Novel DNA sequence variants in the hHR21 DNA repair gene in radiosensitive cancer patients

Cohesin RAD21 Gene Promoter Methylation Correlated with Better Prognosis in Breast Cancer Patients

RAD21 plays multiple roles in numerous cancers. In breast cancer (BC), a high level of RAD21 correlates with poor disease outcomes and resistance to chemotherapy. However, data regarding RAD21 promoter methylation in BC tissue and its correlation with clinical outcomes in patients with BC remain limited. Here, we investigated the clinicopathological features associated with the methylation status of RAD21 in BC to figure out its possible role in pathogenesis and the formation of breast carcinogenesis. The methylation status of the RAD21 gene was significantly associated with better clinical outcomes in patients with BC.

Recurrent Germline Variant in RAD21 Predisposes Children to Lymphoblastic Leukemia or Lymphoma

Somatic loss of function mutations in cohesin genes are frequently associated with various cancer types, while cohesin disruption in the germline causes cohesinopathies such as Cornelia-de-Lange syndrome (CdLS). Here, we present the discovery of a recurrent heterozygous RAD21 germline aberration at amino acid position 298 (p.P298S/A) identified in three children with lymphoblastic leukemia or lymphoma in a total dataset of 482 pediatric cancer patients. While RAD21 p.P298S/A did not disrupt the formation of the cohesin complex, it altered RAD21 gene expression, DNA damage response and primary patient fibroblasts showed increased G2/M arrest after irradiation and Mitomycin-C treatment. Subsequent single-cell RNA-sequencing analysis of healthy human bone marrow confirmed the upregulation of distinct cohesin gene patterns during hematopoiesis, highlighting the importance of RAD21 expression within proliferating B- and T-cells. Our clinical and functional data therefore suggest that RAD21 germline variants can predispose to childhood lymphoblastic leukemia or lymphoma without displaying a CdLS phenotype.

Cohesin subunit RAD21: From biology to disease

RAD21 (also known as KIAA0078, NXP1, HR21, Mcd1, Scc1, and hereafter called RAD21), an essential gene, encodes a DNA double-strand break (DSB) repair protein that is evolutionarily conserved in all eukaryotes from budding yeast to humans. RAD21 protein is a structural component of the highly conserved cohesin complex consisting of RAD21, SMC1a, SMC3, and SCC3 [STAG1 (SA1) and STAG2 (SA2) in metazoans] proteins, involved in sister chromatid cohesion. This function is essential for proper chromosome segregation, post-replicative DNA repair, and prevention of inappropriate recombination between repetitive regions. In interphase, cohesin also functions in the control of gene expression by binding to numerous sites within the genome. In addition to playing roles in the normal cell cycle and DNA DSB repair, RAD21 is also linked to the apoptotic pathways. Germline heterozygous or homozygous missense mutations in RAD21 have been associated with human genetic disorders, including developmental diseases such as Cornelia de Lange syndrome (CdLS) and chronic intestinal pseudo-obstruction (CIPO) called Mungan syndrome, respectively, and collectively termed as cohesinopathies. Somatic mutations and amplification of the RAD21 have also been widely reported in both human solid and hematopoietic tumors. Considering the role of RAD21 in a broad range of cellular processes that are hot spots in neoplasm, it is not surprising that the deregulation of RAD21 has been increasingly evident in human cancers. Herein, we review the biology of RAD21 and the cellular processes that this important protein regulates and discuss the significance of RAD21 deregulation in cancer and cohesinopathies.

Is Clinical Radiosensitivity a Complex Genetically Controlled Event?

New insights into molecular mechanisms responsible for cellular radiation response are coming from recent basic radiobiological studies. Preliminary data supporting the concept of clinical radiosensitivity as a complex genetically controlled event are available, and it seems reasonable to hypothesize that genes encoding for proteins implicated in known radiation-induced pathways, such as DNA repair, could influence normal tissue and tumor response to radiotherapy. Such genes could be considered as candidates for experimental studies and as targets for innovative therapies. Variants that could influence individual radiosensitivity have been recently identified, and specific Single Nucleotide Polymorphisms have been associated to the development of different radiation effects on normal tissues. Allelic architecture of complex traits able to modify phenotypes is difficult to be established, and different grades of interaction between common or rare genetic determinants may be present and should be considered. Many different experimental strategies could be investigated in the future, such as analysis of multiple genes in large irradiated patient cohorts strictly observed for radiation effects or identification of new candidate genes, with the aim of identifying factors that could be employed in predictive testing and individualization of radiation therapy on a genetic basis.

The effect of aberrant expression and genetic polymorphisms of Rad21 on cervical cancer biology

The therapeutic challenge of advanced, recurrent, and refractory cervical cancer (CC) needs to develop new molecularly targeted drugs. Rad21 is an important regulatory gene that maintains the correct dissociation of sister chromatids during cell mitosis. The aim of this study was to investigate the effect of Rad21 on CC. Rad21 expression in CC and cervical intraepithelial neoplasia III was significantly increased. Women with the rs2289937 C genotype (CC+CT) of rs4570 and rs4579555 genotypes and haplotype 1 (TTTCAGGCGC) were significantly associated with CC risk, while women with low frequencies of haplotype 6 (TTTTAGGCGC) also increased the risk of CC.Rad21‐specific shRNA decreased cancerous cell proliferation, migration, and invasion and increased the proportion of cells in G2/M phase as well as sensitivity to radiation. The Rad21 influenced the expression of XPO1, CyclinB1, CDK1, P21, P27, and P53 through up‐and downregulating the Rad21 expression. The TCGA database of CC also showed that Rad21 expression was associated with poor disease survival and XPO1 expression. Moreover, the KEGG pathway indicated that Rad21 is broadly involved in the cell cycle and RNA transportation via XPO1. This suggests that Rad21 involves the development of cervical cancer possibly by participating in the regulation of cell cycle and the nuclear output of the tumor suppressor gene via XPO1.

Non-homologous end-joining protein expression screen from radiosensitive cancer patients yields a novel DNA double strand break repair phenotype

BACKGROUND

Clinical radiosensitivity is a significant impediment to tumour control and cure, in that it restricts the total doses which can safely be delivered to the whole radiotherapy population, within the tissue tolerance of potentially radiosensitive (RS) individuals. Understanding its causes could lead to personalization of radiotherapy.

METHODS

We screened tissues from a unique bank of RS cancer patients for expression defects in major DNA double-strand break repair proteins, using Western blot analysis and subsequently reverse-transcriptase polymerase chain reaction and pulsed-field gel electrophoresis.

RESULTS

We hypothesized that abnormalities in expression of these proteins may explain the radiosensitivity of some of our cancer patients. The cells from one patient showed a reproducibly consistent expression reduction in two complex-forming DNA double-strand break repair protein components (DNA Ligase IV and XRCC4). We also showed a corresponding reduction in both gene products at the mRNA level. Additionally, the mRNA inducibility by ionizing radiation was increased for one of the proteins in the patient's cells. We confirmed the likely functional significance of the non-homologous end-joining (NHEJ) expression abnormalities with a DNA double strand break (DNA DSB) repair assay.

CONCLUSIONS

We have identified a novel biological phenotype linked to clinical radiosensitivity. This is important in that very few molecular defects are known in human radiotherapy subjects. Such knowledge may contribute to the understanding of radiation response mechanisms in cancer patients and to personalization of radiotherapy.

In vitro prediction of breast cancer therapy toxicity

BACKGROUND

Understanding the basis of clinical radiosensitivity is a key goal of radiation research. In this study, we used the limiting dilution assay (LDA) to analyze in vitro radiosensitivity of cell lines from individuals with breast and other cancers, who had been treated with ionizing radiation, and who either had a non-radiosensitive (RS) radiation response or who were clinically RS.

METHODS

Lymphoblastoid cell lines (LCLs) were created from 29 cancer patients including 19 RS patients, 10 controls who had not developed severe normal tissue reactions, and 1 ataxia telangiectasia RS control cell line. The clinically RS patients had grade 3 or grade 4 reactions; one had a grade 2 reaction. All cells were exposed to graded doses of gamma-radiation in vitro and cell survival assessed via LDA. Cell survival was expressed on non-linear regression analysis-fitted survival curves and also as the surviving fraction at 2 Gray (Gy) (SF₂).

RESULTS

Our LDA analysis yielded two notable positive results. Firstly, it could distinguish control cells from cells from pooled breast cancer cases with severe reactions of all types (acute reactors, consequential late reactors and late reactors). Secondly, two radiosensitivity outliers were detected on the fitted curves, corresponding clinically to grade 3 and 4 late radiation reactions in breast and head and neck cancer cases respectively. The assay showed considerable cell survival heterogeneity.

CONCLUSIONS

The LDA as used here may provide unique clinical utility in detecting potential RS breast cancer patients prior to radiotherapy (RT), a form of personalized medicine. The assay may be especially useful in situations where its results can be temporally available prior to therapy initiation (e.g., those patients not undergoing RT until some months after surgery, typically those having adjuvant chemotherapy prior to RT). Two LCLs from RS outliers could potentially yield insight into the cellular and/or genetic basis of radiosensitivity, for example by undertaking genomic analyses on these cell lines.

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

BACKGROUND AND PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSION

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

Intragenic controls utilizing radiation-induced alternative transcript regions improves gene expression biodosimetry

Ionizing-radiation exposure can be life threatening if given to the whole body. In addition, whole body radiation exposure can affect large numbers of people such as after a nuclear reactor accident, a nuclear explosion or a radiological terrorist attack. In these cases, an accurate biodosimeter is essential for triage management. One of the problems for biodosimetry in general is the interindividual variation before and after exposure, which can make it challenging to assign an accurate dose. To begin to address this challenge, lymphocyte cell lines were exposed to 0, 1, 2 and 5 Gy ionizing radiation from a ¹³⁷Cs source at a dose rate of 0.6 Gy/min. Alternative transcripts with regions showing large differential responses to ionizing radiation were determined from exon array data. Gene expression analysis was then performed on isolated mRNA using qRT-PCR with normalization to intergenic (PGK1, GAPDH) and novel intragenic regions for candidate radiation-responsive genes, PPM1D and MDM2. Our studies show that the use of a cis-associated expression reference improved the potential dose prediction approximately 2.3-8.3 fold and provided an advantage for dose prediction compared to distantly or trans-located control ionizing radiation nonresponsive genes. This approach also provides an alternative gene expression normalization method to potentially reduce interindividual variations when untreated basal gene expression levels are unavailable. Using associated noninduced regions of ionizing radiation-induced genes provides a way to estimate basal gene expression in the irradiated sample. This strategy can be utilized as a biodosimeter on its own or to enhance other gene expression candidates for biodosimetry. This normalization strategy may also be generally applicable for other quantitative PCR strategies where normalization is required for a particular response.

Two novel RAD21 mutations in patients with mild Cornelia de Lange syndrome-like presentation and report of the first familial case

Cornelia de Lange syndrome (CdLS) is a developmental disorder characterized by limb reduction defects, characteristic facial features and impaired cognitive development. Mutations in the NIPBL gene predominate; however, mutations in other cohesin complex genes have also been implicated, particularly in atypical and mild CdLS cases. Missense mutations and whole gene deletions in RAD21 have been identified in children with growth retardation, minor skeletal anomalies and facial features that overlap findings in individuals with CdLS. We report the first intragenic deletion and frameshift mutations identified in RAD21 in two patients presenting with atypical CdLS. One patient had an in-frame deletion of exon 13, while the second patient had a c.592_593dup frameshift mutation. The first patient presented with developmental delay, hypospadias, inguinal hernia and dysmorphic features while, the second patient presented with developmental delay, characteristic facial features, hirsutism, and hand and feet anomalies, with the first patient being milder than the second. The in-frame deletion mutation was found to be inherited from the mother who had a history of melanoma and other unspecified medical problems. This study expands the spectrum of RAD21 mutations and emphasizes the clinical utility of performing RAD21 mutation analysis in patients presenting with atypical forms of CdLS. Moreover, the variability of clinical presentation within families and low penetrance of mutations as well as the significance of performing molecular genetic testing in mildly affected patients are discussed.

Follistatin is induced by ionizing radiation and potentially predictive of radiosensitivity in radiation-induced fibrosis patient derived fibroblasts

Follistatin is a potent regulator of the inflammatory response and binds to and inhibits activin A action. Activin A is a member of the TGFβ protein superfamily which has regulatory roles in the inflammatory response and in the fibrotic process. Fibrosis can occur following cell injury and cell death induced by agents such as ionizing radiation (IR). IR is used to treat cancer and marked fibrotic response is a normal tissue (non-tumour) consequence in a fraction of patients under the current dose regimes. The discovery and development of a therapeutic to abate fibrosis in these radiosensitive patients would be a major advance for cancer radiotherapy. Likewise, prediction of which patients are susceptible to fibrosis would enable individualization of treatment and provide an opportunity for pre-emptive fibrosis control and better tumour treatment outcomes. The levels of activin A and follistatin were measured in fibroblasts derived from patients who developed severe radiation-induced fibrosis following radiotherapy and compared to fibroblasts from patients who did not. Both follistatin and activin A gene expression levels were increased following IR and the follistatin gene expression level was lower in the fibroblasts from fibrosis patients compared to controls at both basal levels and after IR. The major follistatin transcript variants were found to have a similar response to IR and both were reduced in fibrosis patients. Levels of follistatin and activin A secreted in the fibroblast culture medium also increased in response to IR and the relative follistatin protein levels were significantly lower in the samples derived from fibrosis patients. The decrease in the follistatin levels can lead to an increased bioactivity of activin A and hence may provide a useful measurement to identify patients at risk of a severe fibrotic response to IR. Additionally, follistatin, by its ability to neutralise the actions of activin A may be of value as an anti-fibrotic for radiation induced fibrosis.

DNA repair genes: alternative transcription and gene expression at the exon level in response to the DNA damaging agent, ionizing radiation

DNA repair is an essential cellular process required to maintain genomic stability. Every cell is subjected to thousands of DNA lesions daily under normal physiological conditions. Ionizing radiation (IR) is a major DNA damaging agent that can be produced by both natural and man-made sources. A common source of radiation exposure is through its use in medical diagnostics or treatments such as for cancer radiotherapy where relatively high doses are received by patients. To understand the detailed DNA repair gene transcription response to high dose IR, gene expression exon array studies have been performed and the response to radiation in two divergent cell types, lymphoblastoid cell lines and primary fibroblasts, has been examined. These exon arrays detect expression levels across the entire gene, and have the advantage of high sensitivity and the ability to identify alternative transcripts. We found a selection of DNA repair genes, including some not previously reported, that are modulated in response to radiation. Detailed dose and time course kinetics of DNA repair transcription was conducted and results have been validated utilizing PCR methods. Alternative transcription products in response to IR were identified in several DNA repair genes including RRM2B and XPC where alternative initiation sites were found. These investigations have advanced the knowledge about the transcriptional response of DNA repair.

A bioinformatics filtering strategy for identifying radiation response biomarker candidates

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

RAD21 mutations cause a human cohesinopathy

The evolutionarily conserved cohesin complex was originally described for its role in regulating sister-chromatid cohesion during mitosis and meiosis. Cohesin and its regulatory proteins have been implicated in several human developmental disorders, including Cornelia de Lange (CdLS) and Roberts syndromes. Here we show that human mutations in the integral cohesin structural protein RAD21 result in a congenital phenotype consistent with a "cohesinopathy." Children with RAD21 mutations display growth retardation, minor skeletal anomalies, and facial features that overlap findings in individuals with CdLS. Notably, unlike children with mutations in NIPBL, SMC1A, or SMC3, these individuals have much milder cognitive impairment than those with classical CdLS. Mechanistically, these mutations act at the RAD21 interface with the other cohesin proteins STAG2 and SMC1A, impair cellular DNA damage response, and disrupt transcription in a zebrafish model. Our data suggest that, compared to loss-of-function mutations, dominant missense mutations result in more severe functional defects and cause worse structural and cognitive clinical findings. These results underscore the essential role of RAD21 in eukaryotes and emphasize the need for further understanding of the role of cohesin in human development.

Independent validation of genes and polymorphisms reported to be associated with radiation toxicity: a prospective analysis study

BACKGROUND

Several studies have reported associations between radiation toxicity and single nucleotide polymorphisms (SNPs) in candidate genes. Few associations have been tested in independent validation studies. This prospective study aimed to validate reported associations between genotype and radiation toxicity in a large independent dataset.

METHODS

92 (of 98 attempted) SNPs in 46 genes were successfully genotyped in 1613 patients: 976 received adjuvant breast radiotherapy in the Cambridge breast IMRT trial (ISRCTN21474421, n=942) or in a prospective study of breast toxicity at the Christie Hospital, Manchester, UK (n=34). A further 637 received radical prostate radiotherapy in the MRC RT01 multicentre trial (ISRCTN47772397, n=224) or in the Conventional or Hypofractionated High Dose Intensity Modulated Radiotherapy for Prostate Cancer (CHHiP) trial (ISRCTN97182923, n=413). Late toxicity was assessed 2 years after radiotherapy with a validated photographic technique (patients with breast cancer only), clinical assessment, and patient questionnaires. Association tests of genotype with overall radiation toxicity score and individual endpoints were undertaken in univariate and multivariable analyses. At a type I error rate adjusted for multiple testing, this study had 99% power to detect a SNP, with minor allele frequency of 0·35, associated with a per allele odds ratio of 2·2.

FINDINGS

None of the previously reported associations were confirmed by this study, after adjustment for multiple comparisons. The p value distribution of the SNPs tested against overall toxicity score was not different from that expected by chance.

INTERPRETATION

We did not replicate previously reported late toxicity associations, suggesting that we can essentially exclude the hypothesis that published SNPs individually exert a clinically relevant effect. Continued recruitment of patients into studies within the Radiogenomics Consortium is essential so that sufficiently powered studies can be done and methodological challenges addressed.

FUNDING

Cancer Research UK, The Royal College of Radiologists, Addenbrooke's Charitable Trust, Breast Cancer Campaign, Cambridge National Institute of Health Research (NIHR) Biomedical Research Centre, Experimental Cancer Medicine Centre, East Midlands Innovation, the National Cancer Institute, Joseph Mitchell Trust, Royal Marsden NHS Foundation Trust, Institute of Cancer Research NIHR Biomedical Research Centre for Cancer.

Alternative transcript initiation and splicing as a response to DNA damage

Humans are exposed to the DNA damaging agent, ionizing radiation (IR), from background radiation, medical treatments, occupational and accidental exposures. IR causes changes in transcription, but little is known about alternative transcription in response to IR on a genome-wide basis. These investigations examine the response to IR at the exon level in human cells, using exon arrays to comprehensively characterize radiation-induced transcriptional expression products. Previously uncharacterized alternative transcripts that preferentially occur following IR exposure have been discovered. A large number of genes showed alternative transcription initiation as a response to IR. Dose-response and time course kinetics have also been characterized. Interestingly, most genes showing alternative transcript induction maintained these isoforms over the dose range and times tested. Finally, clusters of co-ordinately up- and down-regulated radiation response genes were identified at specific chromosomal loci. These data provide the first genome-wide view of the transcriptional response to ionizing radiation at the exon level. This study provides novel insights into alternative transcripts as a mechanism for response to DNA damage and cell stress responses in general.

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.

Identification of SNPs associated with susceptibility for development of adverse reactions to radiotherapy

Although cancer treatment with radiation can produce high cure rates, adverse effects often result from radiotherapy. These toxicities are manifested as damage to normal tissues and organs in the radiation field. In recognition of the substantial variation in the intrinsic response of individuals to radiation, an effort began approximately 10 years ago to discover the genetic markers, primarily SNPs, which are associated with susceptibility for the development of these adverse responses to radiation therapy. The goal of this research is to identify the SNPs that could serve as the basis of an assay to predict which cancer patients are most likely to develop complications resulting from radiotherapy. This would permit personalization and optimization of the treatment plan for each cancer patient.

Lymphoid and fibroblastic cell lineages from radiosensitive cancer patients: molecular analysis of DNA double strand break repair by major non-homologous end-joining sub-pathways

AIMS

Radiation therapy (RT) is used in the treatment of approximately half of all cancer patients. Although there have been great improvements in tumor localization and the technical accuracy of RT delivery, some RT patients still have idiosyncratic hypersensitivity to ionizing radiation (IR) in their normal tissues. Although much effort has been expended in the search for assays that could detect radiosensitive individuals prior to treatment and facilitate tailored therapy; a suitable and clinically practical predictive assay has yet to be realized. Since DNA double-strand breaks (DSB) are a major lesion caused by IR, we hypothesized that radiation hypersensitive individuals might be deficient in the repair of such lesions.

METHODS

To test this hypothesis we quantitatively and functionally characterized DSB repair of the two major non-homologous end-joining (NHEJ) sub-pathways in a pilot study using a plasmid repair reconstitution assay in lymphoblastoid and fibroblast cell lines from radiosensitive cancer patients and controls. Experiments using well-characterized mammalian DSB repair mutants demonstrated the ability of the assay to distinguish NHEJ sub-pathways. The proportion of direct end-joining repair compared with that of microhomology-directed repair was used as a functional end-point of DSB repair competence in the different cell lines.

RESULTS

We found that the overall level of NHEJ sub-pathway repair competency was similar in cell lines from radiosensitive patients and controls.

CONCLUSION

These data suggest that this assay in these cell lineages has limited usefulness as a predictive screen for the endogenous DNA DSB repair competency of radiosensitive cancer patients' cells but can usefully characterize major cellular DSB repair phenotypes.

Methylproamine protects against ionizing radiation by preventing DNA double-strand breaks

PURPOSE

The majority of cancer patients will receive radiotherapy (RT), therefore, investigations into advances of this modality are important. Conventional RT dose intensities are limited by adverse responses in normal tissues and a primary goal is to ameliorate adverse normal tissue effects. The aim of these experiments is to further our understanding regarding the mechanism of radioprotection by the DNA minor groove binder, methylproamine, in a cellular context at the DNA level.

MATERIALS AND METHODS

We used immunocytochemical methods to measure the accumulation of phosphorylated H2AX (γH2AX) foci following ionizing radiation (IR) in patient-derived lymphoblastoid cells exposed to methylproamine. Furthermore, we performed pulsed field gel electrophoresis DNA damage and repair assays to directly interrogate the action of methylproamine on DNA in irradiated cells.

RESULTS

We found that methylproamine-treated cells had fewer γH2AX foci after IR compared to untreated cells. Also, the presence of methylproamine decreased the amount of lower molecular weight DNA entering the gel as shown by the pulsed field gel electrophoresis assay.

CONCLUSIONS

These results suggest that methylproamine acts by preventing the formation of DNA double-strand breaks (dsbs) and support the hypothesis that radioprotection by methylproamine is mediated, at least in part, by decreasing initial DNA damage.

Expression of RAD51, BRCA1 and P53 does not correlate with cellular radiosensitivity of normal human fibroblasts

AIMS

To evaluate the potential role of key DNA repair proteins in the sensitivity of normal human fibroblasts to ionising radiations.

METHODS

Radiosensitivity of six human fibroblast strains established from skin biopsies of women who had undergone conservative breast surgery and received a curative breast conserving radiotherapy was measured by colony-formation assay. The expression level of RAD51, BRCA1 and p53 proteins were studied using western blot analysis.

RESULTS

The six fibroblast strains represent a typical spectrum of normal human radiosensitivity with the surviving fraction measured for a dose of 3.5 Gy (SF3.5) ranging from 0.21 to 0.40. We found that these differences in cell survival did not correlate with the expression of RAD51, BRCA1 nor p53 in the tested normal human fibroblast strains.

CONCLUSIONS

We conclude that measurement of protein expression of the three tested genes (RAD51, BRCA1 and p53) did not reflect sensitivity of normal fibroblasts to IR.

Rad21-cohesin haploinsufficiency impedes DNA repair and enhances gastrointestinal radiosensitivity in mice

Approximately half of cancer-affected patients receive radiotherapy (RT). The doses delivered have been determined upon empirical experience based upon average radiation responses. Ideally higher curative radiation doses might be employed in patients with genuinely normal radiation responses and importantly radiation hypersensitive patients would be spared the consequences of excessive tissue damage if they were identified before treatment. Rad21 is an integral subunit of the cohesin complex, which regulates chromosome segregation and DNA damage responses in eukaryotes. We show here, by targeted inactivation of this key cohesin component in mice, that Rad21 is a DNA-damage response gene that markedly affects animal and cell survival. Biallelic deletion of Rad21 results in early embryonic death. Rad21 heterozygous mutant cells are defective in homologous recombination (HR)-mediated gene targeting and sister chromatid exchanges. Rad21+/- animals exhibited sensitivity considerably greater than control littermates when challenged with whole body irradiation (WBI). Importantly, Rad21+/- animals are significantly more sensitive to WBI than Atm heterozygous mutant mice. Since supralethal WBI of mammals most typically leads to death via damage to the gastrointestinal tract (GIT) or the haematopoietic system, we determined the functional status of these organs in the irradiated animals. We found evidence for GIT hypersensitivity of the Rad21 mutants and impaired bone marrow stem cell clonogenic regeneration. These data indicate that Rad21 gene dosage is critical for the ionising radiation (IR) response. Rad21 mutant mice thus represent a new mammalian model for understanding the molecular basis of irradiation effects on normal tissues and have important implications in the understanding of acute radiation toxicity in normal tissues.

Testicular cancer survivorship: research strategies and recommendations

Testicular cancer represents the most curable solid tumor, with a 10-year survival rate of more than 95%. Given the young average age at diagnosis, it is estimated that effective treatment approaches, in particular, platinum-based chemotherapy, have resulted in an average gain of several decades of life. This success, however, is offset by the emergence of considerable long-term morbidity, including second malignant neoplasms, cardiovascular disease, neurotoxicity, nephrotoxicity, pulmonary toxicity, hypogonadism, decreased fertility, and psychosocial problems. Data on underlying genetic or molecular factors that might identify those patients at highest risk for late sequelae are sparse. Genome-wide association studies and other translational molecular approaches now provide opportunities to identify testicular cancer survivors at greatest risk for therapy-related complications to develop evidence-based long-term follow-up guidelines and interventional strategies. We review research priorities identified during an international workshop devoted to testicular cancer survivors. Recommendations include 1) institution of lifelong follow-up of testicular cancer survivors within a large cohort setting to ascertain risks of emerging toxicities and the evolution of known late sequelae, 2) development of comprehensive risk prediction models that include treatment factors and genetic modifiers of late sequelae, 3) elucidation of the effect(s) of decades-long exposure to low serum levels of platinum, 4) assessment of the overall burden of medical and psychosocial morbidity, and 5) the eventual formulation of evidence-based long-term follow-up guidelines and interventions. Just as testicular cancer once served as the paradigm of a curable malignancy, comprehensive follow-up studies of testicular cancer survivors can pioneer new methodologies in survivorship research for all adult-onset cancer.

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.

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.

Single nucleotide polymorphism at rs1982073:T869C of the TGFbeta 1 gene is associated with the risk of radiation pneumonitis in patients with non-small-cell lung cancer treated with definitive radiotherapy

PURPOSE

In search of reliable biologic markers to predict the risk of normal tissue damage by radio(chemo)therapy before treatment, we investigated the association between single nucleotide polymorphisms (SNPs) in the transforming growth factor 1 (TGFbeta1) gene and risk of radiation pneumonitis (RP) in patients with non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Using 164 available genomic DNA samples from patients with NSCLC treated with definitive radio(chemo)therapy, we genotyped three SNPs of the TGFbeta1 gene (rs1800469:C-509T, rs1800471:G915C, and rs1982073:T869C) by polymerase chain reaction restriction fragment length polymorphism method. We used Kaplan-Meier cumulative probability to assess the risk of grade > or = 3 RP and Cox proportional hazards analyses to evaluate the effect of TGFbeta1 genotypes on such risk.

RESULTS

There were 90 men and 74 women in the study, with median age of 63 years. Radiation doses ranging from 60 to 70 Gy (median = 63 Gy) in 30 to 58 fractions were given to 158 patients (96.3%) and platinum-based chemotherapy to 147 (89.6%). Grade > or = 2 and grade > or = 3 RP were observed in 74 (45.1%) and 36 patients (22.0%), respectively. Multivariate analysis found CT/CC genotypes of TGFbeta1 rs1982073:T869C to be associated with a statistically significantly lower risk of RP grades > or = 2 (hazard ratio [HR] = 0.489; 95% CI, 0.227 to 0.861; P = .013) and grades > or = 3 (HR = 0.390; 95% CI, 0.197 to .774; P = 0.007), respectively, compared with the TT genotype, after adjustment for Karnofsky performance status, smoking status, pulmonary function, and dosimetric parameters.

CONCLUSION

Our results showed that CT/CC genotypes of TGFbeta1 rs1982073:T869C gene were associated with lower risk of RP in patients with NSCLC treated with definitive radio(chemo)therapy and thus may serve as a reliable predictor of RP.

IL12RB2 and ABCA1 genes are associated with susceptibility to radiation dermatitis

PURPOSE

Severe acute radiation dermatitis is observed in approximately 5% to 10% of patients who receive whole-breast radiotherapy. Several factors, including treatment-related and patient-oriented factors, are involved in susceptibility to severe dermatitis. Genetic factors are also thought to be related to a patient's susceptibility to severe dermatitis. To elucidate genetic polymorphisms associated with a susceptibility to radiation-induced dermatitis, a large-scale single-nucleotide polymorphism (SNP) analysis using DNA samples from 156 patients with breast cancer was conducted.

EXPERIMENTAL DESIGN

Patients were selected from more than 3,000 female patients with early breast cancer who received radiotherapy after undergoing breast-conserving surgery. The dermatitis group was defined as patients who developed dermatitis at a National Cancer Institute Common Toxicity Criteria grade of > or =2. For the SNP analysis, DNA samples from each patient were subjected to the genotyping of 3,144 SNPs covering 494 genes.

RESULTS

SNPs that mapped to two genes, ABCA1 and IL12RB2, were associated with radiation-induced dermatitis. In the ABCA1 gene, one of these SNPs was a nonsynonymous coding SNP causing R219K (P = 0.0065). As for the IL12RB2 gene, the strongest association was observed at SNP-K (rs3790568; P = 0.0013). Using polymorphisms of both genes, the probability of severe dermatitis was estimated for each combination of genotypes. These analyses showed that individuals carrying a combination of genotypes accounting for 14.7% of the Japanese population have the highest probability of developing radiation-induced dermatitis.

CONCLUSION

Our results shed light on the mechanisms responsible for radiation-induced dermatitis. These results may also contribute to the individualization of radiotherapy.

Single nucleotide polymorphisms, apoptosis, and the development of severe late adverse effects after radiotherapy

PURPOSE

Evidence has accumulated in recent years suggestive of a genetic basis for a susceptibility to the development of radiation injury after cancer radiotherapy. The purpose of this study was to assess whether patients with severe radiation-induced sequelae (RIS; i.e., National Cancer Institute/CTCv3.0 grade, > or =3) display both a low capacity of radiation-induced CD8 lymphocyte apoptosis (RILA) in vitro and possess certain single nucleotide polymorphisms (SNP) located in candidate genes associated with the response of cells to radiation.

EXPERIMENTAL DESIGN

DNA was isolated from blood samples obtained from patients (n = 399) included in the Swiss prospective study evaluating the predictive effect of in vitro RILA and RIS. SNPs in the ATM, SOD2, XRCC1, XRCC3, TGFB1, and RAD21 genes were screened in patients who experienced severe RIS (group A, n = 16) and control subjects who did not manifest any evidence of RIS (group B, n = 18).

RESULTS

Overall, 13 and 21 patients were found to possess a total of <4 and > or =4 SNPs in the candidate genes. The median (range) RILA in group A was 9.4% (5.3-16.5) and 94% (95% confidence interval, 70-100) of the patients (15 of 16) had > or =4 SNPs. In group B, median (range) RILA was 25.7% (20.2-43.2) and 33% (95% confidence interval, 13-59) of patients (6 of 18) had > or =4 SNPs (P < 0.001).

CONCLUSIONS

The results of this study suggest that patients with severe RIS possess 4 or more SNPs in candidate genes and low radiation-induced CD8 lymphocyte apoptosis in vitro.

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.

Predicting Risk of Radiation-Induced Lung Injury

Radiation-induced lung injury (RILI) is the most common, dose-limiting complication of thoracic radio- and radiochemotherapy. Unfortunately, predicting which patients will suffer from this complication is extremely difficult. Ideally, individual phenotype- and genotype-based risk profiles should be able to identify patients who are resistant to RILI and who could benefit from dose escalation in chemoradiotherapy. This could result in better local control and overall survival. We review the risk predictors that are currently in clinical use--dosimetric parameters of radiotherapy such as normal tissue complication probability, mean lung dose, V20 and V30--as well as biomarkers that might individualize risk profiles. These biomarkers comprise a variety of proinflammatory and profibrotic cytokines and molecules including transforming growth factor beta1 that are implicated in development and persistence of RILI. Dosimetric parameters of radiotherapy show a low negative predictive value of 60% to 80%. Depending on the studied molecule, negative predictive value of biomarkers is approximately 50%. The predictive power of biomarkers might be increased if they are coupled with radiogenomics, e.g., genotyping analysis of single nucleotide polymorphisms in transforming growth factor beta1, transforming growth factor beta1 pathway genes, and other cytokines. Genetic variability and the complexity of RILI and its underlying molecular mechanisms make identification of biological risk predictors challenging. Further investigations are needed to develop more effective risk predictors of RILI.

Possession of ATM sequence variants as predictor for late normal tissue responses in breast cancer patients treated with radiotherapy

PURPOSE

The ATM gene product is a central component of cell cycle regulation and genomic surveillance. We hypothesized that DNA sequence alterations in ATM predict for adverse effects after external beam radiotherapy for early breast cancer.

METHODS AND MATERIALS

A total of 131 patients with a minimum of 2 years follow-up who had undergone breast-conserving surgery and adjuvant radiotherapy were screened for sequence alterations in ATM using DNA from blood lymphocytes. Genetic variants were identified using denaturing high performance liquid chromatography. The Radiation Therapy Oncology Group late morbidity scoring schemes for skin and subcutaneous tissues were applied to quantify the radiation-induced effects.

RESULTS

Of the 131 patients, 51 possessed ATM sequence alterations located within exons or in short intron regions flanking each exon that encompass putative splice site regions. Of these 51 patients, 21 (41%) exhibited a minimum of a Grade 2 late radiation response. In contrast, of the 80 patients without an ATM sequence variation, only 18 (23%) had radiation-induced adverse responses, for an odds ratio of 2.4 (95% confidence interval, 1.1-5.2). Fifteen patients were heterozygous for the G-->A polymorphism at nucleotide 5557, which causes substitution of asparagine for aspartic acid at position 1853 of the ATM protein. Of these 15 patients, 8 (53%) exhibited a Grade 2-4 late response compared with 31 (27%) of the 116 patients without this alteration, for an odds ratio of 3.1 (95% confidence interval, 1.1-9.4).

CONCLUSION

Sequence variants located in the ATM gene, in particular the 5557 G-->A polymorphism, may predict for late adverse radiation responses in breast cancer patients.

Characterization of a 3;6 translocation associated with renal cell carcinoma

The most frequent cause of familial clear cell renal cell carcinoma (RCC) is von Hippel-Lindau disease and the VHL tumor suppressor gene (TSG) is inactivated in most sporadic clear cell RCC. Although there is relatively little information on the mechanisms of tumorigenesis of clear cell RCC without VHL inactivation, a subset of familial cases harbors a balanced constitutional chromosome 3 translocation. To date nine different chromosome 3 translocations have been associated with familial or multicentric clear cell RCC; and in three cases chromosome 6 was also involved. To identify candidate genes for renal tumorigenesis we characterized a constitutional translocation, t(3;6)(q22;q16.1) associated with multicentric RCC without evidence of VHL target gene dysregulation. Analysis of breakpoint sequences revealed a 1.3-kb deletion on chromosome 6 within the intron of a 2 exon predicted gene (NT_007299.434). However, RT-PCR analysis failed to detect the expression of this gene in lymphoblast, fibroblast, or kidney tumor cell lines. No known genes were disrupted by the translocation breakpoints but several candidate TSGs (e.g., EPHB1, EPHA7, PPP2R3A RNF184, and STAG1) map within close proximity to the breakpoints.

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.

Association of DNA repair and steroid metabolism gene polymorphisms with clinical late toxicity in patients treated with conformal radiotherapy for prostate cancer

OBJECTIVE

To explore the possible relationship between single nucleotide polymorphisms (SNP) in candidate genes encoding DNA damage recognition/repair/response and steroid metabolism proteins with respect to clinical radiation toxicity in a retrospective cohort of patients previously treated with three-dimensional conformal radiotherapy (3-DCRT) for prostate cancer.

EXPERIMENTAL DESIGN

One hundred twenty-four patients with prostate cancer underwent 3-DCRT at our institution between September 1996 and December 2000. Of these, 83 consented for follow-up of blood sampling and SNP analysis. Twenty-eight patients were documented as having experienced grade >/=2 late bladder or rectal toxicity (scoring system of Radiation Therapy Oncology Group) on at least one follow-up visit. We analyzed 49 SNPs in BRCA1, BRCA2, ESR1, XRCC1, XRCC2, XRCC3, NBN, RAD51, RAD52, LIG4, ATM, BCL2, TGFB1, MSH6, ERCC2, XPF, NR3C1, CYP1A1, CYP2C9, CYP2C19, CYP3A5, CYP2D6, CYP11B2, and CYP17A1 genes using the Pyrosequencing technique.

RESULTS

Significant univariate associations with late rectal or bladder toxicity (grade >/=2) were found for XRCC3 (A>G 5' untranslated region NT 4541), LIG4 (T>C Asp(568)Asp), MLH1 (C>T, Val(219)Ile), CYP2D6*4 (G>A splicing defect), mean rectal and bladder dose, dose to 30% of rectum or bladder, and age <60 years. On Cox multivariate analysis, significant associations with toxicity were found for LIG4 (T>C, Asp(568)Asp), ERCC2 (G>A, Asp(711)Asp), CYP2D6*4 (G>A, splicing defect), mean bladder dose >60 Gy, and dose to 30% of rectal volume >75 Gy.

CONCLUSIONS

In this study, we identified SNPs in LIG4, ERCC2, and CYP2D6 genes as putative markers to predict individuals at risk for complications arising from radiation therapy in prostate cancer.

Genetic predictors of adverse radiotherapy effects: the Gene-PARE project

PURPOSE

The development of adverse effects resulting from the radiotherapy of cancer limits the use of this treatment modality. The validation of a test capable of predicting which patients would be most likely to develop adverse responses to radiation treatment, based on the possession of specific genetic variants, would therefore be of value. The purpose of the Genetic Predictors of Adverse Radiotherapy Effects (Gene-PARE) project is to help achieve this goal.

METHODS AND MATERIALS

A continuously expanding biorepository has been created consisting of frozen lymphocytes and DNA isolated from patients treated with radiotherapy. In conjunction with this biorepository, a database is maintained with detailed clinical information pertaining to diagnosis, treatment, and outcome. The DNA samples are screened using denaturing high performance liquid chromatography (DHPLC) and the Surveyor nuclease assay for variants in ATM, TGFB1, XRCC1, XRCC3, SOD2, and hHR21. It is anticipated that additional genes that control the biologic response to radiation will be screened in future work.

RESULTS

Evidence has been obtained that possession of variants in genes, the products of which play a role in radiation response, is predictive for the development of adverse effects after radiotherapy.

CONCLUSIONS

It is anticipated that the Gene-PARE project will yield information that will allow radiation oncologists to use genetic data to optimize treatment on an individual basis.

Can risk of radiotherapy-induced normal tissue complications be predicted from genetic profiles?

Over the last decade, increasing efforts have been taken to establish associations between various genetic germline alterations and risk of normal tissue complications after radiotherapy. Though the studies have been relatively small and methodologically heterogeneous, preliminary indications have been provided that single nucleotide polymorphisms in the genes TGFB1 and ATM may modulate risk of particularly late toxicity. In addition, rare ATM alterations may enhance complication susceptibility. Nevertheless, we are still far from having an exhaustive understanding of the genetics that may underlie differences in clinical normal tissue radiosensitivity. Recent technical advances and emerging insights to the structure of inter-individual genetic variation open up unprecedented opportunities to dissect the molecular and genetic basis of normal tissue radiosensitivity. However, to fully exploit these new possibilities well-planed large-scale clinical studies are mandatory. Currently, international initiatives are taken to establish the bio banks and databases needed for this task.

ATM sequence variants and risk of radiation-induced subcutaneous fibrosis after postmastectomy radiotherapy

PURPOSE

To examine the hypothesis that women who are carriers of genetic alterations in the ATM gene are more likely to develop subcutaneous fibrosis after radiotherapy for treatment of breast cancer compared with patients who do not possess DNA sequence variations in this gene.

METHODS AND MATERIALS

DNA samples isolated from fibroblast cell lines established from 41 women treated with postmastectomy radiotherapy for breast cancer were screened for genetic variants in ATM using denaturing high-performance liquid chromatography (DHPLC). A minimum follow-up of 2 years enabled analysis of late effects to generate dose-response curves and to estimate the dose that resulted in a 50% incidence of Grade 3 fibrosis (ED50).

RESULTS

A total of 26 genetic alterations in the expressed portions of the ATM gene, or within 10 bases of each exon in regions encompassing putative splice sites, were detected in 22 patients. The ED50 (95% confidence interval) of 60.2 (55.7-65.1) Gy calculated for patients without a sequence variation did not differ significantly from the ED50 of 58.4 (54.0-63.1) Gy for the group of patients with any ATM sequence abnormality. The ED50 of 53.7 (50.2-57.5) Gy for those patients who were either homozygous or heterozygous for the G-->A polymorphism at nucleotide 5557, which results in substitution of asparagine for aspartic acid at position 1853 of the ATM protein, was substantially lower than the ED50 of 60.8 (57.0-64.8) Gy for patients not carriers of this sequence alteration. This resulted in an enhancement ratio (ratio of the ED50 values) of 1.13 (1.05-1.22), which was significantly greater than unity.

CONCLUSION

The results of this study suggest an association between the ATM codon 1853 Asn/Asp and Asn/Asn genotypes with the development of Grade 3 fibrosis in breast cancer patients treated with radiotherapy.

Microsatellite polymorphisms in DNA repair genes XRCC1, XRCC3 and XRCC5 in patients with gynecological tumors: association with late clinical radiosensitivity and cancer incidence

This study investigates the association of microsatellite polymorphisms in XRCC1, XRCC3 and XRCC5 with the development of late radiation-induced radiotherapy reactions and examines the correlation between these microsatellites and cancer incidence. Sixty-two women with cervical or endometrial cancer treated with radiotherapy were included in the study. According to the CTCAEv3.0 scale, 22 patients showed late adverse radiotherapy reactions (grade 2 or more). PCR on lymphocyte DNA followed by automated fragment analysis was performed to examine the number of tandem repeat units at each locus. No significant association was found between the repeat length at any of the microsatellites in XRCC1, XRCC3 or XRCC5 and the incidence of late radiotherapy complications. Since higher odds ratios (ORs) were found for the rare XRCC1 [AC]11 and [AC]21 repeats (OR = 2.65, P = 0.325 and OR = 8.67, P = 0.093, respectively), the possible involvement of these small and large repeats in clinical radiosensitivity cannot be completely ruled out. When specific numbers of repeats were examined, no significant correlation was found between the microsatellite repeat length in XRCC1 and XRCC5 and cancer incidence. A weak correlation between XRCC3 [AC]16 homozygotes and cancer incidence was found (OR = 2.56, P = 0.055). A large-scale multicenter study of cancer patients with a high number of radiosensitive individuals is needed to clarify the value of rare polymorphic microsatellite repeats in XRCC1 and XRCC3 as a biomarker of clinical radiosensitivity or increased cancer risk.

Chromosomal radiosensitivity in two cell lineages derived from clinically radiosensitive cancer patients

PURPOSE

Despite its prominent contribution to cancer cure and palliation, around 1% to 5% of cancer patients suffer serious side effects from radiotherapy. A cardinal goal in the fields of radiobiology and oncology is to predict normal tissue radiosensitivity of a cancer patient before radiotherapy. Higher tumor control rates are likely if radiotherapy individualization could be achieved by applying predictive approaches.

EXPERIMENTAL DESIGN

Here, we make use of the cytokinesis block micronucleus assay to assess radiosensitivity in cell lines derived from two different cell lineages obtained from clinically radiosensitive patients. We determined the micronucleus frequency after graded doses of ionizing radiation to primary fibroblasts and lymphoblast cell lines derived from 36 highly radiosensitive cancer patients.

RESULTS

Many cell lines, following exposure to ionizing radiation, from patients with severe clinical reactions to radiotherapy showed statistically significantly higher frequencies of micronuclei than those from patients who had normal reactions to radiotherapy. One individual revealed significantly higher micronucleus frequencies in both cell lineages. Interestingly, lymphoblast cell lines from one patient showed micronucleus frequencies similar to ataxia telangiectasia mutated-deficient cells.

CONCLUSIONS

These results indicate that the micronucleus assay may have use for identifying predisposition to clinical radiosensitivity, at least in a subset of patients as a component of a pretreatment radiosensitivity assay for use in the clinic.

Pharmacogenetics for individualized cancer chemotherapy

The same doses of medication cause considerable heterogeneity in efficacy and toxicity across human populations. Genetic factors are thought to represent important determinants of drug efficacy and toxicity. Pharmacogenetics focuses on the prediction of the response of tumor and normal tissue to standard therapy by genetic profiling and, thereby, to select the most appropriate medication at optimal doses for each individual patient. In the present review, we discuss the relevance of single nucleotide polymorphisms (SNP) in genes, whose gene products act upstream of the actual drug target sites, that is, drug transporters and drug metabolizing phase I and II enzymes, or downstream of them, that is, apoptosis-regulating genes and chemokines. SNPs in relevant genes, which encode for proteins that interact with anticancer drugs, were also considered, that is, enzymes of DNA biosynthesis and metabolism, DNA repair enzymes, and proteins of the mitotic spindle. A significant body of evidence supports the concept of predicting drug efficacy and toxicity by SNP genotyping. As the efficacy of cancer chemotherapy, as well as the drug-related toxicity in normal tissues is multifactorial in nature, sophisticated approaches such as genome-wide linkage analyses and integrate drug pathway profiling may improve the predictive power compared with genotyping of single genes. The implementation of pharmacogenetics into clinical routine diagnostics including genotype-based recommendations for treatment decisions and risk assessment for practitioners represents a challenge for the future.

Molecular markers predicting radiotherapy response: report and recommendations from an International Atomic Energy Agency technical meeting

PURPOSE

There is increasing interest in radiogenomics and the characterization of molecular profiles that predict normal tissue and tumor radioresponse. A meeting in Amsterdam was organized by the International Atomic Energy Agency to discuss this topic on an international basis.

METHODS AND MATERIALS

This report is not completely exhaustive, but highlights some of the ongoing studies and new initiatives being carried out worldwide in the banking of tumor and normal tissue samples underpinning the development of molecular marker profiles for predicting patient response to radiotherapy. It is generally considered that these profiles will more accurately define individual or group radiosensitivities compared with the nondefinitive findings from the previous era of cellular-based techniques. However, so far there are only a few robust reports of molecular markers predicting normal tissue or tumor response.

RESULTS

Many centers in different countries have initiated tissue and tumor banks to store samples from clinical trials for future molecular profiling analysis, to identify profiles that predict for radiotherapy response. The European Society for Therapeutic Radiology and Oncology GENEtic pathways for the Prediction of the effects of Irradiation (GENEPI) project, to store, document, and analyze sample characteristics vs. response, is the most comprehensive in this regard.

CONCLUSIONS

The next 5-10 years are likely to see the results of these and other correlative studies, and promising associations of profiles with response should be validated in larger definitive trials.

ATM sequence variants are predictive of adverse radiotherapy response among patients treated for prostate cancer

PURPOSE

To examine whether the presence of sequence variants in the ATM (mutated in ataxia-telangiectasia) gene is predictive for the development of radiation-induced adverse responses resulting from (125)I prostate brachytherapy for early-stage prostate cancer.

MATERIALS AND METHODS

Thirty-seven patients with a minimum of 1-year follow-up who underwent (125)I prostate brachytherapy of early-stage prostate cancer were screened for DNA sequence variations in all 62 coding exons of the ATM gene using denaturing high-performance liquid chromatography. The clinical course and postimplant dosimetry for each genetically characterized patient were obtained from a database of 2,020 patients implanted at Mount Sinai Hospital after 1990.

RESULTS

Twenty-one ATM sequence alterations located within exons, or in short intronic regions flanking each exon, were found in 16 of the 37 patients screened. For this group, 10 of 16 (63%) exhibited at least one form of adverse response. In contrast, of the 21 patients who did not harbor an ATM sequence variation, only 3 of 21 (14%) manifested radiation-induced adverse responses (p = 0.005). Nine of the patients with sequence alterations specifically possessed missense mutations, which encode for amino acid substitutions and are therefore more likely to possess functional importance. For this group, 7 of 9 (78%) exhibited at least one form of adverse response. In contrast, of the 28 patients who did not have a missense alteration, only 6 of 28 (21%) manifested any form of adverse response to the radiotherapy (p = 0.004). Of the patients with missense variants, 5 of 9 (56%) exhibited late rectal bleeding vs. 1 of 28 (4%) without such alterations (p = 0.002). Of those patients who were at risk for developing erectile dysfunction, 5 of 8 (63%) patients with missense mutations developed prospectively evaluated erectile dysfunction as opposed to 2 of 20 (10%) without these sequence alterations (p = 0.009).

CONCLUSIONS

Possession of sequence variants in the ATM gene, particularly those that encode for an amino acid substitution, is predictive for the development of adverse radiotherapy responses among patients treated with (125)I prostate brachytherapy.

The efficacy of hyperbaric oxygen therapy in the treatment of radiation-induced late side effects

PURPOSE

We investigated the efficacy of hyperbaric oxygen therapy (HBOT) in the management of patients with radiation-induced late side effects, the majority of whom had failed previous interventions.

METHODS AND MATERIALS

Of 105 eligible subjects, 30 had either died or were not contactable, leaving 75 who qualified for inclusion in this retrospective study. Patients answered a questionnaire documenting symptom severity before and after treatment (using Radiation Therapy Oncology Group criteria), duration of improvement, relapse incidence, and HBOT-related complications.

RESULTS

The rate of participation was 60% (45/75). Improvement of principal presenting symptoms after HBOT was noted in 75% of head-and-neck, 100% of pelvic, and 57% of "other" subjects (median duration of response of 62, 72, and 68 weeks, respectively). Bone and bladder symptoms were most likely to benefit from HBOT (response rate, 81% and 83%, respectively). Fifty percent of subjects with soft tissue necrosis/mucous membrane side effects improved with HBOT. The low response rate of salivary (11%), neurologic (17%), laryngeal (17%), and upper gastrointestinal symptoms (22%) indicates that these were more resistant to HBOT. Relapse incidence was low (22%), and minor HBOT-related complications occurred in 31% of patients.

CONCLUSION

Hyperbaric oxygen therapy is a safe and effective treatment modality offering durable relief in the management of radiation-induced osteoradionecrosis either alone or as an adjunctive treatment. Radiation soft tissue necrosis, cystitis, and proctitis also seemed to benefit from HBOT, but the present study did not have sufficient numbers to reliably predict long-term response.

Genetic biomarkers of therapeutic radiation sensitivity

The occurrence of acute or late normal tissue reactions after therapeutic radiotherapy and cellular responses in in vitro radiosensitivity assays do not correlate well suggesting that to date no one test system is suitable for predicting the risk or severity of such reactions. New insights into the underlying molecular mechanisms of this sensitivity are coming from studies that assess associations between common polymorphisms in DNA damage detection and repair genes and the development of adverse reactions to radiotherapy. The presence of such variants may alter protein function and an individual's capacity to repair damaged DNA modifying the response of the normal tissue. Polymorphisms in the XRCC1, ATM, hHR21 and TGFbeta1 genes have been shown to be associated with an increased risk of developing an adverse normal tissue reaction to radiotherapy, whilst one variant in the ATM gene has been reported to be radioprotective. Functional studies, taking into account either the haplotypes or the combined genotypes when multiple polymorphisms in a gene are present, will be necessary to establish the mechanistic basis of these associations. In the future association studies can only benefit from the analysis of multiple genes in large, well-characterized cohorts in particular to identify genetic factors that might specifically influence the temporal occurrence of these adverse reactions.

Radiochemotherapy in head and neck cancer

The present paper is based on a talk given, during the meeting of the EORTC Radiotherapy Group, held in Arona (Italy) on April 19-20, 2002. This review analyses many still open questions on combined chemotherapy and radiotherapy in head and neck cancer, on the basis of the available data. The paper may help to point out future directions for novel clinical researches on combined chemotherapy and radiotherapy in head and neck cancer.