G0 and G2 chromosomal assays in the evaluation of radiosensitivity in a cohort of Italian breast cancer patients

Individual Radiosensitivity as a Risk Factor for the Radiation-Induced Acute Radiodermatitis

Background: Up to 95% of irradiated patients suffer from ionizing radiation (IR) induced early skin reaction, acute radiation dermatitis (ARD). Some experts think that additional skin hydration can reduce acute skin reactions. Individual radiosensitivity (IRS) determined from lymphocytes may help to predict acute radiation toxicity. The purpose of this study is to evaluate the clinical manifestation of ARD in different skincare groups during whole breast radiotherapy depending on IRS and other risk factors. Methods: A total of 108 early-stage breast cancer patients were randomized into best supportive care (BSC) and additional skincare (ASC) groups. IRS was evaluated using a G2 assay modified with caffeine-induced G2 checkpoint arrest. All patients received a 50 Gy dose to the breast planning target volume (PTV). Clinical assessment of ARD symptoms according to the CTCAE grading scale was performed once a week. Results: IRS was successfully determined for 91 out of 108 patients. A total of 10 patients (11%) had normal IRS, 47 patients (52%) were categorized as radiosensitive, and 34 (37%) as highly radiosensitive. There was no significant difference in the manifestation of ARD between patient groups by skincare or IRS. According to logistic regression, patients with bigger breasts were prone to more severe ARD (p = 0.002). Conclusions: The additional skincare did not improve skin condition during RT. A total of 89% of patients had increased radiosensitivity. IRS determined before RT did not show the predictive value for the manifestation of ARD. Logistic regression revealed that breast volume was the most significant risk factor for the manifestation of ARD.

Potential application of γ-H2AX as a biodosimetry tool for radiation triage

Radiation triage and biological dosimetry are two initial steps in the medical management of exposed individuals following radiological accidents. Well established biodosimetry methods such as the dicentric (DC) assay, micronucleus (MN) assay, and fluorescence in-situ hybridization (FISH) translocation assay (for residual damage) have been used for this purpose for several decades. Recent advances in scoring methodology and networking among established laboratories have increased triage capacity; however, these methods still have limitations in analysing large sample numbers, particularly because of the ∼ 48 h minimum culture time required prior to analysis. Hence, there is a need for simple, and high throughput markers to identify exposed individuals in case of radiological/nuclear emergencies. In recent years, a few markers were identified, one being phosphorylated histone 2AX (γ-H2AX), which measured a nuclear foci or nuclear staining intensity that was found to be suitable for triage. Measurement of γ-H2AX foci formed at and around the sites of DNA double-strand breaks is a rapid and sensitive biodosimetry method which does not require culturing and is thus promising for the analysis of a large number of samples. In this review, we have summarized the recent developments of γ-H2AX assay in radiation triage and biodosimetry, focusing chiefly on: i) the importance of baseline frequency and reported values among different laboratories, ii) the influence of known and unknown variables on dose estimation, iii) quality assurance such as inter-laboratory comparison between scorers and scoring methods, and iv) current limitations and potential for future development.

Molecular contribution of BRCA1 and BRCA2 to genome instability in breast cancer patients: review of radiosensitivity assays

BACKGROUND

DNA repair pathways, cell cycle arrest checkpoints, and cell death induction are present in cells to process DNA damage and prevent genomic instability caused by various extrinsic and intrinsic ionizing factors. Mutations in the genes involved in these pathways enhances the ionizing radiation sensitivity, reduces the individual's capacity to repair DNA damages, and subsequently increases susceptibility to tumorigenesis.

BODY

BRCA1 and BRCA2 are two highly penetrant genes involved in the inherited breast cancer and contribute to different DNA damage pathways and cell cycle and apoptosis cascades. Mutations in these genes have been associated with hypersensitivity and genetic instability as well as manifesting severe radiotherapy complications in breast cancer patients. The genomic instability and DNA repair capacity of breast cancer patients with BRCA1/2 mutations have been analyzed in different studies using a variety of assays, including micronucleus assay, comet assay, chromosomal assay, colony-forming assay, γ -H2AX and 53BP1 biomarkers, and fluorescence in situ hybridization. The majority of studies confirmed the enhanced spontaneous & radiation-induced radiosensitivity of breast cancer patients compared to healthy controls. Using G2 micronucleus assay and G2 chromosomal assay, most studies have reported the lymphocyte of healthy carriers with BRCA1 mutation are hypersensitive to invitro ionizing radiation compared to non-carriers without a history of breast cancer. However, it seems this approach is not likely to be useful to distinguish the BRCA carriers from non-carrier with familial history of breast cancer.

CONCLUSION

In overall, breast cancer patients are more radiosensitive compared to healthy control; however, inconsistent results exist about the ability of current radiosensitive techniques in screening BRCA1/2 carriers or those susceptible to radiotherapy complications. Therefore, developing further radiosensitivity assay is still warranted to evaluate the DNA repair capacity of individuals with BRCA1/2 mutations and serve as a predictive factor for increased risk of cancer mainly in the relatives of breast cancer patients. Moreover, it can provide more evidence about who is susceptible to manifest severe complication after radiotherapy.

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.

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.

Intra-individual variation in G2 chromosomal radiosensitivity

Intra-individual variation in G(2) chromosomal radiosensitivity was examined by repeatedly taking blood samples from two individuals. Two healthy female volunteers provided a total of 44 blood samples, Donor 1 gave 28 samples in four time periods between 2001 and 2006 and Donor 2 gave 16 samples in two of the same time periods. Lymphocytes were cultured for 72 h prior to irradiation with 0.5 Gy, 300 kV X-rays. Colcemid was added 30 min post-irradiation. Cultures were harvested 90 min post-irradiation and analysed for chromatid gaps and breaks. Donor 1 exhibited significant intra-individual variation in G(2) chromosomal radiosensitivity for two of the four time periods. Variation was not significant for Period 1 (13 samples, P = 0.111) and Period 2 (six samples, P = 0.311) but was significant for Period 3 (two samples, P = 0.030) and Period 4 (seven samples, P = 0.005). Significant intra-individual variation was observed for both time periods involving Donor 2, these being Period 2 (nine samples, P = 0.002) and Period 4 (seven samples, P < 0.001). The combined data from all time periods exhibited a significant intra-individual variation for Donor 1 (P < 0.001) and Donor 2 (P < 0.001). These findings led to the conclusion that too much reliance should not be placed on the result from a single sample when assessing individual radiosensitivity status.