Effects Of high-LET Radiation Research Articles

NF-κB in the Radiation Response of A549 Non-Small Cell Lung Cancer Cells to X-rays and Carbon Ions under Hypoxia.

Cellular hypoxia, detectable in up to 80% of non-small cell lung carcinoma (NSCLC) tumors, is a known cause of radioresistance. High linear energy transfer (LET) particle radiation might be effective in the treatment of hypoxic solid tumors, including NSCLC. Cellular hypoxia can activate nuclear factor κB (NF-κB), which can modulate radioresistance by influencing cancer cell survival. The effect of high-LET radiation on NF-κB activation in hypoxic NSCLC cells is unclear. Therefore, we compared the effect of low (X-rays)- and high (12C)-LET radiation on NF-κB responsive genes' upregulation, as well as its target cytokines' synthesis in normoxic and hypoxic A549 NSCLC cells. The cells were incubated under normoxia (20% O2) or hypoxia (1% O2) for 48 h, followed by irradiation with 8 Gy X-rays or 12C ions, maintaining the oxygen conditions until fixation or lysis. Regulation of NF-κB responsive genes was evaluated by mRNA sequencing. Secretion of NF-κB target cytokines, IL-6 and IL-8, was quantified by ELISA. A greater fold change increase in expression of NF-κB target genes in A549 cells following exposure to 12C ions compared to X-rays was observed, regardless of oxygenation status. These genes regulate cell migration, cell cycle, and cell survival. A greater number of NF-κB target genes was activated under hypoxia, regardless of irradiation status. These genes regulate cell migration, survival, proliferation, and inflammation. X-ray exposure under hypoxia additionally upregulated NF-κB target genes modulating immunosurveillance and epithelial-mesenchymal transition (EMT). Increased IL-6 and IL-8 secretion under hypoxia confirmed NF-κB-mediated expression of pro-inflammatory genes. Therefore, radiotherapy, particularly with X-rays, may increase tumor invasiveness in surviving hypoxic A549 cells.

Investigation of the Impact of Temporal Dose Delivery Patterns of Ion Irradiation with the Local Effect Model.

We present an extension of the Local Effect Model (LEM) to include time-dose relationships for predicting effects of protracted and split-dose ion irradiation at arbitrary LET. With this kinetic extension, the spatial and temporal induction and processing of DNA double strand breaks (DSB) in cellular nuclei can be simulated for a wide range of ion radiation qualities, doses and dose rates. The key concept of the extension is based on the joint spatial and temporal coexistence of initial DSB, leading to the formation of clustered DNA damage on the µm scale (as defined e.g., by the size scale of Mbp chromatin loops), which is considered to have an increased cellular lethality as compared to isolated, single DSB. By simulating the time dependent induction and repair of DSB and scoring of isolated and clustered DSB upon irradiation, the impact of dose rate and split dose on the cell survival probability can be computed. In a first part of this work, we systematically analyze the predicted impact of protraction in dependence of factors like dose, LET, ion species and radiosensitivity as characterized by the photon LQ-parameters. We establish links to common concepts that describe dose rate effects for low LET radiation. We also compare the model predictions to experimental data and find agreement with the general trends observed in the experiments. The relevant concepts of our approach are compared to other models suitable for predicting time effects. We investigate an apparent analogy between spatial and temporal concentration of radiation delivery, both leading to increased effectiveness, and discuss similarities and differences between the general dependencies of these clustering effects on their impacting factors. Finally, we conclude that the findings give additional support for the general concept of the LEM, i.e. the characterization of high LET radiation effects based on the distinction of just two classes of DSB (isolated DSB and clustered DSB).

Non-targeted effects and space radiation risks for astronauts on multiple International Space Station and lunar missions

Future space travel to the earth's moon or the planet Mars will likely lead to the selection of experienced International Space Station (ISS) or lunar crew persons for subsequent lunar or mars missions. Major concerns for space travel are galactic cosmic ray (GCR) risks of cancer and circulatory diseases. However large uncertainties in risk prediction occur due to the quantitative and qualitative differences in heavy ion microscopic energy deposition leading to differences in biological effects compared to low LET radiation. In addition, there are sparse radiobiology data and absence of epidemiology data for heavy ions and other high LET radiation. Non-targeted effects (NTEs) are found in radiobiology studies to increase the biological effectiveness of high LET radiation at low dose for cancer related endpoints. In this paper the most recent version of the NASA Space Cancer Risk model (NSCR-2022) is used to predict mission risks while considering NTEs in solid cancer risk predictions. I discuss predictions of space radiation risks of cancer and circulatory disease mortality for US Whites and US Asian-Pacific Islander (API) populations for 6-month ISS, 80-day lunar missions, and combined ISS-lunar mission. Model predictions suggest NTE increase cancer risks by about ∼2.3 fold over a model that ignores NTEs. US API are predicted to have a lower cancer risks of about 30% compared to US Whites. Cancer risks are slightly less than additive for multiple missions, which is due to the decease of risk with age of exposure and the increased competition with background risks as radiation risks increase. The inclusion of circulatory risks increases mortality estimates about 25% and 37% for females and males, respectively in the model ignoring NTEs, and 20% and 30% when NTEs are assumed to modify solid cancer risk. The predictions made here for combined ISS and lunar missions suggest risks are within risk limit recommendations by the National Council on Radiation Protection and Measurements (NCRP) for such missions.

Enhanced Effects of Chronic Restraint-Induced Psychological Stress on Total Body Fe-Irradiation-Induced Hematopoietic Toxicity in Trp53-Heterozygous Mice.

Humans are exposed to both psychological stress (PS) and radiation in some scenarios such as manned deep-space missions. It is of great concern to verify possible enhanced deleterious effects from such concurrent exposure. Pioneer studies showed that chronic restraint-induced PS (CRIPS) could attenuate Trp53 functions and increase gamma-ray-induced carcinogenesis in Trp53-heterozygous mice while CRIPS did not significantly modify the effects on X-ray-induced hematopoietic toxicity in Trp53 wild-type mice. As high-linear energy transfer (LET) radiation is the most important component of space radiation in causing biological effects, we further investigated the effects of CRIPS on high-LET iron-particle radiation (Fe)-induced hematopoietic toxicity in Trp53-heterozygous mice. The results showed that CRIPS alone could hardly induce significant alteration in hematological parameters (peripheral hemogram and micronucleated erythrocytes in bone marrow) while concurrent exposure caused elevated genotoxicity measured as micronucleus incidence in erythrocytes. Particularly, exposure to either CRISP or Fe-particle radiation at a low dose (0.1 Gy) did not induce a marked increase in the micronucleus incidence; however, concurrent exposure caused a significantly higher increase in the micronucleus incidence. These findings indicated that CRIPS could enhance the deleterious effects of high-LET radiation, particularly at a low dose, on the hematopoietic toxicity in Trp53-heterozygous mice.

Effects of 16O charged-particle irradiation on cognition, hippocampal morphology and mutagenesis in female mice

The effects of radiation in space on human cognition are a growing concern for NASA scientists and astronauts as the possibility for long-duration missions to Mars becomes more tangible. Oxygen (16O) radiation is of utmost interest considering that astronauts will interact with this radiation frequently. 16O radiation is a class of galactic cosmic ray (GCR) radiation and also present within spacecrafts. Whole-body exposure to high linear energy transfer (LET) radiation has been shown to affect hippocampal-dependent cognition. To assess the effects of high-LET radiation, we gave 6-month-old female C57BL/6 mice whole-body exposure to 16O at 0.25 or 0.1 Gy at NASA’s Space Radiation Laboratory. Three months following irradiation, animals were tested for cognitive performance using the Y-maze and Novel Object Recognition paradigms. Our behavioral data shows that 16O radiation significantly impairs object memory but not spatial memory. Also, dendritic morphology characterized by the Sholl analysis showed that 16O radiation significantly decreased dendritic branch points, ends, length, and complexity in 0.1 Gy and 0.25 Gy dosages. Finally, we found no significant effect of radiation on single nucleotide polymorphisms in hippocampal genes related to oxidative stress, inflammation, and immediate early genes. Our data suggest exposure to heavy ion 16O radiation modulates hippocampal neurons and induces behavioral deficits at a time point of three months after exposure in female mice.

A Meta-Analysis of the Effects of High-LET Ionizing Radiations in Human Gene Expression.

The use of high linear energy transfer (LET) ionizing radiation (IR) is progressively being incorporated in radiation therapy due to its precise dose localization and high relative biological effectiveness. At the same time, these benefits of particle radiation become a high risk for astronauts in the case of inevitable cosmic radiation exposure. Nonetheless, DNA Damage Response (DDR) activated via complex DNA damage in healthy tissue, occurring from such types of radiation, may be instrumental in the induction of various chronic and late effects. An approach to elucidating the possible underlying mechanisms is studying alterations in gene expression. To this end, we identified differentially expressed genes (DEGs) in high Z and high energy (HZE) particle-, γ-ray- and X-ray-exposed healthy human tissues, utilizing microarray data available in public repositories. Differential gene expression analysis (DGEA) was conducted using the R programming language. Consequently, four separate meta-analyses were conducted, after DEG lists were grouped depending on radiation type, radiation dose and time of collection post-irradiation. To highlight the biological background of each meta-analysis group, functional enrichment analysis and biological network construction were conducted. For HZE particle exposure at 8–24 h post-irradiation, the most interesting finding is the variety of DNA repair mechanisms that were downregulated, a fact that is probably correlated with complex DNA damage formation. Simultaneously, after X-ray exposure during the same hours after irradiation, DNA repair mechanisms continue to take place. Finally, in a further comparison of low- and high-LET radiation effects, the most prominent result is that autophagy mechanisms seem to persist and that adaptive immune induction seems to be present. Such bioinformatics approaches may aid in obtaining an overview of the cellular response to high-LET particles. Understanding these response mechanisms can consequently aid in the development of countermeasures for future space missions and ameliorate heavy ion treatments.

Effects of High- and Low-LET Radiation on Human Hematopoietic System Reconstituted in Immunodeficient Mice

Over the last 50 years, a number of important physiological changes in humans who have traveled on spaceflights have been catalogued. Of major concern are the short- and long-term radiation-induced injuries to the hematopoietic system that may be induced by high-energy galactic cosmic rays encountered on interplanetary space missions. To collect data on the effects of space radiation on the human hematopoietic system in vivo, we used a humanized mouse model. In this study, we irradiated humanized mice with 0.4 Gy of 350 MeV/n 28Si ions, a dose that has been shown to induce tumors in tumor-prone mice and a reference dose that has a relative biological effectiveness of 1 (1 Gy of 250-kVp X rays). Cell counts, cell subset frequency and cytogenetic data were collected from bone marrow spleen and blood of irradiated and control mice at short-term (7, 30 and 60 days) and long-term ( 6 - 7 months) time points postirradiation. The data show a significant short-term effect on the human hematopoietic stem cell counts imparted by both high- and low-LET radiation exposure. The radiation effects on bone marrow, spleen and blood human cell counts and human cell subset frequency were complex but did not alter the functions of the hematopoietic system. The long-term data acquired from high-LET irradiated mice showed complete recovery of the human hematopoietic system in all hematopoietic compartments. The combined results demonstrate that, in spite of early perturbation, the longer term effects of high-LET radiation are not detrimental to human hematopoiesis in our system of study.

Processing-Challenges Generated by Clusters of DNA Double-Strand Breaks Underpin Increased Effectiveness of High-LET Radiation and Chromothripsis.

Whereas most endogenous and exogenous DNA damaging agents typically generate lesions that are relatively isolated and can be repaired easily, ionizing radiation (IR) also induces clustered lesions causing DNA double strand breaks (DSBs). Moreover, forms of IR characterized by high linearenergytransfer (LET) induce not only isolated DSBs but also DSB clusters- multiple DSBs in close proximity -that pose increased risks for the cell. DSB clusters can destabilize chromatin locally and compromise processing of individual DSBs within the cluster. Since the discovery of chromothripsis, a phenomenon whereby multiple DSBs locally generated by a catastrophic event causes genomic rearrangements that feed carcinogenesis, DSB clusters receive increased attention also in the field of cancer. While formation of DSB clusters after exposure to high LET is a direct and inherent consequence of the spatial distribution of the constituting energy deposition events, also called track structure, the sources of local genomic shattering underpinning chromothripsis are under investigation. Notably, many consequences of DSB clusters in the affected genome reflect processing by pathways that have evolved to repair DSBs, but which operate with widely different degrees of fidelity. The molecular underpinnings and the basis of the underlying repair pathway choices that ultimately lead to the observed consequences from DSB clusters remain unknown. We developed a tractable model of DSB clustering that allows direct analysis in cells of the consequences of certain configurations of DSB clusters. We outline the rationale for the development of this model and describe its key characteristics. We summarize results suggesting that DSB clusters compromise the first-line DSB-processing pathways of c-NHEJ and HRR, increasing as a consequence the contribution of alt-EJ, which has high propensity of generating chromosomal rearrangements. The results suggest a mechanism for the increased toxicity of high LET radiation and the extensive genomic rearrangements associated with chromothripsis.

Effect of low- and high-linear energy transfer radiation on in vitro and orthotopic in vivo models of osteosarcoma by activation of caspase-3 and -9.

Osteosarcoma (OS) is a malignant tumor of the bone derived from primitive transformed cells of the mesenchymal origin. Local low-linear energy transfer (LET) radiotherapy has limited benefits on OS owing to its radioresistance. Thus, this study aimed to investigate the effects of high-LET radiation on human OS. Therefore, the human OS cell lines, U2O2 and KHOS/NP, were examined in vitro, or an orthotopic mouse xenograft model was studied in vivo after treatment with low-LET (gamma-ray) and high-LET (neutron) radiation. Notably, OS cells were significantly more sensitive to high-LET radiation in vitro and in the orthotopic xenograft tumor model. Specifically, neutron radiation treatment increased the relative percentage of apoptotic sub-G1 phase cells via caspase-3/9 activation; increased intracellular reactive oxygen species, autophagy, and DNA damage; and decreased invasion and migration. Similarly, the mean size of gamma-irradiated (8 Gy) orthotopic KHOS/NP OS was 195 mm3 at 6 weeks after gamma-irradiation (8 Gy), but it was only 150 mm3 in mice treated with high-LET neutron radiotherapy. Significantly, our results provide a rationale for the use of high-LET radiotherapy to treat patients with OS.

Dependence and independence of survival parameters on linear energy transfer in cells and tissues

Carbon-ion radiotherapy has been used to treat more than 9000 cancer patients in the world since 1994. Spreading of the Bragg peak is necessary for carbon-ion radiotherapy, and is designed based on the linear–quadratic model that is commonly used for photon therapy. Our recent analysis using in vitro cell kills and in vivo mouse tissue reaction indicates that radiation quality affects mainly the alpha terms, but much less the beta terms, which raises the question of whether this is true in other biological systems. Survival parameters alpha and beta for 45 in vitro mammalian cell lines were obtained by colony formation after irradiation with carbon ions, fast neutrons and X-rays. Relationships between survival parameters and linear energy transfer (LET) below 100 keV/μm were obtained for 4 mammalian cell lines. Mouse skin reaction and tumor growth delay were measured after fractionated irradiation. The Fe-plot provided survival parameters of the tissue reactions. A clear separation between X-rays and high-LET radiation was observed for alpha values, but not for beta values. Alpha values/terms increased with increasing LET in any cells and tissues studied, while beta did not show a systematic change. We have found a puzzle or contradiction in common interpretations of the linear-quadratic model that causes us to question whether the model is appropriate for interpreting biological effectiveness of high-LET radiation up to 500 keV/μm, probably because of inconsistency in the concept of damage interaction. A repair saturation model proposed here was good enough to fit cell kill efficiency by radiation of wide-ranged LET. A model incorporating damage complexity and repair saturation would be suitable for heavy-ion radiotherapy.

Alternative Mathematical Form for Determining the Effectiveness of High-LET Radiations at Lower Doses Region

The Effectiveness of lower doses of high-LET radiations is not accurately determined by using energy-based physical parameters such as absorbed dose and radio-sensitivity parameters. Therefore, an attempt has been carried out in this research to propose alternative parameter that capable to quantify the effectiveness of these high LET radiations at lower doses regions.

Short DNA Fragments Are a Hallmark of Heavy Charged-Particle Irradiation and May Underlie Their Greater Therapeutic Efficacy.

Growing interest in proton and heavy ion therapy has reinvigorated research into the fundamental biological mechanisms underlying the therapeutic efficacy of charged-particle radiation. To improve our understanding of the greater biological effectiveness of high-LET radiations, we have investigated DNA double-strand breaks (DSBs) following exposure of plasmid DNA to low-LET Co-60 gamma photon and electron irradiation and to high-LET Beryllium and Argon ions with atomic force microscopy. The sizes of DNA fragments following radiation exposure were individually measured to construct fragment size distributions from which the DSB per DNA molecule and DSB spatial distributions were derived. We report that heavy charged particles induce a significantly larger proportion of short DNA fragments in irradiated DNA molecules, reflecting densely and clustered damage patterns of high-LET energy depositions. We attribute the enhanced short DNA fragmentation following high-LET radiations as an important determinant of the observed, enhanced biological effectiveness of high-LET irradiations.

The combined effects of dietary supplements and low-dose-rate high-LET radiation on mice in vivo

The purpose of this study was to investigate the combined actions of food supplements and lowdose-rate high-LET radiation on radiosensitivity, induction of the adaptive response, and tumor growth in SHK mice in vivo. The animals were irradiated with 0.11 Gy (0.005 Gy/day) of low-dose-rate high-LET radiation behind the concrete shield of a 70 GeV proton accelerator (Protvino, Moscow oblast). Four groups of the mice were fed with selected products (soy meat, buckwheat, lettuce leaves, and a drug based on cod-liver oil) during the entire irradiation period (22 days). The results of the study indicate that the mice with diets containing soy meat, buckwheat, and lettuce leaves in contrast to those fed with a diet containing cod-liver oil had reduced sensitivity to X-radiation at a dose rate of 1.5 Gy and a significant slowdown in the growth of the Ehrlich carcinoma. The combined effect of high-LET radiation and the food supplements mentioned above (except for the cod-liver oil) reduced the sensitivity of the mice to the irradiation at a dose rate of 1.5 Gy, induced the adaptive response, and caused a decrease in the growth rate of the Ehrlich carcinoma in contrast to the mice that were only irradiated with high-LET radiation.

Sub-micrometer 20 MeV protons or 45 MeV lithium spot irradiation enhances yields of dicentric chromosomes due to clustering of DNA double-strand breaks

In conventional experiments on biological effects of radiation types of diverse quality, micrometer-scale double-strand break (DSB) clustering is inherently interlinked with clustering of energy deposition events on nanometer scale relevant for DSB induction. Due to this limitation, the role of the micrometer and nanometer scales in diverse biological endpoints cannot be fully separated. To address this issue, hybrid human-hamster AL cells have been irradiated with 45MeV (60keV/μm) lithium ions or 20MeV (2.6keV/μm) protons quasi-homogeneously distributed or focused to 0.5×1μm2 spots on regular matrix patterns (point distances up to 10.6×10.6μm), with pre-defined particle numbers per spot to provide the same mean dose of 1.7Gy. The yields of dicentrics and their distribution among cells have been scored. In parallel, track-structure based simulations of DSB induction and chromosome aberration formation with PARTRAC have been performed. The results show that the sub-micrometer beam focusing does not enhance DSB yields, but significantly affects the DSB distribution within the nucleus and increases the chance to form DSB pairs in close proximity, which may lead to increased yields of chromosome aberrations. Indeed, the experiments show that focusing 20 lithium ions or 451 protons per spot on a 10.6μm grid induces two or three times more dicentrics, respectively, than a quasi-homogenous irradiation. The simulations reproduce the data in part, but in part suggest more complex behavior such as saturation or overkill not seen in the experiments. The direct experimental demonstration that sub-micrometer clustering of DSB plays a critical role in the induction of dicentrics improves the knowledge on the mechanisms by which these lethal lesions arise, and indicates how the assumptions of the biophysical model could be improved. It also provides a better understanding of the increased biological effectiveness of high-LET radiation.

Simulation of DSB yield for high LET radiation.

A simulation approach for the calculation of the LET-dependent yield of double-strand breaks (DSB) is presented. The model considers DSB formed as two close-lying single-strand breaks (SSB), whose formation is mediated by both intra-track processes (single electrons) or at local doses larger than about 1000 Gy in particle tracks also by electron inter-track processes (two independent electron tracks). A Monte Carlo algorithm and an analytical formula for the DSB yield are presented. The approach predicts that the DSB yield is enhanced after charged particle irradiation of high LET compared with X-ray or gamma radiation. It is used as an inherent part of the local effect model, which is applied to estimate the relative biological effectiveness of high LET radiation.

Induction of chromosomal aberrations at fluences of less than one HZE particle per cell nucleus.

The assumption of a linear dose response used to describe the biological effects of high-LET radiation is fundamental in radiation protection methodologies. We investigated the dose response for chromosomal aberrations for exposures corresponding to less than one particle traversal per cell nucleus by high-energy charged (HZE) nuclei. Human fibroblast and lymphocyte cells were irradiated with several low doses of <0.1 Gy, and several higher doses of up to 1 Gy with oxygen (77 keV/μm), silicon (99 keV/μm) or Fe (175 keV/μm), Fe (195 keV/μm) or Fe (240 keV/μm) particles. Chromosomal aberrations at first mitosis were scored using fluorescence in situ hybridization (FISH) with chromosome specific paints for chromosomes 1, 2 and 4 and DAPI staining of background chromosomes. Nonlinear regression models were used to evaluate possible linear and nonlinear dose-response models based on these data. Dose responses for simple exchanges for human fibroblasts irradiated under confluent culture conditions were best fit by nonlinear models motivated by a nontargeted effect (NTE). The best fits for dose response data for human lymphocytes irradiated in blood tubes were a linear response model for all particles. Our results suggest that simple exchanges in normal human fibroblasts have an important NTE contribution at low-particle fluence. The current and prior experimental studies provide important evidence against the linear dose response assumption used in radiation protection for HZE particles and other high-LET radiation at the relevant range of low doses.

Live-cell imaging study of mitochondrial morphology in mammalian cells irradiated

Recent reports suggest that extranuclear targets in cytoplasm may have a role in mediating radiation effects in mammalian cells exposed to ionizing radiation. We have focused mitochondria as a target of ionizing radiation, particularly heavy ions, because mitochondria are a kind of organelles existing widely in cytoplasm. They play a vitally important role of ATP formation through the operation of electron transport chain located in the membranes, and generate reactive oxygen species as a by-product in the process of ATP production. As mitochondria are fusing or dividing depended on cell cycle, their morphology is continuously changing [ 1]. Defects of these processes contribute to the pathogenesis of neurodegenerative disease. Effects of high LET irradiation, such as heavy ion bombardment, on mitochondrial morphology, however, remain to be fully elucidated. The object of this study is to reveal effects of high LET radiation on mitochondria.We have performed preliminary test experiments using X-rays. We used NMuMG (Normal murine mammary gland)-FUCCI2 cell line [ 2]. Using the FUCCI2-expressing cells, we can distinguish G1 or S/G2/M phase cells as observed red or green fluorescence in their nucleus. We also labeled mitochondria by another fluorescence probe, Mitotracker Red. Kinetics of mitochondrial morphology was analyzed by the live-cell imaging technique using a fluorescence microscope. Mitochondrial images were captured at certain hours after irradiation, and classified them into three categories, namely tubes, intermediates and fragments (Fig. 1).We found that X-ray irradiation of cells caused mitochondrial fragmentation, and cell population with fragmented mitochondria increased with increasing dose, and also with time after irradiation (Fig. 1). Although the cells became confluent around 48 h after irradiation as indicated by the cell-nucleus color, the mitochondrial morphology was still changing. Particularly, the population of the cells with fragments showed a maximum at 96 h after irradiation when they were exposed to 8 Gy X-rays. Based on the present study, we further investigate morphological changes of mitochondria by high LET particle irradiation in future. Fig. 1.Relative fraction of cells showing each morphology for non-irradiated (control) and charectors of mitochondrial morphology. Irradiated with (1) 0Gy, (2) 6 Gy and (2) 8 Gy. The cell cycles are also shown by solid lines. (a) Mostly mitochondria look tubular. (b) Both tubular and fragment forms are observed with the same rate in a cell. (c) Mitochondria are visible as dots, and straggle in whole cytoplasm.

In VitroEvaluation of Combined Temozolomide and Radiotherapy Using X Rays and High-Linear Energy Transfer Radiation for Glioblastoma

High-linear energy transfer radiation offers superior biophysical properties over conventional radiotherapy and may have a great potential for treating radioresistant tumors, such as glioblastoma. However, very little pre-clinical data exists on the effects of high-LET radiation on glioblastoma cell lines and on the concomitant application of chemotherapy. This study investigates the in vitro effects of temozolomide in combination with low-energy protons and α particles. Cell survival, DNA damage and repair, and cell growth were examined in four human glioblastoma cell lines (LN18, T98G, U87 and U373) after treatment with either X rays, protons (LET 12.91 keV/μm), or α particles (LET 99.26 keV/μm) with or without concurrent temozolomide at clinically-relevant doses of 25 and 50 μM. The relative biological effectiveness at 10% survival (RBE(10)) increased as LET increased: 1.17 and 1.06 for protons, and 1.84 and 1.68 for α particles in the LN18 and U87 cell lines, respectively. Temozolomide administration increased cell killing in the O(6)-methylguanine DNA methyltransferase-methylated U87 and U373 cell lines. In contrast, temozolomide provided no therapeutic enhancement in the methylguanine DNA methyltransferase-unmethylated LN18 and T98G cell lines. In addition, the residual number of γ-H2AX foci at 24 h after treatment with radiation and concomitant temozolomide was found to be lower than or equal to that expected by DNA damage with either of the individual treatments. Kinetics of foci disappearance after X-ray and proton irradiation followed similar time courses; whereas, loss of γ-H2AX foci after α particle irradiation occurred at a slower rate than that by low-LET radiation (half-life 12.51-16.87 h). The combination of temozolomide with different radiation types causes additive rather than synergistic cytotoxicity. Nevertheless, particle therapy combined with chemotherapy may offer a promising alternative with the additional benefit of superior biophysical properties. It is also possible that new fractionation schedules could be designed to exploit the change in DNA repair kinetics when MGMT-methylated cells respond to high-LET radiation.

Neutron medical treatment of tumours — a survey of facilities

Neutron therapy has two branches: Fast Neutron Therapy (FNT) and Boron Neutron Capture Therapy (BNCT). The mean neutron energies used for FNT range from 2 MeV to 25 MeV whereas the maximum energy for BNCT is about 10 keV. Neutron generators for FNT have been cyclotrons, accelerators and reactors, whereas BNCT is so far bound to reactors. Both therapies use the effects of high-LET radiation (secondary recoil protons and alpha particles, respectively) and can attack otherwise radioresistant tumours, however, with the hazard of adverse effects for irradiated healthy tissue.FNT has been administered to about 30,000 patients world-wide. From formerly 40 facilities, only eight are operational or stand-by today. The reasons for this development have been, on the one hand, related to technical and economical conditions; on the other hand, strong side effects and insufficient proof of clinical results in the early years as well as increasing competition with new clinical methods have reduced patient numbers. In fact, strict observations of indications, appropriate therapy-planning including low-LET radiation, and consequent treatment of side effects have lead to remarkable results in the meantime.BNCT initially was developed for the treatment of extremely aggressive forms of brain tumour, taking advantage of the action of the blood-brain-barrier which allows for a boronated compound to be selectively enriched in tumour cells. Meanwhile, also malignant melanoma (MM) and Head-and-Neck (H&T) tumours are treated because of their relative radioresistance. At present, epithermal beams with sufficient flux are available only at two facilities. Existing research reactors were indispensable in the development of BNCT, but are to be replaced by hospital-based epithermal neutron sources. Clinical results indicate significantly increased survival times, but the number of patients ever treated is still below 1,000.3D-dose calculation systems have been developed at several facilities and guarantee a high safety for both therapies, FNT and BNCT.

Mutagenic adaptive response to high-LET radiation in human lymphoblastoid cells exposed to low doses of heavy-ion radiation

Adaptive response (AR) and bystander effect are two important phenomena involved in biological responses to low doses of ionizing radiation (IR). Furthermore, there is a strong interest in better understanding the biological effects of high-LET radiation. We previously demonstrated the ability of low doses of X-rays to induce an AR to challenging heavy-ion radiation [8]. In this study, we assessed in vitro the ability of priming low doses (0.01 Gy) of heavy-ion radiation to induce a similar AR to a subsequent challenging dose (1–4 Gy) of high-LET IR (carbon-ion: 20 and 40 keV/μm, neon-ion: 150 keV/μm) in TK6, AHH-1 and NH32 cells. Our results showed that low doses of high-LET radiation can induce an AR characterized by lower mutation frequencies at hypoxanthine–guanine phosphoribosyl transferase locus and faster DNA repair kinetics, in cells expressing p53.