Genetic markers for prediction of normal tissue toxicity after radiotherapy

Radiation-related changes in serum proteome profiles detected by mass spectrometry in blood of patients treated with radiotherapy due to larynx cancer

The study aimed to detect features of human serum proteome that were associated with exposure to ionizing radiation. The analyzed group consisted of 46 patients treated with radical radiotherapy for larynx cancer; patients were irradiated with total doses in a range from 51 to 72 Gy. Three consecutive blood samples were collected from each patient: before the start, 2 weeks after the start, and 4-6 weeks after the end of radiotherapy. The low-molecular-weight fraction of the serum proteome (2,000-13,000 Da) was analyzed by the MALDI-ToF mass spectrometry. Proteome profiles of serum samples collected before the start of radiotherapy and during the early stage of the treatment were similar. In marked contrast, mass profiles of serum samples collected several weeks after the end of the treatment revealed clear changes. We found that 41 out of 312 registered peptide ions changed their abundance significantly when serum samples collected after the final irradiation were compared with samples collected at the two earlier time points. We also found that abundances of certain serum peptides were associated with total doses of radiation received by patients. The results of this pilot study indicate that features of serum proteome analyzed by mass spectrometry have potential applicability as a retrospective marker of exposure to ionizing radiation.

Association between single nucleotide polymorphisms in the XRCC1 and RAD51 genes and clinical radiosensitivity in head and neck cancer

PURPOSE

Individual variability in radiosensitivity is large in cancer patients. Single nucleotide polymorphisms (SNPs) in genes involved in DNA repair and in protection against reactive oxygen species (ROS) could be responsible for such cases of radiosensitivity. We investigated the association between the occurrence of acute reactions in 101 patients with squamous cell carcinoma of the head and neck (SCCHN) after radiotherapy (RT) and five genetic polymorphisms: XRCC1 c.1196A>G, XRCC3 c.722C>T, RAD51 (c.-3429G>C, c.-3392G>T), and GSTP1 c.313A>G.

MATERIALS AND METHODS

Genetic polymorphisms were detected by high resolution melting analysis (HRMA). The development of acute reactions (oral mucositis, skin erythema and dysphagia) associated with genetic polymorphisms was modeled using Cox proportional hazards, accounting for biologically effective dose (BED).

RESULTS

Development of grade ≥2 mucositis was increased in all patients (chemo-radiotherapy and radiotherapy alone) with XRCC1-399Gln allele (HR=1.72). The likelihood of developing grade ≥2 dysphagia was higher in carriers of RAD51 c.-3429 CC/GC genotypes (HR=4.00). The presence of at least one SNP or the co-presence of both SNPs in XRCC1 p.Gln399Arg /RAD51 c.-3429 G>C status were associated to higher likelihood of occurrence of acute toxicities (HR=2.03).

CONCLUSIONS

Our findings showed an association between genetic polymorphisms, XRCC1 c.1196A>G and RAD51 c.-3429 G>C, and the development of radiation-induced toxicities in SCCHN patients.

Association of XRCC1 variants with acute skin reaction after radiotherapy in breast cancer patients

After irradiation results in cytotoxic effects by DNA damage, base excision repair (BER) pathway is involved in the repair of single-strand breaks and nonhomologous end joining and homologous repair of double-strand breaks caused by radiotherapy. Alterations in the function of BER DNA repair genes may affect DNA repair proficiency and influence the response of patients with cancer to radiotherapy. The association of single nucleotide polymorphisms of BER DNA repair X-ray repair cross-complementing group 1 protein (XRCC1) and risk of radiotherapy-induced ≥grade 2 acute skin reaction in patients with breast cancer was examined. It was found that the risk of ≥grade 2 acute skin toxicity after radiotherapy could be increased by 2.86-fold in patients carrying the XRCC1 -77TC and CC genotypes (p = 0.016). However, the other three coding XRCC1 variants did not influence the risk of ≥grade 2 acute skin toxicity for patients with breast cancer after radiotherapy. Our results suggested that the XRCC1 polymorphism is associated with increased risk of radiation-induced acute skin reaction in a Chinese population.

Test of association between variant tgβ1 alleles and late adverse effects of breast radiotherapy

PURPOSE

To test for association between single nucleotide polymorphisms at the TGFβ1 locus and the risk of late normal tissue injury following whole breast radiotherapy.

METHODS

A retrospective study compared the number of variant alleles at -509 and codons 10 and 25 of the TGFβ1 locus in women followed up in two prospective clinical trials who developed either marked radiotherapy adverse effects or no adverse effects after matching on fractionation schedule, breast size, surgical deficit, chemotherapy and length of follow up.

RESULTS

Median follow up in the two trials was 7.4 (maximum 15) years and 5.3 (maximum 5.3) years. 1237/1716 (72%) women with photographic assessments of radiotherapy adverse effects were alive and well, and 147/1237 (12%) potential cases with the most marked change in photographic change in breast appearance were matched to potential controls recording no change. In an unmatched analysis of 82 cases and 108 controls, no significant difference in the number of genetic variants was observed.

CONCLUSIONS

No association was detected between sequence variations at the TGFβ1 locus and the risk of late adverse effects of breast radiotherapy.

Intraperitoneal administration of chitosan/DsiRNA nanoparticles targeting TNFα prevents radiation-induced fibrosis

BACKGROUND AND PURPOSE

One of the most common and dose-limiting long-term adverse effects of radiation therapy is radiation-induced fibrosis (RIF), which is characterized by restricted tissue flexibility, reduced compliance or strictures, pain and in severe cases, ulceration and necrosis. Several strategies have been proposed to ameliorate RIF but presently no effective one is available. Recent studies have reported that tumor necrosis factor-α (TNFα) plays a role in fibrogenesis.

MATERIAL AND METHODS

Male CDF1 mice were radiated with a single dose of 45 Gy. Chitosan/DsiRNA nanoparticles targeting TNFα were intraperitoneal injected and late radiation-induced fibrosis (RIF) was assessed using a modification of the leg contracture model. Additionally, the effect of these nanoparticles on tumor growth and tumor control probability in the absence of radiation was examined in a C3H mammary carcinoma model.

RESULTS

We show in this work, that targeting TNFα in macrophages by intraperitoneal administration of chitosan/DsiRNA nanoparticles completely prevented radiation-induced fibrosis in CDF1 mice without revealing any cytotoxic side-effects after a long-term administration. Furthermore, such TNFα targeting was selective without any significant influence on tumor growth or irradiation-related tumor control probability.

CONCLUSION

This nanoparticle-based RNAi approach represents a novel approach to prevent RIF with potential application to improve clinical radiation therapeutic strategies.

Differential contextual responses of normal human breast epithelium to ionizing radiation in a mouse xenograft model

Radiotherapy is a key treatment option for breast cancer, yet the molecular responses of normal human breast epithelial cells to ionizing radiation are unclear. A murine subcutaneous xenograft model was developed in which nonneoplastic human breast tissue was maintained with the preservation of normal tissue architecture, allowing us to study for the first time the radiation response of normal human breast tissue in situ. Ionizing radiation induced dose-dependent p53 stabilization and p53 phosphorylation, together with the induction of p21(CDKN1A) and apoptosis of normal breast epithelium. Although p53 was stabilized in both luminal and basal cells, induction of Ser392-phosphorylated p53 and p21 was higher in basal cells and varied along the length of the ductal system. Basal breast epithelial cells expressed ΔNp63, which was unchanged on irradiation. Although stromal responses themselves were minimal, the response of normal breast epithelium to ionizing radiation differed according to the stromal setting. We also demonstrated a dose-dependent induction of γ-H2AX foci in epithelial cells that was similarly dependent on the stromal environment and differed between basal and luminal epithelial cells. The intrinsic differences between human mammary cell types in response to in vivo irradiation are consistent with clinical observation that therapeutic ionizing radiation is associated with the development of basal-type breast carcinomas. Furthermore, there may be clinically important stromal-epithelial interactions that influence DNA damage responses in the normal breast. These findings demonstrate highly complex responses of normal human breast epithelium following ionizing radiation exposure and emphasize the importance of studying whole-tissue effects rather than single-cell systems.

H2AX phosphorylation screen of cells from radiosensitive cancer patients reveals a novel DNA double-strand break repair cellular phenotype

Background:

About 1–5% of cancer patients suffer from significant normal tissue reactions as a result of radiotherapy (RT). It is not possible at this time to predict how most patients’ normal tissues will respond to RT. DNA repair dysfunction is implicated in sensitivity to RT particularly in genes that mediate the repair of DNA double-strand breaks (DSBs). Phosphorylation of histone H2AX (phosphorylated molecules are known as γH2AX) occurs rapidly in response to DNA DSBs, and, among its other roles, contributes to repair protein recruitment to these damaged sites. Mammalian cell lines have also been crucial in facilitating the successful cloning of many DNA DSB repair genes; yet, very few mutant cell lines exist for non-syndromic clinical radiosensitivity (RS).

Methods:

Here, we survey DNA DSB induction and repair in whole cells from RS patients, as revealed by γH2AX foci assays, as potential predictive markers of clinical radiation response.

Results:

With one exception, both DNA focus induction and repair in cell lines from RS patients were comparable with controls. Using γH2AX foci assays, we identified a RS cancer patient cell line with a novel ionising radiation-induced DNA DSB repair defect; these data were confirmed by an independent DNA DSB repair assay.

Conclusion:

γH2AX focus measurement has limited scope as a pre-RT predictive assay in lymphoblast cell lines from RT patients; however, the assay can successfully identify novel DNA DSB repair-defective patient cell lines, thus potentially facilitating the discovery of novel constitutional contributions to clinical RS.

Biomarkers and surrogate endpoints for normal-tissue effects of radiation therapy: the importance of dose-volume effects

Biomarkers are of interest for predicting or monitoring normal tissue toxicity of radiation therapy. Advances in molecular radiobiology provide novel leads in the search for normal tissue biomarkers with sufficient sensitivity and specificity to become clinically useful. This article reviews examples of studies of biomarkers as predictive markers, as response markers, or as surrogate endpoints for radiation side effects. Single nucleotide polymorphisms are briefly discussed in the context of candidate gene and genomewide association studies. The importance of adjusting for radiation dose distribution in normal tissue biomarker studies is underlined. Finally, research priorities in this field are identified and discussed.

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.

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

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSIONS

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

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

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

Postoperative radiotherapy in DBCG during 30 years. Techniques, indications and clinical radiobiological experience

During the time period 1977-2007 postoperative radiotherapy in DBCG has varied considerably with regard to techniques and indications together with changes in the extent of surgery and adjuvant systemic therapy. The radiation treatment has been developed on the basis of clinical, radiophysical and radiobiological principles, encompassing also practical problems such as available equipment in the different centres and at times lack of sufficient machine capacity. The paper focus especially on the comprehensive work done prior to the DBCG 82 b&c studies, in order to optimize radiotherapy in all aspects prior to the evaluation of the efficacy of this treatment modality. The results from these trials did succeed in clear evidence that radiotherapy has an important role in the multidisciplinary treatment of early breast cancer. In parallel to these studies a new and challenging use of radiotherapy after breast conserving surgery was evaluated in the DBCG TM 82 protocol. The experience obtained with different techniques in this study formed the basis for the current principles of radiotherapy after lumpectomy. Reduction of radiation related morbidity has been a major issue for the DBCG radiotherapy group, and in this aspect several studies, including quality control visits, have been carried out to make the relevant modifications and to evaluate deviations from the guidelines between the centres. The background for the changes in radiotherapy is described for each of the programme periods as well as future perspectives which will include further refinements of the target and adjustments of dose and fractionation in selected 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.

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.

Biologically conformal treatment: biomarkers and functional imaging in radiation oncology

'Conformal radiation therapy' is the standard of care in radiation oncology, referring to the process of shaping the radiation beam to precisely match a tumor's physical dimensions. We describe 'biologically conformal radiotherapy', in which the radiation oncologist matches the prescribed treatment to a tumor's biological characteristics and the host's predicted tolerance of radiation. This paradigm emphasizes that not all tumors are equally sensitive to radiation; conversely, some patients are especially susceptible to radiation's side effects. Patients bearing radioresistant tumors or those prone to toxicity may be best treated with the incorporation of targeted radiation modulators or, in extreme cases, by a different modality. The biological characteristics of tumors can be assessed by a wide range of techniques: functional imaging (positron emission tomography and advanced magnetic resonance imaging), single gene/protein molecular techniques and 'omic' technologies. This paper reviews the latest advances in the use of biomarkers and functional imaging in guiding patients to receive the most appropriate treatment.

Predictive markers for normal tissue reactions: fantasy or reality?

Interpatient heterogeneity in normal tissue reactions varies considerably, yet the genetic determinants and the molecular mechanisms of therapeutic radiation sensitivity remain poorly understood. Predictive assays and markers for normal tissue reactions are still in their infancy, although some progress has been made, particularly, for predicting late toxicity. For instance the T-lymphocyte radiation-induced apoptosis assay was shown to significantly predict differences in late toxicity between individuals and an 18 gene classifier based on radiation-induced expression in subcutaneous fibroblasts has also been identified that differentiated between patients with a high and low risk of radiation-induced fibrosis. However, the technical set-up for gene expression measurements means that this latter assay is unlikely to be introduced soon into a routine clinical setting but has importantly allowed the identification of genes that are involved in the fibrotic process. Serum markers have also been identified that show potential for the prediction of patients who will develop acute and late pulmonary toxicity. Few genetic predictive markers for normal tissue reaction have been identified and validated. Many of the single nucleotide polymorphism association studies have been limited by size and the inclusion of subjects with different kinds of radiation morbidity. International collaboration to assemble well-defined cohorts and technological progress should mean that the identification and validation of such markers using candidate gene approaches and whole genome association studies, which have been successful in other research areas, will make rapid progress.