Lymphocyte radiosensitivity in BRCA1 and BRCA2 mutation carriers and implications for breast cancer susceptibility

Towards targeting the breast cancer immune microenvironment

The tumour immune microenvironment is shaped by the crosstalk between cancer cells, immune cells, fibroblasts, endothelial cells and other stromal components. Although the immune tumour microenvironment (TME) serves as a source of therapeutic targets, it is also considered a friend or foe to tumour-directed therapies. This is readily illustrated by the importance of T cells in triple-negative breast cancer (TNBC), culminating in the advent of immune checkpoint therapy in combination with cytotoxic chemotherapy as standard of care for both early and advanced-stage TNBC, as well as recent promising signs of efficacy in a subset of hormone receptor-positive disease. In this Review, we discuss the various components of the immune TME in breast cancer and therapies that target or impact the immune TME, as well as the complexity of host physiology.

Assessing BRCA1 activity in DNA damage repair using human induced pluripotent stem cells as an approach to assist classification of BRCA1 variants of uncertain significance

Establishing a universally applicable protocol to assess the impact of BRCA1 variants of uncertain significance (VUS) expression is a problem which has yet to be resolved despite major progresses have been made. The numerous difficulties which must be overcome include the choices of cellular models and functional assays. We hypothesised that the use of induced pluripotent stem (iPS) cells might facilitate the standardisation of protocols for classification, and could better model the disease process. We generated eight iPS cell lines from patient samples expressing either BRCA1 pathogenic variants, non-pathogenic variants, or BRCA1 VUSs. The impact of these variants on DNA damage repair was examined using a ɣH2AX foci formation assay, a Homologous Repair (HR) reporter assay, and a chromosome abnormality assay. Finally, all lines were tested for their ability to differentiate into mammary lineages in vitro. While the results obtained from the two BRCA1 pathogenic variants were consistent with published data, some other variants exhibited differences. The most striking of these was the BRCA1 variant Y856H (classified as benign), which was unexpectedly found to present a faulty HR repair pathway, a finding linked to the presence of an additional variant in the ATM gene. Finally, all lines were able to differentiate first into mammospheres, and then into more advanced mammary lineages expressing luminal- or basal-specific markers. This study stresses that BRCA1 genetic analysis alone is insufficient to establish a reliable and functional classification for assessment of clinical risk, and that it cannot be performed without considering the other genetic aberrations which may be present in patients. The study also provides promising opportunities for elucidating the physiopathology and clinical evolution of breast cancer, by using iPS cells.

Breast Cancer Adjuvant Radiotherapy in BRCA1/2, TP53, ATM Genes Mutations: Are There Solved Issues?

BRCA1, BRCA2, TP53 and ATM gene mutations are the most studied tumour suppressor genes (TSGs) influencing the loco-regional approach to breast cancer (BC). Due to altered radio sensitivity of mutated cancer cells, mastectomy has always been advised in most patients with BC linked to TSGs mutations in order to avoid or minimize the use of adjuvant radiotherapy (ART). Whether ART is safe or not in these carriers is still debated. As a result, this issue has been widely discussed in the recent ASTRO and ASCO papers, yielding important and useful recommendations on the use of ART according to the mutational status. In this review, we have highlighted the impact of these mutations on local control, toxicities, second tumors, and contralateral breast cancers (CBCs) after ART to solve remaining doubts and encourage the safe use of ART when indicated.

Management of Fanconi Anemia patients with head and neck carcinoma: Diagnosis and treatment adaptation

Fanconi anemia (FA) is a rare genetic disease that is mostly transmitted, according to a recessive model with biallelic germline alterations in one of the 22 genes of the FA pathway, or monoallelic alteration of the 23rd FA gene (RAD51). The FA pathway is implicated in interstrand DNA crosslink repair, induces genome stability, and is a potent driver of tumorigenesis. Patients with FA have a 500 to 1000-fold increased risk of developing head and neck squamous cell carcinoma (HNSCC). Patients with FA developing an HNSCC, usually have severe radiation toxicities. In this context, the modalities of radiation therapy should be adapted. Some patients with FA present a milder phenotype, especially in the case of medullary FA gene spontaneous reversion. Therefore, in an unusual context of HNSCC, such as no risk factors or a young age, it may be very useful to search anemia or development abnormalities, that may unravel a yet undiagnosed FA disease. Besides, in some young patients with HNSCC who did not suffer from FA, a monoallelic germline alteration in an FA gene could be combined with a second risk factor such as HPV infection or APOBEC alteration. Although several in vitro studies showed that normal cells with monoallelic FA gene alteration may have a particular radiosensitivity, these observations have not been confirmed in vivo in FA heterozygotes patients. Finally, some somatic activating alterations have also been found in HSNCC tumor samples and could be associated with radioresistance.

Variants of uncertain significance in the era of high-throughput genome sequencing: a lesson from breast and ovary cancers

The promising expectations about personalized medicine have opened the path to routine large-scale sequencing and increased the importance of genetic counseling for hereditary cancers, among which hereditary breast and ovary cancers (HBOC) have a major impact. High-throughput sequencing, or Next-Generation Sequencing (NGS), has improved cancer patient management, ameliorating diagnosis and treatment decisions. In addition to its undeniable clinical utility, NGS is also unveiling a large number of variants that we are still not able to clearly define and classify, the variants of uncertain significance (VUS), which account for about 40% of total variants. At present, VUS use in the clinical context is challenging. Medical reports may omit this kind of data and, even when included, they limit the clinical utility of genetic information. This has prompted the scientific community to seek easily applicable tests to accurately classify VUS and increase the amount of usable information from NGS data. In this review, we will focus on NGS and classification systems for VUS investigation, with particular attention on HBOC-related genes and in vitro functional tests developed for ameliorating and accelerating variant classification in cancer.

Chromosomal radiosensitivity of triple negative breast cancer patients

Purpose: Based on clinical and molecular data, breast cancer is a heterogeneous disease. Breast cancers that have no expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) are defined as triple negative breast cancers (TNBCs); luminal cancers have different expressions of ER, PR and/or HER2. TNBCs are frequently linked with advanced disease, poor prognosis and occurrence in young African women, and about 15% of the cases are associated with germline BRCA1/2 mutations. Since radiotherapy is utilized as a principle treatment in the management of TNBC, we aimed to investigate the chromosomal instability and radiosensitivity of lymphocytes in TNBC patients compared to luminal breast cancer patients and healthy controls using the micronucleus (MN) assay. The effect of mutations in breast cancer susceptibility genes on chromosomal radiosensitivity was also evaluated.Methods: Chromosomal radiosensitivity was evaluated in the G0 (83 patients and 90 controls) and S/G2 (34 patients and 17 controls) phase of the cell cycle by exposing blood samples from all patients and controls to 2 and 4 Gy ionizing radiation (IR).Results: In the G0 MN assay, the combined cohort of all breast cancer, TNBC and luminal patients' exhibit significantly elevated spontaneous MN values compared to controls indicating chromosomal instability. Chromosomal radiosensitivity is also significantly elevated in the combined cohort of all breast cancer patients compared to controls. The TNBC patients, however, do not exhibit enhanced chromosomal radiosensitivity. Similarly, in the S/G2 phase, 76% of TNBC patients do not show enhanced chromosomal radiosensitivity compared to the controls. In both the G0 and S/G2 phase, luminal breast cancer patients demonstrate a shift toward chromosomal radiosensitivity compared to TNBC patients and controls.Conclusions: The observations of the MN assay suggest increased chromosomal instability and chromosomal radiosensitivity in South African breast cancer patients. However, in TNBC patients, the irradiated MN values are not elevated. Our results suggest that the healthy lymphocytes in TNBC patients could handle higher doses of IR.

SYK expression level distinguishes control from BRCA1-mutated lymphocytes

Background

About 5%-10% of breast cancer and 10%-15% of ovarian cancer are hereditary. BRCA1 and BRCA2 are the most common germline mutations found in both inherited breast and ovarian cancers. Once these mutations are identified and classified, a course of action to reduce the risk of developing either ovarian or breast cancer - including surveillance and surgery - is carried out.

Purpose

The purpose of the current research is to characterize the gene expression differences between healthy cells harboring a mutation in BRCA1/2 genes and normal cells. This will allow detection of candidate genes and help identify women who carry functional BRCA1/2 mutations, which cannot always be detected by the available sequencing methods, for example, carriers of mutations found in regulatory sequences of the genes.

Materials and methods

Our cohort consisted of 50 healthy women, of whom 24 were individuals with BRCA1 or BRCA2 heterozygous mutations and 26 were non-carrier controls. RNA purified from non-irradiated lymphocytes of nine BRCA1/2 mutation carriers versus four control mutation-negative individuals was utilized for RNA-Seq analysis. The selected RNA-Seq transcripts were validated, and the levels of spleen tyrosine kinase (SYK) mRNA were measured by using real-time quantitative polymerase chain reaction.

Results

Differences in gene expression were found when comparing untreated lymphocytes of BRCA1/2 mutation carriers and controls. Among others, the SYK gene was identified as being differently expressed for BRCA1/2 mutation carriers. The expression level of SYK was significantly higher in untreated healthy lymphocytes of BRCA1 heterozygote carriers compared with controls, regardless of irradiation. In contrast to normal tissues, in cancerous breast tissues, the expression levels of the BRCA1 and SYK genes were not intercorrelated.

Conclusion

Collectively, our observations demonstrate that SYK may prove to be a good candidate for better diagnosis, treatment, and prevention of BRCA1 mutation-associated breast cancer.

Utilizing fluorescent life time imaging microscopy technology for identify carriers of BRCA2 mutation

Worldwide, more than one million women are diagnosed with breast cancer every year, making it the most common female malignancy in the developed world. Germline mutations in BRCA1 and BRCA2 genes are estimated to increase the risk for developing breast cancer by up to 87%. From a clinical point of view, identification of BRCA1 and BRCA2 mutation carriers offers an opportunity to early identify or prevent the development of malignancy; therefore the ability to determine which women are more likely to carry BRCA1 or BRCA2 mutations is of great importance. The available diagnostic tests for mutation analysis of BRCA1 and BRCA2 are time- and labor-intensive, expensive, and do not allow the identification of all the functional mutations. We utilized the Fluorescent lifetime (FLT) imaging microscopy method which allows recognizing different cell populations, in order to distinguish between lymphocytes from BRCA1 and BRCA2 mutation carriers and non-carrier women by using easily obtainable lymphocyte cells from peripheral blood. Our results demonstrate that cells originated from BRCA2-mutation carriers have significantly lower FLT values compared with BRCA1 mutation carriers and control cells. This simple, inexpensive and sensitive method may be utilized in the future to detect BRCA2 mutation carriers, particularly those bearing unknown functional mutations.

Increased chromosomal radiosensitivity in asymptomatic carriers of a heterozygous BRCA1 mutation

Background

Breast cancer risk increases drastically in individuals carrying a germline BRCA1 mutation. The exposure to ionizing radiation for diagnostic or therapeutic purposes of BRCA1 mutation carriers is counterintuitive, since BRCA1 is active in the DNA damage response pathway. The aim of this study was to investigate whether healthy BRCA1 mutations carriers demonstrate an increased radiosensitivity compared with healthy individuals.

Methods

We defined a novel radiosensitivity indicator (RIND) based on two endpoints measured by the G₂ micronucleus assay, reflecting defects in DNA repair and G₂ arrest capacity after exposure to doses of 2 or 4 Gy. We investigated if a correlation between the RIND score and nonsense-mediated decay (NMD) could be established.

Results

We found significantly increased radiosensitivity in the cohort of healthy BRCA1 mutation carriers compared with healthy controls. In addition, our analysis showed a significantly different distribution over the RIND scores (p = 0.034, Fisher’s exact test) for healthy BRCA1 mutation carriers compared with non-carriers: 72 % of mutation carriers showed a radiosensitive phenotype (RIND score 1–4), whereas 72 % of the healthy volunteers showed no radiosensitivity (RIND score 0). Furthermore, 28 % of BRCA1 mutation carriers had a RIND score of 3 or 4 (not observed in control subjects). The radiosensitive phenotype was similar for relatives within several families, but not for unrelated individuals carrying the same mutation. The median RIND score was higher in patients with a mutation leading to a premature termination codon (PTC) located in the central part of the gene than in patients with a germline mutation in the 5′ end of the gene.

Conclusions

We show that BRCA1 mutations are associated with a radiosensitive phenotype related to a compromised DNA repair and G₂ arrest capacity after exposure to either 2 or 4 Gy. Our study confirms that haploinsufficiency is the mechanism involved in radiosensitivity in patients with a PTC allele, but it suggests that further research is needed to evaluate alternative mechanisms for mutations not subjected to NMD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0709-1) contains supplementary material, which is available to authorized users.

Clinical relevance of normal and tumour cell radiosensitivity in BRCA1/BRCA2 mutation carriers: a review

Women harbouring BRCA1/2 mutations are known to be at higher lifetime risk of developing breast cancer than non-carriers. Compared to mastectomy, conservative surgery is also associated, in this patient population, with a higher probability to developing recurrent ipsilateral breast cancer following primary treatment. To reduce these risks, the management of BRCA1/2 - associated cancers has therefore focused on optimal prophylactic and therapeutic interventions at the time of diagnosis. In a recent past, comparative analyses of radiosensitivity levels have been carried out in murine embryos harbouring BRCA1/2 gene mutation and in non-carriers. The fact that a number of these experimental data are in favour of higher radiosensitivity levels in carriers of germline mutations leads to concern regarding the potential consequences of exposure to radiation, especially in terms of excessive toxicity in normal tissues and radiation-induced malignancies. The objective of this review is to determine whether or not the potentially higher radiosensitivity of normal and tumour cells has a clinical relevance in BRCA1/2 mutations carriers in terms of disease control, acute and late adverse events, and tumourigenesis.

Clinical application of micronucleus test: a case-control study on the prediction of breast cancer risk/susceptibility

The micronucleus test is a well-established DNA damage assay in human monitoring. The test was proposed as a promising marker of cancer risk/susceptibility mainly on the basis of studies on breast cancer. Our recent meta-analysis showed that the association between micronuclei frequency, either at baseline or after irradiation, and breast cancer risk or susceptibility, has been evaluated in few studies of small size, with inconsistent results. The aim of the present study is to investigate the role of micronucleus assay in evaluating individual breast cancer susceptibility. Two-hundred and twenty untreated breast cancer patients and 295 female controls were enrolled in the study. All women were characterized for cancer family history and 155 subjects were evaluated for the presence of BRCA mutations. Micronuclei frequency was evaluated at baseline and after irradiation with 1-Gy gamma rays from a 137Cs source. The results show a non significant increase of frequency of micronucleated binucleated lymphocytes in cancer patients compared with the controls at baseline (Mean (S.E.): 16.8 (0.7) vs 15.7 (0.5), but not after irradiation (Mean (S.E.): 145.8 (3.0) vs 154.0 (2.6)). Neither a family history of breast cancer nor the presence of a pathogenic mutation in BRCA1/2 genes were associated with an increased micronuclei frequency. Our results do not support a significant role of micronucleus frequency as a biomarker of breast cancer risk/susceptibility.

Determination of molecular markers for BRCA1 and BRCA2 heterozygosity using gene expression profiling

Approximately 5% of all breast cancers can be attributed to an inherited mutation in one of two cancer susceptibility genes, BRCA1 and BRCA2. We searched for genes that have the potential to distinguish healthy BRCA1 and BRCA2 mutation carriers from noncarriers based on differences in expression profiling. Using expression microarrays, we compared gene expression of irradiated lymphocytes from BRCA1 and BRCA2 mutation carriers versus control noncarriers. We identified 137 probe sets in BRCA1 carriers and 1,345 in BRCA2 carriers with differential gene expression. Gene Ontology analysis revealed that most of these genes relate to regulation pathways of DNA repair processes, cell-cycle regulation, and apoptosis. Real-time PCR was conducted on the 36 genes, which were most prominently differentially expressed in the microarray assay; 21 genes were shown to be significantly differentially expressed in BRCA1 and/or BRCA2 mutation carriers as compared with controls (P < 0.05). On the basis of a validation study with 40 mutation carriers and 17 noncarriers, a multiplex model that included six or more coincidental genes of 18 selected genes was constructed to predict the risk of carrying a mutation. The results using this model showed sensitivity 95% and specificity 88%. In summary, our study provides insight into the biologic effect of heterozygous mutations in BRCA1 and BRCA2 genes in response to ionizing irradiation-induced DNA damage. We also suggest a set of 18 genes that can serve as a prediction and screening tool for BRCA1 or BRCA2 mutational carriers by using easily obtained lymphocytes.

A 24-color metaphase-based radiation assay discriminates heterozygous BRCA2 mutation carriers from controls by chromosomal radiosensitivity

Numerous allelic variants identified in the familial breast cancer and DNA repair genes BRCA1 and BRCA2 are of unknown impact on protein function or clinical relevance, referred to as unclassified variants (UCV). Lymphocytes from pathogenic BRCA1/2 mutation carriers exhibit an increased level of chromosomal damage after irradiation. We established a radiation assay for the discrimination of pathogenic BRCA2 variants versus controls based on the level of chromosomal damage upon irradiation (p < 0.001). As a consequence, lymphocytes from UCV carriers could be separated into two distinct groups with normal or diminished DNA double strand break repair capacity. Our results suggested that all five UCV tested were benign and that one family carried a putative mutation in an as yet undetected DNA-repair gene. Thus, our test may serve as a valuable tool that aids the classification of BRCA2 UCV, but very likely also of BRCA1 UCV or aberrations in other genes involved in the DNA-repair system.

Xeroderma pigmentosum variant: complementary molecular approaches to detect a 13 base pair deletion in the DNA polymerase eta gene

Deficiencies of DNA polymerase eta-an enzyme mediating replication past UV-induced DNA damage-predispose individuals to xeroderma pigmentosum variant (XPV) and result in a high incidence of skin cancers. We designed, developed and assessed several complementary molecular approaches to detect a genetically inherited deletion within DNA polymerase eta. RNA was reverse transcribed from XPV fibroblasts and from normal human cells, and standard polymerase chain reaction (PCR) was conducted on the cDNA targeting a region with a 13 base pair deletion within the polymerase eta gene. PCR products were subjected to restriction fragment length polymorphism (RFLP) analysis and cycle DNA sequencing. The deletion was found to eliminate a BsrGI restriction site and affected the number of resultant fragments visualized after gel electrophoresis. Cycle sequencing of polymerase eta-specific amplicons from XPV and normal cells provided a second approach for detecting the mutation. Additionally, the use of a fluorescent nucleic acid dye-EvaGreen-in real-time PCR and melt curve analysis distinguished normal and XPV patient-derived amplicons as well as heteroduplexes that represent heterozygotic carriers without the need for high resolution melt analysis-compatible software. Our approaches are easily adaptable by diagnostic laboratories that screen for or verify genetically inherited disorders and identify carriers of a defective gene.

Influence of homologous recombinational repair on cell survival and chromosomal aberration induction during the cell cycle in gamma-irradiated CHO cells

The repair of DNA double-strand breaks (DSBs) by homologous recombinational repair (HRR) underlies the high radioresistance and low mutability observed in S-phase mammalian cells. To evaluate the contributions of HRR and non-homologous end-joining (NHEJ) to overall DSB repair capacity throughout the cell cycle after gamma-irradiation, we compared HRR-deficient RAD51D-knockout 51D1 to CgRAD51D-complemented 51D1 (51D1.3) CHO cells for survival and chromosomal aberrations (CAs). Asynchronous cultures were irradiated with 150 or 300cGy and separated by cell size using centrifugal elutriation. Cell survival of each synchronous fraction ( approximately 20 fractions total from early G1 to late G2/M) was measured by colony formation. 51D1.3 cells were most resistant in S, while 51D1 cells were most resistant in early G1 (with survival and chromosome-type CA levels similar to 51D1.3) and became progressively more sensitive throughout S and G2. Both cell lines experienced significantly reduced survival from late S into G2. Metaphases were collected from every third elutriation fraction at the first post-irradiation mitosis and scored for CAs. 51D1 cells irradiated in S and G2 had approximately 2-fold higher chromatid-type CAs and a remarkable approximately 25-fold higher level of complex chromatid-type exchanges compared to 51D1.3 cells. Complex exchanges in 51D1.3 cells were only observed in G2. These results show an essential role for HRR in preventing gross chromosomal rearrangements in proliferating cells and, with our previous report of reduced survival of G2-phase NHEJ-deficient prkdc CHO cells [Hinz et al., DNA Repair 4, 782-792, 2005], imply reduced activity/efficiency of both HRR and NHEJ as cells transition from S to G2.

RADIOSENSITIVITY TO HIGH ENERGY IRON IONS IS INFLUENCED BY HETEROZYGOSITY for ATM, RAD9 and BRCA1

Loss of function of DNA repair genes has been implicated in the development of many types of cancer. In the last several years, heterozygosity leading to haploinsufficiency for proteins involved in DNA repair was shown to play a role in genomic instability and carcinogenesis after DNA damage is induced, for example by ionizing radiation. Since the effect of heterozygosity for one gene is relatively small, we hypothesize that predisposition to cancer could be a result of the additive effect of heterozygosity for two or more genes critical to pathways that control DNA damage signaling, repair or apoptosis. We investigated the role of heterozygosity for Atm, Rad9 and Brca1 on cell oncogenic transformation and cell survival induced by 1GeV/n ⁵⁶Fe ions. Our results show that cells heterozygous for both Atm and Rad9 or Atm and Brca1 have high survival rates and are more sensitive to transformation by high energy Iron ions when compared with wild-type controls or cells haploinsufficient for only one of these proteins. Since mutations or polymorphisms for similar genes exist in a small percentage of the human population, we have identified a radiosensitive sub-population. This finding has several implications. First, the existence of a radiosensitive sub-population may distort the shape of the dose-response relationship. Second, it would not be ethical to put exceptionally radiosensitive individuals into a setting where they may potentially be exposed to substantial doses of radiation.

Ionizing radiation or mitomycin-induced micronuclei in lymphocytes of BRCA1 or BRCA2 mutation carriers

BRCA1 and BRCA2 genes are essential in preserving the integrity of genome, and it is not unambiguously clear whether the heterozygosity status may affect BRCA1 or BRCA2 functions. This may have implications for the clinical management of BRCA1 and BRCA2 mutation carriers both in breast cancer (BC) screening modality and in cancer treatment based on DNA-damaging or DNA-repair-inhibiting drugs. We investigated whether lymphocytes carrying BRCA1 or BRCA2 mutations displayed an increased sensitivity to radiation or mitomycin C (MMC) in vitro treatments. Peripheral blood from 21 BRCA1 mutation carriers (12 with BC and 9 healthy), 24 BRCA2 carriers (13 with BC and 11 healthy), 15 familial BC patients without detected mutation in BRCA1 or BRCA2 and 16 controls without familial history of cancer (5 with BC and 11 healthy) were irradiated or treated with MMC. Chromosomal damage was measured using the cytokinesis-block micronucleus assay. We evaluated micronuclei (MN) and nucleoplasmic bridges (NPBs). The BRCA2 mutation carriers and familial BC patients without detected mutation in BRCA1 or BRCA2 showed less basal NPB than BRCA1 carriers and controls. The BRCA1 (+/-) or BRCA2 (+/-) lymphocytes did not have increased frequencies of MN or NPB after irradiation. In contrast, BRCA2 (+/-) lymphocytes presented higher levels of MN after MMC exposure than BRCA1 carriers and controls. The monoallelic BRCA1 or BRCA2 pathogenic mutations seem not to be associated with an enhanced radiosensitivity. The mutation of one BRCA2 allele conferred an increased sensitivity to MMC, presumably because of the role of this gene in the repair of MMC-induced DNA damage. This finding indicates that the MMC-induced MN analysis could be useful in identifying functional deficiencies of BRCA2 or genes related to BRCA2. Since MMC can be used as an anti-cancer drug, these data may be relevant for the management and follow-up of BRCA2 mutation carriers.

Increased chromosomal radiosensitivity in women carrying BRCA1/BRCA2 mutations assessed with the G2 assay

PURPOSE

Several in vitro studies suggest that BRCA1 and BRCA2 mutation carriers present increased sensitivity to ionizing radiation. Different assays for the assessment of deoxyribonucleic acid double-strand break repair capacity have been used, but results are rather inconsistent. Given the concerns about the possible risks of breast screening with mammography in mutation carrier women and the potentially damaging effects of radiotherapy, the purpose of this study was to further investigate the radiosensitivity of this population.

METHODS AND MATERIALS

The G2 chromosomal radiosensitivity assay was used to assess chromosomal breaks in lymphocyte cultures after exposure to 1 Gy. A group of familiar breast cancer patients carrying a mutation in the BRCA1 or BRCA2 gene (n = 15) and a group of healthy mutation carriers (n = 5) were investigated and compared with a reference group of healthy women carrying no mutation (n = 21).

RESULTS

BRCA1 and BRCA2 mutation carriers had a significantly higher number of mean chromatid breaks per cell (p = 0.006) and a higher maximum number of breaks (p = 0.0001) as compared with their matched controls. Both healthy carriers and carriers with a cancer history were more radiosensitive than controls (p = 0.002 and p = 0.025, respectively). Age was not associated with increased radiosensitivity (p = 0.868).

CONCLUSIONS

Our results indicate that BRCA1 and BRCA2 mutation carriers show enhanced radiosensitivity, presumably because of the involvement of the BRCA genes in deoxyribonucleic acid repair and cell cycle control mechanisms.

G2-phase chromosomal radiosensitivity of primary fibroblasts from hereditary retinoblastoma family members and some apparently normal controls

We previously described an enhanced sensitivity for cell killing and gamma-H2AX focus induction after both high-dose-rate and continuous low-dose-rate gamma irradiation in 14 primary fibroblast strains derived from hereditary-type retinoblastoma family members (both affected RB1(+/-) probands and unaffected RB1(+/+) parents). Here we present G(2)-phase chromosomal radiosensitivity assay data for primary fibroblasts derived from these RB family members and five Coriell cell bank controls (four apparently normal individuals and one bilateral RB patient). The RB family members and two normal Coriell strains had significantly higher ( approximately 1.5-fold, P < 0.05) chromatid-type aberration frequencies in the first postirradiation mitosis after doses of 50 cGy and 1 Gy of (137)Cs gamma radiation compared to the remaining Coriell strains. The induction of chromatid-type aberrations by high-dose-rate G(2)-phase gamma irradiation is significantly correlated to the proliferative ability of these cells exposed to continuous low-dose-rate gamma irradiation (reported in Wilson et al., Radiat. Res. 169, 483-494, 2008). Our results suggest that these moderately radiosensitive individuals may harbor hypomorphic genetic variants in genomic maintenance and/or DNA repair genes or may carry epigenetic changes involving genes that more broadly modulate such systems, including G(2)-phase-specific DNA damage responses.

p53 and gamma radiation in the normal breast

PURPOSE

With the increasing use of radiation as adjuvant therapy in breast cancer, the effects of gamma radiation on the remaining normal breast are of increasing importance. The complexities of multiple cellular types within breast tissues and the role of the pleiotropic Tumour Protein 53 (TP53, p53) protein with its downstream transcriptional targets and cellular processes may be central to the effects on residual normal breast tissues.

CONCLUSION

While a detailed understanding of p53 protein-mediated responses in normal breast tissues remains elusive, p53 appears to have a pivotal role in the effects of gamma radiation on normal breast epithelium, but not stromal cells, which may account for the differing clinical effects of gamma radiation in women treated for breast cancer.

Validation of the cell cycle G(2) delay assay in assessing ionizing radiation sensitivity and breast cancer risk

Genetic variations in cell cycle checkpoints and DNA repair genes are associated with prolonged cell cycle G(2) delay following ionizing radiation (IR) treatment and breast cancer risk. However, different studies reported conflicting results examining the association between post-IR cell cycle delay and breast cancer risk utilizing four different parameters: cell cycle G(2) delay index, %G(2)-M, G(2)/G(0)-G(1), and (G(2)/G(0)-G(1))/S. Therefore, we evaluated whether different parameters may influence study results using a data set from 118 breast cancer cases and 225 controls as well as lymphoblastoid and breast cancer cell lines with different genetic defects. Our results suggest that cell cycle G(2) delay index may serve as the best parameter in assessing breast cancer risk, genetic regulation of IR-sensitivity, and mutations of ataxia telangiectasia mutated (ATM) and TP53. Cell cycle delay in 21 lymphoblastoid cell lines derived from BRCA1 mutation carriers was not different from that in controls. We also showed that IR-induced DNA-damage signaling, as measured by phosphorylation of H2AX on serine 139 (γ-H2AX) was inversely associated with cell cycle G(2) delay index. In summary, the cellular responses to IR are extremely complex; mutations or genetic variations in DNA damage signaling, cell cycle checkpoints, and DNA repair contribute to cell cycle G(2) delay and breast cancer risk. The cell cycle G(2) delay assay characterized in this study may help identify subpopulations with elevated risk of breast cancer or susceptibility to adverse effects in normal tissue following radiotherapy.

A BRCA1 mutation is not associated with increased indicators of oxidative stress

BACKGROUND

Several functions have been attributed to the BRCA1 protein. A recent study suggests that BRCA1 is involved in the cellular antioxidant response by inducing the expression of genes involved in the antioxidant defense system and thus conferring resistance to oxidative stress. It is possible that individuals with a BRCA1 mutation might be susceptible to the effects of oxidative stress. The aim of this study was to evaluate whether women with a BRCA1 mutation exhibit increased indicators of oxidative stress.

PATIENTS AND METHODS

We measured 3 markers of oxidative stress in vivo, the amounts of serum malondialdehyde and protein thiols, and 8-oxo-2'-deoxyguanosine (8-oxodG) levels in 25 unaffected BRCA1 mutation carriers and 25 noncarrier control subjects.

RESULTS

There was no significant difference in serum malondialdehyde levels (P=.41), serum thiol levels (P=.85), or the number of 8-oxodG lesions (P=.49) in BRCA1 mutation carriers versus noncarriers.

CONCLUSION

The results of this study suggest that the presence of a heterozygous BRCA1 mutation is not associated with increased levels of indicators of oxidative stress in serum or lymphocytes. Future studies are warranted to evaluate whether strategies aimed at minimizing oxidative stress might aid in the prevention of hereditary breast cancer.