissue after radiotherapy and long-duration space missions such as mission to Mars. Although radiation-induced oxidative stress is linked to chronic diseases such as cancer, effects of carbon irradiation on normal GI tissue have not been fully understood. This study assessed and compared chronic oxidative stress in mouse intestine and colon after different doses of carbon and γ radiation, which are qualitatively different. Mice (C57BL/6J) were exposed to 0.5 or 1.3 Gy of γ or carbon irradiation, and intestinal and colonic tissues were collected 2 months after irradiation. While part of the tissues was used for isolating epithelial cells, tissue samples were also fixed and paraffin embedded for 4 µm thick sections as well as frozen for biochemical assays. In isolated epithelial cells, reactive oxygen species and mitochondrial status were studied using fluorescent probes and flow cytometry. We assessed antioxidant enzymes and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in tissues and formalin-fixed tissue sections were stained for 4-hydroxynonenal, a lipid peroxidation marker. Data show that mitochondrial deregulation, increased NADPH oxidase activity, and decreased antioxidant activity were major contributors to carbon radiation-induced oxidative stress in mouse intestinal and colonic cells. When considered along with higher lipid peroxidation after carbon irradiation relative to γ-rays, our data have implications for functional changes in intestine and carcinogenesis in colon after carbon radiotherapy as well as space travel.

Protection of normal cells from irradiation bystander effects by silica-flufenamic acid nanoparticles

The development of a myriad of nanoparticles types has opened new possibilities for the diagnostics and treatment of many diseases, especially for cancer. However, most of the researches done so far do not focus on the protection of normal cells surrounding a tumor from irradiation bystander effects that might lead to cancer recurrence. Gap-junctions are known to be involved in this process, which leads to genomic instability of neighboring normal cells, and flufenamic acid (FFA) is included in a new group of gap-junction blockers recently discovered. The present work explores the use of mesoporous silica nanoparticles MCM-41 functionalized with 3-Aminopropyltriethoxysilane (APTES) for anchoring the flufenamic acid for its prolonged and controlled release and protection from radiation bystander effects. MCM-41 and functionalized samples were structurally and chemically characterized with multiple techniques. The biocompatibility of all samples was tested in a live/dead assay performed in cultured MRC-5 and HeLa cells. HeLa cells cultured were exposed to 50 Gy of gamma-rays and the media transferred to fibroblast cells cultured separately. Our results show that MCM-41 and functionalized samples have high biocompatibility with MCR-5 and HeLa cells, and most importantly, the FFA delivered by these NPs was able to halt apoptosis, one of main bystander effects.

Astragalus Polysaccharide Inhibits Ionizing Radiation-Induced Bystander Effects by Regulating MAPK/NF-kB Signaling Pathway in Bone Mesenchymal Stem Cells (BMSCs)

Background

This study investigated the effect of Astragalus polysaccharides (APS) on radiation-induced bystander effects (RIBE) in human bone mesenchymal stem cells (BMSCs) induced by irradiated A549 cells.

Material/Methods

A549 cells were irradiated with 2 Gy X-rays to obtain conditioned medium. BMSCs were incubated with the conditioned medium or APS. The levels of reactive oxygen species (ROS) and TGF-β were detected by ELISA. Cell survival, genomic instability, and DNA damages were detected by CCK-8 assay, colony formation assay, the micronucleus test and immunofluorescence assay, respectively. The protein and phosphorylation protein expression of p38, c-Jun N-terminal kinase (JNK), extracellular regulated protein kinase (ERK1/2), P65, and cyclooxygenase-2 (COX-2) in bystander effect cells were detected by Western blot.

Results

The expression of COX-2 and ROS increased following stimulation with conditioned medium; this effect was inhibited by pre-exposing the cells to APS. BMSCs growth and colony formation rate decreased following stimulation with conditioned medium; this effect was suppressed by pre-exposing the cells to APS. In addition, the micronucleus rate and 53BP1 foci number increased after treatment with conditioned medium; this increase in BMSCs was inhibited by APS. The levels of phosphorylated p38, JNK, ERK1/2, NF-κB P65, and COX-2 proteins were increased by conditioned medium but were decreased by pre-treatment with APS.

Conclusions

RIBE in BMSCs induced by the irradiated A549 was mediated by the ROS in the conditioned medium and might be related to MAPK/NF-κB signal pathways in BMSCs. APS may block RIBE through regulating the MAPK/NF-κB pathway.

Molecular mechanism of bystander effects and related abscopal/cohort effects in cancer therapy

Cancer cells subjected to ionizing radiation may release signals which can influence nearby non-irradiated cells, termed bystander effects. The transmission of bystander effects among cancer cells involves the activation of inflammatory cytokines, death ligands, and reactive oxygen/nitrogen species. In addition to bystander effects, two other forms of non-target effects (NTEs) have been identified in radiotherapy, as one is called cohort effects and the other is called abscopal effects. Cohort effects represent the phenomenon where irradiated cells can produce signals that reduce the survival of neighboring cells within an irradiated volume. The effects suggest the importance of cellular communication under irradiation with non-uniform dose distribution. In contrast, abscopal effects describe the NTEs that typically occur in non-irradiated cells distant from an irradiated target. These effects can be mediated primarily by immune cells such as T cells. Clinical trials have shown that application of radiation along with immunotherapy may enhance abscopal effects and improve therapeutic efficacy on non-target lesions outside an irradiated field. According to NTEs, cell viability is reduced not only by direct irradiation effects, but also due to signals emitted from nearby irradiated cells. A clinical consideration of NTEs could have a revolutionary impact on current radiotherapy via the establishment of more efficient and less toxic radiobiological models for treatment planning compared to conventional models. Thus, we will review the most updated findings about these effects and outline their mechanisms and potential applications in cancer treatment with a special focus on the brain, lung, and breast cancers.

Reactive oxygen species and nitric oxide signaling in bystander cells

It is now well accepted that radiation induced bystander effects can occur in cells exposed to media from irradiated cells. The aim of this study was to follow the bystander cells in real time following addition of media from irradiated cells and to determine the effect of inhibiting these signals. A human keratinocyte cell line, HaCaT cells, was irradiated (0.005, 0.05 and 0.5 Gy) with γ irradiation, conditioned medium was harvested after one hour and added to recipient bystander cells. Reactive oxygen species, nitric oxide, Glutathione levels, caspase activation, cytotoxicity and cell viability was measured after the addition of irradiated cell conditioned media to bystander cells. Reactive oxygen species and nitric oxide levels in bystander cells treated with 0.5Gy ICCM were analysed in real time using time lapse fluorescence microscopy. The levels of reactive oxygen species were also measured in real time after the addition of extracellular signal-regulated kinase and c-Jun amino-terminal kinase pathway inhibitors. ROS and glutathione levels were observed to increase after the addition of irradiated cell conditioned media (0.005, 0.05 and 0.5 Gy ICCM). Caspase activation was found to increase 4 hours after irradiated cell conditioned media treatment (0.005, 0.05 and 0.5 Gy ICCM) and this increase was observed up to 8 hours and there after a reduction in caspase activation was observed. A decrease in cell viability was observed but no major change in cytotoxicity was found in HaCaT cells after treatment with irradiated cell conditioned media (0.005, 0.05 and 0.5 Gy ICCM). This study involved the identification of key signaling molecules such as reactive oxygen species, nitric oxide, glutathione and caspases generated in bystander cells. These results suggest a clear connection between reactive oxygen species and cell survival pathways with persistent production of reactive oxygen species and nitric oxide in bystander cells following exposure to irradiated cell conditioned media.

Intercellular communication of DNA damage and oxidative status underpin bystander effects

PURPOSE

A well-known phenomenon in the field of radiation biology is that cells exposed to ionizing radiation (IR) (targeted cells) can induce in non-irradiated (non-targeted), bystander cells effects reminiscent of DNA damage responses (DDR) normally expected, exclusively in targeted cells. These phenomena are collectively referred to as radiation-induced bystander effects (RIBE) and have different manifestations depending on the endpoint studied. Although it is now recognized that RIBE reflects to a considerable extent communication by the targeted cells to undamaged cells of their damaged status, the molecular underpinnings of this communication and its significance for the organism are only partly understood. In particular, it remains unknown why and how targeted cells induce DNA damage in non-targeted, bystander cells threatening their genomic stability and risking thus their transformation to cancer cells. Here, we outline observations hinting to possible sources of artifacts in experiments designed to detect RIBE and summarize a model according to which targeted cells modulate their redox status as part of their overall response to IR and use this modified redox status as a source to generate signals that are transmitted to non-irradiated cells of the organism.

MATERIAL AND METHODS

A synthesis of published evidence is presented.

RESULTS

Depending on type, RIBE signals may be transmitted through various forms of direct intercellular contact, through molecules acting locally in a paracrine fashion, or through molecules acting remotely in an endocrine fashion. We reason that DNA damage generated in bystander cells is unlikely to manifest the clustered character exhibited in directly exposed cells and postulate that RIBE will depend on complications generated when simpler forms of damage encounter the DNA replication fork.

CONCLUSIONS

We suggest that RIBE result from intercellular communication mechanisms designed to spread within tissues, or the organism, alarm signals of DNA damage inflicted in subsets of the constituent cells. This response likely evolved to protect organisms by appropriately modulating stress response, repair or apoptosis, and may in some instances also cause adverse effects, e.g. as collateral damage.

Radiation and hypoxia-induced non-targeted effects in normoxic and hypoxic conditions in human lung cancer cells

PURPOSE

Many cell lines with anaerobic metabolism do not show cytotoxic abscopal effect (AE) following irradiation. Further, there is no existing data on the radiation- and hypoxia (H)-induced AE. The purpose of this study was to investigate and compare the status of radiation-induced abscopal effect (RIAE) in normoxic and hypoxic conditions.

METHODS

Lung cancer cells (A549, H460) were exposed either to hypoxia or normoxia and then irradiated (2 or 10 Gy). After 24 h, unirradiated hypoxic (H-CM) or normoxic (N-CM) conditioned media (CM) and irradiated hypoxic (H-RCM) or normoxic (N-RCM) CM was collected. Hypoxia-resistant clones (HR: A549/HR, H460/HR) were generated by continuous exposure of the cells to hypoxia. Unirradiated parental cells or HR were exposed to H-CM, N-CM, H-RCM or N-RCM. In some groups, 24 h after exposure to CM, cells were directly irradiated with 2 Gy. Cell growth was monitored using real-time cell electronic sensing system. Further, levels of hypoxia and HIF1α regulated angiogenesis related growth factors, basic fibroblast growth factor (bFGF), placental growth factor (PlGF), soluble fms-like tyrosine kinase (sFlt-1) and vascular endothelial growth factor (VEGF) were assessed in CM.

RESULTS

In the radio-resistant A549 cells, H-RCM was much more effective in inducing growth delay compared to N-RCM. In the radio-sensitive H460 cells, both N-RCM and H-RCM induced growth delay. Interestingly, effects of N-RCM were completely reversed in HR cells. Exposure of cells to direct irradiation (2 Gy) 24 h after incubation with CM resulted in 50-60% reduction in cell proliferation in A549/HR cells and a very significant induction of death (>95%) in H460/HR cells. Direct irradiation of parental or HR clones of A549 and H460 cells exposed to H-CM 24 h with 2 Gy induced significant reduction in cell proliferation (from 40% to >95%) in all the cells. Further, levels of sFlt-1 correlated with growth delay in all the cells.

CONCLUSIONS

These results for the first time demonstrate that irradiation of hypoxic cells and exposing the cells to acute hypoxia lead to significant AE.

Assessment of The Dose-Response Relationship of Radiation-Induced Bystander Effect in Two Cell Lines Exposed to High Doses of Ionizing Radiation (6 and 8 Gy)

OBJECTIVES

The dose-response relationship of radiation-induced bystander effect (RIBE) is controversial at high dose levels. The aim of the present study is to assess RIBE at high dose levels by examination of different endpoints.

MATERIALS AND METHODS

This experimental study used the medium transfer technique to induce RIBE. The cells were divided into two main groups: QU-DB cells which received medium from autologous irradiated cells and MRC5 cells which received medium from irradiated QU-DB cells. Colony, MTT, and micronucleus assays were performed to quantify bystander responses. The medium was diluted and transferred to bystander cells to investigate whether medium dilution could revive the RIBE response that disappeared at a high dose.

RESULTS

The RIBE level in QU-DB bystander cells increased in the dose range of 0.5 to 4 Gy, but decreased at 6 and 8 Gy. The Micronucleated cells per 1000 binucleated cells (MNBN) frequency of QU-DB bystander cells which received the most diluted medium from 6 and 8 Gy QU-DB irradiated cells reached the maximum level compared to the MNBN frequency of the cells that received complete medium (P<0.0001). MNBN frequency of MRC5 cells which received the most diluted medium from 4 Gy QU-DB irradiated cells reached the maximum level compared to MNBN frequency of cells that received complete medium (P<0.0001).

CONCLUSIONS

Our results showed that RIBE levels decreased at doses above 4 Gy; however, RIBE increased when diluted conditioned medium was transferred to bystander cells. This finding confirmed that a negative feedback mechanism was responsible for the decrease in RIBE response at high doses. Decrease of RIBE at high doses might be used to predict that in radiosurgery, brachytherapy and grid therapy, in which high dose per fraction is applied, normal tissue damage owing to RIBE may decrease.

Spatial function of the oxidative DNA damage response in radiation induced bystander effects in intra- and inter-system of Caenorhabditis elegans

Though the signaling events involved in radiation induced bystander effects (RIBE) have been investigated both in vitro and in vivo, the spatial function of these communications, especially the related signaling pathways, is not fully elucidated. In the current study, significant increases of DNA damage were clearly observed in C. elegans germline upon irradiation to both intra-system of posterior pharynx and inter-system of vulva, in which more severe damage, even to F1 generation worms, was shown for vulva irradiation. Spatial function assay indicated the DDR key components of mrt-2/hus-1/cep-1/ced-4 were indispensable in germ cells for both sites irradiation, while those components in somatic cells were either not (cep-1/ced-4) or partially (mrt-2/hus-1) required to promote apoptosis. Moreover, production of reactive oxygen species (ROS) indicated by the superoxide dismutase expression and the unfolded protein response of the mitochondria was found systemically involved in the initiation of these processes for both two site irradiation. These results will give a better understanding of the RIBE mechanisms in vivo, and invaluable to assess the clinical relevance to radiotherapy.

Identification of stable housekeeping genes in response to ionizing radiation in cancer research

Housekeeping genes (HKGs) are essential for basic maintenance of a variety of cellular processes. They ideally maintain uniform expression independent of experimental conditions. However, the effects of ionizing radiation (IR) on HKG expression is unclear. Statistical algorithms, geNorm and Normfinder were used for estimating the stability of HKGs as raw quantification cycle (Cq) values were not a reliable factor for normalization. Head and neck, non-small lung and pancreas cells were exposed to 2, 4 and 6 Gy IR doses and expression of fourteen HKGs was measured at 5 min to 48 h post-irradiation within a given tissue. Paired and single cell line analyses under these experimental conditions identified TATA-Box Binding Protein (TBP) and Importin 8 (IPO8) to be stable in non-small cell lung cancer. In addition to these two genes, Ubiquitin C (UBC) in head and neck cancer and Transferrin receptor (TFRC) and β-Glucuronidase (GUSB) in pancreatic cancer were identified to be stable as well. In summary we present a resource for top ranked five stable HKGs and their transcriptional behavior in commonly used cancer model cell lines and suggest the use of multiple HKGs under radiation treatment conditions is a reliable metric for quantifying gene expression.

Enhanced Radiosensitization of Gold Nanospikes via Hyperthermia in Combined Cancer Radiation and Photothermal Therapy

Metallic nanostructures as excellent candidates for nanosensitizers have shown enormous potentials in cancer radiotherapy and photothermal therapy. Clinically, a relatively low and safe radiation dose is highly desired to avoid damage to normal tissues. Therefore, the synergistic effect of the low-dosed X-ray radiation and other therapeutic approaches (or so-called "combined therapeutic strategy") is needed. Herein, we have synthesized hollow and spike-like gold nanostructures by a facile galvanic replacement reaction. Such gold nanospikes (GNSs) with low cytotoxicity exhibited high photothermal conversion efficiency (η = 50.3%) and had excellent photostability under cyclic near-infrared (NIR) laser irradiations. We have demonstrated that these GNSs can be successfully used for in vitro and in vivo X-ray radiation therapy and NIR photothermal therapy. For the in vitro study, colony formation assay clearly demonstrated that GNS-mediated photothermal therapy and X-ray radiotherapy reduced the cell survival fraction to 89% and 51%, respectively. In contrast, the cell survival fraction of the combined radio- and photothermal treatment decreased to 33%. The synergistic cancer treatment performance was attributable to the effect of hyperthermia, which efficiently enhanced the radiosensitizing effect of hypoxic cancer cells that were resistant to ionizing radiation. The sensitization enhancement ratio (SER) of GNSs alone was calculated to be about 1.38, which increased to 1.63 when the GNS treatment was combined with the NIR irradiation, confirming that GNSs are effective radiation sensitizers to enhance X-ray radiation effect through hyperpyrexia. In vivo tumor growth study indicated that the tumor growth inhibition (TGI) in the synergistically treated group reached 92.2%, which was much higher than that of the group treated with the GNS-enhanced X-ray radiation (TGI = 29.8%) or the group treated with the GNS-mediated photothermal therapy (TGI = 70.5%). This research provides a new method to employ GNSs as multifunctional nanosensitizers for synergistic NIR photothermal and X-ray radiation therapy in vitro and in vivo.

Bystander effects and compartmental stress response to X-ray irradiation in L929 cells

Bystander effects are indirect consequences of radiation and many other stress factors. They occur in cells that are not directly exposed to these factors, but receive signals from affected cells either by gap junctions or by molecules released in the medium. Characterizing these effects and deciphering the underlying mechanisms involved in radiation-induced bystander effects are relevant for cancer radiotherapy and radioprotection. At doses of X-ray radiation 0.5 and 1 Gy, we detected bystander effects as increased numbers of micronuclei shortly after the treatment, through medium transfer and by co-cultures. Interestingly, bystander cells did not exhibit long-term adverse changes in viability. Evaluation of several compartmental stress markers (CHOP, BiP, mtHsp60, cytHsp70) by qRT-PCR did not reveal expression changes at transcriptional level. We investigated the involvement of ROS and NO in this process by addition of specific scavengers of these molecules, DMSO or c-PTIO in the transferred medium. This approach proved that ROS but not NO is involved in the induction of lesions in the acceptor cells. These results indicate that L929 cells are susceptible to stress effects of radiation-induced bystander signaling.

Bystander Effect Induced by Electroporation is Possibly Mediated by Microvesicles and Dependent on Pulse Amplitude, Repetition Frequency and Cell Type

Bystander effect, a known phenomenon in radiation biology, where irradiated cells release signals which cause damage to nearby, unirradiated cells, has not been explored in electroporated cells yet. Therefore, our aim was to determine whether bystander effect is present in electroporated melanoma cells in vitro, by determining viability of non-electroporated cells exposed to medium from electroporated cells and by the release of microvesicles as potential indicators of the bystander effect. Here, we demonstrated that electroporation of cells induces bystander effect: Cells exposed to electric pulses mediated their damage to the non-electroporated cells, thus decreasing cell viability. We have shown that shedding microvesicles may be one of the ways used by the cells to mediate the death signals to the neighboring cells. The murine melanoma B16F1 cell line was found to be more electrosensitive and thus more prone to bystander effect than the canine melanoma CMeC-1 cell line. In B16F1 cell line, bystander effect was present above the level of electropermeabilization of the cells, with the threshold at 800 V/cm. Furthermore, with increasing electric field intensities and the number of pulses, the bystander effect also increased. In conclusion, electroporation can induce bystander effect which may be mediated by microvesicles, and depends on pulse amplitude, repetition frequency and cell type.

Purinergic Signaling Is a Novel Mechanism of the Cellular Response to Ionizing Radiation

Recent studies suggest the effect of radiation is observed not only in irradiated cells but also in adjacent non-irradiated cells (bystander effect), although the mechanism has not yet been fully revealed. This bystander effect may be caused by intercellular communication via a gap junction or by messengers released from irradiated cells, such as reactive oxygen species, nitric oxide, or cytokines. However, an unknown mechanism is also possible in the bystander effect. On the other hand, it is known that extracellular ATP, ADP, uridine 5'-triphosphate (UTP), and uridine 5'-diphosphate (UDP), which are released from cells, act as intercellular signaling molecules by activating purinergic P2X and P2Y receptors (purinergic signaling). Recently, I have suggested these extracellular nucleotides may be novel mediators of a radiation-induced bystander effect, because our recent studies indicated that purinergic signaling is involved in important cellular responses to radiation. Our data indicate that ionizing irradiation causes activation of the transient receptor potential melastatin type 2 (TRPM2) channel, and then ATP is released from cells through the anion channel or connexin43 hemichannel mediated by the activation of a P2X7 receptor. The released nucleotides activate P2Y6 and P2Y12 receptors, which are involved in the DNA damage response after irradiation. Activation of the P2Y6 receptor is also involved in radiation-induced activation of the epithelial growth factor receptor-extracellular signal regulated protein kinase (EGFR-ERK)1/2 pathway and subsequent nuclear translocation of EGFR, which plays a role in DNA repair. Further, the induction of an antioxidant after irradiation is also mediated by the activation of the P2Y receptor. In conclusion, purinergic signaling could play an important role in the protective cellular response to ionizing irradiation.

Non-targeted effects and radiation-induced carcinogenesis: a review

Exposure to ionising radiation is clearly associated with an increased risk of developing some types of cancer. However, the contribution of non-targeted effects to cancer development after exposure to ionising radiation is far less clear. The currently used cancer risk model by the international radiation protection community states that any increase in radiation exposure proportionately increases the risk of developing cancer. However, this stochastic cancer risk model does not take into account any contribution from non-targeted effects. Nor does it consider the possibility of a bystander mechanism in the induction of genomic instability. This paper reviews the available evidence to date for a possible role for non-targeted effects to contribute to cancer development after exposure to ionising radiation. An evolution in the understanding of the mechanisms driving non-targeted effects after exposure to ionising radiation is critical to determine the true contribution of non-targeted effects on the risk of developing cancer. Such an evolution will likely only be achievable through coordinated multidisciplinary teams combining several fields of study including: genomics, proteomics, cell biology, molecular epidemiology, and traditional epidemiology.

Effects of Charged Particles on Human Tumor Cells

The use of charged particle therapy in cancer treatment is growing rapidly, in large part because the exquisite dose localization of charged particles allows for higher radiation doses to be given to tumor tissue while normal tissues are exposed to lower doses and decreased volumes of normal tissues are irradiated. In addition, charged particles heavier than protons have substantial potential clinical advantages because of their additional biological effects, including greater cell killing effectiveness, decreased radiation resistance of hypoxic cells in tumors, and reduced cell cycle dependence of radiation response. These biological advantages depend on many factors, such as endpoint, cell or tissue type, dose, dose rate or fractionation, charged particle type and energy, and oxygen concentration. This review summarizes the unique biological advantages of charged particle therapy and highlights recent research and areas of particular research needs, such as quantification of relative biological effectiveness (RBE) for various tumor types and radiation qualities, role of genetic background of tumor cells in determining response to charged particles, sensitivity of cancer stem-like cells to charged particles, role of charged particles in tumors with hypoxic fractions, and importance of fractionation, including use of hypofractionation, with charged particles.

Systemic mechanisms and effects of ionizing radiation: A new 'old' paradigm of how the bystanders and distant can become the players

Exposure of cells to any form of ionizing radiation (IR) is expected to induce a variety of DNA lesions, including double strand breaks (DSBs), single strand breaks (SSBs) and oxidized bases, as well as loss of bases, i.e., abasic sites. The damaging potential of IR is primarily related to the generation of electrons, which through their interaction with water produce free radicals. In their turn, free radicals attack DNA, proteins and lipids. Damage is induced also through direct deposition of energy. These types of IR interactions with biological materials are collectively called 'targeted effects', since they refer only to the irradiated cells. Earlier and sometimes 'anecdotal' findings were pointing to the possibility of IR actions unrelated to the irradiated cells or area, i.e., a type of systemic response with unknown mechanistic basis. Over the last years, significant experimental evidence has accumulated, showing a variety of radiation effects for 'out-of-field' areas (non-targeted effects-NTE). The NTE involve the release of chemical and biological mediators from the 'in-field' area and thus the communication of the radiation insult via the so called 'danger' signals. The NTE can be separated in two major groups: bystander and distant (systemic). In this review, we have collected a detailed list of proteins implicated in either bystander or systemic effects, including the clinically relevant abscopal phenomenon, using improved text-mining and bioinformatics tools from the literature. We have identified which of these genes belong to the DNA damage response and repair pathway (DDR/R) and made protein-protein interaction (PPi) networks. Our analysis supports that the apoptosis, TLR-like and NOD-like receptor signaling pathways are the main pathways participating in NTE. Based on this analysis, we formulate a biophysical hypothesis for the regulation of NTE, based on DNA damage and apoptosis gradients between the irradiation point and various distances corresponding to bystander (5mm) or distant effects (5cm). Last but not least, in order to provide a more realistic support for our model, we calculate the expected DSB and non-DSB clusters along the central axis of a representative 200.6MeV pencil beam calculated using Monte Carlo DNA damage simulation software (MCDS) based on the actual beam energy-to-depth curves used in therapy.

Key mechanisms involved in ionizing radiation-induced systemic effects. A current review

Organisms respond to physical, chemical and biological threats by a potent inflammatory response, aimed at preserving tissue integrity and restoring tissue homeostasis and function. Systemic effects in an organism refer to an effect or phenomenon which originates at a specific point and can spread throughout the body affecting a group of organs or tissues. Ionizing radiation (IR)-induced systemic effects arise usually from a local exposure of an organ or part of the body. This stress induces a variety of responses in the irradiated cells/tissues, initiated by the DNA damage response and DNA repair (DDR/R), apoptosis or immune response, including inflammation. Activation of this IR-response (IRR) system, especially at the organism level, consists of several subsystems and exerts a variety of targeted and non-targeted effects. Based on the above, we believe that in order to understand this complex response system better one should follow a 'holistic' approach including all possible mechanisms and at all organization levels. In this review, we describe the current status of knowledge on the topic, as well as the key molecules and main mechanisms involved in the 'spreading' of the message throughout the body or cells. Last but not least, we discuss the danger-signal mediated systemic immune effects of radiotherapy for the clinical setup.