Indicators of late normal tissue response after radiotherapy for head and neck cancer: fibroblasts, lymphocytes, genetics, DNA repair, and chromosome aberrations

Applications of Premature Chromosome Condensation technique for genetic analysis

Cytogenetic techniques are used to detect aberrations in the genetic material and such techniques have a wide range of applications including for disease diagnosis, drug discovery and for the detection and quantification of mutagenic exposures. Although different types of cytogenetic techniques are in use, the Premature Chromosome Condensation (PCC) is one which is unique by virtue of it not requiring culture of peripheral blood mononucleate cells (PBMNCs) to detect chromatid and chromosomal aberrations. Such an advantage is useful in situations where rapid assessments of genetic damage is required, for example, during radiation exposures. PCC utilizes condensation of interphase chromatin by either biological or chemical means. The most widely used application of PCC is for biodosimetry. However, the rapidness of aberration detection has made PCC a useful technique for other applications such as for cancer diagnosis, drug-induced genotoxicity and preimplantation or assisted reproductive techniques. Also, PCC can be utilized for understanding the fundamental cellular mechanisms involved in chromatin condensation and chromosome morphologies. We present here the various approaches to obtain PCC, its applications and the endpoints which are used while using PCC as a cytogenetic technique.

Role of circ-FOXO3 and miR-23a in radiosensitivity of breast cancer

Identifying the radiosensitivity of cells before radiotherapy (RT) in breast cancer (BC) patients allows appropriate switching between routinely used treatment regimens and reduces adverse side effects in exposed patients. In this study, blood was collected from 60 women diagnosed with Invasive Ductal Carcinoma (IDC) BC and 20 healthy women. To predict cellular radiosensitivity, a standard G2-chromosomal assay was performed. From these 60 samples, 20 BC patients were found to be radiosensitive based on the G2 assay. Therefore, molecular studies were finally performed on two equal groups (20 samples each) of patients with and without cellular radiosensitivity. QPCR was performed to examine the expression levels of circ-FOXO3 and miR-23a in peripheral blood mononuclear cells (PBMCs) and RNA sensitivity and specificity were determined by plotting Receiver Operating Characteristic (ROC) curves. Binary logistic regression was performed to identify RNA involvement in BC and cellular radiosensitivity (CR) in BC patients. Meanwhile, qPCR was used to compare differential RNA expression in the radiosensitive MCF-7 and radioresistant MDA-MB-231 cell lines. An annexin -V FITC/PI binding assay was used to measure cell apoptosis 24 and 48 h after 2 Gy, 4 Gy, and 8 Gy gamma-irradiation. Results indicated that circ-FOXO3 was downregulated and miR-23a was upregulated in BC patients. RNA expression levels were directly associated with CR. Cell line results showed that circ-FOXO3 overexpression induced apoptosis in the MCF-7 cell line and miR-23a overexpression inhibited apoptosis in the MDA-MB-231 cell line. Evaluation of the ROC curves revealed that both RNAs had acceptable specificity and sensitivity in predicting CR in BC patients. Binary logistic regression showed that both RNAs were also successful in predicting breast cancer. Although only circ-FOXO3 has been shown to predict CR in BC patients, circ-FOXO3 may function as a tumor suppressor and miR-23a may function as oncomiR in BC. Circ-FOXO3 and miR-23a may be promising potential biomarkers for BC prediction. Furthermore, Circ-FOXO3 could be a potential biomarker for predicting CR in BC patients.

Cytogenetic Damage Induced by Radioiodine Therapy: A Follow-Up Case Study

The risk of toxicity attributable to radioiodine therapy (RIT) remains a subject of ongoing research, with a whole-body dose of 2 Gy proposed as a safe limit. This article evaluates the RIT-induced cytogenetic damage in two rare differentiated thyroid cancer (DTC) cases, including the first follow-up study of a pediatric DTC patient. Chromosome damage in the patient's peripheral blood lymphocytes (PBL) was examined using conventional metaphase assay, painting of chromosomes 2, 4, and 12 (FISH), and multiplex fluorescence in situ hybridization (mFISH). Patient 1 (female, 1.6 y.o.) received four RIT courses over 1.1 years. Patient 2 (female, 49 y.o.) received 12 courses over 6.4 years, the last two of which were examined. Blood samples were collected before and 3-4 days after the treatment. Chromosome aberrations (CA) analyzed by conventional and FISH methods were converted to a whole-body dose accounting for the dose rate effect. The mFISH method showed an increase in total aberrant cell frequency following each RIT course, while cells carrying unstable aberrations predominated in the yield. The proportion of cells containing stable CA associated with long-term cytogenetic risk remained mostly unchanged during follow-up for both patients. A one-time administration of RIT was safe, as the threshold of 2 Gy for the whole-body dose was not exceeded. The risk of side effects projected from RIT-attributable cytogenetic damage was low, suggesting a good long-term prognosis. In rare cases, such as the ones reviewed in this study, individual planning based on cytogenetic biodosimetry is strongly recommended.

Heat Killed Salmonella typhimurium Protects Intestine Against Radiation Injury Through Wnt Signaling Pathway

Gastrointestinal (GI) toxicity caused by ionizing radiation (IR) is a dose limiting factor in radiotherapy and a great threat for individual nuclear-related military missions. However, there are currently no available strategies to effectively prevent the damage on the intestine induced by IR. In the present study, the protective activity of Heat Killed Salmonella typhimurium (HKST) on intestine against IR was investigated. Through mouse intestinal organoids and whole body irradiation of mice, we found that the pretreatment with HKST significantly preserved the structure of small intestine upon IR exposure and promoted the proliferation of intestinal cells post-IR. Further study revealed that the radioprotective effects of HKST were involved in DNA damage response (DDR) signaling. Moreover, the stimulation of DDR signaling by HKST upon radiation damage was mediated by Wnt signaling, in which the inhibition of Wnt signaling diminished the radioprotective effects of HKST. To sum up, our study suggested HKST as a potential radioprotectant used for prevention of IR-induced GI toxicity.

The DNA damage response network in the treatment of head and neck squamous cell carcinoma

BACKGROUND

We sought to determine whether DNA damage response (DDR)-related aberrations predict therapeutic benefit in cisplatin-treated head and neck squamous cell carcinoma (HNSCC) patients and how DDR pathways are modulated after treatment with olaparib alone or in combination with cisplatin or durvalumab.

PATIENTS AND METHODS

Oxidative stress, abasic sites and DDR-related parameters, including endogenous DNA damage, DNA repair mechanisms and apoptosis rates, were evaluated in HNSCC cell lines and peripheral blood mononuclear cells from 46 healthy controls (HC) and 70 HNSCC patients at baseline and following treatment with cisplatin-containing chemoradiation or nivolumab or enrolled in the OPHELIA phase II trial (NCT02882308; olaparib alone, olaparib plus cisplatin, olaparib plus durvalumab).

RESULTS

HNSCC patients at diagnosis exhibited deregulated DDR-related parameters and higher levels of oxidative stress and abasic sites compared with HC (all P < 0.05). Accordingly, nucleotide excision repair (NER; ERCC1, ERCC2/XPD, XPA, XPC) and base excision repair (APEX1, XRCC1) genes were downregulated in patients versus HC whereas double-strand breaks repair (MRE11A, RAD50, RAD51, XRCC2) and mismatch repair (MLH1, MSH2, MSH3) genes were overexpressed. Corresponding results were obtained in cell lines (all P < 0.001). Excellent correlations were observed between individual ex vivo and in vivo/therapeutic results, with cisplatin non-responders showing higher levels of endogenous DNA damage, augmented oxidative stress and abasic sites, increased NER capacities and reduced apoptosis than responders (all P < 0.05). Also, longer progression-free survival correlated with lower NER capacity (P = 0.037) and increased apoptosis (P = 0.029). Interestingly, treatment with olaparib-containing regimens results in the accumulation of cytotoxic DNA damage and exerts an extra antitumor effect by elevating oxidative stress (all P < 0.05). Nivolumab induced no significant changes in the DDR parameters examined.

CONCLUSIONS

Aberrations in DDR signals are implicated in the response to HNSCC chemotherapy and can be exploited as novel therapeutic targets, sensitive/effective non-invasive biomarkers as well as for the design of novel clinical trials.

Prediction of the Acute or Late Radiation Toxicity Effects in Radiotherapy Patients Using Ex Vivo Induced Biodosimetric Markers: A Review

A search for effective methods for the assessment of patients' individual response to radiation is one of the important tasks of clinical radiobiology. This review summarizes available data on the use of ex vivo cytogenetic markers, typically used for biodosimetry, for the prediction of individual clinical radiosensitivity (normal tissue toxicity, NTT) in cells of cancer patients undergoing therapeutic irradiation. In approximately 50% of the relevant reports, selected for the analysis in peer-reviewed international journals, the average ex vivo induced yield of these biodosimetric markers was higher in patients with severe reactions than in patients with a lower grade of NTT. Also, a significant correlation was sometimes found between the biodosimetric marker yield and the severity of acute or late NTT reactions at an individual level, but this observation was not unequivocally proven. A similar controversy of published results was found regarding the attempts to apply G2- and γH2AX foci assays for NTT prediction. A correlation between ex vivo cytogenetic biomarker yields and NTT occurred most frequently when chromosome aberrations (not micronuclei) were measured in lymphocytes (not fibroblasts) irradiated to relatively high doses (4-6 Gy, not 2 Gy) in patients with various grades of late (not early) radiotherapy (RT) morbidity. The limitations of existing approaches are discussed, and recommendations on the improvement of the ex vivo cytogenetic testing for NTT prediction are provided. However, the efficiency of these methods still needs to be validated in properly organized clinical trials involving large and verified patient cohorts.

Radiation Biomarkers in Large Scale Human Health Effects Studies

Following recent developments, the RENEB network (Running the European Network of biological dosimetry and physical retrospective dosimetry) is in an excellent position to carry out large scale molecular epidemiological studies of ionizing radiation effects, with validated expertise in the dicentric, fluorescent in situ hybridization (FISH)-translocation, micronucleus, premature chromosome condensation, gamma-H2AX foci and gene expression assays. Large scale human health effects studies present complex challenges such as the practical aspects of sample logistics, assay costs, effort, effect modifiers and quality control/assurance measures. At Public Health England, the dicentric, automated micronucleus and gamma-H2AX radiation-induced foci assays have been tested for use in a large health effects study. The results of the study and the experience gained in carrying out such a large scale investigation provide valuable information that could help minimise random and systematic errors in biomarker data sets for health surveillance analyses going forward.

Late Soft Tissue Complications of Head and Neck Cancer Therapy: Lymphedema and Fibrosis

Head and neck cancer and its treatment result in soft tissue damage secondary to lymphedema and fibrosis. Lymphedema is the result of pathological accumulation of interstitial fluid in tissues. It is caused by the inability of the lymphatic system to transport lymph fluid from the tissues to the central circulatory system and is manifested clinically by tissue swelling. Fibrosis is defined as an overaccumulation of fibrotic tissues within the skin and soft tissues after a single or repetitive injury and is characterized by hardening of the soft tissues with associated loss of elasticity. Lymphedema and fibrosis are common yet overlooked late effects of head and neck cancer and its therapy. They may result in profound long-term symptom burden, loss of critical functions, and altered quality of life. The following review will discuss the current pathobiology, clinical manifestations, and future directions for research related to lymphedema and fibrosis.

CLINICAL APPLICATIONS OF BIOMARKERS OF RADIATION EXPOSURE: LIMITATIONS AND POSSIBLE SOLUTIONS THROUGH COORDINATED RESEARCH

Dosimetric biomarkers have been effectively and intensively used for a long time in the area of radiation protection. In contrast to that, no robust standards or widely accepted protocols for application of these end-points in radiotherapy, diagnostic and interventional radiology and nuclear medicine exist to date. The International Atomic Energy Agency (IAEA) organized the review of the available data on the possibilities of the use of dosimetric biomarkers in medical irradiation scenarios. The resultant Technical Report also contains a summary of identified problems, gaps in knowledge, limitations in methodology and recommendations for their overcoming. This work provided a conceptual background for the initiation of a new IAEA Coordinated Research Project E35010, MEDBIODOSE (2017-21), which is aimed specifically at the development and improvement of applications of biodosimetric markers in clinical practice.

Altered Fractionation Radiotherapy in Head and Neck Cancer: Clinical Issues and Pitfalls of “Evidence-Based Medicine”

The authors present a critical appraisal of the biological bases of altered fractionation and a brief overview of published randomized trials with conventional fractionation as the control arm, reviews and meta-analysis on altered fractionation radiotherapy in head and neck cancer. The major controversial issues emerging from these studies are reviewed and the limiting factors which so far have prevented the widespread use of altered fractionation regimens in current clinical practice are analyzed. Future perspectives regarding predictive biological assays for patient selection and the integration of altered fractionation regimens with radiochemotherapy protocols, biomodulators and novel radiotherapy techniques are also reviewed and summarized.

Dicentric Dose Estimates for Patients Undergoing Radiotherapy in the RTGene Study to Assess Blood Dosimetric Models and the New Bayesian Method for Gradient Exposure

The RTGene study was focused on the development and validation of new transcriptional biomarkers for prediction of individual radiotherapy patient responses to ionizing radiation. In parallel, for validation purposes, this study incorporated conventional biomarkers of radiation exposure, including the dicentric assay. Peripheral blood samples were taken with ethical approval and informed consent from a total of 20 patients undergoing external beam radiotherapy for breast, lung, gastrointestinal or genitourinary tumors. For the dicentric assay, two samples were taken from each patient: prior to radiotherapy and before the final fraction. Blood samples were set up using standard methods for the dicentric assay. All the baseline samples had dicentric frequencies consistent with the expected background for the normal population. For blood taken before the final fraction, all the samples displayed distributions of aberrations, which are indicative of partial-body exposures. Whole-body and partial-body cytogenetic doses were calculated with reference to a 250-kVp X-ray calibration curve and then compared to the dose to blood derived using two newly developed blood dosimetric models. Initial comparisons indicated that the relationship between these measures of dose appear very promising, with a correlation of 0.88 (P = 0.001). A new Bayesian zero-inflated Poisson finite mixture method was applied to the dicentric data, and partial-body dose estimates showed no significant difference (P > 0.999) from those calculated by the contaminated Poisson technique. The next step will be further development and validation in a larger patient group.

Is C-11 Methionine PET an alternative to 18-F FDG-PET for identifying recurrent laryngeal cancer after radiotherapy?

OBJECTIVE

18F FDG-PET is superior to other imaging techniques in revealing residual laryngeal cancer after radiotherapy. Unfortunately, its specificity is low, due to FDG uptake in inflammation and in anaerobic conditions. PET imaging with the amino acid-based radiopharmaceutical C11-methionine (MET) should be less influenced by post-radiation conditions. The aim of this study was to investigate the potential of MET in diagnosing recurrent laryngeal cancer after radiotherapy as compared to 18F-FDG.

METHODS

Forty-eight patients with a clinical suspicion of local residual disease at least 3 months after completion of radiotherapy or chemoradiotherapy for a T2-4 laryngeal carcinoma, along with an indication for direct laryngoscopy, were included. They received MET-PET and FDG-PET prior to the direct laryngoscopy. One senior nuclear medicine physician assessed both the FDG-PET and MET-PET images visually for the degree of abnormal uptake. The gold standard was a biopsy-proven recurrence 12 months after PET. The nuclear physician had no access to the medical charts and was blinded to the results of the other PET. Sensitivity, specificity and positive and negative predictive value were calculated.

RESULTS

The sensitivity of FDG was 77.3% and the specificity 56.0% after the conservative reading, with these values equalling 54.5% and 76.0% for MET. The positive predictive value of FDG was 60.7% and the negative predictive value 73.7%. The PPV of MET was 66.7%, and the NPV was 65.5%. The McNemar test within diseased (sensitivity comparison) shows a p-value of 0.125, and the McNemar test within non-diseased (specificity comparison) shows a P-value of 0.180.

CONCLUSION

MET-PET is not superior to FDG-PET in terms of identifying recurrent laryngeal cancer.

Heat-killed salmonella typhimurium (HKST) protects mice against radiation in TLR4-dependent manner

It is urgently required to develop novel safe and effective radioprotectors to alleviate radiation damages. Recently, several toll like receptors (TLRs), including TLR2, TLR4, TLR5, TLR9, have been proved to exert protective effects against ionizing radiation. Due to different tissue-distribution and distinct functions of TLRs, we hypothesized that co-activation of multiple TLRs simultaneously may produce extensive and stronger radioprotective effects. In this study, we found the co-agonist of TLR2, TLR4 and TLR5, heat-killed salmonella typhimurium (HKST) significantly inhibited radiation-induced cell apoptosis, increased cell survival and alleviated DNA damage. HKST also prolonged animal survival and protected radiosensitive tissues against radiation damages, such as bone marrow, spleen and testis. Decrease of CD4+ and CD8+ cells were also reversed by HKST treatment. By using TLR2 and TLR4 knockout mice, we found that most of radioprotective effects of HKST were abrogated in TLR4 knock out mice. And HKST failed to inhibited cell apoptosis in TLR5 knock down cells. In conclusion, we demonstrated that HKST effectively protected cells and radiosensitive tissues against radiation injury in a TLR4 biased mechanism, suggesting HKST as a potential radioprotector with low toxicity.

Radiogenomics: A systems biology approach to understanding genetic risk factors for radiotherapy toxicity?

Adverse reactions in normal tissue after radiotherapy (RT) limit the dose that can be given to tumour cells. Since 80% of individual variation in clinical response is estimated to be caused by patient-related factors, identifying these factors might allow prediction of patients with increased risk of developing severe reactions. While inactivation of cell renewal is considered a major cause of toxicity in early-reacting normal tissues, complex interactions involving multiple cell types, cytokines, and hypoxia seem important for late reactions. Here, we review 'omics' approaches such as screening of genetic polymorphisms or gene expression analysis, and assess the potential of epigenetic factors, posttranslational modification, signal transduction, and metabolism. Furthermore, functional assays have suggested possible associations with clinical risk of adverse reaction. Pathway analysis incorporating different 'omics' approaches may be more efficient in identifying critical pathways than pathway analysis based on single 'omics' data sets. Integrating these pathways with functional assays may be powerful in identifying multiple subgroups of RT patients characterised by different mechanisms. Thus 'omics' and functional approaches may synergise if they are integrated into radiogenomics 'systems biology' to facilitate the goal of individualised radiotherapy.

In vitro cellular radiosensitivity in relationship to late normal tissue reactions in breast cancer patients: a multi-endpoint case-control study

PURPOSE

A minority of patients exhibits severe late normal tissue toxicity after radiotherapy (RT), possibly related to their inherent individual radiation sensitivity. This study aimed to evaluate four different candidate in vitro cellular radiosensitivity assays for prediction of late normal tissue reactions, in a retrospective matched case-control set-up of breast cancer patients.

METHODS

The study population consists of breast cancer patients expressing severe radiation toxicity (12 cases) and no or minimal reactions (12 controls), with a follow-up for at least 3 years. Late adverse reactions were evaluated by comparing standardized photographs pre- and post-RT resulting in an overall cosmetic score and by clinical examination using the LENT-SOMA scale. Four cellular assays on peripheral blood lymphocytes reported to be associated with normal tissue reactions were performed after in vitro irradiation of patient blood samples to compare case and control radiation responses: radiation-induced CD8+ late apoptosis, residual DNA double-strand breaks, G0 and G2 micronucleus assay.

RESULTS

A significant difference was observed for all cellular endpoints when matched cases and controls were compared both pairwise and grouped. However, it is important to point out that most case-control pairs showed a substantial overlap in standard deviations, which questions the predictive value of the individual assays. The apoptosis assay performed best, with less apoptosis seen in CD8+ lymphocytes of the cases (average: 14.45%) than in their matched controls (average: 30.64%) for 11 out of 12 patient pairs (p < .01). The number of residual DNA DSB was higher in cases (average: 9.92 foci/cell) compared to their matched control patients (average: 9.17 foci/cell) (p < .01). The average dose response curve of the G0 MN assay for cases lies above the average dose response curve of the controls. Finally, a pairwise comparison of the G2 MN results showed a higher MN yield for cases (average: 351 MN/1000BN) compared to controls (average: 219 MN/1000BN) in 9 out of 10 pairs (p < .01).

CONCLUSION

This matched case-control study in breast cancer patients, using different endpoints for in vitro cellular radiosensitivity related to DNA repair and apoptosis, suggests that patients' intrinsic radiosensitivity is involved in the development of late normal tissue reactions after RT. Larger prospective studies are warranted to validate the retrospective findings and to use in vitro cellular assays in the future to predict late normal tissue radiosensitivity and discriminate individuals with marked RT responses.

Correlation between DNA damage responses of skin to a test dose of radiation and late adverse effects of earlier breast radiotherapy

AIM

To correlate residual double strand breaks (DSB) 24h after 4Gy test doses to skin in vivo and to lymphocytes in vitro with adverse effects of earlier breast radiotherapy (RT).

PATIENTS AND METHODS

Patients given whole breast RT ⩾5years earlier were identified on the basis of moderate/marked or minimal/no adverse effects despite the absence ('RT-Sensitive', RT-S) or presence ('RT-Resistant', RT-R) of variables predisposing to late adverse effects. Residual DSB were quantified in skin 24h after a 4Gy test dose in 20 RT-S and 15 RT-R patients. Residual DSB were quantified in lymphocytes irradiated with 4Gy in vitro in 30/35 patients.

RESULTS

Mean foci per dermal fibroblast were 3.29 (RT-S) vs 2.80 (RT-R) (p=0.137); 3.28 (RT-S) vs 2.60 (RT-R) in endothelium (p=0.158); 2.50 (RT-S) vs 2.41 (RT-R) in suprabasal keratinocytes (p=0.633); 2.70 (RT-S) vs 2.35 (RT-R) in basal epidermis (p=0.419); 12.1 (RT-S) vs 10.3 (RT-R) in lymphocytes (p=0.0052).

CONCLUSIONS

Residual DSB in skin following a 4Gy dose were not significantly associated with risk of late adverse effects of breast radiotherapy, although exploratory analyses suggested an association in severely affected individuals. By contrast, a significant association was detected based on the in vitro response of lymphocytes.

Correlation between the radiation responses of fibroblasts cultured from individual patients and the risk of late reaction after breast radiotherapy

Late normal tissue toxicity varies widely between patients and limits breast radiotherapy dose. Here we aimed to determine its relationship to DNA damage responses of fibroblast cultures from individual patients. Thirty-five breast cancer patients, with minimal or marked breast changes after breast-conserving therapy consented to receive a 4 Gy test irradiation to a small skin field of the left buttock and have punch biopsies taken from irradiated and unirradiated skin. Early-passage fibroblast cultures were established by outgrowth and irradiated in vitro with 0 or 4 Gy. 53BP1 foci, p53 and p21/CDKN1A were detected by immunofluorescence microscopy. Residual 53BP1 foci counts 24 h after in vitro irradiation were significantly higher in fibroblasts from RT-sensitive versus RT-resistant patients. Furthermore, significantly larger fractions of p53- but not p21/CDKN1A-positive fibroblasts were found in cultures from RT-sensitive patients without in vitro irradiation, and 2 h and 6 d post-irradiation. Exploratory analysis showed a stronger p53 response 2 h after irradiation of fibroblasts established from patients with severe reaction. These results associate the radiation response of fibroblasts with late reaction of the breast after RT and suggest a correlation with severity.

Polymorphisms in double strand break repair related genes influence radiosensitivity phenotype in lymphocytes from healthy individuals

BACKGROUND

A range of individual radiosensitivity observed in humans can influence individual's susceptibility toward cancer risk and radiotherapy outcome. Therefore, it is important to measure the variation in radiosensitivity and to identify the genetic factors influencing it.

METHODS

By adopting a pathway specific genotype-phenotype design, we established the variability in cellular radiosensitivity by performing γ-H2AX foci assay in healthy individuals. Further, we genotyped ten selected SNPs in candidate genes XRCC3 (rs861539), XRCC4 (rs1805377), XRCC5 (rs3835), XRCC6 (rs2267437), ATM (rs3218698, rs1800057), LIG4 (rs1805388), NBN (rs1805794), RAD51 (rs1801320) and PRKDC (rs7003908), and analysed their influence on observed variation in radiosensitivity.

RESULTS

The rs2267437 polymorphisms in XRCC6 was associated (P=0.0326) with increased DSB induction while rs1805388 in LIG4 (P=0.0240) was associated with increased radioresistance. Further, multiple risk alleles decreased the DSB repair capacity in an additive manner. Polymorphisms in candidate DSB repair genes can act individually or in combination to the efficacy of DSB repair process, resulting in variation of cellular radiosensitivity.

CONCLUSIONS

Current study suggests that γ-H2AX assay may fulfil the role of a rapid and sensitive biomarker that can be used for epidemiological studies to measure variations in radiosensitivity. DSB repair gene polymorphisms can impact the formation and repair of DSBs.

IMPACT

γ-H2AX foci analysis as well as DSBs repair gene polymorphisms can be used to assess cellular radiosensitivity, which will be useful in population risk assessment, disease prediction, individualization of radiotherapy and also in setting the radiation protection standards.

Variations in the Processing of DNA Double-Strand Breaks Along 60-MeV Therapeutic Proton Beams

Purpose

To investigate the variations in induction and repair of DNA damage along the proton path, after a previous report on the increasing biological effectiveness along clinically modulated 60-MeV proton beams.

Methods and Materials

Human skin fibroblast (AG01522) cells were irradiated along a monoenergetic and a modulated spread-out Bragg peak (SOBP) proton beam used for treating ocular melanoma at the Douglas Cyclotron, Clatterbridge Centre for Oncology, Wirral, Liverpool, United Kingdom. The DNA damage response was studied using the 53BP1 foci formation assay. The linear energy transfer (LET) dependence was studied by irradiating the cells at depths corresponding to entrance, proximal, middle, and distal positions of SOBP and the entrance and peak position for the pristine beam.

Results

A significant amount of persistent foci was observed at the distal end of the SOBP, suggesting complex residual DNA double-strand break damage induction corresponding to the highest LET values achievable by modulated proton beams. Unlike the directly irradiated, medium-sharing bystander cells did not show any significant increase in residual foci.

Conclusions

The DNA damage response along the proton beam path was similar to the response of X rays, confirming the low-LET quality of the proton exposure. However, at the distal end of SOBP our data indicate an increased complexity of DNA lesions and slower repair kinetics. A lack of significant induction of 53BP1 foci in the bystander cells suggests a minor role of cell signaling for DNA damage under these conditions.

DNA damage at respiratory distress, but not acute time-points, correlates with tissue fibrosis following thoracic radiation exposure in mice

PURPOSE

Radiation exposure can result in DNA damage but whether the extent of DNA damage correlates with the radiation-induced tissue injury in the lung is not known. We aimed to determine whether numbers of γH2AX foci, representing histone H2AX phosphorylation a marker of DNA damage, measured within days of radiation exposure, correlated with known later lung injury responses in eight inbred mouse strains.

MATERIALS AND METHODS

Mice received 18 Gy pulmonary irradiation and numbers of γH2AX positive nuclei in the lung were immunohistochemically determined.

RESULTS

Numbers of γH2AX foci, assessed up to seven days post irradiation did not correlate with pulmonary fibrosis. γH2AX counts from mice in respiratory distress, however, significantly correlated with fibrosis and lungs from mice treated with a fibrosis-reducing antagonist had fewer γH2AX foci.

CONCLUSIONS

Acute response measures of pulmonary DNA damage did not predict for pathology, but levels of this marker in distressed mice were correlative of fibrosis.

Identification of a radiation sensitivity gene expression profile in primary fibroblasts derived from patients who developed radiotherapy-induced fibrosis

BACKGROUND AND PURPOSE

During radiotherapy, normal tissue is unavoidably exposed to radiation which results in severe normal tissue reactions in a small fraction of patients. Because those who are sensitive cannot be determined prior to radiotherapy, the doses are limited to all patients to avoid an unacceptable number of severe adverse normal tissue responses. This limitation restricts the optimal treatment for individuals who are more tolerant to radiation. Genetic variation is a likely source for the normal tissue radiosensitivity variation observed between individuals. Therefore, understanding the radiation response at the genomic level may provide knowledge to develop individualized treatment and improve radiotherapy outcomes.

MATERIAL AND METHODS

Exon arrays were utilized to compare the basal expression profile between cell lines derived from six cancer patients with and without severe fibrosis. These data were supported by qRT-PCR and RNA-Seq techniques.

RESULTS

A set of genes (FBN2, FST, GPRC5B, NOTCH3, PLCB1, DPT, DDIT4L and SGCG) were identified as potential predictors for radiation-induced fibrosis. Many of these genes are associated with TGFβ or retinoic acid both having known links to fibrosis.

CONCLUSION

A combinatorial gene expression approach provides a promising strategy to predict fibrosis in cancer patients prior to radiotherapy.

Finding the genetic determinants of adverse reactions to radiotherapy

Individual variation in radiosensitivity is thought to be at least partly determined by genetic factors. The remaining difference between individuals is caused by comorbidities, variation in treatment, body habitus and stochastic factors. Evidence for the heritability of radiosensitivity comes from rare genetic disorders and from cell-based studies. To what extent common and rare genetic variants might explain the genetic component of radiosensitivity has not been fully elucidated. If the genetic variants accounting for this heritability were to be determined, they could be incorporated into any future predictive statistical model of adverse reactions to radiotherapy. With the evolution of DNA sequencing and bioinformatics, radiogenomics has emerged as a new research field with the aim of finding the genetic determinants of adverse reactions to radiotherapy. Similar to the investigation of other complex genetic disease traits, early studies in radiogenomics involved candidate gene association studies--many plagued by false associations caused by low sample sizes and problematic experimental design. More recently, some promising genetic associations (e.g. with tumour necrosis factor) have emerged from large multi-institutional cohorts with built-in replication. At the same time, several small- to medium-sized genome-wide association studies (GWAS) have been or are about to be published. These studies will probably lead to an increasing number of genetic polymorphisms that may predict adverse reactions to radiotherapy. The future of the field is to create large patient cohorts for multiple cancer types, to validate the genetic loci and build reliable predictive models. For example, the REQUITE project involves multiple groups in Europe and North America. For further discovery studies, larger GWAS will be necessary to include rare sequence variants through next generation sequencing. Ultimately, radiogenomics seeks to predict which cancer patients will show radiosensitivity or radioresistance, so oncologists and surgeons can alter treatment accordingly to lower adverse reactions or increase the efficacy of radiotherapy.

Reduced activity of double-strand break repair genes in prostate cancer patients with late normal tissue radiation toxicity

PURPOSE

To investigate clinical parameters and DNA damage response as possible risk factors for radiation toxicity in the setting of prostate cancer.

METHODS AND MATERIALS

Clinical parameters of 61 prostate cancer patients, 34 with (overresponding, OR) and 27 without (non-responding, NR) severe late radiation toxicity were assembled. In addition, for a matched subset the DNA damage repair kinetics (γ-H2AX assay) and expression profiles of DNA repair genes were determined in ex vivo irradiated lymphocytes.

RESULTS

Examination of clinical data indicated none of the considered clinical parameters to be correlated with the susceptibility of patients to develop late radiation toxicity. Although frequencies of γ-H2AX foci induced immediately after irradiation were similar (P=.32), significantly higher numbers of γ-H2AX foci were found 24 hours after irradiation in OR compared with NR patients (P=.03). Patient-specific γ-H2AX foci decay ratios were significantly higher in NR patients than in OR patients (P<.0001). Consequently, NR patients seem to repair DNA double-strand breaks (DSBs) more efficiently than OR patients. Moreover, gene expression analysis indicated several genes of the homologous recombination pathway to be stronger induced in NR compared with OR patients (P<.05). A similar trend was observed in genes of the nonhomologous end-joining repair pathway (P=.09). This is congruent with more proficient repair of DNA DSBs in patients without late radiation toxicity.

CONCLUSIONS

Both gene expression profiling and DNA DSB repair kinetics data imply that less-efficient repair of radiation-induced DSBs may contribute to the development of late normal tissue damage. Induction levels of DSB repair genes (eg, RAD51) may potentially be used to assess the risk for late radiation toxicity.

Simultaneous analysis of p53 protein expression and cell proliferation in irradiated human lymphocytes by flow cytometry

P53 protein has an intrinsic role in modulating the cellular response against DNA radioinduced damages and has been pointed out as an indirect indicator of individual radiosensitivity. The rate of cell proliferation is also a parameter that has been related to tissue sensitivity to radiation. However, this feature is yet understudied. In this context, the aim of this work was to employ Flow Cytometry (FC) for simultaneously assessing of p53 protein expression levels together with cellular proliferation rate of irradiated human lymphocytes. From in vitro irradiated human blood samples, mononuclear cells were isolated and labeled with Carboxylfluorescein Diacetate Succinimidyl Ester (CFSE) prior to phytohaemagglutinin (PHA) stimulation in culture for 96 hours. Cells were also labeled with anti-p53 monoclonal antibody PE-conjugated in order to analyze either proliferation rate or p53 expression levels by FC. It was verified a reduction in the proliferation rate of irradiated lymphocytes and, in parallel, a rise in the p53 expression levels, similar for quiescent and proliferating lymphocytes. The results emphasize the importance of the use of CFSE-stained lymphocytes in assays associated to proliferation rate and the use of this methodology in several studies, such as for evaluating individual radiosensitivity.

Direct and bystander radiation effects: a biophysical model and clinical perspectives

In planning treatment for each new patient, radiation oncologists pay attention to the aspects that they control. Thus their attention is usually focused on volume and dose. The dilemma for the physician is how to protract the treatment in a way that maximizes control of the tumor and minimizes normal tissue injury. The initial radiation-induced damage to DNA may be a biological indicator of the quantity of energy transferred to the DNA. However, until now the biophysical models proposed cannot explain either the early or the late adverse effects of radiation, and a more general theory appears to be required. The bystander component of tumor cell death after radiotherapy measured in many experimental works highlights the importance of confirming these observations in a clinical situation.

Investigating chromosome damage using fluorescent in situ hybridization to identify biomarkers of radiosensitivity in prostate cancer patients

PURPOSE

In order to evaluate fluorescent in situ hybridization (FISH) as a method for predicting radiosensitivity, this study examined the incidence of translocations, after exposure to in vitro radiation, in both normally responding patients and those exhibiting severe late effects after radiotherapy treatment.

MATERIALS AND METHODS

Patients were selected from a randomized trial for intermediate-risk prostate cancer. Of the patients entered on trial with mature follow-up, 3% developed grade 3 late proctitis. Blood samples were taken from this radiosensitive cohort along with matched control patients with no late proctitis. Whole blood samples were exposed to 0 or 4 Gy and cultured according to the International Atomic Energy Agency (IAEA) recommended methods. Colour junctions were evaluated in the resulting metaphases and scored according to the Protocol for Aberration Identification and Nomenclature Terminology (PAINT) system.

RESULTS

Both groups were statistically similar at 0 Gy. After 4 Gy in vitro radiation, the radiosensitive group had significantly higher rates of chromosome damage in the number of colour junctions per cell (p = 0.002), the number of deletions per cell (p = 0.01) and the number of dicentrics per cell (p = 0.005).

CONCLUSIONS

These results indicate that the analysis of translocations using FISH after in vitro irradiation correlates with clinical response to radiation. This cytogenetic assay should be considered as a potential predictor of radiosensitivity.

Comparative analysis of three functional predictive assays in lymphocytes of patients with breast and gynaecological cancer treated by radiotherapy

Purpose

There is a need to develop predictive tests that would allow identifying cancer patients with a high risk of developing side effects to radiotherapy. We compared the predictive value of three functional assays: the G₀ aberration assay, the G₂ aberration assay and the alkaline comet assay in lymphocytes of breast cancer and gynaecological cancer patients.

Material and methods

Peripheral blood was collected from 35 patients with breast cancer and 34 patients with gynaecological cancer before the onset of therapy. Chromosomal aberrations were scored in lymphocytes irradiated in the G₀ or G₂ phase of the cell cycle. DNA repair kinetics was performed with the alkaline comet assay following irradiation of unstimulated lymphocytes. The results were compared with the severity of early and late side effects to radiotherapy.

Results

No correlation was observed between the results of the assays and the severity of side effects. Moreover, each assay identified different patients as radiosensitive.

Conclusions

There is no simple correlation between the in vitro sensitivity of lymphocytes and the risk of developing early and late side effects.

Correlation of in vitro lymphocyte radiosensitivity and gene expression with late normal tissue reactions following curative radiotherapy for breast cancer

BACKGROUND AND PURPOSE

Identification of mechanisms of late normal tissue responses to curative radiotherapy that discriminate individuals with marked or mild responses would aid response prediction. This study aimed to identify differences in gene expression, apoptosis, residual DNA double strand breaks and chromosomal damage after in vitro irradiation of lymphocytes in a series of patients with marked (31 cases) or mild (28 controls) late adverse reaction to adjuvant breast radiotherapy.

MATERIALS AND METHODS

Gene expression arrays, residual γH2AX, apoptosis, G2 chromosomal radiosensitivity and G0 micronucleus assay were used to compare case and control lymphocyte radiation responses.

RESULTS

Five hundred and thirty genes were up-regulated and 819 down-regulated by ionising radiation. Irradiated samples were identified with an overall cross-validated error rate of 3.4%. Prediction analyses to classify cases and controls using unirradiated (0Gy), irradiated (4Gy) or radiation response (4-0Gy) expression profiles correctly identified samples with, respectively, 25%, 22% or 18.5% error rates. Significant inter-sample variation was observed for all cellular endpoints but cases and controls could not be distinguished.

CONCLUSIONS

Variation in lymphocyte radiosensitivity does not necessarily correlate with normal tissue response to radiotherapy. Gene expression analysis can predict of radiation exposure and may in the future help prediction of normal tissue radiosensitivity.

Chromosome damage and cell proliferation rates in in vitro irradiated whole blood as markers of late radiation toxicity after radiation therapy to the prostate

PURPOSE

In vitro irradiated blood samples from prostate cancer patients showing late normal tissue damage were examined for lymphocyte response by measuring chromosomal aberrations and proliferation rate.

METHODS AND MATERIALS

Patients were selected from a randomized trial evaluating the optimal timing of dose-escalated radiation and short-course androgen deprivation therapy. Of 438 patients, 3% experienced grade 3 late radiation proctitis and were considered to be radiosensitive. Blood samples were taken from 10 of these patients along with 20 matched samples from patients with grade 0 proctitis. The samples were irradiated at 6 Gy and, along with control samples, were analyzed for dicentric chromosomes and excess fragments per cell. Cells in first and second metaphase were also enumerated to determine the lymphocyte proliferation rate.

RESULTS

At 6 Gy, there were statistically significant differences between the radiosensitive and control cohorts for 3 endpoints: the mean number of dicentric chromosomes per cell (3.26 ± 0.31, 2.91 ± 0.32; P=.0258), the mean number of excess fragments per cell (2.27 ± 0.23, 1.43 ± 0.37; P<.0001), and the proportion of cells in second metaphase (0.27 ± 0.10, 0.46 ± 0.09; P=.0007).

CONCLUSIONS

These results may be a valuable indicator for identifying radiosensitive patients and for tailoring radiation therapy.

A bioinformatics filtering strategy for identifying radiation response biomarker candidates

The number of biomarker candidates is often much larger than the number of clinical patient data points available, which motivates the use of a rational candidate variable filtering methodology. The goal of this paper is to apply such a bioinformatics filtering process to isolate a modest number (<10) of key interacting genes and their associated single nucleotide polymorphisms involved in radiation response, and to ultimately serve as a basis for using clinical datasets to identify new biomarkers. In step 1, we surveyed the literature on genetic and protein correlates to radiation response, in vivo or in vitro, across cellular, animal, and human studies. In step 2, we analyzed two publicly available microarray datasets and identified genes in which mRNA expression changed in response to radiation. Combining results from Step 1 and Step 2, we identified 20 genes that were common to all three sources. As a final step, a curated database of protein interactions was used to generate the most statistically reliable protein interaction network among any subset of the 20 genes resulting from Steps 1 and 2, resulting in identification of a small, tightly interacting network with 7 out of 20 input genes. We further ranked the genes in terms of likely importance, based on their location within the network using a graph-based scoring function. The resulting core interacting network provides an attractive set of genes likely to be important to radiation response.

Suppression of vascular endothelial growth factor via siRNA interference modulates the biological behavior of human nasopharyngeal carcinoma cells

PURPOSE

The aim was to study the effect of vascular endothelial growth factor (VEGF) down-regulation by small interfering (si)RNA-mediated interference (RNAi) on the biological features of nasopharyngeal carcinoma cell line CNE-2.

MATERIALS AND METHODS

The combined plasmids pU-siVEGF and pU-siCONT were transfected into CNE-2 cells with lipofectamine. The transfected cells were placed in fresh medium containing G418. Expression of VEGF mRNA and protein were measured by reverse transcriptase-polymerase chain reaction and Western blot, respectively. The transwell chamber model was employed to test the ability of cell invasion in vitro. The distribution of cell cycle phases was determined by flow cytometry. Cell survival was assessed by clonogenic assays.

RESULTS

Both VEGF mRNA and protein expression were significantly decreased in the pU-siVEGF group compared with controls (P < 0.05). The cell cycle was arrested in the G(1) phase (P < 0.05). A higher apoptotic ratio and lower invasion ability were seen in the pU-siVEGF group. The D(0) (mean lethal dose) and SF(2) values were significantly lower than those in the control group (P < 0.05).

CONCLUSION

Delivery of siRNA targeting VEGF seems efficient in down-regulating VEGF expression and diminishing the growth, proliferation, and invasiveness of CNE-2 cells. It also enhanced the sensitivity of CNE-2 cells to radiation.

Residual DNA and chromosomal damage in ex vivo irradiated blood lymphocytes correlated with late normal tissue response to breast radiotherapy

PURPOSE

To test the association of DNA double-strand break (DSB) repair and chromosomal radiosensitivity in ex vivo irradiated blood lymphocytes with late-onset normal tissue responses following breast radiotherapy.

METHODS

Breast cancer patients with minimal (controls) or marked late radiotherapy changes (cases) were retrospectively selected. DSB were quantified by γH2AX/53BP1 immunofluorescence microscopy 0.5 and 24 h after exposure of unstimulated blood lymphocytes to 0.5 and 4 Gy X-rays, respectively. Chromosomal aberrations were scored in blood lymphocyte metaphases after 6 Gy X-rays.

RESULTS

Despite similar foci levels at 0.5 h in cases (n=7) and controls (n=7), foci levels 24 h after 4 Gy irradiation differed significantly between them (foci per cell were 12.8 in cases versus 10.2 in controls, p=0.004). Increased chromosomal radiosensitivity was also observed in cases (aberrations per cell were 5.84 in cases versus 3.79 in controls, p=0.001) with exchange and deletion type aberrations contributing equally to the difference between cases and controls. Residual foci correlated with formation of deletions (Spearman's R=0.589, p=0.027) but not exchanges (R=0.367, p=0.197) in blood lymphocytes from the same patients.

CONCLUSIONS

Higher levels of exchange type aberrations observed among radiosensitive breast cancer patients suggest a role for DSB misrepair, in addition to residual damage, as determinants of late normal tissue damage. Correlation of residual foci levels with deletion type aberration yields in the same cohort confirms their mechanistic linkage.

Chromosomal radiosensitivity and acute radiation side effects after radiotherapy in tumour patients--a follow-up study

Background

Radiotherapists are highly interested in optimizing doses especially for patients who tend to suffer from side effects of radiotherapy (RT). It seems to be helpful to identify radiosensitive individuals before RT.

Thus we examined aberrations in FISH painted chromosomes in in vitro irradiated blood samples of a group of patients suffering from breast cancer. In parallel, a follow-up of side effects in these patients was registered and compared to detected chromosome aberrations.

Methods

Blood samples (taken before radiotherapy) were irradiated in vitro with 3 Gy X-rays and analysed by FISH-painting to obtain aberration frequencies of first cycle metaphases for each patient. Aberration frequencies were analysed statistically to identify individuals with an elevated or reduced radiation response. Clinical data of patients have been recorded in parallel to gain knowledge on acute side effects of radiotherapy.

Results

Eight patients with a significantly elevated or reduced aberration yield were identified by use of a t-test criterion. A comparison with clinical side effects revealed that among patients with elevated aberration yields one exhibited a higher degree of acute toxicity and two patients a premature onset of skin reaction already after a cumulative dose of only 10 Gy. A significant relationship existed between translocations in vitro and the time dependent occurrence of side effects of the skin during the therapy period.

Conclusions

The results suggest that translocations can be used as a test to identify individuals with a potentially elevated radiosensitivity.

Biological effects of low level exposures to ionizing radiation: theory and practice

This paper briefly reviewed recent reports on the epidemiological and experimental data on low dose radiation effects that support the concept of radiation hormesis. These reports point to the possibility of existence of a threshold dose in cancer induction by ionizing radiation and in some cases the occurrence of hormetic effects with stimulation of host defense mechanisms. The possibility of the use of low dose radiation in cancer treatment to improve the outcome of conventional radiotherapy was raised by citing previous reports on experimental studies, which showed increased efficacy in tumor control with significant reduction of total dose of radiation when low dose radiation was used in the combined treatment protocol.

Unexpectedly severe acute radiotherapy side effects are associated with single nucleotide polymorphisms of the melanocortin-1 receptor

PURPOSE

The melanocortin-1 receptor (MC1R) regulates melanin biogenesis. Deoxyribonucleic acid sequence variants in the form of single nucleotide polymorphisms (SNPs) of MC1R affect melanin expression and are linked to skin phenotype. We aimed to determine whether SNPs of MC1R were associated with unexpectedly severe ionizing radiation reactions.

METHODS AND MATERIALS

The MC1R genotype of a cohort of Australians with unexpectedly severe acute and/or late reactions (Common Terminology Criteria Version 3 (CTCv3) Grade 3 or 4) to radiotherapy (RT) for cancer (n = 30) was analyzed. The findings were compared with control data from our previous study of MC1R representative of the general Australian population (n = 1,787).

RESULTS

The difference in frequency of alleles encoding a "red hair color" phenotype in the cohort of patients with unexpectedly severe acute radiation reactions (n = 12) was significantly increased compared with the control population (p = 0.003). Acute radiosensitivity was especially associated with the R160W variant allele (odds ratio, 3.64 [95% confidence interval, 1.3-10.27]). The corresponding comparison of MC1R controls with unexpectedly severe late radiation reactions (n = 18) was not significant. It was also found that R160W as a part of the genotype in the patients with unexpectedly severe acute RT side effects as compared with the control group was also significant (p = 0.043).

CONCLUSIONS

In this small cohort of cancer patients, deoxyribonucleic acid sequence variants of the MC1R gene, especially the R160W variant, have been associated with unexpectedly severe acute reactions to RT. This result needs to be verified in a larger cohort of patients.

Comparative study of two evaluation methods for the genotoxic effects of environmental heavy metals on normal cells

Genetic modifications caused by chronic exposure to low levels of toxic metals may activate stress-signaling pathways, thus increasing cancer incidence among affected individuals. The aim of this study was to evaluate the relationship between exposure to heavy metals and the incidence of chromosomal aberrations and DNA lesions in a chronically exposed population by using specific biomarkers. The study included 156 subjects divided into two major groups: exposed individuals (in a heavy metal contaminated region, Maramures, Romania) and non-exposed population, as control group (Cluj, Romania). We compared the results of two cytogenetic methods for the detection and quantification of DNA lesions and chromosomal aberrations in normal human cells: Single Cell Gel Electrophoresis or Comet assay and Cytokinesis Block Micronucleus assay. The methods were performed on lymphocytes isolated from whole blood in density gradient. The basal DNA lesions and chromosomal aberrations were evaluated, as well as the repair capacity of the supplementary lesions induced by genotoxic agents such as ionizing radiations. Our results showed a great interindividual variability in the basal level of the DNA lesions and chromosomal aberrations, between and within the groups, the most affected being the heavy metals-exposed groups. Non-exposed subjects from rural area Cluj appeared to be more susceptible to the induction of supplementary DNA lesions and chromosomal aberrations by irradiation. The most efficient repair capacity of the radio-induced DNA lesions was observed in the non-exposed Cluj urban group. Both cytogenetic assays (as tools for detection of DNA lesions and chromosomal aberrations) may be used in human biomonitoring studies as indicators of early biological effects induced by exposure to heavy metals.

Genetic variants and normal tissue toxicity after radiotherapy: a systematic review

During the last decade, nearly 60 studies have addressed possible associations between various genetic sequence alterations and risk of adverse reactions after radiotherapy. We report here an overview of these studies with information on the genetic variants, tumour type, number of patients included, the endpoint studied, the mechanism(s) by which the candidate genes are involved in the pathogenesis of normal tissue toxicity, and odds ratios (ORs) for candidate variants. Though many positive results have been reported, inconsistent findings and non-replication of previous results have frequently occurred. This can presumably be attributed to certain methodological shortcomings including lack of statistical power to detect small effect sizes. Based on theoretical considerations and experiences from other scientific fields, we discuss how future studies should be designed in order to successfully unravel the genetics of normal tissue radiosensitivity. We propose a model of the allelic architecture that may underlie differences in normal tissue radiosensitivity. Genome wide association studies have proven a powerful tool to identify novel loci that affect various phenotypes. Nonetheless, genome wide association studies are extremely demanding in terms of sample size. Furthermore, certain limitations still relate to this kind of studies, emphasizing the need for international consortia such as the ESTRO GENEPI.

Correlation between mitotic delay and aberration burden, and their role for the analysis of chromosomal damage

The aim was to investigate further the relationship between radiation-induced mitotic delay and the expression of chromosome damage in V79 cells. Recently published data on the time-course of chromosome aberrations in V79 first-cycle metaphases after exposure to 10.4 MeV u(-1) Ar ions (LET = 1226 keV microm(-1)) were supplemented and reanalysed. A statistical analysis of the distribution of aberrations among cells was performed. Furthermore, cells were grouped into subpopulations carrying 0, 1 -2, 3-4, 5- 6 and 7 or more aberrations. Then, based on the mitotic index, the flux of each subgroup through the first mitosis was determined and the average entrance time to mitosis was estimated. For comparison, the flux of aberrant V79 cells generated by X-irradiation was analysed. Analysis of the Ar ion data revealed that the flux of each subpopulation through the first mitosis is strongly affected by its aberration burden, i.e. a positive correlation between the mitotic delay and the number of aberrations carried by a cell was observed. The distribution of aberrations among cells could be well described by Neyman-type A statistics; the corresponding fit parameters also reflect the damage-dependent mitotic delay. Interestingly, comparison of the flux of Ar ion and X-ray-irradiated V79 cells through mitosis revealed (1) that a direct correlation exists between the number of aberrations carried by a cell and its average entrance time to mitosis, and (2) that this effect is independent of the linear energy transfer. The role of these observations for radiation cytogenetics is discussed.

No correlation between radiosensitivity or double-strand break repair capacity of normal fibroblasts and acute normal tissue reaction after radiotherapy of breast cancer patients

The aim was to study the relationship between cellular radiosensitivity or double-strand break (dsb) repair capacity of skin fibroblasts and the extent of acute reaction after radiotherapy for breast cancer. The study was performed with 25 breast cancer patients submitted to the radiotherapy unit of the Egyptian National Cancer Institute after conserving surgery. Dermal fibroblasts, established from skin biopsies, were used to determine the cellular radiosensitivity via colony assay and the capacity of dsb repair by constant-field gel electrophoresis. Acute reactions were scored using the Radiation Therapy Oncology Group (RTOG) classification. The spectrum of acute reactions varied from grade 1 to 4, whereby most patients developed a grade 1 reaction after total doses ranging between 46 and 70 Gy. Skin fibroblasts showed a pronounced variation in both cellular radiosensitivity expressed as the mean inactivation dose (Dbar) (coefficient of variation, CV=25%) as well as in the number of residual dsb (CV=33%) with no significant correlation between these two endpoints (r2=0.20, p=0.14). Both parameters did not correlate with the extent of acute reaction of the respective patient. The data obtained indicate that the sensitivity of fibroblasts measured either by colony assay or by dsb repair capacity is not a major parameter determining the extent of acute reaction after radiotherapy of breast cancer patients.

In vitroradiosensitivity of peripheral blood lymphocytes in multiple sclerosis patients

PURPOSE

To assess the in vitro radiosensitivity of peripheral blood lymphocytes of secondary progressive multiple sclerosis (MS) patients in comparison to healthy individuals.

MATERIAL AND METHODS

Radiosensitivity of MS patients lymphocytes to in vitro irradiation of 2 Gy 60Co gamma-rays was studied in whole blood cultures and separated peripheral blood mononuclear cell (PBMC) cultures. Chromosomal radiosensitivity was investigated by means of the G0-micronucleus (MN) assay. The radio-induction of micronuclei was also studied in separated subsets of CD4+ (helper) and CD8+ (suppressor) T cells. Apoptosis was analysed in PBMC cultures using fluorescence microscopy techniques.

RESULTS

The spontaneous MN induction was significantly higher in MS patients compared to healthy controls for whole blood and PBMC cultures. After gamma-irradiation of whole blood cultures no difference in radiosensitivity was observed between patients and controls for MN induction. In irradiated PBMC cultures, the CD4+ lymphocytes of MS patients were less radiosensitive compared to healthy controls and this more resistant behaviour increased with increasing illness duration. Radiation induced apoptosis in G0 lymphocytes of MS patients was lower than in controls.

CONCLUSION

After gamma irradiation, a radioresistant behaviour in PBMC cultures of MS patients was revealed. This radioresistant behaviour was expressed by lower MN induction in CD4+ lymphocytes and by lower apoptosis induction in G0 PBMC cultures and may point to an adaptive response. The higher radiation response in whole blood cultures compared to PBMC cultures was significantly more pronounced in MS patients, suggesting special characteristics of the whole blood environment associated with this pathology.

Genetic variations in DNA repair genes, radiosensitivity to cancer and susceptibility to acute tissue reactions in radiotherapy-treated cancer patients

Ionizing radiation is a well established carcinogen for human cells. At low doses, radiation exposure mainly results in generation of double strand breaks (DSBs). Radiation-related DSBs could be directly linked to the formation of chromosomal rearrangements as has been proven for radiation-induced thyroid tumors. Repair of DSBs presumably involves two main pathways, non-homologous end joining (NHEJ) and homologous recombination (HR). A number of known inherited syndromes, such as ataxia telangiectasia, ataxia-telangiectasia like-disorder, radiosensitive severe combined immunodeficiency, Nijmegen breakage syndrome, and LIG4 deficiency are associated with increased radiosensitivity and/or cancer risk. Many of them are caused by mutations in DNA repair genes. Recent studies also suggest that variations in the DNA repair capacity in the general population may influence cancer susceptibility. In this paper, we summarize the current status of DNA repair proteins as potential targets for radiation-induced cancer risk. We will focus on genetic alterations in genes involved in HR- and NHEJ-mediated repair of DSBs, which could influence predisposition to radiation-related cancer and thereby explain interindividual differences in radiosensitivity or radioresistance in a general population.