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

Evaluation of Relationship between Intrinsic Radiosensitivity (Survival Fraction at 2 Gy) and Gamma-H2AX Test and Apoptosis of Lymphocytes in Breast Cancer Patients

Background

Radiotherapy is one of the routine treatment strategies for breast cancer (BC) patients. Different responses of the patient to radiation due to different intrinsic radiosensitivity (RS) were induced to the researcher try to introduce a standard assay for the prediction of RS. Clonogenic assay is recognized as a gold standard method in this subject but because of some of its disadvantages, it is needed for alternative assays. In this study, two assays were evaluated for this reason in ten BC patients with different RSs.

Methods

The peripheral blood of 10 volunteers with BC was obtained, and the peripheral blood mononuclear cells were extracted. After exposed with 2 Gy, survival fraction at 2 Gy (SF2) was calculated by clonogenic assay. γ-H2AX assay was performed for all patients, and apoptosis assay was evaluated for three represented categorized patients.

Results

RS of patients showed SF2 and categorized in three groups (high, medium, and low RS). Double-strand breaks (DSBs) were decreased in high radiosensitive patients, but the residual DSBs were clearly higher than other two groups. It is shown that the repair system in these patients is lower active than others. Apoptosis frequency in patient 4 is highly active which could induce the enhancement of her RS.

Conclusion

γ-H2AX and apoptosis assays could predict the intrinsic RS, but evaluation of them separately is not sufficient for this aim. It is necessary to consider all the parameters together and consideration of the combination of assays could fit a better prediction of intrinsic RS.

Inter-BRCT linker is probably the most intolerant region of the BRCA1 BRCT domain

Pathogenic mutations in BRCA1 are associated with an increased risk of hereditary breast, ovarian, and some other cancers; however, the clinical significance of many mutations in this gene remains unknown (Variants of Unknown Significance/VUS). Since mutations in intolerant regions of a protein lead to dysfunction and pathogenicity, identifying these regions helps to predict the clinical importance of VUSs. This study aimed to identify intolerant regions of BRCA1 and understand the possible root of this susceptibility. Intolerant regions appear to carry more pathogenic mutations than expected due to their lower tolerance to missense variations. Therefore, we hypothesized that among the BRCA1 regions, the higher the mutation density, the greater the intolerance. Thus, pathogenic mutation density and regional intolerance scores were calculated to identify BRCA1-intolerant regions. To investigate the pathogenic mechanisms of missense-intolerant regions in BRCA1, transcription activation (TA) experiments and molecular dynamics (MD) simulations were also performed. The results showed that the RING domain, followed by the BRCT domain, has the highest density of pathogenic mutations. In the BRCT domain, a higher density of pathogenic mutations was observed in the inter-BRCT linker. Additionally, scores generated by Missense Tolerance Ratio-3D (MTR3D) and the Missense Tolerance Ratio consensus (MTRX) showed that the inter-BRCT linker is more intolerant than other regions of the BRCT domain. The MD results showed that mutations in the inter-BRCT linker led to cancer susceptibility, likely due to disruption of the interaction between BRCA1 and phosphopeptides. TA laboratory assays further supported the importance of the inter-BRCT linker.Communicated by Ramaswamy H. Sarma.

Cosmic Whirl: Navigating the Comet Trail in DNA: H2AX Phosphorylation and the Enigma of Uncertain Significance Variants

Pathogenic variations in the BRCA2 gene have been detected with the development of next-generation sequencing (NGS)-based hereditary cancer panel testing technology. It also reveals an increasing number of variants of uncertain significance (VUSs). Well-established functional tests are crucial to accurately reclassifying VUSs for effective diagnosis and treatment. We retrospectively analyzed the multi-gene cancer panel results of 922 individuals and performed in silico analysis following ClinVar classification. Then, we selected five breast cancer-diagnosed patients' missense BRCA2 VUSs (T1011R, T1104P/M1168K, R2027K, G2044A, and D2819) for reclassification. The effects of VUSs on BRCA2 function were analyzed using comet and H2AX phosphorylation (γH2AX) assays before and after the treatment of peripheral blood mononuclear cells (PBMCs) of subjects with the double-strand break (DSB) agent doxorubicin (Dox). Before and after Dox-induction, the amount of DNA in the comet tails was similar in VUS carriers; however, notable variations in γH2AX were observed, and according to combined computational and functional analyses, we reclassified T1001R as VUS-intermediate, T1104P/M1168K and D2819V as VUS (+), and R2027K and G2044A as likely benign. These findings highlight the importance of the variability of VUSs in response to DNA damage before and after Dox-induction and suggest that further investigation is needed to understand the underlying mechanisms.

Understanding the mechanistic pathways and clinical aspects associated with protein and gene based biomarkers in breast cancer

Cancer is one of the most widespread and severe diseases with a huge mortality rate. In recent years, the second-leading mortality rate of any cancer globally has been breast cancer, which is one of the most common and deadly cancers found in women. Detecting breast cancer in its initial stages simplifies treatment, decreases death risk, and recovers survival rates for patients. The death rate for breast cancer has risen to 0.024 % in some regions. Sensitive and accurate technologies are required for the preclinical detection of BC at an initial stage. Biomarkers play a very crucial role in the early identification as well as diagnosis of women with breast cancer. Currently, a wide variety of cancer biomarkers have been discovered for the diagnosis of cancer. For the identification of these biomarkers from serum or other body fluids at physiological amounts, many detection methods have been developed. In the case of breast cancer, biomarkers are especially helpful in discovering those who are more likely to develop the disease, determining prognosis at the time of initial diagnosis and choosing the best systemic therapy. In this study we have compiled various clinical aspects and signaling pathways associated with protein-based biomarkers and gene-based biomarkers.

A prognostic risk model for programmed cell death and revealing TRIB3 as a promising apoptosis suppressor in renal cell carcinoma

Programmed cell death (PCD), a common modality of cell death, affects tumor development and acts as a target for tumor therapeutics. Many modalities of PCD regulate genesis, progression and metastasis of cancers, thus affecting the patients' prognosis, but the comprehensive molecular mechanisms of PCD in tumors are lacking, especially in renal cancer. Here, seventeen PRPCDGs were identified from 1257 genes associated with thirteen PCD modalities, which were highly differentially expressed and significantly affected patients' prognosis. Then, LASSO regression analysis of these PRPCDGs screened the 9-gene PRPCDGs risk signature in TCGA-KIRC database. The PRPCDGs risk signature was closely associated with the patients' prognosis and presented stable prediction efficacy for 5- and 7-year overall survival (OS) in three different cohorts of renal cancer. Immune cell infiltration, immune checkpoint expression and pathway enrichment (including GO, KEGG pathway, tumor-associated pathways and metabolism-associated pathways) were significantly different in the high- or low-PRPCDGs-risk group. Finally, we illustrated that TRIB3 might be a protumor factor responsible for the elevated proliferation and invasion capacities of renal cell carcinoma (RCC) cells. In summary, the PRPCDGs risk signature was developed and showed stable prediction efficacy for the prognosis of patients and that (such as TRIB3) could be a potential target for RCC management.

Ex Vivo Chromosomal Radiosensitivity Testing in Patients with Pathological Germline Variants in Breast Cancer High-Susceptibility Genes BReast CAncer 1 and BReast CAncer 2

BACKGROUND

Individual radiosensitivity is an important factor in the occurrence of undesirable consequences of radiotherapy. The potential for increased radiosensitivity has been linked to highly penetrant heterozygous mutations in DNA repair genes such as BRCA1 and BRCA2. By studying the chromosomal radiosensitivity of BRCA1/2 mutation carriers compared to the general population, we study whether increased chromosomal radiation sensitivity is observed in patients with BRCA1/2 variants.

METHODS

Three-color-fluorescence in situ hybridization was performed on ex vivo-irradiated peripheral blood lymphocytes from 64 female patients with a heterozygous germline BRCA1 or BRCA2 mutation. Aberrations in chromosomes #1, #2 and #4 were analyzed. Mean breaks per metaphase (B/M) served as the parameter for chromosomal radiosensitivity. The results were compared with chromosomal radiosensitivity in a cohort of generally healthy individuals and patients with rectal cancer or breast cancer.

RESULTS

Patients with BRCA1/2 mutations (n = 64; B/M 0.47) overall showed a significantly higher chromosomal radiosensitivity than general healthy individuals (n = 211; B/M 0.41) and patients with rectal cancer (n = 379; B/M 0.44) and breast cancer (n = 147; B/M 0.45) without proven germline mutations. Chromosomal radiosensitivity varied depending on the locus of the BRCA1/2 mutation.

CONCLUSIONS

BRCA1/2 mutations result in slightly increased chromosomal sensitivity to radiation. A few individual patients have a marked increase in radiation sensitivity. Therefore, these patients are at a higher risk for adverse therapeutic consequences.

Fertility Counseling in BRCA1/2-Mutated Women with Breast Cancer and Healthy Individuals

Breast cancer is the most commonly diagnosed cancer worldwide and the fifth leading cause of cancer death. In 2020, there were 2.3 million new cases, and 685,000 women died from it. Breast cancer among young women under 40 years of age accounts for 5% to 10% of all cases of this cancer. The greater availability of multi-gene sequence analysis by next-generation sequencing has improved diagnosis and, consequently, the possibility of using appropriate therapeutic approaches in BRCA1/2 gene mutation carriers. Treatment of young breast cancer patients affects their reproductive potential by reducing ovarian reserve. It can lead to reversible or permanent premature menopause, decreased libido, and other symptoms of sex hormone deficiency. This requires that, in addition to oncological treatment, patients are offered genetic counseling, oncofertility, psychological assistance, and sexological counseling. Given the number of BRCA1/2 gene mutation carriers among young breast cancer patients, but also thanks to growing public awareness, among their healthy family members planning offspring, the possibility of benefiting from preimplantation testing and performing cancer-risk-reduction procedures: RRM (risk-reducing mastectomy) and RRSO (risk-reducing salpingo-oophorectomy) significantly increase the chance of a genetically burdened person living a healthy life and giving birth to a child not burdened by the parent's germline mutation. The goal of this paper is to show methods and examples of fertility counselling for BRCA1/2 gene mutation carriers, including both patients already affected by cancer and healthy individuals.

Functions of Breast Cancer Predisposition Genes: Implications for Clinical Management

Approximately 5–10% of all breast cancer (BC) cases are caused by germline pathogenic variants (GPVs) in various cancer predisposition genes (CPGs). The most common contributors to hereditary BC are BRCA1 and BRCA2, which are associated with hereditary breast and ovarian cancer (HBOC). ATM, BARD1, CHEK2, PALB2, RAD51C, and RAD51D have also been recognized as CPGs with a high to moderate risk of BC. Primary and secondary cancer prevention strategies have been established for HBOC patients; however, optimal preventive strategies for most hereditary BCs have not yet been established. Most BC-associated CPGs participate in DNA damage repair pathways and cell cycle checkpoint mechanisms, and function jointly in such cascades; therefore, a fundamental understanding of the disease drivers in such cascades can facilitate the accurate estimation of the genetic risk of developing BC and the selection of appropriate preventive and therapeutic strategies to manage hereditary BCs. Herein, we review the functions of key BC-associated CPGs and strategies for the clinical management in individuals harboring the GPVs of such genes.

Lymphocyte-based challenge DNA-repair assays for personalized health risk assessment

Combinations of genetic and environmental factors are responsible for the development of many human diseases, such as cancer, as demonstrated using various biomarkers. Within this scenario, DNA repair holds a gate-keeper position which determines outcomes after appearance of DNA damage and, therefore, adverse cellular consequences, e.g., initiation of carcinogenesis. DNA repair deficiency and some of the subsequent events can be validated from studies using live cells from cancer patients. However, these deficiencies/events are difficult to demonstrate in live cells from normal individuals because individual variations in DNA repair capacities (DRC) are too low to be measured easily. Such lack of information has been hindering progress in developing personalized disease prevention and intervention protocols, especially among exposed populations. However, using a variety of challenge assays as biomarkers, variations in individual's DRC can be amplified in live cells and be determined. Furthermore, evidence indicates that DRC are not only inherited but can also be modified by environmental factors (e.g., nutritional status and exposure to genotoxic substances). Using these challenge assays, e.g., in live lymphocytes, individual's DRC can be holistically and functionally determined as well as quantitated. With the more precise information, assessment of health risk can be better determined on an individual rather than on a population basis. This review provides a succinct summary on the development and application of recent challenge assays in lymphocytes which can provide measurements of individuals' DRC, and on the latest data for more precise disease prevention and intervention.

Clinical and Molecular Insights of Radiation-Induced Breast Sarcomas: Is There Hope on the Horizon for Effective Treatment of This Aggressive Disease?

Radiation-induced breast sarcomas (RIBS) are rare entities representing <1% of all primary breast malignancies, limiting most reports to small retrospective case series. They constitute a heterogeneous group of neoplasms, with high-grade angiosarcoma being the most common subtype. Other sarcoma histotypes, such as undifferentiated pleomorphic sarcoma and leiomyosarcoma, can also be identified. Radiation-induced breast angiosarcoma (RIBA) has an incidence of approximately 0.1% after breast-conserving therapy and arises mainly from the dermis of the irradiated breast. MYC gene amplification is highly indicative of secondary breast angiosarcomas. Their clinical presentation often mimics benign port-radiation lesions, leading to a delay in diagnosis and a lost window of opportunity for cure. Surgery with negative margins is the mainstay of treatment of localized RIBS. In the case of angiosarcoma, technical difficulties, including multifocality, infiltrative margins, and difficulty in assessing tumor margins, render surgical treatment quite challenging. A limited number of studies showed that adjuvant radiation therapy reduces local recurrences; therefore, it is proposed by many groups for large, high-grade tumors. Chemotherapy has been evaluated retrospectively in a small subset of patients, with some evidence supporting its use in angiosarcoma patients. Approximately half of patients with RIBA will show local recurrence. In the advanced setting, different therapeutic options are discussed in the review, including chemotherapy, antiangiogenic therapy, and immunotherapy, whereas the need for further research on molecular therapeutic targets is pointed out.

Synergistic radiosensitizing effect of BR101801, a specific DNA-dependent protein kinase inhibitor, in various human solid cancer cells and xenografts

DNA-dependent protein kinase (DNA-PK), an essential component of the non-homologous end-joining (NHEJ) repair pathway, plays an important role in DNA damage repair (DDR). Therefore, DNA-PK inhibition is a promising approach for overcoming radiotherapy or chemotherapy resistance in cancers. In this study, we demonstrated that BR101801, a potent DNA-PK inhibitor, acted as an effective radiosensitizer in various human solid cancer cells and an in vivo xenograft model. Overall, BR101801 strongly elevated ionizing radiation (IR)-induced genomic instability via induction of cell cycle G₂/M arrest, autophagic cell death, and impairment of DDR pathway in human solid cancer cells. Interestingly, BR101801 inhibited not only phosphorylation of DNA-PK catalytic subunit in NHEJ factors but also BRCA2 protein level in homologous recombination (HR) factors. In addition, combination BR101801 and IR suppressed tumor growth compared with IR alone by reducing phosphorylation of DNA-PK in human solid cancer xenografts. Our findings suggested that BR101801 is a selective DNA-PK inhibitor with a synergistic radiosensitizing effect in human solid cancers, providing evidence for clinical applications.

α-Mangostin Nanoparticles Cytotoxicity and Cell Death Modalities in Breast Cancer Cell Lines

α-Mangostin (AMG) is a potent anticancer xanthone that was discovered in mangosteen (Garcinia mangostana Linn.). AMG possesses the highest opportunity for chemopreventive and chemotherapeutic therapy. AMG inhibits every step in the process of carcinogenesis. AMG suppressed multiple breast cancer (BC) cell proliferation and apoptosis by decreasing the creation of cancerous compounds. Accumulating BC abnormalities and their associated molecular signaling pathways promotes novel treatment strategies. Chemotherapy is a commonly used treatment; due to the possibility of unpleasant side effects and multidrug resistance, there has been substantial progress in searching for alternative solutions, including the use of plant-derived natural chemicals. Due to the limitations of conventional cancer therapy, nanotechnology provides hope for effective and efficient cancer diagnosis and treatment. Nanotechnology enables the delivery of nanoparticles and increased solubility of drugs and drug targeting, resulting in increased cytotoxicity and cell death during BC treatment. This review summarizes the progress and development of AMG’s cytotoxicity and the mechanism of death BC cells. The combination of natural medicine and nanotechnology into a synergistic capital will provide various benefits. This information will aid in the development of AMG nanoparticle preparations and may open up new avenues for discovering an effective BC treatment.

Risks and Function of Breast Cancer Susceptibility Alleles

Family history remains one of the strongest risk factors for breast cancer. It is well established that women with a first-degree relative affected by breast cancer are twice as likely to develop the disease themselves. Twins studies indicate that this is most likely due to shared genetics rather than shared epidemiological/lifestyle risk factors. Linkage and targeted sequencing studies have shown that rare high- and moderate-penetrance germline variants in genes involved in the DNA damage response (DDR) including BRCA1, BRCA2, PALB2, ATM, and TP53 are responsible for a proportion of breast cancer cases. However, breast cancer is a heterogeneous disease, and there is now strong evidence that different risk alleles can predispose to different subtypes of breast cancer. Here, we review the associations between the different genes and subtype-specificity of breast cancer based on the most comprehensive genetic studies published. Genome-wide association studies (GWAS) have also been used to identify an additional hereditary component of breast cancer, and have identified hundreds of common, low-penetrance susceptibility alleles. The combination of these low penetrance risk variants, summed as a polygenic risk score (PRS), can identify individuals across the spectrum of disease risk. However, there remains a substantial bottleneck between the discovery of GWAS-risk variants and their contribution to tumorigenesis mainly because the majority of these variants map to the non-protein coding genome. A range of functional genomic approaches are needed to identify the causal risk variants and target susceptibility genes and establish their underlying role in disease biology. We discuss how the application of these multidisciplinary approaches to understand genetic risk for breast cancer can be used to identify individuals in the population that may benefit from clinical interventions including screening for early detection and prevention, and treatment strategies to reduce breast cancer-related mortalities.

The other side of the coin: dissecting molecular mechanisms behind hereditary breast cancer in search of therapeutic opportunities

Over the last quarter century several genetic alterations have been implicated in hereditary breast cancer (HBC). Two papers recently published in the New England Journal of Medicine explored the mutation prevalence in breast cancer predisposition genes across a large population of affected and unaffected subjects. These analyses designated ATM, BARD1, BRCA1, BRCA2, CHEK2, PALB2, RAD51C and RAD51D as the core set of genes associated with a significantly increased risk of developing breast cancer. A deeper understanding of the biological role of these genes unearths an intricate mechanism involving DNA repair and cell cycle regulation. Exploiting these inherited alterations for targeted treatments, as is currently the case with PARP inhibitors, may provide additional therapeutic opportunities for HBC patients.