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

Mechanisms of radioresistance and the underlying signaling pathways in colorectal cancer cells

Radiotherapy is one of the most common modalities for the treatment of a wide range of tumors, including colorectal cancer (CRC); however, radioresistance of cancer cells remains a major limitation for this treatment. Following radiotherapy, the activities of various cellular mechanisms and cell signaling pathways are altered, resulting in the development of radioresistance, which leads to therapeutic failure and poor prognosis in patients with cancer. Furthermore, even though several inhibitors have been developed to target tumor resistance, these molecules can induce side effects in nontumor cells due to low specificity and efficiency. However, the role of these mechanisms in CRC has not been extensively studied. This review discusses recent studies regarding the relationship between radioresistance and the alterations in a series of cellular mechanisms and cell signaling pathways that lead to therapeutic failure and tumor recurrence. Our review also presents recent advances in the in vitro/in vivo study models aimed at investigating the radioresistance mechanism in CRC. Furthermore, it provides a relevant biochemical basis in theory, which can be useful to improve radiotherapy sensitivity and prolong patient survival.

The cross-talk between Bax, Bcl2, caspases, and DNA damage in bystander HepG2 cells is regulated by γ-radiation dose and time of conditioned media transfer

Although radiation-induced bystander effects have been broadly explored in various biological systems, the molecular mechanisms and the consequences of different regulatory factors (dose, time, cell type) on bystander responses are not clearly understood. This study investigates the effects of irradiated cell-conditioned media (ICCM) collected at different times post-irradiation on bystander cancer cells regarding DNA damage and apoptosis induction. Human hepatocellular carcinoma HepG2 cells were exposed to γ-ray doses of 2 Gy, 5 Gy, and 8 Gy. In the early and late stages (1 h, 2 h, and 24 h) after irradiation, the ICCM was collected and transferred to unirradiated cells. Compared to control, bystander cells showed an increased level of H2AX phosphorylation, mitochondrial membrane depolarization, and elevation of intrinsic apoptotic pathway mediators such as p53, Bax, cas9, cas-3, and PARP cleavage. These results were confirmed by phosphatidylserine (PS) externalization and scanning electron microscopic observations, suggesting a rise in bystander HepG2 cell apoptosis. Anti-apoptotic Bcl2-level and viability were lower in bystander cells compared to control. The highest effects were observed in 8 Gy γ radiation-induced bystander cells. Even though the bystander effect was persistent at all time points of the study, ICCM at the early time points (1 or 2 h) had the most significant impact on the apoptosis markers in bystander cells. Nevertheless, 24 h ICCM induced the highest increase in H2AX and p53 phosphorylation and Bax levels. The effects of ICCM of irradiated HepG2 cells were additionally studied in normal liver cells BRL-3A to simulate actual radiotherapy conditions. The outcomes suggest that the expression of the signaling mediators in bystander cells is highly dynamic. A cross-talk between those signaling mediators regulates bystander responses depending on the radiation dose and time of incubation post-irradiation.

Involvement of miRNAs in cellular responses to radiation

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Synchrotron X-Ray Radiation-Induced Bystander Effect: An Impact of the Scattered Radiation, Distance From the Irradiated Site and p53 Cell Status

Synchrotron radiation, especially microbeam radiotherapy (MRT), has a great potential to improve cancer radiotherapy, but non-targeted effects of synchrotron radiation have not yet been sufficiently explored. We have previously demonstrated that scattered synchrotron radiation induces measurable γ-H2AX foci, a biomarker of DNA double-strand breaks, at biologically relevant distances from the irradiated field that could contribute to the apparent accumulation of bystander DNA damage detected in cells and tissues outside of the irradiated area. Here, we quantified an impact of scattered radiation to DNA damage response in "naïve" cells sharing the medium with the cells that were exposed to synchrotron radiation. To understand the effect of genetic alterations in naïve cells, we utilised p53-null and p53-wild-type human colon cancer cells HCT116. The cells were grown in two-well chamber slides, with only one of nine zones (of equal area) of one well irradiated with broad beam or MRT. γ-H2AX foci per cell values induced by scattered radiation in selected zones of the unirradiated well were compared to the commensurate values from selected zones in the irradiated well, with matching distances from the irradiated zone. Scattered radiation highly impacted the DNA damage response in both wells and a pronounced distance-independent bystander DNA damage was generated by broad-beam irradiations, while MRT-generated bystander response was negligible. For p53-null cells, a trend for a reduced response to scattered irradiation was observed, but not to bystander signalling. These results will be taken into account for the assessment of genotoxic effects in surrounding non-targeted tissues in preclinical experiments designed to optimise conditions for clinical MRT and for cancer treatment in patients.

The γH2AX DSB marker may not be a suitable biodosimeter to measure the biological MRT valley dose

PURPOSE

γH2AX biodosimetry has been proposed as an alternative dosimetry method for microbeam radiation therapy (MRT) because conventional dosimeters, such as ionization chambers, lack the spatial resolution required to accurately measure the MRT valley dose. Here we investigated whether γH2AX biodosimetry should be used to measure the biological valley dose of MRT-irradiated mammalian cells.

MATERIALS AND METHODS

We irradiated human skin fibroblasts and mouse skin flaps with synchrotron MRT and broad beam (BB) radiation. BB doses of 1-5 Gy were used to generate a calibration curve in order to estimate the biological MRT valley dose using the γH2AX assay.

RESULTS

Our key finding was that MRT induced a non-linear dose response compared to BB, where doses 2-3 times greater showed the same level of DNA DSB damage in the valley in cell and tissue studies. This indicates that γH2AX may not be an appropriate biodosimeter to estimate the biological valley doses of MRT-irradiated samples. We also established foci yields of 5.9 ± 0 . 04 and 27.4 ± 2 . 5   foci/cell/Gy in mouse skin tissue and human fibroblasts respectively, induced by BB. Using Monte Carlo simulations, a linear dose response was seen in cell and tissue studies and produced predicted peak-to-valley dose ratios (PVDRs) of ∼30 and ∼107 for human fibroblasts and mouse skin tissue respectively.

CONCLUSIONS

Our report highlights novel MRT radiobiology, attempts to explain why γH2AX may not be an appropriate biodosimeter and suggests further studies aimed at revealing the biological and cellular communication mechanisms that drive the normal tissue sparing effect, which is characteristic of MRT.

Suppression of innate immune signaling molecule, MAVS, reduces radiation-induced bystander effect

PURPOSE

Mitochondrial antiviral signaling (MAVS) protein, located in the mitochondrial out-membrane, is necessary for IFN-beta induction and IFN-stimulated gene expression in response to external stress such as viral invasion and ionizing radiation (IR). Although the involvement of radiation induced bystander effect (RIBE) has been investigated for decades for secondary cancer risk related to radiotherapy, the underlying regulatory mechanisms remain largely unclear, especially the roles played by the immune factors such as MAVS.

MATERIAL AND METHODS

MAVS gene knockout cells using CRISPR/Cas9 technology were used as donor cells or recipient cells to assess the role of MAVS in RIBE by means of co-cultured system. The micronucleus and γH2AX foci in the recipient cells were counted to demonstrate the degree of RIBE. The reactive oxygen species (ROS) level in the recipient was measured using the fluorescent dye 2'7'-dichlorofluorescein.

RESULTS

Firstly, we found that MAVS expression level was different in A549, BEAS-2B, U937 and HepG2 cells. Cell co-culture experiments showed that MAVS participate in RIBE. Interestingly, the RIBE response was more significant in recipient cells with higher level of MAVS (i.e. A549) than that in recipient cells showing lower level of MAVS (i.e. BEAS-2B). Further, the bystander response was dramatically suppressed in MAVS-silenced A549 and BEAS-2B recipient cells. MAVS-silenced recipient cells exhibited lower level of ROS induced by IR.

CONCLUSIONS

Our results indicated that the innate immune signaling molecule MAVS in recipient cells participate in RIBE. ROS is an important factor in RIBE via MAVS pathway and MAVS may be a potential target for the precise radiotherapy and radioprotection.

Integrated analysis of transcriptomic and metabolomic profiling reveal the p53 associated pathways underlying the response to ionizing radiation in HBE cells

Background

Radiation damage to normal tissues is a serious concern. P53 is a well-known transcription factor which is closely associated with radiation-induced cell damage. Increasing evidence has indicated that regulation of metabolism by p53 represents a reviving mechanism vital to protect cell survival. We aimed to explore the interactions of radiation-induced transcripts with the cellular metabolism regulated by p53.

Methods

Human bronchial epithelial (HBE) cell line was used to knockout p53 using CRISPR/cas9. Transcriptomic analysis was conducted by microarray and metabolomic analysis was conducted by GC–MS. Integrative omics was performed using MetaboAnalyst.

Results

326 mRNAs showed significantly altered expression in HBE p53-/- cells post-radiation, of which 269 were upregulated and 57 were downregulated. A total of 147 metabolites were altered, including 45 that increased and 102 that decreased. By integrated analysis of both omic data, we found that in response to radiation insult, nitrogen metabolism, glutathione metabolism, arachidonic acid metabolism, and glycolysis or gluconeogenesis may be dysregulated due to p53.

Conclusions

Our study provided a pilot comprehensive view of the metabolism regulated by p53 in response to radiation exposure. Detailed evaluation of these important p53-regulated metabolic pathways, including their roles in the response to radiation of cells, is essential to elucidate the molecular mechanisms of radiation-induced damage.

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

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

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

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

An investigation into neutron-induced bystander effects: How low can you go?

Neutron radiation is very harmful to both individual organisms and the environment. A n understanding of all aspects of both direct and indirect effects of radiation is necessary to accurately assess the risk of neutron radiation exposure. This review seeks to review current evidence in the literature for radiation-induced bystander effects and related effects attributable to neutron radiation. It also attempts to determine if the suggested evidence in the literature is sufficient to justify claims that neutron-based radiation can cause radiation-induced bystander effects. Lastly, the present paper suggests potential directions for future research concerning neutron radiation-induced bystander effects. Data was collected from studies investigating radiation-induced bystander effects and was used to mathematically generate pooled datasets and putative trends; this was done to potentially elucidate both the appearance of a conventional trend for radiation-induced bystander effects in studies using different types of radiation. Furthermore, literature review was used to compare studies utilizing similar tissue models to determine if neutron effects follow similar trends as those produced by electromagnetic radiation. We conclude that the current understanding of neutron-attributable radiation-induced bystander effects is incomplete. Various factors such as high gamma contamination during the irradiations, unestablished thresholds for gamma effects, different cell lines, energies, and different dose rates affected our ability to confirm a relationship between neutron irradiation and RIBE, particularly in low-dose regions below 100 mGy. It was determined through meta-analysis of the data that effects attributable to neutrons do seem to exist at higher doses, while gamma effects seem likely predominant at lower dose regions. Therefore, whether neutrons can induce bystander effects at lower doses remains unclear. Further research is required to confirm these findings and various recommendations are made to assist in this effort. With these recommendations, we hope that research conducted in the future will be better equipped to explore the indirect effects of neutron radiation as they pertain to biological and ecological phenomena.

Bystander effectors of chondrosarcoma cells irradiated at different LET impair proliferation of chondrocytes

While the dose-response relationship of radiation-induced bystander effect (RIBE) is controversial at low and high linear energy transfer (LET), mechanisms and effectors of cell-to-cell communication stay unclear and highly dependent of cell type. In the present study, we investigated the capacity of chondrocytes in responding to bystander factors released by chondrosarcoma cells irradiated at different doses (0.05 to 8 Gy) with X-rays and C-ions. Following a medium transfer protocol, cell survival, proliferation and DNA damages were quantified in bystander chondrocytes. The bystander factors secreted by chondrosarcoma cells were characterized. A significant and major RIBE response was observed in chondrocyte cells (T/C-28a2) receiving conditioned medium from chondrosarcoma cells (SW1353) irradiated with 0.1 Gy of X-rays and 0.05 Gy of C-ions, resulting in cell survivals of 36% and 62%, respectively. Micronuclei induction in bystander cells was observed from the same low doses. The cell survival results obtained by clonogenic assays were confirmed using impedancemetry. The bystander activity was vanished after a heat treatment or a dilution of the conditioned media. The cytokines which are well known as bystander factors, TNF-α and IL-6, were increased as a function of doses and LET according to an ELISA multiplex analysis. Together, the results demonstrate that irradiated chondrosarcoma cells can communicate stress factors to non-irradiated chondrocytes, inducing a wide and specific bystander response related to both doses and LET.

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

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

The Optimal Radiation Dose to Induce Robust Systemic Anti-Tumor Immunity

The synergy of radiation and the immune system is currently receiving significant attention in oncology as numerous studies have shown that cancer irradiation can induce strong anti-tumor immune responses. It remains unclear, however, what are the best radiation fractionation protocols to maximize the therapeutic benefits of this synergy. Here, we present a novel mathematical model that can be used to predict and dissect the complexity of the immune-mediated response at multiple tumor sites after applying focal irradiation and systemic immunotherapy. We successfully calibrate the proposed framework with published experimental data, in which two tumors were grown in mice at two spatially-separated sites from which only one was irradiated using various radiation fractionation protocols with and without concurrent systemic immunotherapy. The proposed model is calibrated to fit the temporal dynamics of tumor volume at both sites and can predict changes in immune infiltration in the non-irradiated tumors. The model was then used to investigate additional radiation fractionation protocols. Model simulations suggest that the optimal radiation doses per fraction to maximize anti-tumor immunity are between 10 and 13 Gy, at least for the experimental setting used for model calibration. This work provides the framework for evaluating radiation fractionation protocols for radiation-induced immune-mediated systemic anti-tumor responses.

Differential Radiation Sensitivity in p53 Wild-Type and p53-Deficient Tumor Cells Associated with Senescence but not Apoptosis or (Nonprotective) Autophagy

Studies of radiation interaction with tumor cells often focus on apoptosis as an end point; however, clinically relevant doses of radiation also promote autophagy and senescence. Moreover, functional p53 has frequently been implicated in contributing to radiation sensitivity through the facilitation of apoptosis. To address the involvement of apoptosis, autophagy, senescence and p53 status in the response to radiation, the current studies utilized isogenic H460 non-small cell lung cancer cells that were either p53-wild type (H460wt) or null (H460crp53). As anticipated, radiosensitivity was higher in the H460wt cells than in the H460crp53 cell line; however, this differential radiation sensitivity did not appear to be a consequence of apoptosis. Furthermore, radiosensitivity did not appear to be reduced in association with the promotion of autophagy, as autophagy was markedly higher in the H460wt cells. Despite radiosensitization by chloroquine in the H460wt cells, the radiation-induced autophagy proved to be essentially nonprotective, as inhibition of autophagy via 3-methyl adenine (3-MA), bafilomycin A1 or ATG5 silencing failed to alter radiation sensitivity or promote apoptosis in either the H460wt or H460crp53 cells. Radiosensitivity appeared to be most closely associated with senescence, which occurred earlier and to a greater extent in the H460wt cells. This finding is consistent with the in-depth proteomics analysis on the secretomes from the H460wt and H460crp53 cells (with or without radiation exposure) that showed no significant association with radioresistance-related proteins, whereas several senescence-associated secretory phenotype (SASP) factors were upregulated in H460wt cells relative to H460crp53 cells. Taken together, these findings indicate that senescence, rather than apoptosis, plays a central role in determination of radiosensitivity; furthermore, autophagy is likely to have minimal influence on radiosensitivity under conditions where autophagy takes the nonprotective form.

Changes in gene expression as one of the key mechanisms involved in radiation-induced bystander effect

The radiation-induced bystander effect (RIBE) refers to the manifestation of responses by non-targeted/non-hit cells or tissues situated in proximity to cells and tissues directly exposed to ionizing radiation (IR). The RIBE is elicited by agents and factors released by IR-hit cells. The growing body of data suggests that the underlying mechanisms of the RIBE are multifaceted depending both on the biological (characteristics of directly IR-exposed cells, bystander cells, intercellular milieu) and the physical (dose, rate and type of IR, time after exposure) factors/parameters. Although the exact identity of bystander signal(s) is yet to be identified, the published data indicate changes in gene expression for multiple types of RNA (mRNA, microRNA, mitochondrial RNA, long non-coding RNA, small nucleolar RNA) as being one of the major responses of cells and tissues in the context of the RIBE. Gene expression profiles demonstrate a high degree of variability between distinct bystander cell and tissue types. These alterations could independently, or in a signaling cascade, result in the manifestation of readily observable endpoints, including changes in viability and genomic instability. Here, the relevant publications on the gene candidates and signaling pathways involved in the RIBE are reviewed, and a framework for future studies, both in vitro and in vivo, on the genetic aspect of the RIBE is provided.

Inhibition of survivin enhances radiosensitivity of esophageal cancer cells by switching radiation-induced senescence to apoptosis

Purpose

Strategies to increase radiosensitivity are urgently needed. Combining radiosensitizing reagents with radiotherapy could improve the outcome of cancer treatment. Some preclinical studies showed that sepantronium bromide (YM155) could sensitize cancer cells to radiation by inhibiting the survivin protein. In this study, we try to investigate the function of YM155 on radiosensitivity of esophageal squamous cell carcinoma (ESCC) cells.

Materials and methods

ESCC cell lines were treated with radiation and YM155, and the radiation efficacy was evaluated by cell counting kit-8 assay and clonogenic survival assay. Cell senescence was measured by senescence-associated β-galactosidase staining. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay, fluorescein isothiocyanate-labeled Annexin V/propidium iodide assay, and poly ADP-ribose polymerase cleavage were used to detect apoptosis. KYSE150 xenografts model was used to test the efficacy of radiation combined with YM155.

Results

YM155 could inhibit the upregulation of survivin induced by radiation in all ESCC cell lines, but the efficacy of radiosensitization varied in different cell lines. Radiation-induced senescence in KYSE150 and KYSE410 cells, and the combination with YM155 inhibited senescence and promoted apoptosis of ESCC cells, thereby enhancing radiosensitivity. Combination with YM155 and radiation delayed the growth of KYSE150 xenografts in nude mice by switching radiation-induced senescence to apoptosis. When p21 was inhibited in KYSE150 cells, radiation did not induce senescence, and the radiosensitization of YM155 was also attenuated. In KYSE510 and KYSE180 cells, radiation did not induce senescence, and YM155 could not enhance the radiosensitivity.

Conclusion

Our results suggest a new mechanism that YM155 might sensitize ESCC cells to radiation by switching radiation-induced senescence to apoptosis. The major determinant of radiosensitization by YM155 might be the induction of senescence by radiation.

The node-weighted Steiner tree approach to identify elements of cancer-related signaling pathways

Background

Cancer constitutes a momentous health burden in our society. Critical information on cancer may be hidden in its signaling pathways. However, even though a large amount of money has been spent on cancer research, some critical information on cancer-related signaling pathways still remains elusive. Hence, new works towards a complete understanding of cancer-related signaling pathways will greatly benefit the prevention, diagnosis, and treatment of cancer.

Results

We propose the node-weighted Steiner tree approach to identify important elements of cancer-related signaling pathways at the level of proteins. This new approach has advantages over previous approaches since it is fast in processing large protein-protein interaction networks. We apply this new approach to identify important elements of two well-known cancer-related signaling pathways: PI3K/Akt and MAPK. First, we generate a node-weighted protein-protein interaction network using protein and signaling pathway data. Second, we modify and use two preprocessing techniques and a state-of-the-art Steiner tree algorithm to identify a subnetwork in the generated network. Third, we propose two new metrics to select important elements from this subnetwork. On a commonly used personal computer, this new approach takes less than 2 s to identify the important elements of PI3K/Akt and MAPK signaling pathways in a large node-weighted protein-protein interaction network with 16,843 vertices and 1,736,922 edges. We further analyze and demonstrate the significance of these identified elements to cancer signal transduction by exploring previously reported experimental evidences.

Conclusions

Our node-weighted Steiner tree approach is shown to be both fast and effective to identify important elements of cancer-related signaling pathways. Furthermore, it may provide new perspectives into the identification of signaling pathways for other human diseases.

Modulation by neighboring cells of the responses and fate of melanoma cells irradiated with UVA

UVA radiation, which accounts for about 95% of the solar spectrum, contributes to and may be the etiological factor of skin cancers of which malignant melanoma is the most aggressive. UVA causes oxidative stress in various types of cells in the skin, keratinocyte, melanocytes, and fibroblasts, which is responsible for its cytotoxic effect. Here we used a transwell system to explore how the responses of melanoma cells to a low dose of UVA (20kJ/m², ~10% of the minimal erythema dose) are influenced by neighboring co-cultured melanoma cells or fibroblasts. This dose had a low toxicity for melanoma cells, but after irradiation, co-culture with non-irradiated melanoma cells caused a strong decline in their viability and an increased frequency of apoptosis, whereas co-culture with fibroblast exerted a protective effect on irradiated melanoma cells. At the same time, the presence of non-irradiated cells, especially fibroblasts, decreased the level of UVA-induced reactive oxygen and nitrogen species. Interleukins efficiently produced by fibroblasts seem to be main players in these effects. Our studies reveal that coexistence of fibroblasts with melanoma cells may strongly modulate the direct action and may change bystander effects exerted by UVA light. Similar modulation of the effect of UVA on melanoma cells in vivo by bystander-like signaling from neighboring cells would have consequences for the development of malignant melanoma.

Sarcomatoid Carcinoma Manifesting as Recurrent Rectal Cancer and Mimicking Radiation-Induced Extraskeletal Osteosarcoma: A Case Report

Here, we report an unusual case of sarcomatoid carcinoma mimicking extraskeletal osteosarcoma that manifested as recurrent rectal cancer. Five years earlier, a 76-year-old male patient had undergone neoadjuvant chemoradiotherapy followed by a laparoscopic low anterior resection due to adenocarcinoma of the rectum. He was admitted because of pain in the anus and left hip. He underwent abdominal computed tomography that revealed a newly developed left perirectal mass with gluteus maximus invasion measuring up to 8 cm, and therefore, an abdominoperineal resection was performed. Histologically, the tumor revealed sheets of spindled or epithelioid cells, an absence of gland formation, mucicarmine and periodic acid-Schiff stain negativity, and prominent intercellular deposits of osteoid-like calcified tissue. Tumor cells were diffusely immunoreactive for vimentin and cytokeratins. Ultrastructural examination demonstrated microvilli on the surface or within intercellular spaces. In this report, we also discuss the possible pathogenesis as well as the differential diagnosis.

Development of a population of cancer cells: Observation and modeling by a Mixed Spatial Evolutionary Games approach

Living cells, like whole living organisms during evolution, communicate with their neighbors, interact with the environment, divide, change their phenotypes, and eventually die. The development of specific ways of communication (through signaling molecules and receptors) allows some cellular subpopulations to survive better, to coordinate their physiological status, and during embryonal development to create tissues and organs or in some conditions to become tumors. Populations of cells cultured in vitro interact similarly, also competing for space and nutrients and stimulating each other to better survive or to die. The results of these intercellular interactions of different types seem to be good examples of biological evolutionary games, and have been the subjects of simulations by the methods of evolutionary game theory where individual cells are treated as players. Here we present examples of intercellular contacts in a population of living human cancer HeLa cells cultured in vitro and propose an evolutionary game theory approach to model the development of such populations. We propose a new technique termed Mixed Spatial Evolutionary Games (MSEG) which are played on multiple lattices corresponding to the possible cellular phenotypes which gives the possibility of simulating and investigating the effects of heterogeneity at the cellular level in addition to the population level. Analyses performed with MSEG suggested different ways in which cellular populations develop in the case of cells communicating directly and through factors released to the environment.

Transcription Factors in the Cellular Response to Charged Particle Exposure

Charged particles, such as carbon ions, bear the promise of a more effective cancer therapy. In human spaceflight, exposure to charged particles represents an important risk factor for chronic and late effects such as cancer. Biological effects elicited by charged particle exposure depend on their characteristics, e.g., on linear energy transfer (LET). For diverse outcomes (cell death, mutation, transformation, and cell-cycle arrest), an LET dependency of the effect size was observed. These outcomes result from activation of a complex network of signaling pathways in the DNA damage response, which result in cell-protective (DNA repair and cell-cycle arrest) or cell-destructive (cell death) reactions. Triggering of these pathways converges among others in the activation of transcription factors, such as p53, nuclear factor κB (NF-κB), activated protein 1 (AP-1), nuclear erythroid-derived 2-related factor 2 (Nrf2), and cAMP responsive element binding protein (CREB). Depending on dose, radiation quality, and tissue, p53 induces apoptosis or cell-cycle arrest. In low LET radiation therapy, p53 mutations are often associated with therapy resistance, while the outcome of carbon ion therapy seems to be independent of the tumor's p53 status. NF-κB is a central transcription factor in the immune system and exhibits pro-survival effects. Both p53 and NF-κB are activated after ionizing radiation exposure in an ataxia telangiectasia mutated (ATM)-dependent manner. The NF-κB activation was shown to strongly depend on charged particles' LET, with a maximal activation in the LET range of 90-300 keV/μm. AP-1 controls proliferation, senescence, differentiation, and apoptosis. Nrf2 can induce cellular antioxidant defense systems, CREB might also be involved in survival responses. The extent of activation of these transcription factors by charged particles and their interaction in the cellular radiation response greatly influences the destiny of the irradiated and also neighboring cells in the bystander effect.

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

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