Detection of individual differences in radiation-induced apoptosis of peripheral blood lymphocytes in normal individuals, ataxia telangiectasia homozygotes and heterozygotes, and breast cancer patients after radiotherapy

Protective Effect of Epigallocatechin-3-Gallate in Hydrogen Peroxide-Induced Oxidative Damage in Chicken Lymphocytes

Epigallocatechin-3-gallate (EGCG) is one of the fundamental compounds in green tea. The present study was to evaluate the protective effect of EGCG in oxidative damage and apoptosis induced by hydrogen peroxide (H₂O₂) in chicken lymphocytes. Results showed that preincubation of lymphocytes with EGCG significantly decreased H₂O₂-reduced cell viability and apoptotic cells with DNA damage, restored the H₂O₂-dependent reduction in total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX), superoxide dismutase (SOD), glutathione (GSH), and glutathione disulfide (GSSG), and suppressed the increase in intracellular reactive oxygen species (ROS), nitric oxide (NO), nitric oxide synthesis (NOS), malondialdehyde (MDA), lipid peroxide (LPO), and protein carbonyl (Carbonyl). In addition, preincubation of the cells with EGCG increased mitochondrial membrane potential (MMP) and reduced calcium ion ([Ca²⁺]i) load. The protective effect of EGCG in oxidative damage in lymphocytes was accompanied by mRNA expression of SOD, Heme oxygenase-1 (HO-1), Catalase (CAT), GSH-PX, nuclear factor erythroid 2-related factor 2 (Nrf2), and thioredoxin-1 (Trx-1). As EGCG had been removed before lymphocytes were challenged with H₂O₂, the activation of genes such as Nrf2 and Trx-1 by preincubation with EGCG could be the main reason for EGCG to protect the cells from oxidative damage by H₂O_2. Since oxidative stress is an important mechanism of biological damage and is regarded as the reasons of several pathologies, the present findings may be helpful for the use of tea products to prevent oxidative stress and maintain healthy in both humans and animals.

Association of CD4+ Radiation-Induced Lymphocyte Apoptosis with Fibrosis and Telangiectasia after Radiotherapy in 272 Breast Cancer Patients with >10-Year Follow-up

PURPOSE

Radiation-induced lymphocyte apoptosis (RILA) has been suggested as a predictive assay for adverse late reactions after radiotherapy. Thus, low RILA values of T-lymphocyte subpopulations have been associated with increased risk for various endpoints at 2 to 3 years of follow-up. The purpose was to test if such associations persist for specific endpoints (subcutaneous fibrosis, telangiectasia) in breast cancer patients with at least 10 years of follow-up.Experimental Design: Two hundred and seventy-two female patients who had received breast-conserving therapy within the German ISE study were included (median follow-up: 11.6 years). Radiotherapy-induced side effects were scored according to the Late Effects in Normal Tissues-Subjective, Objective, Management, and Analytic (LENT-SOMA) classification system. RILA in the CD4⁺, CD8⁺, and natural killer (NK) subpopulations from peripheral blood was analyzed by flow cytometry. Multivariate predictive modeling was performed including relevant clinical risk factors.

RESULTS

Low CD4⁺ RILA was associated with increased risk for both fibrosis (P = 0.011) and telangiectasia (P < 0.001). For fibrosis, the association was stronger outside the surgical area (Fib_out; P = 0.004) than within (Fib_in; P = 0.17). Predictive multivariate modeling including clinical risk factors yielded OR of 3.48 (95% confidence interval, 1.84-6.58) for any fibrosis and 8.60 (2.71-27.3) for telangiectasia. Addition of CD4⁺ RILA to the clinical variables improved discrimination (c statistics) from 0.62 to 0.68 for any fibrosis, 0.62 to 0.66 for Fib_in, 0.61 to 0.69 for Fib_out, and from 0.65 to 0.76 for telangiectasia. CD8⁺ and NK RILA were not significantly associated with radiotherapy-related late reactions.

CONCLUSIONS

The results provide first evidence that low CD4⁺ RILA is associated with increased subcutaneous fibrosis and telangiectasia even after 10 years. This supports the potential usefulness for predicting individual clinical risk.

Monitoring of platelet function parameters and microRNA expression levels in patients with prostate cancer treated with volumetric modulated arc radiotherapy

Radiotherapy (RT) may result in platelet activation and thrombosis development. To the best of our knowledge, the potential effect of volumetric-modulated arc therapy (VMAT), a novel radiotherapy technique, on platelet function and microRNA (miRNA/miR) expression has not been previously investigated. The present study aimed to determine the effect of VMAT on the alterations in platelet function parameters and miRNA expression levels. A total of 25 patients with prostate cancer and 25 healthy subjects were included in the present study. Blood samples were collected from the patient group on the day prior to RT (pre-RT), the day RT was completed (post-RT day 0), and 40 days following the end of therapy (post-RT day 40). Platelet count, mean platelet volume (MPV) value, platelet aggregation, plasma P-selectin, thrombospondin-1, platelet factor 4, plasma miR-223 and miR-126 expression levels were measured. A significant decrease in platelet count in the post-RT day 0 group was measured in comparison with the pre-RT and the post-RT day 40 groups. Pre-RT MPV values were higher than those of the post-RT day 0 and the post-RT day 40 groups. No significant differences were observed in the levels of platelet activation markers or miR-223 and miR-126 expression levels between the RT groups. Although RT may result in a reduction in platelet and MPV counts, the results of the present study indicate that platelet activation markers are not affected by VMAT. Therefore, it is possible that no platelet activation occurs during VMAT, owing to the conformal dose distributions, improved target volume coverage and the sparing of normal tissues from undesired radiation.

A Serum Small Molecule Biosignature of Radiation Exposure from Total Body Irradiated Patients

The potential for radiological accidents and nuclear terrorism has increased the need for the development of new rapid biodosimetry methods. In addition, in a clinical setting the issue of an individual's radiosensitivity should be taken into consideration during radiotherapy. We utilized metabolomics and lipidomics to investigate changes of metabolites in serum samples following exposure to total body ionizing radiation in humans. Serum was collected prior to irradiation, at 3-8 h after a single dose of 1.25-2 Gy, and at 24 h with a total delivered dose of 2-3.75 Gy. Metabolomics revealed perturbations in glycerophosphocholine, phenylalanine, ubiquinone Q2, and oxalic acid. Alterations were observed in circulating levels of lipids from monoacylglycerol, triacylglycerol, phosphatidylcholine, and phosphatidylglycerol lipid classes. Polyunsaturated fatty acids were some of the most dysregulated lipids, with increased levels linked to proinflammatory processes. A targeted metabolomics approach for eicosanoids was also employed. The results showed a rapid response for proinflammatory eicosanoids, with a dampening of the signal at the later time point. Sex differences were observed in the markers from the untargeted approach but not the targeted method. The ability to identify and quantify small molecules in blood can therefore be utilized to monitor radiation exposure in human populations.

Active caspase-3 expression levels as bioindicator of individual radiosensitivity

Several molecules and events involved in cell response to radiation-induced damage have been investigated towards a personalized radiotherapy. Considering the importance of active caspase-3 in the proteolytic cascade that ensures radiation-induced apoptosis execution, this research was designed to evaluate the expression levels of this protein as a bioindicator of individual radiosensitivity. Peripheral blood samples of 10 healthy individuals were gamma-irradiated (cobalt-60 source) with 1, 2 and 4 Gy (control: non-irradiated samples), and active caspase-3 expression levels were measured in lymphocytes, by flow cytometry, ex vivo and after different times of in vitro incubation (24, 48 and 72 hours). Short-term incubation of 24 h was the most adequate condition to evidence correlations between dose radiation and active caspase-3 expression. For each radiation dose, it was observed a significant inter-individual variation in active caspase-3 expression intensity, suggesting that this parameter may be suitable for evidence individual radiosensitivity. The methodology presented and discussed in this work may help to predict healthy tissues response to radiation exposure toward the better patient outcome.

Apoptotic capacity and risk of squamous cell carcinoma of the head and neck

BACKGROUND

Tobacco smoke and alcohol drinking are the major risk factors for squamous cell carcinoma of the head and neck (SCCHN). Smoking and drinking cause DNA damage leading to apoptosis, and insufficient apoptotic capacity may favour development of cancer because of the dysfunction of removing damaged cells. In the present study, we investigated the association between camptothecin (CPT)-induced apoptotic capacity and risk of SCCHN in a North American population.

METHODS

In a case-control study of 708 SCCHN patients and 685 matched cancer-free controls, we measured apoptotic capacity in cultured peripheral blood lymphocytes in response to in vitro exposure to CPT by using the flow cytometry-based method.

RESULTS

We found that the mean level of apoptotic capacity in the cases (45.9 ± 23.3%) was significantly lower than that in the controls (49.0 ± 23.1%) (P = 0.002). When we used the median level of apoptotic capacity in the controls as the cutoff value for calculating adjusted odds ratios, subjects with a reduced apoptotic capacity had an increased risk (adjusted odds ratio = 1.42, 95% confidence interval = 1.13-1.78, P = 0.002), especially for those who were age ≥57 (1.73, 1.25-2.38, 0.0009), men (1.76, 1.36-2.27, <0.0001) and ever drinkers (1.67, 1.27-2.21, 0.0003), and these variables significantly interacted with apoptotic capacity (Pinteraction = 0.015, 0.005 and 0.009, respectively). A further fitted prediction model suggested that the inclusion of apoptotic capacity significantly improved in the prediction of SCCHN risk.

CONCLUSION

Individuals with a reduced CPT-induced apoptotic capacity may be at an increased risk of developing SCCHN, and apoptotic capacity may be a biomarker for susceptibility to SCCHN.

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.

Prediction of radiation-induced toxicity by in vitro radiosensitivity of lymphocytes in prostate cancer patients

Aim: To identify predictive assays for radiation-induced toxicity in prostate cancer patients. Patients & methods: Patients have been surveyed prospectively before and up to 16 months after radiotherapy using a validated questionnaire. Subgroups of 25 patients with minor and larger score changes, respectively, were selected for γ-H2AX, G2 and Annexin V assays. Results: A significantly higher spontaneous chromatid aberration yield (HR: 1.46 [95% CI: 1.02–2.09]; p = 0.04), higher levels of early apoptotic (HR: 1.12 [95% CI: 1.01–1.24]; p = 0.04) and late apoptotic and necrotic (HR: 1.10 [95% CI: 0.99–1.23]; p = 0.08) lymphocytes 24 h post-irradiation were found in patients with a bowel bother score decrease greater than 20 points more than 1 year after treatment. Conclusion: Chromatid aberration and apoptosis/necrosis assays appear to be suitable for the prediction of radiation-induced toxicity.

Analysis of Residual DSBs in Ataxia-Telangiectasia Lymphoblast Cells Initiating Apoptosis

In order to examine the relationship between accumulation of residual DNA double-strand breaks (DSBs) and cell death, we have used a control and an ATM (Ataxia-Telangiectasia Mutated) defective cell line, as Ataxia-Telangiectasia (AT) cells tend to accumulate residual DSBs at long times after damage infliction. After irradiation, AT cells showed checkpoint impairment and a fraction of cells displayed an abnormal centrosome number and tetraploid DNA content, and this fraction increased along with apoptosis rates. At all times analyzed, AT cells displayed a significantly higher rate of radiation-induced apoptosis than normal cells. Besides apoptosis, 70-85% of the AT viable cells (TUNEL-negative) carried ≥ 10 γH2AX foci/cell, while only 12-27% of normal cells did. The fraction of AT and normal cells undergoing early and late apoptosis were isolated by flow cytometry and residual DSBs were concretely scored in these populations. Half of the γH2AX-positive AT cells undergoing early apoptosis carried ≥ 10 γH2AX foci/cell and this fraction increased to 75% in late apoptosis. The results suggest that retention of DNA damage-induced γH2AX foci is an indicative of lethal DNA damage, as cells undergoing apoptosis are those accumulating more DSBs. Scoring of residual γH2AX foci might function as a predictive tool to assess radiation-induced apoptosis.

Apoptosis for prediction of radiotherapy late toxicity: lymphocyte subset sensitivity and potential effect of TP53 Arg72Pro polymorphism

We tested apoptosis levels in in vitro irradiated T-lymphocytes from breast cancer (BC) patients with radiotherapy-induced late effects. Previous results reported in the literature were revised. We also examined the effect of TP53 Arg72Pro polymorphism on irradiation-induced apoptosis (IA). Twenty BC patients, ten with fibrosis and/or telangiectasias and ten matched controls with no late reactions, were selected from those receiving radiotherapy between 1993 and 2007. All patients were followed-up at least 6 years after radiotherapy. Using the combination of both CD3 and CD8 antibodies the in vitro IA was measured in CD3, CD8 and CD4 T-lymphocytes, and CD8 natural killer lymphocytes (CD8 NK) by flow cytometry. The TP53 Arg72Pro genotype was determined by sequencing. Patients with late radiotherapy toxicity showed less IA for all T-lymphocytes except for the CD8 NK. CD8 NK showed the highest spontaneous apoptosis and the lowest IA. IA in patients with toxicity appears to be lower than the control patients only in TP53 Arg/Arg patients (P = 0.077). This difference was not present in patients carrying at least one Pro allele (P = 0.8266). Our data indicate that late side effects induced by radiotherapy of BC are associated to low levels of IA. CD8 NK cells have a different response to in vitro irradiation compared to CD8 T-lymphocytes. It would be advisable to distinguish the CD8 NK lymphocytes from the pool of CD8+ lymphocytes in IA assays using CD8+ cells. Our data suggest that the 72Pro TP53 allele may influence the IA of patients with radiotherapy toxicity.

Prediction of normal tissue toxicity as part of the individualized treatment with radiotherapy in oncology patients

Normal tissue toxicity caused by radiotherapy conditions the success of the treatment and the quality of life of patients. Radiotherapy is combined with surgery in both the preoperative or postoperative setting for the treatment of most localized solid tumour types. Furthermore, radical radiotherapy is an alternative to surgery in several tumour locations. The possibility of predicting such radiation-induced toxicity would make possible a better treatment schedule for the individual patient. Radiation-induced toxicity is, at least in part, genetically determined. From decades, several predictive tests have been proposed to know the individual sensitivity of patients to the radiotherapy schedules. Among them, initial DNA damage, radiation-induced apoptosis, gene expression profiles, and gene polymorphisms have been proposed. We report here an overview of the main studies regarding to this field. Radiation-induced apoptosis in peripheral blood lymphocytes seem to be the most promising assay tested in prospective clinical trials, although they have to be validated in large clinical studies. Other promising assays, as those related with single nucleotide polymorphisms, need to be validated as well.

Combined low initial DNA damage and high radiation-induced apoptosis confers clinical resistance to long-term toxicity in breast cancer patients treated with high-dose radiotherapy

Background

Either higher levels of initial DNA damage or lower levels of radiation-induced apoptosis in peripheral blood lymphocytes have been associated to increased risk for develop late radiation-induced toxicity. It has been recently published that these two predictive tests are inversely related. The aim of the present study was to investigate the combined role of both tests in relation to clinical radiation-induced toxicity in a set of breast cancer patients treated with high dose hyperfractionated radical radiotherapy.

Methods

Peripheral blood lymphocytes were taken from 26 consecutive patients with locally advanced breast carcinoma treated with high-dose hyperfractioned radical radiotherapy. Acute and late cutaneous and subcutaneous toxicity was evaluated using the Radiation Therapy Oncology Group morbidity scoring schema. The mean follow-up of survivors (n = 13) was 197.23 months. Radiosensitivity of lymphocytes was quantified as the initial number of DNA double-strand breaks induced per Gy and per DNA unit (200 Mbp). Radiation-induced apoptosis (RIA) at 1, 2 and 8 Gy was measured by flow cytometry using annexin V/propidium iodide.

Results

Mean DSB/Gy/DNA unit obtained was 1.70 ± 0.83 (range 0.63-4.08; median, 1.46). Radiation-induced apoptosis increased with radiation dose (median 12.36, 17.79 and 24.83 for 1, 2, and 8 Gy respectively). We observed that those "expected resistant patients" (DSB values lower than 1.78 DSB/Gy per 200 Mbp and RIA values over 9.58, 14.40 or 24.83 for 1, 2 and 8 Gy respectively) were at low risk of suffer severe subcutaneous late toxicity (HR 0.223, 95%CI 0.073-0.678, P = 0.008; HR 0.206, 95%CI 0.063-0.677, P = 0.009; HR 0.239, 95%CI 0.062-0.929, P = 0.039, for RIA at 1, 2 and 8 Gy respectively) in multivariate analysis.

Conclusions

A radiation-resistant profile is proposed, where those patients who presented lower levels of initial DNA damage and higher levels of radiation induced apoptosis were at low risk of suffer severe subcutaneous late toxicity after clinical treatment at high radiation doses in our series. However, due to the small sample size, other prospective studies with higher number of patients are needed to validate these results.

Radiation induced apoptosis and initial DNA damage are inversely related in locally advanced breast cancer patients

Background

DNA-damage assays, quantifying the initial number of DNA double-strand breaks induced by radiation, have been proposed as a predictive test for radiation-induced toxicity. Determination of radiation-induced apoptosis in peripheral blood lymphocytes by flow cytometry analysis has also been proposed as an approach for predicting normal tissue responses following radiotherapy. The aim of the present study was to explore the association between initial DNA damage, estimated by the number of double-strand breaks induced by a given radiation dose, and the radio-induced apoptosis rates observed.

Methods

Peripheral blood lymphocytes were taken from 26 consecutive patients with locally advanced breast carcinoma. Radiosensitivity of lymphocytes was quantified as the initial number of DNA double-strand breaks induced per Gy and per DNA unit (200 Mbp). Radio-induced apoptosis at 1, 2 and 8 Gy was measured by flow cytometry using annexin V/propidium iodide.

Results

Radiation-induced apoptosis increased in order to radiation dose and data fitted to a semi logarithmic mathematical model. A positive correlation was found among radio-induced apoptosis values at different radiation doses: 1, 2 and 8 Gy (p < 0.0001 in all cases). Mean DSB/Gy/DNA unit obtained was 1.70 ± 0.83 (range 0.63-4.08; median, 1.46). A statistically significant inverse correlation was found between initial damage to DNA and radio-induced apoptosis at 1 Gy (p = 0.034). A trend toward 2 Gy (p = 0.057) and 8 Gy (p = 0.067) was observed after 24 hours of incubation.

Conclusions

An inverse association was observed for the first time between these variables, both considered as predictive factors to radiation toxicity.

Prediction of clinical toxicity in locally advanced head and neck cancer patients by radio-induced apoptosis in peripheral blood lymphocytes (PBLs)

Head and neck cancer is treated mainly by surgery and radiotherapy. Normal tissue toxicity due to x-ray exposure is a limiting factor for treatment success. Many efforts have been employed to develop predictive tests applied to clinical practice. Determination of lymphocyte radio-sensitivity by radio-induced apoptosis arises as a possible method to predict tissue toxicity due to radiotherapy. The aim of the present study was to analyze radio-induced apoptosis of peripheral blood lymphocytes in head and neck cancer patients and to explore their role in predicting radiation induced toxicity. Seventy nine consecutive patients suffering from head and neck cancer, diagnosed and treated in our institution, were included in the study. Toxicity was evaluated using the Radiation Therapy Oncology Group scale. Peripheral blood lymphocytes were isolated and irradiated at 0, 1, 2 and 8 Gy during 24 hours. Apoptosis was measured by flow cytometry using annexin V/propidium iodide. Lymphocytes were marked with CD45 APC-conjugated monoclonal antibody. Radiation-induced apoptosis increased in order to radiation dose and fitted to a semi logarithmic model defined by two constants: α and β. α, as the origin of the curve in the Y axis determining the percentage of spontaneous cell death, and β, as the slope of the curve determining the percentage of cell death induced at a determined radiation dose, were obtained. β value was statistically associated to normal tissue toxicity in terms of severe xerostomia, as higher levels of apoptosis were observed in patients with low toxicity (p = 0.035; Exp(B) 0.224, I.C.95% (0.060-0.904)). These data agree with our previous results and suggest that it is possible to estimate the radiosensitivity of peripheral blood lymphocytes from patients determining the radiation induced apoptosis with annexin V/propidium iodide staining. β values observed define an individual radiosensitivity profile that could predict late toxicity due to radiotherapy in locally advanced head and neck cancer patients. Anyhow, prospective studies with different cancer types and higher number of patients are needed to validate these results.

Prediction of clinical toxicity in localized cervical carcinoma by radio-induced apoptosis study in peripheral blood lymphocytes (PBLs)

Background

Cervical cancer is treated mainly by surgery and radiotherapy. Toxicity due to radiation is a limiting factor for treatment success. Determination of lymphocyte radiosensitivity by radio-induced apoptosis arises as a possible method for predictive test development. The aim of this study was to analyze radio-induced apoptosis of peripheral blood lymphocytes.

Methods

Ninety four consecutive patients suffering from cervical carcinoma, diagnosed and treated in our institution, and four healthy controls were included in the study. Toxicity was evaluated using the Lent-Soma scale. Peripheral blood lymphocytes were isolated and irradiated at 0, 1, 2 and 8 Gy during 24, 48 and 72 hours. Apoptosis was measured by flow cytometry using annexin V/propidium iodide to determine early and late apoptosis. Lymphocytes were marked with CD45 APC-conjugated monoclonal antibody.

Results

Radiation-induced apoptosis (RIA) increased with radiation dose and time of incubation. Data strongly fitted to a semi logarithmic model as follows: RIA = βln(Gy) + α. This mathematical model was defined by two constants: α, is the origin of the curve in the Y axis and determines the percentage of spontaneous cell death and β, is the slope of the curve and determines the percentage of cell death induced at a determined radiation dose (β = ΔRIA/Δln(Gy)). Higher β values (increased rate of RIA at given radiation doses) were observed in patients with low sexual toxicity (Exp(B) = 0.83, C.I. 95% (0.73-0.95), p = 0.007; Exp(B) = 0.88, C.I. 95% (0.82-0.94), p = 0.001; Exp(B) = 0.93, C.I. 95% (0.88-0.99), p = 0.026 for 24, 48 and 72 hours respectively). This relation was also found with rectal (Exp(B) = 0.89, C.I. 95% (0.81-0.98), p = 0.026; Exp(B) = 0.95, C.I. 95% (0.91-0.98), p = 0.013 for 48 and 72 hours respectively) and urinary (Exp(B) = 0.83, C.I. 95% (0.71-0.97), p = 0.021 for 24 hours) toxicity.

Conclusion

Radiation induced apoptosis at different time points and radiation doses fitted to a semi logarithmic model defined by a mathematical equation that gives an individual value of radiosensitivity and could predict late toxicity due to radiotherapy. Other prospective studies with higher number of patients are needed to validate these results.

gamma-H2AX foci formation in peripheral blood lymphocytes of tumor patients after local radiotherapy to different sites of the body: Dependence on the dose-distribution, irradiated site and time from start of treatment

PURPOSE

To evaluate the relationship between an estimated integral total body radiation dose delivered and phosphorylated histone H2AX protein (gamma-H2AX) foci formation in peripheral blood lymphocytes of cancer patients.

MATERIAL AND METHODS

gamma-H2AX formation was quantified as the mean number of foci per lymphocyte (N(meanH2AX)) and the percentage of lymphocytes with > or =n foci. The integrated total body radiation dose was estimated from the dose volume histogram of patient's body corrected for the proportion of the body scanned by computed tomography for 3D treatment planning.

RESULTS

There was a strong linear correlation between the mean number of gamma-H2AX foci per lymphocyte in the peripheral blood sample and integrated total body radiation dose (r = 0.83, p < 0.0001). The slope of the relationship was dependent on the site of body irradiated. In comparison to chest irradiation with a slope of 8.7 +/- 0.8 foci Gy(-1), the slopes for brain, upper leg and pelvic sites were significantly shallower by -4.7, -4.3, and -3.8 Gy(-1), respectively (p < 0.0001), while the slope for upper abdomen irradiation was significantly larger by 9.1 +/- 2.6 Gy(-1) (p = 0.0007). There was a slight time effect since the start of radiotherapy on the slopes of the in vivo dose responses leading to shallower slopes (-1.5 +/- 0.7 Gy(-1), p = 0.03) later (> or =10 day) during radiotherapy. After in vitro irradiation, lymphocytes showed 10.41 +/- 0.12 foci per Gy with no evidence of inter-individual heterogeneity.

CONCLUSIONS

gamma-H2AX measurements in peripheral lymphocytes after local radiotherapy allow the estimation of the applied integral body dose. The site and time dependence have to be considered.

Radiation-induced lymphocyte apoptosis to predict radiation therapy late toxicity in prostate cancer patients

PURPOSE

To examine a potential correlation between the in vitro apoptotic response of lymphocytes to radiation and the risk of developing late gastrointestinal (GI)/genitourinary (GU) toxicity from radiotherapy for prostate cancer.

METHODS AND MATERIALS

Prostate cancer patients formerly enrolled in a randomized study were tested for radiosensitivity by using a radiation-induced lymphocyte apoptosis assay. Apoptosis was measured using flow cytometry-based Annexin-FITC/7AAD and DiOC(6)/7AAD assays in subpopulations of lymphocytes (total lymphocytes, CD4+, CD8+ and CD4-/CD8-) after exposure to an in vitro dose of 0, 2, 4, or 8 Gy.

RESULTS

Patients with late toxicity after radiotherapy showed lower lymphocyte apoptotic responses to 8 Gy than patients who had not developed late toxicity (p = 0.01). All patients with late toxicity had apoptosis levels that were at or below the group mean. The negative predictive value in both apoptosis assays ranged from 95% to 100%, with sensitivity values of 83% to 100%. Apoptosis at lower dose points and in lymphocyte subpopulations had a weaker correlation with the occurrence of late toxicity.

CONCLUSIONS

Lymphocyte apoptosis after 8 Gy of radiation has the potential to predict which patients will be spared late toxicity after radiation therapy. Further research should be performed to identify the specific subset of lymphocytes that correlates with late toxicity, followed by a corresponding prospective study.

Evidence for significant heritability of apoptotic and cell cycle responses to ionising radiation

Genetic factors are likely to affect individual cancer risk, but few quantitative estimates of heritability are available. Public health radiation protection policies do not in general take this potentially important source of variation in risk into account. Two surrogate cellular assays that relate to cancer susceptibility have been developed to gain an insight into the role of genetics in determining individual variation in radiosensitivity. These flow cytometric assays for apoptosis induction and cell cycle delay following radiation are sufficiently sensitive to distinguish lymphocytes from a healthy donor population from those of a sample of obligate carriers of ATM mutations (P = 0.01 and P = 0.02, respectively). Analysis of 54 unselected twin pairs (38 dizygotic, 16 monozygotic) indicated much greater intrapair correlation in response in monozygotic than in dizygotic pairs. Structural equation modelling indicated that models including unique environmental factors only fitted the data less well than those incorporating two or more of additive genetic factors, common environmental factors and unique environmental factors. A model incorporating additive genetic factors and unique environmental factors yielded estimates of heritability for the two traits of 68% (95% CI 40-82%, cell cycle) and 59% (95% CI 22-79%, apoptosis). Thus, these data suggest that genetic factors contribute significantly to human variation in these two measures of radiosensitivity that relate to cancer susceptibility.

Individual radiosensitivity and its relevance to health physics

Radiation protection regulations have been established to reduce exposure of individuals to acceptable safe levels. These limits assume that people have similar responses to ionizing radiation and that there is no variation in individual radiation risk. The purpose of this research was to determine if apoptosis in lymphocytes can be used to assess individual sensitivity to ionizing radiation. Blood samples were taken from 54 males ranging in age from 19-85 years. Apoptosis was measured using modified flow cytometry based Annexin-FITC/7AAD and DiOC(6)/7AAD assays in different populations of lymphocytes (total mixed lymphocyte population, subset CD4+ or CD8+ lymphocytes) after exposure to in vitro doses of 0, 2, 4 or 8Gy (dose rate 0.1Gy/min). The variation in individual responses to radiation was large. The variation was the largest in the CD4+ lymphocyte sub-population. Radiation-induced apoptosis decreased with age of donor demonstrating that as people age their lymphocytes may become relatively more resistant to radiation. This research shows that individuals have marked differences in their sensitivity to radiation and protection policies may someday need to be tailored for some individuals.

Radiation-induced DNA damage as a predictor of long-term toxicity in locally advanced breast cancer patients treated with high-dose hyperfractionated radical radiotherapy

This 14-year-long study makes a novel contribution to the debate on the relationship between the in vitro radiosensitivity of peripheral blood lymphocytes and normal tissue reactions after radiation therapy. The aims were (1) to prospectively assess the degree and time of onset of skin side effects in 40 prospectively recruited consecutive patients with locally advanced breast cancer treated with a hyperfractionated dose-escalation radiotherapy schedule and (2) to assess whether initial radiation-induced DNA damage in peripheral blood lymphocytes of these patients could be used to determine their likelihood of suffering severe late damage to normal tissue. Initial radiation-induced DNA double-strand breaks (DSBs) were assessed in peripheral blood lymphocytes of these patients by pulsed-field electrophoresis. Acute and late cutaneous and subcutaneous toxicity was evaluated using the Radiation Therapy Oncology Group morbidity score. A wide interindividual variation was observed in toxicity grades and in radiation-induced DNA DSBs in peripheral blood lymphocytes (mean 1.61 +/- 0.76 DSBs/Gy per 200 MBp, range 0.63- 4.08), which were not correlated. Multivariate analysis showed a correlation (P < 0.008) between late toxicity and higher prescribed protocol dose (81.6 Gy). Analysis of the 29 patients referred to 81.6 Gy revealed significantly (P < 0.031) more frequent late subcutaneous toxicity in those with intrinsic sensitivity to radiation-induced DNA DSBs of >1.69 DSBs/Gy per DNA unit. Our demonstration of a relationship between the sensitivity of in vitro-irradiated peripheral blood lymphocytes and the risk of developing late toxic effects opens up the possibility of predicting normal tissue response to radiation in individual patients, at least in high-dose non-conventional radiation therapy regimens.

Chromosomal Instability and Delayed Apoptosis in Long-Term T-Lymphocyte Cultures Irradiated with Carbon Ions and X Rays

In this study, we examined genomic instability induced by 250 kV X rays and 100 MeV/nucleon carbon ions in long-term lymphocyte cultures from two healthy donors. Two biological end points, delayed apoptosis and chromosomal instability, were studied in descendants of cells irradiated with three different doses of the particular radiation up to 22 population doublings. The delayed apoptosis showed no clear dependence on radiation dose, culture time or radiation quality. A persistent significant increase in the rate of apoptosis up to 36 days after X irradiation was observed for a dose of 4 Gy in donor 1 only. For both donors and radiations, de novo aberration yields were significantly increased in comparison to control values up to day 36. For both radiations, chromosome-type aberrations were seen more frequently than chromatid-type aberrations in both donors up to 22 days postirradiation. In both donors, carbon ions were more effective than X rays with respect to the induction of chromosome instability. A dose of 0.25 Gy of carbon ions corresponding to 1.4 ion traversals per cell nucleus was effective in the induction of instability in our cell system.

Analysis of gene expression using gene sets discriminates cancer patients with and without late radiation toxicity

BACKGROUND

Radiation is an effective anti-cancer therapy but leads to severe late radiation toxicity in 5%-10% of patients. Assuming that genetic susceptibility impacts this risk, we hypothesized that the cellular response of normal tissue to X-rays could discriminate patients with and without late radiation toxicity.

METHODS AND FINDINGS

Prostate carcinoma patients without evidence of cancer 2 y after curative radiotherapy were recruited in the study. Blood samples of 21 patients with severe late complications from radiation and 17 patients without symptoms were collected. Stimulated peripheral lymphocytes were mock-irradiated or irradiated with 2-Gy X-rays. The 24-h radiation response was analyzed by gene expression profiling and used for classification. Classification was performed either on the expression of separate genes or, to augment the classification power, on gene sets consisting of genes grouped together based on function or cellular colocalization.X-ray irradiation altered the expression of radio-responsive genes in both groups. This response was variable across individuals, and the expression of the most significant radio-responsive genes was unlinked to radiation toxicity. The classifier based on the radiation response of separate genes correctly classified 63% of the patients. The classifier based on affected gene sets improved correct classification to 86%, although on the individual level only 21/38 (55%) patients were classified with high certainty. The majority of the discriminative genes and gene sets belonged to the ubiquitin, apoptosis, and stress signaling networks. The apoptotic response appeared more pronounced in patients that did not develop toxicity. In an independent set of 12 patients, the toxicity status of eight was predicted correctly by the gene set classifier.

CONCLUSIONS

Gene expression profiling succeeded to some extent in discriminating groups of patients with and without severe late radiotherapy toxicity. Moreover, the discriminative power was enhanced by assessment of functionally or structurally related gene sets. While prediction of individual response requires improvement, this study is a step forward in predicting susceptibility to late radiation toxicity.

Inter-relation of apoptosis and DNA double-strand breaks in patients with multiple primary cancers

Since the development of multiple primary cancers in an individual is considered an unlikely event, it is suspected that a defect in DNA repair or apoptosis is the underlying cause for some of these patients. Therefore, this study was based on the hypothesis that such patients have increased remaining DNA double-strand breaks (DSBs) and reduced levels of apoptosis after in vitro irradiation. To investigate these mechanisms in cancer patients, 19 with multiple primary cancers were selected out of 25 121 cancer patients. For inclusion in this study, patients had to present with first malignancy at an early age, have a positive family history of cancer and no risk factors. The exclusion criteria were recurrence of cancer or metastasis, haematological tumours and tumours possibly connected to a patient risk factor such as smoking or drinking. Their peripheral blood lymphocytes were tested for proper repair of DNA DSBs and apoptosis after in vitro irradiation. DSBs were measured using constant field gel electrophoresis at 0, 8 and 24 h after irradiation. Apoptotic rates were determined at 24, 48 and 72 h after irradiation using the TUNEL assay. We found that patients' lymphocytes had significantly more initial DNA DSBs compared with controls, but there was no difference in the number of remaining DNA DSBs. Apoptotic rates of lymphocytes were only slightly lower in patients than in controls. These findings show that there are limited differences between patients with multiple cancers and healthy individuals. However, we found a trend towards an inverse correlation between remaining DNA DSBs and apoptotic rates in patients' lymphocytes. This is indicative of DNA DSBs persisting in patients' cells, presumably leading to a higher level of stable chromosomal aberrations that may contribute to tumour formation.

Apoptose radio-induite: une nouvelle approche par microspectroscopie infrarouge

Purpose: to characterize radiation-induced apoptosis in human cells using Fourier transform infrared microspectroscopy (FT-IRM) as a new analytical tool. Material and methods: Normal human circulating lymphocytes were given a γ ray dose of 6 Gy, or treated with t-butyl hydroperoxide (t-BuOH). HaCaT keratinocytes were given a dose of 20 Gy. Cells were deposited on ZnS windows for infrared spectral acquisition 2 days and 2 h after irradiation and 2 h after t-BuOH treatment. Apoptosis was simultaneously assessed by flow cytometry analysis of cells displaying annexin-V-positive staining. Results. The flow cytometry study showed that about 90% of sham and irradiated cells were annexin-V negative 2 h after irradiation. Two days after irradiation, 68% of lymphocytes and 76% of HaCaT cells were apoptotic, as well as 43% of lymphocytes treated with t-BuOH. In infrared spectra of these apoptotic cells, qualitative and quantitative changes were observed. In the 960–1245 and 1690–1720 cm–1 ranges, mainly attributed to nucleic acids, changes corresponding to conformational changes in DNA were associated with a decrease in the amount of detectable DNA. Conformational changes were also observed in secondary protein structure, in particular an increase in the amount of β structures. These DNA and protein changes were associated with an increase in the detectable amount of lipids in apoptotic HaCaT cells only. Two hours after irradiation, depending on the dose and (or) the cell type, qualitative and quantitative changes were observed in the IR spectra in the amide I and amide II bands, mainly attributed to proteins. These changes were associated with a significant decrease in the 1700–1750 cm–1 range, mainly attributed to the –C=O ester groups of DNA and phospholipids, in the irradiated HaCaT cells only. Conclusion: Our results are in agreement with biochemical published data on radiation-induced apoptosis, and show that DNA is the first cellular target of radiation-induced apoptosis, which, however, also requires conformational changes and synthesis of cell proteins. They also demonstrate that FT-IRM may be useful for assessing the early radiation damage at the molecular level in human cells.Key words: apoptosis, Fourier transform infrared microspectroscopy, γ irradiation, human lymphocytes, HaCaT keratinocytes.

Lymphocyte radiosensitivity correlated with pelvic radiotherapy morbidity

PURPOSE

To test the hypothesis that, before treatment, prostate cancer patients who demonstrate a high yield of ex vivo radiation-induced micronucleus (MN) in G(0) lymphocytes represent a patient population with a greater-than-average risk of developing radiotherapy (RT)-related morbidity.

METHODS AND MATERIALS

We prospectively conducted the cytokinesis-block MN assay of peripheral blood lymphocytes (PBLs) in 38 prostate cancer patients. Before the initiation of RT, PBLs from each patient were irradiated (1-4 Gy). The mean patient age +/- SEM was 68.7 +/- 1.0 years. The clinical stage was T1 in 17, T2 in 15, and T3 in 6. The preoperative prostate-specific antigen level was < or =4 ng/mL in 5, 4-10 ng/mL in 18, and >10 ng/mL in 15. All patients underwent standardized pelvic external beam radiotherapy (range 41.4-50.4 Gy) and boost (range 16-26 Gy). The mean follow-up +/- SEM was 32.8 +/- 4.6 months. At the end of follow-up, a radiation oncologist scored the GI or GU morbidity according to the Radiation Therapy Oncology Group criteria without knowledge of the MN data.

RESULTS

We found that between the average reactors (n = 25; i.e., patients who had Grade 1 or less RT-related morbidity) and over reactors (n = 13; i.e., patients who developed Grade 2 or greater RT-related morbidity), the differences in the ex vivo radiation dose-response relationship of MN yield in PBLs were highly significant, especially at doses of > or =2 Gy. Also, the development of RT-related morbidity correlated with the radiation dose-response relationship of MN yield in PBLs before treatment, but did not correlate with any of the patients' clinical variables.

CONCLUSION

Our findings suggest that the pre-RT ex vivo radiation dose-response relationship of MN yield in PBLs may be a significant predictive factor for the development of GI or GU morbidity in prostate cancer patients after pelvic RT.

Infrared microspectroscopic characteristics of radiation-induced apoptosis in human lymphocytes

Infrared microspectroscopic characterization of radiation-induced apoptosis was used as a new analytical tool to study the kinetics of apoptosis in human peripheral blood lymphocytes at the molecular level. This vibrational technique, which has already been used to investigate biomolecules in normal and tumor cells, allows the simultaneous detection of the biochemical changes in the various subcellular compartments. Normal circulating lymphocytes from five healthy human donors were given a single dose of 6 Gy ((60)Co) and deposited on ZnS windows for infrared spectral acquisition 1, 2 and 4 days after irradiation. Apoptosis was assessed simultaneously by flow cytometry analysis of lymphocytes displaying annexin V-positive staining, and by detection of the DNA laddering that is characteristic of apoptosis. The flow cytometry study showed that about 80% of sham-irradiated lymphocytes were annexin V(neg)/PI(neg) at 1, 2 and 4 days. One day after irradiation, 46% of irradiated lymphocytes were annexin V(neg)/PI(neg), 48% were annexin V(pos)/PI(neg), 5% were annexin V(pos)/PI(pos), and 1% were annexin V(neg)/PI(pos). These mean percentages were respectively 31, 59, 9 and 1 at day 2 and 23, 36, 30, and 11 at day 4. Irradiated lymphocytes presented a DNA laddering pattern characteristic of apoptosis from day 1 after irradiation. In the infrared spectra of irradiated lymphocytes, qualitative and quantitative changes were observed from days 1 and 2, respectively. In the range of 960-1245 cm(-1) mainly attributed to nucleic acids, changes corresponding to conformational changes in DNA were associated with a decrease in the amount of detectable DNA. Conformational changes were also observed in secondary protein structures, in particular an increase in the amount of beta structures. These DNA and protein changes were associated with an increase in the detectable amount of lipids at day 4 after irradiation. These results showed that DNA is probably the first cellular target of radiation-induced apoptosis, which, however, also requires conformational changes and synthesis of cell proteins. Our results are in agreement with biochemical and morphological data on radiation-induced apoptosis of normal human circulating lymphocytes, and they demonstrate that infrared microspectroscopy may be useful for assessing the process of apoptosis at the molecular level.

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

PURPOSE

To investigate the relationship between late tissue response after radiotherapy, cellular sensitivity and DNA repair capacity measured in dermal fibroblasts and chromosomal aberrations measured in lymphocytes. The study was in particular designed to compare cellular parameters of patients with maximum differences in late tissue reactions.

MATERIALS AND METHODS

The study was performed with 16 pair-wise matched head and neck cancer patients 2-7 years after curative therapy exhibiting maximum differences (grade 1 vs. grade 3) in late normal tissue reactions. Clinical endpoints were fibrosis, telangiectasia, mucositis and xerostomia using the radiation therapy oncology group score. Patients with grade 3 reactions were tested for mutations in ataxia telangiectasia (AT), Nijmegen Breakage Syndrome (NBS), MRE11, RAD50 and DNA ligase IV genes by means of polymerase chain reaction-single-strand conformation polymorphism and sequencing analysis. Skin fibroblasts obtained from biopsies were used to determine the cellular sensitivity by colony formation and the induction and repair of DNA double-strand breaks (dsb) using constant-field gel electrophoresis. Lymphocytes were taken to measure chromosomal damage either in metaphase using conventional chromosome analysis or in G(0) using premature chromosome condensation (PCC)-technique.

RESULTS

Patients with extreme late reactions (grade 3) showed no evidence for an AT, NBS, MRE11 or RAD50 mutation. Studies with fibroblasts revealed that extreme late reactions were associated neither with a pronounced cellular radiosensitivity nor with a difference in dsb repair capacity. In contrast, there was a significant difference in chromosomal damage measured in lymphocytes. After in vitro irradiation with 6Gy, lymphocytes taken from overreacting patients showed on average a significantly higher number of lethal aberrations than lymphocytes isolated from patients with mild reactions (7.2+/-0.8 vs. 5.0+/-0.3). Similar differences were found for PCC fragments.

CONCLUSION

This study suggests that lymphocytes are more promising than fibroblasts to predict patient's normal tissue response after radiotherapy.

The generation and characterization of a radiation-resistant model system to study radioresistance in human breast cancer cells

To systematically study the selection of radioresistant cells in clinically advanced breast cancer, a model system was generated by treating MDA-MB231 breast cancer cells with fractionated gamma radiation. A clonogenic assay of the surviving cell populations showed that 2-6 Gy per fraction resulted in a rapid selection of radioresistant populations, within three to five fractions. Irradiation with additional fractions after this initial increase did not increase the radioresistance of the surviving population significantly. Doses of 0.5 and 8 Gy per fraction were not effective in selecting radioresistant cells. To further determine the cause of the changes in radiosensitivity, 15 clones were isolated from the cell populations treated with 40 or 60 Gy with 2 or 4 Gy per fraction, respectively, and were analyzed for radiosensitivity. The average D(10) for these clones was 6.75 +/- 0.36 Gy, which was higher than that for the parental cell population (D(10) = 6.0 +/- 0.2 Gy). The operation of cell cycle checkpoints and the doubling time were similar for both the nonirradiated parental population and the isolated radioresistant subclones. In contrast, a decrease in the apoptotic potential was correlated (r = 0.7, P < 0.01) with increased survival after irradiation, suggesting that apoptosis is an important factor in determining radioresistance under our experimental conditions. We also isolated several subclones from the nonirradiated parental cell population and analyzed them to determine their radiosensitivity after fractionated irradiation. Ten fractions of 4 Gy (40 Gy in total) did not result in a significant increase in the radioresistance of these subclones compared to the irradiated cell populations. The possible mechanisms of the increased radioresistance after fractionated irradiation are discussed.

Differential rates of cytokine production and apoptosis in venipuncture and finger-stab derived blood cultures

The collection of finger-stab (FS) blood is a convenient and non-invasive method of rapidly acquiring human blood and is becoming increasingly popular for use in human biomonitoring studies. This study compared whole blood (WB) and peripheral blood mononuclear cell (PBMC) cultures derived from venipuncture (VP) and FS blood, to determine whether they respond similarly under culture conditions. The rates of spontaneous- and radiation-induced apoptosis and pro-inflammatory cytokine production were monitored over 72 h in each of four culture conditions. In non-irradiated WB cultures, the spontaneous rate of apoptosis was significantly lower in cultures from FS-derived blood than from VP-derived blood. However, FS- and VP-derived cultures responded similarly to radiation-induced apoptosis. PBMC cultures, regardless of the source, were the most responsive to radiation. When the levels of pro-inflammatory cytokines were measured, a significant time-dependent increase in TNF-alpha, IL-6 and IL-1beta production was observed in FS-derived cultures, but not in VP-derived cultures. While VP and FS blood cultures were found to respond similarly to radiation-induced apoptosis, there was a significant difference in the rate of spontaneous apoptosis in non-irradiated WB cultures and in the in situ production of pro-inflammatory cytokines between VP- and FS-derived blood cultures.

Radiation-induced bystander effects: past history and future directions

There has been a recent upsurge of interest in the phenomenon now known as radiation-induced bystander effects. This is largely due to the increased awareness of the contribution of indirect and delayed effects, such as genomic instability, to cellular outcomes after low-dose exposures. It is also due to the availability of tools such as the microbeam and advanced cell culture systems and to the ability to study end points such as gene or protein expression at low doses which were previously difficult to study. This review looks at the history of bystander effects in the earlier literature, in which the clastogenic effect of plasma from irradiated patients was well known. The effect was known to persist for several years and to cause transgenerational effects, making it similar to what we now call genomic instability. The review then examines the current data and controversies which are now beginning to resolve the questions concerning the mechanisms underlying the induction and transmission of both bystander effects and genomic instability. Finally, the possible impact of data concerning radiation-induced bystander effects on radiotherapy and radiation protection is discussed.

Sources of variation in patient response to radiation treatment

PURPOSE

To investigate sources of variation in radiosensitivity displayed by cancer patients and blood donors using the leukocyte apoptosis assay.

METHODS AND MATERIALS

Probes were obtained from 105 healthy blood donors, 48 cancer patients displaying normal sensitivity to radiotherapy, 12 cancer patients displaying hypersensitivity to radiotherapy, 12 Ataxia telangiectasia blood donors, and 4 additional individuals with genetic diseases of potentially modified radiosensitivity; 2 neurofibromatosis (NF) donors, a Nijmegen breakage syndrome (NBS) donor, and an Immunodeficiency, Chromosome fragility, Facial anomaly syndrome (ICF) donor. Heparinized blood was diluted in medium, irradiated, and left to incubate for 48 h. CD4 and CD8 T-lymphocyte DNA was stained with propidium iodide and the cells were analyzed by flow cytometry.

RESULTS

Radiation-induced apoptosis depended on age and cell type. Cohorts of hypersensitive cancer patients, NBS and AT donors displayed compromised apoptotic response. An asymmetric apoptotic response of T-lymphocytes was observed in an ICF donor and a cryptic hypersensitivity donor. Two NF donors displayed no abnormal sensitivity to radiotherapy but compromised apoptotic T-cell response to X-rays.

CONCLUSION

Our studies reveal 4 physiologic sources of variation in radiation response-2 are genetic: cryptic hypersensitivity and hereditary disease, and 2 are epigenetic: cell type and donor age. They emphasize the important role of proteins involved in the recognition and repair of DNA double-strand breaks in determining the response of individuals to radiotherapy.