Systemic DNA damage related to cancer

The Role of MRE11 in the IL-6/STAT3 Pathway of Lung Cancer Cells

MRE11 is a pivotal protein for ATM activation during double-strand DNA break. ATM kinase activations may act as lung cancer biomarkers. The IL-6/STAT3 pathway plays an important role in tumor metastasis, including lung cancer. However, the mechanism between MRE11 and the IL-6/STAT3 pathway is still unclear. In this study, we discovered that MRE11 can interact with STAT3 under IL-6 treatment and regulate STAT3 Tyr705 phosphorylation. After the knockdown of MRE11 in lung cancer cells, we discovered that IL-6 or the conditional medium of THP-1 cells can induce the mRNA expression of STAT3 downstream genes, including CCL2, in the control cells, but not in MRE11-knockdown lung cancer cells. Moreover, CCL2 secretion was lower in MRE11-knockdown lung cancer cells than in control cells after treatment with the conditional medium of RAW264.7 cells. In addition, MRE11 deficiency in lung cancer cells decreases their ability to recruit RAW 264.7 cells. Furthermore, MRE11 is a potential target for lung cancer therapy.

Systemic benefit of radiation therapy via abscopal effect

Evidence of a systemic response related to localized radiation therapy (RT) in cancer management is rare. However, enhancing the immune response via immunotherapy followed by localized RT has shown evidence of tumor shrinkage to non-irradiated metastatic disease thereby inducing an "abscopal effect." Combined induction of the cGAS-STING pathway and activation of IFN-gamma signaling cascade related to RT within an activated immune environment promotes neoantigen presentation and expansion of cytotoxic effector cells enabling enhancement of systemic immune response. A proposed mechanism, case examples, and clinical trial evidence of "abscopal effect" benefit are reviewed. Results support strategic therapeutic testing to enhance "abscopal effect."

Systematic Characterization of the Disruption of Intestine during Liver Tumor Progression in the xmrk Oncogene Transgenic Zebrafish Model

The crosstalk between tumors and their local microenvironment has been well studied, whereas the effect of tumors on distant tissues remains understudied. Studying how tumors affect other tissues is important for understanding the systemic effect of tumors and for improving the overall health of cancer patients. In this study, we focused on the changes in the intestine during liver tumor progression, using a previously established liver tumor model through inducible expression of the oncogene xmrk in zebrafish. Progressive disruption of intestinal structure was found in the tumor fish, displaying villus damage, thinning of bowel wall, increase in goblet cell number, decrease in goblet cell size and infiltration of eosinophils, most of which were observed phenotypes of an inflammatory intestine. Intestinal epithelial cell renewal was also disrupted, with decreased cell proliferation and increased cell death. Analysis of intestinal gene expression through RNA-seq suggested deregulation of genes related to intestinal function, epithelial barrier and homeostasis and activation of pathways in inflammation, epithelial mesenchymal transition, extracellular matrix organization, as well as hemostasis. Gene set enrichment analysis showed common gene signatures between the intestine of liver tumor fish and human inflammatory bowel disease, the association of which with cancer has been recently noticed. Overall, this study represented the first systematic characterization of the disruption of intestine under the liver tumor condition and suggested targeting intestinal inflammation as a potential approach for managing cancer cachexia.

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.

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.

In Situ Detection of Complex DNA Damage Using Microscopy: A Rough Road Ahead

Complexity of DNA damage is considered currently one if not the primary instigator of biological responses and determinant of short and long-term effects in organisms and their offspring. In this review, we focus on the detection of complex (clustered) DNA damage (CDD) induced for example by ionizing radiation (IR) and in some cases by high oxidative stress. We perform a short historical perspective in the field, emphasizing the microscopy-based techniques and methodologies for the detection of CDD at the cellular level. We extend this analysis on the pertaining methodology of surrogate protein markers of CDD (foci) colocalization and provide a unique synthesis of imaging parameters, software, and different types of microscopy used. Last but not least, we critically discuss the main advances and necessary future direction for the better detection of CDD, with important outcomes in biological and clinical setups.

A Functional Immune System Is Required for the Systemic Genotoxic Effects of Localized Irradiation

PURPOSE

Nontargeted effects of ionizing radiation, by which unirradiated cells and tissues are also damaged, are a relatively new paradigm in radiobiology. We recently reported radiation-induced abscopal effects (RIAEs) in normal tissues; namely, DNA damage, apoptosis, and activation of the local and systemic immune responses in C57BL6/J mice after irradiation of a small region of the body. High-dose-rate, synchrotron-generated broad beam or multiplanar x-ray microbeam radiation therapy was used with various field sizes and doses. This study explores components of the immune system involved in the generation of these abscopal effects.

METHODS AND MATERIALS

The following mice with various immune deficiencies were irradiated with the microbeam radiation therapy beam: (1) SCID/IL2γR^-/- (NOD SCID gamma, NSG) mice, (2) wild-type C57BL6/J mice treated with an antibody-blocking macrophage colony-stimulating factor 1 receptor, which depletes and alters the function of macrophages, and (3) chemokine ligand 2/monocyte chemotactic protein 1 null mice. Complex DNA damage (ie, DNA double-strand breaks), oxidatively induced clustered DNA lesions, and apoptotic cells in tissues distant from the irradiation site were measured as RIAE endpoints and compared with those in wild-type C57BL6/J mice.

RESULTS

Wild-type mice accumulated double-strand breaks, oxidatively induced clustered DNA lesions, and apoptosis, enforcing our RIAE model. However, these effects were completely or partially abrogated in mice with immune disruption, highlighting the pivotal role of the immune system in propagation of systemic genotoxic effects after localized irradiation.

CONCLUSIONS

These results underline the importance of not only delineating the best strategies for tumor control but also mitigating systemic radiation toxicity.

Quantitative proteomic profiling of primary cancer-associated fibroblasts in oesophageal adenocarcinoma

BACKGROUND

Cancer-associated fibroblasts (CAFs) form the major stromal component of the tumour microenvironment (TME). The present study aimed to examine the proteomic profiles of CAFs vs. normal fibroblasts (NOFs) from patients with oesophageal adenocarcinoma to gain insight into their pro-oncogenic phenotype.

METHODS

CAFs/NOFs from four patients were sub-cultured and analysed using quantitative proteomics. Differentially expressed proteins (DEPs) were subjected to bioinformatics and compared with published proteomics and transcriptomics  datasets.

RESULTS

Principal component analysis of all profiled proteins showed that CAFs had high heterogeneity and clustered separately from NOFs. Bioinformatics interrogation of the DEPs demonstrated inhibition of adhesion of epithelial cells, adhesion of connective tissue cells and cell death of fibroblast cell lines in CAFs vs. NOFs (p < 0.0001). KEGG pathway analysis showed a significant enrichment of the insulin-signalling pathway (p = 0.03). Gene ontology terms related with myofibroblast phenotype, metabolism, cell adhesion/migration, hypoxia/oxidative stress, angiogenesis, immune/inflammatory response were enriched in CAFs vs. NOFs. Nestin, a stem-cell marker up-regulated in CAFs vs. NOFs, was confirmed to be expressed in the TME with immunohistochemistry.

CONCLUSIONS

The identified pathways and participating proteins may provide novel insight on the tumour-promoting properties of CAFs and unravel novel adjuvant therapeutic targets in the TME.

Microvesicles Contribute to the Bystander Effect of DNA Damage

Genotoxic treatments elicit DNA damage response (DDR) not only in cells that are directly exposed but also in cells that are not in the field of treatment (bystander cells), a phenomenon that is commonly referred to as the bystander effect (BE). However, mechanisms underlying the BE remain elusive. We report here that etoposide and ultraviolet (UV) exposure stimulate the production of microvesicles (MVs) in DU145 prostate cancer cells. MVs isolated from UV-treated DU145 and A431 epidermoid carcinoma cells as well as etoposide-treated DU145 cells induced phosphorylation of ataxia-telangiectasia mutated (ATM) at serine 1981 (indicative of ATM activation) and phosphorylation of histone H2AX at serine 139 (γH2AX) in naïve DU145 cells. Importantly, neutralization of MVs derived from UV-treated cells with annexin V significantly reduced the MV-associated BE activities. Etoposide and UV are known to induce DDR primarily through the ATM and ATM- and Rad3-related (ATR) pathways, respectively. In this regard, MV is likely a common source for the DNA damage-induced bystander effect. However, pre-treatment of DU145 naïve cells with an ATM (KU55933) inhibitor does not affect the BE elicited by MVs isolated from etoposide-treated cells, indicating that the BE is induced upstream of ATM actions. Taken together, we provide evidence supporting that MVs are a source of the DNA damage-induced bystander effect.

Cell-free chromatin from dying cancer cells integrate into genomes of bystander healthy cells to induce DNA damage and inflammation

Bystander cells of the tumor microenvironment show evidence of DNA damage and inflammation that can lead to their oncogenic transformation. Mediator(s) of cell-cell communication that brings about these pro-oncogenic pathologies has not been identified. We show here that cell-free chromatin (cfCh) released from dying cancer cells are the key mediators that trigger both DNA damage and inflammation in the surrounding healthy cells. When dying human cancer cells were cultured along with NIH3T3 mouse fibroblast cells, numerous cfCh emerged from them and rapidly entered into nuclei of bystander NIH3T3 cells to integrate into their genomes. This led to activation of H2AX and inflammatory cytokines NFκB, IL-6, TNFα and IFNγ. Genomic integration of cfCh triggered global deregulation of transcription and upregulation of pathways related to phagocytosis, DNA damage and inflammation. None of these activities were observed when living cancer cells were co-cultivated with NIH3T3 cells. However, upon intravenous injection into mice, both dead and live cells were found to be active. Living cancer cells are known to undergo extensive cell death when injected intravenously, and we observed that cfCh emerging from both types of cells integrated into genomes of cells of distant organs and induced DNA damage and inflammation. γH2AX and NFκB were frequently co-expressed in the same cells suggesting that DNA damage and inflammation are closely linked pathologies. As concurrent DNA damage and inflammation is a potent stimulus for oncogenic transformation, our results suggest that cfCh from dying cancer cells can transform cells of the microenvironment both locally and in distant organs providing a novel mechanism of tumor invasion and metastasis. The afore-described pro-oncogenic pathologies could be abrogated by concurrent treatment with chromatin neutralizing/degrading agents suggesting therapeutic possibilities.

Dynamic alterations of bone marrow cytokine landscape of myelodysplastic syndromes patients treated with 5-azacytidine

Myelodysplastic syndromes (MDS) represent a heterogeneous group of clonal stem cell disorders characterized by ineffective hematopoiesis frequently progressing into acute myeloid leukemia (AML), with emerging evidence implicating aberrant bone marrow (BM) microenvironment and inflammation-related changes. 5-azacytidine (5-AC) represents standard MDS treatment. Besides inhibiting DNA/RNA methylation, 5-AC has been shown to induce DNA damage and apoptosis in vitro. To provide insights into in vivo effects, we assessed the proinflammatory cytokines alterations during MDS progression, cytokine changes after 5-AC, and contribution of inflammatory comorbidities to the cytokine changes in MDS patients. We found that IL8, IP10/CXCL10, MCP1/CCL2 and IL27 were significantly elevated and IL12p70 decreased in BM of MDS low-risk, high-risk and AML patients compared to healthy donors. Repeated sampling of the high-risk MDS patients undergoing 5-AC therapy revealed that the levels of IL8, IL27 and MCP1 in BM plasma were progressively increasing in agreement with in vitro experiments using several cancer cell lines. Moreover, the presence of inflammatory diseases correlated with higher levels of IL8 and MCP1 in low-risk but not in high-risk MDS. Overall, all forms of MDS feature a deregulated proinflammatory cytokine landscape in the BM and such alterations are further augmented by therapy of MDS patients with 5-AC.

Mean frequency and relative fluorescence intensity measurement of γ-H2AX foci dose response in PBL exposed to γ-irradiation: An inter- and intra-laboratory comparison and its relevance for radiation triage

Measurement of γ-H2AX protein changes in the peripheral blood lymphocytes (PBL) of individuals exposed to ionizing radiation is a simple, sensitive, and rapid assay for radiation triage and early marker of dose estimation. The qualitative and quantitative measurements of the protein changes were examined using flow cytometry and microscopy. Whole blood and isolated lymphocytes were exposed in vitro between 0.1 and 5 Gy doses of (60) Co γ-radiation at a dose rate of 1 Gy/min. Radiation induced γ-H2AX foci frequency (n = 3) and relative fluorescence intensity (n = 7) in PBL was measured at 0.5 and 2 hrs postexposure. The observed dose response for γ-H2AX foci frequency at both time points, for whole blood and isolated lymphocytes did not show any significant (P > 0.05) differences. However, when compared with γ-H2AX foci frequency scored manually (microscopy), the semiautomated analysis (captured images) showed a better correlation (r(2) = 0.918) than that obtained with automated (Metafer) scoring (r(2) = 0.690). It is noteworthy to mention that, the γ-H2AX foci frequency quantified using microscopy showed a dose dependent increase up to 2 Gy and the relative fluorescence intensity (RFI) measured with flow cytometry revealed an increase up to 5 Gy in the PBL exposed in vitro. Moreover, a better correlation was observed between the γ-H2AX foci frequency obtained by manual scoring and RFI (r(2) = 0.910). Kinetic studies showed that the γ-H2AX foci remain more or less unchanged up to 4 hrs and reduces gradually over 48 hrs of postexposure at 37°C. Further, inter and intra-laboratory comparisons showed consistency in the scoring of γ-H2AX foci frequency by manual and semiautomated scoring. The overall results suggest that measurement of γ-H2AX (microscopy and flow cytometry) should be employed within 4 to 6 hrs for a reliable dosimetry either by sharing the work load between the laboratories or investing more manpower; however, triage can be possible even up to 48 hrs of postirradiation.

DNA damage foci: Meaning and significance

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

γ-H2AX as a marker for dose deposition in the brain of wistar rats after synchrotron microbeam radiation

Objective

Synchrotron radiation has shown high therapeutic potential in small animal models of malignant brain tumours. However, more studies are needed to understand the radiobiological effects caused by the delivery of high doses of spatially fractionated x-rays in tissue. The purpose of this study was to explore the use of the γ-H2AX antibody as a marker for dose deposition in the brain of rats after synchrotron microbeam radiation therapy (MRT).

Methods

Normal and tumour-bearing Wistar rats were exposed to 35, 70 or 350 Gy of MRT to their right cerebral hemisphere. The brains were extracted either at 4 or 8 hours after irradiation and immediately placed in formalin. Sections of paraffin-embedded tissue were incubated with anti γ-H2AX primary antibody.

Results

While the presence of the C6 glioma does not seem to modulate the formation of γ-H2AX in normal tissue, the irradiation dose and the recovery versus time are the most important factors affecting the development of γ-H2AX foci. Our results also suggest that doses of 350 Gy can trigger the release of bystander signals that significantly amplify the DNA damage caused by radiation and that the γ-H2AX biomarker does not only represent DNA damage produced by radiation, but also damage caused by bystander effects.

Conclusion

In conclusion, we suggest that the γ-H2AX foci should be used as biomarker for targeted and non-targeted DNA damage after synchrotron radiation rather than a tool to measure the actual physical doses.

Transmembrane voltage potential of somatic cells controls oncogene-mediated tumorigenesis at long-range

The microenvironment is increasingly recognized as a crucial aspect of cancer. In contrast and complement to the field's focus on biochemical factors and extracellular matrix, we characterize a novel aspect of host:tumor interaction - endogenous bioelectric signals among non-excitable somatic cells. Extending prior work focused on the bioelectric state of cancer cells themselves, we show for the first time that the resting potentials of distant cells are critical for oncogene-dependent tumorigenesis. In the Xenopus laevis tadpole model, we used human oncogenes such as mutant KRAS to drive formation of tumor-like structures that exhibited overproliferation, increased nuclear size, hypoxia, acidity, and leukocyte attraction. Remarkably, misexpression of hyperpolarizing ion channels at distant sites within the tadpole significantly reduced the incidence of these tumors. The suppression of tumorigenesis could also be achieved by hyperpolarization using native CLIC1 chloride channels, suggesting a treatment modality not requiring gene therapy. Using a dominant negative approach, we implicate HDAC1 as the mechanism by which resting potential changes affect downstream cell behaviors. Based on published data on the voltage-mediated changes of butyrate flux through the SLC5A8 transporter, we present a model linking resting potentials of host cells to the ability of oncogenes to initiate tumorigenesis. Antibiotic data suggest that the relevant butyrate is generated by a native bacterial species, identifying a novel link between the microbiome and cancer that is mediated by alterations in bioelectric signaling.

Building immunity to cancer with radiation therapy

Over the last decade there has been a dramatic shift in the focus of cancer research toward understanding how the body's immune defenses can be harnessed to promote the effectiveness of cytotoxic anti-cancer therapies. The ability of ionizing radiation to elicit anti-cancer immune responses capable of controlling tumor growth has led to the emergence of promising combination-based radio-immunotherapeutic strategies for the treatment of cancer. Herein we review the immunoadjuvant properties of localized radiation therapy and discuss how technological advances in radio-oncology and developments in the field of tumor-immunotherapy have started to revolutionize the therapeutic application of radiotherapy.

Radioprotection of targeted and bystander cells by methylproamine

Introduction

Radioprotective agents are of interest for application in radiotherapy for cancer and in public health medicine in the context of accidental radiation exposure. Methylproamine is the lead compound of a class of radioprotectors which act as DNA binding anti-oxidants, enabling the repair of transient radiation-induced oxidative DNA lesions. This study tested methylproamine for the radioprotection of both directly targeted and bystander cells.

Methods

T98G glioma cells were treated with 15 μM methylproamine and exposed to ¹³⁷Cs γ-ray/X-ray irradiation and He²⁺ microbeam irradiation. Radioprotection of directly targeted cells and bystander cells was measured by clonogenic survival or γH2AX assay.

Results

Radioprotection of directly targeted T98G cells by methylproamine was observed for ¹³⁷Cs γ-rays and X-rays but not for He²⁺ charged particle irradiation. The effect of methylproamine on the bystander cell population was tested for both X-ray irradiation and He²⁺ ion microbeam irradiation. The X-ray bystander experiments were carried out by medium transfer from irradiated to non-irradiated cultures and three experimental designs were tested. Radioprotection was only observed when recipient cells were pretreated with the drug prior to exposure to the conditioned medium. In microbeam bystander experiments targeted and nontargeted cells were co-cultured with continuous methylproamine treatment during irradiation and postradiation incubation; radioprotection of bystander cells was observed.

Discussion and conclusion

Methylproamine protected targeted cells from DNA damage caused by γ-ray or X-ray radiation but not He²⁺ ion radiation. Protection of bystander cells was independent of the type of radiation which the donor population received.

Systemic DNA damage accumulation under in vivo tumor growth can be inhibited by the antioxidant Tempol

Recently we found that mice bearing subcutaneous non-metastatic tumors exhibited elevated levels of two types of complex DNA damage, i.e., double-strand breaks and oxidatively-induced clustered DNA lesions in various tissues throughout the body, both adjacent to and distant from the tumor site. This DNA damage was dependent on CCL2, a cytokine involved in the recruitment and activation of macrophages, suggesting that this systemic DNA damage was mediated via tumor-induced chronic inflammatory responses involving cytokines, activation of macrophages, and consequent free radical production. If free radicals are involved, then a diet containing an antioxidant may decrease the distant DNA damage. Here we repeated our standard protocol in cohorts of two syngeneic tumor-bearing C57BL/6NCr mice that were on a Tempol-supplemented diet. We show that double-strand break and oxidatively-induced clustered DNA lesion levels were considerably decreased, about two- to three fold, in the majority of tissues studied from the tumor-bearing mice fed the antioxidant Tempol compared to the control tumor-bearing mice. Similar results were also observed in nude mice suggesting that the Tempol effects are independent of functioning adaptive immunity. This is the first in vivo study demonstrating the effect of a dietary antioxidant on abscopal DNA damage in tissues distant from a localized source of genotoxic stress. These findings may be important for understanding the mechanisms of genomic instability and carcinogenesis caused by chronic stress-induced systemic DNA damage and for developing preventative strategies.

Does bacterial infection cause genome instability and cancer in the host cell?

Research of the past several decades suggests that bacterial infection can lead to genome instability of the host cell often resulting in cancer development. However, there is still a substantial lack of knowledge regarding possible mechanisms involved in the development of genomic instability. Several questions remain unanswered, namely: Why has the causative relationship between the bacterial infection and cancer been established only for a small number of cancers? What is the mechanism responsible for the induction of genome instability and cancer? Is the infection process required to cause genome instability and cancer? In this review, we present a hypothesis that the bacterial infection, exposure to heat-killed bacteria or even some bacterial determinants may trigger genome instability of exposed and distal cells, and thus may cause cancer. We will discuss the mechanisms of host responses to the bacterial infection and present the possible pathways leading to genome instability and cancer through exposure to bacteria.

The role of oxidative DNA damage in radiation induced bystander effect

Ionizing radiation (IR) has been described as a double-edged sword, since it is used for diagnostic and therapeutic medical applications, and at the same time it is a well known human mutagen and carcinogen, causing wide-ranging chromosomal aberrations. It is nowadays accepted that the detrimental effects of IR are not restricted only in the irradiated cells, but also to non-irradiated bystander or even distant cells manifesting various biological effects. This review presents the role of oxidative stress in the induction of bystander effects referring to the types of the implicated oxidative DNA lesions, the contributing intercellular and intracellular stress mediators, the way they are transmitted from irradiated to bystander cells and finally, the complex role of the bystander effect in the therapeutic efficacy of radiation treatment of cancer.

Abscopal effects of radiation therapy: a clinical review for the radiobiologist

An "abscopal" effect occurs when localized irradiation perturbs the organism as a whole, with consequences that can be either beneficial or detrimental. Mechanistic explanations of this effect are challenging. From the oncologist's perspective, the term refers to distant tumor regression after localized irradiation. On the other hand, from a biologist's point of view, abscopal effects include induction of genomic instability, cell death, and oncogenic transformation in normal tissues. This conceptual dichotomy is explored in this review, with a focus on clinically documented cases of anti-tumor abscopal effects and abscopal effects in normal tissues. This review also outlines several suggested mechanisms for abscopal effects.

Oxidative DNA damage caused by inflammation may link to stress-induced non-targeted effects

A spectrum of radiation-induced non-targeted effects has been reported during the last two decades since Nagasawa and Little first described a phenomenon in cultured cells that was later called the "bystander effect". These non-targeted effects include radiotherapy-related abscopal effects, where changes in organs or tissues occur distant from the irradiated region. The spectrum of non-targeted effects continue to broaden over time and now embrace many types of exogenous and endogenous stressors that induce a systemic genotoxic response including a widely studied tumor microenvironment. Here we discuss processes and factors leading to DNA damage induction in non-targeted cells and tissues and highlight similarities in the regulation of systemic effects caused by different stressors.

DNA damage response in peritumoral regions of oesophageal cancer microenvironment

Oesophageal cancer is a highly aggressive disease, ranking among the 10 most common cancers in the world. Oesophageal cancer patients often suffer from multi-origin tumours, and therefore, it is important to improve our understanding of the complex biology, which underpins microenvironmental interactions in this disease. Extensive evidence indicates that the interaction of tumours with their microenvironment may play a crucial role in tumour initiation and progression. In this study, we analysed DNA damage response (DDR), immune cell invasion and cancer progression in 47 patients with oesophageal cancer from three different regions (tumour tissue, tumour-proximal non-malignant tissue and distant non-malignant tissue). Accumulated DDR (positive staining for γH2AX and phospho-ATM) was evident within tumour tissue and significantly increased in non-malignant tissue surrounding the tumour cells although activation of p53 by phosphorylation at serine 15 was observed only in tumour tissue. The level of DDR detected in cancer microenvironment depended largely on the distance from the tumour, as stronger DDR was observed in tumour-proximal areas compared with that in tumour-distant tissue. Induction of DDR in non-malignant tissues correlated with increased invasion of lymphocytes and macrophages and with precancerous progression. Our results support that DDR is induced in oesophageal cancer surrounding non-malignant epithelial cells, via activation of an inflammatory process, which in turn contributes to the progression of precancerous lesions. These findings provide novel pathological evidence for inflammation and DDR in influencing non-metastatic progression of cancer in its microenvironment.

Non-targeted effects of photon and particle irradiation and the interaction with the immune system

Ionizing irradiation is an important clinical approach to treat solid tumors. Modern radiation technologies aim to selectively kill tumor cells and protect the surrounding normal tissue. The standard paradigm for radiation effects in cellular systems involves damage of the DNA including DNA double-strand breaks, which are considered as most effective in destroying tumor cells. Due to their enhanced physical and radiobiological properties, high-linear energy transfer radiation qualities are of special interest in tumor therapy. Future radiation therapy strategies aim to utilize carbon ions to effectively treat highly aggressive tumors. More recently, evidence is emerging for non-DNA targeted effects of radiation, including mutations, chromosomal aberrations, and changes in gene expression, which can occur in cells that were not directly exposed to radiation. Radiation oncologists are only gradually beginning to appreciate the clinical relevance of radiation-induced bystander effects, genomic instability, and abscopal effects. Since these effects are sensed by the immune system, a combination of immunotherapy and irradiation presents a new therapeutic opportunity in the future.

Ionizing radiation-induced metabolic oxidative stress and prolonged cell injury

Cellular exposure to ionizing radiation leads to oxidizing events that alter atomic structure through direct interactions of radiation with target macromolecules or via products of water radiolysis. Further, the oxidative damage may spread from the targeted to neighboring, non-targeted bystander cells through redox-modulated intercellular communication mechanisms. To cope with the induced stress and the changes in the redox environment, organisms elicit transient responses at the molecular, cellular and tissue levels to counteract toxic effects of radiation. Metabolic pathways are induced during and shortly after the exposure. Depending on radiation dose, dose-rate and quality, these protective mechanisms may or may not be sufficient to cope with the stress. When the harmful effects exceed those of homeostatic biochemical processes, induced biological changes persist and may be propagated to progeny cells. Physiological levels of reactive oxygen and nitrogen species play critical roles in many cellular functions. In irradiated cells, levels of these reactive species may be increased due to perturbations in oxidative metabolism and chronic inflammatory responses, thereby contributing to the long-term effects of exposure to ionizing radiation on genomic stability. Here, in addition to immediate biological effects of water radiolysis on DNA damage, we also discuss the role of mitochondria in the delayed outcomes of ionization radiation. Defects in mitochondrial functions lead to accelerated aging and numerous pathological conditions. Different types of radiation vary in their linear energy transfer (LET) properties, and we discuss their effects on various aspects of mitochondrial physiology. These include short and long-term in vitro and in vivo effects on mitochondrial DNA, mitochondrial protein import and metabolic and antioxidant enzymes.

Molecular markers for cancer prognosis and treatment: have we struck gold?

The last decade has witnessed an emerging role for molecular or biochemical markers indicating a specific cellular mechanism or tissue function, often called 'biomarkers'. Biomarkers such as altered DNA, proteins and inflammatory cytokines are critical in cancer research and strategizing treatment in the clinic. In this review we look at the application of biological indicators to cancer research and highlight their roles in cancer detection and treatment. With technological advances in gene expression, genomic and proteomic analysis, biomarker discovery is expanding fast. We focus on some of the predominantly used markers in different types of malignancies, their advantages, and their limitations. Finally we conclude by looking at the future of biomarkers, their utility in the tumorigenic studies, and the progress towards personalized treatment strategies.

Detection of clustered DNA lesions: Biological and clinical applications

Humans are daily exposed to background radiation and various sources of oxidative stress. My research has focused in the last 12 years on the effects of ionizing radiation on DNA, which is considered as the key target of radiation in the cell. Ionizing radiation and endogenous cellular oxidative stress can also induce closely spaced oxidatively induced DNA lesions called “clusters” of DNA damage or locally multiply damage sites, as first introduced by John Ward. I am now interested in the repair mechanisms of clustered DNA damage, which is considered as the most difficult for the cell to repair. A main part of my research is devoted to evaluating the role of clustered DNA damage in the promotion of carcinogenesis in vitro and in vivo. Currently in my laboratory, there are two main ongoing projects. (1) Study of the role of BRCA1 and DNA-dependent protein kinase catalytic subunit repair proteins in the processing of clustered DNA damage in human cancer cells. For this project, we use several tumor cell lines, such as breast cancer cell lines MCF-7 and HCC1937 (BRCA1 deficient) and human glioblastoma cells MO59J/K; and (2) Possible use of DNA damage clusters as novel cancer biomarkers for prognostic and therapeutic applications related to modulation of oxidative stress. In this project human tumor and mice tissues are being used.