Lymphocyte radiosensitivity is a significant prognostic factor for morbidity in carcinoma of the cervix

Normal Tissue Toxicity Prediction: Clinical Translation on the Horizon

Improvements in radiotherapy delivery have enabled higher therapeutic doses and improved efficacy, contributing to the growing number of long-term cancer survivors. These survivors are at risk of developing late toxicity from radiotherapy, and the inability to predict who is most susceptible results in substantial impact on quality of life and limits further curative dose escalation. A predictive assay or algorithm for normal tissue radiosensitivity would allow more personalized treatment planning, reducing the burden of late toxicity, and improving the therapeutic index. Progress over the last 10 years has shown that the etiology of late clinical radiotoxicity is multifactorial and informs development of predictive models that combine information on treatment (eg, dose, adjuvant treatment), demographic and health behaviors (eg, smoking, age), co-morbidities (eg, diabetes, collagen vascular disease), and biology (eg, genetics, ex vivo functional assays). AI has emerged as a useful tool and is facilitating extraction of signal from large datasets and development of high-level multivariable models. Some models are progressing to evaluation in clinical trials, and we anticipate adoption of these into the clinical workflow in the coming years. Information on predicted risk of toxicity could prompt modification of radiotherapy delivery (eg, use of protons, altered dose and/or fractionation, reduced volume) or, in rare instances of very high predicted risk, avoidance of radiotherapy. Risk information can also be used to assist treatment decision-making for cancers where efficacy of radiotherapy is equivalent to other treatments (eg, low-risk prostate cancer) and can be used to guide follow-up screening in instances where radiotherapy is still the best choice to maximize tumor control probability. Here, we review promising predictive assays for clinical radiotoxicity and highlight studies that are progressing to develop an evidence base for clinical utility.

Immune correlates of therapy outcomes in women with cervical cancer treated with chemoradiotherapy: A systematic review

Background

Immune markers have been correlated with prognosis in a variety of solid tumors, including cervical cancer.

Objective

To review the literature on hematologic and immune markers and their association with recurrence and survival among patients with cervical cancer treated with chemoradiation.

Evidence review

This systematic review was conducted in accordance with PRISMA guidelines via searches of Ovid MEDLINE, Ovid Embase, and the Cochrane Library using keywords regarding cervical cancer, immune markers, and HIV. Studies involving patients treated with cisplatin‐based chemoradiotherapy were selected and reviewed by at least two independent reviewers, with disagreements resolved by a third reviewer.

Findings

A total of 737 studies were identified, of which 314 assessed immune biomarkers in immunocompetent patients (30 included in the final analysis) and 327 studies in immunosuppressed patients (5 included in the final analysis). The strongest prognostic indicators were lymphopenia and elevated neutrophil‐to‐lymphocyte ratio. Other potential markers included HPV‐specific lymphocyte response, cytokine profile, expression of immune‐blocking antigens on cell surfaces, and tumor‐associated lymphocyte, macrophage, and neutrophil infiltration. Studies of immunosuppressed patients described more severe cytopenic changes overall and concluded that viral suppression led to improved outcomes.

Conclusions

The immunologic interplay at work in cervical cancer development, progression, and treatment is complex. Strong evidence was found in favor of lymphopenia and elevated neutrophil‐to‐lymphocyte ratio being prognostic for worse outcomes with other markers showing potential associations as well. Although the interpretation of immune status with regard to treatment approach remains unclear, future studies should aim to tailor treatment that minimizes possible detrimental immune effects.

Immune markers have been correlated with prognosis in a variety of solid tumors, including cervical cancer. In this systematic review of immune markers for cervical cancer patients being treated with chemoradiation, we surveyed the literature for immunologic and hematologic prognostic markers and found the strongest negative prognostic indicators were lymphopenia and elevated neutrophil‐to‐lymphocyte ratio.

[Treatment of radiation-induced late effects: What's new?]

Mechanisms of late radio-induced lesions are the result of multiple and complex phenomena, with many entangled cellular and tissue factors. The biological continuum between acute and late radio-induced effects will be described, with firstly a break in homeostasis that leads to cellular redistributions. New insights into late toxicity will finally be addressed. Individual radiosensitivity is a primary factor for the development of late toxicity, and clinicians urgently need predictive tests to offer truly personalized radiation therapy. An update will be made on the various functional and genetic tests currently being validated. The management of radio-induced side effects remains a frequent issue for radiation oncologists, and an update will be made for certain specific clinical situations. Finally, an innovative management for patients with significant side effects after pelvic radiotherapy will be developed, involved mesenchymal stem cell transplantation, with the presentation of the "PRISME" protocol currently open to patients recruitment.

A tumor-immune interaction model for hepatocellular carcinoma based on measured lymphocyte counts in patients undergoing radiotherapy

PURPOSE

The impact of radiation therapy on the immune system has recently gained attention particularly when delivered in combination with immunotherapy. However, it is unclear how different treatment fractionation regimens influence the interaction between the immune system and radiation. The goal of this work was to develop a mathematical model that quantifies both the immune stimulating as well as the immunosuppressive effects of radiotherapy and simulates the effects of different fractionation regimens based on patient data.

METHODS AND MATERIALS

The framework describes the temporal evolution of tumor cells, lymphocytes, and inactivated dying tumor cells releasing antigens during radiation therapy, specifically modeling how recruited lymphocytes inhibit tumor progression. The parameters of the model were partly taken from the literature and in part extracted from blood samples (circulating lymphocytes: CLs) collected from hepatocellular carcinoma patients undergoing radiotherapy and their outcomes. The dose volume histograms to circulating lymphocytes were calculated with a probability-based model.

RESULTS

Based on the fitted parameters, the model enabled a study into the depletion and recovery of CLs in patients as a function of fractionation regimen. Our results quantify the ability of short fractionation regimens to lead to shorter periods of lymphocyte depletion and predict faster recovery after the end of treatment. The model shows that treatment breaks between fractions can prolong the period of lymphocyte depletion and should be avoided.

CONCLUSIONS

This study introduces a mathematical model for tumor-immune interactions using clinically extracted radiotherapy patient data, which can be applied to design trials aimed at minimizing lymphocyte depleting effects in radiation therapy.

THE DEPENDENCE OF DOSE-EFFECTS IN HUMAN RADIATION CYTOGENETICS

OBJECTIVE

To study the frequency and spectrum of chromosome aberrations in human peripheral blood lymphocytes depending on the radiation dose, the stage of the mitotic cycle and the periods of fixation of the cell culture.

MATERIALS AND METHODS

The test system of blood lymphocytes of donors, the metaphase analysis of chromosome aberrations (a uniform staining of the drugs). The gamma-irradiation was performed on the device with the source 60Co at the dose rate of 0.5 Gy/min, the dose range was 0.25-4.0 Gy. The lymphocyte culture was irradiated after 0, 24, 40 and 48 hours from the beginning of the incubation, which corresponds to G0-, G1-, S-, G2-stages of the mitot- ic cycle. The cells were fixed after 52 hours and 62 hours from the beginning of the incubation.

RESULTS

The author's experimental data on the regularities of chromosome aberrations formation during irradiation at the different periods of the mitotic cycle of human lymphocyte culture are presented. The character of the dose dependences of structural damages of chromosomes during the mitotic cycle with an application of the linear, lin- ear-square and parabolic models is analyzed. The greatest yield of exchange-type aberrations is registered at the irradiation in G0- and G1-stages of the mitotic cycle, which submits to the linear-square dependence on an irradia- tion dose. When irradiating cells in the S- and G2-stages, the main contribution to the spectrum of radiation-induced chromosome aberrations is made by deletions, the level of which increases linearly with the dose. This is evidenced by the negative values of the quadratic term in the regression equations for these stages. The analysis of the curves using the parabolic model Y = k · Dn has shown that, at the irradiation of lymphocytes in G0- and G1-stages, the dose dependences approach the quadratic ones, which confirms the reasonableness of the interpretation of the obtained cytogenetic data from the point of view of the «classical» theory of the radiation-induced chromosome aberrations formation. However, the model of the spline regression is more accurate at the approximation of the dependences of the cytogenetic effects in the region of low doses of irradiation.

CONCLUSIONS

The results obtained by the irradiation of human lymphocyte culture at different stages of the mitot- ic cycle indicate that the same radiation dose induces different qualitative and quantitative cytogenetic effects depending on the physiological state of the cell at the time of irradiation. The combination of such factors as a radi- ation dose rate, a mitotic cycle stage, the post-irradiation conditions, and an individual radiosensitivity are reflect- ed in quantitative and qualitative variations of the cellular radiosensitivity.

Data-Based Radiation Oncology: Design of Clinical Trials in the Toxicity Biomarkers Era

The ability to stratify patients using a set of biomarkers, which predict that toxicity risk would allow for radiotherapy (RT) modulation and serve as a valuable tool for precision medicine and personalized RT. For patients presenting with tumors with a low risk of recurrence, modifying RT schedules to avoid toxicity would be clinically advantageous. Indeed, for the patient at low risk of developing radiation-associated toxicity, use of a hypofractionated protocol could be proposed leading to treatment time reduction and a cost-utility advantage. Conversely, for patients predicted to be at high risk for toxicity, either a more conformal form or a new technique of RT, or a multidisciplinary approach employing surgery could be included in the trial design to avoid or mitigate RT when the potential toxicity risk may be higher than the risk of disease recurrence. In addition, for patients at high risk of recurrence and low risk of toxicity, dose escalation, such as a greater boost dose, or irradiation field extensions could be considered to improve local control without severe toxicities, providing enhanced clinical benefit. In cases of high risk of toxicity, tumor control should be prioritized. In this review, toxicity biomarkers with sufficient evidence for clinical testing are presented. In addition, clinical trial designs and predictive models are described for different clinical situations.

Decision support systems for personalized and participative radiation oncology

A paradigm shift from current population based medicine to personalized and participative medicine is underway. This transition is being supported by the development of clinical decision support systems based on prediction models of treatment outcome. In radiation oncology, these models 'learn' using advanced and innovative information technologies (ideally in a distributed fashion - please watch the animation: http://youtu.be/ZDJFOxpwqEA) from all available/appropriate medical data (clinical, treatment, imaging, biological/genetic, etc.) to achieve the highest possible accuracy with respect to prediction of tumor response and normal tissue toxicity. In this position paper, we deliver an overview of the factors that are associated with outcome in radiation oncology and discuss the methodology behind the development of accurate prediction models, which is a multi-faceted process. Subsequent to initial development/validation and clinical introduction, decision support systems should be constantly re-evaluated (through quality assurance procedures) in different patient datasets in order to refine and re-optimize the models, ensuring the continuous utility of the models. In the reasonably near future, decision support systems will be fully integrated within the clinic, with data and knowledge being shared in a standardized, dynamic, and potentially global manner enabling truly personalized and participative medicine.

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.

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

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

A flow cytometry assay that measures cellular sensitivity to DNA-damaging agents, customized for clinical routine laboratories

OBJECTIVES

The clonogenic assay examines cell sensitivity to toxic agents and has been shown to correlate with normal tissue sensitivity to radiotherapy in cancer patients. The clonogenic assay is not clinically applicable due to its intra-individual variability and the time frame of the protocol. We aimed to develop a clinically applicable assay that correlated with the clonogenic assay.

DESIGN AND METHODS

We have developed a faster and less labor-intensive cell division assay (CD assay) using flow cytometry and incorporation of a fluorescent thymidine analogue. The CD assay was calibrated to the clonogenic assay and optimized for peripheral blood lymphocytes.

RESULTS

Following ionizing radiation of primary human skin fibroblasts, the four-day CD assay gave similar results as the 14-day clonogenic survival assay. In lymphocytes isolated from patient blood samples, the CD assay was able to detect increased radiosensitivity in ataxia telangiectasia patients and increased radiosensitivity after in vitro treatment with DNA-PK and ATM inhibitors. The CD assay found a variation in the intrinsic radiosensitivity of lymphocytes isolated from healthy control samples. The CD assay was able to measure the anti-proliferation effect of different chemotherapeutic drugs in lymphocytes.

CONCLUSIONS

Our results indicate that the CD assay is a fast and reliable method to measure the anti-proliferation effect of DNA-damaging agents with a potential to find the most sensitive patients in the work-up before cancer treatment.

Incorporating Genetic Biomarkers into Predictive Models of Normal Tissue Toxicity

There is considerable variation in the level of toxicity patients experience for a given dose of radiotherapy, which is associated with differences in underlying individual normal tissue radiosensitivity. A number of syndromes have a large effect on clinical radiosensitivity, but these are rare. Among non-syndromic patients, variation is less extreme, but equivalent to a ±20% variation in dose. Thus, if individual normal tissue radiosensitivity could be measured, it should be possible to optimise schedules for individual patients. Early investigations of in vitro cellular radiosensitivity supported a link with tissue response, but individual studies were equivocal. A lymphocyte apoptosis assay has potential, and is currently under prospective validation. The investigation of underlying genetic variation also has potential. Although early candidate gene studies were inconclusive, more recent genome-wide association studies are revealing definite associations between genotype and toxicity and highlighting the potential for future genetic testing. Genetic testing and individualised dose prescriptions could reduce toxicity in radiosensitive patients, and permit isotoxic dose escalation to increase local control in radioresistant individuals. The approach could improve outcomes for half the patients requiring radical radiotherapy. As a number of patient- and treatment-related factors also affect the risk of toxicity for a given dose, genetic testing data will need to be incorporated into models that combine patient, treatment and genetic data.

Exploiting biological and physical determinants of radiotherapy toxicity to individualize treatment

The recent advances in radiation delivery can improve tumour control probability (TCP) and reduce treatment-related toxicity. The use of intensity-modulated radiotherapy (IMRT) in particular can reduce normal tissue toxicity, an objective in its own right, and can allow safe dose escalation in selected cases. Ideally, IMRT should be combined with image guidance to verify the position of the target, since patients, target and organs at risk can move day to day. Daily image guidance scans can be used to identify the position of normal tissue structures and potentially to compute the daily delivered dose. Fundamentally, it is still the tolerance of the normal tissues that limits radiotherapy (RT) dose and therefore tumour control. However, the dose-response relationships for both tumour and normal tissues are relatively steep, meaning that small dose differences can translate into clinically relevant improvements. Differences exist between individuals in the severity of toxicity experienced for a given dose of RT. Some of this difference may be the result of differences between the planned dose and the accumulated dose (DA). However, some may be owing to intrinsic differences in radiosensitivity of the normal tissues between individuals. This field has been developing rapidly, with the demonstration of definite associations between genetic polymorphisms and variation in toxicity recently described. It might be possible to identify more resistant patients who would be suitable for dose escalation, as well as more sensitive patients for whom toxicity could be reduced or avoided. Daily differences in delivered dose have been investigated within the VoxTox research programme, using the rectum as an example organ at risk. In patients with prostate cancer receiving curative RT, considerable daily variation in rectal position and dose can be demonstrated, although the median position matches the planning scan well. Overall, in 10 patients, the mean difference between planned and accumulated rectal equivalent uniform doses was -2.7 Gy (5%), and a dose reduction was seen in 7 of the 10 cases. If dose escalation was performed to take rectal dose back to the planned level, this should increase the mean TCP (as biochemical progression-free survival) by 5%. Combining radiogenomics with individual estimates of DA might identify almost half of patients undergoing radical RT who might benefit from either dose escalation, suggesting improved tumour cure or reduced toxicity or both.

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.

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.

Will SNPs be useful predictors of normal tissue radiosensitivity in the future?

The ability to predict individual risk of radiation-induced normal tissue complications is a long sought goal in radiobiology. The last decade saw increasing interest in identifying associations between single nucleotide polymorphisms (SNPs) and normal tissue complication risk. Nevertheless, it remains controversial whether SNPs will be useful predictors of normal tissue radiosensitivity. This paper provides a summary of a scientific debate held at the 31st ESTRO conference in which four scientists argued in favor or against the motion that SNPs will be useful predictors of normal tissue radiosensitivity in the future.

Predicting outcomes in radiation oncology--multifactorial decision support systems

With the emergence of individualized medicine and the increasing amount and complexity of available medical data, a growing need exists for the development of clinical decision-support systems based on prediction models of treatment outcome. In radiation oncology, these models combine both predictive and prognostic data factors from clinical, imaging, molecular and other sources to achieve the highest accuracy to predict tumour response and follow-up event rates. In this Review, we provide an overview of the factors that are correlated with outcome-including survival, recurrence patterns and toxicity-in radiation oncology and discuss the methodology behind the development of prediction models, which is a multistage process. Even after initial development and clinical introduction, a truly useful predictive model will be continuously re-evaluated on different patient datasets from different regions to ensure its population-specific strength. In the future, validated decision-support systems will be fully integrated in the clinic, with data and knowledge being shared in a standardized, instant and global manner.

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.

Investigating micronucleus assay applicability for prediction of normal tissue intrinsic radiosensitivity in gynecological cancer patients

BACKGROUND

Pelvic organs morbidity after irradiation of cancer patients remains a major problem although new technologies have been developed and implemented. A relatively simple and suitable method for routine clinical practice is needed for preliminary assessment of normal tissue intrinsic radiosensitivity. The micronucleus test (MNT) determines the frequency of the radiation induced micronuclei (MN) in peripheral blood lymphocytes, which could serve as an indicator of intrinsic cell radiosensitivity.

AIM

To investigate a possible use of the micronucleus test (MNT) for acute radiation morbidity prediction in gynecological cancer patients.

MATERIALS AND METHODS

Forty gynecological cancer patients received 50 Gy conventional external pelvic irradiation after radical surgery. A four-field "box" technique was applied with 2D planning. The control group included 10 healthy females. Acute normal tissue reactions were graded according to NCI CTCAE v.3.0. From all reaction scores, the highest score named "summarized clinical radiosensitivity" was selected for a statistical analysis. MNT was performed before and after in vitro irradiation with 1.5 Gy. The mean radiation induced frequency of micronuclei per 1000 binucleated cells (MN/1000) and lymphocytes containing micronuclei per 1000 binucleated cells (cells with MN/1000) were evaluated for both patients and controls. AN ARBITRARY CUT OFF VALUE WAS CREATED TO PICK UP A RADIOSENSITIVE INDIVIDUAL: the mean value of spontaneous frequency of cells with MN/1000 ± 2SD, found in the control group.

RESULTS

Both mean spontaneous frequency of cells with MN/1000 and MN/1000 were registered to be significantly higher in cancer patients compared to the control group (t = 2.46, p = 0.02 and t = 2.51, p = 0.02). No statistical difference was registered when comparing radiation induced MN frequencies between those groups. Eighty percent (32) of patients developed grade 2 summarized clinical radiosensitivity, with great variations in MNT parameters. Only three patients with grade 2 "summarized clinical radiosensitivity" had values of cells with MN/1000 above the chosen radiosensitivity threshold.

CONCLUSION

The present study was not able to confirm in vitro MNT applicability for radiosensitivity prediction in pelvic irradiation.

Genetics and genomics of radiotherapy toxicity: towards prediction

Radiotherapy is involved in many curative treatments of cancer; millions of survivors live with the consequences of treatment, and toxicity in a minority limits the radiation doses that can be safely prescribed to the majority. Radiogenomics is the whole genome application of radiogenetics, which studies the influence of genetic variation on radiation response. Work in the area focuses on uncovering the underlying genetic causes of individual variation in sensitivity to radiation, which is important for effective, safe treatment. In this review, we highlight recent advances in radiotherapy and discuss results from four genome-wide studies of radiotoxicity.

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.

Radiation pharmacogenomics: a genome-wide association approach to identify radiation response biomarkers using human lymphoblastoid cell lines

Radiation therapy is used to treat half of all cancer patients. Response to radiation therapy varies widely among patients. Therefore, we performed a genome-wide association study (GWAS) to identify biomarkers to help predict radiation response using 277 ethnically defined human lymphoblastoid cell lines (LCLs). Basal gene expression levels and 1.3 million genome-wide single nucleotide polymorphism (SNP) markers from both Affymetrix and Illumina platforms were assayed for all 277 human LCLs. MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assays for radiation cytotoxicity were also performed to obtain area under the curve (AUC) as a radiation response phenotype for use in the association studies. Functional validation of candidate genes, selected from an integrated analysis that used SNP, expression, and AUC data, was performed with multiple cancer cell lines using specific siRNA knockdown, followed by MTS and colony-forming assays. A total of 27 loci, each containing at least two SNPs within 50 kb with P-values less than 10(-4) were associated with radiation AUC. A total of 270 expression probe sets were associated with radiation AUC with P < 10(-3). The integrated analysis identified 50 SNPs in 14 of the 27 loci that were associated with both AUC and the expression of 39 genes, which were also associated with radiation AUC (P < 10(-3)). Functional validation using siRNA knockdown in multiple tumor cell lines showed that C13orf34, MAD2L1, PLK4, TPD52, and DEPDC1B each significantly altered radiation sensitivity in at least two cancer cell lines. Studies performed with LCLs can help to identify novel biomarkers that might contribute to variation in response to radiation therapy and enhance our understanding of mechanisms underlying that variation.

Association of single nucleotide polymorphisms in ATM, GSTP1, SOD2, TGFB1, XPD and XRCC1 with clinical and cellular radiosensitivity

PURPOSE

To examine the association of polymorphisms in ATM (codon 158), GSTP1 (codon 105), SOD2 (codon 16), TGFB1 (position -509), XPD (codon 751), and XRCC1 (codon 399) with fibrosis and also individual radiosensitivity.

METHODS AND MATERIALS

Retrospective analysis with 69 breast cancer patients treated with breast-conserving radiotherapy; total dose delivered was restricted to vary between 54 and 55Gy. Fibrosis was evaluated according to LENT/SOMA score. DNA was extracted from blood samples; cellular radiosensitivity was measured using the G0 assay and polymorphisms by PCR-RFLP and MALDI-TOF, respectively.

RESULTS

Twenty-five percent of all patients developed fibrosis of grade 2 or 3. This proportion tends to be higher in patients being polymorphic in TGFB1 or XRCC1 when compared to patients with wildtype genotype, whereas for ATM, GSTP1, SOD2 and XPD the polymorphic genotype appears to be associated with a lower risk of fibrosis. However, none of these associations are significant. In contrast, when a risk score is calculated based on all risk alleles, there was significant association with an increased risk of fibrosis (per risk allele odds ratio (ORs)=2.09, 95% confidence interval (CI): 1.32-3.55, p=0.0005). All six polymorphisms were found to have no significant effect on cellular radiosensitivity.

CONCLUSIONS

It is most likely that risk for radiation-induced fibrosis can be assessed by a combination of risk alleles. This finding needs to be replicated in further studies.

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.

Normal tissue reactions to radiotherapy: towards tailoring treatment dose by genotype

A key challenge in radiotherapy is to maximize radiation doses to cancer cells while minimizing damage to surrounding healthy tissue. As severe toxicity in a minority of patients limits the doses that can be safely given to the majority, there is interest in developing a test to measure an individual's radiosensitivity before treatment. Variation in sensitivity to radiation is an inherited genetic trait and recent progress in genotyping raises the possibility of genome-wide studies to characterize genetic profiles that predict patient response to radiotherapy.

Response of lymphocytes to radiation in untreated breast cancer patients as detected with three different genetic assays

OBJECTIVE

To detect the response of lymphocytes to radiation in untreated breast cancer patients with three different genetic assays.

METHODS

Blood samples were collected from 25 untreated patients and 25 controls. Each blood sample was divided into two parts: one was irradiated by 3-Gy X-ray (irradiated sample), the other was not irradiated (non-irradiated sample). The radiosensitivity of lymphocytes was assessed by comet assay, cytokinesis-block micronucleus (CBMN) assay and 6-TG-resistant cells scored (TG) assay.

RESULTS

The baseline values of micronucleated cell frequency (MCF) and micronucleus frequency (MNF) in the patients were significantly higher than those in the controls (P < 0.01), and 3-Gy X-ray induced genetic damage to lymphocytes in the patients increased significantly as compared with that in the controls as detected with the three genetic assays (P < 0.01). The proportion of radiosensitive cases in the patient group was 48% for the mean tail length (MTL), 40% for the mean tail moment (MTM), 40% for MCF, 44% for MNF, and 48% for mutation frequencies of the hprt gene (Mfs-hprt), respectively, whereas the proportion of radiosensitive cases in the control group was only 8% for all the parameters.

CONCLUSION

The difference in the lymphocyte radiosensitivity between the breast cancer patients and the controls is significant. Moreover, there are wide individual variations in lymphocyte radiosensitivity of patients with breast cancer. In some cases, the radiosensitivity of the same patient may be different as detected with the different assays. It is suggested that multiple assays should be used to assess the radiosensitivity of patients with breast cancer before therapy.

Relationships between acute reactions to radiotherapy in head and neck cancer patients and parameters of radiation-induced DNA damage and repair in their lymphocytes

PURPOSE

To study the relationship between lymphocyte radiosensitivity measured in vitro and acute reactions to radiotherapy in patients with head and neck cancer.

MATERIALS AND METHODS

Acute reactions were measured in 34 patients using the Dische scale. Lymphocyte radiosensitivity was measured using the alkaline comet assay, the micronucleus assay, the nuclear division index and morphological assessment of apoptosis.

RESULTS

There was a weak, statistically significant correlation between in vitro radiosensitivity measured as the rate of DNA damage repair and the cumulative radiation dose exerting the maximum acute reaction scored (r = -0.366, p = 0.039, n = 34). Subgroup analyses showed that for patients with a low level of radiation-induced DNA damage there was a statistically significant relationship between lymphocyte radiosensitivity measured as inhibition of proliferation and acute toxicity (r = -0.621, p = 0.007, n = 18). For patients with a high level of residual DNA damage, there was a relationship between lymphocyte radiosensitivity measured using the micronucleus assay and acute toxicity (r = -0.597, p = 0.023, n = 14).

CONCLUSIONS

Combining two measures of radiosensitivity improves the ability to correlate in vitro lymphocyte radiosensitivity and acute radiotherapy toxicity data.

Individual radiosensitivity measured with lymphocytes may predict the risk of acute reaction after radiotherapy

PURPOSE

We tested whether the chromosomal radiosensitivity of in vitro irradiated lymphocytes could be used to predict the risk of acute reactions after radiotherapy.

METHODS AND MATERIALS

Two prospective studies were performed: study A with 51 patients included different tumor sites and study B included 87 breast cancer patients. Acute reaction was assessed using the Radiation Therapy Oncology Group score. In both studies, patients were treated with curative radiotherapy, and the mean tumor dose applied was 55 Gy (40-65) +/- boost with 11 Gy (6-31) in study A and 50.4 Gy +/- boost with 10 Gy in study B. Individual radiosensitivity was determined with lymphocytes irradiated in vitro with X-ray doses of either 3 or 6 Gy and scoring the number of chromosomal deletions.

RESULTS

Acute reactions displayed a typical spectrum with 57% in study A and 53% in study B showing an acute reaction of Grade 2-3. Individual radiosensitivity in both studies was characterized by a substantial variation and the fraction of patients with Grade 2-3 reaction was found to increase with increasing individual radiosensitivity measured at 6 Gy (study A, p = 0.238; study B, p = 0.023). For study B, this fraction increased with breast volume, and the impact of individual radiosensitivity on acute reaction was especially pronounced (p = 0.00025) for lower breast volume. No such clear association with acute reaction was observed when individual radiosensitivity was assessed at 3 Gy.

CONCLUSION

Individual radiosensitivity determined at 6 Gy seems to be a good predictor for risk of acute effects after curative radiotherapy.

Aberrant CDKN1A transcriptional response associates with abnormal sensitivity to radiation treatment

Normal tissue reactions to radiation therapy vary in severity among patients and cannot be accurately predicted, limiting treatment doses. The existence of heritable radiosensitivity syndromes suggests that normal tissue reaction severity is determined, at least in part, by genetic factors and these may be revealed by differences in gene expression. To test this hypothesis, peripheral blood lymphocyte cultures from 22 breast cancer patients with either minimal (11) or very severe acute skin reactions (11) have been used to analyse gene expression. Basal and post-irradiation expression of four radiation-responsive genes (CDKN1A, GADD45A, CCNB1, and BBC3) was determined by quantitative real-time PCR in T-cell cultures established from the two patient groups before radiotherapy. Relative expression levels of BBC3, CCNB1, and GADD45A 2 h following 2 Gy X-rays did not discriminate between groups. However, post-irradiation expression response was significantly reduced for CDKN1A (P<0.002) in severe reactors compared to normal. Prediction of reaction severity of approximately 91% of individuals sampled was achieved using this end point. Analysis of TP53 Arg72Pro and CDKN1A Ser31Arg single nucleotide polymorphisms did not show any significant association with reaction sensitivity. Although these results require confirmation and extension, this study demonstrates the possibility of predicting the severity of acute skin radiation toxicity in simple tests.

Genetic markers for prediction of normal tissue toxicity after radiotherapy

During the last decade, a number of studies have supported the hypothesis that there is an important genetic component to the observed interpatient variability in normal tissue toxicity after radiotherapy. This review summarizes the candidate gene association studies published so far on the risk of radiation-induced morbidity and highlights some recent successful whole-genome association studies showing feasibility in other research areas. Future genetic association studies are discussed in relation to methodological problems such as the characterization of clinical and biological phenotypes, genetic haplotypes, and handling of confounding factors. Finally, candidate gene studies elucidating the genetic component of radiation-induced morbidity and the functional consequences of single nucleotide polymorphisms by studying intermediate phenotypes will be discussed.

Residual γH2AX after irradiation of human lymphocytes and monocytes in vitro and its relation to late effects after prostate brachytherapy

BACKGROUND AND PURPOSE

Retention of gammaH2AX foci in irradiated cells can signify a deficiency in DNA double-strand break repair that may be useful as an indicator of individual radiosensitivity.

MATERIALS AND METHODS

To examine this possibility, the retention of gammaH2AX after irradiation was compared using white blood cells from 20 prostate brachytherapy patients who developed late normal tissue toxicity and 20 patients with minimal toxicity. Peripheral blood lymphocytes and monocytes were coded for analysis, exposed in vitro to 4 doses of 0.7 Gy X-rays at 3 hourly intervals, and retention of gammaH2AX was measured by flow cytometry 18 hours after the final irradiation.

RESULTS

Excellent reproducibility in duplicate samples and a range in residual gammaH2AX from 7% above background to 244% above background were observed. Residual gammaH2AX in lymphocytes showed a positive correlation with patient age. However, no relation was observed between the level of residual gammaH2AX in peripheral blood mononuclear cells and late normal tissue damage.

CONCLUSIONS

We conclude that the method of detection of residual gammaH2AX after in vitro irradiation of lymphocytes and monocytes was simple, reproducible, and sensitive. However, it failed to predict for late normal tissue toxicity after brachytherapy. Possible reasons are discussed.

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.

Radiation-induced gene expression in human subcutaneous fibroblasts is predictive of radiation-induced fibrosis

BACKGROUND AND PURPOSE

Breast cancer patients show a large variation in normal tissue reactions after ionizing radiation (IR) therapy. One of the most common long-term adverse effects of ionizing radiotherapy is radiation-induced fibrosis (RIF), and several attempts have been made over the last years to develop predictive assays for RIF. Our aim was to identify basal and radiation-induced transcriptional profiles in fibroblasts from breast cancer patients that might be related to the individual risk of RIF in these patients.

MATERIALS AND METHODS

Fibroblast cell lines from 31 individuals with variable risk of RIF (grouped into five classes from low to high risk) were irradiated with two different schemes: 1 x 3.5 Gy with RNA isolated 2 and 24h after irradiation, and a fractionated scheme with 3 x 3.5 Gy in intervals of 24h with RNA isolated 2h after the last dose. RNA was also isolated from non-treated fibroblasts. Transcriptional differences in basal and radiation-induced gene expression profiles were investigated using 15K cDNA microarrays, and results analyzed by both SAM and PAM.

RESULTS

Sixty differentially expressed genes were identified by applying SAM on 10 patients with the highest risk of RIF and the four patients with the lowest risk of RIF after the fractionated scheme. The genes were associated with known functions in processes like apoptosis, extracellular matrix remodelling/cell adhesion, proliferation and ROS scavenging. A minimum set of 18 genes were identified that could differentiate high risk from low risk-patients after the fractionated scheme.

CONCLUSIONS

The classifier of 18 genes may provide basis for a predictive assay for normal tissue reactions after radiotherapy, and provide new insight into the molecular mechanisms of RIF.

Genetic determination of chromosomal radiosensitivities in G0- and G2-phase human lymphocytes

BACKGROUND AND PURPOSE

The radiosensitivity of human lymphocytes measured using a G0- or G2-assay has been linked with an individual's risk of developing normal tissue complications following radiotherapy. This study was performed to increase basic knowledge of the genetics of the human radiation response, and chromosomal aberration induction in particular.

MATERIALS AND METHODS

The study was carried out with blood samples taken from 15 monozygotic twin pairs. G0-assay was performed for cells irradiated with 6 Gy counting only deletions and G2-assay for cells irradiated with 0.5 Gy scoring only chromatid breaks.

RESULTS

The mean number of deletions measured at 6 Gy for all 30 samples using the G0-assay amounted to 2.96+/-0.37 (means+/-SD), which corresponds to a coefficient of variation (CV) of 13%. There is a highly significant intra-pair correlation for this number among twins (r(2)=0.911) demonstrating that this parameter is mostly determined by genetic factors. According to the mean number of deletions, a theoretical classification based on the definition < or = MV-SD as resistant, MV+/-SD as normal and > or = MV+SD as sensitive was made, identifying two pairs as sensitive or resistant, respectively, while nine were normal and two pairs are intermediate. For chromatid breaks measured at 0.5 Gy with the G2-assay the mean number was 1.35+/-0.42 (means+/-SD) corresponding to a CV of 31%. There was again a strong intra-pair correlation among twins with r(2)=0.837 showing that this sensitivity is also determined mostly by genetic factors. There was, however, no inter-assay correlation between the G0- and G2-sensitivity (r(2)=0.006) demonstrating that these two sensitivities depend on different genetic factors.

CONCLUSION

The chromosomal radiosensitivity of lymphocytes as defined by G0- or G2-assay is largely determined by different genetic factors, which may allow the use of genetic profiling as an indicator of the respective individual radiosensitivity.

The genomics revolution and radiotherapy

The expansion of our knowledge through the Human Genome Project has been accompanied by the development of new high-throughput techniques, which provide extensive capabilities for the analysis of a large number of genes or the whole genome. These assays can be carried out in various clinical samples at the DNA (genome), RNA (transcriptome) or protein (proteome) level. There is a belief that this genomic revolution, i.e. sequencing of the human genome and developments in high-throughput technology, heralds a future of personalised medicine. For clinical oncology, this progress should increase the possibility of predicting individual patient responses to radiotherapy. This review highlights some of the work involving sparsely ionising radiation and the new technologies.

Short-term culture and gammaH2AX flow cytometry determine differences in individual radiosensitivity in human peripheral T lymphocytes

Histone H2AX, a subfamily of histone H2A, is phosphorylated and forms proteinaceous repair foci at the sites of DNA double-strand breaks in response to genotoxic insults, such as ionizing radiation. This process is believed to play a key role in the repair of DNA damage. In this study, we established a flow cytometry (FCM) system for measuring radiation-induced phosphorylated histone H2AX (gammaH2AX) in cultured human T lymphocytes to evaluate individual radiation sensitivity in vitro. Irradiation of short-term ( approximately 7 days) cultured T lymphocytes exhibited significant interindividual, but not interexperimental, differences in the cellular content of gammaH2AX 6 hr after 4 Gy of X-irradiation in three independent experiments using peripheral blood lymphocytes from six healthy donors. However, these differences were not as marked in uncultured lymphocytes, or lymphocytes that were cultured for a prolonged period ( approximately 13 days). The variation of gammaH2AX focus formation in lymphocytes of individuals was reproducible, with differences reaching about 1.5-fold following 7 days of culture. Therefore, the FCM-based gammaH2AX measurement appeared to reflect both the temporal course and the amount of DNA damage within the irradiated lymphocytes. Further, we confirmed that the differences in residual lymphocyte subsets were not involved in individual radiosensitivity. These results suggest that the FCM-based gammaH2AX assay using cultured T lymphocytes might be useful for the rapid and reliable assessment of individual radiation sensitivity involved in DNA damage repair.

Lymphoblastoid cell lines differing in p53 status show clear differences in basal gene expression with minor changes after irradiation

BACKGROUND AND PURPOSE

The genetic profile as determined by microarray is considered to be an ideal marker of the individual radiosensitivity. However, it is still an open question, whether this profile has to be determined prior to or only after irradiation, since the expression of some genes is affected by irradiation. These changes are induced mainly due to a p53-dependent transactivation.

MATERIALS AND METHODS

In this study gene expression profiles were measured for 3 lymphoblastoid cell lines differing in p53 status (p53 wt: TK6; p53null: TK6E6, p53mut: WTK1) measured either prior to or 3h after exposure to 2Gy. The gene expression profile was determined using the Affymetrix Human HG U133A GeneChip and for selective genes, variation in gene expression was validated by qRT-PCR. In addition, different assays were used to characterize the radioresponse of these three strains.

RESULTS

The three strains were found to be different in all aspects of radiosensitivity studied. Cells with p53wt showed more apoptosis, slightly stronger arrest in G1, but less lethal aberrations and a lower viability when compared to cells with mutated p53, whereas cells absent in p53 are characterized by an intermediate response. The gene expression profile measured prior to irradiation already revealed huge differences. Significance analysis of microarrays (SAM) identified 141 genes that changed expression twofold or more with a false discovery rate (FDR) of 5.4%. When compared to p53null cell line with p53wt showed a twofold difference in up- or down-regulation in 28 genes. A much higher variation was even found when p53mut cells were compared with p53null cells with a twofold difference in even 123 genes. The respective genes were found to be involved mainly in apoptosis, cell cycle regulation, metabolisms and signalling but with only one gene relevant for DNA repair. Radiation was found to affect this profile solely for cells with p53wt with a twofold significant up-regulation in only five genes. For selective genes (BCL2, CASP1, CCND2, DDB2, XPC, RAD51C, SESN1, FUCA1, CDKN1A, MDM2, XPC) array data were confirmed by qRT-PCR.

CONCLUSION

The result, that the gene expression profile of lymphoblastoid cells differing in p53 status already displayed clear differences when measured prior to irradiation with only few changes after irradiation, which are solely seen for p53wt cells, suggests, that the differences in radiosensitivity observed for these cells are primarily determined by the variation in expression profile present already prior to irradiation.

Low-Dose Hyper-radiosensitivity is not Caused by a Failure to Recognize DNA Double-Strand Breaks

One of the earliest cellular responses to radiation-induced DNA damage is the phosphorylation of the histone variant H2AX (gamma-H2AX). gamma-H2AX facilitates the local concentration and focus formation of numerous repair-related proteins within the vicinity of DNA DSBs. Previously, we have shown that low-dose hyper-radiosensitivity (HRS), the excessive sensitivity of mammalian cells to very low doses of ionizing radiation, is a response specific to G(2)-phase cells and is attributed to evasion of an ATM-dependent G(2)-phase cell cycle checkpoint. To further define the mechanism of low-dose hyper-radiosensitivity, we investigated the relationship between the recognition of radiation-induced DNA double-strand breaks as defined by gamma-H2AX staining and the incidence of HRS in three pairs of isogenic cell lines with known differences in radiosensitivity and DNA repair functionality (disparate RAS, ATM or DNA-PKcs status). Marked differences between the six cell lines in cell survival were observed after high-dose exposures (>1 Gy) reflective of the DNA repair capabilities of the individual six cell lines. In contrast, the absence of functional ATM or DNA-PK activity did not affect cell survival outcome below 0.2 Gy, supporting the concept that HRS is a measure of radiation sensitivity in the absence of fully functional repair. No relationship was evident between the initial numbers of DNA DSBs scored immediately after either low- or high-dose radiation exposure with cell survival for any of the cell lines, indicating that the prevalence of HRS is not related to recognition of DNA DSBs. However, residual DNA DSB damage as indicated by the persistence of gamma-H2AX foci 4 h after exposure was significantly correlated with cell survival after exposure to 2 Gy. This observation suggests that the persistence of gamma-H2AX foci could be adopted as a surrogate assay of cellular radiosensitivity to predict clinical radiation responsiveness.

Detecting Normal Cell Radiosensitivity via Assay of DNA Damage in Lymphocytes for Individualizing Radiotherapy in Head and Neck Cancer Patients

PURPOSE

The purpose of this study was to determine whether the distribution of radiosensitivities in normal tissues of head and neck cancer patients, measured using a DNA damage assay on lymphocytes, is likely to provide sufficient discrimination to enable reliable identification of patients with abnormal sensitivities.

MATERIAL AND METHODS

Radiosensitivity was assessed in 307 lymphocyte samples from unselected head and neck cancer patients and was quantified as the initial number of DNA double-strand breaks (dsb) induced per Gray and per DNA unit (200 Mbp).

RESULTS

The existence of an inter-individual variation in the radiosensitivity parameter is described by the range (0.41--9.38 dsb/Gy/DNA unit) of the values found. We detected 37 patients who developed severe skin reactions during radiotherapy treatment and we compared their radiosensitivity values with the remaining patients treated. Radiosensitivity values of >7.20 dsb/Gy/DNA unit should theoretically correspond to highly radiosensitive patients.

CONCLUSIONS

Our results suggest that initial DNA damage measured on lymphocytes offers an approach to predict the acute response of human normal tissues prior to radiotherapy. .

Radiation-induced damage to normal tissues after radiotherapy in patients treated for gynecologic tumors: association with single nucleotide polymorphisms in XRCC1, XRCC3, and OGG1 genes and in vitro chromosomal radiosensitivity in lymphocytes

PURPOSE

To examine the association of polymorphisms in XRCC1 (194Arg/Trp, 280Arg/His, 399Arg/Gln, 632Gln/Gln), XRCC3 (5' UTR 4.541A>G, IVS5-14 17.893A>G, 241Thr/Met), and OGG1 (326Ser/Cys) with the development of late radiotherapy (RT) reactions and to assess the correlation between in vitro chromosomal radiosensitivity and clinical radiosensitivity.

METHODS AND MATERIALS

Sixty-two women with cervical or endometrial cancer treated with RT were included in the study. According to the Common Terminology Criteria for Adverse Events, version 3.0, scale, 22 patients showed late adverse RT reactions. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays were performed to examine polymorphic sites, the G2 assay was used to measure chromosomal radiosensitivity, and patient groups were compared using actuarial methods.

RESULTS

The XRCC3 IVS5-14 polymorphic allele was significantly associated with the risk of developing late RT reactions (odds ratio 3.98, p = 0.025), and the XRCC1 codon 194 variant showed a significant protective effect (p = 0.028). Patients with three or more risk alleles in XRCC1 and XRCC3 had a significantly increased risk of developing normal tissue reactions (odds ratio 10.10, p = 0.001). The mean number of chromatid breaks per cell was significantly greater in patients with normal tissue reactions than in patients with no reactions (1.16 and 1.34, respectively; p = 0.002). Patients with high chromosomal radiosensitivity showed a 9.2-fold greater annual risk of complications than patients with intermediate chromosomal radiosensitivity. Combining the G2 analysis with the risk allele model allowed us to identify 23% of the patients with late normal tissue reactions, without false-positive results.

CONCLUSION

The results of the present study showed that clinical radiosensitivity is associated with an enhanced G2 chromosomal radiosensitivity and is significantly associated with a combination of different polymorphisms in DNA repair genes.

Correlation between DNA Repair Capacity in Lymphocytes and Acute Side Effects to Skin during Radiotherapy in Nasopharyngeal Cancer Patients

PURPOSE

Repair of radiation-induced DNA damage plays a critical role for both the susceptibility of patients to side effects after radiotherapy and their subsequent cancer risk. The study objective was to evaluate whether DNA repair data determined in vitro are correlated with the occurrence of acute side effects during radiotherapy.

EXPERIMENTAL DESIGN

Nasopharyngeal cancer patients receiving radiation therapy were recruited in a prospective epidemiologic study. As an indicator for clinical radiosensitivity, adverse reactions of the skin were recorded. Cryopreserved lymphocytes from 100 study participants were gamma-irradiated with 5 Gy in vitro and analyzed using the alkaline comet assay. Reproducibility of the assay was determined by repeated analysis (n = 22) of cells from a healthy donor. A coefficient of variation of 0.24 was calculated.

RESULTS

The various parameters determined to characterize the individual DNA repair capacity showed large differences between patients. Twenty-one patients were identified with considerably enhanced DNA damage induction, and 19 patients exhibited severely reduced DNA repair capacity after 15 and 30 minutes. Eight patients were considered as clinically radiosensitive, indicated by moist desquamation of the skin after a total radiation dose of 70 Gy.

CONCLUSIONS

Using the alkaline comet assay as described here, nasopharyngeal cancer patients were identified showing abnormal cellular radiation effects, but this repair deficiency corresponded only at a very limited extent to the acute radiation sensitivity of the skin.

Early and late skin reactions to radiotherapy for breast cancer and their correlation with radiation-induced DNA damage in lymphocytes

Introduction

Radiotherapy outcomes might be further improved by a greater understanding of the individual variations in normal tissue reactions that determine tolerance. Most published studies on radiation toxicity have been performed retrospectively. Our prospective study was launched in 1996 to measure the in vitro radiosensitivity of peripheral blood lymphocytes before treatment with radical radiotherapy in patients with breast cancer, and to assess the early and the late radiation skin side effects in the same group of patients. We prospectively recruited consecutive breast cancer patients receiving radiation therapy after breast surgery. To evaluate whether early and late side effects of radiotherapy can be predicted by the assay, a study was conducted of the association between the results of in vitro radiosensitivity tests and acute and late adverse radiation effects.

Methods

Intrinsic molecular radiosensitivity was measured by using an initial radiation-induced DNA damage assay on lymphocytes obtained from breast cancer patients before radiotherapy. Acute reactions were assessed in 108 of these patients on the last treatment day. Late morbidity was assessed after 7 years of follow-up in some of these patients. The Radiation Therapy Oncology Group (RTOG) morbidity score system was used for both assessments.

Results

Radiosensitivity values obtained using the in vitro test showed no relation with the acute or late adverse skin reactions observed. There was no evidence of a relation between acute and late normal tissue reactions assessed in the same patients. A positive relation was found between the treatment volume and both early and late side effects.

Conclusion

After radiation treatment, a number of cells containing major changes can have a long survival and disappear very slowly, becoming a chronic focus of immunological system stimulation. This stimulation can produce, in a stochastic manner, late radiation-related adverse effects of varying severity. Further research is warranted to identify the major determinants of normal tissue radiation response to make it possible to individualize treatments and improve the outcome of radiotherapy in cancer patients.

Clinical and cellular radiosensitivity in inherited human syndromes

AIMS

It has been proposed that in-vitro measurements of radiosensitivity might allow individualisation of patient radiotherapy schedules, with concomitant increases in the therapeutic ratio between tumours and normal tissues. Most predictive assay research on normal tissues to date has been based on the radiosensitivity of normal lymphocytes and skin fibroblasts as determined by clonogenic cell-survival assays. Studies comparing the radiosensitivity of fibroblasts or lymphocytes with acute or late radiation damage have reported variable results.

METHODS

In this study, we measured the radiosensitivity of lymphocytes from three patients displaying clinical radiation hypersensitivity who were known or suspected to carry germline mutations in genes that have been linked to increased radiosensitivity (a BRCA2 mutation carrier, a patient with Bloom's syndrome and a patient with a Fanconi anaemia-like condition), to investigate whether there is a correlation between cellular radiosensitivity and normal tissue response.

RESULTS

We found no association between lymphocyte radiosensitivity and the development of adverse radiation reactions in this group of patients, as is observed in the paradigm radiosensitivity syndrome, ataxia-telangiectasia.

CONCLUSIONS

Our results, and those of others, show that, at present, the evidence is not strong enough to justify routine clinical use of clonogenic cell survival assays to predict radiation response.