Radiation-induced bystander effects: past history and future directions

Abscopal Effects, Clastogenic Effects and Bystander Effects: 70 Years of Non-Targeted Effects of Radiation

In vitro and in vivo observations accumulated over several decades have firmly shown that the biological effects of ionizing radiation can spread from irradiated cells/tissues to non-targeted cells/tissues. Redox-modulated intercellular communication mechanisms that include a role for secreted factors and gap junctions, can mediate these non-targeted effects. Clearly, the expression of such effects and their transmission to progeny cells has implications for issues related to radiation protection. Their elucidation is also relevant towards enhancing the efficacy of cancer radiotherapy and reducing its impact on the development of normal tissue toxicities. In addition, the study of non-targeted effects is pertinent to our basic understanding of intercellular communications under conditions of oxidative stress. This review will trace the history of non-targeted effects of radiation starting with early reports of abscopal effects which described radiation induced effects in tissues distant from the site of radiation exposure. A related effect involved the production of clastogenic factors in plasma following irradiation which can induce chromosome damage in unirradiated cells. Despite these early reports suggesting non-targeted effects of radiation, the classical paradigm that a direct deposition of energy in the nucleus was required still dominated. This paradigm was challenged by papers describing radiation induced bystander effects. This review will cover mechanisms of radiation-induced bystander effects and the potential impacts on radiation protection and radiation therapy.

AAPM Task Group Report 267: A joint AAPM GEC-ESTRO report on biophysical models and tools for the planning and evaluation of brachytherapy

Brachytherapy utilizes a multitude of radioactive sources and treatment techniques that often exhibit widely different spatial and temporal dose delivery patterns. Biophysical models, capable of modeling the key interacting effects of dose delivery patterns with the underlying cellular processes of the irradiated tissues, can be a potentially useful tool for elucidating the radiobiological effects of complex brachytherapy dose delivery patterns and for comparing their relative clinical effectiveness. While the biophysical models have been used largely in research settings by experts, it has also been used increasingly by clinical medical physicists over the last two decades. A good understanding of the potentials and limitations of the biophysical models and their intended use is critically important in the widespread use of these models. To facilitate meaningful and consistent use of biophysical models in brachytherapy, Task Group 267 (TG-267) was formed jointly with the American Association of Physics in Medicine (AAPM) and The Groupe Européen de Curiethérapie and the European Society for Radiotherapy & Oncology (GEC-ESTRO) to review the existing biophysical models, model parameters, and their use in selected brachytherapy modalities and to develop practice guidelines for clinical medical physicists regarding the selection, use, and interpretation of biophysical models. The report provides an overview of the clinical background and the rationale for the development of biophysical models in radiation oncology and, particularly, in brachytherapy; a summary of the results of literature review of the existing biophysical models that have been used in brachytherapy; a focused discussion of the applications of relevant biophysical models for five selected brachytherapy modalities; and the task group recommendations on the use, reporting, and implementation of biophysical models for brachytherapy treatment planning and evaluation. The report concludes with discussions on the challenges and opportunities in using biophysical models for brachytherapy and with an outlook for future developments.

Application of Stem Cells Shows Antiinflammatory Effect in an Irradiated Random Pattern Flap Model

BACKGROUND

In reconstructive surgery, local flaps might develop tissue necrosis or partial flap loss especially after previous irradiation, which may be necessary in many tumor entities. The application of stem cells seems promising to improve flap perfusion and might be a possible solution to optimize flap survival.

METHODS

Twenty rats received harvesting of bilateral random pattern fasciocutaneous flaps. The right flaps received 20 Gy ionizing radiation 4 weeks prior to the surgery, while the left flaps served as the non-irradiated control. After flap harvest, four different stem cell mixtures (5 × 106 ASC, ASC-HUVEC, MSC, MSC-HUVEC) were applied under both right and left flaps using 1 mL fibrin glue as the delivery vehicle. Flap size and its necrotic area were examined clinically. Two weeks after the surgery, HE staining and immunohistochemical staining for CD68 and ERG, as well as PCR analysis (Interleukin 6, HIF-1α and VEGF), were performed.

RESULTS

Application of ASCs, ASCs-HUVECs and MSCs resulted in a lower number of CD68-stained cells compared to the no cell group. The expression of Hif1α was higher in the ASC group compared to those in the MSC and previously treated no cell groups. Treatment with MSCs and MSCs-HUVECs prevented shrinking of the flaps in this series.

CONCLUSION

Application of ASCs, MSCs and ASCs-HUVECs was shown to have an antiinflammatory effect. Treatment with MSCs and MSCs-HUVECs can prevent early shrinking of the flaps.

In Vitro Antimicrobial Photodynamic Therapy for Pseudomonas aeruginosa (P. aeruginosa) and methicillin-resistant Staphylococcus aureus (MRSA) Inhibition Using a Green Light Source

Photodynamic therapy (PDT) has been based on using photosensitizers (PS) and applying light of a specific wavelength. When this technique is used for treating infections, it is known as antimicrobial photodynamic therapy (aPDT). Currently, the use of lighting sources for in vitro studies using aPDT is generally applied in multiwell cell culture plates; however, depending on the lighting arrangement, there are usually errors in the application of the technique because the light from a well can affect the neighboring wells or it may be that not all the wells are used in the same experiment. In addition, one must be awarded high irradiance values, which can cause unwanted photothermal problems in the studies. Thus, this manuscript presents an in vitro antimicrobial photodynamic therapy for a Pseudomonas aeruginosa (P. aeruginosa) and methicillin-resistant Staphylococcus aureus (MRSA) inhibition study using an arrangement of thermally isolated and independently illuminated green light source systems for eight tubes in vitro aPDT, determining the effect of the following factors: (i) irradiance level, (ii) exposure time, and (iii) Rose Bengal (RB) concentration (used as a PS), registering the Pseudomonas aeruginosa (P. aeruginosa) and methicillin-resistant Staphylococcus aureus (MRSA) inhibition rates. The results show that in the dark, RB had a poor antimicrobial rate for P. aeruginosa, finding the maximum inhibition (2.7%) at 30 min with an RB concentration of 3 µg/mL. However, by applying light in a correct dosage (time × irradiance) and the adequate RB concentration, the inhibition rate increased by over 37%. In the case of MRSA, there was no significant inhibition with RB in complete darkness and, in contrast, the rate was 100% for those experiments that were irradiated.

Nocardia rubra cell-wall skeleton mitigates whole abdominal irradiation-induced intestinal injury via regulating macrophage function

Background

Ionizing radiation (IR)-induced intestinal injury is a major side effect and dose-limiting toxicity in patients receiving radiotherapy. There is an urgent need to identify an effective and safe radioprotectant to reduce radiation-induced intestinal injury. Immunoregulation is considered an effective strategy against IR-induced injury. The purpose of this article was to investigate the protective effect of Nocardia rubra cell wall skeleton (Nr-CWS), an immunomodulator, on radiation-induced intestinal damage and to explore its potential mechanism.

Methods

C57BL/6 J male mice exposed to 12 Gy whole abdominal irradiation (WAI) were examined for survival rate, morphology and function of the intestine and spleen, as well as the gut microbiota, to comprehensively evaluate the therapeutic effects of Nr-CWS on radiation-induced intestinal and splenetic injury. To further elucidate the underlying mechanisms of Nr-CWS-mediated intestinal protection, macrophages were depleted by clodronate liposomes to determine whether Nr-CWS-induced radioprotection is macrophage dependent, and the function of peritoneal macrophages stimulated by Nr-CWS was detected in vitro.

Results

Our data showed that Nr-CWS promoted the recovery of intestinal barrier function, enhanced leucine-rich repeat-containing G protein-coupled receptor 5+ intestinal stem cell survival and the regeneration of intestinal epithelial cells, maintained intestinal flora homeostasis, protected spleen morphology and function, and improved the outcome of mice exposed to 12 Gy WAI. Mechanistic studies indicated that Nr-CWS recruited macrophages to reduce WAI-induced intestinal damage. Moreover, macrophage depletion by clodronate liposomes blocked Nr-CWS-induced radioprotection. In vitro, we found that Nr-CWS activated the nuclear factor kappa-B signaling pathway and promoted the phagocytosis and migration ability of peritoneal macrophages.

Conclusions

Our study suggests the therapeutic effect of Nr-CWS on radiation-induced intestinal injury, and provides possible therapeutic strategy and potential preventive and therapeutic drugs to alleviate it.

Acute Genetic Damage Induced by Ethanol and Corticosterone Seems to Modulate Hippocampal Astrocyte Signaling

Astrocytes maintain CNS homeostasis but also critically contribute to neurological and psychiatric disorders. Such functional diversity implies an extensive signaling repertoire including extracellular vesicles (EVs) and nanotubes (NTs) that could be involved in protection or damage, as widely shown in various experimental paradigms. However, there is no information associating primary damage to the astrocyte genome, the DNA damage response (DDR), and the EV and NT repertoire. Furthermore, similar studies were not performed on hippocampal astrocytes despite their involvement in memory and learning processes, as well as in the development and maintenance of alcohol addiction. By exposing murine hippocampal astrocytes to 400 mM ethanol (EtOH) and/or 1 μM corticosterone (CTS) for 1 h, we tested whether the induced DNA damage and DDR could elicit significant changes in NTs and surface-attached EVs. Genetic damage and initial DDR were assessed by immunolabeling against the phosphorylated histone variant H2AX (γH2AX), DDR-dependent apoptosis by BAX immunoreactivity, and astrocyte activation by the glial acidic fibrillary protein (GFAP) and phalloidin staining. Surface-attached EVs and NTs were examined via scanning electron microscopy, and labeled proteins were analyzed via confocal microscopy. Relative to controls, astrocytes exposed to EtOH, CTS, or EtOH+CTS showed significant increases in nuclear γlH2AX foci, nuclear and cytoplasmic BAX signals, and EV frequency at the expense of the NT amount, mainly upon EtOH, without detectable signs of morphological reactivity. Furthermore, the largest and most complex EVs originated only in DNA-damaged astrocytes. Obtained results revealed that astrocytes exposed to acute EtOH and/or CTS preserved their typical morphology but presented severe DNA damage, triggered canonical DDR pathways, and early changes in the cell signaling mediated by EVs and NTs. Further deepening of this initial morphological and quantitative analysis is necessary to identify the mechanistic links between genetic damage, DDR, cell-cell communication, and their possible impact on hippocampal neural cells.

The COX-2/PGE2 Response Pathway Upregulates Radioresistance in A549 Human Lung Cancer Cells through Radiation-Induced Bystander Signaling

This study aimed to determine the mechanism underlying the modulation of radiosensitivity in cancer cells by the radiation-induced bystander effect (RIBE). We hypothesized that the RIBE mediates cyclooxygenase-2 (COX-2) and its metabolite prostaglandin E2 (PGE2) in elevating radioresistance in unirradiated cells. In this study, we used the SPICE-QST microbeam irradiation system to target 0.07-0.7% cells by 3.4-MeV proton microbeam in the cell culture sample, such that most cells in the dish became bystander cells. Twenty-four hours after irradiation, we observed COX-2 protein upregulation in microbeam-irradiated cells compared to that of controls. Additionally, 0.29% of the microbeam-irradiated cells exhibited increased cell survival and a reduced micronucleus rate against X-ray irradiation compared to that of non-microbeam irradiated cells. The radioresistance response was diminished in both cell groups with the hemichannel inhibitor and in COX-2-knockout cells under cell-to-cell contact and sparsely distributed conditions. The results indicate that the RIBE upregulates the cell radioresistance through COX-2/PGE2 intercellular responses, thereby contributing to issues, such as the risk of cancer recurrence.

The Influence of Different Irradiation Regimens on Inflammation and Vascularization in a Random-Pattern Flap Model

BACKGROUND

Irradiation plays an important role in the oncological treatment of various tumor entities. The aim of the study was to investigate the influence of different irradiation regimens on random-pattern flaps at the molecular and histopathological levels.

METHODS

Twenty-five rats underwent harvesting of bilateral random-pattern fasciocutaneous flaps. The right flaps received irradiation, while the left flaps served as non-irradiated intraindividual controls. Five rats served as a non-irradiated control group. Four different irradiation regimens with give rats each were tested: 20 Gy postoperatively, 3 × 12 Gy postoperatively, 20 Gy preoperatively, and 3 × 12 Gy preoperatively. Two weeks after surgery, HE staining and immunohistochemical staining for CD68 and ERG, as well as PCR analysis to detect Interleukin 6, HIF-1α, and VEGF, were performed.

RESULTS

A postoperative cumulative higher dose of irradiation appeared to result in an increase in necrosis, especially in the superficial layers of the flap compared to preoperative or single-stage irradiation. In addition, we observed increased expression of VEGF and HIF-1α in all irradiation groups.

CONCLUSION

Even though no statistically significant differences were found between the different groups, there was a tendency for fractional postoperative irradiation with a higher total dose to have a more harmful effect compared to preoperative or single-dose irradiation.

Understanding the Photodynamic Therapy Induced Bystander and Abscopal Effects: A Review

Photodynamic therapy (PDT) is a clinically approved minimally/non-invasive treatment modality that has been used to treat various conditions, including cancer. The bystander and abscopal effects are two well-documented significant reactions involved in imparting long-term systemic effects in the field of radiobiology. The PDT-induced generation of reactive oxygen and nitrogen species and immune responses is majorly involved in eliciting the bystander and abscopal effects. However, the results in this regard are unsatisfactory and unpredictable due to several poorly elucidated underlying mechanisms and other factors such as the type of cancer being treated, the irradiation dose applied, the treatment regimen employed, and many others. Therefore, in this review, we attempted to summarize the current knowledge regarding the non-targeted effects of PDT. The review is based on research published in the Web of Science, PubMed, Wiley Online Library, and Google Scholar databases up to June 2023. We have highlighted the current challenges and prospects in relation to obtaining clinically relevant robust, reproducible, and long-lasting antitumor effects, which may offer a clinically viable treatment against tumor recurrence and metastasis. The effectiveness of both targeted and untargeted PDT responses and their outcomes in clinics could be improved with more research in this area.

Stereotactic Arrhythmia Radioablation Treatment of Ventricular Tachycardia: Current Technology and Evolving Indications

Ventricular tachycardia in patients with structural heart disease is a significant cause of morbidity and mortality. According to current guidelines, cardioverter defibrillator implantation, antiarrhythmic drugs, and catheter ablation are established therapies in the management of ventricular arrhythmias but their efficacy is limited in some cases. Sustained ventricular tachycardia can be terminated by cardioverter-defibrillator therapies although shocks in particular have been demonstrated to increase mortality and worsen patients' quality of life. Antiarrhythmic drugs have important side effects and relatively low efficacy, while catheter ablation, even if it is actually an established treatment, is an invasive procedure with intrinsic procedural risks and is frequently affected by patients' hemodynamic instability. Stereotactic arrhythmia radioablation for ventricular arrhythmias was developed as bail-out therapy in patients unresponsive to traditional treatments. Radiotherapy has been mainly applied in the oncological field, but new current perspectives have developed in the field of ventricular arrhythmias. Stereotactic arrhythmia radioablation provides an alternative non-invasive and painless therapeutic strategy for the treatment of previously detected cardiac arrhythmic substrate by three-dimensional intracardiac mapping or different tools. Since preliminary experiences have been reported, several retrospective studies, registries, and case reports have been published in the literature. Although, for now, stereotactic arrhythmia radioablation is considered an alternative palliative treatment for patients with refractory ventricular tachycardia and no other therapeutic options, this research field is currently extremely promising.

Investigation of presence and impact of radiation-induced bystander effect in Acheta domesticus

PURPOSE

Radiation-induced bystander effect (RIBE), a non-targeted effect of ionizing radiation in which non-irradiated individuals behave as if they have been irradiated after interactions with irradiated individuals, has been well documented in vertebrates. However, little research has been done investigating RIBE in terrestrial insects, this paucity of invertebrate RIBE leads to lack of knowledge on invertebrates living in fallout and exclusion zones. This paper aims to better understand the impacts of RIBE on terrestrial insects.Methods and materials: House crickets who have interacted with irradiated crickets were examined to investigate population effects of ionizing radiation exposure to better understand RIBE in insects.

RESULTS

The results demonstrated RIBE in crickets and found that cohabitated males had higher growth rate (mg/day) when compared to non-cohabitated males. Further, cohabitated males and females matured significantly faster with no significant difference in maturation weight than non-cohabitated populations. Experiment with adult irradiated crickets found saturability of bystander signals and similar shifts in maturation parameters. These results highlight that bystander signals can impacted development and maturation in crickets.

CONCLUSION

Given long-term impacts of RIBE in insects, these results may have significant implications for interactions between insects inhabiting fringe nuclear exclusion zones and those outside of it.

Main radiation pathways in the landscape of Armenia

PURPOSE

To investigate sources, accumulation, and vertical migration of radionuclides in Armenia, and their impact on biota.

CONCLUSIONS

This review describes the radiation status in the landscape of Armenia and features of the impact of natural and human-generated radiation on human and non-human biotas, according to studies of Armenian scientists carried out since the middle of the last century. The mountain landscape demonstrates the diversity, speciation, and radioresistance of the biota, which arise under radiation exposure in a variable environment. Although the effects of radiation have been described for a long time, some of them require further study. It is important to present the data collected in order to produce a base line for future studies of radiation effects and interactions with other stressors caused by climate change.

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.

Radiation responses of cancer and normal cells to split dose fractions with uniform and grid fields: increasing the therapeutic ratio

PURPOSE

Radiation treatment of cancer is usually delivered in a prescribed sequence of dose fractions within which the dependence of dose on time is determined by the treatment plan. New techniques, such as stereotactic body radiation therapy (SBRT) and image guided radiation therapy (IGRT) have been introduced with the motivation of improving therapeutic outcomes, with the consequence that the time dependence of the dose within a fraction is modified. Here, we test whether an increased toxicity to cancer cells arises when a radiation treatment fraction is delivered in two equal parts, allowing time for the expression of factors, for example, RONS and cytokines, in response to the first dose which may sensitize cells to the second dose. A medium time delay between 15 and 60 minutes is proposed to allow factors to be expressed before repair takes place. A grid field is used to enhance diffusion of the factors.

MATERIALS AND METHODS

The cell lines used in the study were two prostate cancers (LNCaP and DU 145), a normal prostate (PNT1A), a non-small cell lung cancer (NCI-H460), and a glioma (Hs 683). Uniform or spatially modulated grid fields, delivering the same mean dose, were used. The results for the clonogenic survival fractions were grouped into a 'short' delay (under 10 minutes) and a 'medium' delay (between 15 and 60 minutes).

RESULTS

The medium delay with a grid field yielded a significant increase in toxicity for the four cancer cell lines. The medium delay with a uniform field gave a significant increase in toxicity for the two prostate cancer cell lines. A highly significant increase was found in the therapeutic ratio, defined as the ratio of the survival of prostate normal to prostate cancer cells.

CONCLUSIONS

The findings show that the intra-fractional dose schedule with medium time delay offers an opportunity to increase the toxicity of radiation to cancer cells, relative to a single radiation delivery. For all cancer cell lines, a grid field gives a greater toxic effect than a uniform field. The split dose treatment offers an increase in cancer toxicity while preserving normal cells, improving the outcomes of a treatment.

Involvement of miRNAs in cellular responses to radiation

PURPOSE

Exposure of living cells to ionizing radiation has different consequences, depending on the dose and cell type. Changes of gene expression at the level of transcription and translation, including those regulated by microRNAs (miRNAs), play a role in intrinsic radiosensitivity of different cells and define their fate, survival or death. The aim of our work was to examine how ionizing radiation may influence the expression of genes regulated by different miRNAs and miRNA biogenesis.

MATERIALS AND METHODS

The work was performed on cultured human melanoma Me45 cells, transiently transfected with plasmids containing Renilla luciferase reporter gene targeted by miRNAs Let-7, miR-21 or miR-24. The levels of reporter mRNAs and mRNAs coding for proteins participating in miRNA biogenesis were assayed at different time points in irradiated and non-irradiated cells using RT-qPCR, and reporter protein by luciferase activity assays. MiRNA-targeted motifs in mRNAs coding for proteins engaged in miRNA biogenesis were extracted from the miRTarBase database.

RESULTS

Messenger RNA and protein levels of transfected luciferase genes fluctuated in time in patterns which depended on the type of miRNA regulation and changed upon irradiation of the cells. The average levels of reporter mRNAs were higher in irradiated cells, whereas the levels of proteins changed in either direction. Radiation also influenced the levels of miRNAs and the expression of genes engaged in their biogenesis suggesting that the changes in gene expression following ionizing radiation result mainly from these changes in expression of genes regulating miRNA biogenesis and the influence of miRNA on mRNA translation.

CONCLUSIONS

Currently, the responses of cells to ionizing radiation are mainly ascribed to changes of their redox conditions and increased intracellular levels of ROS, but the experiments described here suggest that a further important factor is modulation of translation through changes in biogenesis and levels of miRNAs.

Preventive effect of sanguinarine on intestinal injury in mice exposed to whole abdominal irradiation

Intestinal injury is one of the major side effects that are induced by medical radiation exposure, and has limited effective therapies. In this study, we investigated the beneficial effects of sanguinarine (SAN) on intestinal injury induced by ionizing radiation (IR) both in vitro and in vivo. Mice were exposed to whole abdominal irradiation (WAI) to mimic clinical scenarios. SAN was injected intraperitoneally to mitigate IR-induced injury. Histological examination was performed to assess the tissue injuries of the spleen and small intestine. A small intestinal epithelial cell line-6 (IEC-6) was analyzed for its viability and apoptosis in vitro under different treatments. Inflammation-related pathways and serum inflammatory cytokines were detected via Western blot analysis and ELISA, respectively. High-throughput sequencing was used to characterize the gut microbiota profile. High-performance liquid chromatography was performed to assess short-chain fatty acid contents in the colon. In vitro, SAN pretreatment protected cell viability and reduced apoptosis in IEC-6 cells. In vivo, SAN pretreatment protected immune organs, alleviated intestinal injury, and promoted intestinal recovery. SAN also reduced the levels of inflammatory cytokines, suppressed high mobility group box 1 (HMGB1)/ Toll-like receptor 4 (TLR4) pathway activation, and modulated gut microbiota composition. Our findings demonstrate that the beneficial properties of SAN alleviated intestinal radiation injury. Thus, SAN represents a therapeutic option for protecting against IR-induced intestinal injury in preclinical settings.

Current Strategies for Cancer Cell-Derived Extracellular Vesicles for Cancer Therapy

Cancer cell-derived extracellular vesicles (CEVs), a novel type of therapeutic agent in cancer treatment, can be prepared from the autocrine secretion of various cancer cells, the direct extraction of cancer cells and the combination of cancer cell-derived membranes with advanced materials. With various bioactive molecules, exosomes are produced by cells for intercellular communication. Although cancer cell-derived exosomes are known to inhibit tumor apoptosis and promote the progression of cancer, researchers have developed various innovative strategies to prepare anti-tumor vesicles from cancer cells. With current strategies for anti-tumor vesicles, four different kinds of CEVs are classified including irradiated CEVs, advanced materials combined CEVs, chemotherapeutic drugs loaded CEVs and genetically engineered CEVs. In this way, CEVs can not only be the carriers for anti-tumor drugs to the target tumor area but also act as immune-active agents. Problems raised in the strategies mainly concerned with the preparation, efficacy and application. In this review, we classified and summarized the current strategies for utilizing the anti-tumor potential of CEVs. Additionally, the challenges and the prospects of this novel agent have been discussed.

A Proteomic Study Suggests Stress Granules as New Potential Actors in Radiation-Induced Bystander Effects

Besides the direct effects of radiations, indirect effects are observed within the surrounding non-irradiated area; irradiated cells relay stress signals in this close proximity, inducing the so-called radiation-induced bystander effect. These signals received by neighboring unirradiated cells induce specific responses similar with those of direct irradiated cells. To understand the cellular response of bystander cells, we performed a 2D gel-based proteomic study of the chondrocytes receiving the conditioned medium of low-dose irradiated chondrosarcoma cells. The conditioned medium was directly analyzed by mass spectrometry in order to identify candidate bystander factors involved in the signal transmission. The proteomic analysis of the bystander chondrocytes highlighted 20 proteins spots that were significantly modified at low dose, implicating several cellular mechanisms, such as oxidative stress responses, cellular motility, and exosomes pathways. In addition, the secretomic analysis revealed that the abundance of 40 proteins in the conditioned medium of 0.1 Gy irradiated chondrosarcoma cells was significantly modified, as compared with the conditioned medium of non-irradiated cells. A large cluster of proteins involved in stress granules and several proteins involved in the cellular response to DNA damage stimuli were increased in the 0.1 Gy condition. Several of these candidates and cellular mechanisms were confirmed by functional analysis, such as 8-oxodG quantification, western blot, and wound-healing migration tests. Taken together, these results shed new lights on the complexity of the radiation-induced bystander effects and the large variety of the cellular and molecular mechanisms involved, including the identification of a new potential actor, namely the stress granules.

The Rapidly-Developing Area of Radiocardiology: Principles, Complications and Applications of Radiotherapy on the Heart

Ventricular arrhythmias are the leading cause of sudden cardiac death. Current treatment strategies for VT, including antiarrhythmic drugs and catheter ablation, have limited efficacy in patients with structural heart disease. Non-invasive ablation with the use of externally applied radiation (cardiac radio-ablation) has emerged as a promising and novel approach to treating recurrent VTs. However, the heart is generally an "organ at risk" for radiation treatments, such that very little is known on the effects of radiotherapy on cardiac ultrastructure and electrophysiological properties. Furthermore, there has been limited interaction between the fields of cardiology and radiation oncology and physics. The advent of cardiac radio-ablation will undoubtedly increase interactions between cardiologists, cardiac electrophysiologists, radiation oncologists and physicists There is an important knowledge gap separating these specialties while scientific developments, technical optimization and improvements are dependent on intense multidisciplinary collaboration. This manuscript seeks to review the basic of radiation physics and biology for cardiovascular specialists in an effort to facilitate constructive scientific and clinical collaborations to improve patient outcomes.

Quantification of Differential Response of Tumour and Normal Cells to Microbeam Radiation in the Absence of FLASH Effects

Microbeam radiotherapy (MRT) is a preclinical method of delivering spatially-fractionated radiotherapy aiming to improve the therapeutic window between normal tissue complication and tumour control. Previously, MRT was limited to ultra-high dose rate synchrotron facilities. The aim of this study was to investigate in vitro effects of MRT on tumour and normal cells at conventional dose rates produced by a bench-top X-ray source. Two normal and two tumour cell lines were exposed to homogeneous broad beam (BB) radiation, MRT, or were separately irradiated with peak or valley doses before being mixed. Clonogenic survival was assessed and compared to BB-estimated surviving fractions calculated by the linear-quadratic (LQ)-model. All cell lines showed similar BB sensitivity. BB LQ-model predictions exceeded the survival of cell lines following MRT or mixed beam irradiation. This effect was stronger in tumour compared to normal cell lines. Dose mixing experiments could reproduce MRT survival. We observed a differential response of tumour and normal cells to spatially fractionated irradiations in vitro, indicating increased tumour cell sensitivity. Importantly, this was observed at dose rates precluding the presence of FLASH effects. The LQ-model did not predict cell survival when the cell population received split irradiation doses, indicating that factors other than local dose influenced survival after irradiation.

A Case of Symptomatic Cerebral Radiation Necrosis for an Extra-Cranial Neoplasm from Conventional Radiotherapy With Concurrent Immunotherapy

Cerebral radiation necrosis (RN) is a known complication of brain radiotherapy (RT). The incidence rate of RN varies with the total dose, dose fractionation, and radiotherapy modality. Concurrent treatment with immunotherapy can increase the risk factors for developing RN through a synergistic mechanism. Here, we describe a patient who developed cerebral RN after receiving conventional RT to an extra-cranial site, while he was receiving immune checkpoint inhibitor (ICI) therapy.

Radiation-induced bystander effects impair transplanted human hematopoietic stem cells via oxidative DNA damage

Total body irradiation (TBI) is commonly used in host conditioning regimens for human hematopoietic stem cell (HSC) transplantation to treat various hematological disorders. Exposure to TBI not only induces acute myelosuppression and immunosuppression, but also injures the various components of the HSC niche in recipients. Our previous study demonstrated that radiation-induced bystander effects (RIBE) of irradiated recipients decreased the long-term repopulating ability of transplanted mouse HSCs. However, RIBE on transplanted human HSCs have not been studied. Here, we report that RIBE impaired the long-term hematopoietic reconstitution of human HSCs as well as the colony-forming ability of human hematopoietic progenitor cells (HPCs). Our further analyses revealed that the RIBE-affected human hematopoietic cells showed enhanced DNA damage responses, cell-cycle arrest, and p53-dependent apoptosis, mainly because of oxidative stress. Moreover, multiple antioxidants could mitigate these bystander effects, though at different efficacies in vitro and in vivo. Taken together, these findings suggest that RIBE impair human HSCs and HPCs by oxidative DNA damage. This study provides definitive evidence for RIBE on transplanted human HSCs and further justifies the necessity of conducting clinical trials to evaluate different antioxidants to improve the efficacy of HSC transplantation for the patients with hematological or nonhematological disorders.

Preclinical Studies and Clinical Prospects of Wharton's Jelly-Derived MSC for Treatment of Acute Radiation Syndrome

Purpose of Review

Wharton’s jelly-derived mesenchymal stem cells (WJ-MSCs) have received widespread attention from researchers owing to the remarkable benefits offered by these cells over other stem cells. The primitive nature of WJ-MSCs, ease of isolation, differentiation ability, and immuno-modulatory nature make these cells superior to bone marrow MSCs and ideal to treat various human ailments. This review explores ability of WJ-MSCs to mitigate acute radiation syndrome caused by planned or unplanned radiation exposure.

Recent Findings

Recent reports suggest that WJ-MSCs home to damaged tissues in irradiated host and mitigate radiation induced damage to radiosensitive tissues such as hematopoietic and gastrointestinal systems. WJ-MSCs and conditioned media were found to protect mice from radiation induced mortality and also prevent radiation dermatitis. Local irradiation-induced lung toxicity in mice was significantly reduced by CXCR4 over-expressing WJ-MSCs.

Summary

Emerging evidences support safety and effectiveness of WJ-MSCs for treatment of acute radiation syndrome and lung injury after planned or accidental exposure. Additionally, conditioned media collected after culturing WJ-MSCs can also be used for mitigation of radiation dermatitis. Clinical translation of these findings would be possible after careful evaluation of resilience, effectiveness, and molecular mechanism of action of xenogeneic WJ-MSCs in non-human primates.

Chk1 inhibition induces a DNA damage bystander effect in cocultured tumour cells

Inhibitors of Chk1 kinase, a key effector of the DNA damage response pathway, are currently undergoing Phase 1 and 2 clinical trials as single agents and in combination with cytotoxic chemotherapy. Understanding the biological effects of Chk1 inhibitors on cancer cells is critical for their continued clinical development. Treatment of adherent HT29 or HCC1937 cancer cells or suspension Jurkat or THP1 cells with a Chk1 inhibitor increased γH2AX in these cells. Chk1i pre-treated HCC1937 or HT29 cells resulted in γH2AX induction in cocultured Jurkat or THP1 cells despite these cells never being treated with a Chk1i. Pre-treatment of HT29 cells with camptothecin or gemcitabine followed by a Chk1i increased the DNA damage bystander effect in naïve cocultured THP1 cells compared to camptothecin or gemcitabine alone. This bystander effect appeared to occur through soluble factors via ATR, ATM, and DNA-PKcs activation in the bystander cells. Chk1 silencing by siRNA in HCC1937 or HT29 cells induced a DNA damage bystander effect in cocultured THP1 cells. However, this bystander effect induced by siRNA appeared mechanistically different to that induced by the Chk1 inhibitor. This work suggests that a Chk1 inhibitor-induced bystander effect may increase the clinical effectiveness of Chk1 inhibitors by inducing additional DNA damage or replication stress in cancer cells not directly exposed to the inhibitor. Conversely, it may also contribute to Chk1 inhibitor toxicity by increasing DNA damage in non-tumour cells.

The role of connexin proteins and their channels in radiation-induced atherosclerosis

Radiotherapy is an effective treatment for breast cancer and other thoracic tumors. However, while high-energy radiotherapy treatment successfully kills cancer cells, radiation exposure of the heart and large arteries cannot always be avoided, resulting in secondary cardiovascular disease in cancer survivors. Radiation-induced changes in the cardiac vasculature may thereby lead to coronary artery atherosclerosis, which is a major cardiovascular complication nowadays in thoracic radiotherapy-treated patients. The underlying biological and molecular mechanisms of radiation-induced atherosclerosis are complex and still not fully understood, resulting in potentially improper radiation protection. Ionizing radiation (IR) exposure may damage the vascular endothelium by inducing DNA damage, oxidative stress, premature cellular senescence, cell death and inflammation, which act to promote the atherosclerotic process. Intercellular communication mediated by connexin (Cx)-based gap junctions and hemichannels may modulate IR-induced responses and thereby the atherosclerotic process. However, the role of endothelial Cxs and their channels in atherosclerotic development after IR exposure is still poorly defined. A better understanding of the underlying biological pathways involved in secondary cardiovascular toxicity after radiotherapy would facilitate the development of effective strategies that prevent or mitigate these adverse effects. Here, we review the possible roles of intercellular Cx driven signaling and communication in radiation-induced atherosclerosis.

Immunostimulatory Effects of Radiotherapy for Local and Systemic Control of Melanoma: A Review

Recently, modern therapies involving immune checkpoint inhibitors, cytokines, and oncolytic virus have been developed. Because of the limited treatment effect of modern therapy alone, the immunostimulatory effect of radiotherapy attracted increasing attention. The combined use of radiotherapy and modern therapy has been examined clinically and non-clinically, and its effectiveness has been confirmed recently. Because melanomas have high immunogenicity, better therapeutic outcomes are desired when using immunotherapy. However, sufficient therapeutic effects have not yet been achieved. Thus far, radiotherapy has been used only for local control of tumors. Although extremely rare, radiotherapy has also been reported for systemic control, i.e., abscopal effect. This is thought to be due to an antitumor immune response. Therefore, we herein summarize past information on not only the mechanism of immune effects on radiotherapy but also biomarkers reported in case reports on abscopal effects. We also reviewed the animal model suitable for evaluating abscopal effects. These results pave the way for further basic research or clinical studies on new treatment methods for melanoma. Currently, palliative radiation is administered to patients with metastatic melanoma for local control. If it is feasible to provide both systemic and local control, the treatment benefit for the patients is very large.

Ionizing Radiation-Induced Epigenetic Modifications and Their Relevance to Radiation Protection

The present system of radiation protection assumes that exposure at low doses and/or low dose-rates leads to health risks linearly related to the dose. They are evaluated by a combination of epidemiological data and radiobiological models. The latter imply that radiation induces deleterious effects via genetic mutation caused by DNA damage with a linear dose-dependence. This picture is challenged by the observation of radiation-induced epigenetic effects (changes in gene expression without altering the DNA sequence) and of non-linear responses, such as non-targeted and adaptive responses, that in turn can be controlled by gene expression networks. Here, we review important aspects of the biological response to ionizing radiation in which epigenetic mechanisms are, or could be, involved, focusing on the possible implications to the low dose issue in radiation protection. We examine in particular radiation-induced cancer, non-cancer diseases and transgenerational (hereditary) effects. We conclude that more realistic models of radiation-induced cancer should include epigenetic contribution, particularly in the initiation and progression phases, while the impact on hereditary risk evaluation is expected to be low. Epigenetic effects are also relevant in the dispute about possible "beneficial" effects at low dose and/or low dose-rate exposures, including those given by the natural background radiation.

History and current perspectives on the biological effects of high-dose spatial fractionation and high dose-rate approaches: GRID, Microbeam & FLASH radiotherapy

The effects of various forms of ionising radiation are known to be mediated by interactions with cellular and molecular targets in irradiated and in some cases non-targeted tissue volumes. Despite major advances in advanced conformal delivery techniques, the probability of normal tissue complication (NTCP) remains the major dose-limiting factor in escalating total dose delivered during treatment. Potential strategies that have shown promise as novel delivery methods in achieving effective tumour control whilst sparing organs at risk involve the modulation of critical dose delivery parameters. This has led to the development of techniques using high dose spatial fractionation (GRID) and ultra-high dose rate (FLASH) which have translated to the clinic. The current review discusses the historical development and biological basis of GRID, microbeam and FLASH radiotherapy as advanced delivery modalities that have major potential for widespread implementation in the clinic in future years.

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.

The future of radiation-induced abscopal response: beyond conventional radiotherapy approaches

Advances in the immunological pharmaceuticals, such as checkpoint inhibitors and agonists, have positive implications for the future of the radiotherapy abscopal response. A once rare phenomenon, whereby distant nonirradiated tumor sites regressed after radiotherapy alone, may become more common when combined with the immune modulating agents. Radiotherapy can increase neoantigen expression, increased tumor PD-L1 expression, increase MHC class I expression, reverse exhausted CD8 T cells and increase tumor-infiltrating tumors within the tumor microenvironment. These changes in the tumor and the tumor microenvironment after radiotherapy could potentiate responses to anti-CTL-4, anti-PD-L1/PD-1 and other immunotherapy agents. Thus, advances in checkpoint inhibitors have increased interest in re-evaluation of the role of conventional radiotherapy approaches on the immune system. We reviewed newer nonconventional approaches such as SBRT-PATHY, GRID, FLASH, carbon ion and proton therapy and their role in eliciting immune responses. We believe that combining these novel radiation methods may enhance the outcome with the newly US FDA approved immune modulating agents.

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.

Blood Gene Expression Profile Study Revealed the Activation of Apoptosis and p53 Signaling Pathway May Be the Potential Molecular Mechanisms of Ionizing Radiation Damage and Radiation-Induced Bystander Effects

Radiotherapy is an effective treatment for local solid tumors, but the mechanism of damage to human body caused by radiation therapy needs further study. In this study, gene expression profiles of human peripheral blood samples exposed to different doses and rates of ionizing radiation (IR) were used for bioinformatics analysis to investigate the mechanism of IR damage and radiation-induced bystander effect (RIBE). Differentially expressed genes analysis, weighted gene correlation network analysis, functional enrichment analysis, hypergeometric test, gene set enrichment analysis, and gene set variation analysis were applied to analyze the data. Moreover, receiver operating characteristic curve analysis was performed to identify core genes of IR damage. Weighted gene correlation network analysis identified 3 modules associated with IR damage, 2 were positively correlated and 1 was negatively correlated. The analysis showed that the positively correlated modules were significantly involved in apoptosis and p53 signaling pathway, and ESR1, ATM, and MYC were potential transcription factors regulating these modules. Thus, the study suggested that apoptosis and p53 signaling pathway may be the potential molecular mechanisms of IR damage and RIBE, which could be driven by ESR1, ATM, and MYC.

Hadrontherapy Interactions in Molecular and Cellular Biology

The resistance of cancer cells to radiotherapy is a major issue in the curative treatment of cancer patients. This resistance can be intrinsic or acquired after irradiation and has various definitions, depending on the endpoint that is chosen in assessing the response to radiation. This phenomenon might be strengthened by the radiosensitivity of surrounding healthy tissues. Sensitive organs near the tumor that is to be treated can be affected by direct irradiation or experience nontargeted reactions, leading to early or late effects that disrupt the quality of life of patients. For several decades, new modalities of irradiation that involve accelerated particles have been available, such as proton therapy and carbon therapy, raising the possibility of specifically targeting the tumor volume. The goal of this review is to examine the up-to-date radiobiological and clinical aspects of hadrontherapy, a discipline that is maturing, with promising applications. We first describe the physical and biological advantages of particles and their application in cancer treatment. The contribution of the microenvironment and surrounding healthy tissues to tumor radioresistance is then discussed, in relation to imaging and accurate visualization of potentially resistant hypoxic areas using dedicated markers, to identify patients and tumors that could benefit from hadrontherapy over conventional irradiation. Finally, we consider combined treatment strategies to improve the particle therapy of radioresistant cancers.

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.

Radiation-Induced Bystander Effect is Mediated by Mitochondrial DNA in Exosome-Like Vesicles

Exosome-like vesicles (ELV) are involved in mediating radiation-induced bystander effect (RIBE). Here, we used ELV from control cell conditioned medium (CCCM) and from 4 Gy of X-ray irradiated cell conditioned medium (ICCM), which has been used to culture normal human fibroblast cells to examine the possibility of ELV mediating RIBE signals. We investigated whether ELV from 4 Gy irradiated mouse serum mediate RIBE signals. Induction of DNA damage was observed in cells that were treated with ICCM ELV and ELV from 4 Gy irradiated mouse serum. In addition, we treated CCCM ELV and ICCM ELV with RNases, DNases, and proteinases to determine which component of ELV is responsible for RIBE. Induction of DNA damage by ICCM ELV was not observed after treatment with DNases. After treatment, DNA damages were not induced in CCCM ELV or ICCM ELV from mitochondria depleted (ρ0) normal human fibroblast cells. Further, we found significant increase in mitochondrial DNA (mtDNA) in ICCM ELV and ELV from 4 Gy irradiated mouse serum. ELV carrying amplified mtDNA (ND1, ND5) induced DNA damage in treated cells. These data suggest that the secretion of mtDNA through exosomes is involved in mediating RIBE signals.

Radiotherapy in Combination With Cytokine Treatment

Radiotherapy (RT) plays an important role in the management of cancer patients. RT is used in more than 50% of patients during the course of their disease in a curative or palliative setting. In the past decades it became apparent that the abscopal effect induced by RT might be dependent on the activation of immune system, and that the induction of immunogenic cancer cell death and production of danger-associated molecular patterns from dying cells play a major role in the radiotherapy-mediated anti-tumor efficacy. Therefore, the combination of RT and immunotherapy is of a particular interest that is reflected in designing clinical trials to treat patients with various malignancies. The use of cytokines as immunoadjuvants in combination with RT has been explored over the last decades as one of the immunotherapeutic combinations to enhance the clinical response to anti-cancer treatment. Here we review mainly the data on the efficacy of IFN-α, IL-2, IL-2-based immunocytokines, GM-CSF, and TNF-α used in combinations with various radiotherapeutic techniques in clinical trials. Moreover, we discuss the potential of IL-15 and its analogs and IL-12 cytokines in combination with RT based on the efficacy in preclinical mouse tumor models.

Effects of historic radiation dose on the frequency of sex-linked recessive lethals in Drosophila populations following the Chernobyl nuclear accident

Contrary to the effects of high doses of radiation, the effects of low doses of radiation are still being investigated. Low doses and their non-targeted effects in particular are of special interest for researchers. The accident that occurred at the Chernobyl Nuclear Power Plant (NPP) gives researchers the opportunity to view these effects outside of a laboratory environment. For this paper, the relationship between low historic radiation doses and the persistent genetic damage observed in populations of fruit flies (Drosophila melanogaster) around the Chernobyl NPP over 3 years will be investigated. Data from Zainullin et al. (1992) on the frequency of sex-linked recessive lethals (SLRLs) in D. melanogaster around the Chernobyl NPP. To calculate the absorbed historic external dose, a method based on the Gaussian plume model was used to find the external dose from both plume shine and ground shine. The dose attributed to the ground shine dose made a greater contribution to the overall absorbed external historic radiation dose than the plume shine dose. For earlier generations of Drosophila living in the radioactive contaminated sites, the SLRL frequencies appeared to correlate with the dose in a linear no-threshold relationship. The later descendent generations appeared to have developed a radio-adaptive-like response. This work contributes to the understanding of historic dose effects on wildlife health following the accidental release of high mount of radioactive materials into the environment.

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.

Radiation Therapy and its Effects Beyond the Primary Target: An Abscopal Effect

Radiation therapy (RT) has been used for the treatment of various malignancies since decades with curative or palliative intent. RT for primary disease is often used with curative intent while its use in metastatic settings has been essentially palliative. However, in certain malignancies with metastatic disease, RT to primary disease has led to the regression of not only the primary site but also of the metastatic sites, a phenomenon known as "abscopal effect." Keeping in view the positive effects of RT beyond the primary site, we review the clinical utility of RT regarding its abscopal effect.

Bystander Me45 Melanoma Cells Increase Damaging Effect in UVC-irradiated Cells

The aim of our study was to investigate the possible mechanism(s) of the bystander effect induced by UVC light in malignant melanoma Me45 cells that were co-incubated with irradiated cells of the same line. We have found that the UVC band effectively generated apoptosis, premature senescence, single and double DNA strand breaks and reduced clonogenic survival of bystander cells. However, in the feedback response, the bystander cells intensified damage in directly irradiated cells, especially seen at the level of apoptosis and survival of clonogenic cells. Pretreatment of bystander cells with inhibitor of inducible nitric oxide synthase blocks this signaling. It seems that the mediators of this phenomenon produced and secreted by neighboring cells are superoxide, nitric oxide and TGF-β. The reverse deleterious effect caused by cells not exposed to UVC in directly exposed cells is opposed to the protective/rescue effect exerted by the bystander cells in the case of ionizing radiation known in the literature. Whether this opposite adverse effect is a feature of only Me45 melanoma cells or whether it is a general phenomenon occurring between cells of other types exposed to ultraviolet radiation requires further research.

Transgenerational effects of historic radiation dose in pale grass blue butterflies around Fukushima following the Fukushima Dai-ichi Nuclear Power Plant meltdown accident

Low dose radiation effects have been investigated in Chernobyl for many years but there is uncertainty about initial doses received by many animal species. However, the Fukushima Dai-ichi Nuclear Power Plant accident opens an opportunity to study the effects of the initial low historic dose on directly exposed species and their progeny during a time where the contaminating radionuclides are decaying. In this paper, it is proposed that historic acute exposure and its resulting non-targeted effects (NTEs) may be partially involved in the high mortality/abnormality rates seen across generations of pale grass blue butterflies (Zizeeria maha) around Fukushima. Data from Hiyama et al. (2012) on the morphological abnormality frequencies in Z. maha collected around Fukushima and their progeny were used in this paper. Two dose reconstruction methods based on the Gaussian plume model were used to determine the external absorbed dose to the first exposed generation from both ground shine and plume shine. One method involved the use of the dose rate recorded at the time of collection and only took Cs-137 into account. The other involved using release rates and atmospheric conditions to determine the doses and considered Cs-137 and Cs-134. The reconstructed doses were plotted against the mortality rates and abnormality frequencies across generations. The mortality rates of the progeny from irradiated progenitors increased linearly with the increasing historic radiation doses reconstructed using both Cs-137 and Cs-134 sources. Additionally, a higher level of morphological abnormalities was observed in progeny than in the progenitors. The mean abnormality frequencies also increased throughout generations. As these results are a sign of NTEs being involved, it can be suggested that increasing mutation levels across generations may result, in part, from NTEs induced by the initial low dose received by the first exposed generation. However, continual accumulation of mutations over generations in their natural contaminated habitats remains a likely contributor into the observed outcome.

Effect of gamma radiation on the production of bystander signals from three earthworm species irradiated in vivo

The effect of gamma radiation delivered over 24 h on the induction of bystander signals of three earthworm species exposed in vivo was investigated: A. chlorotica, A. caliginosa, and E. tetraedra. Worms were exposed to external gamma irradiation (Co-60 source) for 24 h and samples of head, body, and clitellum were dissected from exposed and control worms and placed in culture medium for 24 h at 19 C. The harvested medium was filtered and assayed for expression of bystander signals using both clonogenic and mitochondrial reporter assays. Different responses were observed in the different species and in the different tissues. A. chlorotica worm-treated reporters show insignificant mitochondrial response for all sections, yet a significant clonogenic reduction in survival for body sections. A. caliginosa worm-treated reporters show a significant mitochondrial response for some sections and insignificant mitochondrial response and insignificant reduction in clonogenic survival for the rest. E. tetraedra worms from a control site show significant evidence of bystander signalling, measured by mitochondrial response in reporter cells, for all sections while those harvested from a contaminated site show insignificant changes in baseline signalling when exposed to the challenge dose. In vivo exposure of earthworm species shows evidence of bystander signalling using two different reporter assays. This effect varied between the different species and tissues. There is also evidence of attenuated bystander signalling in worms harvested from a site contaminated with radiation.

Intra-patient and inter-patient comparisons of DNA damage response biomarkers in Nasopharynx Cancer (NPC): analysis of NCC0901 randomised controlled trial of induction chemotherapy in locally advanced NPC

BACKGROUND

Inter-patient heterogeneity in radiation-induced DNA damage responses is proposed to reflect intrinsic variations in tumour and normal tissue radiation sensitivity, but the prediction of phenotype by a molecular biomarker is influenced by clinical confounders and assay reproducibility. Here, we characterised the intrapatient and inter-patient heterogeneity in biomarkers of DNA damage and repair and radiation-induced apoptosis.

METHODS

We enrolled 85 of 172 patients with locally advanced nasopharynx cancer from a randomised controlled phase II/III trial of induction chemotherapy added to chemo-radiotherapy. G0 blood lymphocytes were harvested from these patients, and irradiated with 1, 4, and 8 Gy ex vivo. DNA damage induction (1 Gy 0.5 h) and repair (4 Gy 24 h) were assessed by duplicate γH2AX foci assays in 50-100 cells. Duplicate FLICA assays performed at 48 h post-8 Gy were employed as surrogate of radiation-induced apoptosis; %FLICA-positive cells were quantified by flow cytometry.

RESULTS

We observed limited intrapatient variation in γH2AX foci and %FLICA readouts; median difference of duplicate foci scores was - 0.37 (IQR = - 1.256-0.800) for 1 Gy 0.5 h and 0.09 (IQR = - 0.685-0.792) for 4 Gy 24 h; ICC of ≥0.80 was observed for duplicate %FLICA0Gy and %FLICA8Gy assays of CD4+ and CD8+ T lymphocytes. As expected, we observed wide inter-patient heterogeneity in both assays that was independent of intrapatient variation and clinical covariates, with the exception of age, which was inversely correlated with %FLICAbackground-corrected (Spearman R = - 0.406, P < 0.001 [CD4+]; R = - 0.220, P = 0.04 [CD8+]). Lastly, an exploratory case-control analysis indicates increased levels of γH2AX foci at 4 Gy 24 h in patients with severe late radiotherapy-induced xerostomia (P = 0.05).

CONCLUSION

Here, we confirmed the technical reproducibility of DNA damage response assays for clinical implementation as biomarkers of clinical radiosensitivity in nasopharynx cancer patients.