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

Intercellular pathways of cancer treatment-related cardiotoxicity and their therapeutic implications: The paradigm of radiotherapy

Advances in cancer therapeutics have improved patient survival rates. However, cancer survivors may suffer from adverse events either at the time of therapy or later in life. Cardiovascular diseases (CVD) represent a clinically important, but mechanistically understudied complication, which interfere with the continuation of best-possible care, induce life-threatening risks, and/or lead to long-term morbidity. These concerns are exacerbated by the fact that targeted therapies and immunotherapies are frequently combined with radiotherapy, which induces durable inflammatory and immunogenic responses, thereby providing a fertile ground for the development of cardiovascular diseases (CVDs). Stressed and dying irradiated cells produce 'danger' signals including, but not limited to, major histocompatibility complexes, cell-adhesion molecules, proinflammatory cytokines, and damage-associated molecular patterns. These factors activate intercellular signaling pathways which have potentially detrimental effects on the heart tissue homeostasis. Herein, we present the clinical crosstalk between cancer and heart diseases, describe how it is potentiated by cancer therapies, and highlight the multifactorial nature of the underlying mechanisms. We particularly focus on radiotherapy, as a case known to often induce cardiovascular complications even decades after treatment. We provide evidence that the secretome of irradiated tumors entails factors that exert systemic, remote effects on the cardiac tissue, potentially predisposing it to CVDs. We suggest how diverse disciplines can utilize pertinent state-of-the-art methods in feasible experimental workflows, to shed light on the molecular mechanisms of radiotherapy-related cardiotoxicity at the organismal level and untangle the desirable immunogenic properties of cancer therapies from their detrimental effects on heart tissue. Results of such highly collaborative efforts hold promise to be translated to next-generation regimens that maximize tumor control, minimize cardiovascular complications, and support quality of life in cancer survivors.

Integrating evolutionarily conserved mechanism of response to radiation for exploring novel Caenorhabditis elegans radiation-responsive genes for estimation of radiation dose associated with spaceflight

During space exploration, space radiation is widely recognized as an inescapable perilous stressor, owing to its capacity to induce genomic DNA damage and escalate the likelihood of detrimental health outcomes. Rapid and reliable estimation of space radiation dose holds paramount significance in accurately assessing the health risks associated with spaceflight. However, the identification of space radiation-responsive genes, with their potential to serve as early indicators for diagnosing radiation dose associated with spaceflight, continues to pose a significant challenge. In this study, based on the evolutionarily conserved mechanism of radiation response, an in silico analysis method of homologous comparison was performed to identify the Caenorhabditis elegans orthologues of human radiation-responsive genes with possible roles in the major processes of response to radiation, and thereby to explore the potential C. elegans radiation-responsive genes for evaluating the levels of space radiation exposure. The results showed that there were 60 known C. elegans radiation-responsive genes and 211 C. elegans orthologues of human radiation-responsive genes implicated in the major processes of response to radiation. Through an investigation of all available transcriptomic datasets obtained from space-flown C. elegans, it was observed that the expression levels of the majority of these putative C. elegans radiation-responsive genes identified in this study were notably changed across various spaceflight conditions. Furthermore, this study indicated that within the identified genes, 19 known C. elegans radiation-responsive genes and 40 newly identified C. elegans orthologues of human radiation-responsive genes exhibited a remarkable positive correlation with the duration of spaceflight. Moreover, a noteworthy presence of substantial multi-collinearity among the majority of these identified genes was observed. This observation lends support to the possibility of treating each identified gene as an independent indicator of radiation dose in space. Ultimately, a subset of 15 potential radiation-responsive genes was identified, presenting the most promising indicators for estimation of radiation dose associated with spaceflight in C. elegans.

Radiation-induced gastric injury during radiotherapy: molecular mechanisms and clinical treatment

Radiotherapy (RT) has been the standard of care for treating a multitude of cancer types. Radiation-induced gastric injury (RIGI) is a common complication of RT for thoracic and abdominal tumors. It manifests acutely as radiation gastritis or gastric ulcers, and chronically as chronic atrophic gastritis or intestinal metaplasia. In recent years, studies have shown that intracellular signals such as oxidative stress response, p38/MAPK pathway and transforming growth factor-β signaling pathway are involved in the progression of RIGI. This review also summarized the risk factors, diagnosis and treatment of this disease. However, the root of therapeutic challenges lies in the incomplete understanding of the mechanisms. Here, we also highlight the potential mechanistic, diagnostic and therapeutic directions of RIGI.

A Self-Assembled Organic Probe with Activatable Near-Infrared Fluoro-Photoacoustic Signals for In Vivo Evaluation of the Radiotherapy Effect

Early evaluation and prediction of the radiotherapy effect against tumors are crucial for effective radiotherapy management. The clinical approach generally relies on anatomical changes in tumor size, which is unable to promptly reflect clinical outcomes and guide a timely adjustment of therapy regimens. To resolve it, we herein develop a self-assembled organic probe (dCyFFs) with caspase-3 (Casp-3)-activatable near-infrared (NIR) fluoro-photoacoustic signals for early evaluation and prediction of radiotherapy efficacy. The probe contains an NIR dye that is caged with a Casp-3-cleavable substrate and linked to a self-assembly initiating moiety. In the presence of Casp-3, the self-assembled probe can undergo secondary assembly into larger nanoparticles and simultaneously activate NIR fluoro-photoacoustic signals. Such a design endows a superior real-time longitudinal imaging capability of Casp-3 generated by radiotherapy as it facilitates the passive accumulation of the probe into tumors, activated signal output with enhanced optical stability, and retention capacity relative to a nonassembling small molecular control probe (dCy). As a result, the probe enables precise prediction of the radiotherapy effect as early as 3 h posttherapy, which is further evidenced by the changes in tumor size after radiotherapy. Overall, the probe with Casp-3-mediated secondary assembly along with activatable NIR fluoro-photoacoustic signals holds great potential for evaluating and predicting the response of radiotherapy in a timely manner, which can also be explored for utilization in other therapeutic modalities.

Epigenetic modifications in radiation-induced non-targeted effects and their clinical significance

BACKGROUND

Ionizing radiation (IR) plays an important role in the diagnosis and treatment of cancer. Besides the targeted effects, the non-targeted effects, which cause damage to non-irradiated cells and genomic instability in normal tissues, also play a role in the side effects of radiotherapy and have been shown to involve both alterations in DNA sequence and regulation of epigenetic modifications.

SCOPE OF REVIEW

We summarize the recent findings regarding epigenetic modifications that are involved in radiation-induced non-targeted effects as well as their clinical significance in radiotherapy and radioprotection.

MAJOR CONCLUSIONS

Epigenetic modifications play an important role in both the realization and modulation of radiobiological effects. However, the molecular mechanisms underlying non-targeted effects still need to be clarified.

GENERAL SIGNIFICANCE

A better understanding of the epigenetic mechanisms related to radiation-induced non-targeted effects will guide both individualized clinical radiotherapy and individualized precise radioprotection.

Low-Dose Non-Targeted Effects and Mitochondrial Control

Non-targeted effects (NTE) have been generally regarded as a low-dose ionizing radiation (IR) phenomenon. Recently, regarding long distant abscopal effects have also been observed at high doses of IR) relevant to antitumor radiation therapy. IR is inducing NTE involving intracellular and extracellular signaling, which may lead to short-ranging bystander effects and distant long-ranging extracellular signaling abscopal effects. Internal and "spontaneous" cellular stress is mostly due to metabolic oxidative stress involving mitochondrial energy production (ATP) through oxidative phosphorylation and/or anaerobic pathways accompanied by the leakage of O₂^- and other radicals from mitochondria during normal or increased cellular energy requirements or to mitochondrial dysfunction. Among external stressors, ionizing radiation (IR) has been shown to very rapidly perturb mitochondrial functions, leading to increased energy supply demands and to ROS/NOS production. Depending on the dose, this affects all types of cell constituents, including DNA, RNA, amino acids, proteins, and membranes, perturbing normal inner cell organization and function, and forcing cells to reorganize the intracellular metabolism and the network of organelles. The reorganization implies intracellular cytoplasmic-nuclear shuttling of important proteins, activation of autophagy, and mitophagy, as well as induction of cell cycle arrest, DNA repair, apoptosis, and senescence. It also includes reprogramming of mitochondrial metabolism as well as genetic and epigenetic control of the expression of genes and proteins in order to ensure cell and tissue survival. At low doses of IR, directly irradiated cells may already exert non-targeted effects (NTE) involving the release of molecular mediators, such as radicals, cytokines, DNA fragments, small RNAs, and proteins (sometimes in the form of extracellular vehicles or exosomes), which can induce damage of unirradiated neighboring bystander or distant (abscopal) cells as well as immune responses. Such non-targeted effects (NTE) are contributing to low-dose phenomena, such as hormesis, adaptive responses, low-dose hypersensitivity, and genomic instability, and they are also promoting suppression and/or activation of immune cells. All of these are parts of the main defense systems of cells and tissues, including IR-induced innate and adaptive immune responses. The present review is focused on the prominent role of mitochondria in these processes, which are determinants of cell survival and anti-tumor RT.

The miRNA Content of Bone Marrow-Derived Extracellular Vesicles Contributes to Protein Pathway Alterations Involved in Ionising Radiation-Induced Bystander Responses

Extracellular vesicles (EVs), through their cargo, are important mediators of bystander responses in the irradiated bone marrow (BM). MiRNAs carried by EVs can potentially alter cellular pathways in EV-recipient cells by regulating their protein content. Using the CBA/Ca mouse model, we characterised the miRNA content of BM-derived EVs from mice irradiated with 0.1 Gy or 3 Gy using an nCounter analysis system. We also analysed proteomic changes in BM cells either directly irradiated or treated with EVs derived from the BM of irradiated mice. Our aim was to identify key cellular processes in the EV-acceptor cells regulated by miRNAs. The irradiation of BM cells with 0.1 Gy led to protein alterations involved in oxidative stress and immune and inflammatory processes. Oxidative stress-related pathways were also present in BM cells treated with EVs isolated from 0.1 Gy-irradiated mice, indicating the propagation of oxidative stress in a bystander manner. The irradiation of BM cells with 3 Gy led to protein pathway alterations involved in the DNA damage response, metabolism, cell death and immune and inflammatory processes. The majority of these pathways were also altered in BM cells treated with EVs from mice irradiated with 3 Gy. Certain pathways (cell cycle, acute and chronic myeloid leukaemia) regulated by miRNAs differentially expressed in EVs isolated from mice irradiated with 3 Gy overlapped with protein pathway alterations in BM cells treated with 3 Gy EVs. Six miRNAs were involved in these common pathways interacting with 11 proteins, suggesting the involvement of miRNAs in the EV-mediated bystander processes. In conclusion, we characterised proteomic changes in directly irradiated and EV-treated BM cells, identified processes transmitted in a bystander manner and suggested miRNA and protein candidates potentially involved in the regulation of these bystander processes.

Translocations are induced in hematopoietic stem cells after irradiation of fetal mice

Although mammalian fetuses have been suggested to be sensitive to radiation, an increased frequency of translocations was not observed in blood lymphocytes from atomic bomb (A-bomb) survivors who were exposed to the bomb in utero and examined as adults. Since experiments using hematopoietic cells of mice and rats confirmed this finding, it was hypothesized that either irradiated fetal hematopoietic stem cells (f-HSCs) cannot generate exchange-type chromosomal aberrations or cells bearing induced aberrations are eliminated before the animals reach adulthood. In the present study, pregnant mice (12.5-15.5 days post coitum [dpc]) were irradiated with 2 Gy of X-rays and long-term HSCs (LT-HSCs) were isolated 24 h later. Multicolor fluorescence in situ hybridization (mFISH) analysis of LT-HSC clones proliferated in vitro showed that nine out of 43 (21%) clones from fetuses and 21 out of 41 (51%) clones from mothers bore translocations. These results indicate that cells with translocations can arise in mouse f-HSCs but exist at a lower frequency than in the mothers 24 h after X-ray exposure. Thus, it seems likely that translocation-bearing f-HSCs are generated but subsequently disappear, so that the frequency of lymphocyte translocations may decrease and reach the control level by the time the animals reach adulthood.

Radiation-induced increases in cancer mortality result from an earlier onset of the disease in mice and atomic bomb survivors

PURPOSE

It has long been thought that the carcinogenic effect of radiation is due to the induction of oncogenic mutations, which means that a fraction of the irradiated individuals will be affected in a dose-dependent manner. This dogma was recently challenged because it was found that the model does not properly explain the life shortening effect of radiation which is seen as a parallel shift of mouse survival curves toward younger ages following an exposure to radiation. Specifically, according to the mutation induction theory, an irradiated mouse or human population evolves into two subpopulations with different mean lifespans, which would lead to a wider distribution of individual lifespans, and hence to a shallower slope in the survival curve, which is not what is observed. Instead, the parallel shift indicates that a large fraction of the irradiated mice are affected (but there are exceptions). Thus, it was thought important to pursue how the excess risk for cancer develops following an exposure to radiation.

METHOD

In the present study, cancer mortality data from mice and atomic-bomb survivors is presented to understand the increasing patterns of cancer risks.

RESULTS

In both species, it was found that cancer mortality starts to increase earlier in the exposed group.

CONCLUSION

The results are consistent with the notion that in many irradiated organs (but not all) radiation-induced tissue damage can lead to the development of an altered microenvironment (most probably inflammation), which is favorable to the growth of spontaneously arising tumor cells and can lead to an earlier onset of the diseases or to an apparently increased risk of cancer.

Out-of-field effects: lessons learned from partial body exposure

Partial body exposure and inhomogeneous dose delivery are features of the majority of medical and occupational exposure situations. However, mounting evidence indicates that the effects of partial body exposure are not limited to the irradiated area but also have systemic effects that are propagated outside the irradiated field. It was the aim of the "Partial body exposure" session within the MELODI workshop 2020 to discuss recent developments and insights into this field by covering clinical, epidemiological, dosimetric as well as mechanistic aspects. Especially the impact of out-of-field effects on dysfunctions of immune cells, cardiovascular diseases and effects on the brain were debated. The presentations at the workshop acknowledged the relevance of out-of-field effects as components of the cellular and organismal radiation response. Furthermore, their importance for the understanding of radiation-induced pathologies, for the discovery of early disease biomarkers and for the identification of high-risk organs after inhomogeneous exposure was emphasized. With the rapid advancement of clinical treatment modalities, including new dose rates and distributions a better understanding of individual health risk is urgently needed. To achieve this, a deeper mechanistic understanding of out-of-field effects in close connection to improved modelling was suggested as priorities for future research. This will support the amelioration of risk models and the personalization of risk assessments for cancer and non-cancer effects after partial body irradiation.

The emerging role of exosomes in radiotherapy

Presently, more than half of cancer patients receive radiotherapy to cure localized cancer, palliate symptoms, or control the progression of cancer. However, radioresistance and radiation-induced bystander effects (RIBEs) are still challenging problems in cancer treatment. Exosomes, as a kind of extracellular vesicle, have a significant function in mediating and regulating intercellular signaling pathways. An increasing number of studies have shown that radiotherapy can increase exosome secretion and alter exosome cargo. Furthermore, radiation-induced exosomes are involved in the mechanism of radioresistance and RIBEs. Therefore, exosomes hold great promise for clinical application in radiotherapy. In this review, we not only focus on the influence of radiation on exosome biogenesis, secretion and cargoes but also on the mechanism of radiation-induced exosomes in radioresistance and RIBEs, which may expand our insight into the cooperative function of exosomes in radiotherapy.

Radiation-response in primary fibroblasts of long-term survivors of childhood cancer with and without second primary neoplasms: the KiKme study

Background

The etiology and most risk factors for a sporadic first primary neoplasm in childhood or subsequent second primary neoplasms are still unknown. One established causal factor for therapy-associated second primary neoplasms is the exposure to ionizing radiation during radiation therapy as a mainstay of cancer treatment. Second primary neoplasms occur in 8% of all cancer survivors within 30 years after the first diagnosis in Germany, but the underlying factors for intrinsic susceptibilities have not yet been clarified. Thus, the purpose of this nested case–control study was the investigation and comparison of gene expression and affected pathways in primary fibroblasts of childhood cancer survivors with a first primary neoplasm only or with at least one subsequent second primary neoplasm, and controls without neoplasms after exposure to a low and a high dose of ionizing radiation.

Methods

Primary fibroblasts were obtained from skin biopsies from 52 adult donors with a first primary neoplasm in childhood (N1), 52 with at least one additional primary neoplasm (N2+), as well as 52 without cancer (N0) from the KiKme study. Cultured fibroblasts were exposed to a high [2 Gray (Gy)] and a low dose (0.05 Gy) of X-rays. Messenger ribonucleic acid was extracted 4 h after exposure and Illumina-sequenced. Differentially expressed genes (DEGs) were computed using limma for R, selected at a false discovery rate level of 0.05, and further analyzed for pathway enrichment (right-tailed Fisher’s Exact Test) and (in-) activation (z ≥|2|) using Ingenuity Pathway Analysis.

Results

After 0.05 Gy, least DEGs were found in N0 (n = 236), compared to N1 (n = 653) and N2+ (n = 694). The top DEGs with regard to the adjusted p-value were upregulated in fibroblasts across all donor groups (SESN1, MDM2, CDKN1A, TIGAR, BTG2, BLOC1S2, PPM1D, PHLDB3, FBXO22, AEN, TRIAP1, and POLH). Here, we observed activation of p53 Signaling in N0 and to a lesser extent in N1, but not in N2+. Only in N0, DNA (excision-) repair (involved genes: CDKN1A, PPM1D, and DDB2) was predicted to be a downstream function, while molecular networks in N2+ were associated with cancer, as well as injury and abnormalities (among others, downregulation of MSH6, CCNE2, and CHUK). After 2 Gy, the number of DEGs was similar in fibroblasts of all donor groups and genes with the highest absolute log₂ fold-change were upregulated throughout (CDKN1A, TIGAR, HSPA4L, MDM2, BLOC1SD2, PPM1D, SESN1, BTG2, FBXO22, PCNA, and TRIAP1). Here, the p53 Signaling-Pathway was activated in fibroblasts of all donor groups. The Mitotic Roles of Polo Like Kinase-Pathway was inactivated in N1 and N2+. Molecular Mechanisms of Cancer were affected in fibroblasts of all donor groups. P53 was predicted to be an upstream regulator in fibroblasts of all donor groups and E2F1 in N1 and N2+. Results of the downstream analysis were senescence in N0 and N2+, transformation of cells in N0, and no significant effects in N1. Seven genes were differentially expressed in reaction to 2 Gy dependent on the donor group (LINC00601, COBLL1, SESN2, BIN3, TNFRSF10A, EEF1AKNMT, and BTG2).

Conclusion

Our results show dose-dependent differences in the radiation response between N1/N2+ and N0. While mechanisms against genotoxic stress were activated to the same extent after a high dose in all groups, the radiation response was impaired after a low dose in N1/N2+, suggesting an increased risk for adverse effects including carcinogenesis, particularly in N2+.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00520-6.

Poly(ADP-ribosyl)ation of acetyltransferase NAT10 by PARP1 is required for its nucleoplasmic translocation and function in response to DNA damage

Background

N-acetyltransferase 10 (NAT10), an abundant nucleolar protein with both lysine and RNA cytidine acetyltransferase activities, has been implicated in Hutchinson-Gilford progeria syndrome and human cancer. We and others recently demonstrated that NAT10 is translocated from the nucleolus to the nucleoplasm after DNA damage, but the underlying mechanism remains unexplored.

Methods

The NAT10 and PARP1 knockout (KO) cell lines were generated using CRISPR-Cas9 technology. Knockdown of PARP1 was performed using specific small interfering RNAs targeting PARP1. Cells were irradiated with γ-rays using a ¹³⁷Cs Gammacell-40 irradiator and subjected to clonogenic survival assays. Co-localization and interaction between NAT10 and MORC2 were examined by immunofluorescent staining and immunoprecipitation assays, respectively. PARylation of NAT10 and translocation of NAT10 were determined by in vitro PARylation assays and immunofluorescent staining, respectively.

Results

Here, we provide the first evidence that NAT10 underwent covalent PARylation modification following DNA damage, and poly (ADP-ribose) polymerase 1 (PARP1) catalyzed PARylation of NAT10 on three conserved lysine (K) residues (K1016, K1017, and K1020) within its C-terminal nucleolar localization signal motif (residues 983–1025). Notably, mutation of those three PARylation residues on NAT10, pharmacological inhibition of PARP1 activity, or depletion of PARP1 impaired NAT10 nucleoplasmic translocation after DNA damage. Knockdown or inhibition of PARP1 or expression of a PARylation-deficient mutant NAT10 (K3A) attenuated the co-localization and interaction of NAT10 with MORC family CW-type zinc finger 2 (MORC2), a newly identified chromatin-remodeling enzyme involved in DNA damage response, resulting in a decrease in DNA damage-induced MORC2 acetylation at lysine 767. Consequently, expression of a PARylation-defective mutant NAT10 resulted in enhanced cellular sensitivity to DNA damage agents.

Conclusion

Collectively, these findings indicate that PARP1-mediated PARylation of NAT10 is key for controlling its nucleoplasmic translocation and function in response to DNA damage. Moreover, our findings provide novel mechanistic insights into the sophisticated paradigm of the posttranslational modification-driven cellular response to DNA damage.

Video Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12964-022-00932-1.

Interaction of Radiotherapy and Hyperthermia with the Immune System: a Brief Current Overview

Purpose of Review

This review focuses on the opposing effects on the immune system of radiotherapy (RT) and the consequences for combined cancer treatment strategies of RT with immunotherapies, including hyperthermia (HT). How RT and HT might affect cancer stem cell populations is also briefly outlined in this context.

Recent Findings

RT is one of the crucial standard cancer therapies. Most patients with solid tumors receive RT for curative and palliative purposes in the course of their disease. RT achieves a local tumor control by inducing DNA damage which can lead to tumor cell death. In recent years, it has become evident that RT does not only have local effects, but also systemic effects which involves induction of anti-tumor immunity and possible alteration of the immunosuppressive properties of the tumor microenvironment. Though, often RT alone is not able to induce potent anti-tumor immune responses since the effects of RT on the immune system can be both immunostimulatory and immunosuppressive.

Summary

RT with additional therapies such as HT and immune checkpoint inhibitors (ICI) are promising approaches to induce anti-tumor immunity effectively. HT is not only a potent sensitizer for RT, but it might also improve the efficacy of RT and certain chemotherapeutic agents (CT) by additionally sensitizing resistant cancer stem cells (CSCs).

Graphical abstract

Evidence for Recombinant GRP78, CALR, PDIA3 and GPI as Mediators of Genetic Instability in Human CD34+ Cells

Soluble factors released from irradiated human mesenchymal stromal cells (MSC) may induce genetic instability in human CD34+ cells, potentially mediating hematologic disorders. Recently, we identified four key proteins in the secretome of X-ray-irradiated MSC, among them three endoplasmic reticulum proteins, the 78 kDa glucose-related protein (GRP78), calreticulin (CALR), and protein disulfide-isomerase A3 (PDIA3), as well as the glycolytic enzyme glucose-6-phosphate isomerase (GPI). Here, we demonstrate that exposition of CD34+ cells to recombinant GRP78, CALR, PDIA3 and GPI induces substantial genetic instability. Increased numbers of γH2AX foci (p < 0.0001), centrosome anomalies (p = 0.1000) and aberrant metaphases (p = 0.0022) were detected in CD34+ cells upon incubation with these factors. Specifically, γH2AX foci were found to be induced 4−5-fold in response to any individual of the four factors, and centrosome anomalies by 3−4 fold compared to control medium, which contained none of the recombinant proteins. Aberrant metaphases, not seen in the context of control medium, were detected to a similar extent than centrosome anomalies across the four factors. Notably, the strongest effects were observed when all four factors were collectively provided. In summary, our data suggest that specific components of the secretome from irradiated MSC act as mediators of genetic instability in CD34+ cells, thereby possibly contributing to the pathogenesis of radiation-induced hematologic disorders beyond direct radiation-evoked DNA strand breaks.

Cellular Damage in the Target and Out-Of-Field Peripheral Organs during VMAT SBRT Prostate Radiotherapy: An In Vitro Phantom-Based Study

Simple Summary

New developments show that patients with prostate cancer can benefit from radiotherapy delivered with a hypo-fractionated regimen. The aim of our study was to investigate the effect of hypo-fractionated stereotactic body radiation therapy (SBRT) of prostate cancer on out-of-field organs. We used a humanoid phantom to irradiate prostate cells in conditions similar to patient therapy, using SBRT planning. Our results show that radiation doses in the location of the intestine and lung resulted in significantly higher radiation doses than the further locations. We observed a high radiotoxic effect in the cells irradiated in the prostate, and a small increase in DNA damage and cell killing in the intestine location. Gene expression analysis revealed significant enrichment of the biological processes related to the radiation response in the prostate. In the lung and thyroid, the enrichment of several gene groups was revealed, however the processes were not clearly related to the response to radiation. Our study provides extensive data on out-of-field safety of prostate SBRT.

Abstract

Hypo-fractionated stereotactic body radiation therapy (SBRT) is an effective treatment for prostate cancer (PCa). Although many studies have investigated the effects of SBRT on the prostate and adjacent organs, little is known about the effects further out-of-field. The aim of this study was to investigate, both in vitro and in a quasi-humanoid phantom, the biological effects (using a dose-scaling approach) of radiation in the out-of-field peripheral organs delivered by 6 MV volumetric modulated arc therapy (VMAT) SBRT in a prostate cancer model. Healthy prostate cells were irradiated in a phantom at locations corresponding to the prostate, intestine, lung, thyroid, and brain. Seven 10 Gy fractions of VMAT SBRT were delivered to the target in a single session without intermission (scaled-up method). Radiochromic films were used to measure the doses. The radiobiological response was assessed by measuring DNA breaks, the cell survival fraction, and differences in gene expression profile. Our results showed a strong, multiparametric radiobiological response of the cells in the prostate. Outside of the radiation field, the highest doses were observed in the intestine and lung. A small increase (not statistically significant) in DNA damage and cell death was observed in the intestines. Several gene groups (cell cycle, DNA replication) were depleted in the lung and thyroid (DNA replication, endocytosis), but further analysis revealed no changes in the relevant biological processes. This study provides extensive evidence of the types and extent of radiobiological responses during VMAT SBRT in a prostate cancer model. Additional research is needed to determine whether the radiobiological effects observed in the peripheral organs are validated in a clinical context.

Low and high doses of ionizing radiation evoke discrete global (phospho)proteome responses

BACKGROUND

Although cancer risk is assumed to be linear with ionizing radiation (IR) dose, it is unclear to what extent low doses (LD) of IR from medical and occupational exposures pose a cancer risk for humans. Improved mechanistic understanding of the signaling responses to LD may help to clarify this uncertainty. Here, we performed quantitative mass spectrometry-based proteomics and phosphoproteomics experiments, using mouse embryonic stem cells, at 0.5 h and 4 h after exposure to LD (0.1 Gy) and high doses (HD; 1 Gy) of IR.

RESULTS

The proteome remained relatively stable (29; 0.5% proteins responded), whereas the phosphoproteome changed dynamically (819; 7% phosphosites changed) upon irradiation. Dose-dependent alterations of 25 IR-responsive proteins were identified, with only four in common between LD and HD. Mitochondrial metabolic proteins and pathways responded to LD, whereas transporter proteins and mitochondrial uncoupling pathways responded to HD. Congruently, mitochondrial respiration increased after LD exposure but decreased after HD exposure. While the bulk of the phosphoproteome response to LD (76%) occurred already at 0.5 h, an equivalent proportion of the phosphosites responded to HD at both time points. Motif, kinome/phosphatome, kinase-substrate, and pathway analyses revealed a robust DNA damage response (DDR) activation after HD exposure but not after LD exposure. Instead, LD-irradiation induced (de)phosphorylation of kinases, kinase-substrates and phosphatases that predominantly respond to reactive oxygen species (ROS) production.

CONCLUSION

Our analyses identify discrete global proteome and phosphoproteome responses after LD and HD, uncovering novel proteins and protein (de)phosphorylation events involved in the dose-dependent ionizing radiation responses.

Immunomodulation by radiotherapy in tumour control and normal tissue toxicity

Radiotherapy (RT) is a highly effective anticancer treatment that is delivered to more than half of all patients with cancer. In addition to the well-documented direct cytotoxic effects, RT can have immunomodulatory effects on the tumour and surrounding tissues. These effects are thought to underlie the so-called abscopal responses, whereby RT generates systemic antitumour immunity outside the irradiated tumour. The full scope of these immune changes remains unclear but is likely to involve multiple components, such as immune cells, the extracellular matrix, endothelial and epithelial cells and a myriad of chemokines and cytokines, including transforming growth factor-β (TGFβ). In normal tissues exposed to RT during cancer therapy, acute immune changes may ultimately lead to chronic inflammation and RT-induced toxicity and organ dysfunction, which limits the quality of life of survivors of cancer. Here we discuss the emerging understanding of RT-induced immune effects with particular focus on the lungs and gut and the potential immune crosstalk that occurs between these tissues.

Early Biomarkers Associated with P53 Signaling for Acute Radiation Injury

Accurate dose assessment within 1 day or even 12 h after exposure through current methods of dose estimation remains a challenge, in response to a large number of casualties caused by nuclear or radiation accidents. P53 signaling pathway plays an important role in DNA damage repair and cell apoptosis induced by ionizing radiation. The changes of radiation-induced P53 related genes in the early stage of ionizing radiation should compensate for the deficiency of lymphocyte decline and γ-H2AX analysis as novel biomarkers of radiation damage. Bioinformatic analysis was performed on previous data to find candidate genes from human peripheral blood irradiated in vitro. The expression levels of candidate genes were detected by RT-PCR. The expressions of screened DDB2, AEN, TRIAP1, and TRAF4 were stable in healthy population, but significantly up-regulated by radiation, with time specificity and dose dependence in 2–24 h after irradiation. They are early indicators for medical treatment in acute radiation injury. Their effective combination could achieve a more accurate dose assessment for large-scale wounded patients within 24 h post exposure. The effective combination of p53-related genes DDB2, AEN, TRIAP1, and TRAF4 is a novel biodosimetry for a large number of people exposed to acute nuclear accidents.

Mechanism and Protection of Radiotherapy Induced Sensorineural Hearing Loss for Head and Neck Cancer

Purpose

Radiotherapy-induced sensorineural hearing loss (RISNHL) is a common adverse effect in patients with head and neck cancer. Given that there are few studies on the pathogenesis of RISNHL at present, we summarized the possible pathogenesis of RISNHL and possible protective measures found at present by referring to relevant literatures.

Methods

We performed a comprehensive literature search in the PubMed database, using keywords “sensorineural hearing loss,” “radiotherapy,” and “cancer,” among others. The literature was examined for the possible mechanism and preventive measures of sensorineural hearing loss induced by radiotherapy.

Results

We found that the incidence of RISNHL was closely related to the damage directly caused by ionizing radiation and the radiation-induced bystander effect. It also depends on the dose of radiation and the timing of chemotherapy. Studies confirmed that RISNHL is mainly involved in post-RT inflammatory response and changes in reactive oxygen species, mitogen-activated protein kinase, and p53 signaling pathways, leading to specific manners of cell death. We expect to reduce the incidence of hearing loss through advanced radiotherapy techniques, dose limitation of organs at risk, application of cell signaling inhibitors, use of antioxidants, induction of cochlear hair cell regeneration, and cochlear implantation.

Conclusion

RISNHL is associated with radiation damage to DNA, oxidative stress, and inflammation of cochlear cells, stria vascularis endothelial cells, vascular endothelial cells, spiral ganglion neurons, and other supporting cells. At present, the occurrence mechanism of RISNHL has not been clearly illustrated, and further studies are needed to better understand the underlying mechanism, which is crucial to promote the formulation of better strategies and prevent the occurrence of RISNHL.

Water is a preservative of microbes

Water is the cellular milieu, drives all biochemistry within Earth's biosphere and facilitates microbe-mediated decay processes. Instead of reviewing these topics, the current article focuses on the activities of water as a preservative-its capacity to maintain the long-term integrity and viability of microbial cells-and identifies the mechanisms by which this occurs. Water provides for, and maintains, cellular structures; buffers against thermodynamic extremes, at various scales; can mitigate events that are traumatic to the cell membrane, such as desiccation-rehydration, freeze-thawing and thermal shock; prevents microbial dehydration that can otherwise exacerbate oxidative damage; mitigates against biocidal factors (in some circumstances reducing ultraviolet radiation and diluting solute stressors or toxic substances); and is effective at electrostatic screening so prevents damage to the cell by the intense electrostatic fields of some ions. In addition, the water retained in desiccated cells (historically referred to as 'bound' water) plays key roles in biomacromolecular structures and their interactions even for fully hydrated cells. Assuming that the components of the cell membrane are chemically stable or at least repairable, and the environment is fairly constant, water molecules can apparently maintain membrane geometries over very long periods provided these configurations represent thermodynamically stable states. The spores and vegetative cells of many microbes survive longer in the presence of vapour-phase water (at moderate-to-high relative humidities) than under more-arid conditions. There are several mechanisms by which large bodies of water, when cooled during subzero weather conditions remain in a liquid state thus preventing potentially dangerous (freeze-thaw) transitions for their microbiome. Microbial life can be preserved in pure water, freshwater systems, seawater, brines, ice/permafrost, sugar-rich aqueous milieux and vapour-phase water according to laboratory-based studies carried out over periods of years to decades and some natural environments that have yielded cells that are apparently thousands, or even (for hypersaline fluid inclusions of mineralized NaCl) hundreds of millions, of years old. The term preservative has often been restricted to those substances used to extend the shelf life of foods (e.g. sodium benzoate, nitrites and sulphites) or those used to conserve dead organisms, such as ethanol or formaldehyde. For living microorganisms however, the ultimate preservative may actually be water. Implications of this role are discussed with reference to the ecology of halophiles, human pathogens and other microbes; food science; biotechnology; biosignatures for life and other aspects of astrobiology; and the large-scale release/reactivation of preserved microbes caused by global climate change.

Quantitative modeling of carcinogenesis induced by single beams or mixtures of space radiations using targeted and non-targeted effects

Ionizing radiations encountered by astronauts on deep space missions produce biological damage by two main mechanisms: (1) Targeted effects (TE) due to direct traversals of cells by ionizing tracks. (2) Non-targeted effects (NTE) caused by release of signals from directly hit cells. The combination of these mechanisms generates non-linear dose response shapes, which need to be modeled quantitatively to predict health risks from space exploration. Here we used a TE + NTE model to analyze data on APC^(1638N/+) mouse tumorigenesis induced by space-relevant doses of protons, ⁴He, ¹²C, ¹⁶O, ²⁸Si or ⁵⁶Fe ions, or γ rays. A customized weighted Negative Binomial distribution was used to describe the radiation type- and dose-dependent data variability. This approach allowed detailed quantification of dose–response shapes, NTE- and TE-related model parameters, and radiation quality metrics (relative biological effectiveness, RBE, and radiation effects ratio, RER, relative to γ rays) for each radiation type. Based on the modeled responses for each radiation type, we predicted the tumor yield for a Mars-mission-relevant mixture of these radiations, using the recently-developed incremental effect additivity (IEA) synergy theory. The proposed modeling approach can enhance current knowledge about quantification of space radiation quality effects, dose response shapes, and ultimately the health risks for astronauts.

Mast1 mediates radiation-induced gastric injury via the P38 MAPK pathway

Radiation-induced gastric injury is a serious adverse effect and reduces the efficacy of radiotherapy treatment. However, the mechanisms underlying radiation-induced stomach injury remain unclear. Here, mouse stomach and gastric epithelial cells were irradiated with different doses of X-ray radiation. The results showed that radiation induced gastric injury in vivo and in vitro. Differentially expressed functional mRNAs in irradiation-induced gastric tissues were screened from the Gene Expression Omnibus (GEO) database. We found that the expression of microtubule-associated serine/threonine kinase 1 (Mast1) was downregulated in mouse gastric tissues and gastric epithelial cells after irradiation. Furthermore, functional assays showed that knockdown of Mast1 inhibited growth and promoted apoptosis in gastric epithelial cells, while overexpression of Mast1 protected gastric epithelial cells from radiation damage. Mechanistically, Mast1 negatively regulated radiation-induced injury in gastric epithelial cells by inhibiting the activation of P38. The apoptosis caused by knockdown of Mast1 in gastric epithelial cells could be partially reversed by the P38 inhibitor SB203580. Moreover, data from several gastric cancer cell lines and online databases revealed that Mast1 was not involved in the development of gastric cancer. Collectively, our findings demonstrated that Mast1 is essential for radiation-induced gastric injury, providing a promising prognostic and therapeutic target.

Gene Signatures Induced by Ionizing Radiation as Prognostic Tools in an In Vitro Experimental Breast Cancer Model

Simple Summary

The present work analyzed the expression of genes involved in radiation, using an in vitro experimental breast cancer model developed by the combined treatment of low doses of high linear energy transfer (LET) radiation α particle radiation and estrogen yielding different stages in a malignantly transformed breast cancer cell model called Alpha model. Results showed important findings of genes involved in cancers of the breast, lung, and nervous system, and others. Most of those genes analyzed in these studies such as ATM, selenoproteins, GABA receptor, interleukins, epsin, and cathepsin inhibitors like stefins, and metallothioneins can be used for new prognostic tools and future therapies since they affect cancer progression and metastasis. In conclusion, gene signature demonstrated to be specific to cell line types, hence cell-dependency must be considered in future radiotherapy treatment planning since molecular and clinical features affect such results. Thus, using gene technology and molecular information is possible to improve therapies and reduction of side effects.

Abstract

This study aimed to analyze the expression of genes involved in radiation, using an Affymetrix system with an in vitro experimental breast cancer model developed by the combined treatment of low doses of high linear energy transfer (LET) radiation α particle radiation and estrogen yielding different stages in a malignantly transformed breast cancer cell model called Alpha model. Altered expression of different molecules was detected in the non-tumorigenic Alpha3, a malignant cell line transformed only by radiation and originally derived from the parental MCF-10F human cell line; that was compared with the Alpha 5 cell line, another cell line exposed to radiation and subsequently grown in the presence 17β-estradiol. This Alpha5, a tumorigenic cell line, originated the Tumor2 cell line. It can be summarized that the Alpha 3 cell line was characterized by greater gene expression of ATM and IL7R than control, Alpha5, and Tumor2 cell lines, it presented higher selenoprotein gene expression than control and Tumor2; epsin 3 gene expression was higher than control; stefin A gene expression was higher than Alpha5; and metallothionein was higher than control and Tumor2 cell line. Therefore, radiation, independently of estrogen, induced increased ATM, IL7R, selenoprotein, GABA receptor, epsin, stefin, and metallothioneins gene expression in comparison with the control. Results showed important findings of genes involved in cancers of the breast, lung, nervous system, and others. Most genes analyzed in these studies can be used for new prognostic tools and future therapies since they affect cancer progression and metastasis. Most of all, it was revealed that in the Alpha model, a breast cancer model developed by the authors, the cell line transformed only by radiation, independently of estrogen, was characterized by greater gene expression than other cell lines. Understanding the effect of radiotherapy in different cells will help us improve the clinical outcome of radiotherapies. Thus, gene signature has been demonstrated to be specific to tumor types, hence cell-dependency must be considered in future treatment planning. Molecular and clinical features affect the results of radiotherapy. Thus, using gene technology and molecular information is possible to improve therapies and reduction of side effects while providing new insights into breast cancer-related fields.

Low dose ionizing radiation and the immune response: what is the role of non-targeted effects?

OBJECTIVES

This review aims to trace the historical narrative surrounding the low dose effects of radiation on the immune system and how our understanding has changed from the beginning of the 20th century to now. The particular focus is on the non-targeted effects (NTEs) of low dose ionizing radiation (LDIR) which are effects that occur when irradiated cells emit signals that cause effects in the nearby or distant non-irradiated cells known as radiation induced bystander effect (RIBE). Moreover, radiation induced genomic instability (RIGI) and abscopal effect (AE) also regarded as NTE. This was prompted by our recent discovery that ultraviolet A (UVA) photons are emitted by the irradiated cells and that these photons can trigger NTE such as the RIBE in unirradiated recipients of these photons. Given the well-known association between UV radiation and the immune response, where these biophotons may pose as bystander signals potentiating processes in deep tissues as a consequence of LDIR, it is timely to review the field with a fresh lens. Various pathways and immune components that contribute to the beneficial and adverse types of modulation induced by LDR will also be revisited.

CONCLUSION

There is limited evidence for LDIR induced immune effects by way of a non-targeted mechanism in biological tissue. The literature examining low to medium dose effects of ionizing radiation on the immune system and its components is complex and controversial. Early work was compromised by lack of good dosimetry while later work mainly looks at the involvement of immune response in radiotherapy. There is a lack of research in the LDIR/NTE field focusing on immune response although bone marrow stem cells and lineages were critical in the identification and characterization of NTE where effects like RIGI and RIBE were heavily researched. This may be in part, a result of the difficulty of isolating NTE in whole organisms which are essential for good immune response studies. Models involving inter organism transmission of NTE are a promising route to overcome these issues.

Revisiting the Radiobiology of Targeted Alpha Therapy

Targeted alpha therapy (TAT) using alpha particle-emitting radionuclides is in the spotlight after the approval of ²²³RaCl₂ for patients with metastatic castration-resistant prostate cancer and the development of several alpha emitter-based radiopharmaceuticals. It is acknowledged that alpha particles are highly cytotoxic because they produce complex DNA lesions. Hence, the nucleus is considered their critical target, and many studies did not report any effect in other subcellular compartments. Moreover, their physical features, including their range in tissues (<100 μm) and their linear energy transfer (50–230 keV/μm), are well-characterized. Theoretically, TAT is indicated for very small-volume, disseminated tumors (e.g., micrometastases, circulating tumor cells). Moreover, due to their high cytotoxicity, alpha particles should be preferred to beta particles and X-rays to overcome radiation resistance. However, clinical studies showed that TAT might be efficient also in quite large tumors, and biological effects have been observed also away from irradiated cells. These distant effects are called bystander effects when occurring at short distance (<1 mm), and systemic effects when occurring at much longer distance. Systemic effects implicate the immune system. These findings showed that cells can die without receiving any radiation dose, and that a more complex and integrated view of radiobiology is required. This includes the notion that the direct, bystander and systemic responses cannot be dissociated because DNA damage is intimately linked to bystander effects and immune response. Here, we provide a brief overview of the paradigms that need to be revisited.

Reexamining the role of tissue inflammation in radiation carcinogenesis: a hypothesis to explain an earlier onset of cancer

PURPOSE

Ionizing radiation is a well-known carcinogen, and epidemiologic efforts have been made to evaluate cancer risks following a radiation exposure. The basic approach has been to estimate increased levels of cancer mortality resulting from exposures to radiation, which is consistent with the somatic mutation theory of cancer. However, the possibility that an irradiation might cause an earlier onset of cancer has also been raised since the earliest days of animal studies. Recently, the mutation induction model has been challenged because it is unable to explain the observed dose-related parallel shift of entire mouse survival curves toward younger ages following an irradiation. This is because if it is assumed that only a fraction of the irradiated individuals are affected, the irradiated population would consist of two subpopulations with different mean lifespans, which makes the overall distribution of individual lifespans broader, and hence the slope of the survival curves shallower. To explain this parallel shift, it is necessary to assume that all individuals of a population are affected. As a result of these observations, possible mechanisms which could account for the parallel shift of mouse survival curves were sought by examining the radiation induction of various types of tissue damage which could facilitate an earlier onset of spontaneously arising cancers.

CONCLUSION

A proposed mechanism postulates that a radiation exposure leads to tissue inflammation which subsequently stimulates spontaneously arising cancers and allows them to appear earlier than usual. This notion is not unprecedented, and because the background incidence of cancer increases exponentially with an increase in age, a slight shift of the onset age toward younger ages may make it appear as if the risk is increased. In this scenario, a radiation exposure induces DNA damage, cell death, chromosome aberrations etc., which leads to the multi-pathway responses including activation of stromal fibroblasts, macrophages and various inflammatory factors. Such an inflamed microenvironment favors the growth of spontaneously arising tumor cells although currently, the sequential order or relative importance of the individual factors remains to be known.

Reactive oxygen species (ROS): utilizing injectable antioxidative hydrogels and ROS-producing therapies to manage the double-edged sword

Reactive oxygen species (ROS) are generated in cellular metabolism and are essential for cellular signalling networks and physiological functions. However, the functions of ROS are 'double-edged swords' to living systems that have a fragile redox balance between ROS generation and elimination. A modest increase of ROS leads to enhanced cell proliferation, survival and benign immune responses, whereas ROS stress that overwhelms the cellular antioxidant capacity can damage nucleic acids, proteins and lipids, resulting in oncogenic mutations and cell death. ROS are therefore involved in many pathological conditions. On the other hand, ROS present selective toxicity and have been utilised against cancer and pathogens, thus also acting as a double-edged sword in the healthcare field. Injectable antioxidative hydrogels are gel precursors that form hydrogel constructs in situ upon delivery in vivo to maintain an antioxidative capacity. These hydrogels have been developed to counter ROS-induced pathological conditions, with significant advantages of biocompatibility, excellent moldability, and minimally invasive delivery. The intrinsic, readily controllable ROS-scavenging ability of the functionalised hydrogels overcomes many drawbacks of small molecule antioxidants. This review summarises the roles of ROS under pathological conditions and describes the state-of-the-art of injectable antioxidative hydrogels. A particular emphasis is also given to current ROS-producing therapeutic interventions, enabling potential application of injectable antioxidant hydrogels to prevent the adverse effects of many cancer and infection treatments.

Proteins Marking the Sequence of Genotoxic Signaling from Irradiated Mesenchymal Stromal Cells to CD34+ Cells

Non-targeted effects (NTE) of ionizing radiation may initiate myeloid neoplasms (MN). Here, protein mediators (I) in irradiated human mesenchymal stromal cells (MSC) as the NTE source, (II) in MSC conditioned supernatant and (III) in human bone marrow CD34+ cells undergoing genotoxic NTE were investigated. Healthy sublethal irradiated MSC showed significantly increased levels of reactive oxygen species. These cells responded by increasing intracellular abundance of proteins involved in proteasomal degradation, protein translation, cytoskeleton dynamics, nucleocytoplasmic shuttling, and those with antioxidant activity. Among the increased proteins were THY1 and GNA11/14, which are signaling proteins with hitherto unknown functions in the radiation response and NTE. In the corresponding MSC conditioned medium, the three chaperones GRP78, CALR, and PDIA3 were increased. Together with GPI, these were the only four altered proteins, which were associated with the observed genotoxic NTE. Healthy CD34+ cells cultured in MSC conditioned medium suffered from more than a six-fold increase in γH2AX focal staining, indicative for DNA double-strand breaks, as well as numerical and structural chromosomal aberrations within three days. At this stage, five proteins were altered, among them IQGAP1, HMGB1, and PA2G4, which are involved in malign development. In summary, our data provide novel insights into three sequential steps of genotoxic signaling from irradiated MSC to CD34+ cells, implicating that induced NTE might initiate the development of MN.

Investigating Molecular Determinants of Cancer Cell Resistance to Ionizing Radiation Through an Integrative Bioinformatics Approach

Eradication of cancer cells through exposure to high doses of ionizing radiation (IR) is a widely used therapeutic strategy in the clinical setting. However, in many cases, cancer cells can develop remarkable resistance to radiation. Radioresistance represents a prominent obstacle in the effective treatment of cancer. Therefore, elucidation of the molecular mechanisms and pathways related to radioresistance in cancer cells is of paramount importance. In the present study, an integrative bioinformatics approach was applied to three publicly available RNA sequencing and microarray transcriptome datasets of human cancer cells of different tissue origins treated with ionizing radiation. These data were investigated in order to identify genes with a significantly altered expression between radioresistant and corresponding radiosensitive cancer cells. Through rigorous statistical and biological analyses, 36 genes were identified as potential biomarkers of radioresistance. These genes, which are primarily implicated in DNA damage repair, oxidative stress, cell pro-survival, and apoptotic pathways, could serve as potential diagnostic/prognostic markers cancer cell resistance to radiation treatment, as well as for therapy outcome and cancer patient survival. In addition, our findings could be potentially utilized in the laboratory and clinical setting for enhancing cancer cell susceptibility to radiation therapy protocols.

The Roles of HIF-1α in Radiosensitivity and Radiation-Induced Bystander Effects Under Hypoxia

Radiation-induced bystander effects (RIBE) may have potential implications for radiotherapy, yet the radiobiological impact and underlying mechanisms in hypoxic tumor cells remain to be determined. Using two human tumor cell lines, hepatoma HepG2 cells and glioblastoma T98G cells, the present study found that under both normoxic and hypoxic conditions, increased micronucleus formation and decreased cell survival were observed in non-irradiated bystander cells which had been co-cultured with X-irradiated cells or treated with conditioned-medium harvested from X-irradiated cells. Although the radiosensitivity of hypoxic tumor cells was lower than that of aerobic cells, the yield of micronucleus induced in bystander cells under hypoxia was similar to that measured under normoxia indicating that RIBE is a more significant factor in overall radiation damage of hypoxic cells. When hypoxic cells were treated with dimethyl sulfoxide (DMSO), a scavenger of reactive oxygen species (ROS), or aminoguanidine (AG), an inhibitor of nitric oxide synthase (NOS), before and during irradiation, the bystander response was partly diminished. Furthermore, when only hypoxic bystander cells were pretreated with siRNA hypoxia-inducible factor-1α (HIF-1α), RIBE were decreased slightly but if irradiated cells were treated with siRNA HIF-1α, hypoxic RIBE decreased significantly. In addition, the expression of HIF-1α could be increased in association with other downstream effector molecules such as glucose transporter 1 (GLUT-1), vascular endothelial growth factor (VEGF), and carbonic anhydrase (CA9) in irradiated hypoxic cells. However, the expression of HIF-1α expression in bystander cells was decreased by a conditioned medium from isogenic irradiated cells. The current results showed that under hypoxic conditions, irradiated HepG2 and T98G cells showed reduced radiosensitivity by increasing the expression of HIF-1α and induced a syngeneic bystander effect by decreasing the expression of HIF-1α and regulating its downstream target genes in both the irradiated or bystander cells.

Combinations of Radiotherapy with Vaccination and Immune Checkpoint Inhibition Differently Affect Primary and Abscopal Tumor Growth and the Tumor Microenvironment

Radiotherapy (RT) is known to have immune-modulatory properties. We hypothesized that RT and inactivated whole tumor cell vaccines generated with high hydrostatic pressure (HHP) synergize to retard the tumor growth which can be additionally improved with anti-PD-1 treatment. In abscopal tumor models, we injected mice with B16-F10 melanoma or TS/A mammary tumors. To evaluate the efficiency of RT in combination with HHP vaccines, we locally irradiated only one tumor with 2 × 8 Gy or 3 × 8 Gy. HHP vaccines further retarded the growth of locally irradiated (2 × 8 Gy) tumors. However, HHP vaccination combined with RT failed to induce abscopal anti-tumor immune responses, namely those to non-irradiated tumors, and even partly abrogated those which were induced with RT plus anti-PD-1. In the latter group, the abscopal effects were accompanied by an elevated infiltration of CD8+ T cells, monocytes/macrophages, and dendritic cells. 3 × 8 Gy failed to induce abscopal effects in association with increased expression of immunosuppressive checkpoint molecules compared to 2 × 8 Gy. We conclude that HHP vaccines induce anti-tumor effects, but only if the tumor microenvironment was previously modulated by hypofractionated RT with not too many fractions, but failed to improve RT plus anti-PD-induced abscopal responses that are characterized by distinct immune alterations.

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.

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.

Ionizing radiation-induced circulatory and metabolic diseases

Risks to health are the prime consideration in all human situations of ionizing radiation exposure and therefore of relevance to radiation protection in all occupational, medical, and public exposure situations. Over the past few decades, advances in therapeutic strategies have led to significant improvements in cancer survival rates. However, a wide range of long-term complications have been reported in cancer survivors, in particular circulatory diseases and their major risk factors, metabolic diseases. However, at lower levels of exposure, the evidence is less clear. Under real-life exposure scenarios, including radiotherapy, radiation effects in the whole organism will be determined mainly by the response of normal tissues receiving relatively low doses, and will be mediated and moderated by systemic effects. Therefore, there is an urgent need for further research on the impact of low-dose radiation. In this article, we review radiation-associated risks of circulatory and metabolic diseases in clinical, occupational or environmental exposure situations, addressing epidemiological, biological, risk modelling, and systems biology aspects, highlight the gaps in knowledge and discuss future directions to address these gaps.

Characterization of Cardiac, Vascular, and Metabolic Changes in Young Childhood Cancer Survivors

Background: Childhood cancer survivors (CCS) are at an increased risk for cardiovascular diseases (CVD). It was the primary aim of this study to determine different measures of cardiac, carotid, lipid, and apolipoprotein status in young adult CCS and in healthy controls. Methods: Cardiac and common carotid artery (CCA) structure and function were measured by ultrasonography. Lipids and apolipoproteins were measured in the blood. Peripheral arterial endothelial vasomotor function was assessed by measuring digital reactive hyperemia index (PAT-RHI) using the Endo-PAT 2000. Results: Fifty-three CCS (20-30 years, 35 men) and 53 sex-matched controls were studied. The CCS cohort was divided by the median dose of anthracyclines into a low anthracycline dose (LAD) group (50-197 mg/m², n = 26) and a high anthracycline dose (HAD) group (200-486 mg/m², n = 27). Carotid distensibility index (DI) and endothelial function determined by PAT-RHI were both lower in the CCS groups compared with controls (p < 0.05 and p = 0.02). There was no difference in carotid intima media thickness. Atherogenic apolipoprotein-B (Apo-B) and the ratio between Apo-B and Apoliprotein-A1 (Apo-A1) were higher in the HAD group compared with controls (p < 0.01). Apo-B/Apo-A1-ratio was over reference limit in 29.6% of the HAD group, in 15.4% of LAD group, and in 7.5% of controls (p = 0.03). Measured lipid markers (low density lipoprotein and total cholesterol and triglycerides) were higher in both CCS groups compared with controls (p < 0.05). Systolic and diastolic function were measurably decreased in the HAD group, as evidenced by lower EF (p < 0.001) and lower é-wave (p < 0.005) compared with controls. CCA DI correlated with Apo-B/Apo-A1-ratio and Apo-A1. Follow-up time after treatment correlated with decreased left ventricular ejection fraction (p = 0.001). Conclusion: Young asymptomatic CCS exhibit cardiac, vascular, lipid, and apolipoprotein changes that could account for increased risk for CVD later in life. These findings emphasize the importance of cardiometabolic monitoring even in young CCS.

Chemoradiation impairs myofiber hypertrophic growth in a pediatric tumor model

Pediatric cancer treatment often involves chemotherapy and radiation, where off-target effects can include skeletal muscle decline. The effect of such treatments on juvenile skeletal muscle growth has yet to be investigated. We employed a small animal irradiator to administer fractionated hindlimb irradiation to juvenile mice bearing implanted rhabdomyosarcoma (RMS) tumors. Hindlimb-targeted irradiation (3 × 8.2 Gy) of 4-week-old mice successfully eliminated RMS tumors implanted one week prior. After establishment of this preclinical model, a cohort of tumor-bearing mice were injected with the chemotherapeutic drug, vincristine, alone or in combination with fractionated irradiation (5 × 4.8 Gy). Single myofiber analysis of fast-contracting extensor digitorum longus (EDL) and slow-contracting soleus (SOL) muscles was conducted 3 weeks post-treatment. Although a reduction in myofiber size was apparent, EDL and SOL myonuclear number were differentially affected by juvenile irradiation and/or vincristine treatment. In contrast, a decrease in myonuclear domain (myofiber volume/myonucleus) was observed regardless of muscle or treatment. Thus, inhibition of myofiber hypertrophic growth is a consistent feature of pediatric cancer treatment.

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.

Role of DNA damage and repair in radiation cancer therapy: a current update and a look to the future

Radiation Therapy (RT), a widely used modality against cancer, depends its effectiveness on three pillars: tumor targeting precision, minimum dose determination and co-administrated agents. The underlying biological processes of the latter two pillars are DNA damage and repair. Hopefully, Radiation treatment has nowadays been improved a lot, in terms of tumor targeting precision as well as in minimization of side effects, by reducing normal tissue radiation exposure and therefore its occurred toxicity. Normal tissue toxicity is a major risk factor for induction of genomic instability which may lead to secondary cancer development, due to the radiation therapy itself. We discuss, in this review, the biological significance of IR-induced complex DNA damage, which is currently accepted as the definite regulator of biological response to radiation, as well as the regulator of the implications of this IR signature in radiation therapy. We unite accumulating evidence and knowledge over the last 20 years or so on the importance of radiation treatment of cancer. This radiation-based therapy comes unfortunately with a deficit and this is the radiation-induced genetic instability which can fuel radiation toxicity, even several years after the initial treatment on patients through the activation of DNA damage response (DDR) and the immune system.

MiR-1587 Regulates DNA Damage Repair and the Radiosensitivity of CRC Cells via Targeting LIG4

DNA is subject to a range of endogenous and exogenous insults that can impair DNA replication and lead to DNA double-strand breaks (DSBs). The repair capacity of cancer cells mediates their radiosensitivity, but the roles of miR-1587 during radiation resistance are poorly characterized. In this study, we explored whether miR-1587 regulates the growth and radiosensitivity of colorectal cancer (CRC) cells through its ability to regulate DNA Ligase4 (LIG4). We found that CRC cells in which miR-1587 was overexpressed inhibited cell growth and promoted apoptosis through increasing DSBs and promoting cell cycle arrest. We found that overexpression of miR-1587 significantly inhibited LIG4 messenger RNA and protein expression and further revealed the ability of miR-1587 to directly bind to the LIG4-3′-untranslated region through dual-luciferase reporter assays. More notably, miR-1587 mimics increased the radiosensitivity of CRC cells. Taken together, we show that miR-1587 overexpression enhances the formation of DSBs, arrests CRC cell growth, and enhances the radiosensivity of CRC cells through the direct repression of LIG4 expression. These results reveal novel roles for miR-1587 during DNA damage repair and the radiosensivity of CRC cells. This highlights miR-1587 as a novel therapeutic target for CRC.

Evaluation of the role of mitochondria in the non-targeted effects of ionizing radiation using cybrid cellular models

Radiobiology is moving towards a better understanding of the intercellular signaling that occurs upon radiation and how its effects relate to the dose applied. The mitochondrial role in orchestrating this biological response needs to be further explored. Cybrids (cytoplasmic hybrids) are useful cell models for studying the involvement of mitochondria in cellular processes. In the present study we used cybrid cell lines to investigate the role of mitochondria in the response to radiation exposure. Cybrid cell lines, derived from the osteosarcoma human cell line 143B, harboring, either wild-type mitochondrial DNA (Cy143Bwt), cells with mitochondria with mutated DNA that causes mitochondrial dysfunction (Cy143Bmut), as well as cells without mitochondrial DNA (mtDNA) (143B-Rho0), were irradiated with 0.2 Gy and 2.0 Gy. Evaluation of the non-targeted (or bystander) effects in non-irradiated cells were assessed by using conditioned media from the irradiated cells. DNA double stranded breaks were assessed with the γH2AX assay. Both directly irradiated cells and cells treated with the conditioned media, showed increased DNA damage. The effect of the irradiated cells media was different according to the cell line it derived from: from Cy143Bwt cells irradiated with 0.2 Gy (low dose) and from Cy143Bmut irradiated with 2.0 Gy (high dose) induced highest DNA damage. Notably, media obtained from cells without mtDNA, the143B-Rho0 cell line, produced no effect in DNA damage. These results point to a possible role of mitochondria in the radiation-induced non-targeted effects. Furthermore, it indicates that cybrid models are valuable tools for radiobiological studies.

Targeting of cellular redox metabolism for mitigation of radiation injury

Accidental exposure to ionizing radiation is a serious concern to human life. Studies on the mitigation of side effects following exposure to accidental radiation events are ongoing. Recent studies have shown that radiation can activate several signaling pathways, leading to changes in the metabolism of free radicals including reactive oxygen species (ROS) and nitric oxide (NO). Cellular and molecular mechanisms show that radiation can cause disruption of normal reduction/oxidation (redox) system. Mitochondria malfunction following exposure to radiation and mutations in mitochondria DNA (mtDNA) have a key role in chronic oxidative stress. Furthermore, exposure to radiation leads to infiltration of inflammatory cells such as macrophages, lymphocytes and mast cells, which are important sources of ROS and NO. These cells generate free radicals via upregulation of some pro-oxidant enzymes such as NADPH oxidases, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Epigenetic changes also have a key role in a similar way. Other mediators such as mammalian target of rapamycin (mTOR) and peroxisome proliferator-activated receptor (PPAR), which are involved in the normal metabolism of cells have also been shown to regulate cell death following exposure to radiation. These mechanisms are tissue specific. Inhibition or activation of each of these targets can be suggested for mitigation of radiation injury in a specific tissue. In the current paper, we review the cellular and molecular changes in the metabolism of cells and ROS/NO following exposure to radiation. Furthermore, the possible strategies for mitigation of radiation injury through modulation of cellular metabolism in irradiated organs will be discussed.

Identification of potential radiation-responsive biomarkers based on human orthologous genes with possible roles in DNA repair pathways by comparison between Arabidopsis thaliana and homo sapiens

Rapid and reliable ionization radiation (IR) exposure estimation has become increasingly important in environment due to the urgent requirement of medical evaluation and treatment in the event of nuclear accident emergency. Human DNA repair genes can be identified as important candidate biomarkers to assess IR exposure, while how to find the enough sensitive and specific biomarkers in the DNA repair networks is still challenged and not fully determined. The conserved features of DNA repair pathways may facilitate interdisciplinary studies that cross the traditional boundaries between animal and plant biology, with the aim of identifying undiscovered human DNA repair genes for potential radiation-responsive biomarkers. In this work, an in silico method of homologous comparison was performed to identify the human orthologues of A. thaliana DNA repair genes, and thereby to explore the sensitive and specific human radiation-responsive genes to evaluate the IR exposure levels. The results showed that a total of 16 putative candidate genes were involved in the human DNA repair pathways of homologous recombination (HR) and non-homologous end joining (NHEJ), and most of them were confirmed by previous experiments. Additionally, we analyzed the gene expression patterns of these 16 candidate genes in several human transcript microarray datasets with different IR treatments. The results indicated that most of the gene expression levels for these candidate genes were significantly changed under different radiation treatments. Based on these results, we integrated these putative human DNA repair genes into the DNA repair pathways to propose new insights of the HR and NHEJ pathways, which can also provide the potential targets for the development of radiation biomarkers. Notably, two putative DNA repair genes, named ERCC1 and ESCO2, were identified and were considered to be the sensitive and specific biomarkers in response to γ-ray exposures.

Immune biological rationales for the design of combined radio- and immunotherapies

Cancer immunotherapies are promising treatments for many forms of cancer. Nevertheless, the response rates to, e.g., immune checkpoint inhibitors (ICI), are still in low double-digit percentage. This calls for further therapy optimization that should take into account combination of immunotherapies with classical tumor therapies such as radiotherapy. By designing multimodal approaches, immune modulatory properties of certain radiation schemes, additional immune modulation by immunotherapy with ICI and hyperthermia, as well as patient stratification based on genetic and immune constitutions have to be considered. In this context, both the tumor and its microenvironment including cells of the innate and adaptive immune system have to be viewed in synopsis. Knowledge of immune activation and immune suppression by radiation is the basis for well-elaborated addition of certain immunotherapies. In this review, the focus is set on additional immune stimulation by hyperthermia and restoration of an immune response by ICI. The impact of radiation dose and fractionation on immune modulation in multimodal settings has to be considered, as the dynamics of the immune response and the timing between radiotherapy and immunotherapy. Another big challenge is the patient stratification that should be based on matrices of biomarkers, taking into account genetics, proteomics, radiomics, and “immunomics”. One key aim is to turn immunological “cold” tumors into “hot” tumors, and to eliminate barriers of immune-suppressed or immune-excluded tumors. Comprehensive knowledge of immune alterations induced by radiation and immunotherapy when being applied together should be utilized for patient-adapted treatment planning and testing of innovative tumor therapies within clinical trials.

Role of Endoplasmic Reticulum and Mitochondrion in Proton Microbeam Radiation-Induced Bystander Effect

It is well known that mitochondria and the endoplasmic reticulum (ER) play important roles in radiation response, but their functions in radiation-induced bystander effect (RIBE) are largely unclear. In this study, we found that when a small portion of cells in a population of human lung fibroblast MRC-5 cells were precisely irradiated through either the nuclei or cytoplasm with counted microbeam protons, the yield of micronuclei (MN) and the levels of intracellular reactive oxygen species (ROS) in nonirradiated cells neighboring irradiated cells were significantly increased. Mito/ER-tracker staining demonstrated that the mitochondria were clearly activated after nuclear irradiation and ER mass approached a higher level after cytoplasmic irradiation. Moreover, the radiation-induced ROS was diminished by rotenone, an inhibitor of mitochondria activation, but it was not influenced by siRNA interference of BiP, an ER regulation protein. While for nuclear irradiation, rotenone-enhanced radiation-induced ER expression, and BiP siRNA eliminated radiation-induced activation of mitochondria, these phenomena were not observed for cytoplasmic irradiation. Bystander MN was reduced by rotenone but enhanced by BiP siRNA. When the cells were treated with both rotenone and BiP siRNA, the MN yield was reduced for nuclear irradiation but was enhanced for cytoplasmic irradiation. Our results suggest that the organelles of mitochondria and ER have different roles in RIBE with respect to nuclear and cytoplasmic irradiation, and the function of ER is a prerequisite for mitochondrial activation.

Extracellular Vesicles in Modifying the Effects of Ionizing Radiation

Extracellular vesicles (EVs) are membrane-coated nanovesicles actively secreted by almost all cell types. EVs can travel long distances within the body, being finally taken up by the target cells, transferring information from one cell to another, thus influencing their behavior. The cargo of EVs comprises of nucleic acids, lipids, and proteins derived from the cell of origin, thereby it is cell-type specific; moreover, it differs between diseased and normal cells. Several studies have shown that EVs have a role in tumor formation and prognosis. It was also demonstrated that ionizing radiation can alter the cargo of EVs. EVs, in turn can modulate radiation responses and they play a role in radiation-induced bystander effects. Due to their biocompatibility and selective targeting, EVs are suitable nanocarrier candidates of drugs in various diseases, including cancer. Furthermore, the cargo of EVs can be engineered, and in this way they can be designed to carry certain genes or even drugs, similar to synthetic nanoparticles. In this review, we describe the biological characteristics of EVs, focusing on the recent efforts to use EVs as nanocarriers in oncology, the effects of EVs in radiation therapy, highlighting the possibilities to use EVs as nanocarriers to modulate radiation effects in clinical applications.

Actin and Nuclear Envelope Components Influence Ectopic Recombination in the Absence of Swr1

The accuracy of most DNA processes depends on chromatin integrity and dynamics. Our analyses in the yeast Saccharomyces cerevisiae show that an absence of Swr1 (the catalytic and scaffold subunit of the chromatin-remodeling complex SWR) leads to the formation of long-duration Rad52, but not RPA, foci and to an increase in intramolecular recombination. These phenotypes are further increased by MMS, zeocin, and ionizing radiation, but not by double-strand breaks, HU, or transcription/replication collisions, suggesting that they are associated with specific DNA lesions. Importantly, these phenotypes can be specifically suppressed by mutations in: (1) chromatin-anchorage internal nuclear membrane components (mps3∆75-150 and src1∆); (2) actin and actin regulators (act1-157, act1-159, crn1∆, and cdc42-6); or (3) the SWR subunit Swc5 and the SWR substrate Htz1 However, they are not suppressed by global disruption of actin filaments or by the absence of Csm4 (a component of the external nuclear membrane that forms a bridging complex with Mps3, thus connecting the actin cytoskeleton with chromatin). Moreover, swr1∆-induced Rad52 foci and intramolecular recombination are not associated with tethering recombinogenic DNA lesions to the nuclear periphery. In conclusion, the absence of Swr1 impairs efficient recombinational repair of specific DNA lesions by mechanisms that are influenced by SWR subunits, including actin, and nuclear envelope components. We suggest that these recombinational phenotypes might be associated with a pathological effect on homologous recombination of actin-containing complexes.