A standardized G2-assay for the prediction of individual radiosensitivity

Biological Response of Human Cancer Cells to Ionizing Radiation in Combination with Gold Nanoparticles

Simple Summary

Various types of metallic nanoparticles and especially gold nanoparticles (AuNPs) have been utilized in radiation studies to enhance the radiosensitization of cancer cells while minimizing detrimental effects in normal tissue. The aim of our study was to investigate the biological responses of various human cancer cells to gold-nanoparticle-induced radiosensitization. This was accomplished by using different AuNPs and several techniques in order to provide valuable insights regarding the multiple adverse biological effects, following ionizing radiation (IR) in combination with AuNPs. Insightful methodologies such as transmission electron microscopy were employed to identify comprehensively the complexity of the biological damage occurrence. Our findings confirm that AuNP radiosensitization may occur due to extensive and/or complex DNA damage, cell death, or cellular senescence. This multiparameter study aims to further elucidate the biological mechanisms and at the same time provide new information regarding the use of AuNPs as radiosensitizers in cancer treatment.

Abstract

In the context of improving radiation therapy, high-atomic number (Z) metallic nanoparticles and, more importantly, gold-based nanostructures are developed as radiation enhancers/radiosensitizers. Due to the diversity of cell lines, nanoparticles, as well as radiation types or doses, the resulting biological effects may differ and remain obscure. In this multiparameter study, we aim to shed light on these effects and investigate them further by employing X-irradiation and three human cancer cell lines (PC3, A549, and U2OS cells) treated by multiple techniques. TEM experiments on PC3 cells showed that citrate-capped AuNPs were found to be located mostly in membranous structures/vesicles or autophagosomes, but also, in the case of PEG-capped AuNPs, inside the nucleus as well. The colony-forming capability of cancer cells radiosensitized by AuNPs decreased significantly and the DNA damage detected by cytogenetics, γH2AX immunostaining, and by single (γH2AX) or double (γH2AX and OGG1) immunolocalization via transmission electron microscopy (TEM) was in many cases higher and/or persistent after combination with AuNPs than upon individual exposure to ionizing radiation (IR). Moreover, different cell cycle distribution was evident in PC3 but not A549 cells after treatment with AuNPs and/or irradiation. Finally, cellular senescence was investigated by using a newly established staining procedure for lipofuscin, based on a Sudan Black-B analogue (GL13) which showed that based on the AuNPs’ concentration, an increased number of senescent cells might be observed after exposure to IR. Even though different cell lines or different types and concentrations of AuNPs may alter the levels of radiosensitization, our results imply that the complexity of damage might also be an important factor of AuNP-induced radiosensitization.

Chronic human exposure to ionizing radiation: Individual variability of chromosomal aberration frequencies and G0 radiosensitivities

Bio-monitoring of human radiation exposure is based, as a rule, on a single analysis of chromosomal aberrations. Factors such as radiosensitivity, adaptation, and the stability of cytogenetic indices are not taken into account. We studied frequency of chromosome aberrations (FCA) and G₀ chromosome radiosensitivity following in vitro γ-exposure, over a 2.5-year period, for 129 residents of the Dolon settlement, part of the extreme radiation risk zone, Semipalatinsk nuclear test site region, Kazakhstan. Radiosensitivity was evaluated on the basis of FCA and dose assessment by physical dosimetry. FCA was 3-fold higher in Dolon inhabitants as in the control group (p ≤ 0.01). The average coefficient of variability of spontaneous FCA was 31 %. In 20 % of the subjects, it was very high (50-70 %). Individual dose estimation in a single study in such individuals may lead to significant errors. Individual G₀-chromosomal radiosensitivity showed less variation (18.7 %). Chronic low-dose irradiation was an adaptive factor to the damaging dose (1 Gy). Three methods of individual radiosensitivity assessment were considered, based on: G₀-chromosomal radiosensitivity under additional in vitro γ-radiation; FCA and average dose per year; FCA and total dose received during years of residence in a radiocontaminated settlement, according to physical dosimetry. There is a significant difference in response (FCA) between radiosensitive and radioresistant individuals. This should be taken into account in individual dosimetry and risk assessment of radiation exposure.

Individual Radiosensitivity as a Risk Factor for the Radiation-Induced Acute Radiodermatitis

Background: Up to 95% of irradiated patients suffer from ionizing radiation (IR) induced early skin reaction, acute radiation dermatitis (ARD). Some experts think that additional skin hydration can reduce acute skin reactions. Individual radiosensitivity (IRS) determined from lymphocytes may help to predict acute radiation toxicity. The purpose of this study is to evaluate the clinical manifestation of ARD in different skincare groups during whole breast radiotherapy depending on IRS and other risk factors. Methods: A total of 108 early-stage breast cancer patients were randomized into best supportive care (BSC) and additional skincare (ASC) groups. IRS was evaluated using a G2 assay modified with caffeine-induced G2 checkpoint arrest. All patients received a 50 Gy dose to the breast planning target volume (PTV). Clinical assessment of ARD symptoms according to the CTCAE grading scale was performed once a week. Results: IRS was successfully determined for 91 out of 108 patients. A total of 10 patients (11%) had normal IRS, 47 patients (52%) were categorized as radiosensitive, and 34 (37%) as highly radiosensitive. There was no significant difference in the manifestation of ARD between patient groups by skincare or IRS. According to logistic regression, patients with bigger breasts were prone to more severe ARD (p = 0.002). Conclusions: The additional skincare did not improve skin condition during RT. A total of 89% of patients had increased radiosensitivity. IRS determined before RT did not show the predictive value for the manifestation of ARD. Logistic regression revealed that breast volume was the most significant risk factor for the manifestation of ARD.

G2/M Checkpoint Abrogation With Selective Inhibitors Results in Increased Chromatid Breaks and Radiosensitization of 82-6 hTERT and RPE Human Cells

While technological advances in radiation oncology have led to a more precise delivery of radiation dose and a decreased risk of side effects, there is still a need to better understand the mechanisms underlying DNA damage response (DDR) at the DNA and cytogenetic levels, and to overcome tumor resistance. To maintain genomic stability, cells have developed sophisticated signaling pathways enabling cell cycle arrest to facilitate DNA repair via the DDR-related kinases and their downstream targets, so that DNA damage or DNA replication stress induced by genotoxic therapies can be resolved. ATM, ATR, and Chk1 kinases are key mediators in DDR activation and crucial factors in treatment resistance. It is of importance, therefore, as an alternative to the conventional clonogenic assay, to establish a cytogenetic assay enabling reliable and time-efficient results in evaluating the potency of DDR inhibitors for radiosensitization. Toward this goal, the present study aims at the development and optimization of a chromosomal radiosensitivity assay using the DDR and G2-checkpoint inhibitors as a novel modification compared to the classical G2-assay. Also, it aims at investigating the strengths of this assay for rapid radiosensitivity assessments in cultured cells, and potentially, in tumor cells obtained from biopsies. Specifically, exponentially growing RPE and 82-6 hTERT human cells are irradiated during the G2/M-phase transition in the presence or absence of Caffeine, VE-821, and UCN-1 inhibitors of ATM/ATR, ATR, and Chk1, respectively, and the induced chromatid breaks are used to evaluate cell radiosensitivity and their potency for radiosensitization. The increased yield of chromatid breaks in the presence of DDR inhibitors, which underpins radiosensitization, is similar to that observed in cells from highly radiosensitive AT-patients, and is considered here as 100% radiosensitive internal control. The results highlight the potential of our modified G2-assay using VE-821 to evaluate cell radiosensitivity, the efficacy of DDR inhibitors in radiosensitization, and reinforce the concept that ATM, ATR, and Chk1 represent attractive anticancer drug targets in radiation oncology.

Comparing Lymphocyte Radiosensitivity of Prostate Cancer Patients with Healthy Donors Using Micronuclei and Chemical Premature Chromosome Condensation Tests

Background:

Cytogenetic tests are usually used for diagnosing predisposed individuals to cancer by determining their lymphocyte radiosensitivity.

Objective:

To determine the potential role of radiosensitivity in predisposition of prostate cancer by comparing lymphocyte radiosensitivity of prostate cancer patients with healthy donors.

Materials and Methods:

In this experimental study, the blood samples of 10 prostate cancer patients and 10 healthy donors were irradiated to 0.25, 0.5, 1, 2, 4 and 6 Gy ionizing radiation produced by a 6MV Linac. One sample of each group receiving no radiation was regarded as the background. The micronuclei (MN) and chemical premature chromosome condensation (PCC) cytogenetic tests were performed on all samples and the numbers of MN and PCC rings were scored. Dose-response curves were plotted for both healthy and cancerous groups with two tests.

Results:

There was a significant difference between the numbers of MN within each group due to different levels of radiation doses. There was also a significant difference between the two groups in all identical doses, with the exception of 6 Gy. The chemical PCC test indicated a significant difference between the scored PCC rings in each group at doses higher than 0.25 Gy. However, no differences were noted between the healthy donors and prostate cancer patients receiving the same level of doses.

Conclusion:

MN test can be considered as a reliable indicator of predisposition of prostate cancer. On the other hand, the chemical PCC test could not differentiate between healthy donors and prostate cancer patients at the dose range examined in this study.

Individual Radiosensitivity in Oncological Patients: Linking Adverse Normal Tissue Reactions and Genetic Features

Introduction: Adverse effects of radiotherapy (RT) significantly affect patient's quality of life (QOL). The possibility to identify patient-related factors that are associated with individual radiosensitivity would optimize adjuvant RT treatment, limiting the severity of normal tissue reactions, and improving patient's QOL. In this study, we analyzed the relationships between genetic features and toxicity grading manifested by RT patients looking for possible biomarkers of individual radiosensitivity.

Methods: Early radiation toxicity was evaluated on 143 oncological patients according to the Common Terminology Criteria for Adverse Events (CTCAE). An individual radiosensitivity (IRS) index defining four classes of radiosensitivity (highly radiosensitive, radiosensitive, normal, and radioresistant) was determined by a G₂-chromosomal assay on ex vivo irradiated, patient-derived blood samples. The expression level of 15 radioresponsive genes has been measured by quantitative real-time PCR at 24 h after the first RT fraction, in blood samples of a subset of 57 patients, representing the four IRS classes.

Results: By applying univariate and multivariate statistical analyses, we found that fatigue was significantly associated with IRS index. Interestingly, associations were detected between clinical radiation toxicity and gene expression (ATM, CDKN1A, FDXR, SESN1, XPC, ZMAT3, and BCL2/BAX ratio) and between IRS index and gene expression (BBC3, FDXR, GADD45A, and BCL2/BAX).

Conclusions: In this prospective cohort study we found that associations exist between normal tissue reactions and genetic features in RT-treated patients. Overall, our findings can contribute to the identification of biological markers to predict RT toxicity in normal tissues.

A method for the cell-cycle-specific analysis of radiation-induced chromosome aberrations and breaks

The classical G₂-assay is widely used to assess cell-radiosensitivity and cancer phenotype: Cells are exposed to low doses of ionizing-radiation (IR) and collected for cytogenetic- analysis ˜1.5 h later. In this way, chromosome-damage is measured in cells irradiated in G₂-phase, without retrieving information regarding kinetics of chromosome-break-repair. Modification of the assay to include analysis at multiple time-points after IR, has enabled kinetic-analysis of chromatid-break-repair and assessment of damage in a larger proportion of G₂-phase cells. This modification, however, increases the probability that at later time points not only cells irradiated in G₂-phase, but also cells irradiated in S-phase will reach metaphase. However, the response of cells irradiated in G₂-phase can be mechanistically different from that of cells irradiated in S-phase. Therefore, indiscriminate analysis may confound the interpretation of experiments designed to elucidate mechanisms of chromosome-break-repair and the contributions of the different DSB-repair-pathways in this response. Here we report an EdU based modification of the assay that enables S- and G₂-phase specific analysis of chromatid break repair. Our results show that the majority of metaphases captured during the first 2 h after IR originate from cells irradiated in G₂-phase (EdU^- metaphases) in both rodent and human cells. Metaphases originating from cells irradiated in S-phase (EdU⁺ metaphases) start appearing at 2 h and 4 h after IR in rodent and human cells, respectively. The kinetics of chromatid-break-repair are similar in cells irradiated in G₂- and S-phase of the cell-cycle, both in rodent and human cells. The protocol is applicable to classical-cytogenetic experiments and allows the cell-cycle specific analysis of chromosomal-aberrations. Finally, the protocol can be applied to the kinetic analysis of chromosome-breaks in prematurely-condensed-chromosomes of G₂-phase cells. In summary, the developed protocol provides means to enhance the analysis of IR-induced-cytogenetic-damage by providing information on the cell-cycle phase where DNA damage is inflicted.

Individual Radiosensitivity Assessment of the Families of Ataxia-Telangiectasia Patients by G2-Checkpoint Abrogation

Objectives

Ataxia-telangiectasia (A-T) is an autosomal recessive multisystem disorder characterised by cerebellar degeneration, telangiectasia, radiation sensitivity, immunodeficiency, oxidative stress and cancer susceptibility. Epidemiological research has shown that carriers of the heterozygous ataxia-telangiectasia mutated (ATM) gene mutation are radiosensitive to ionising irradiation and have a higher risk of cancers, type 2 diabetes and atherosclerosis. However, there is currently no fast and reliable laboratory-based method to detect heterozygous ATM carriers for family screening and planning purposes. This study therefore aimed to evaluate the ability of a modified G2-assay to identify heterozygous ATM carriers in the families of A-T patients.

Methods

This study took place at the Tehran University of Medical Sciences, Tehran, Iran, between February and December 2017 and included 16 A-T patients, their parents (obligate heterozygotes) and 30 healthy controls. All of the subjects underwent individual radiosensitivity (IRS) assessment using a modified caffeine-treated G2-assay with G2-checkpoint abrogation.

Results

The mean IRS of the obligate ATM heterozygotes was significantly higher than the healthy controls (55.13% ± 5.84% versus 39.03% ± 6.95%; P <0.001), but significantly lower than the A-T patients (55.13% ± 5.84% versus 87.39% ± 8.29%; P = 0.001). A receiver operating characteristic (ROC) curve analysis of the G2-assay values indicated high sensitivity and specificity, with an area under the ROC curve of 0.97 (95% confidence interval: 0.95-1.00).

Conclusion

The modified G2-assay demonstrated adequate precision and relatively high sensitivity and specificity in detecting heterozygous ATM carriers.

APPLICATION OF REFLECTANCE CONFOCAL MICROSCOPY FOR EARLY DIAGNOSIS OF RADIATION-INDUCED ACUTE DERMATITIS IN RADIOSENSITIVE PATIENT: CASE STUDY

According to the guidelines on cancer treatment up to 52% of newly diagnosed cancer patients should be treated with external beam radiotherapy. Ionizing radiation (IR)-induced skin injury (radiation dermatitis) occurs in up to 95% of radiotherapy patients and can manifest from mild erythema till necrosis and ulceration. Individual radiosensitivity was proposed to be an important factor for the development of adverse reactions to IR. Therefore, assessment of radiosensitivity could be useful in predicting and dealing with radiation injuries caused by both radiotherapy and accidental overexposure. Here, we present a case of early diagnosis of IR-induced skin lesions performed by reflectance confocal microscopy in comparison to clinical evaluation in a highly radiosensitive patient.

Single nucleotide polymorphisms in ATM, TNF-α and IL6 genes and risk of radiotoxicity in breast cancer patients

Although oncological therapies have improved in the last decades, breast cancer (BC) remains a serious health problem worldwide. Radiotherapy (RT) is one of the most frequently used treatments for cancer aimed at eliminating tumor cells. However, it can also alter the surrounding normal tissue, especially the skin, and patient reactions may vary as a result of extrinsic and intrinsic factors. We evaluated the association of gene polymorphisms ATM Asp1853Asn, IL-6 G-174C and TNF-α G-308A involved in central phenotype pathways and development of individual radiosensitivity in BC patients with an exacerbated response to RT. Although univariate analysis results did not show a significant association with this trait, the interaction analysis between polymorphisms showed an increased risk of patients presenting wild-type TNF-α G-308A genotype and mutant IL-6 G-174C genotype, and heterozygous TNF-α G-308A genotype and heterozygous IL-6G-174C genotype. On the other hand, our results showed that breast size and patient age influenced the determination of RT-associated effects. Considering that the trait is multifactorial, other significant elements for the determination of individual radiosensitivity should be considered, together with the establishment of specific polymorphic variants.

Assessment of Correlation between Chromosomal Radiosensitivity of Peripheral Blood Lymphocytes after In vitro Irradiation and Normal Tissue Side Effects for Cancer Patients Undergoing Radiotherapy

Patients receiving identical radiation treatments experience different effects, from undetectable to severe, on normal tissues. A crucial factor of radiotherapy related side effects is individual radiosensitivity. It is difficult to spare surrounding normal tissues delivering radiation to cancer cells during radiotherapy. Therefore, it may be useful to develop a simple routine cytogenetic assay which would allow the screening of a large number of individuals for radiosensitivity optimizing tumor control rates and minimizing severe radiotherapy effects with possibility to predict risk level for developing more severe early normal tissue adverse events after irradiation. This study was conducted to assess the correlation between in vitro radiosensitivity of peripheral blood lymphocytes from cancer patients who are undergoing radiotherapy using the cytokinesis-block micronucleus (CBMN), G2 chromosomal radiosensitivity assays, and normal tissue acute side effects. The CBMN and G2 chromosomal radiosensitivity assays were performed on blood samples taken from cancer patients before radiotherapy, after first fractionation, and after radiotherapy. Acute normal tissue reactions were graded according to the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer. This study suggests that there is a correlation between higher frequency of micronuclei after in vitro irradiation of blood samples and higher degree of normal tissue reactions. In addition, higher number of chromatid breaks was observed in patients with more severe normal tissue reactions. This pilot study included only 5 cancer patients, and therefore, further studies with a bigger cohort are required to identify radiosensitive patients.

Biodosimetry for High-Dose Exposures Based on Dicentric Analysis in Lymphocytes Released from the G2-Block by Caffeine

High-dose assessments using the conventional dicentric assay are essentially restricted to doses up to 5 Gy and only to lymphocytes that succeed to proceed to first post-exposure mitosis. Since G2-checkpoint activation facilitates DNA damage recognition and arrest of damaged cells, caffeine is used to release G2-blocked lymphocytes overcoming the mitotic index and dicentric yield saturation problems, enabling thus dicentric analysis even at high-dose exposures. Using the fluorescence in situ hybridization technique with telomere and centromere peptide nucleic acid probes, the released lymphocytes, identified as metaphases with decondensed chromosomes following 1.5 h caffeine treatment, show increased yield of dicentrics compared to that obtained in lymphocytes that reach metaphase without G2-checkpoint abrogation by caffeine. Here, a 3-h caffeine/colcemid co-treatment before harvesting at 55 h post-exposure is used so that the dicentric analysis using Giemsa staining is based predominantly on lymphocytes released from the G2-block, increasing thus dicentric yield and enabling construction of a dose-response calibration curve with improved precision of high-dose estimates.

Differences in DNA Repair Capacity, Cell Death and Transcriptional Response after Irradiation between a Radiosensitive and a Radioresistant Cell Line

Normal tissue toxicity after radiotherapy shows variability between patients, indicating inter-individual differences in radiosensitivity. Genetic variation probably contributes to these differences. The aim of the present study was to determine if two cell lines, one radiosensitive (RS) and another radioresistant (RR), showed differences in DNA repair capacity, cell viability, cell cycle progression and, in turn, if this response could be characterised by a differential gene expression profile at different post-irradiation times. After irradiation, the RS cell line showed a slower rate of γ-H2AX foci disappearance, a higher frequency of incomplete chromosomal aberrations, a reduced cell viability and a longer disturbance of the cell cycle when compared to the RR cell line. Moreover, a greater and prolonged transcriptional response after irradiation was induced in the RS cell line. Functional analysis showed that 24 h after irradiation genes involved in “DNA damage response”, “direct p53 effectors” and apoptosis were still differentially up-regulated in the RS cell line but not in the RR cell line. The two cell lines showed different response to IR and can be distinguished with cell-based assays and differential gene expression analysis. The results emphasise the importance to identify biomarkers of radiosensitivity for tailoring individualized radiotherapy protocols.

Increased chromosomal radiosensitivity in asymptomatic carriers of a heterozygous BRCA1 mutation

Background

Breast cancer risk increases drastically in individuals carrying a germline BRCA1 mutation. The exposure to ionizing radiation for diagnostic or therapeutic purposes of BRCA1 mutation carriers is counterintuitive, since BRCA1 is active in the DNA damage response pathway. The aim of this study was to investigate whether healthy BRCA1 mutations carriers demonstrate an increased radiosensitivity compared with healthy individuals.

Methods

We defined a novel radiosensitivity indicator (RIND) based on two endpoints measured by the G₂ micronucleus assay, reflecting defects in DNA repair and G₂ arrest capacity after exposure to doses of 2 or 4 Gy. We investigated if a correlation between the RIND score and nonsense-mediated decay (NMD) could be established.

Results

We found significantly increased radiosensitivity in the cohort of healthy BRCA1 mutation carriers compared with healthy controls. In addition, our analysis showed a significantly different distribution over the RIND scores (p = 0.034, Fisher’s exact test) for healthy BRCA1 mutation carriers compared with non-carriers: 72 % of mutation carriers showed a radiosensitive phenotype (RIND score 1–4), whereas 72 % of the healthy volunteers showed no radiosensitivity (RIND score 0). Furthermore, 28 % of BRCA1 mutation carriers had a RIND score of 3 or 4 (not observed in control subjects). The radiosensitive phenotype was similar for relatives within several families, but not for unrelated individuals carrying the same mutation. The median RIND score was higher in patients with a mutation leading to a premature termination codon (PTC) located in the central part of the gene than in patients with a germline mutation in the 5′ end of the gene.

Conclusions

We show that BRCA1 mutations are associated with a radiosensitive phenotype related to a compromised DNA repair and G₂ arrest capacity after exposure to either 2 or 4 Gy. Our study confirms that haploinsufficiency is the mechanism involved in radiosensitivity in patients with a PTC allele, but it suggests that further research is needed to evaluate alternative mechanisms for mutations not subjected to NMD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0709-1) contains supplementary material, which is available to authorized users.

Stress induced by premature chromatin condensation triggers chromosome shattering and chromothripsis at DNA sites still replicating in micronuclei or multinucleate cells when primary nuclei enter mitosis

Combination of next-generation DNA sequencing, single nucleotide polymorphism array analyses and bioinformatics has revealed the striking phenomenon of chromothripsis, described as complex genomic rearrangements acquired in a single catastrophic event affecting one or a few chromosomes. Via an unproven mechanism, it is postulated that mechanical stress causes chromosome shattering into small lengths of DNA, which are then randomly reassembled by DNA repair machinery. Chromothripsis is currently examined as an alternative mechanism of oncogenesis, in contrast to the present paradigm that considers a stepwise development of cancer. While evidence for the mechanism(s) underlying chromosome shattering during cancer development remains elusive, a number of hypotheses have been proposed to explain chromothripsis, including ionizing radiation, DNA replication stress, breakage-fusion-bridge cycles, micronuclei formation and premature chromosome compaction. In the present work, we provide experimental evidence on the mechanistic basis of chromothripsis and on how chromosomes can get locally shattered in a single catastrophic event. Considering the dynamic nature of chromatin nucleoprotein complex, capable of rapid unfolding, disassembling, assembling and refolding, we first show that chromatin condensation at repairing or replicating DNA sites induces the mechanical stress needed for chromosome shattering to ensue. Premature chromosome condensation is then used to visualize the dynamic nature of interphase chromatin and demonstrate that such mechanical stress and chromosome shattering can also occur in chromosomes within micronuclei or asynchronous multinucleate cells when primary nuclei enter mitosis. Following an aberrant mitosis, chromosomes could find themselves in the wrong place at the wrong time so that they may undergo massive DNA breakage and rearrangement in a single catastrophic event. Specifically, our results support the hypothesis that premature chromosome condensation induces mechanical stress and triggers shattering and chromothripsis in chromosomes or chromosome arms still undergoing DNA replication or repair in micronuclei or asynchronous multinucleate cells, when primary nuclei enter mitosis.

The effect of ionizing radiation on regulatory T cells in health and disease

Treg cells are key elements of the immune system which are responsible for the immune suppressive phenotype of cancer patients. Interaction of Treg cells with conventional anticancer therapies might fundamentally influence cancer therapy response rates. Radiotherapy, apart from its direct tumor cell killing potential, has a contradictory effect on the antitumor immune response: it augments certain immune parameters, while it depresses others. Treg cells are intrinsically radioresistant due to reduced apoptosis and increased proliferation, which leads to their systemic and/or intratumoral enrichment. While physiologically Treg suppression is not enhanced by irradiation, this is not the case in a tumorous environment, where Tregs acquire a highly suppressive phenotype, which is further increased by radiotherapy. This is the reason why the interest for combined radiotherapy and immunotherapy approaches focusing on the abrogation of Treg suppression has increased in cancer therapy in the last few years. Here we summarize the basic mechanisms of Treg radiation response both in healthy and cancerous environments and discuss Treg-targeted pre-clinical and clinical immunotherapy approaches used in combination with radiotherapy. Finally, the discrepant findings regarding the predictive value of Tregs in therapy response are also reviewed.

Curcumin and trans-resveratrol exert cell cycle-dependent radioprotective or radiosensitizing effects as elucidated by the PCC and G2-assay

Curcumin and trans-resveratrol are well-known antioxidant polyphenols with radiomodulatory properties, radioprotecting non-cancerous cells while radiosensitizing tumor cells. This dual action may be the result of their radical scavenging properties and their effects on cell-cycle checkpoints that are activated in response to radiation-induced chromosomal damage. It could be also caused by their effect on regulatory pathways with impact on detoxification enzymes, the up-regulation of endogenous protective systems, and cell-cycle-dependent processes of DNA damage. This work aims to elucidate the mechanisms underlying the dual action of these polyphenols and investigates under which conditions they exhibit radioprotecting or radiosensitizing properties. The peripheral blood lymphocyte test system was used, applying concentrations ranging from 1.4 to 140μM curcumin and 2.2 to 220μM trans-resveratrol. The experimental design focuses first on their radioprotective effects in non-cycling lymphocytes, as uniquely visualized using cell fusion-mediated premature chromosome condensation, excluding, thus, cell-cycle interference to repair processes and activation of checkpoints. Second, the radiosensitizing potential of these chemicals on the induction of chromatid breaks in cultured lymphocytes following G2-phase irradiation was evaluated by a standardized G2-chromosomal radiosensitivity predictive assay. This assay uses caffeine for G2-checkpoint abrogation and it was applied to obtain an internal control for radiosensitivity testing, which simulates conditions similar to those of the highly radiosensitive lymphocytes of AT patients. The results demonstrate for the first time the cell-cycle-dependent action of these polyphenols. When non-cycling cells are irradiated, the radioprotective properties of curcumin and trans-resveratrol are more prominent. However, when cycling cells are irradiated during G2-phase, the radiosensitizing features of these compounds are more pronounced. This observation offers a new biological basis for the mechanisms underlying the action of these polyphenols in cancer radiotherapy.

Individual radiosensitivity in a breast cancer collective is changed with the patients' age

BACKGROUND

Individual radiosensitivity has a crucial impact on radiotherapy related side effects. Our aim was to study a breast cancer collective for its variation of individual radiosensitivity depending on the patients' age.

MATERIALS AND METHODS

Peripheral blood samples were obtained from 129 individuals. Individual radiosensitivity in 67 breast cancer patients and 62 healthy individuals was estimated by 3-color fluorescence in situ hybridization.

RESULTS

Breast cancer patients were distinctly more radiosensitive compared to healthy controls. A subgroup of 9 rather radiosensitive and 9 rather radio-resistant patients was identified. A subgroup of patients aged between 40 and 50 was distinctly more radiosensitive than younger or older patients.

CONCLUSIONS

In the breast cancer collective a distinct resistant and sensitive subgroup is identified, which could be subject for treatment adjustment. Preliminary results indicate that especially in the range of age 40 to 50 patients with an increased radiosensitivity are more frequent and may have an increased risk to suffer from therapy related side effects.

Variant ataxia telangiectasia: clinical and molecular findings and evaluation of radiosensitive phenotypes in a patient and relatives

Variant ataxia telangiectasia (A-T) may be an underdiagnosed entity. We correlate data from radiosensitivity and kinase assays with clinical and molecular data from a patient with variant A-T and relatives. The coding region of ATM was sequenced. To evaluate the functional effect of the mutations, we performed kinase assays and developed a novel S-G2 micronucleus test. Our patient presented with mild dystonia, moderately dysarthric speech, increased serum α-fetoprotein but no ataxia nor telangiectasias, no nystagmus or oculomotor dyspraxia. She has a severe IgA deficiency, but does not have recurrent infections. She is compound heterozygote for ATM c.8122G>A (p.Asp2708Asn) and c.8851-1G>T, leading to in frame loss of 63 nucleotides at the cDNA level. A trace amount of ATM protein is translated from both alleles. Residual kinase activity is derived only from the p.Asp2708Asn allele. The conventional G0 micronucleus test, based on irradiation of resting lymphocytes, revealed a radiosensitive phenotype for the patient, but not for the heterozygous relatives. As ATM is involved in homologous recombination and G2/M cell cycle checkpoint, we optimized an S-G2 micronucleus assay, allowing to evaluate micronuclei in lymphocytes irradiated in the S and G2 phases. This test showed increased radiosensitivity for both the patient and the heterozygous carriers. Intriguingly, heterozygous carriers of c.8851-1G>T (mutation associated with absence of kinase activity) showed a stronger radiosensitive phenotype with this assay than heterozygous carriers of p.Asp2708Asn (mutation associated with residual kinase activity). The modified S-G2 micronucleus assay provided phenotypic insight into complement the diagnosis of this atypical A-T patient.

Circulating regulatory T cells of cancer patients receiving radiochemotherapy may be useful to individualize cancer treatment

BACKGROUND AND PURPOSE

Dendritic cells (DCs) and regulatory T cells (Treg) play a major role in anti-tumor immune response of cancer patients. We investigated the effect of radiochemotherapy on patients' blood immune cells and their predictive value for tumor response.

MATERIALS AND METHODS

DCs and Treg of colorectal cancer (CRC) or breast cancer (BC) patients were examined through multicolor flow cytometry before the beginning and after the first week of radiochemotherapy (RCT). DCs were stained for BDCA1 and BDCA2, Treg were stained for CD4, CD25, CD127 and FoxP3. IL-2, IL-10 and TNF-α plasma levels of CRC patients were also determined. We examined the interrelationship between immune cell count alterations, applied dose values, cytokine plasma levels as well as histopathological parameters.

RESULTS

DCs were increased in BC and CRC patients compared to healthy control individuals (HC). CRC patients had higher levels of Treg (59.0%) compared to BC patients (31.3%) and HC (27.0%). Treg of CRC (58.7% vs. 41.3% p<0.001) but not BC patients (31.3% vs. 38.8%, p=0.164) decreased distinctly after the first week of radiation therapy. Applied dose values and decrease of Treg correlated positively (r=0.216, p=0.054). We also found a positive correlation of IL-10 plasma levels and Treg levels (r=0.748, p=0.021). CRC patients with favorable tumor stage (<ypT3a) have higher levels of Treg after 5 days of RCT (49.4% vs. 34.0%, p=0.043).

CONCLUSION

Higher Treg levels are associated with favorable tumor stage. We hypothesize that a dramatic decrease of Treg after in vivo irradiation may be a good indicator for necessary dose adjustments in radiation therapy of CRC patients.

Targeting DNA damage and repair: embracing the pharmacological era for successful cancer therapy

DNA is under constant assault from genotoxic agents which creates different kinds of DNA damage. The precise replication of the genome and the continuous surveillance of its integrity are critical for survival and the avoidance of carcinogenesis. Cells have evolved an arsenal of repair pathways and cell cycle checkpoints to detect and repair DNA damage. When repair fails, typically cell cycle progression is halted and apoptosis is initiated. Here, we review the different sources and types of DNA damage including DNA replication stress and oxidative stress, the repair pathways that cells utilize to repair damaged DNA, and discuss their biological significance, especially with reference to cancer induction and cancer therapy. We also describe the main methodologies currently used for the detection of DNA damage with their strengths and limitations. We conclude with an outline as to how this information can be used to identify novel pharmacological targets for DNA repair pathways or enhancers of DNA damage to develop improved treatment strategies that will benefit cancer patients.